Abstract
The surface of any implant device plays an important role in their biocompatibility. After implantation, the physico-chemical surface properties of any biomaterial determine its good/bad response against protein adsorption, cell attachment and proliferation and bacterial adhesion [1]. In this sense, the knowledge of hydrophobicity and surface tension of any new-developed biomaterial is an added value for the final product. Polymeric implants, among which are poly-D-Lactic acid (PLDA), are well characterized biodegradable biomaterials that have been proposed as an alternative to metallic implants for fracture fixation. However, their use in the clinical practice has been limited due to insufficient osseointegration and adverse tissue reactions. Recently it has been demonstrated the feasibility of introducing Mg particles within the PLDA matrix as a new strategy to improve the bioactivity and mechanical properties of PLDA whereas simultaneously modulating the degradation rate of Mg [2]. In this work, the surface of new amorphous and crystalline composites of PLDA with two different Mg concentrations are characterized in terms of hydrophobicity and surface tension.
Amorphous and crystalline PLDA from Natureworks were reinforced with Mg particles through a processing route that contained four different stages: drying, hot extrusion, grinding and compression moulding. Two different Mg concentration were used: 1 wt.% and 10 wt.% Hydrophobicity was obtained by goniometry using water as probe liquid (θW). The surface tension was determined through the Young Equation using water, formamide and diiodomethane as probe liquids. Van Oss approach was used to split the surface tension into the Lifshitz-van der Waals component (γLW) and acid-base component (γAB). The acid-base was also divided into the electron-donor (γ−) and electron-acceptor parameters (γ+).
The water contact angle was similar in amorphous and crystalline samples. Mg always reduced the θW value, no matter the Mg concentration used. Reductions were similar for both Mg concentrations. The surface tension in amorphous samples was comprised between 26 and 36 mJ/m2 and in crystalline samples was between 30 and 36 mJ/m2. Although values were very similar, the deviations observed for crystalline samples were always smaller than for amorphous. An important effect of Mg in the composites was the increase in the parameter γ-.
Mg addition makes the polymer less hydrophobic. The increase of γ− may be related to an increase in the negative surface charge of Mg samples. The hydrophobic reduction plus the more negative surface could impair the bacterial approach and further adhesion to the surface of the new composites, which implies an advance in the fight against infections.
