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<front>
<journal-meta>
<journal-id journal-id-type="publisher-id">Front. Bioeng. Biotechnol.</journal-id>
<journal-title>Frontiers in Bioengineering and Biotechnology</journal-title>
<abbrev-journal-title abbrev-type="pubmed">Front. Bioeng. Biotechnol.</abbrev-journal-title>
<issn pub-type="epub">2296-4185</issn>
<publisher>
<publisher-name>Frontiers Media S.A.</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="publisher-id">1226065</article-id>
<article-id pub-id-type="doi">10.3389/fbioe.2023.1226065</article-id>
<article-categories>
<subj-group subj-group-type="heading">
<subject>Bioengineering and Biotechnology</subject>
<subj-group>
<subject>Original Research</subject>
</subj-group>
</subj-group>
</article-categories>
<title-group>
<article-title>Biosafety evaluation of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS composite elastomers</article-title>
<alt-title alt-title-type="left-running-head">Zhang et al.</alt-title>
<alt-title alt-title-type="right-running-head">
<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.3389/fbioe.2023.1226065">10.3389/fbioe.2023.1226065</ext-link>
</alt-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname>Zhang</surname>
<given-names>Zheyuan</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="fn" rid="fn1">
<sup>&#x2020;</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Zong</surname>
<given-names>Mingrui</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="fn" rid="fn1">
<sup>&#x2020;</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Liu</surname>
<given-names>Jinrong</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Ren</surname>
<given-names>Jianing</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Liu</surname>
<given-names>Xiaoming</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Zhang</surname>
<given-names>Ran</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Cui</surname>
<given-names>Jiayu</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Sun</surname>
<given-names>Lingxiang</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Song</surname>
<given-names>Hao</given-names>
</name>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Zhang</surname>
<given-names>Yanjie</given-names>
</name>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Li</surname>
<given-names>Bing</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="corresp" rid="c001">&#x2a;</xref>
<uri xlink:href="https://loop.frontiersin.org/people/1624611/overview"/>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Wu</surname>
<given-names>Xiuping</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="corresp" rid="c001">&#x2a;</xref>
<uri xlink:href="https://loop.frontiersin.org/people/2292873/overview"/>
</contrib>
</contrib-group>
<aff id="aff1">
<sup>1</sup>
<institution>School and Hospital of Stomatology</institution>, <institution>Shanxi Medical University</institution>, <addr-line>Taiyuan</addr-line>, <addr-line>Shanxi</addr-line>, <country>China</country>
</aff>
<aff id="aff2">
<sup>2</sup>
<institution>Shanxi Province Key Laboratory of Oral Diseases Prevention and New Materials</institution>, <addr-line>Taiyuan</addr-line>, <addr-line>Shanxi</addr-line>, <country>China</country>
</aff>
<aff id="aff3">
<sup>3</sup>
<institution>Research Institute of Photonics</institution>, <institution>Dalian Polytechnic University</institution>, <addr-line>Dalian</addr-line>, <addr-line>Liaoning</addr-line>, <country>China</country>
</aff>
<author-notes>
<fn fn-type="edited-by">
<p>
<bold>Edited by:</bold> <ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/1955074/overview">Xianqi Li</ext-link>, Matsumoto Dental University, Japan</p>
</fn>
<fn fn-type="edited-by">
<p>
<bold>Reviewed by:</bold> <ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/1898278/overview">Xiangxiang Hu</ext-link>, The Ohio State University, United States</p>
<p>
<ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/936161/overview">Dengfeng Peng</ext-link>, Shenzhen University, China</p>
<p>
<ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/1265136/overview">Jiachi Zhang</ext-link>, Lanzhou University, China</p>
</fn>
<corresp id="c001">&#x2a;Correspondence: Bing Li, <email>libing-1975@163.com</email>; Xiuping Wu, <email>77wxp@163.com</email>
</corresp>
<fn fn-type="equal" id="fn1">
<label>
<sup>&#x2020;</sup>
</label>
<p>These authors share first authorship</p>
</fn>
</author-notes>
<pub-date pub-type="epub">
<day>07</day>
<month>07</month>
<year>2023</year>
</pub-date>
<pub-date pub-type="collection">
<year>2023</year>
</pub-date>
<volume>11</volume>
<elocation-id>1226065</elocation-id>
<history>
<date date-type="received">
<day>20</day>
<month>05</month>
<year>2023</year>
</date>
<date date-type="accepted">
<day>29</day>
<month>06</month>
<year>2023</year>
</date>
</history>
<permissions>
<copyright-statement>Copyright &#xa9; 2023 Zhang, Zong, Liu, Ren, Liu, Zhang, Cui, Sun, Song, Zhang, Li and Wu.</copyright-statement>
<copyright-year>2023</copyright-year>
<copyright-holder>Zhang, Zong, Liu, Ren, Liu, Zhang, Cui, Sun, Song, Zhang, Li and Wu</copyright-holder>
<license xlink:href="http://creativecommons.org/licenses/by/4.0/">
<p>This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.</p>
</license>
</permissions>
<abstract>
<p>In recent years, mechanoluminescent (ML) materials have shown great potential in stress sensing, mechanical energy collection and conversion, so they have attracted wide attention in the field of stomatology. In the early stage of this study, BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup> ML phosphors were synthesized by two-step high temperature solid state method, and then mixed with Polydimethylsiloxane (PDMS) in different proportions to obtain BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS ML composites with different mass fractions (10%,20%,30%,40%,50%). Then its biosafety was evaluated by Cell Counting Kit-8 (CCK-8), Calcein-AM/PI fluorescence staining, hemolysis, oral mucosal irritation, acute and subacute systemic toxicity tests. The experimental results show that the biosafety of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS ML composite elastomers with different mass fraction is in line with the existing standards, and other related properties can be further studied.</p>
</abstract>
<kwd-group>
<kwd>mechanoluminescent</kwd>
<kwd>BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>
</kwd>
<kwd>polydimethylsiloxane</kwd>
<kwd>composite</kwd>
<kwd>biosafety</kwd>
</kwd-group>
<custom-meta-wrap>
<custom-meta>
<meta-name>section-at-acceptance</meta-name>
<meta-value>Biomaterials</meta-value>
</custom-meta>
</custom-meta-wrap>
</article-meta>
</front>
<body>
<sec id="s1">
<title>1 Introduction</title>
<p>In recent years, a unique luminescence phenomenon&#x2014;mechanoluminescent (ML) has attracted widespread attention (<xref ref-type="bibr" rid="B22">Wang et al., 2022</xref>), which first originated in 1605&#x2033;Advancement of Learning&#x201d; (<xref ref-type="bibr" rid="B8">Jha and Chandra, 2014</xref>). ML in a broad sense refers to all luminescence phenomena generated by various mechanical effects such as friction, extrusion, etc. In a narrow sense, it refers specifically to the luminescence caused by elastic deformation, plastic deformation or fracture deformation (<xref ref-type="bibr" rid="B3">Bai et al., 2021</xref>; <xref ref-type="bibr" rid="B6">Fujio et al., 2022</xref>). Since mechanical interactions permeate all aspects of life, ML could theoretically provide new solutions to challenging problems in biology, optoelectronics, and energy and environmental sciences (<xref ref-type="bibr" rid="B25">Xiong et al., 2021</xref>; <xref ref-type="bibr" rid="B28">Zhuang and Xie, 2021</xref>). In addition, it has received a lot of attention in dental materials science because of its demonstrated potential in stress sensing, mechanical energy harvesting and conversion (<xref ref-type="bibr" rid="B20">Shin et al., 2022</xref>).</p>
