Functionalization of the Parylene C Surface Enhances the Nucleation of Calcium Phosphate : Combined Experimental and Molecular Dynamics Simulations Approach

Interactions at the solid-body fluid interfaces play a vital role in bone tissue formation at the implant surface. In this study, fully atomistic molecular dynamics (MD) simulations were performed to investigate interactions between the physiological components of body fluids (Ca2+, HPO42-, H2PO4-, Na+, Cl-, and H2O) and functionalized parylene C surface. In comparison to the native parylene C (-Cl surface groups), the introduction of -OH, -CHO, and -COOH surface groups significantly enhances the interactions between body fluid ions and the polymeric surface. The experimentally observed formation of calcium phosphate nanocrystals is discussed in terms of MD simulations of the calcium phosphate clustering. Surface functional groups promote the clustering of calcium and phosphate ions in the following order: -OH > -CHO > -Cl (parent parylene C) approximate to -COO-. This promoting role of surface functional groups is explained as stimulating the number of Ca2+ and HPO42- surface contacts as well as ion chemisorption. The molecular mechanism of calcium phosphate cluster formation at the functionalized parylene C surface is proposed.Peer reviewe

Molecular Dynamics Insights into Water–Parylene C Interface: Relevance of Oxygen Plasma Treatment for Biocompatibility

Solid–water interfaces play a vital role in biomaterials science because they provide a natural playground for most biochemical reactions and physiological processes. In the study, fully atomistic molecular dynamics simulations were performed to investigate interactions between water molecules and several surfaces modeling for unmodified and modified parylene C surfaces. The introduction of −OH, −CHO, and −COOH to the surface and alterations in their coverage significantly influence the energetics of interactions between water molecules and the polymer surface. The theoretical studies were complemented with experimental measurements of contact angle, surface free energy, and imaging of osteoblast cells adhesion. Both MD simulations and experiments demonstrate that the optimal interface, in terms of biocompatibility, is obtained when 60% of native −Cl groups of parylene C surface is exchanged for −OH groups. By exploring idealized models of bare and functionalized parylene C, we obtained a unique insight into molecular interactions at the water–polymer interface. The calculated values of interaction energy components (electrostatic and dispersive) correspond well with the experimentally determined values of surface free energy components (polar and dispersive), revealing their optimal ratio for cells adhesion. The results are discussed in the context of controllable tuning and functionalization of implant polymeric coating toward improved biocompatibility

Sonochemical Formation of Fluorouracil Nanoparticles : Toward Controlled Drug Delivery from Polymeric Surfaces

The biomaterial surface can be essentially upgraded with the therapeutic function by the introduction of controlled, local elution of biologically active molecules. The use of ultrasonic -assisted formation of nanoparticles with controlled size and morphology can be readily utilized for such functionalization. In this study, the synthesis route for the generation of nanoparticles of fluorouracil, the bioactive molecule used in anticancer therapy, was reported. The tandem of experimental (TEM, NTA, ATR-IR) and computational (MD simulations) approaches allowed us to obtain a molecular-level picture of the cavitation bubble interface where the enrichment of fluorouracil molecules takes place. Thanks to the originally developed computational model of cavitation bubbles, we revealed that the bubble interface plays a key role in the prearrangement of drug and solvent molecules, initiating the formation of nanoparticles' seeds. The proposed mechanism can be applied to other biologically relevant molecules, suggesting that the sonochemical method can be used for the controlled formation of their nanoparticles. The results indicate a feasible way to tailor the surface of polymeric biomaterials via the embedment of nanoparticles, thus having the potential to be used for practical implications as drug delivery systems.Peer reviewe