Cross-Linking and Degradation Properties of Plasma Enhanced Chemical Vapor Deposited Poly(2-hydroxyethyl methacrylate)

Layer-by-Layer Fabrication of PAH/PAMAM/Nano-CaCO3 Composite Films and Characterization for Enhanced Biocompatibility

Nanoparticle production and functionalization for various biomedical uses are still challenging. Polymer composites constituted of poly(amidoamine) (PAMAM), polyallylamine hydrochloride (PAH), and calcium carbonate (CaCO₃) nanoparticles have good biocompatibility with physiological tissue and fluids, making them excellent candidates for biomedical applications. This study investigated the characteristics of polymeric/nano-CaCO₃ composite films based on a PAH/PAMAM matrix, which were fabricated through layer-by-layer synthesis on quartz glass substrates. It was found that the as-prepared elastic moduli of the resultant (PAH/PAMAM)_n-CaCO₃ (where n represents the number of bilayers) composite films varied from 1.40 to 23.70 GPa for different degrees of cross-linking when 0.1 M nano-CaCO₃ particles were incorporated into the polymer matrix. The highly cross-linked (PAH/PAMAM)₁₅-CaCO₃ composite film had the highest recorded elastic modulus of 23.70 GPa, while it was observed that for all the composite films fabricated for the present study, the addition of the nano-CaCO₃ particles approximately doubled the elastic modulus regardless of the degree of polymerization. Live/Dead assays were used to determine whether the produced composite films were compatible with human lung fibroblast cells. The findings indicate that the (PAH/PAMAM)_7.5-CaCO₃ composite film had the most positive effect on cell growth and proliferation, with the (PAH/PAMAM)₁₅-CaCO₃ composite film demonstrating significant ion transport behavior with low impedance, which was considered good for in vivo rapid cell-to-cell communication. Therefore, the (PAH/PAMAM)_7.5-CaCO₃ and (PAH/PAMAM)₁₅-CaCO₃ composite films are potential tissue engineering biomaterials, but further studies are essential to generate more data to evaluate the suitability of these composites for this and other biomedical functions.

Polymer Thin Films and Surface Modification by Chemical Vapor Deposition: Recent Progress

Chemical vapor deposition (CVD) polymerization uses vapor phase monomeric reactants to synthesize organic thin films directly on substrates. These thin films are desirable as conformal surface engineering materials and functional layers. The facile tunability of the films and their surface properties allow successful integration of CVD thin films into prototypes for applications in surface modification, device fabrication, and protective films. CVD polymers also bridge microfabrication technology with chemical and biological systems. Robust coatings can be achieved via CVD methods as antifouling, anti-icing, and antihydrate surfaces, as well as stimuli-responsive or biocompatible polymers and novel nanostructures. Use of low-energy input, modest vacuum, and room-temperature substrates renders CVD polymerization compatible with thermally sensitive substrates and devices. Compared with solution-based methods, CVD is particularly useful for insoluble materials, such as electrically conductive polymers and controllably crosslinked networks, and has the potential to reduce environmental, health, and safety impacts associated with solvents. This review discusses the relevant background and selected applications of recent advances by two methods that display and use the high retention of the organic functional groups from their respective monomers, initiated CVD (iCVD) and oxidative CVD (oCVD) polymerization.

pH-Responsive 2-hydroxyethyl methacrylate/citraconic anhydride–modified collagen hydrogels as ciprofloxacin carriers for wound dressings

pH-Sensitive hydrogels of 2-hydroxyethyl methacrylate/citraconic anhydride–modified collagen were obtained by free radical copolymerization/crosslinking in the presence of ammonium persulfate/ N,N,N′, N′-tetramethylethylenediamine redox initiator system. Their pH-responsiveness was demonstrated by swelling behavior and ciprofloxacin release tests. Both unloaded and loaded hydrogels were characterized by Fourier transform infrared, scanning electron microscopy, and biocompatibility tests. The enzymatic degradation in the presence of Clostridium histolyticum mainly depends on initiator content. In vivo biocompatibility tests involving intraperitoneal hydrogels’ implantation in rats following the analysis by the granuloma test, leukocyte formula, immune parameters, and hepatic transaminases demonstrated their non-toxicity and biocompatibility with living tissues. The in vitro antimicrobial activity, in vivo biocompatibility, and in vitro biodegradability tests attest the possibility to use these new polymeric hydrogels with tailored properties as matrices for bioactive products in medical and pharmaceutical applications as wound care and targeting drug delivery systems. The ciprofloxacin release studies proved their potential as materials for wound dressings.

Photoinitiated chemical vapor deposition of cytocompatible poly(2-hydroxyethyl methacrylate) films

Poly(2-hydroxyethyl methacrylate) (pHEMA) is a widely utilized biomaterial due to lack of toxicity and suitable mechanical properties; conformal thin pHEMA films produced via chemical vapor deposition (CVD) would thus have broad biomedical applications. Thin films of pHEMA were deposited using photoinitiated CVD (piCVD). Incorporation of ethylene glycol diacrylate (EGDA) into the pHEMA polymer film as a crosslinker, confirmed via Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, resulted in varied swelling and degradation behavior. 2-Hydroxyethyl methacrylate-only films showed significant thickness loss (up to 40%), possibly due to extraction of low-molecular-weight species or erosion, after 24 h in aqueous solution, whereas films crosslinked with EGDA (9.25-12.4%) were stable for up to 21 days. These results differ significantly from those obtained with plasma-polymerized pHEMA, which degraded steadily over a 21-day period, even with crosslinking. This suggests that the piCVD films differ structurally from those fabricated via plasma polymerization (plasma-enhanced CVD). piCVD pHEMA coatings proved to be good cell culture materials, with Caco-2 cell attachment and viability comparable to results obtained on tissue-culture polystyrene. Thus, thin film CVD pHEMA offers the advantage of enabling conformal coating of a cell culture substrate with tunable properties depending on method of preparation and incorporation of crosslinking agents.

