In Vitro and In Silico Studies of Functionalized Polyurethane Surfaces toward Understanding Biologically Relevant Interactions

The solid-aqueous boundary formed upon biomaterial implantation provides a playground for most biochemical reactions and physiological processes involved in implant-host interactions. Therefore, for biomaterial development, optimization, and application, it is essential to understand the biomaterial-water interface in depth. In this study, oxygen plasma-functionalized polyurethane surfaces that can be successfully utilized in contact with the tissue of the respiratory system were prepared and investigated. Through experiments, the influence of plasma treatment on the physicochemical properties of polyurethane was investigated by atomic force microscopy, attenuated total reflection infrared spectroscopy, differential thermal analysis, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and contact angle measurements, supplemented with biological tests using the A549 cell line and two bacteria strains (Staphylococcus aureus and Pseudomonas aeruginosa). The molecular interpretation of the experimental findings was achieved by molecular dynamics simulations employing newly developed, fully atomistic models of unmodified and plasma-functionalized polyurethane materials to characterize the polyurethane-water interfaces at the nanoscale in detail. The experimentally obtained polar and dispersive surface free energies were consistent with the calculated free energies, verifying the adequacy of the developed models. A 20% substitution of the polymeric chain termini by their oxidized variants was observed in the experimentally obtained plasma-modified polyurethane surface, indicating the surface saturation with oxygen-containing functional groups.

The Effect of Reactive Sputtering on the Microstructure of Parylene-C

Sputtering technique involves the use of plasma that locally heats surfaces of substrates during the deposition of atoms or molecules. This modifies the microstructure by increasing crystallinity and the adhesive properties of the substrate. In this study, the effect of sputtering on the microstructure of parylene-C was investigated in an aluminum nitride (AlN)-rich plasma environment. The sputtering process was carried out for 30, 45, 90 and 120 min on a 5 μm thick parylene-C film. Topography and morphology analyses were conducted on the parylene-C/AlN bilayers. Based on the experimental data, the results showed that the crystallinity of parylene-C/AlN bilayers was increased after 30 min of sputtering and remained saturated for 120 min. A scratch-resistance test conducted on the bilayers depicted that a higher force is required to delaminate the bilayers on top of the substrate. Thus, the adhesion properties of parylene-C/AlN bilayers were improved on glass substrate by about 17% during the variation of sputtering time.

Highly Selective Self-Powered Organic-Inorganic Hybrid Heterojunction of a Halide Perovskite and InGaZnO NO2 Sensor

Self-powered sensors can lead to disruptive advances in self-sustainable sensing systems that are imperative for evolving human lifestyles. For the first time, we demonstrate the fabrication of a heterojunction sensor using p-type hybrid-halide perovskites (CH₃NH₃PbBr₃) and an n-type semiconducting metal oxide thin film [InGaZnO (IGZO)] for the detection of NO₂ gas and power generation. Combining the excellent photoelectric properties of perovskites and the remarkable gas-sensing properties of IGZO at room temperature, the devised sensors generate open-circuit voltage and modulate according to the ambient NO₂ concentration. The major challenge in devising self-powered gas sensors is to attain harvesting capability and selectivity simultaneously, owing to perovskites reactivity in the presence of oxygen and humidity. In this work, we developed a novel approach and fabricated a heterojunction sensor using parylene-c as an additional layer to curb the cross-sensitivity and to enhance the selectivity of the sensor. Even under the low concentrations of NO₂, the developed sensor exhibits remarkable sensitivity, selectivity, and repeatability. The devices are sensitive and robust even under extreme humidity conditions (80% R_H) and synthetic air. The devised sensor configuration is one way to eliminate the cross-sensitivity issue of the perovskite-based devices and serves as a reference for the development of self-powered sensors.

Enhenced cell adhesion on collagen I treated parylene-C microplates

On account of unique mechanical property and inertia, parylene-C has become a promising material for microdevices especially in three-dimensional microstructures loaded with cells. However, parylene-C is not favorable for cell adhesion, and a routine procedure is to modify it with a new adhesive layer. Herein, the parylene-C substrates with or without collagen Ӏ (Col-I) coating were adopted to estimate the influence of micro-environment change on cell attachment and spreading. After modification with Col-I, cauliflower-like particles presented on the substrate surface. Contact angle was significantly decreased after Col-I modification, which suggested the surface hydrophilicity was enhanced. Furthermore, cells cultured on parylene-C surface with Col-I treatment showed increased proliferation rate and spreading areas. In order to test the adhesion strength, a series of fixed size parylene-C microplates was fabricated, and cell suspension concentration was adjusted to culture a single cell on one microplate. The microplate was folded by the autogenous shrinkage force of cell. The folding angles of parylene-C microplates with Col-I treatment exhibited higher folding angle (112.6 ± 15.6°) than untreated samples (46.7 ± 5.9°). The work proved the existence of Col-I layer was particularly important, especially in analysis of cells mechanics using parylene-C microplate as a substrate.