<p>Temporomandibular disorders (TMD) is one of the common diseases in oral clinic, and its pathogenic factors are various, including joint, masticatory muscle, occlusal and psychological disorders (<xref ref-type="bibr" rid="B12">Li and Leung, 2021</xref>), so it has always been an important and difficult point in the process of clinical diagnosis and treatment. Occlusal abnormalities are often considered by clinicians as a potential factor in TMD (<xref ref-type="bibr" rid="B14">Manfredini et al., 2017</xref>), and the relationship between them has always been concerned and controversial. Some scholars believe that the position of the condyle during apical malocclusion (intercuspalocclusion, ICO) determines the balance of the masticatory system, while the abnormal occlusal relationship may destroy this phenomenon, change the functional position of the mandible and the relationship between the condyle and the articular fossa, and then increase the risk of TMD (<xref ref-type="bibr" rid="B15">Ohrbach et al., 2020</xref>). Occlusal splint is a common and effective method for the treatment of abnormal occlusal function (<xref ref-type="bibr" rid="B23">Wieckiewicz et al., 2015</xref>). It is found that after stable occlusal splint treatment, abnormal muscle and joint activity in patients with TMD are significantly reduced, abnormal occlusal contact and mandibular movement are improved, and symptoms such as limited opening and joint pain are greatly solved (<xref ref-type="bibr" rid="B1">Al-Moraissi et al., 2020</xref>). However, some studies have shown that the existing occlusal materials have some shortcomings, such as high water absorption and solubility, easy to be affected by saliva and can not accurately reflect the actual occlusal situation (<xref ref-type="bibr" rid="B7">Grymak et al., 2022</xref>). Therefore, it is necessary to look for an alternative material which can provide accurate occlusal detection function and better comprehensive performance.</p>
<p>The emergence of ML materials provides a new idea for optimizing occlusal detection and analysis in oral clinic and realizing occlusal visualization. ML materials have good physical and chemical stability, and the luminous intensity is proportional to the stress (<xref ref-type="bibr" rid="B2">Bai et al., 2022</xref>). Among them, the nitrogen oxide fluorescent material BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup> (BSON:Eu<sup>2&#x2b;</sup>) shows super ML (<xref ref-type="bibr" rid="B19">Seibald et al., 2012</xref>). After mechanical stimulation such as pressing and stretching, the green ML can last for tens of seconds. Because the material type is nitrogen oxide and the preparation process has no pollution to the environment (<xref ref-type="bibr" rid="B27">Yun et al., 2016</xref>), it can be mixed with flexible matrix polydimethylsiloxane (PDMS), which is widely used in clinic, to prepare ML composite elastomer, so as to establish the relationship between mechanical force and optical signal.</p>
<p>In this study, BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup> phosphors were synthesized by two-step high temperature solid state method to further improve their luminous intensity, and then mixed with PDMS to prepare a series of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS composite elastomers with different mass fraction. Medical biomaterials related to oral cavity need to be strictly tested by relevant regulatory agencies before they are used in clinic, in order to minimize the adverse effects caused by direct contact with tissues, including <italic>in vitro</italic> cell tests, animal tests and so on (<xref ref-type="bibr" rid="B24">Xie et al., 2017</xref>). Therefore, according to the ISO7405/ISO10993 standard, the biological safety of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS composite elastomer was preliminarily evaluated by Cell Counting Kit-8 (CCK-8) cytotoxicity test, Calcein-AM/PI fluorescence staining, hemolysis test, oral mucosal irritation test, subacute and acute systemic toxicity test, in order to explore the possibility of its clinical application and provide experimental basis for future clinical application.</p>
</sec>
<sec id="s2">
<title>2 Experimental sections</title>
<sec id="s2-1">
<title>2.1 Preparation of materials</title>
<sec id="s2-1-1">
<title>2.1.1 Preparation of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup> phosphors</title>
<p>As shown in <xref ref-type="fig" rid="F1">Figure 1</xref>, BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup> phosphors was prepared by two-step high temperature solid state method.</p>
<fig id="F1" position="float">
<label>FIGURE 1</label>
<caption>
<p>Synthesis of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup> phosphors.</p>
</caption>
<graphic xlink:href="fbioe-11-1226065-g001.tif"/>
</fig>
<p>Step one: first, BaCO<sub>3</sub> and SiO<sub>2</sub> are ground and mixed and placed in a 1180&#xb0;C box muffle furnace, sintered for 5&#xa0;h and cooled, and Ba<sub>2</sub>SiO<sub>4</sub> is obtained after re-grinding. Then add Si<sub>3</sub>N<sub>4</sub>, put it into a high temperature tube furnace after grinding and put into the reducing atmosphere with H<sub>2</sub>/N<sub>2</sub> ratio of 3/97 (atmosphere flow rate is 120&#xa0;mL/min). After sintering at 1450&#xb0;C for 5&#xa0;h, BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub> is obtained by cooling grinding.</p>
<p>Step two: add metal oxide Eu<sub>2</sub>O<sub>3</sub> on the basis of the first step, grind it in a high temperature tube furnace and put it into a reducing atmosphere with a H<sub>2</sub>/N<sub>2</sub> ratio of 3/97 (120&#xa0;mL/min), sintering at 1450&#xb0;C for 5&#xa0;h, cooling and grinding to obtain BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup> phosphors, which is put into a sealed bag for subsequent performance characterization and testing.</p>
</sec>
<sec id="s2-1-2">
<title>2.1.2 Preparation of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS composite elastomers</title>
<p>The core content of the process is to mix the luminescent material of the powder with the organic matrix. The organic matrix selected in this experiment is PDMS (composed of the main body and curing agent, the mixing ratio is 10:1). BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup> phosphors and PDMS were weighed at the mass ratio of 10%&#x3001;20%&#x3001;30%&#x3001;40%&#x3001;50%, mixed and stirred to get the ML complex, which was left for a period of time to eliminate bubbles, and then cured at room temperature for 24&#xa0;h to obtain the target BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS composite elastomer.</p>
</sec>
<sec id="s2-1-3">
<title>2.1.3 Preparation of ML occlusal splint</title>
<p>The initial model of the occlusal plate was coated on the single jaw plaster tooth model, then the silicone rubber was coated on the outer layer, and the single jaw plaster dental mold covered with the splint was stripped off after the silicone rubber was cured. BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS was injected into the silicone rubber, then the silicone rubber was covered with a single jaw plaster dental mold, and then cured at 80&#xb0;C for 1&#xa0;h.</p>
</sec>
</sec>
<sec id="s2-2">
<title>2.2 Characterization</title>
<p>X-ray diffractometer (XRD) is used to observe the phase structure and crystal structure of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>, and then field-emission scanning electron microscopy (FESEM) is usually used to detect the micro-morphology and observe the distribution of particles. The prepared ML composite elastomer was irradiated under ultraviolet lamp for 3&#x2013;5&#xa0;min, then in a completely dark environment, simulated tooth bite force was applied to it after the afterglow disappeared completely, and its ML Phenomenon was observed.</p>
</sec>
<sec id="s2-3">
<title>2.3 Preparation of the specimens and extracts</title>
<p>The material samples were uniformly made into long 4&#xa0;mm, wide 5&#xa0;mm and 1&#xa0;mm thick, and the BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS ML composite elastomers were washed in anhydrous ethanol for 20&#xa0;min, then washed with distilled water, routinely sterilized, dried and sterilized by high pressure steam. Put it in normal saline (the ratio of the surface area of the specimen to the extraction medium is 6&#xa0;cm<sup>2</sup>/mL) and put it in a water bath at 37&#xb0;C for 72&#xa0;h.</p>
