Antibacterial and osteogenic properties of silver-containing hydroxyapatite coatings produced using a sol gel process

Stability of antibacterial self-assembled monolayers on hydroxyapatite

Open fractures are common in battlefields, motor vehicle accidents, gunshot wounds, sports injuries, and high-energy falls. Such fractures are treated using hydroxyapatite (HA)-based bone graft substitutes. However, open fracture wounds are highly susceptible to bacterial infections. Hence, this study was focused on incorporating antibacterial properties to HA using silver (Ag) carrying self-assembled monolayers (SAMs). Also, the stability of Ag carrying SAMs on HA was investigated under sterilization and physiological conditions. Initially, the -COOH terminated phosphonic acid SAMs of two different chain lengths (11 carbon atoms - shorter chain and 16 carbon atoms - longer chain) were deposited on HA. Antibacterial SAMs (ASAMs) were prepared by chemically attaching Ag to shorter and longer chain SAMs coated HA. X-ray photoelectron spectroscopy, atomic force microscopy, and contact angle goniometry collectively confirmed the attachment of Ag onto SAMs coated HA. The bacterial adhesion study showed that the adherence of Staphylococcus aureus was significantly reduced on ASAMs coated HA when compared to control-HA. The stability studies showed that gas plasma, dry heat and autoclave degraded most of the ASAMs on HA. UV irradiation did not damage the shorter chain ASAMs as vigorously as other treatments, while it degraded the longer chain ASAMs completely. Ethylene oxide treatment did not degrade the longer chain ASAMs unlike all other treatments but it severely damaged the shorter chain ASAMs. Both shorter and longer chain ASAMs significantly desorbed from the HA surfaces under physiological conditions although longer chain ASAMs exhibited better stability than shorter chain ASAMs. This study demonstrated the potential for using ASAMs to provide antibacterial properties to HA and the need for developing techniques to improve stability of SAMs under sterilization and physiological conditions.

Functionally graded hydroxyapatite coatings doped with antibacterial components

A series of functionally graded hydroxyapatite (FGHA) coatings incorporated with various percentages of silver were deposited on titanium substrates using ion beam-assisted deposition. The analysis of the coating's cross-section using transmission electron microscopy (TEM) and scanning transmission electron microscopy equipped with energy dispersive X-ray spectroscopy has shown a decreased crystallinity as well as a distribution of nanoscale (10-50nm) silver particles from the coating/substrate interface to top surface. Both X-ray diffraction and fast Fourier transforms on high-resolution TEM images revealed the presence of hydroxyapatite within the coatings. The amount of Ag (wt.%) on the outer surface of the FGHA, as determined from X-ray photoelectron spectroscopy, ranged from 1.09 to 6.59, which was about half of the average Ag wt.% incorporated in the entire coating. Average adhesion strengths evaluated by pull-off tests were in the range of 83+/-6 to 88+/-3MPa, which is comparable to 85MPa for FGHA without silver. Further optical observations of failed areas illustrated that the dominant failure mechanism was epoxy failure, and FGHA coating delamination was not observed.

Biological and antibacterial properties of plasma sprayed wollastonite/silver coatings

In this work, plasma sprayed wollastonite/silver coatings were prepared to obtain an implant material having excellent bioactivity, cytocompatibility as well as antibacterial property. The surface characteristics of wollastonite/silver coating were investigated by scanning electron microscopy, energy dispersive spectrometer, atomic absorbance spectroscope and x-ray diffraction. The bioactivity was examined by simulated body fluid soaking test. The antibacterial activity against Escherichia coli was examined by bacterial counting method. And the cytocompatibility and in vitro osteotoxicity was evaluated by alamarBlue Assay using MG-63 osteoblasts. The results showed that silver existed in the wollastonite coating homogeneously as silver oxide and metal silver, which ensured a sustained release of silver for 28 days in deionized water. The loaded silver showed strong inhibition against the growth of Escherichia coli, however exhibited no osteotoxicity. Although the wollastonite/silver coating can not induce apatite formation as quickly as the wollastonite coating did in simulated body fluid, it still exhibited good bioactivity. Therefore, the plasma sprayed wollastonite/silver coating is a promising implant material to be applied in surgery, reducing postoperative infections.