Adhesion of electrosprayed chitosan coatings using silane surface chemistry

Abstract

Biomedical implant devices for dental/craniofacial and orthopedic applications are a reliable and effective means for repairing/re-storing function of damaged, diseased or missing tissues. Electrospray coating technologies provide an additive manufacturing route to endow implant surfaces with properties to improve their performance by controlled deposition of desired materials, compounds and/or agents in the form of nano- or micro-particles on the surface of implant devices under relatively mild conditions. They provide a means to control the structure of coatings with high precision that allows the functionalization of complex 3D geometries of the implants with a range of desired physical and bioactive properties. Devices such as dental implants, total joint replacement devices, bone plates and screws that cannot be easily coated by other manufacturing methodologies such as solution casting, sputtering, or electrochemical treatments, can be robustly handled by the electrospray technique. This study focuses on assessing the adhesion of electrosprayed chitosan coatings on model titanium surfaces and screws to explore their potential as an implant treatment technology. To maximize the adhesion strength between the chitosan coating and a titanium surface, a tri-ethoxy-silylbutyraldhyde silane-based treatment is applied to chemically bond the coated chitosan to the substrate. Adhesion strength values are reported and compared between electrosprayed and solution cast chitosan coatings. For both methods, the role played by the silanation process is also explored. It is seen that silanation significantly improves the adhesion of the coatings, and electrosprayed, silanated coatings have a strength (5.87 MPa ± 2.03 MPa) that is comparable to solution-cast, silanated coatings (4.85 MPa ± 1.34 MPa) and offer control and flexibility as an additive manufacturing/coating process. We also, coat titanium screws and measure the loss of mass of chitosan coating during simulated surgery of screwing them into a polyurethane bone foam. The average loss of mass of chitosan is 34.3%, with most of it coming from the leading edge of the screw that experiences maximum shear during drilling. The merits and shortcomings of the electrospray for coating chitosan are discussed with possible improvements for future developments.