Biocompatibility and antimicrobial activity of poly(3-hydroxyoctanoate) grafted with vinylimidazole

Vinylimidazole-grafted poly(3-hydroxyoctanoate) (VI-g-PHO) copolymers were prepared by heating homogeneous solutions of PHO, VI monomer, and benzoylperoxide initiator. The Fourier transform infrared spectroscopy attenuated total reflection and electron spectroscopy for chemical analyses showed that VI was successfully grafted onto the PHO chains. The surfaces and the bulk of VI-g-PHO copolymers became more hydrophilic as the VI grafting density in the copolymer increased. Measurements of the growth of Chinese hamster ovary cells and the adsorption of blood proteins and platelets in vitro showed that biocompatibility was also enhanced by grafting of VI groups. Antimicrobial activity of the VI-g-PHO copolymers was studied against Escherichia coli, Staphylococcus aureus, and Candida albicans. Treatment of each culture suspension with 2.0% (w/v) copolymers for 12h resulted in >90% reduction in viable cell counts against all test microorganisms. These results indicate that the VI-g-PHO copolymers are promising materials for biomedical applications, as they exhibited both biocompatibility and broad spectrum antimicrobial activity.     

Introducing amine functionalities on a poly(3-hydroxybutyrate-co-3-hydroxyvalerate) surface: comparing the use of ammonia plasma treatment and ethylenediamine aminolysis

Amine functionalities were introduced onto the surface of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) films by applying radio frequency ammonia plasma treatment and wet ethylenediamine treatment. The modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS) for chemical composition and Raman microspectroscopy for the spatial distribution of the chemical moieties. The relative amount of amine functionalities introduced onto the PHBV surface was determined by exposing the treated films to the vapor of trifluoromethylbenzaldehyde (TFBA) prior to XPS analysis. The highest amount of amino groups on the PHBV surface could be introduced by use of ammonia plasma at short treatment times of 5 and 10 s, but no effect of plasma power within the range of 2.5-20 W was observed. Ethylenediamine treatment yielded fewer surface amino groups, and in addition an increase in crystallinity as well as degradation of PHBV was evident from Fourier transform infrared spectroscopy. Raman maps showed that the coverage of amino groups on the PHBV surfaces was patchy with large areas having no amine functionalities.     

Covalent grafting of poly(L-lactide) to tune the in vitro degradation rate

The in vitro rate of degradation was purposely affected by covalently grafting the surface of poly(l-lactide) (PLLA). PLLA films were surface modified by our vapor-phase nondestructive photografting technique. Films were grafted for 20 min with one of the following monomers: acryl amide (AAm), N-vinyl pyrrolidone (VP), or acrylic acid (AA) and thereafter incubated in vitro in a phosphate-buffered saline solution at 37 degrees C for 154 days. The films were studied with contact angle measurements, SEM, ATR-FTIR, SEC, and DSC. The analyses verified that the in vitro rate of degradation was enhanced and that the grafted surface layer did remain covalently attached to the surface during the initial stages of incubation.     

Improving the attachment and proliferation of umbilical cord mesenchymal stem cells on modified polystyrene by nitrogen-containing plasma

Wharton’s jelly mesenchymal stem cells (WJMSCs) are important alternative source of pluripotent cells for several therapeutic purposes. Understanding of adhesion properties of such cells is necessary to regulate the attachment, growth and proliferation on targeted culture surfaces. BCP-K1, a line of WJMSCs, and polystyrene (PS) culture dishes were used as membrane samples. A 13.56 MHz inductively coupled discharge plasma reactor with a mixture of N-containing gas and noble gas was used. This was expected to introduce the more hydrophilic groups on PS surface and enhance the cell adhesion. The plasma-treated PS dishes with the mixed gas of N₂ + He at 50 W and NH₃ + He at 100 W were reactive towards BCP-K1. Cellular adhesion and proliferation was significantly twice as efficient on the treated surfaces than on PS dishes. BCP-K1 also secreted more focal adhesion kinase to adhere and proliferate when cultured on N₂-treated PS dishes than on the NH₃-treated PS dishes. Stable stemness markers were detected, including CD105, CD9 and SSEA-4, expressed on BCP-K1 growing on the modified PS dish surfaces, during 7 days of culturing. The presence of –NH₂ groups on the PS dish surface were revealed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. A large amount of oxygen- and nitrogen-containing functional groups, up to 9.0 %, were introduced by NH₃ plasma and N₂ plasma. The functional groups introduced on to the PS surfaces were clearly the key factors which enhanced WJMSCs attachment and stemness stability.     

Graft copolymerization of glycerol 1,3-diglycerolate diacrylate onto poly(3-hydroxyoctanoate) to improve physical properties and biocompatibility

Glycerol 1,3-diglycerol diacrylate-grafted poly(3-hydroxyoctanoate) (GDD-g-PHO) copolymers were prepared by heating homogeneous solutions of PHO, GDD monomer and benzoylperoxide initiator. Experiments showed that GDD was successfully grafted onto the PHO chains and that the resulting copolymers had enhanced thermal properties and mechanical strengths. The surfaces and the bulk of GDD-g-PHO copolymers became more hydrophilic as the GDD grafting density in the copolymer increased. Measurements of the growth of Chinese hamster ovary cells and the adsorption of blood proteins and platelets in vitro showed that biocompatibility was also enhanced by grafting of GDD groups. These results indicate that the GDD-g-PHO copolymers are promising materials for biocompatible biomedical applications.     

