Sterilization effects on starPEG coated polymer surfaces: characterization and cell viability

Sterilization is frequently an issue for polymeric biomaterials including hydrogels, where autoclaving needs to be discarded, and γ-irradiation and low temperature hydrogen peroxide gas plasma sterilization are already important alternatives. Coatings based on poly(ethylene glycol) are a well-known strategy to reduce unspecific protein interactions on biomaterial surfaces. Dense, ultrathin coatings of isocyanate terminated star-shaped poly(ethylene glycol) (starPEG) molecules have proven to be resistant to unspecific adsorption of proteins and enable direct biofunctionalization. The effectivity and stability of the starPEG coatings on poly(vinylidene fluoride) (PVDF) were studied after γ-irradiation (normed dosis 25 kGy) and plasma sterilization (Sterrad 100S). The selected surface properties determined were: surface composition (X-ray photoelectron spectroscopy, XPS), wettability (sessile drop contact angle) and protein adsorption by fluorescence microscopy (Avidin-TexasRed, Bovine Serum Albumin-Rhodamin). Preliminary cell experiments with the cell line L929 were performed prior and after sterilization to investigate the cell repellence of the starPEG coatings as well as cell viability and specific cell adhesion on GRGDS-modified coatings. The starPEG coating undergoes a slight oxidation due to plasma and γ-sterilization; this represents a minor variation confirmed by XPS and contact angle results. The non-sterilized starPEG and the plasma-sterilized coatings are protein repellent, however the protein adsorption on starPEG coated substrates is much stronger after γ-sterilization for both avidin and bovine serum albumin. The cell experiments indicate that the starPEG coatings are appliable homogeneously by incubation and are non-cell adherent. Moreover, after both sterilization processes the starPEG coatings remain cell repellent and the GRGDS-modified coatings presented vital cells. Thus we conclude that the plasma sterilization is more convenient for the starPEG coatings and GRGDS-modified starPEG coatings.     

Nanocarbon-induced rapid transformation of polymer surfaces into superhydrophobic surfaces

We present a facile method for fabricating superhydrophobic polymer surfaces by solubility modulation and nanocarbon (NC)-induced crystallization of polycarbonate (PC). The method consists of dipping polymer sheets in a solvent in which the polymer is partially soluble and then inducing solution crystallization by dipping the sheet in a poor solvent for several seconds. A solvent mixture of methyl ethyl ketone and isopropyl alcohol (IPA) was optimized to shorten the crystallization time in a poor solvent. Single-walled carbon nanotubes, multiwalled carbon nanotubes (MWNTs), and graphene sheets were used to nucleate PC crystallization. In particular, monolayer graphene sheets were prepared by reducing graphene oxide with hydrazine. Crystalline micro- and nanostructures rapidly formed upon dipping of the PC sheets in the solution containing NCs, followed by immersion in IPA. The structures depended on the dimensions of the NCs. Especially, in the MWNT solution, dipping for 10 s was sufficient to create a superhydrophobic surface. Crystallization of PC and the incorporation of NCs during crystallization were characterized by Raman spectroscopy.     

Shape-memory surfaces for cell mechanobiology

Shape-memory polymers (SMPs) are a new class of smart materials, which have the capability to change from a temporary shape ‘A’ to a memorized permanent shape ‘B’ upon application of an external stimulus. In recent years, SMPs have attracted much attention from basic and fundamental research to industrial and practical applications due to the cheap and efficient alternative to well-known metallic shape-memory alloys. Since the shape-memory effect in SMPs is not related to a specific material property of single polymers, the control of nanoarchitecture of polymer networks is particularly important for the smart functions of SMPs. Such nanoarchitectonic approaches have enabled us to further create shape-memory surfaces (SMSs) with tunable surface topography at nano scale. The present review aims to bring together the exciting design of SMSs and the ever-expanding range of their uses as tools to control cell functions. The goal for these endeavors is to mimic the surrounding mechanical cues of extracellular environments which have been considered as critical parameters in cell fate determination. The untapped potential of SMSs makes them one of the most exciting interfaces of materials science and cell mechanobiology.     

Shape-memory surfaces for cell mechanobiology

Abstract

Shape-memory polymers (SMPs) are a new class of smart materials, which have the capability to change from a temporary shape ‘A’ to a memorized permanent shape ‘B’ upon application of an external stimulus. In recent years, SMPs have attracted much attention from basic and fundamental research to industrial and practical applications due to the cheap and efficient alternative to well-known metallic shape-memory alloys. Since the shape-memory effect in SMPs is not related to a specific material property of single polymers, the control of nanoarchitecture of polymer networks is particularly important for the smart functions of SMPs. Such nanoarchitectonic approaches have enabled us to further create shape-memory surfaces (SMSs) with tunable surface topography at nano scale. The present review aims to bring together the exciting design of SMSs and the ever-expanding range of their uses as tools to control cell functions. The goal for these endeavors is to mimic the surrounding mechanical cues of extracellular environments which have been considered as critical parameters in cell fate determination. The untapped potential of SMSs makes them one of the most exciting interfaces of materials science and cell mechanobiology.     

