gms | German Medical Science

Objectives: Numerous arthroplasties require revision due to implant loosening, a failure of osteointegration on account of fibrous tissue or infection. The micro-to-nano-features of implant surfaces greatly influence cell behaviour at the tissue-implant-interface and thereby the subsequent osteointegration. The goal of the study was to test the cellular response towards titanium (Ti) implants harbouring a novel laser-based surface structure, with the overall aim to achieve augmented osteointegration. To create the designer topography, shifted Laser Surface Texturing (sLST) technology was implemented. Human mesenchymal stem cells (hMSCs), which are naturally available at the bone-implant-interface and osteoinducible, were used to evaluate the biological response.

Methods: Disk-shaped Ti grade 2 scaffolds were used. The rough surface microtopography with squared or circular open pores (diameter 500 µm) was generated by sLST using a SPI G3 series laser (wavelength 1064 nm, pulse 200 ns; TRUMPF Laser). For the SLA control surface, Ti disks were sandblasted and afterwards acid-etched with HCl/H2SO4. hMSCs (n=6; 3 female, 3 male; age 29+-6) were studied in passages 2-4. Cells were examined for survival by live/dead staining at day 1/5 of cultivation. To examine cell metabolic activity and proliferation, Resazurin assay was conducted on day 1, 3, 5 and 7. Osteogenic differentiation was carried out over 21 days and validated with Alizarin Red S staining and quantification. Statistical testing was performed with unpaired t-test and/or one way ANOVA.

Results and Conclusion: Laser structuring produced precisely the desired Ti microgeometries. On the nanostructural level, Ti droplets of different sizes were stochastically formed by laser-induced Ti plasma. Live/dead staining and Resazurin assay showed a high and comparable survival rate and metabolic activity of hMSCs at each time point on both scaffold types. Alizarin quantification revealed significantly higher (p<0.0001) mineralization for cells cultured on lasered Ti compared to SLA. Moreover, poorly differentiating donors showed significant improvement on the lasered Ti. Comparison of square to circular pores did not detect significant difference in the Alizarin Red values.

Varying the surface micro-topography did not result in significant differences, suggesting the effect of micro-topography as negligible and the nanotopography as the key factor for cellular response. Osteogenesis was significantly augmented on lasered Ti compared to SLA and interestingly, even poorly differentiating donors had a significant increase in osteoinduction. This donor effect suggests that the novel surface can rescue osteogenically compromised cells, which may be related to mechanisms controlling cellular shape, tension and fate; further investigations are currently ongoing. In sum, laser-textured Ti materials are safe and have designer surface topographies, thus representing a great potential to develop into next-generation-implants suitable for different patient cohorts.