</sec>
<sec id="s2-4">
<title>2.4 Biosafety tests</title>
<sec id="s2-4-1">
<title>2.4.1 Cytotoxicity test</title>
<sec id="s2-4-1-1">
<title>2.4.1.1 CCK-8 assay</title>
<p>L929 fibroblasts were resuscitated and passaged for 2&#x2013;3&#xa0;times, then Dulbecco&#x2019;s modified Eagle medium (DMEM) culture medium containing 10% embryonic bovine serum was used to make single cell suspension (2.5&#xd7;10<sup>4</sup> cells/mL) and inoculated on 24-well plate (400&#xa0;&#x3bc;L/well). Then the cells were incubated in a cell incubator of 37&#xb0;C and 5%CO<sub>2</sub> for 24&#xa0;h. After observing the adhesion of the cells, the original medium was discarded and a new medium was added. The BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS composite elastomers with the same specifications and different mass fractions (the experimental group) were clamped into a 24-well plate with ophthalmic tweezers, while the control group only added DMEM medium. Three 24-well plates were inoculated under the same conditions and cultured in cell incubator for 1, 3 and 5&#xa0;days.</p>
<p>On the first, third and fifth day, 24-well plates were taken out, and the morphology of cells was observed under inverted microscope. 40&#xa0;&#x3bc;L WST-8 solution was added to each well, and then transferred to 96-well plate (100&#xa0;&#x3bc;L/well) after 1.5&#xa0;h of incubation. The oplical densiy (OD) of each well was measured at 450&#xa0;nm wavelength by enzyme-linked immunosorbent assay (Elisa), and the cell survival rate was calculated.<disp-formula id="equ1">
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</sec>
<sec id="s2-4-1-2">
<title>2.4.1.2 Calcein-AM/PI fluorescence staining</title>
<p>Calcein-AM/PI double staining method was used to stain living cells and dead cells, in which Calcein-AM only stained living cells because it could easily penetrate the living cell membrane, hydrolyze in the cytoplasm and emit strong green fluorescence, while PI only stained dead cells because it could not pass through the living cell membrane and could pass through the disordered region of the dead cell membrane to reach the nucleus and embedded into the DNA double helix of the cell to produce red fluorescence. The method of culturing cells and adding materials was the same as 2.4.1.1.24-well plates were taken out on the first, third and fifth day, respectively, and the morphology of cells was observed under inverted microscope. 100&#xa0;&#x3bc;L Calcein-AM was added to each 10&#xa0;mL medium, and 20&#xa0;min&#x2013;25&#xa0;min was incubated at 37&#xb0;C. After that, 20&#x2013;200&#xa0;&#x3bc;L PI solution was added to each 10&#xa0;mL medium, and 5&#xa0;min was stained at room temperature. Finally, live cells (yellow-green fluorescence) and dead cells (red fluorescence) were detected by fluorescence microscope at 490 &#xb1; 10&#xa0;nm; in addition, only dead cells could be observed in 545&#xa0;nm.</p>
</sec>
</sec>
<sec id="s2-4-2">
<title>2.4.2 Oral mucosa irritation test</title>
<p>The subjects were 25 healthy golden gophers aged about 5&#xa0;months, and every 5 gophers were set as an experimental group. There was no abnormality in bilateral buccal mucosa. The buccal mucosa of one side of each golden gopher was sutured with medical sutures to fix the BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS composite elastomers of the same size, and the contralateral buccal mucosa was used as a blank control without any treatment. Every day after operation, whether the specimen fell off, whether the mucosa around the specimen was abnormal, such as hyperemia, swelling and erosion, and whether the animals had signs of poisoning and death were observed. Two weeks later, the golden gophers were killed under excessive anesthesia, and the specimens were removed. The mucosa and surrounding tissues of the contact and contralateral parts were embedded, fixed and sliced, and stained with hematoxylin-eosin (HE) for histopathological observation.</p>
</sec>
<sec id="s2-4-3">
<title>2.4.3 Subacute systemic toxicity test</title>
<p>60 healthy SD rats weighing about 130&#xa0;g were randomly divided into 6 groups (5 experimental groups, 1 control group, half male and half female). They adapted to the laboratory environment 7&#xa0;days in advance and had to fast overnight without water before the experiment. The rats in the experimental group were perfused with BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS composite elastomers extract (10%&#x3001;20%&#x3001;30%&#x3001;40%&#x3001;50%) with the dose of 50&#xa0;mL/kg, while the rats in the control group were perfused with the same dose of normal saline. Once a day for 28&#xa0;days, and then observed for 7&#xa0;days. During this period, the signs of poisoning and death were observed, and the food utilization rate and relative growth rate of body weight were calculated by measuring weekly food consumption and weight gain of rats. At the end of the experiment, the animals were killed under excessive anesthesia, and the important tissues and organs were selected for dissection to observe the abnormal changes of each tissue and organ.<disp-formula id="equ2">
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</sec>
<sec id="s2-4-4">
<title>2.4.4 Acute systemic toxicity test</title>
<p>60 healthy C57 mice with about 17&#xa0;g were randomly divided into 6 groups (5 experimental groups, 1 control group, half male and half female). The mice in the experimental group were intravenously injected with BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS composite elastomers extract (10%, 20%, 30%, 40%, 50%) at the dose of 50&#xa0;mL/kg every day, while the control group was injected with the same dose of normal saline. The symptoms of collapse, cyanosis, dyspnea, abdominal irritation, diarrhea and tremor were observed immediately after injection. The general behavior, clinical toxic symptoms and death were observed at 4, 24, 48 and 72&#xa0;h after injection. at the same time, the experimental mice were weighed and recorded, and the body weight changes of mice were monitored. 72&#xa0;h later, the animals were killed under excessive anesthesia, and the important tissues and organs were dissected to observe the abnormal changes of each tissue and organ.</p>
</sec>
<sec id="s2-4-5">
<title>2.4.5 Hemolysis test</title>
<p>Heart puncture took 6-week-old New Zealand rabbit whole blood 10mL, add 2% potassium oxalate normal saline solution 0.5&#xa0;mL anticoagulation, and then add normal saline diluted at 4:5. The experimental group was 5&#xa0;g of different mass fraction of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS composite elastomers (10%, 20%, 30%, 40%, 50%), respectively, adding 10&#xa0;mL 0.9% normal saline, the negative control group was 10&#xa0;mL 0.9% normal saline, and the positive control group (complete hemolysis) was 10&#xa0;mL distilled water. The test tube was placed in a 37&#xb0;C water bath for 30&#xa0;min (3 parallel samples in each group). Diluted fresh anticoagulant rabbit blood 0.2&#xa0;mL was added and kept warm for 60&#xa0;min. The supernatant OD value of the supernatant was measured by spectrophotometer 576&#xa0;nm and the hemolysis rate was calculated after centrifugation at 758&#xa0;<italic>g</italic> for 5&#xa0;min.<disp-formula id="equ4">
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<p>in which OD<sub>X</sub> is the experimental group (BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS composite elastomers with different mass fractions), OD<sub>Y</sub> is the positive control group (10&#xa0;mL distilled water), and OD<sub>Z</sub> is the negative control group (10&#xa0;mL 0.9% saline).</p>
</sec>
</sec>
</sec>
<sec sec-type="results|discussion" id="s3">
<title>3 Results and discussion</title>
<sec id="s3-1">
<title>3.1 Characterization</title>
<p>