Bacterial adhesion onto nanopatterned polymer surfaces

Two-dimensional nanopore arrays, consisting of hydrophilic SiO₂-like holes within hydrophobic poly(hydroxymethylsiloxane) (PHMS) surfaces, were fabricated by using a colloidal template-assisted method. The pores typically were deep 2–3 nm and wide ∼100 nm, as measured by tapping mode AFM. The adhesion behaviour of Pseudomonas aeruginosa, i.e. a micrometer width cell, was investigated by Fluorescence Microscopy both onto the nanopatterned PHMS surfaces and the homogeneous corresponding substrates of unmodified PHMS as well as the SiO₂-like surfaces obtained by plasma modification of PHMS films. The nanostructured films were able to induce a general increase of adhered cells with respect to the unmodified hydrophobic surfaces and a spot grown of biofilm-like aggregates. The observed effects are discussed in terms of the surface free energy of the patterned films as well as of the homogeneity and total integrated area of the 2D nanopore array.     

Cell interactions with laser-modified polymer surfaces

The performance of a polymeric biomaterial depends on the bulk and surface properties. Often, however, the suitability of the surface properties is compromised in favour of the bulk properties. Altering the surface properties of these materials will have a profound effect on how cells and proteins interact with them. Here, we have used an excimer laser to modify the surface wettability of nylon 12. The surface treatment is rapid, cost-effective and can cause reproducible changes in the surface structure of the polymers. Polymers were treated with short wavelength ( < 200 nm) UV light. These wavelengths have sufficient photon energy (6.4eV) to cause bond scission at the material surface. This results in a surface reorganisation with incorporation of oxygen. Surface wettability changes were confirmed using contact angle measurements. Cell interactions with the surfaces were examined using 3T3 fibroblast and HUVEC cells. Cells morphology was examined using a confocal laser scanning microscope (CLSM). Cell activity and cell number on the treated nylon were assessed using biochemical assays for up to seven days. Both fibroblasts and endothelial cells initially proliferated better on treated compared with untreated samples. However, over seven days activity decreased for both cell types on the control samples and endothelial cell activity and cell number also decreased on the treated polymer.     

Elastic modulus of nanostructured polymer surfaces

Living cell cultures exhibit improved adhesion on polymer surfaces engineered with nano-scale structures as compared to their flat counterparts. During fabrication their polymer-chain structure can be altered, thus affecting their mechanical properties. Here, we demonstrate using atomic-force-microscope nanoindentation that the modulus of nanostructured PDMS is doubled, while that of nanostructured ORMOCER increases by an order of magnitude, when compared to their flat counterparts.     

Tribological behaviors of plasma-treated carbon composite grooved surfaces

The tribological behavior of carbon epoxy composites whose surfaces have many small grooves of 100 μm width were compared with respect to plasma treatment duration under dry sliding conditions. The surface coating material on the grooved surface was high-density polyethylene (HDPE) and suitable plasma treatment time for grooved composite surface for atmospheric pressure plasma system was experimentally investigated by measuring the friction coefficient and wear volume. The wear morphology of the composites observed with a scanning electron microscopic (SEM) revealed that the surface coating layer on the grooved surface significantly improved the wear resistance and the plasma treatment can improve the durability of the coating layer.     

X-ray photoelectron spectroscopy studies of polymer surfaces

X-ray photoelectron spectroscopy (XPS) has been used to study the chromic acid etching of polyethylene (low density) and polypropylene film surfaces. Both core and valence levels have been used to monitor changes in surface composition and these results correlated with contact angle measurements. Besides the expected observation of oxygenated species, the technique detects a sulphur containing species, identified as -SO₃H. Information about the depth of polymer attack has been obtained from two types of data (comparative core level intensities and angular variation of relative peak intensities) which provide depth resolution. Differences in behaviour of the two polyolefins are discussed in connection with previous non-surface specific data.     

A perturbation analysis on solid polymer surfaces

A linear stability model was formulated to analyze the perturbation of solid polymer surfaces. Surface energy and thermal stress were considered as the main variables. The surface tends to more unstable as the temperature increase. This is interpreted as the dominancy of the lattice vacancy diffusion over surface mass diffusion and the increase in thermal stress.     

X-ray photoelectron spectroscopy studies of polymer surfaces

The effect of melting polyethylene on aluminium has been re-examined using X-ray photoelectron spectroscopy. Even at 150° C, low and high density polyethylenes show degrees of oxidation similar to that observed with conventional pretreatments; large increases in adhesion are also observed. The results are discussed in relation to transcrystalline regions and weak boundary layers.     

X-ray photoelectron spectroscopy studies of polymer surfaces

X-ray photoelectron spectroscopy showed that a normal flame treatment caused a high level of oxidation in low-density polyethylene. 0.02% of the antioxidant 2,6-ditertbuty-p-cresol did not reduce the degree of oxidation or the level of adhesion in contrast to the extrusion of low-density polyethylene. It is estimated that the depth of oxidation is between 40 and 90 Å which is much less than for a moderate chromic acid treatment or with extrusion. There were no significant changes in the XP-spectra or adhesion levels of flame treated samples after 12 months.     

功能高分子材料及其应用

着重介绍了电磁功能高分子材料、生物医用功能高分子材料、化学功能高分子材料和光功能高分子材料的性质及应用领域。