Surface modification using RF oxygen plasma in tissue engineering

Scaffolds intended for use in tissue engineering applications often invoke a foreign body response upon implantation leading to undesirable effects, such as encapsulation or rejection of the scaffold. Therefore to develop their full potential, biodegradable tissue engineering scaffold surfaces must be modified to overcome this foreign body response. Current research has suggested that negatively charged and hydrophilic surfaces avoid this response by inducing apoptosis in the responsible immune cells. One approach which has shown potential in functionalising biodegradable polymer surfaces with a negatively charged surface is oxygen plasma treatment. It has the advantages of controllability, versatility, and simultaneous sterilisation of the implant. Examples from our studies into the use of oxygen plasma treatment of the commonly used polymer poly(lactic-coglycolic acid) (PLGA) will illustrate a number of important issues. In these studies PLGA was thinly and uniformly coated on glass coverslips to mimic the internal pore surfaces of tissue engineering scaffolds produced by thermally induced phase separation (TIPS). It was found that oxygen plasma, at pressures within the limits of current testing (4x10-4 to 10-4 mbar; 10-60 s), significantly reduces the advancing and receding water contact angle. Contact angles obtained from samples washed once in ethanol after treatment consistently yielded contact angle values up to 10° higher than unwashed samples, supporting theories that oxygen plasma treatment cleaves PLGA chains, liberating soluble oligomeric products. XPS data indicates an increase in atomic oxygen content after plasma treatment by 1% in washed samples and by 2% in unwashed samples. AFM was used to visualise the extent of etching resulting from the oxygen plasma treatment, and surface roughness was found to change from < 1 nm (untreated sample) to 14 ± 3 nm (10 s oxygen plasma treatment at 150 mTorr). The findings of this study highlight the dual effect of oxygen plasma treatment and cautions the use of materials subjected to oxygen plasma in biological assays that have not been washed prior to their use