Ring-Shaped Surface Microstructures for Improved Lubrication Performance of Joint Prostheses

The Impact of Ultrashort Pulse Laser Structuring of Metals on In-Vitro Cell Adhesion of Keratinocytes

Besides the need for biomaterial surface modification to improve cellular attachment, laser-structuring is favorable for designing a new surface topography for external bone fixator pins or implants. The principle of this study was to observe how bioinspired (deer antler) laser-induced nano-microstructures influenced the adhesion and growth of skin cells. The goal was to create pins that allow the skin to attach to the biomaterial surface in a bacteria-proof manner. Therefore, typical fixator metals, steel, and titanium alloy were structured using ultrashort laser pulses, which resulted in periodical nano- and microstructures. Surface characteristics were investigated using a laser scanning microscope and static water contact angle measurements. In vitro studies with human HaCaT keratinocytes focused on cell adhesion, morphology, actin formation, and growth within 7 days. The study showed that surface functionalization influenced cell attachment, spreading, and proliferation. Micro-dimple clusters on polished bulk metals (DC20) will not hinder viability. Still, they will not promote the initial adhesion and spreading of HaCaTs. In contrast, additional nanostructuring with laser-induced periodic surface structures (LIPSS) promotes cell behavior. DC20 + LIPSS induced enhanced cell attachment with well-spread cell morphology. Thus, the bioinspired structures exhibited a benefit in initial cell adhesion. Laser surface functionalization opens up new possibilities for structuring, and is relevant to developing bioactive implants in regenerative medicine.

Surface Texturing of Prosthetic Hip Implant Bearing Surfaces: A Review

More than 300,000 total hip replacement surgeries are performed in the United States each year to treat degenerative joint diseases that cause pain and disability. The statistical survivorship of these implants declines significantly after 15-25 years of use because wear debris causes inflammation, osteolysis, and mechanical instability of the implant. This limited longevity has unacceptable consequences, such as revision surgery to replace a worn implant, or surgery postponement, which leaves the patient in pain. Innovations such as highly cross-linked polyethylene and new materials and coatings for the femoral head have reduced wear significantly, but longevity remains an imminent problem. Another method to reduce wear is to add a patterned microtexture composed of micro-sized texture features to the smooth bearing surfaces. We critically review the literature on textured orthopedic biomaterial surfaces in the context of prosthetic hip implants. We discuss the different functions of texture features by highlighting experimental and simulated results documented by research groups active in this area. We also discuss and compare different manufacturing techniques to create texture features on orthopedic biomaterial surfaces and emphasize the key difficulties that must be overcome to produce textured prosthetic hip implants.

Study of the tribological properties of surface structures using ultrashort laser pulses to reduce wear in endoprosthetics

Background

Loosening of prostheses and functional disorders represent a far-reaching problem in the clinic, and the long-term outcomes are essentially determined by wear. Despite all advances, up to 10% of prostheses still fail after 10 years. In particular, more active patients show increased revision rates.

Methods

The objective of this thesis is to examine whether the applied microstructures of the articulating surfaces can lead to a reduction in abrasion. Three different structural geometries (dimples, offset lines, grid lines) were defined. In an experimental test setup according to DIN ISO 6474 (Deutsches Institut für Normung, International Organization for Standardization), a tribological test of metal and ceramic pairings was performed using two-dimensional ring-on-disc (RoD) tests.

Results

In both material groups, the structuring had a positive effect on the wear behaviour. In the ceramic group, an abrasion reduction of 22.6% was achieved. However, it is important to take into account the limited informative value due to the hardness of the material. Two of the three Cobalt-Chrome-Molybdenum (CoCrMo) structure geometries (grids, offset lines) also showed a significant reduction in abrasion compared to the reference group, with a maximum wear reduction of 55.5%.

Conclusion

By reducing abrasion, surface structuring could be used to extend the life of prostheses and minimise the number of revisions.