Plasma surface engineering to biofunctionalise polymers for β-cell adhesion

Implant devices containing insulin-secreting β-cells hold great promise for the treatment of diabetes. Using in vitro cell culture, long-term function and viability are enhanced when β-cells are cultured with extracellular matrix (ECM) proteins. Here, our goal is to engineer a favorable environment within implant devices, where ECM proteins are stably immobilized on polymer scaffolds, to better support β-cell adhesion. Four different polymer candidates (low-density polyethylene (LDPE), polystyrene (PS), polyethersulfone (PES) and polysulfone (PSU)) were treated using plasma immersion ion implantation (PIII) to enable the covalent attachment of laminin on their surfaces. Surface characterisation analysis shows the increased hydrophilicity, polar groups and radical density on all polymers after the treatment. Among the four polymers, PIII-treated LDPE has the highest water contact angle and the lowest radical density which correlate well with the non-significant protein binding improvement observed after 2 months of storage. The study found that the radical density created by PIII treatment of aromatic polymers was higher than that created by the treatment of aliphatic polymers. The higher radical density significantly improves laminin attachment to aromatic polymers, making them better substrates for β-cell adhesion

Optical properties and oxidation of carbonized and cross-linked structures formed in polycarbonate by plasma immersion ion implantation

At ion fluences higher than 5 10 15 ions/cm2 , plasma immersion ion implantation (PIII) of polycarbonate (PC) results in a formation of a carbonized surface layer. The thickness of this layer is close to the depth of ion penetration. A comparison of PIII treated, spin-coated PC films with pre-treatment thicknesses designed to match and exceed the carbonized layer thickness is employed to study the properties of the carbonised layer independently from the less modified underlying structure. At ion fluencies higher than 10 16 ions/cm2 , the thinner PC film is completely transformed into an amorphous carbon-like material with no traces of the initial PC structure. The thicker films, however, incorporated two layers: a top carbonised layer and a cross-linked layer below. Compared to the two-layered PC film, the completely carbonized layer was found to have a much higher concentration of C@O bonds and much lower concentration of O-H bonds after exposure to atmospheric oxygen. The refractive index of the thicker PC films PIII treated with high ion fluencies is close to the refractive index of diamond-like carbon. Anomalous dispersion of the refractive index of the thicker PC films is observed after formation of the carbonised layer. The refractive index of the thinner PC film has normal dispersion at all ion fluences. At ion fluences of 2 10 16 ions/cm2 , both PC films were found to have the same etching rate as polystyrene. Washing in dichloromethane had no effect on the carbonised layer but affected the underlying material in the case of the thicker PC films leading to a wrinkled structure up to ion fluences of 2 10 16 ions/cm2 . At this and higher fluence, areas of an ordered island-like structure were observed

Orientation and conformation of anti-CD34 antibody immobilised on untreated and plasma treated polycarbonate

The conformation and orientation of proteins immobilised on synthetic materials determine their ability to bind their antigens and thereby the sensitivity of the microarrays and biosensors employing them. Plasma immersion ion implantation (PIII) of polymers significantly increases both their wettability and protein binding capacity. This paper addresses the hypothesis that a PIII treated polymer surface modifies the native protein conformation less significantly than a more hydrophobic untreated surface and that the differences in surface properties also affect the protein orientation. To prove this, the orientation and conformation of rat anti-mouse CD34 antibody immobilized on untreated and PIII treated polycarbonate (PC) were investigated using ToF-SIMS and FTIR-ATR spectroscopy. Analysis of the primary structure of anti-CD34 antibody and principal component analysis of ToF-SIMS data were applied to detect the difference in the orientation of the antibody attached to untreated and PIII treated PC. The difference in the antibody conformation was analysed using deconvolution of the Amide I peak (in FTIR-ATR spectra) and curve-fitting. It was found that compared to the PIII treated sample, the antibody immobilized on the untreated PC sample has a secondary structure with a lower fraction of β-sheets and a higher fraction of α-helices and disordered fragments. Also, it was found that anti-CD34 antibody has a higher tendency to occur in the inactive ‘tail-up’ orientation when immobilized on an untreated PC surface than on a PIII treated surface. These findings confirm the above hypothesis

