The field of coatings for biomedical applications is wide and well established following many years of extensive R&D efforts worldwide. Coatings are used, for example, to improve the corrosion resistance of materials or to improve mechanical, optical and chemical properties of the substrate materials. There are numerous coating processes being widely used nowadays like dip coating, plasma spraying or electrophoretic deposition. The focus of this work is on coatings produced by electrophoretic deposition (EPD). EPD is a two-step colloidal process that requires simple equipment, being more cost-effective than other coating techniques.
One significant challenge with orthopedic implants is the adhesion between bone and implant. If this interface fails, the implant loses and the device has to be removed or fixed again, which results in an economic burden for the health care system and pain and inconveniences for the patient. Coatings with bioactive materials like bioactive glasses that accelerate bone formation and therewith the adhesion of the implant to the bone, represent an attractive approach to tackle the mentioned issues. Another problem that can occur at implant site is a bacterial infection that also can lead to a failure of the implant resulting in a second surgery to remove the implant. There are two main ways to overcome this problem, either by using drugs (antibiotics) or the use of antibacterial agents (ions) such as silver. Drugs can be released directly at the implant site by using a degradable polymer matrix that releases the drug over a longer time period. In this project the naturally derived polymer chitosan was selected as a matrix for bioactive glass particles and the antibiotic tetracycline. Coatings of this material combination were developed and characterized. It was shown that tetracycline can be released over several weeks with an initial burst to prevent early infections directly after the surgery when the immune system of the patient is weakened.
Bacterial studies using E. coli cells confirmed the successful antibacterial effect of these coatings that can be adjusted by changing the antibiotic concentration in suspension. In addition, studies in simulated body fluid (SBF) showed the bioactive properties of the coatings by the formation of hydroxyapatite on the surface after immersion for 21 days in SBF. Different bioactive glass particle sizes were used ranging from nanometer to micrometer size and it was confirmed that the optimum properties in terms of bioactivity, cell attachment and spreading can be achieved using nano-sized bioactive glass particles.