[en] In this study, X-ray photoelectron spectroscopy (XPS) was used to evaluate the hypothesis that macrophage cells and their released compounds change Ti-6Al-4V surface oxide composition. Ti-6Al-4V surfaces, prepared to simulate clinical conditions, were exposed for 3 days to cell culture medium, macrophage cells, or macrophage cells activated to release inflammatory reactive chemical species (RCS). The as-polished samples were used as controls. The as-polished samples exhibited typical TiO₂ surface oxides. After samples were exposed to medium, only C, O and N peaks from absorbed proteins were observed. When cultured with cells or activated cells, the Ti peaks reappeared and there was a significant shift in the O 1s peak to lower metal oxide binding energies (∼530 eV). This shift was associated with a significant increase in total metal oxides on sample surfaces as compared to medium only surfaces. With activated cells, the enhancement of the surface oxides was attributed to oxidation of the surface by the RCS released by activated macrophage cells (e.g. O₂+NO→NO₃^- and M+NO₃^-→M=O+NO₂^-). These data support the hypothesis that macrophage cells and released RCS affect Ti-6Al-4V surface oxides. Changes in surface oxides are important since they may affect alloy-tissue interactions

[en] Electrospun chitosan membranes have been investigated for guided bone regeneration but are susceptible to swelling, dissolution, and loss of biomimetic nanofiber structure due to residual acid salts. A novel process was investigated for acidic salt removal from chitosan electrospun in 70% trifluoroacetic acid (TFA) by treating with triethylamine (TEA)/acetone and di-tert-butyl dicarbonate (tBOC) instead of the common Na₂CO₃ treatment. TFA salt removal and nanofiber structure stabilization were confirmed by EDS, FTIR, ¹⁹F NMR and electron microscopy before and after soaking in water. Membrane degradation after 4 weeks in PBS with 100 µ g ml⁻¹ lysozyme and osteoblastic proliferation were similar between TEA/tBOC-treated and Na₂CO₃-treated membranes. A simulated surgical tear test using surgical tacks showed that the peak tensile tear strength of the TEA/tBOC-treated chitosan membranes (62.1  ±  1.9 N mm⁻¹) was significantly greater than a commercial polylactic acid (PLA) membrane (13.4  ±  0.4 N mm⁻¹), similar to one commercial collagen membrane (55.3  ±  7.5 N mm⁻¹) but lower than another commercial collagen membrane (133.9  ±  21.5 N mm⁻¹). Rat 8 mm critical-sized calvarial defects covered with TEA/tBOC-treated chitosan membranes prevented soft tissue infiltration and supported new bone growth (15.76  ±  10.28%) similar to a commercial collagen membrane (16.08  ±  10.69%) at 12 weeks based on microCT analyses. Hence our novel TEA/tBOC process significantly improved nanofiber structure and mechanical strengths of electrospun chitosan membranes as compared to Na₂CO₃ treated membranes, without affecting in vitro degradation or cytocompatibility, improved membrane mechanical properties to be greater than a commercial PLA membrane and to be in range of commercial collagen membranes and supported calvarial bone defect healing similar to collagen. Thus TEA/tBOC-treated chitosan membranes exhibit many characteristics and properties that strongly support their potential for use in guided bone regeneration. (paper)

[en] The use of chitosan based nanofiber membranes in guided bone regeneration (GBR) is limited by its uncontrolled swelling and mechanical instability in aqueous environments. This paper describes the significantly improved stability and properties of surface butyrylated chitosan nanofiber (BCSNF) membranes that greatly enhance their potential in GBR. The BCSNF membranes exhibited an overall degree of substitution of 1.61, an average diameter of 99.3 ± 33.7 nm, and a 75% decrease in swelling with an approximate doubling in suture pull out strengths as compared to unmodified fibers in aqueous environment. In a five week phosphate-buffered saline–lysozyme degradation study, it was found that the remaining mass fraction of BCSNF membranes was 11.5% more than that of unmodified fibers. In vitro, the BCSNF membranes were found to support the adhesion and proliferation of fibroblasts and were cell occulusive. In vivo, the BCSNF membranes were found to significantly improve the regeneration of a rat calvarial critical size defect in a 12 week healing period and showed better barrier function than commercially available collagen membranes with little soft tissue penetration through the membranes. Taken together, these data provide strong scientific evidence for use of BCSNF membranes in GBR applications. (paper)