A nonviral pHEMA+chitosan nanosphere-mediated high-efficiency gene delivery system

The transport of DNA into eukaryotic cells is minimal because of the cell membrane barrier, and this limits the application of DNA vaccines, gene silencing, and gene therapy. Several available transfection reagents and techniques have been used to circumvent this problem. Alternatively, nonviral nanoscale vectors have been shown to bypass the eukaryotic cell membrane. In the present work, we developed a unique nanomaterial, pHEMA+chitosan nanospheres (PCNSs), which consisted of poly(2-hydroxyethyl methacrylate) nanospheres surrounded by a chitosan cationic shell, and we used this for encapsulation of a respiratory syncytial virus (RSV)-F gene construct (a model for a DNA vaccine). The new nanomaterial was capable of transfecting various eukaryotic cell lines without the use of a commercial transfection reagent. Using transmission electron microscopy, (TEM), fluorescence activated cell sorting (FACS), and immunofluorescence, we clearly demonstrated that the positively charged PCNSs were able to bind to the negatively charged cell membrane and were taken up by endocytosis, in Cos-7 cells. Using quantitative polymerase chain reaction (qPCR), we also evaluated the efficiency of transfection achieved with PCNSs and without the use of a liposomal-based transfection mediator, in Cos-7, HEp-2, and Vero cells. To assess the transfection efficiency of the PCNSs in vivo, these novel nanomaterials containing RSV-F gene were injected intramuscularly into BALB/c mice, resulting in high copy number of the transgene. In this study, we report, for the first time, the application of the PCNSs as a nanovehicle for gene delivery in vitro and in vivo.

Plasma-enhanced copolymerization of amino acid and synthetic monomers

In this paper we report the use of plasma-enhanced chemical vapor deposition (PECVD) for the simultaneous deposition and copolymerization of an amino acid with other organic and inorganic monomers. We investigate the fundamental effects of plasma-enhanced copolymerization on different material chemistries in stable ultrathin coatings of mixed composition with an amino acid component. This study serves to determine the feasibility of a direct, facile method for integrating biocompatible/active materials into robust polymerized coatings with the ability to plasma copolymerize a biological molecule (L-tyrosine) with different synthetic materials in a dry, one-step process to form ultrathin coatings of mixed composition. This process may lead to a method of interfacing biologic systems with synthetic materials as a way to enhance the biomaterial-tissue interface and preserve biological activity within composite films.

Chemical vapor deposition of conformal, functional, and responsive polymer films

Chemical vapor deposition (CVD) polymerization utilizes the delivery of vapor-phase monomers to form chemically well-defined polymeric films directly on the surface of a substrate. CVD polymers are desirable as conformal surface modification layers exhibiting strong retention of organic functional groups, and, in some cases, are responsive to external stimuli. Traditional wet-chemical chain- and step-growth mechanisms guide the development of new heterogeneous CVD polymerization techniques. Commonality with inorganic CVD methods facilitates the fabrication of hybrid devices. CVD polymers bridge microfabrication technology with chemical, biological, and nanoparticle systems and assembly. Robust interfaces can be achieved through covalent grafting enabling high-resolution (60 nm) patterning, even on flexible substrates. Utilizing only low-energy input to drive selective chemistry, modest vacuum, and room-temperature substrates, CVD polymerization is compatible with thermally sensitive substrates, such as paper, textiles, and plastics. CVD methods are particularly valuable for insoluble and infusible films, including fluoropolymers, electrically conductive polymers, and controllably crosslinked networks and for the potential to reduce environmental, health, and safety impacts associated with solvents. Quantitative models aid the development of large-area and roll-to-roll CVD polymer reactors. Relevant background, fundamental principles, and selected applications are reviewed.

Rapid Formation of Acrylated Microstructures by Microwave-Induced Thermal Crosslinking

We present a rapid and highly efficient method to form microstructure of poly(ethylene glycol) (PEG)-based acrylates by microwave-induced thermal crosslinking. PEG-based polymeric microstructures such as polymer microarrays and microwells were fabricated on 3-(trimethoxysilyl)propyl methacrylate (TMSPMA)-coated glass slides that were placed on top of a silicon wafer. In comparison to ultraviolet (UV) irradiation curing, microwave-induced thermal crosslinking could be completed within 10 s, without thermal degradation or oxygen inhibition in the presence of ambient oxygen. Furthermore, the activation of surviving free radical impurities by microwave-induced heating enabled crosslinking even without an exogenous radical initiator (e.g., 2,2'-azoisobutyronitrile (AIBN)). This approach can be beneficial for fabricating various PEG-based microstructures for high-throughput screening assays, cell-based biosensors, and biomedical microdevices.