<xref ref-type="fig" rid="F2">Figure 2A</xref> is the X-ray diffraction pattern of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup> phosphor and BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub> matrix prepared by two-step high temperature solid state method. From the diagram, we can see that all the diffraction peaks of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup> prepared by this method are consistent with the standard data of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub> crystal (ICSD number 419450). No other impurity phases are found. Eu<sup>2&#x2b;</sup> ions are effectively doped into the BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub> matrix lattice to form BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup> phosphors. <xref ref-type="fig" rid="F2">Figure 2B</xref> shows the crystal structure of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub> with space group Pbcn. BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub> is formed by periodic stratification of (Si<sub>2</sub>O<sub>2</sub>N<sub>2</sub>)<sup>2-</sup> anions and Ba<sup>2&#x2b;</sup> cations. Ba<sup>2&#x2b;</sup> cations exist at only one crystal site, which coordinates with eight O atoms and two long N atoms to form a cube structure; (Si<sub>2</sub>O<sub>2</sub>N<sub>2</sub>)<sup>2-</sup> anions are composed of high-density SiON<sub>3</sub> tetrahedrons with a common vertex.</p>
<fig id="F2" position="float">
<label>FIGURE 2</label>
<caption>
<p>XRD patterns of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup> <bold>(A)</bold> and Crystal structure of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub> <bold>(B)</bold>.</p>
</caption>
<graphic xlink:href="fbioe-11-1226065-g002.tif"/>
</fig>
<p>
<xref ref-type="fig" rid="F3">Figures 3A, B</xref> are FESEM images of phosphors with different magnification respectively, showing clear layered structure of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>, smooth surface, good particle dispersion and cubic phase consistent with crystal structure. Therefore, BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup> phosphors were synthesized by two-step high temperature solid state method, which laid a foundation for the preparation of ML composite elastomers.</p>
<fig id="F3" position="float">
<label>FIGURE 3</label>
<caption>
<p>High <bold>(A)</bold> and low <bold>(B)</bold> magnification FESEM images of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>.</p>
</caption>
<graphic xlink:href="fbioe-11-1226065-g003.tif"/>
</fig>
<p>The ML occlusal splint emits cyan fluorescence after being stressed in the dark environment. It can be seen from <xref ref-type="fig" rid="F4">Figures 4A&#x2013;D</xref> that different parts of the dentition produce ML after stress. This phenomenon can guide us to find the site of abnormal occlusion as soon as possible and carry out the next step of targeted treatment.</p>
<fig id="F4" position="float">
<label>FIGURE 4</label>
<caption>
<p>ML in different parts of dentition. <bold>(A)</bold> ML of the whole dentition <bold>(B)</bold> ML of anterior teeth <bold>(C)</bold> ML of left posterior teeth <bold>(D)</bold> ML of bilateral posterior teeth.</p>
</caption>
<graphic xlink:href="fbioe-11-1226065-g004.tif"/>
</fig>
</sec>
<sec id="s3-2">
<title>3.2 Cytotoxicity test</title>
<sec id="s3-2-1">
<title>3.2.1 CCK-8 assay</title>
<p>After 1, 3 and 5&#xa0;days of culture, the cells in each group were observed under inverted microscope, and the growth and morphology of cells in the blank control group and each experimental group were normal. The OD values and cell viability of each group were shown in <xref ref-type="fig" rid="F5">Figure 5</xref>. The cell viability of each group was more than 90%, and the cytotoxicity grade (CTG) was 0. There was no significant difference between the experimental group and the blank control group and between different experimental groups (<italic>p</italic> &#x3e; 0.05). The results showed that different mass fractions of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS composite elastomers had no cytotoxicity.</p>
<fig id="F5" position="float">
<label>FIGURE 5</label>
<caption>
<p>OD values <bold>(A)</bold> and cell viability <bold>(B)</bold> of each group.</p>
</caption>
<graphic xlink:href="fbioe-11-1226065-g005.tif"/>
</fig>
</sec>
<sec id="s3-2-2">
<title>3.2.2 Calcein-AM/PI fluorescence staining</title>
<p>As shown in <xref ref-type="fig" rid="F6">Figure 6</xref>, after Calcein-AM/PI fluorescence staining, most of the cells in the experimental group and control group showed green on the first, third and fifth day, and the cells survived well and the morphology was normal, which indicated that the mass ratio of 10%&#x3001;20%&#x3001;30%&#x3001;40%&#x3001;50% BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS composite elastomers did not cause obvious harm to the cell activity.</p>
<fig id="F6" position="float">
<label>FIGURE 6</label>
<caption>
<p>Calcein-AM/PI fluorescence staining of each group.</p>
</caption>
<graphic xlink:href="fbioe-11-1226065-g006.tif"/>
</fig>
<p>The main methods of cytotoxicity assessment include CCK-8 assay and Calcein-AM/PI fluorescence staining to evaluate whether the cytocompatibility of materials meets the needs of biomaterials by measuring the effects of toxic substances on the morphological number, metabolic activity and proliferation of cultured cells (<xref ref-type="bibr" rid="B4">Cai et al., 2019</xref>; <xref ref-type="bibr" rid="B21">Sun et al., 2022</xref>; <xref ref-type="bibr" rid="B5">Dzedulionyte et al., 2023</xref>). Lmur929 fibroblasts were selected in the above two experiments, which have the advantages of strong reproductive ability, sensitivity to changes in environmental factors, and timely response to toxic substances in the materials (<xref ref-type="bibr" rid="B11">Lendahl et al., 2022</xref>).</p>
<p>The CCK-8 method is based on WST-8 (2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2-methoxy-4-disulfonated phenyl)-2H-tetrazolium monosodium salt) in the presence of electronic carrier 1-methoxy-5-methylphenazinonium sulfate dimethyl ester (1-MethoxyPMS), which is reduced by dehydrogenase in mitochondria to orange-yellow methyl Zan products with high water solubility. The more cells proliferate, the faster the color, the darker the color; the greater the cytotoxicity, the lighter the color (<xref ref-type="bibr" rid="B9">Kawano et al., 2019</xref>). For the same cells, the color is directly proportional to the number of living cells, and the absorbance at 450&#xa0;nm wavelength can be measured by enzyme-linked immunosorbent assay (Elisa), which can indirectly reflect the activity of cells. In addition, according to the 10993&#x2013;5 standard of the International Organization for Standardization, the cell survival rate is more than 90%, indicating that the material has no cytotoxicity.</p>
<p>The principle of Calcein-AM/PI fluorescence staining experiment is that Calcein-AM can only stain living cells, because it can easily penetrate the living cell membrane, hydrolyze in the cytoplasm and emit strong green fluorescence; PI only staining dead cells, because it can not pass through the living cell membrane, can pass through the disordered region of the dead cell membrane to reach the nucleus, and embedded into the DNA double helix of the cell to produce red fluorescence (<xref ref-type="bibr" rid="B26">Xue et al., 2019</xref>; <xref ref-type="bibr" rid="B10">Ke et al., 2020</xref>). It is worth mentioning that the premise of effective staining is that the changes in the activity of the corresponding cell model are physical and biochemical characteristics such as changes in esterase activity and plasma membrane integrity, and cytotoxic events that do not affect these cell characteristics may not be accurately evaluated by this method.</p>
</sec>
</sec>
<sec id="s3-3">
<title>3.3 Oral mucosa irritation test</title>
<p>During the experiment, it was observed that the specimens of all groups of golden gophers were in good retention, normal behavior and mental state, without any abnormal conditions or adverse reactions. In addition, no adverse reactions such as redness, swelling, erosion and ulcer were found at the contact site of the specimen and its surrounding tissue.</p>
<p>
