In vitro inflammatory cell response to ultra-thin hydroxyapatite surfaces
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1
Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Department of Biomaterials, Sweden
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2
BIOMATCELL VINN Excellence Center of Biomaterials and Cell Therapy, Sweden
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3
Faculty of Odontology, Malmö University, Department of Prosthodontics, Sweden
Introduction: Coating of titanium implant with thin hydroxyapatite (HA) has been suggested to improve implant performance. However, there is a lack of knowledge on which biological factors that would contribute to the HA-induced response. The fast recruitment of monocytes and the capacity of HA to promote bone regeneration raise the questions: firstly if certain properties of HA are of importance for the inflammatory response, and secondly, if these cells might contribute to the osteogenesis at the implant surface.
The aim of this study was to investigate the early inflammatory cell response (monocytes/macrophages) to titanium implants with either amorphous or crystalline thin HA coatings, and to compare that to the native machined titanium surface.
Material and Methods: Thin HA coating (0.1 μm thickness) on titanium discs was produced using radiofrequency magnetron sputtering, resulting in a thin amorphous HA coating. Half of the amorphous HA coated discs were subjected to heat treatment (HT) resulting in a crystalline HA coating. Human monocytes were cultured on four different surfaces: (i) thin amorphous HA; (ii) thin crystalline HA; (iii) titanium; (iv) polystyrene; (n=6). The surface properties were characterized with respect to surface chemistry (using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD)), surface topography (using optical interferometer and scanning electron microscopy (SEM)) and wettability (by contact angle measurement). The number of cells adherent to the surfaces was evaluated using NucleoCounter. The response of primary human monocytes was evaluated by measuring the release of pro-inflammatory cytokine, tumor necrosis factor-alpha (TNF-α), and the pro-osteogenic growth factor, bone morphogenetic protein (BMP-2). For surface characterization, one-way ANOVA and Tukey tests were used. For the in vitro cell culture studies, non-parametric Friedman and Wilcoxon signed-rank tests were used (p < 0.05 is significant).
Results and Discussion: All implants revealed comparable micro-topography, but different nano-topography, wettability (Fig.1) and surface chemistry and phase composition. On the nano-scale level, crystalline HA showed a smooth surface structure while the amorphous HA showed a porous structure. The XRD confirmed the HA crystallinity after HT. The highest contact angle was shown for the amorphous HA (least hydrophilic) as compared to Ti and crystalline HA (Fig.1).
When human monocytes were cultured on the different surfaces, their secretion of TNF-α was significantly higher in the amorphous HA group (Fig.2). However, no secretion for BMP-2 was detected in response to any of the surfaces. The latter observation extends our previous findings[1] disputing the release of BMP-2 from primary human monocytes/macrophages[2]. The cell counting indicated that the amorphous HA are associated with higher number of adhering cells compared to polystyrene (Fig.2).
Conclusion: The present results show that variations in surface chemistry, phase composition, nano-scale roughness and wettability are associated with different monocyte response. Within the limit of the in vitro assays, it is concluded that amorphous HA, but not crystalline HA, with the relatively low wettability and rougher surface at the nano-scale, elicits higher inflammatory response, while tentatively not affecting the osteogenic capacity of human monocytes.
This study was supported by the Swedish Research Council (K2015-52X-09495-28-4), BIOMATCELL VINN Excellence Center of Biomaterials and Cell Therapy, the Region Västra Götaland and the Hjalmar Svensson Research Foundation.
References:
[1] Omar O. et al. Biomaterials 2011
[2] Champagne CM. et al. Bone 2002
Keywords:
in vitro,
Surface modification,
Calcium phosphate,
Ultra-thin coating
Conference:
10th World Biomaterials Congress, Montréal, Canada, 17 May - 22 May, 2016.
Presentation Type:
Poster
Topic:
Biomaterials in immune response
Citation:
Rydén
L,
Omar
O,
Johansson
A,
Jimbo
R,
Palmquist
A and
Thomsen
P
(2016). In vitro inflammatory cell response to ultra-thin hydroxyapatite surfaces.
Front. Bioeng. Biotechnol.
Conference Abstract:
10th World Biomaterials Congress.
doi: 10.3389/conf.FBIOE.2016.01.02324
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Received:
27 Mar 2016;
Published Online:
30 Mar 2016.