[show abstract][hide abstract] ABSTRACT: Grafting of methoxypoly(ethylene glycol) (mPEG) to cells and biomaterials is a promising non-pharmacological immunomodulation technology. However, due to the labile nature of cells, surface-plasma interactions are poorly understood; hence, a latex bead model was studied. PEGylation of beads resulted in a density and molecular weight dependent decrease in total adsorbed protein with a net reduction from (159.9±6.4) ng cm(-2) on bare latex to (18.4±0.8) and (52.3±5.3) ng cm(-2) on PEGylated beads (1 mmol L(-1) of 2 or 20 kD SCmPEG, respectively). SDS-PAGE and iTRAQ-MS analysis revealed differential compositions of the adsorbed protein layer on the PEGylated latex with a significant reduction in the compositional abundance of proteins involved in immune system activation. Thus, the biological efficacy of immunocamouflaged cells and materials is mediated by both biophysical obfuscation of antigens and reduced surface-macromolecule interactions.
Science China. Life sciences 03/2012; 55(3):191-201. · 2.02 Impact Factor
[show abstract][hide abstract] ABSTRACT: Development of novel approaches for the immunomodulation of donor cells would have significant utility in transfusion and transplantation medicine. Immunocamouflage of cell surfaces by covalently grafted methoxypoly(ethylene glycol) (mPEG) (PEGylation) has emerged as a promising approach. While previous studies demonstrated the in vitro and in vivo efficacy of immunocamouflaged allogeneic blood cells, the biophysical mechanisms of immunoprotection have not been well-defined due to the fragility of intact cells. To overcome this limitation, polystyrene beads (1.2 and 8.0 microm) were used to elucidate the biophysical effects of polymer size, density and linker chemistry on charge camouflage and protein adsorption. These findings were correlated with biological studies using red blood cells and lymphocytes. Charge camouflage of both beads and cells was best achieved with long polymers. However, protein adsorption studies demonstrated an unexpected effect of target size. For 1.2 microm beads, decreased protein adsorption was best achieved with short (2 kDa) polymers whereas long chain (20 kDa) polymers were optimal for 8.0 microm particles. The biophysical findings correlated well with biological immunocamouflage as measured by particle electrophoresis and the inhibition of antibody-antigen (CD3, CD4 and CD28) recognition. Moreover, it was observed that antigen topography (CD28 vs. CD4) was of significance in selecting the appropriate polymer size. The biophysical interactions of PEGylated surfaces and macromolecules involve complex mechanisms dependent on the molecular weight, grafting concentration, target size and surface complexity. Cellular PEGylation strategies must be customized to account for target cell size, membrane complexity and antigen density and height.
[show abstract][hide abstract] ABSTRACT: Three hydrolytically stable polyethyleneglycol (PEG)-based N-substituted acrylamide macromonomers, methoxypolyethyleneglycol (350) acrylamide (MPEG350Am) methoxypolyethyleneglycol (750) acrylamide(MPEG750Am) and methoxypolyethyleneglycol (2000)acrylamide (MPEG2000Am) with increasing PEG chain length were synthesized. Surface-initiated aqueous atom transfer radical polymerization (ATRP) using CuCl/1,1,4,7,10,10-hexamethyl triethylene tetramine (HMTETA) catalyst was utilized to generate dense polymer brushes from these monomers via an ester linker group on the surface of model polystyrene (PS) particles. The molecular weight, hydrodynamic thickness, and graft densities of the grafted polymer layers were controlled by changing the reaction parameters of monomer concentration, addition of Cu(II)Cl2, and sodium chloride. The graft densities of surface-grafted brushes decreased with increasing PEG macromonomer chain length, 350 > 750 > 2000, under similar experimental conditions. The molecular weight of grafts increased with increase in monomer concentration, and only selected conditions produced narrow distributed polymer chains. The molecular weight of grafted polymer chains differs significantly to those formed in solution. The hydrodynamic thicknesses of the grafted polymer layers were fitted to the Daoud and Cotton model (DCM) for brush height on spherical surfaces. The results show that the size of the pendent groups on the polymer chains has a profound effect on the hydrodynamic thickness of the brush for a given degree of polymerization. The new PEG-based surfaces show good protection against nonspecific protein adsorption from blood plasma compared to the bare surface. Protein adsorption decreased with increasing surface density of grafted polymer chains. Poly(MPEG750Am) brushes were more effective in preventing protein adsorption than poly(MPEG350Am) even at low graft densities, presumably due to the increase in PEG content in the grafted layer.
[show abstract][hide abstract] ABSTRACT: A micromachined vibrating membrane is used to remove adsorbed proteins on a surface. A lead zirconate titanate (PZT) composite (3 x 1 x 0.5 mm) is attached to a silicon membrane (2,000 x 500 x 3 microm) and vibrates in a flexural plate wave (FPW) mode with wavelength of 4,000/3 microm at a resonant frequency of 308 kHz. The surface charge on the membrane and fluid shear stress contribute in minimizing the protein adsorption on the SiO(2) surface. In vitro characterization shows that 57 +/- 10% of the adsorbed bovine serum albumin (BSA), 47 +/- 13% of the immunoglobulin G (IgG), and 55.3~59.2 +/- 8% of the proteins from blood plasma are effectively removed from the vibrating surface. A simulation study of the vibration-frequency spectrum and vibrating amplitude distribution matches well with the experimental data. Potentially, a microelectromechanical system (MEMS)-based vibrating membrane could be the tool to minimize biofouling of in vivo MEMS devices.
[show abstract][hide abstract] ABSTRACT: Growing polymer chains from surface initiators in principle allows much more dense polymer surface layers to be created than can be produced by grafting of whole (self-excluding) chains. We have utilized aqueous atom transfer radical polymerization to graft a series of cleavable hydrophilic poly(N-isopropylacrylamide) (PNIPAM) homopolymers and block copolymers of substituted acrylamides from polystyrene latex to give brushes of controlled MW and surface density. Average chain separations much less than their free solution radii of gyration have been achieved. Exposure to radiolabeled single proteins or to whole plasma and subsequent analysis by SDS-PAGE shows that PNIPAM brushes decrease protein adsorption relative to the latex surface or other substituted polyacrylamides. The PNIPAM brushes exhibit a second-order phase transition around 30 degrees C as reflected by a decrease in the hydrodynamic thickness of the brush at higher temperatures. Total plasma protein adsorption is increased at 40 degrees C compared to 20 degrees C but there is significant differential adsorption behavior among the proteins detected by gel-electrophoresis analysis.