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Introduction: In the last years, partly given to the changes in the age structure of the population, there has been a skyrocketing increase of the number of orthopaedic surgeries [1]. With the rising number of implantations, the absolute number of complications is inevitably increasing at the same pace, causing not only distress for the patients but also a significant economic burden [2]. One of the major causes of implant failure is biofilm-associated infections, which represent a huge challenge given their high tolerance to antibiotic therapy. Drop on demand technology has proven to be a valuable tool to develop antimicrobial coatings to avoid bacterial attachment and biofilm development onto the implant surface. This technique enables the production of complex drug release profiles allowing a sustained release of antibiotics and biofilm inhibitors [3]. In this work, we developed PLGA antimicrobial coatings on titanium discs using drop on demand technology. N-(abiet-8,11,13-trien-18-oyl) cyclohexyl-L-alanine (DHA1) was used as a biofilm inhibitor.
Methodology: PLGA (PDLG 5004A, Corbion) and PEG (35 kDa, Sigma) were dissolved in organic solvents. DHA1 was added to the solution at different concentrations (10, 20 and 30% w/w). The viscosity of ink formulations was studied with a viscometer (DV-III Ultra, Brookfield). The printability of the different formulations was studied using a 3D Discovery (regenHU) inkjet microvalve-based 3D printer. The printing parameters were optimized, studying the pressure, opening valve time (OT), distance nozzle-sample, and nozzle diameter. The antimicrobial properties of this coating were studied by assessing its capacity preventing Staphylococcus aureus ATCC 25923 adhesion to the titanium surface.
Results: The viscosity and printability of different ink formulations were studied. A small range of viscosity was observed to obtain a good droplet formation and printability. A too high viscosity produced the clog of the nozzle, while a too low viscosity produced splashes and formation of satellites. The thickness of the coatings was in the range of 30-40 mm and 3 mg×cm-2 per layer. The presence of DHA1 in the coatings was confirmed by FTIR. The coatings loaded with different concentrations of DHA1 (10, 20 and 30% DHA1) reduced bacterial adherence up to 4-logs when compared with the titanium coated with PLGA-PEG with no load. Moreover, the released eluates from the coating with 30% DHA1 load managed to inhibit biofilm formation up to 24 h.
Conclusions: Drop on demand is a suitable technique for the development of antimicrobial coatings. The coating developed here proved high capacity preventing S. aureus biofilm formation. As far as we know, this is one of the first drop on demand coatings incorporating a biofilm inhibitor.
References
[1] S Veerachamy et al., Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine 228 (10), 1083 (2014).
[2] SM Kurtz et al., The Journal of arthroplasty 27 (8 Suppl), 61 (2012).
[3] CL Ventola, P T 39 (10), 704 (2014).
[4] I Reigada et al., Microorganisms 8 (3) (2020).
[5] R Perez-Tanoira et al., J. Biomed. Mater. Res. Part A 105 (1), 62 (2017).
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