Abstract
Titanium is widely used as a bone implant material due to its biocompatibility and high resilience. Since its Young’s modulus differs from bone tissue, the resulting “stress shielding” could lead to scaffold loosening. However, by using a scaffold-shaped geometry, the Young’s modulus can be adjusted. Also, a porous geometry enables vascularisation and bone ingrowth inside the implant itself. Additionally, growth factors can improve these effects. In order to create a deposit and release system for these factors, the titanium scaffolds could be coated with degradable polymers. Therefore, in the present study, synthetic poly-ε-caprolactone (PCL) and the biopolymer poly(3-hydroxybutyrate) (P(3HB)) were tested for coating efficiency, cell adhesion, and biocompatibility to find a suitable coating material. The underlying scaffold was created from titanium by Selective Laser Melting (SLM) and coated with PCL or P(3HB) via dip coating. To test the biocompatibility, Live Cell Imaging (LCI) as well as vitality and proliferation assays were performed. In addition, cell adhesion forces were detected via Single Cell Force Spectroscopy, while the coating efficiency was observed using environmental scanning electron microscopy (ESEM) and energy-dispersive X-ray (EDX) analyses. Regarding the coating efficiency, PCL showed higher values in comparison to P(3HB). Vitality assays revealed decent vitality values for both polymers, while values for PCL were significantly lower than those for blank titanium. No significant differences could be observed between PCL and P(3HB) in proliferation and cell adhesion studies. Although LCI observations revealed decreasing values in cell number and populated area over time on both polymer-coated scaffolds, these outcomes could be explained by the possibility of coating diluent residues accumulating in the culture medium. Overall, both polymers fulfill the requirements regarding biocompatibility. Nonetheless, since only PCL coating ensured the maintenance of the porous implant structure, it is preferable to be used as a coating material for creating a deposit and release system for growth factors.
Highlights
While titanium is widely used as a biocompatible bone implant material, the long-term side effects of stress shielding and the resulting implant loosening due to the difference in Young’s moduli of titanium and bone are still given [1,2,3]
Adult C57Bl6 mice or green fluorescent protein (GFP)*C57Bl6 mice were used for osteoblast isolation
Synthetic PCL and biologically generated P(3HB) were tested for coating efficiency, biocompatibility, and cell adhesion in order to prove their suitability as coating materials for porous biocompatibility, and cell adhesion in order to prove their suitability as coating materials for porous titanium scaffolds to possibly act as a deposit and release system for growth factors
Summary
While titanium is widely used as a biocompatible bone implant material, the long-term side effects of stress shielding and the resulting implant loosening due to the difference in Young’s moduli of titanium and bone are still given [1,2,3]. These challenges can be overcome by creating porous scaffold-shaped implants whose Young’s modulus is influenced by the underlying material, and by their porosity. Pore sizes of 160–270 μm are reported to support fast and broad vascularisation, which is needed for nutrition of newly built tissue [9]
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