<xref ref-type="fig" rid="F7">Figure 7</xref> shows the histological observation of oral mucosa in the experimental groups and the control group. The microscopic observation shows that compared with the blank control group, the cell morphology and structure of buccal mucosa and its surrounding tissue in each experimental group are normal, there is no epithelial hyperplasia, and the cells are well-delaminated and uniformly arranged. There is no inflammatory.</p>
<fig id="F7" position="float">
<label>FIGURE 7</label>
<caption>
<p>Histological observation of the oral mucosa.</p>
</caption>
<graphic xlink:href="fbioe-11-1226065-g007.tif"/>
</fig>
<p>Cell infiltration in connective tissue, no hyperkeratosis, granular layer changes or other adverse changes. As the occlusal splint has been in direct contact with the oral mucosa for a long time, there is a certain degree of dissolution in the process (<xref ref-type="bibr" rid="B18">Reyes-Sevilla et al., 2018</xref>), so it is required that the material itself and tissue contact will not produce toxic substances. Oral mucosal irritation test is used to evaluate the irritation of materials to oral mucosa by suturing and fixing biomaterials in animals. In this experiment, after the buccal mucosa of golden gophers were exposed to BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS composite elastomers with different mass fraction, no abnormal reaction of color, morphology and texture was observed in the buccal mucosa and its surrounding tissue, indicating that all of them had good biosafety.</p>
</sec>
<sec id="s3-4">
<title>3.4 Subacute systemic toxicity test: oral route</title>
<p>During the experiment, it was observed that the behavior and mental state of all SD rats were normal, and there were no abnormal conditions or adverse reactions. According to the daily body weight changes and food consumption, the relative growth rate of body weight and food utilization rate could be calculated (<xref ref-type="fig" rid="F8">Figures 8A, B</xref>). There was no significant difference between the experimental group and the control group and between different experimental groups by test of variance. In addition, compared with the control group, the important organs of the experimental group were normal in shape and size, and there were no abnormal changes; histopathological examination (<xref ref-type="fig" rid="F8">Figure 8C</xref>) showed no pathological changes such as atrophy, degeneration or pigmentation, and no inflammatory cell infiltration.</p>
<fig id="F8" position="float">
<label>FIGURE 8</label>
<caption>
<p>The relative growth rate of body weight <bold>(A)</bold> and food utilization rate <bold>(B)</bold> of SD rats and HE staining for the subacute systemic toxicity test of each group <bold>(C)</bold>.</p>
</caption>
<graphic xlink:href="fbioe-11-1226065-g008.tif"/>
</fig>
<p>Occlusal splint is in contact with human teeth and periodontal tissue for a long time and bears a variety of long-term stress. Its chemical composition and small substances may enter the human body along with the digestive tract, resulting in toxic effects and harm to tissues and organs of the whole body. Therefore, through the method of intragastric administration, we can ensure that enough drugs enter the digestive tract, simulate the way of toxic substances into the human body to a large extent, and evaluate the biosafety of the materials by observing the clinical symptoms and histological manifestations of animals (<xref ref-type="bibr" rid="B16">Okado et al., 2015</xref>).</p>
</sec>
<sec id="s3-5">
<title>3.5 Acute systemic toxicity test</title>
<p>After injection of material extract, there were no symptoms such as collapse, dyspnea, cyanosis, diarrhea and tremor. Within 72&#xa0;h, the mice in the experimental group and control group moved freely, had a normal appetite, and had no clinical toxic symptoms or death. There was no significant difference in the relative growth rate of body weight of C57 mice between the experimental group and the control group and between different experimental groups (<xref ref-type="fig" rid="F9">Figure 9A</xref>). There were no abnormal pathological changes such as inflammatory cell infiltration in the tissues and organs of mice in the experimental group (<xref ref-type="fig" rid="F9">Figure 9B</xref>). The acute systemic toxicity test is different from the mucosal irritation test, which is not to detect the effect on the contact site, but to evaluate whether the material is potentially toxic to the whole body tissues and organs. If more than one mouse is abnormal during the experiment, such as dyspnea or even death or significant weight loss (more than 2&#xa0;g), the material is proved to be toxic (<xref ref-type="bibr" rid="B17">Pillai et al., 2017</xref>). In this experiment, no abnormality was found in mice, and there was no death or weight loss in mice, indicating that the material has good biological safety.</p>
<fig id="F9" position="float">
<label>FIGURE 9</label>
<caption>
<p>The relative growth rate of body weight of C57 mice <bold>(A)</bold> and HE staining for the acute systemic toxicity test of each group <bold>(B)</bold>.</p>
</caption>
<graphic xlink:href="fbioe-11-1226065-g009.tif"/>
</fig>
</sec>
<sec id="s3-6">
<title>3.6 Hemolysis test</title>
<p>The experimental results are obvious (<xref ref-type="fig" rid="F10">Figure 10</xref>). A large number of red blood cells in the positive control group were destroyed until the supernatant was red, while the supernatant in the negative control group and each experimental group was clear and transparent, and almost no red blood cells were destroyed. The hemolysis rate of each experimental group was less than 5% (<xref ref-type="table" rid="T1">Table 1</xref>). There was no significant difference between the experimental group and the control group and each experimental group by variance test.</p>
<fig id="F10" position="float">
<label>FIGURE 10</label>
<caption>
<p>Hemolysis test supernatant.</p>
</caption>
<graphic xlink:href="fbioe-11-1226065-g010.tif"/>
</fig>
<table-wrap id="T1" position="float">
<label>TABLE 1</label>
<caption>
<p>OD values of the hemolysis test.</p>
</caption>
<table>
<thead valign="top">
<tr>
<th rowspan="2" align="left">Groups</th>
<th colspan="3" align="center">OD value</th>
<th rowspan="2" align="center">Average OD value</th>
<th rowspan="2" align="center">Hemolysis ratio (%)</th>
</tr>
<tr>
<th align="center">1</th>
<th align="center">2</th>
<th align="center">3</th>
</tr>
</thead>
<tbody valign="top">
<tr>
<td align="left">
<bold>Positive control</bold>
</td>
<td align="center">1.3425</td>
<td align="center">1.3902</td>
<td align="center">1.2843</td>
<td align="center">1.3390</td>
<td align="center">-</td>
</tr>
<tr>
<td align="left">
<bold>Blank control</bold>
</td>
<td align="center">0.0196</td>
<td align="center">0.0212</td>
<td align="center">0.0187</td>
<td align="center">0.0198</td>
<td align="center">-</td>
</tr>
<tr>
<td align="left">
<bold>10 wt%BSON:EU</bold>
<sup>
<bold>2&#x2b;</bold>
</sup>
<bold>/PDMS</bold>
</td>
<td align="center">0.0314</td>
<td align="center">0.0303</td>
<td align="center">0.0313</td>
<td align="center">0.0310</td>
<td align="center">0.8465</td>
</tr>
<tr>
<td align="left">
<bold>20 wt%BSON:EU</bold>
<sup>
<bold>2&#x2b;</bold>
</sup>
<bold>/PDMS</bold>
</td>
<td align="center">0.0295</td>
<td align="center">0.0329</td>
<td align="center">0.0314</td>
<td align="center">0.0313</td>
<td align="center">0.8667</td>
</tr>
<tr>
<td align="left">
<bold>30 wt%BSON:EU</bold>
<sup>
<bold>2&#x2b;</bold>
</sup>
<bold>/PDMS</bold>
</td>
<td align="center">0.0311</td>
<td align="center">0.0318</td>
<td align="center">0.0291</td>
<td align="center">0.0307</td>
<td align="center">0.8213</td>
</tr>
<tr>
<td align="left">
<bold>40 wt%BSON:EU</bold>
<sup>
<bold>2&#x2b;</bold>
</sup>
<bold>/PDMS</bold>
</td>
<td align="center">0.0325</td>
<td align="center">0.0316</td>
<td align="center">0.0293</td>
<td align="center">0.0311</td>
<td align="center">0.8566</td>
</tr>
<tr>
<td align="left">
<bold>50 wt%BSON:EU</bold>
<sup>
<bold>2&#x2b;</bold>
</sup>
<bold>/PDMS</bold>
</td>
