Introduction: Properties of polydimethylsiloxane (PDMS) promise a great convenience in clinical applications because of the good mechanical and chemical characteristics. In general, bioceramics exhibit excellent biological performance that can promote new bone formation to produce a pore-like structure. Hydroxyapatite (HA) is similar to primary constituent of bone. HA may form a bond with bone tissues and it possesses excellent biocompatibility. However, HA is brittle. So it is interesting to combine the advantages of HA and PDMS and to form a new material system[1]-[3]. An important use of the PDMS has been to develop stents, especially for tracheobronchial applications. One approach to improving the bioactivity in this case is a mixture of biologically active PDMS and nanosized-HA (n-HA). A new method was developed in order to produce stents with PDMS incorporated with bioactive inorganic substances. In this process the formation of CP nanoparticles occurs in situ facilitating the production and incorporation of CP.
Materials and Methods: To produce PDMS/CP composite, Ca(OH)2 was mixed to PDMS in an open two-roll mixer. Suitable quantity of H3PO4 was added and homogenized. Biomaterial was pressed in metallic molds to obtain samples and cross-linked at 185 oC for 45 min. Phase composition was analyzed by XRD under 40 kV and 40 mA. TEM was performed to observe the nanoparticles of the material. In vitro tests were carried out dipped samples in SBF to simulate the behavior of the material into the human body. Shore A hardness was measured according to ASTM D2240 in five samples.
Results and Discussion: The method to produce PDMS/CP consists in obtain the CP in situ during the production of PDMS composite. According to literature, dibasic calcium phosphate dihydrate (DCPD) can transform in dibasic calcium phosphate anhydrate (DCPA) at temperatures around 80oC[4]. Therefore, after cross-linking reaction, DCPD suffered dehydration to form DCPA. XRD presents DCPA and HA as filler phases in the composite. The pH measurement is around 7.12, that is recommended range for implantable materials[5]. Shore A is 30.50 ± 0.75 for PDMS and is 42.00 ± 0.52 for PDMS/CP. The higher hardness of composite occurs due to presence of filler phases (HA and DCPA). TEM analysis shows presence of spherical nanoparticles of CP with dimensions around 20 nm homogeneously distributed.
Conclusion: Composite produced by biomimetic method shown HA and DCPA after cross-linked. Shore A shown higher values for PDMS/CP, because of the presence of filler phases. Composite presented CP nanoparticles homogenously distributed. The pH found is recommended range to implantation of the biomaterial.
CNPq – Brazil; FINEP - Brazil
References:
[1] Thein-Han, W.W., et. al, Superior in vitro biological response and mechanical properties of an implantable nanostructured biomaterial: nanohydroxyatite-silicone rubber composite, 5, 2668-2679.
[2] Ferreira, O.J.B., 2012. Desenvolvimento de compósitos polidimetilsiloxano/fosfatos de cálcio, dissertação de mestrado, 1-127.
[3] Santos, L. A., et. al., 2012. Compósito nanoestruturado de fosfato de cálcio e borracha de silicone. Brasil. Patente: Privilégio de Inovação. Número de registro: PI 10 2012-01, 29/05/2012.
[4] Dorozhkin, S. V., Calcium orthophosphates in nature, biology and medicine, 2, 399 – 498.
[5] Driessens, F. C. M., 1997. In: Bioceramics Vol 8 - 4° Euro Ceramics, 1998, Bologna/Italia. Anais. Faenza: Faenza Editrice, 77–83.