Titanium implant coatings composed of chitosan and heparin to promote osseointegration

Details

Supervisors

Dupont-Gillain, Christine C.

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil biomédical

Abstract

Total hip arthroplasty (THA) is a surgical procedure in which the hip joint of the patient is replaced by a hip prosthesis. Aseptic loosening and prosthetic joint infection (PJI) are the two most significant causes of prosthetic implant failure. In such cases, revision surgery is required and the implant must be replaced. To prevent such interventions, the ideal implant should be able to promote osseointegration and prevent bacterial adhesion. In this master thesis, a coating is developed to improve the performances of titanium prostheses. This coating will be based on chitosan and heparin, two polysaccharides, that each have a specific action; repel bacteria and attract bone cells respectively. The coating is constructed using a technique called layer-by-layer self-assembly in which layers of the two polyelectrolytes are alternately deposited on titanium coupons owing to electrostatic interactions. Films were created with different number of layers or according to different deposition protocols, in order to analyse the effect of their composition. The different obtained layers were characterised using a combination of surface analysis techniques. The static water contact angle (WCA) technique is first used to collect information about the wettability of the layers. The adhesion of both polyelectrolytes could be confirmed with the WCA as a saw-tooth pattern was identified when alternately adding chitosan and heparin. The contact angle of the final condition made of 3 bilayers of chitosan and heparin, (CHI/HEP)3, was equal to 40.5° ± 7.5, 5 days after layer deposition on the samples. After that, the chemical composition of the surface of the samples was determined by X-ray photoelectron spectroscopy (XPS). The results showed the chemical signature of chitosan and heparin, reinforcing the hypothesis that layers are adequately formed on the titanium coupons. Also, the surface molar fraction of titanium decreased from approximately 10% to 2% for the condition (CHI/HEP)3, showing that the coating screens the original titanium. Finally, the layer thickness was measured using the quartz-crystal microbalance, and a thickness of approximately 13 nm was found for the (CHI/HEP)3 multilayer. Thereafter, cell viability and proliferation were investigated on the previously characterised layers. To quantify cell viability, the AlamarBlue assay was used. Proliferation was monitored using a DNA assay and fluorescence microscopy. Taken together, the results suggest that the developed coatings present no cytotoxicity and could be used as a basis to design a more complex coating. To conclude, it is shown in this work that heparin and chitosan can be successfully assembled on titanium coupons using the layer-by-layer method, with a certain degree of control on the physicochemical properties of the obtained coatings according to the number of deposited layers. The developed systems are shown to be suitable for bone cell-related applications. This master thesis contributes to the development of antibacterial coatings prepared for metal prostheses and could be developed further to prevent the formation of biofilms while promoting osseointegration.