Arend J. Schouten

Solvent-free functionalization of silicone rubber and efficacy of PAAm brushes grafted from an amino-PPX layer against bacterial adhesion

Silicone rubber is a frequently employed biomaterial that is prone to bacterial adhesion and biofilm formation. In this study, the surface of silicone rubber was solvent-free functionalized by chemical vapor deposition (CVD) of poly(o-amino-p-xylylene-co-p-xylylene (amino-PPX). Subsequently, the amino groups of the amino-PPX layer were used to introduce the initiator from a vapor phase for atom transfer radical polymerization of acrylamide to form polyacrylamide (PAAm) brushes. The modification steps were verified by means of X-ray photoelectron spectroscopy and attenuated total reflection-Fourier transform infrared spectroscopy. Adhesion of Staphylococcus aureus ATCC 12600 and Escherichia coli 3.14 to an amino-PPX-PAAm brush coating in a parallel plate flow chamber was strongly reduced with respect to non-coated silicone rubber - by 93% and 99%, respectively. For E. coli 3.14, this reduction is larger than that obtained for solvent functionalization of γ-aminopropyltriethoxysilane-PAAm brushes due to the higher density of amino groups introduced by the CVD of amino-PPX.

Microbial adhesion to surface-grafted polyacrylamide brushes after long-term exposure to PBS and reconstituted freeze-dried saliva

Polyacrylamide (PAAm) brushes, covalently grafted from silicon wafer surfaces were examined for their ability to inhibit microbial adhesion after long-term exposure to PBS or reconstituted freeze-dried saliva for time intervals from 48 h up to 1 month at 37 degrees C. Microbial adhesion after exposure was studied in a parallel plate flow chamber. Infrared spectra showed that PAAm brushes exhibit good chemical stability upon incubation in both PBS and reconstituted freeze-dried saliva up to 1 month. Reductions in microbial adhesion on PAAm brushes after exposure to PBS or reconstituted freeze-dried saliva varied from 63 to 93% depending on the microbial strain considered, even after 1 month of exposure of the brushes to reconstituted freeze-dried saliva.

Annealing-Induced Changes in Double-Brush Langmuir-Blodgett Films of alpha-Helical Diblock Copolypeptides

The effect of annealing on the structure and the helix orientation in Langmuir-Blodgett (LB) monolayers of diblock copolymers (PLGA-b-PMLGSLGs) of poly(alpha-L-glutamic acid) (PLGA) and poly(gamma-methyl-L-glutamate-ran-gamma-stearyl-L-glutamate) with 30 mol % of stearyl substituents (PMLGSLG) with unidirectional helix orientation deposited on hydrophilic silicon substrates was characterized by means of small-angle X-ray reflectivity, transmission Fourier transform infrared spectroscopy, and atomic force microscopy. Upon annealing at 100 degrees C for 24 h, the alpha-helices became less tilted toward the substrate surface normal. Surface area shrinkage accompanied the change in tilt, indicated by an increase in both film thickness and electron density, resulting in more compact and uniform films. The enhancement of the helix orientation by thermal annealing was greater for the PMLGSLG block and for the diblock copolymers with the shorter block lengths. For these diblock copolymers, annealing resulted in postorientation of the PMLGSLG block helices almost perpendicular to the substrate surface. This effect originates from a considerable increase in intermolecular packing of the PLGA block caused by hydrogen bonds between the carboxylic groups upon annealing, as well as the high mobility of the PMLGSLG block helices for rearrangement favored by the melted side chain mantle at elevated temperatures.

Novel polyurethanes with interconnected porous structure induce in vivo tissue remodeling and accompanied vascularization

Tissue engineering and regenerative medicine have furnished a vast range of modalities to treat either damaged tissue or loss of soft tissue or its function. In most approaches, a temporary porous scaffold is required to support tissue regeneration. The scaffold should be designed such that the turnover synchronizes with tissue remodeling and regeneration at the implant site. Segmented polyester urethanes (PUs) used in this study were based on epsilon-caprolactone (CL) and co-monomers D,L-lactide (D,L-L) and gamma-butyrolactone (BL), and 1,4-butanediisocyanate (BDI). In vitro, the PUs were nontoxic and haemocompatible. To test in vivo biocompatibility, the PUs were further processed into porous structures and subcutaneously implanted in rats for a period up to 21 days. Tissue remodeling and scaffold turnover was associated with a mild tissue response. The tissue response was characterized by extensive vascularization through the interconnected pores, with low numbers of macrophages on the edges and stroma formation inside the pores of the implants. The tissue ingrowth appeared to be related to the extent of microphase separation of the PUs and foam morphology. By day 21, all of the PU implants were highly vascularized, confirming the pores were interconnected. Degradation of P(CL/D,L-L)-PU was observed at this time, whereas the other two PU types remained intact. The robust method reported here of manufacturing and processing, good mechanical properties, and in vivo tissue response of the porous P(CL/D,L-L)-PU and PBCL-PU makes them excellent candidates as biomaterials with an application for soft tissue remodeling, for example, for cardiovascular regeneration.

Surface Potentials in Langmuir Mono layers of Unidirectionally Oriented alpha-Helical Diblock Copolypeptides

The surface potentials and effective dipole moments of alpha-helical amphiphilic diblock copolypeptides during monolayer compression at the air-water interface are reported. Amphiphilic diblock copolypeptides (PLGA-b-PMLGSLGs) of poly(alpha-L-glutamic acid) (PLGA) and poly(gamma-methyl-L-glutamate-ran-gamma-stearyl-L-glutamate) with 30 mol % of stearyl substituents (PMLGSLG) of various block lengths were studied during the double-brush formation process at the water surface. Upon monolayer spreading of PLGA-b-PMLGSLGs, surface potentials of hundreds of millivolts were recorded, attributed to the dipole moments of water molecules reorienting due to interactions with the monolayers. Upon compression, the effective dipole moments derived from the surface potentials of the PLGA-b-PMLGSLG monolayers decrease gradually, most likely as a result of the immersion of the hydrophilic block in water and cancellation of the interactions between the hydrophobic block and the underlying water molecules. The polypeptide macrodipole moment immersed in water was apparently effectively screened out. The remaining effective dipole moment of the monolayer contributes mainly to the hydrophobic block, and upon tilting away from the water surface toward the surface normal, it was found to increase with the hydrophobic block length, indicating the gradual formation of unidirectional aligned polypeptide molecules in the double-brush monolayer.

Dipping-Induced Azimuthal Helix Orientation in Langmuir-Blodgett Monolayers of alpha-Helical Amphiphilic Diblock Copolypeptides

The azimuthal helix orientation of the rigid-rod amphiphilic diblock copolypeptides (PLGA-b-PMLGSLGs) of poly(alpha-L-glutamic acid) (PLGA) and poly(gamma-methyl-L-glutamate-ran-gamma-stearyl-L-glutamate) with 30 mol % of stearyl substituents (PMLGSLG) in Langmuir-Blodgett (LB) monolayers was investigated using polarized transmission Fourier transform infrared spectroscopy. The relative position of dipping with respect to the previous transfer position can be used to manipulate the azimuthal orientation of the helices parallel to or tilted by an angle of 45 degrees with respect to the dipping direction in the transferred films. The study of the azimuthal order for the LB monolayers of PLGA-b-PMLGSLGs of various block lengths revealed that the observed effect arises mainly from the deformation of the PMLGSLG top brush layer, induced by the flow orientation around the transfer region. In those cases where the PMLGSLG block is tilted by a sufficiently large angle with respect to the surface normal, high azimuthal order parameters of 0.5-0.75 were obtained.