<td align="center">0.0301</td>
<td align="center">0.0316</td>
<td align="center">0.0295</td>
<td align="center">0.0304</td>
<td align="center">0.8010</td>
</tr>
</tbody>
</table>
</table-wrap>
<p>The principle of hemolysis test is that if the test material is toxic, it will destroy the erythrocyte membrane and release hemoglobin in red blood cells. According to ISO10993-4, if the hemolysis rate of the material is less than 5%, it is proved to be non-toxic and meets the standard of biomedical application (<xref ref-type="bibr" rid="B13">Liu et al., 2022</xref>). In this experiment, the hemolysis rate of each experimental group is far less than the standard value, indicating that the material has good blood compatibility.</p>
</sec>
</sec>
<sec sec-type="conclusion" id="s4">
<title>4 Conclusion</title>
<p>The ML phosphor BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>, was prepared by two-step high temperature solid state method, and then mixed with matrix PDMS to obtain ML composite elastomer&#x2014;BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS. The biocompatibility of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS composite elastomers with different mass fractions (10%, 20%, 30%, 40%, 50%) was evaluated by CCK-8 assay and Calcein-AM/PI fluorescence staining at the cellular level, acute and subacute systemic toxicity test, oral mucosal irritation test and hemolysis test. The results showed that the biosafety of different mass fractions of BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2&#x2b;</sup>/PDMS composite elastomers met the current standards, and other properties could be tested in the next step. For example, elasticity, wear resistance, solubility, stability and so on, select the best quality ratio, with a view to clinical application, to provide a more efficient method for occlusal visualization.</p>
</sec>
</body>
<back>
<sec sec-type="data-availability" id="s5">
<title>Data availability statement</title>
<p>The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding authors.</p>
</sec>
<sec id="s6">
<title>Ethics statement</title>
<p>The animal study was reviewed and approved by Laboratory Animal Center, Shanxi Medical University (Authorization Number KQDW-2023-002).</p>
</sec>
<sec id="s7">
<title>Author contributions</title>
<p>ZZ designed the structure and content, assembled the literature and wrote this review. MZ, JL, JR, XL, RZ, JC, LS, HS, YZ, BL, and XW provided suggestions and revised this review. All authors contributed to the article and approved the submitted version.</p>
</sec>
<sec id="s8">
<title>Funding</title>
<p>This work was supported by Shanxi Province Science and Technology Innovation Key Talent Team (202204051002034), Central guide local science and technology development funds (transfer of scientific and technological achievements) project (YDZJSX 2021C011), Shanxi Province Key R&#x26;D Program (202102130501002) and Key country-specific science and technology cooperation projects of Shanxi Provincial Science and Technology Department (202204041101004).</p>
</sec>
<sec sec-type="COI-statement" id="s9">
<title>Conflict of interest</title>
<p>The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.</p>
</sec>
<sec sec-type="disclaimer" id="s10">
<title>Publisher&#x2019;s note</title>
<p>All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.</p>
</sec>
<ref-list>
<title>References</title>
<ref id="B1">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Al-Moraissi</surname>
<given-names>E. A.</given-names>
</name>
<name>
<surname>Farea</surname>
<given-names>R.</given-names>
</name>
<name>
<surname>Qasem</surname>
<given-names>K. A.</given-names>
</name>
<name>
<surname>Al-Wadeai</surname>
<given-names>M. S.</given-names>
</name>
<name>
<surname>Al-Sabahi</surname>
<given-names>M. E.</given-names>
</name>
<name>
<surname>Al-Iryani</surname>
<given-names>G. M.</given-names>
</name>
</person-group> (<year>2020</year>). <article-title>Effectiveness of occlusal splint therapy in the management of temporomandibular disorders: Network meta-analysis of randomized controlled trials</article-title>. <source>Int. J. Oral Maxillofac. Surg.</source> <volume>49</volume> (<issue>8</issue>), <fpage>1042</fpage>&#x2013;<lpage>1056</lpage>. <pub-id pub-id-type="doi">10.1016/j.ijom.2020.01.004</pub-id>
</citation>
</ref>
<ref id="B2">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Bai</surname>
<given-names>Y.</given-names>
</name>
<name>
<surname>Guo</surname>
<given-names>X.</given-names>
</name>
<name>
<surname>Tian</surname>
<given-names>B.</given-names>
</name>
<name>
<surname>Liang</surname>
<given-names>Y.</given-names>
</name>
<name>
<surname>Peng</surname>
<given-names>D.</given-names>
</name>
<name>
<surname>Wang</surname>
<given-names>Z.</given-names>
</name>
</person-group> (<year>2022</year>). <article-title>Self-charging persistent mechanoluminescence with mechanics storage and visualization activities</article-title>. <source>Adv. Sci. (Weinheim, Baden-Wurttemberg, Ger.</source> <volume>9</volume> (<issue>28</issue>), <fpage>e2203249</fpage>. <pub-id pub-id-type="doi">10.1002/advs.202203249</pub-id>
</citation>
</ref>
<ref id="B3">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Bai</surname>
<given-names>Y.</given-names>
</name>
<name>
<surname>Zheng</surname>
<given-names>Z.</given-names>
</name>
<name>
<surname>Wu</surname>
<given-names>L.</given-names>
</name>
<name>
<surname>Kong</surname>
<given-names>Y.</given-names>
</name>
<name>
<surname>Zhang</surname>
<given-names>Y.</given-names>
</name>
<name>
<surname>Xu</surname>
<given-names>J.</given-names>
</name>
</person-group> (<year>2021</year>). <article-title>Construction of a novel mechanoluminescent phosphor Li(2)MgGeO(4):xMn(2&#x2b;) by defect control</article-title>. <source>Dalton Trans.</source> <volume>50</volume> (<issue>25</issue>), <fpage>8803</fpage>&#x2013;<lpage>8810</lpage>. <pub-id pub-id-type="doi">10.1039/d1dt01125a</pub-id>
</citation>
</ref>
<ref id="B4">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Cai</surname>
<given-names>L.</given-names>
</name>
<name>
<surname>Qin</surname>
<given-names>X.</given-names>
</name>
<name>
<surname>Xu</surname>
<given-names>Z.</given-names>
</name>
<name>
<surname>Song</surname>
<given-names>Y.</given-names>
</name>
<name>
<surname>Jiang</surname>
<given-names>H.</given-names>
</name>
<name>
<surname>Wu</surname>
<given-names>Y.</given-names>
</name>
<etal/>
</person-group> (<year>2019</year>). <article-title>Comparison of cytotoxicity evaluation of anticancer drugs between real-time cell analysis and CCK-8 method</article-title>. <source>ACS Omega</source> <volume>4</volume> (<issue>7</issue>), <fpage>12036</fpage>&#x2013;<lpage>12042</lpage>. <pub-id pub-id-type="doi">10.1021/acsomega.9b01142</pub-id>
</citation>
</ref>
<ref id="B5">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Dzedulionyte</surname>
<given-names>K.</given-names>
</name>
<name>
<surname>Fuxreiter</surname>
<given-names>N.</given-names>
</name>
<name>
<surname>Schreiber-Brynzak</surname>
<given-names>E.</given-names>
</name>
<name>
<surname>Zukauskaite</surname>
<given-names>A.</given-names>
</name>
<name>
<surname>Sackus</surname>
<given-names>A.</given-names>
</name>
<name>
<surname>Pichler</surname>
<given-names>V.</given-names>
</name>
<etal/>
</person-group> (<year>2023</year>). <article-title>Pyrazole-based lamellarin O analogues: Synthesis, biological evaluation and structure-activity relationships</article-title>. <source>RSC Adv.</source> <volume>13</volume> (<issue>12</issue>), <fpage>7897</fpage>&#x2013;<lpage>7912</lpage>. <pub-id pub-id-type="doi">10.1039/d3ra00972f</pub-id>
</citation>
</ref>
<ref id="B6">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Fujio</surname>
<given-names>Y.</given-names>
</name>
<name>
<surname>Xu</surname>
<given-names>C. N.</given-names>
</name>
<name>
<surname>Terasaki</surname>
<given-names>N.</given-names>
</name>
</person-group> (<year>2022</year>). <article-title>Flexible mechanoluminescent SrAl(2)O(4):Eu film with tracking performance of CFRP fracture phenomena</article-title>. <source>Sensors (Basel)</source> <volume>22</volume> (<issue>15</issue>), <fpage>5476</fpage>. <pub-id pub-id-type="doi">10.3390/s22155476</pub-id>