DNA immobilization/hybridization on plasma-polymerized pyrrole

The present work describes the fabrication and characterization of the conducting polymer coatings prepared by the continuous wave plasma polymerization and the applications as adhesion layers for studying DNA immobilization/hybridization. The stability of plasma polymerized pyrrole (ppPY) in the aqueous solution was characterized by ellipsometry. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to investigate polymer matrix properties and oligonucleotide/DNA binding interaction. The successful DNA immobilization on ppPY surfaces was found to depend on the macromolecular architecture of plasma polymerized films. The plasma polymers with similar thickness deposited at different input powers showed various comparable immobilization properties. The plasma-polymerized films prepared at the low input power showed a lower sensitivity toward DNA binding than those films deposited at the high input power. This result will be important to study plasma polymerized films as potential DNA biosensors in the future.     

One step processing of aminofunctionalized gate oxides

A plasma discharge process has been developed that allows the growth of biosensor gate oxides with adapted surface properties for the direct application of biomolecular immobilization cascades. The process involves an accurate selection of processing conditions, mainly, low temperature evaporation of (3-aminopropyl)triethoxysilane (APTS) and dynamic power and flow conditions. Room temperature evaporation of APTS was achieved by designing a vessel with an internal capillary network. The initial high power (100 W) plasma conditions were replaced by milder molecular fragmentation (50 W, 25 W) in a pure Ar discharge. Under these conditions the thin SiO₂ layers presented graded properties with a denser layer at the Si (100) interface and a hybrid organic–inorganic structure at the surface. The chemistry of the films was analysed by Fourier transformed infrared spectroscopy (FTIR) and Rutherford backscattering spectroscopy combined with elastic recoil detection analysis (RBS, ERDA), which confirmed the presence of the SiO₂ and organic phases. Contact angle measurements indicate the higher contribution of the basic polar component to the surface free energy. Furthermore, the higher affinity of the surface towards biomolecular immobilization was confirmed by fluorescence microscopy. Finally, penetration of nitrobenzaldehyde was obtained by application of a molecular permeation method evaluated by UV–vis spectroscopy onto fused silica substrates.     

Surface modification of polyhydroxyalkanoate films and their interaction with human fibroblasts

A poly(3-hydroxybutylate-co-hydroxyvalerate) (PHA) film containing 34 mol.% 3-hydroxyvalerate (Biopol D600P) was prepared by the solvent cast method using a 10 wt.% chloroform solution of PHA. The PHA film was exposed to an oxygen plasma glow discharge to produce peroxides on its surfaces. These peroxides were then used as catalysts for the polymerization of acrylic acid (AA) in order to prepare carboxyl group-introduced PHA (PHA-C). Insulin-immobilized PHA was prepared using the coupling reaction of PU-C with insulin. The surface-modified PHAs were then characterized by attenuated total reflection Fourier transform infrared spectroscopy, electron spectroscopy for chemical analysis, and a contact angle goniometer. The amounts of insulin directly coupled to the carboxyl groups on PHA-C and coupled to the terminus amino groups of the grafted polyethylene oxide were 2.9 and 0.8 microg cm(-2), respectively. The PHA water contact angle (75 degrees ) decreased with AA grafting (33 degrees ) and insulin immobilization (31 degrees ), thereby exhibiting the increased hydrophilicity of the modified PHAs. When compared with PHA and PHA-C, the proliferation of human fibroblasts in the presence of serum was significantly accelerated on the insulin-immobilized PHAs.     

UV-induced graft copolymerization of monoacrylate-poly(ethylene glycol) onto poly(3-hydroxyoctanoate) to reduce protein adsorption and platelet adhesion

Homogeneous solutions of poly(3-hydroxyoctanoate) (PHO) and the monoacrylate-poly(ethylene glycol) (PEGMA) monomer in chloroform were irradiated with UV light to obtain PEGMA-grafted PHO (PEGMA-g-PHO) copolymers. Variables affecting the degree of grafting (DG), such as the time of UV irradiation and the concentrations of the PEGMA monomer and initiator, were investigated. The PEGMA-g-PHO copolymers were characterized by measuring the water contact angle, molecular weight, thermal transition temperatures and mechanical properties, as well as by nuclear magnetic resonance spectroscopy. The results from all of these measurements indicate that PEGMA groups were present on the PHO polymer. The protein adsorption and platelet adhesion on the PEGMA-g-PHO surfaces were examined using poly(L-lactide) (PLLA) surfaces as the control. The proteins and platelets had a significantly lower tendency to adhere to the PEGMA-g-PHO copolymers than to PLLA. The graft copolymer with a high DG of PEGMA was very effective in reducing the protein adsorption and platelet adhesion and did not activate the platelets. The results obtained in this study suggest that PEGMA-g-PHO copolymers have the potential to be used as blood-contacting devices in a broad range of biomedical applications.     

Solvent-free vapor-phase photografting of acrylamide onto poly(ethylene terephthalate)

Poly(ethylene terphthalate) (PET) films were photografted under reduced pressure in a solvent-free vapor of acrylamide and a co-initiator, benzophenone. Characterization of grafted samples by ESCA and contact angles showed that the grafting increased with grafting time and temperature. The amide groups obtained by the acrylamide grafting were converted into amine groups by the Hofmann rearrangement to be used in coupling reactions. The amine groups were confirmed by reaction with pentafluorobenzoyl chloride, which provides a fluorine label for ESCA. Surface grafting of polymeric substrates in the vapor phase induced by plasma or high energy and UV irradiation is reviewed.