Analysis of cellular morphology, adhesion, and proliferation on uncoated and differently coated PVC tubes used in extracorporeal circulation (ECC)

Manufacture of non-thrombogenic polymer surfaces by gamma irradiation to induce simultaneous grafting and heparinization of thin PVC films

Investigations regarding alternative methods for producing polymeric materials with hydrophilic properties have increased considerably. In this context, polymeric biomaterials with hemocompatible surface properties have been successfully obtained by grafting hydrophilic monomers onto commercial polymer films by simultaneous irradiation processes. In this study, simultaneous irradiation and grafting were used to produce a copolymer PVC-co-DMAEMA-co-heparin with hemocompatible surface properties. Characterization by FTIR of the graft copolymer indicates that the increase in monomer grafting levels inhibits the bonding sites to heparin. FTIR-PAS analyses of the graft copolymers showed that the highest graft levels were obtained for the irradiated samples containing 45% of monomer. Heparin, however, could only be detected in the irradiated samples containing 30% of DMAEMA. The analysis of the micrographs, on the other hand, showed that increasing the monomer concentration enhances surface roughness of the graft copolymers. Roughness however decreased with heparin addition. It was possible to verify that an excess of surface roughness of the graft copolymers inhibits anticoagulant properties of heparin, triggering thrombus formation. Platelet adhesion, on its turn, was not significantly affected by the presence of heparin when PVC-co-DMAEMA and PVC-co-DMAEMA-co-heparin, obtained from the systems containing 45% of monomer, are compared. The addition of heparin in the systems containing 30% of DMAEMA resulted in fewer thrombogenic surfaces.

A novel small animal model for biocompatibility assessment of polymeric materials for use in prosthetic heart valves

A composite polymeric material, poly(styrene-block-isobutylene-block-styrene) (SIBS) with an embedded reinforcement polyethylene terephthalate (PET) fabric, is undergoing investigation for potential use in a novel heart valve. The purpose of this study was to develop and implement a small animal model to assess the biocompatibility of composite samples in a cardiovascular tissue and blood-contacting environment. Composite samples were manufactured using dip coating and solvent casting with two coating thicknesses (25 and 50 microm). A novel rat abdominal aorta model was developed to test the dip-coated samples in a similar pulsatile flow condition to its intended use, and both dip-coated and solvent-cast samples were tested using a rat subcutaneous model. Tissue response, defined by degree of cellular infiltration and encapsulation, was minimized when a smooth coating of SIBS shielded the PET fabric from exposure to blood and tissue, and the degree of tissue response was directly correlated with the degree of surface roughness. Surface modification using phospholipid further reduces the tissue response. We have demonstrated the applicability of using a novel rat abdominal aorta model for biocompatibility assessment of polymeric materials that will be used in cardiovascular implants. For the purpose of this study, our results indicate that solvent casting with a 25-microm SIBS coating thickness will provide optimal biocompatibility for the SIBS valve.

Cell loss in integrated microfluidic device

Cell loss during sample transporting from macro-components to micro-components in integrated microfluidic devices can considerably deteriorate cell detection sensitivity. This intrinsic cell loss was studied and effectively minimized through (a) increasing the tubing diameter connecting the sample storage and the micro-device, (b) applying a hydrodynamic focusing approach for sample delivering to reduce cells contacting and adhesion on the walls of micro-channel and chip inlet; (c) optimizing the filter design with a zigzag arrangement of pillars (13 microm in chamber depth and 0.8 microm in gap) to prolong the effective filter length, and iv) the use of diamond shaped pillar instead of normally used rectangular shape to reduce the gap length between any two given pillar (i.e. pressure drop) at the filter region. Cell trapping and immunofluorescent detection of 12 Giardia lamblia and 12 Cryptosporidium parvum cells in 150 microl solution and 50 MCF-7 breast cancer cells in 150 microl solution was completed within 15 min with trapping efficiencies improved from 79+/-11%, 50.8+/-5.5% and 41.3+/-3.6% without hydrodynamic focusing, respectively, to 90.8+/-5.8%, 89.8+/-16.6% and 77.0+/-9.2% with hydrodynamic focusing.

Phospholipids as implant coatings

Bio-interfaces such as bio-membranes are of outmost importance for a variety of live processes. Among them are cell-interactions which take place in, on or through cell membranes. Therefore we propose to cover metallic surfaces with phospholipids to facilitate cell-material interaction. Four lipids, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), 1-palmitoyl-2- oleoyl-sn-glycero-3-[phospho-L-serine] (POPS) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-rac-(1-glycerol) (POPG), were applied to four metallic growth substrates with different surface structure, roughness and porosity. The interaction of the osteosarcoma cell line MG-63 was investigated in terms of cell adhesion and viability (MTT (methylthiazolyldiphenyl-tetrazolium bromide) assay). While POPS in general had a negative influence, the most suitable combination in terms of viability per adherent MG-63 is the coating of porous Ti6Al4V material with the phospholipids POPE or POPC. The analysis of viability of mouse macrophages RAW 264.7 and their tumor necrosis factor alpha (TNF-alpha) release showed that the adhesion and viability is worst on POPS while the TNF-alpha release was highest. To elucidate the potential of phospholipids to prevent or support bacterial growth, the bacterial number of Gram positive and Gram negative bacteria was investigated. For lipid concentrations higher than 1 mM in solution a growth stimulating effect independent of the lipid type was detected. On a lipid coated surface the number of bacteria was reduced by 81%, 74% and 51% for POPC, POPG and POPE.

Activation of Neutrophil Granulocytes in an In Vitro Model of a Cardiopulmonary Bypass

Activated neutrophils play a central role in the pathogenesis of postoperative organ dysfunction after surgery with cardiopulmonary bypass. The researchers used an in vitro roller pump model to investigate the relative importance of the biomaterial, platelets, plasma proteins including activated complement, and flow mode on neutrophil activation as shown by the adhesion, degranulation, and increased the surface expression of CD11b. Neutrophil adhesion to the biomaterial increased with platelet addition, but not with plasma. Biomaterial contact activated neutrophils in a serum-free buffer, but was significantly increased by activated complement. Platelets increased neutrophil degranulation in a serum-free buffer but tended to reduce it in plasma. CD11b expression increased in both media. Complement activation was higher with neutrophils alone than with neutrophils and platelets combined. The roller pump reduced neutrophil adhesion and increased degranulation compared to passive rotation. Neutrophil interaction with platelets and complement were more important for activation than biomaterial contact and use of the roller pump. Improvement of biocompatibility is dependent on modifying complement activation and platelet interaction with neutrophils.