Resumen de Development of metallic functionalized biomaterials with low elastic modulus for orthopedic applications
Titanium (Ti) and Ti allor-; have been used for decades for bone implants and prostheses dueto its mechanical reliability and good biocompatibility. However, implant-related infections, lack ofosteointegration with the surrounding bone, and the mism atch of mechanical properties between implant and bone, remain among the leading reasons for implant failure . In the present PhD thesis, two strategies have been studied to increase implant lñability: fabrication of porous Ti structures and surface functionali zation.
The stiffness mismatch between titanium implant and bone can cause significant bone resorption, which can lead to serious complications such as periprosthetic fracture during or after relñsion surgery. Titanium surface piar-; a major role in the bone prosthesis interactions, notonlyto promote initial cell adhesion butalso to avoid bacterial adhesion . One strategystudied in the thesis has been the developmentand manufacturing ofporous Ti structures.
A scaffold with a porosity of75% has been preparad bydirect ink writing, with the objective of reducing the apparent modulus elasticityofli prostheses. In this wor1<:, porous Ti structures with a stiffness and compressive strength of2.6 GPa and 64.5 MPa respectively has been manufacturad. To this end, a new ink fonnulation was designad based on the mixture of a thenn ose nsitive h rogel with Ti irregular powder particles with a mean particle size of 22.45 µm.
A thennal treatrnentwas optimized to ensure the complete elimination ofthe binder before the sintering process, in orderto avoid contamination ofthe titanium structures.
The understanding of infections is closely linked to the concept ofthe "race for the surface". The winner of this race (cell versus bacteria) decides if a solid anchoring between implant and bone will be achieved or if bacteria! growth will lead to a periprosthetic infection. Another strategy studied on this thesis focuses on the functionalization of the Ti surface. First. surface of Ti scaffolds were functionalized with a cell adhesion fibronectin recombinant fragment for optimizing cell adhesion. Mditionally, a multifunctional coating based on the potential of calcium phosphate coatings to be used as carriers for drug deliverywas also studied to achieve a balance between cell attachmentand reduction ofbacterial adhesion. Porous Ti structures have beén successfullycoated with a one-step pulsed electrodeposition process achielñng a unifonn calcium phosphate layer both on the inner and outer the surface ofthe scaffold, with adhesion strengths over 22 MPa. The co deposition of an antibacterial agentwith a pulsad and reverse pulsed electrodeposition was achieved on both smooth and open-cell Ti surfaces. The ralease rate ofthe antibacterial agentcan be modulated within hours ordar-; timeframe by adjusting the coating conditions and without altering the antimicrobial potential ofthe loaded antibacterial agent itself. The biofunctionalized coatings exhibited a noteworthy in lñtro antibacterial actilñty against S. aureus and E. coli bacteria strains, with a significant decrease of lñable attached bacteria to the treated surfaces. Cell culture tests also showed that CHX-loaded Ti structures presentad an improved cell adhesion comparad to thatofuntreated Ti.
Therefore, the proposed strategies can efficiently impro-.e orthopedic implants in tenns of improlñng biointegration and microbial adhesion resistance.
