115 - Prescriptive surface etching with femtosecond Laser achieves nano-topography

INTRODUCTION
Implant surface modification offers meaningful advantages for enhancing stability for bone-interfaced implants. A technique based on femtosecond laser etching was used for prescriptive structuring Titanium alloy (Ti6Al4V) surfaces. Manufacturing methods were developed that were isotropic to macro patterning, variably graduated in differential channel depth, and guided to predictable nano resolutions enhancing cell attachment (Figure 1).
AIMS/OBJECTIVES
This study was designed to determine the impact of surface pattern using femtosecond laser etching on Titanium alloy implants with regard to the adhesion and preferential differentiation of osteogenic progenitors derived from mouse bone marrow stem cells (BMSCs).
METHODS
Electron Dispersive Analysis for compositional analysis was performed using a Hitachi Regulus 8230 SEM (Tokyo, JP). Freshly prepared BMSCs were derived from a double transgenic reporter mouse (BspGFPtpz/DmpRFPchry (Bone sialoprotein/Dental Matrix Protein) that activated sequentially at the early (green) and late stages (red) of osteogenic differentiation. Cells were seeded onto the test coupons and evaluated at 0, 3, 7, 14, and 21 days for cell distribution and state of osteogenic differentiation by scanning confocal microscopy, high resolution cell morphometry by SEM, and gene expression by multiplex PCR. Isotropic patterning was generated from micro-CT CAD scaffold architecture based on bone subjected to microgravity. Laser etching was performed with GF Femto Flexi GR laser source with a static emission wavelength and specified pulse duration (GF Industries, Schaffhausen, SZ). Different depths and post-process peening were contrasted with smooth Titanium coupons.
RESULTS
Post-etching elemental analysis revealed a consistent expression of Ti, Al, and V in empiric quantity consistent with composition that was maintained at nanometric resolution. A 20-watt power source with femtosecond wavelength and high repetition rate were designed to reduce potential for embrittled oxygen diffusion zone, thus avoiding cracks and preventing material phase transitions. By day 3, early osteogenesis had commenced with BSP+ (green cells) distributed preferentially on the surface and not the channels of the disc. At day 7, the cells outlining the contours of the channels showed extensive numbers of DMP+ cells, and by day 14, these cells had become multilayered on the surface and extended into the sides and floor of the channels. SEM revealed cells that were actively attached identified with the prescribed pattern and exuded nanopodia that bridged areas of surface bouquets resulting from the laser treatment. RNA expression studies confirm the morphology showing cell expression resulted in RNA specific for proteins supporting osteogenic differentiation.
CONCLUSIONS
Using prescriptive laser engraving with advanced femtosecond technology, it was possible to create nanometric surface modulation without affecting composition while at the same time enhancing osteogenic differentiation demonstrating extensive bridging of cell processes. These material properties predict a potential for optimal implant integration with surrounding bone tissue.