Optimization of Acrylic Acid Grafting onto POSS-PCU Nanocomposite Using Response Surface Methodology

The novel nanocomposite based on poly(carbonate-urea)urethane and polyhedral oligomeric silsesquioxanes (POSS) has been used in medicine especially in cardiovascular applications. It is also known that the cell affinity towards biomaterials can be promoted by immobilization of extracellular matrix proteins onto these materials surfaces. The inert surface of POSS-PCU nanocomposite is notdirectly suitable for immobilization of such biomolecules and therefore, its biocompatibility should be improved. In this study, design of experiment methodology was used to develop a predictive model to optimize the operating conditions for grafting controlled amounts of carboxylic functional groups onto the surface of POSS-PCU, which may then be used for the coupling of ECM proteins. The grafting of poly(acrylic acid) was carried out using a two-step plasma treatment. The grafted films were characterized by ATR-FTIR spectroscopy, SEM, and water contact angle measurements. The presence of the grafted layers was confirmed by the appearance of a broad peak of the hydroxyl groups in ATR-FTIR spectrum, decreased in water contact angle, and morphological changes observed by SEM micrographs. The effects of two identified process variables (pretreatment and copolymerization time length) each in five levels, on the grafting density were investigated and optimized using central composite design in the response surface methodology. The accuracy of the model was verified and found to be high. In process optimization, it was found that the maximum value of grafting density was 13.9 (± 28) μg/cm2, by using the appropriate values of process variables which were achieved through the experimental conditions of 75 s and 120 s for pretreatment time and copolymerization time, respectively.