</citation>
</ref>
<ref id="B7">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Grymak</surname>
<given-names>A.</given-names>
</name>
<name>
<surname>Waddell</surname>
<given-names>J. N.</given-names>
</name>
<name>
<surname>Aarts</surname>
<given-names>J. M.</given-names>
</name>
<name>
<surname>Ma</surname>
<given-names>S.</given-names>
</name>
<name>
<surname>Choi</surname>
<given-names>J. J. E.</given-names>
</name>
</person-group> (<year>2022</year>). <article-title>Evaluation of wear behaviour of various occlusal splint materials and manufacturing processes</article-title>. <source>J. Mech. Behav. Biomed. Mater.</source> <volume>126</volume>, <fpage>105053</fpage>. <pub-id pub-id-type="doi">10.1016/j.jmbbm.2021.105053</pub-id>
</citation>
</ref>
<ref id="B8">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Jha</surname>
<given-names>P.</given-names>
</name>
<name>
<surname>Chandra</surname>
<given-names>B. P.</given-names>
</name>
</person-group> (<year>2014</year>). <article-title>Survey of the literature on mechanoluminescence from 1605 to 2013</article-title>. <source>Luminescence</source> <volume>29</volume> (<issue>8</issue>), <fpage>977</fpage>&#x2013;<lpage>993</lpage>. <pub-id pub-id-type="doi">10.1002/bio.2647</pub-id>
</citation>
</ref>
<ref id="B9">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Kawano</surname>
<given-names>M.</given-names>
</name>
<name>
<surname>Hokazono</surname>
<given-names>E.</given-names>
</name>
<name>
<surname>Osawa</surname>
<given-names>S.</given-names>
</name>
<name>
<surname>Sato</surname>
<given-names>S.</given-names>
</name>
<name>
<surname>Tateishi</surname>
<given-names>T.</given-names>
</name>
<name>
<surname>Manabe</surname>
<given-names>M.</given-names>
</name>
<etal/>
</person-group> (<year>2019</year>). <article-title>A novel assay for triglycerides using glycerol dehydrogenase and a water-soluble formazan dye, WST-8</article-title>. <source>Ann. Clin. Biochem.</source> <volume>56</volume> (<issue>4</issue>), <fpage>442</fpage>&#x2013;<lpage>449</lpage>. <pub-id pub-id-type="doi">10.1177/0004563219830715</pub-id>
</citation>
</ref>
<ref id="B10">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Ke</surname>
<given-names>X.</given-names>
</name>
<name>
<surname>Li</surname>
<given-names>M.</given-names>
</name>
<name>
<surname>Wang</surname>
<given-names>X.</given-names>
</name>
<name>
<surname>Liang</surname>
<given-names>J.</given-names>
</name>
<name>
<surname>Wang</surname>
<given-names>X.</given-names>
</name>
<name>
<surname>Wu</surname>
<given-names>S.</given-names>
</name>
<etal/>
</person-group> (<year>2020</year>). <article-title>An injectable chitosan/dextran/&#x3b2; -glycerophosphate hydrogel as cell delivery carrier for therapy of myocardial infarction</article-title>. <source>Carbohydr. Polym.</source> <volume>229</volume>, <fpage>115516</fpage>. <pub-id pub-id-type="doi">10.1016/j.carbpol.2019.115516</pub-id>
</citation>
</ref>
<ref id="B11">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Lendahl</surname>
<given-names>U.</given-names>
</name>
<name>
<surname>Muhl</surname>
<given-names>L.</given-names>
</name>
<name>
<surname>Betsholtz</surname>
<given-names>C.</given-names>
</name>
</person-group> (<year>2022</year>). <article-title>Identification, discrimination and heterogeneity of fibroblasts</article-title>. <source>Nat. Commun.</source> <volume>13</volume> (<issue>1</issue>), <fpage>3409</fpage>. <pub-id pub-id-type="doi">10.1038/s41467-022-30633-9</pub-id>
</citation>
</ref>
<ref id="B12">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Li</surname>
<given-names>D. T. S.</given-names>
</name>
<name>
<surname>Leung</surname>
<given-names>Y. Y.</given-names>
</name>
</person-group> (<year>2021</year>). <article-title>Temporomandibular disorders: Current concepts and controversies in diagnosis and management</article-title>. <source>Diagn. (Basel)</source> <volume>11</volume> (<issue>3</issue>), <fpage>459</fpage>. <pub-id pub-id-type="doi">10.3390/diagnostics11030459</pub-id>
</citation>
</ref>
<ref id="B13">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Liu</surname>
<given-names>X.</given-names>
</name>
<name>
<surname>Yan</surname>
<given-names>J.</given-names>
</name>
<name>
<surname>Wu</surname>
<given-names>X.</given-names>
</name>
<name>
<surname>Wu</surname>
<given-names>X.</given-names>
</name>
<name>
<surname>Zhang</surname>
<given-names>Y.</given-names>
</name>
<name>
<surname>Li</surname>
<given-names>B.</given-names>
</name>
</person-group> (<year>2022</year>). <article-title>Biosafety evaluation of Li2Si2O5whisker-reinforced glass-ceramics</article-title>. <source>Biomed. Mater. (Bristol, Engl.</source> <volume>17</volume> (<issue>2</issue>), <fpage>025011</fpage>. <pub-id pub-id-type="doi">10.1088/1748-605x/ac4e65</pub-id>
</citation>
</ref>
<ref id="B14">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Manfredini</surname>
<given-names>D.</given-names>
</name>
<name>
<surname>Lombardo</surname>
<given-names>L.</given-names>
</name>
<name>
<surname>Siciliani</surname>
<given-names>G.</given-names>
</name>
</person-group> (<year>2017</year>). <article-title>Temporomandibular disorders and dental occlusion. A systematic review of association studies: End of an era?</article-title> <source>J. oral rehabilitation</source> <volume>44</volume> (<issue>11</issue>), <fpage>908</fpage>&#x2013;<lpage>923</lpage>. <pub-id pub-id-type="doi">10.1111/joor.12531</pub-id>
</citation>
</ref>
<ref id="B15">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Ohrbach</surname>
<given-names>R.</given-names>
</name>
<name>
<surname>Slade</surname>
<given-names>G. D.</given-names>
</name>
<name>
<surname>Bair</surname>
<given-names>E.</given-names>
</name>
<name>
<surname>Rathnayaka</surname>
<given-names>N.</given-names>
</name>
<name>
<surname>Diatchenko</surname>
<given-names>L.</given-names>
</name>
<name>
<surname>Greenspan</surname>
<given-names>J. D.</given-names>
</name>
<etal/>
</person-group> (<year>2020</year>). <article-title>Premorbid and concurrent predictors of TMD onset and persistence</article-title>. <source>Eur. J. Pain</source> <volume>24</volume> (<issue>1</issue>), <fpage>145</fpage>&#x2013;<lpage>158</lpage>. <pub-id pub-id-type="doi">10.1002/ejp.1472</pub-id>
</citation>
</ref>
<ref id="B16">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Okado</surname>
<given-names>N.</given-names>
</name>
<name>
<surname>Sugi</surname>
<given-names>M.</given-names>
</name>
<name>
<surname>Ueda</surname>
<given-names>M.</given-names>
</name>
<name>
<surname>Mizuhashi</surname>
<given-names>F.</given-names>
</name>
<name>
<surname>Lynch</surname>
<given-names>B. S.</given-names>
</name>
<name>
<surname>Vo</surname>
<given-names>T. D.</given-names>
</name>
<etal/>
</person-group> (<year>2015</year>). <article-title>Safety evaluation of AMP deaminase from Aspergillus oryzae</article-title>. <source>Food Chem. Toxicol.</source> <volume>86</volume>, <fpage>342</fpage>&#x2013;<lpage>350</lpage>. <pub-id pub-id-type="doi">10.1016/j.fct.2015.11.001</pub-id>
</citation>
</ref>
<ref id="B17">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Pillai</surname>
<given-names>G. K. G.</given-names>
</name>
<name>
<surname>Bharate</surname>
<given-names>S. S.</given-names>
</name>
<name>
<surname>Awasthi</surname>
<given-names>A.</given-names>
</name>
<name>
<surname>Verma</surname>
<given-names>R.</given-names>
</name>
<name>
<surname>Mishra</surname>
<given-names>G.</given-names>
</name>
<name>
<surname>Singh</surname>
<given-names>A. T.</given-names>
</name>
<etal/>
</person-group> (<year>2017</year>). <article-title>Antidiabetic potential of polyherbal formulation DB14201: Preclinical development, safety and efficacy studies</article-title>. <source>J. Ethnopharmacol.</source> <volume>197</volume>, <fpage>218</fpage>&#x2013;<lpage>230</lpage>. <pub-id pub-id-type="doi">10.1016/j.jep.2016.07.062</pub-id>
</citation>
</ref>
<ref id="B18">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Reyes-Sevilla</surname>