[en] Highlights: • Electrospray technique is evaluated for coating chitosan on titanium surfaces. • A silane-based treatment is used to chemically bond the chitosan to the substrate. • Adhesion of chitosan coating with titanium is evaluated by the tensile strength. • Titanium screws are coated by electrospray. • Mass loss of chitosan coating from screws during simulated surgery is measured. -- 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.

[en] A bioactive coating has the ability to create a strong interface between bone tissue and implant. Chitosan, a biopolymer derived from the exoskeletons of shellfish, exhibits many bioactive properties that make it an ideal material for use as a coating such as antibacterial, biodegradable, non-toxic, and the ability to attract and promote bone cell growth and organized bone formation. A previous study reported on the bonding of chitosan to a titanium surface using a three-step process. In the current study, 86.4% de-acetylated chitosan coatings were bound to implant quality titanium in a two-step process that involved the deposition of triethoxsilylbutyraldehyde (TESBA) in toluene, followed by a reaction between the aldehyde of TESBA with chitosan. The chitosan coatings were examined on two different metal treatments to determine if any major differences in the ability of titanium to bind chitosan could be detected. The surface of the titanium metal and the individual reaction steps were examined using X-ray photoelectron spectroscopy (XPS). Following the deposition of TESBA, significant changes were seen in the amounts of oxygen, silicon, carbon, and titanium present on the titanium surface, which were consistent with the anticipated reaction steps. It was demonstrated that more TESBA was bound to the piranha-treated titanium surface as compared to the passivated titanium surface. The two different silane molecules, aminopropyltriethoxysilane (APTES) and TESBA, did not affect the chemistry of the resultant chitosan films. XPS showed that both the formation of unwanted polysiloxanes and the removal of the reactive terminal groups were prevented by using toluene as the carrier solvent to bond TESBA to the titanium surfaces, instead of an aqueous solvent. Qualitatively, the chitosan films demonstrated improved adhesion after using toluene, as the films remained attached to the titanium surface even when placed under the ultra-high vacuum necessary for XPS, unlike the chitosan films deposited using an aqueous solvent, which were removed when exposed to the ultra-high vacuum environment of XPS

[en] Bioactive coatings have been investigated to enhance the integration of orthopaedic and dental-craniofacial implants in the surrounding bone tissue. Chitosan has been shown to possess many properties desirable in implant coatings, such as cell attachment and growth, and encouraging ordered bone tissue formation. Previous studies have produced methods to deposit chitosan onto a titanium surface using both two-step and three-step reaction schemes. In the current study, two different titanium surface treatments were evaluated for determining the strength of chitosan coatings bonded to titanium via two reaction processes. The chitosan coatings produced from the four treatment combinations were examined using X-ray Photoelectron Spectroscopy, which demonstrated that the final coatings were similar in composition to the previously reported coatings. Coatings examined by nano-indentation, exhibited hardness (0.19 ± 0.08 GPa) and elastic modulus (4.90 ± 1.82 GPa) values similar to the hardness and elastic modulus values previously reported. Scanning Electron Microscopy examination of the nano-indentation marks revealed cracks only at sites of applied stress, demonstrating that the chitosan coatings were able to absorb the applied stress. Bulk adhesion of the chitosan coatings demonstrated significant increases in bond strength (19.50 ± 1.63 MPa) over previously reported data (1.5-1.8 MPa), but no significant differences were seen between the four treatment combinations. Contact angle testing demonstrated that the chitosan coatings were more hydrophobic (98.0 ± 3.6 deg.) than published values (76.4 ± 5.1 deg.). Overall, mechanical testing demonstrated that, while the bulk properties of the chitosan coating were unaffected by the four treatment combinations, the bulk adhesion of the chitosan coating was greatly increased and high quality coatings were produced