Effect of plasma immersion ion implantation on polycaprolactone with various molecular weights and crystallinity

Polycaprolactone with five different molecular weights was spin-coated on silicon wafers and plasma immersion ion implanted (PIII) with ion fluence in the range 5 × 1014–2 × 1016 ions/cm2. The effects of PIII treatment on the optical properties, chemical structure, crystallinity, morphology, gel fraction formation and wettability were investigated. As in the case of a number of previously studied polymers, oxidation and hydrophobic recovery of the PIII treated PCL follow second order kinetics. CAPA 6250, which has the lowest molecular weight and the highest degree of crystallinity of the untreated PCL films studied, has the highest carbonization of the modified layer after PIII treatment. Untreated medical grade PCL films, mPCL PC12 (Perstorp) and mPCL OsteoporeTM have similar chemical structures and crystallinity. Accordingly, the chemical and structural transformations caused by PIII treatment and post-treatment oxidation are almost identical for these two polymers. In general, PIII treatment destroys the nano-scale lamellar structure and results in a reduction of PCL crystallinity. Examination after washing PIII treated PCL films in toluene confirmed our hypothesis that cross-linking due to PIII treatment is significantly higher in semi-crystalline PCL as compared with amorphous polymers

Improved Multiprotein Microcontact Printing on Plasma Immersion Ion Implanted Polystyrene

Multiprotein micropatterning allows the creation of complex, controlled microenvironments for single cells that can be used for the study of the localized effects of various proteins and signals on cell survival, development, and functions. To enable analysis of cell interactions with microprinted proteins, the multiprotein micropattern must have low cross-contamination and high long-term stability in a cell culture medium. To achieve this, we employed an optimized plasma ion immersion implantation (PIII) treatment to provide polystyrene (PS) with the ability to covalently immobilize proteins on contact while retaining sufficient transparency and suitable surface properties for contact printing and retention of protein activity. The quality and long-term stability of the micropatterns on untreated and PIII treated PS were compared with those on glass using confocal microscopy. The protein micropattern on the PIII treated PS was more uniform and had a significantly higher contrast that was not affected by long-term incubation in cell culture media because the proteins were covalently bonded to PIII treated PS. The immunostaining of mouse pancreatic β cells interacting with E-cadherin and fibronectin striped surfaces showed phosphorylated paxillin concentrated on cell edges over the fibronectin stripes. This indicates that multiprotein micropatterns printed on PIII treated PS can be used for high-resolution studies of local influence on cell morphology and protein production

Soft X-ray absorption spectroscopy investigation of the surface chemistry and treatments of copper indium gallium diselenide (CIGS)

The surface and near surface structure of copper-indium-gallium-selenide (CIGS) absorber layers is integral to the producing a high-quality photovoltaic junction. By using X-ray absorption spectroscopy (XAS) and monitoring multiple elemental absorption edges with both theory and experiment, we are able to identify several features of the surface of CIGS as a function of composition and surface treatments. The XAS data shows trends in the near surface region of oxygen, copper, indium and gallium species as the copper content is varied in the films. The oxygen surface species are also monitored through a series of experiments that systematically investigates the effects of water and various solutions of: ammonium hydroxide, cadmium sulfate, and thiourea. These being components of cadmium sulfide chemical bath deposition (CBD). Characteristics of the CBD are correlated with a restorative effect that produces as normalized, uniform surface chemistry as measured by XAS. This surface chemistry is found in CIGS solar cells with excellent power conversion efficiency (<19%). The results provide new insight for CIGS processing strategies that seek to replace CBD and/or cadmium sulfide