<given-names>M.</given-names>
</name>
<name>
<surname>Kuijs</surname>
<given-names>R. H.</given-names>
</name>
<name>
<surname>Werner</surname>
<given-names>A.</given-names>
</name>
<name>
<surname>Kleverlaan</surname>
<given-names>C. J.</given-names>
</name>
<name>
<surname>Lobbezoo</surname>
<given-names>F.</given-names>
</name>
</person-group> (<year>2018</year>). <article-title>Comparison of wear between occlusal splint materials and resin composite materials</article-title>. <source>J. Oral Rehabil.</source> <volume>45</volume> (<issue>7</issue>), <fpage>539</fpage>&#x2013;<lpage>544</lpage>. <pub-id pub-id-type="doi">10.1111/joor.12636</pub-id>
</citation>
</ref>
<ref id="B19">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Seibald</surname>
<given-names>M.</given-names>
</name>
<name>
<surname>Rosenthal</surname>
<given-names>T.</given-names>
</name>
<name>
<surname>Oeckler</surname>
<given-names>O.</given-names>
</name>
<name>
<surname>Fahrnbauer</surname>
<given-names>F.</given-names>
</name>
<name>
<surname>Tucks</surname>
<given-names>A.</given-names>
</name>
<name>
<surname>Schmidt</surname>
<given-names>P. J.</given-names>
</name>
<etal/>
</person-group> (<year>2012</year>). <article-title>Unexpected luminescence properties of Sr(0.25)Ba(0.75)Si2O2N2:Eu(2&#x2b;)-a narrow blue emitting oxonitridosilicate with cation ordering</article-title>. <source>Chemistry</source> <volume>18</volume> (<issue>42</issue>), <fpage>13446</fpage>&#x2013;<lpage>13452</lpage>. <pub-id pub-id-type="doi">10.1002/chem.201201953</pub-id>
</citation>
</ref>
<ref id="B20">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Shin</surname>
<given-names>H. G.</given-names>
</name>
<name>
<surname>Timilsina</surname>
<given-names>S.</given-names>
</name>
<name>
<surname>Sohn</surname>
<given-names>K. S.</given-names>
</name>
<name>
<surname>Kim</surname>
<given-names>J. S.</given-names>
</name>
</person-group> (<year>2022</year>). <article-title>Digital image correlation compatible mechanoluminescent skin for structural health monitoring</article-title>. <source>Adv. Sci. (Weinh).</source> <volume>9</volume> (<issue>11</issue>), <fpage>e2105889</fpage>. <pub-id pub-id-type="doi">10.1002/advs.202105889</pub-id>
</citation>
</ref>
<ref id="B21">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Sun</surname>
<given-names>H.</given-names>
</name>
<name>
<surname>Gao</surname>
<given-names>K.</given-names>
</name>
<name>
<surname>Yi</surname>
<given-names>Z.</given-names>
</name>
<name>
<surname>Han</surname>
<given-names>C.</given-names>
</name>
<name>
<surname>Liu</surname>
<given-names>Z.</given-names>
</name>
<name>
<surname>Wang</surname>
<given-names>Q.</given-names>
</name>
<etal/>
</person-group> (<year>2022</year>). <article-title>Cytotoxicity and bonding property of bioinspired nacre-like ceramic-polymer composites</article-title>. <source>Front. Bioeng. Biotechnol.</source> <volume>10</volume>, <fpage>913899</fpage>. <pub-id pub-id-type="doi">10.3389/fbioe.2022.913899</pub-id>
</citation>
</ref>
<ref id="B22">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Wang</surname>
<given-names>W.</given-names>
</name>
<name>
<surname>Tasset</surname>
<given-names>A.</given-names>
</name>
<name>
<surname>Pyatnitskiy</surname>
<given-names>I.</given-names>
</name>
<name>
<surname>Mohamed</surname>
<given-names>H. G.</given-names>
</name>
<name>
<surname>Taniguchi</surname>
<given-names>R.</given-names>
</name>
<name>
<surname>Zhou</surname>
<given-names>R.</given-names>
</name>
<etal/>
</person-group> (<year>2022</year>). <article-title>Ultrasound triggered organic mechanoluminescence materials</article-title>. <source>Adv. Drug Deliv. Rev.</source> <volume>186</volume>, <fpage>114343</fpage>. <pub-id pub-id-type="doi">10.1016/j.addr.2022.114343</pub-id>
</citation>
</ref>
<ref id="B23">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Wieckiewicz</surname>
<given-names>M.</given-names>
</name>
<name>
<surname>Boening</surname>
<given-names>K.</given-names>
</name>
<name>
<surname>Wiland</surname>
<given-names>P.</given-names>
</name>
<name>
<surname>Shiau</surname>
<given-names>Y. Y.</given-names>
</name>
<name>
<surname>Paradowska-Stolarz</surname>
<given-names>A.</given-names>
</name>
</person-group> (<year>2015</year>). <article-title>Reported concepts for the treatment modalities and pain management of temporomandibular disorders</article-title>. <source>J. Headache Pain</source> <volume>16</volume>, <fpage>106</fpage>. <pub-id pub-id-type="doi">10.1186/s10194-015-0586-5</pub-id>
</citation>
</ref>
<ref id="B24">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Xie</surname>
<given-names>H.</given-names>
</name>
<name>
<surname>Cao</surname>
<given-names>T.</given-names>
</name>
<name>
<surname>Rodriguez-Lozano</surname>
<given-names>F. J.</given-names>
</name>
<name>
<surname>Luong-Van</surname>
<given-names>E. K.</given-names>
</name>
<name>
<surname>Rosa</surname>
<given-names>V.</given-names>
</name>
</person-group> (<year>2017</year>). <article-title>Graphene for the development of the next-generation of biocomposites for dental and medical applications</article-title>. <source>Dent. Mater</source> <volume>33</volume> (<issue>7</issue>), <fpage>765</fpage>&#x2013;<lpage>774</lpage>. <pub-id pub-id-type="doi">10.1016/j.dental.2017.04.008</pub-id>
</citation>
</ref>
<ref id="B25">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Xiong</surname>
<given-names>P.</given-names>
</name>
<name>
<surname>Peng</surname>
<given-names>M.</given-names>
</name>
<name>
<surname>Yang</surname>
<given-names>Z.</given-names>
</name>
</person-group> (<year>2021</year>). <article-title>Near-infrared mechanoluminescence crystals: A review</article-title>. <source>iScience</source> <volume>24</volume> (<issue>1</issue>), <fpage>101944</fpage>. <pub-id pub-id-type="doi">10.1016/j.isci.2020.101944</pub-id>
</citation>
</ref>
<ref id="B26">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Xue</surname>
<given-names>H.</given-names>
</name>
<name>
<surname>Hu</surname>
<given-names>L.</given-names>
</name>
<name>
<surname>Xiong</surname>
<given-names>Y.</given-names>
</name>
<name>
<surname>Zhu</surname>
<given-names>X.</given-names>
</name>
<name>
<surname>Wei</surname>
<given-names>C.</given-names>
</name>
<name>
<surname>Cao</surname>
<given-names>F.</given-names>
</name>
<etal/>
</person-group> (<year>2019</year>). <article-title>Quaternized chitosan-Matrigel-polyacrylamide hydrogels as wound dressing for wound repair and regeneration</article-title>. <source>Carbohydr. Polym.</source> <volume>226</volume>, <fpage>115302</fpage>. <pub-id pub-id-type="doi">10.1016/j.carbpol.2019.115302</pub-id>
</citation>
</ref>
<ref id="B27">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Yun</surname>
<given-names>Y. J.</given-names>
</name>
<name>
<surname>Kim</surname>
<given-names>J. K.</given-names>
</name>
<name>
<surname>Ju</surname>
<given-names>J. Y.</given-names>
</name>
<name>
<surname>Choi</surname>
<given-names>S. K.</given-names>
</name>
<name>
<surname>Park</surname>
<given-names>W. I.</given-names>
</name>
<name>
<surname>Jung</surname>
<given-names>H. K.</given-names>
</name>
<etal/>
</person-group> (<year>2016</year>). <article-title>Eu(2&#x2b;)-Activated phase-pure oxonitridosilicate phosphor in a Ba-Si-O-N system via facile silicate-assisted routes designed by first-principles thermodynamic simulation</article-title>. <source>Inorg. Chem.</source> <volume>55</volume> (<issue>17</issue>), <fpage>8750</fpage>&#x2013;<lpage>8757</lpage>. <pub-id pub-id-type="doi">10.1021/acs.inorgchem.6b01278</pub-id>
</citation>
</ref>
<ref id="B28">
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Zhuang</surname>
<given-names>Y.</given-names>
</name>
<name>
<surname>Xie</surname>
<given-names>R. J.</given-names>
</name>
</person-group> (<year>2021</year>). <article-title>Mechanoluminescence rebrightening the prospects of stress sensing: A review</article-title>. <source>Adv. Mater</source> <volume>33</volume> (<issue>50</issue>), <fpage>e2005925</fpage>. <pub-id pub-id-type="doi">10.1002/adma.202005925</pub-id>
</citation>
</ref>
</ref-list>
</back>
</article>