Platelet adhesion and contact activation time tests on HEMA coated cellulose acetate membranes

Surface modification of polymeric biomaterials: Utilization of cyclodextrins for blood compatibility improvement

A novel modified polymeric biomaterial surface using cyclodextrins (CDs) for improved blood compatibility was studied. Plasticized poly(vinyl chloride) (PVC-P) was selected for modification and polyethylene was used as a reference material. The modification was achieved by polymer blending. Fibrinogen and albumin adsorption were utilized as indices for the assessment of the blood compatibility. Surface characterization confirmed that CDs were able to accumulate at the PVC surface and alter the surface properties. The combination of other hydrophilic polymers such as poly(ethylene oxide) (PEO) and PEO/poly(propylene oxide) (PPO) copolymers, such as Pluronic F68 (F68), with CDs were also investigated. These modified materials have a remarkable protein-resistant surface. The combination of B-cyclodextrin (B-CD)/PEO and B-CD/F68 in certain feeding ratio are synergistic in producing enhanced blood compatibility.

Permeability of PEUU membranes: their modification towards blood compatibility

An attempt was made to develop haemodialysis membranes using polyether urethane urea synthesised in our laboratory. It was observed that the processing parameters such as precipitation medium, precipitation temperature etc. can influence the porosity of the membrane and subsequently the permeability property. It was also noted that the permeability of the dried membrane was negligible even though it was kept in distilled water overnight before use. The effect of pH on permeability through the membrane was studied by dialysis experiment using mixtures of various components such as urea, creatinine, uric acid, inulin, albumin, NaCl and KCl at various pH. Standard cellulose acetate (CA) membrane was used for comparison. Membranes were also prepared using biomer solution by precipitating in distilled water at room temperature and the monomer, 2-hydroxy ethyl methacrylate (HEMA) was grafted onto it by glow discharge technique. It was found that the permeability was increased by HEMA grafting with some loss of tensile strength and strain. A comparative study of fibrinogen adsorption during dialysis and adsorption by direct exposure of samples to a mixture containing urea, uric acid, creatinine, dextran, fibrinogen and electrolytes like sodium and potassium ions was also done with 125I labelled fibrinogen. Platelet adhesion studies indicated that the number of adhered platelets was less on the HEMA grafted samples which may enhance blood compatibility. Finally, the membranes were subjected to different sterilization processes possible under wet conditions such as glutaraldehyde treatment and autoclaving. The contact angle, permeability, mechanical property and platelet adhesion studies indicated that the sterilization method can affect the performance of the membrane.

Hemocompatibility of hydrogel with polyethyleneoxide chains

We have synthesized a hydrogel with long polyethyleneoxide (PEO) chains and evaluated its hemocompatibility. The hydrogel significantly suppressed the adsorption of plasma proteins and adhesion of platelets. In addition, the marked retardation of thrombus formation on its surface was recognized. These findings seems to be caused by the volume restriction effects derived from the highly flexible and hydrophilic PEO chains.

Hydrogels by irradiation of a synthetic heparinoid polyelectrolyte

Gamma irradiation of aqueous solutions of a synthetic heparinoid polyelectrolyte results in the formation of hydrogels, varying in water content and mechanical strength. The equilibrium water content and the mechanical strength of the hydrogels are dependent on the initial polyelectrolyte concentration, the molecular weight of the polyelectrolyte, the percentage of double bonds in the polyelectrolyte and the radiation dose. The polyelectrolyte hydrogels do not deplete Antithrombin III from blood and there is no activation of factor XII according to an in vitro kallikrein generation test. However, in a very sensitive test for factor XII activation (contact promoted shortening of the thrombotest) a slight activation of this factor was observed.

Evaluation of plasma polymerized hexamethylcyclotrisiloxane biomaterials towards adhesion of canine platelets and leucocytes

Silicone coated Celgard-2400 and Silastic membranes were prepared by plasma polymerization of hexamethylcyclotrisiloxane. The adhesion of canine platelets and leucocytes was tested by passing whole blood from the anaesthetized mongrel dog in an ex-vivo shunt system. The silicone control Celgard and silicone coated Silastic membranes had fewer platelets and fewer leucocytes compared to those on the control Silastic membranes. Furthermore, these blood cells underwent fewer morphological changes on the silicone coated Celgard and Silastic compared to those on the control Silastic. From these observations the silicone coated biomaterials were judged to be better than the Silastic as far as the adhesion of platelets and leucocytes are concerned.

In vivo interactions between novel filler free silicone rubber and blood

To evaluate the thrombogenicity of the novel filler free silicone rubber (FFSR) prepared in our laboratory, its interactions with blood were studied. The test samples (FFSR) along with control Silastic samples were placed in an extracorporeal shunt and primed with sterilized normal saline. The blood from an anaesthetized and systemically heparinized dog was passed over these samples for predetermined time intervals. After washing, fixing, etc., the platelets adhering to the samples were counted under light microscopy. To study the morphological changes of the platelets adhering to the samples, they were examined under scanning electron microscope. The number of platelets adhering to the FFSR samples was very small compared to the Silastic samples. For example, when the blood was passed over the samples for 10 min the number of platelets sticking per 0.14 mm2 surface area was 10 for FFSR samples compared to 380 for Silastic. Furthermore, there were no leukocytes on FFSR samples compared to 10 on Silastic. From these studies, the novel filler free silicone rubber prepared in our laboratory was judged to be more compatible with formed elements of blood compared to the Silastic material.