What affects the biocompatibility of polymers?

In recent decades synthetic polymers have gained increasing popularity, and nowadays they are an integral part of people's daily lives. In addition, owing to their competitive advantage and being susceptible to modification, polymers have stimulated the fast development of innovative technologies in many areas of science. Biopolymers are of particular interest in various branches of medicine, such as implantology of bones, cartilage and skin tissues as well as blood vessels. Biomaterials with such specific applications must have appropriate mechanical and strength characteristics and above all they must be compatible with the surrounding tissues, human blood and its components, i.e. exhibit high hemo- and biocompatibility, low or no thrombo- and carcinogenicity, foreign body response (host response), appropriate osteoconduction, osteoinduction and mineralization. For biocompatibility improvement many surface treatment techniques have been utilized leading to fabricate the polymer biomaterials of required properties, also at nanoscale. This review paper discusses the most important physicochemical and biological factors that affect the biocompatibility, thus the reaction of the living organism after insertion of the polymer-based biomaterials, i.e. surface modification and/or degradation, surface composition (functional groups and charge), size and shapes, hydrophilic-hydrophobic character, wettability and surface free energy, topography (roughness, stiffness), crystalline and amorphous structure, nanostructure, cell adhesion and proliferation, cellular uptake. Particularly, the application of polysaccharides (chitosan, cellulose, starch) in the tissue engineering is emphasized.

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) ≈ -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.

Self-Folded Three-Dimensional Graphene with a Tunable Shape and Conductivity

Three-dimensional (3D) graphene architectures are of great interest as applications in flexible electronics and biointerfaces. In this study, we demonstrate the facile formation of predetermined 3D polymeric microstructures simply by transferring monolayer graphene. The graphene adheres to the surface of polymeric films via noncovalent π-π stacking bonding and induces a sloped internal strain, leading to the self-rolling of 3D microscale architectures. Micropatterns and varied thicknesses of the 2D films prior to the self-rolling allows for control over the resulting 3D geometries. The strain then present on the hexagonal unit cell of the graphene produces a nonlinear electrical conductivity across the device. The driving force behind the self-folding process arises from the reconfiguration of the molecules within the crystalline materials. We believe that this effective and versatile way of realizing a 3D graphene structure is potentially applicable to alternative 2D layered materials as well as other flexible polymeric templates.

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.

Multifunctional PLGA/Parylene C Coating for Implant Materials: An Integral Approach for Biointerface Optimization

Functionalizing implant surfaces is critical for improving their performance. An integrated approach was employed to develop a multifunctional implant coating based on oxygen plasma-modified parylene C and drug-loaded, biodegradable poly(dl-lactide-co-glycolide) (PLGA). The key functional attributes of the coating (i.e., anti-corrosion, biocompatible, anti-infection, and therapeutic) were thoroughly characterized at each fabrication step by spectroscopic, microscopic, and biologic methods and at different scales, ranging from molecular, through the nano- and microscales to the macroscopic scale. The chemistry of each layer was demonstrated separately, and their mutual affinity was shown to be indispensable for the development of versatile coatings for implant applications.

Human astrocytic grid networks patterned in parylene-C inlayed SiO2 trenches

Recent literature suggests that glia, and in particular astrocytes, should be studied as organised networks which communicate through gap junctions. Astrocytes, however, adhere to most surfaces and are highly mobile cells. In order to study, such organised networks effectively in vitro it is necessary to influence them to pattern to certain substrates whilst being repelled from others and to immobilise the astrocytes sufficiently such that they do not continue to migrate further whilst under study. In this article, we demonstrate for the first time how it is possible to facilitate the study of organised patterned human astrocytic networks using hNT astrocytes in a SiO2 trench grid network that is inlayed with the biocompatible material, parylene-C. We demonstrate how the immobilisation of astrocytes lies in the depth of the SiO2 trench, determining an optimum trench depth and that the optimum patterning of astrocytes is a consequence of the parylene-C inlay and the grid node spacing. We demonstrate high fidelity of the astrocytic networks and demonstrate that functionality of the hNT astrocytes through ATP evoked calcium signalling is also dependent on the grid node spacing. Finally, we demonstrate that the location of the nuclei on the grid nodes is also a function of the grid node spacing. The significance of this work, is to describe a suitable platform to facilitate the study of hNT astrocytes from the single cell level to the network level to improve knowledge and understanding of how communication links to spatial organisation at these higher order scales and trigger in vitro research further in this area with clinical applications in the area of epilepsy, stroke and focal cerebral ischemia.

Surface modification of polysulfonamide fiber treated by air plasma

The surface of polysulfonamide (PSA) fiber was modified by air plasma to improve the wettability and interfacial bonding performance of the fiber.