INTERACTIONS OF BLOOD AND BLOOD COMPONENTS AT HYDROGEL INTERFACES

Mechanical Enhancement of the Gelatin/Poly(zinc acrylate) Hydrogel Stent in Bile

Hydrogels with the features of softness, biocompatibility, and modifiability have emerged as excellent materials in the biomedical field. However, the poor mechanical properties of the hydrogels limit their further practical applications. Double-network and metal ion coordination, such as Cu2+ and Zn2+, have achieved a significant reinforcement of the mechanical strength of the hydrogels. Herein, we report a Zn2+-enhanced polyelectrolyte double-network hydrogel stent with a mechanical enhancement phenomenon in bile. The gelatin/poly(zinc acrylate) (PZA) stent was constructed by dip-coating and UV irradiation. Although the mechanical strength of the as-prepared stent was quite weak, it was discovered to be mechanically enhanced by the natural bile. After exploring the effect of different components on the stents according to the components of bile, we found that Ca2+ in bile made a contribution to the mechanical enhancement of the stent. It is envisioned that this bile-enhanced gelatin/PZA stent provides a train of thought for the potential application of hydrogels in the biliary environment.

Fibrinogen adsorption to biomaterials

Fibrinogen (Fg) adsorption is an important mechanism underlying cell adhesion to biomaterials and was the major focus of the author's research career. This article summarizes our work on Fg adsorption, with citations of related work as appropriate. The molecular properties of Fg that promote adsorption and cell adhesion will be described. In addition, the adsorption behavior of Fg from buffer, binary solutions with other proteins, and blood plasma will be discussed, including the Vroman effect. Studies of platelet adhesion to surfaces preadsorbed with blood plasmas selectively deficient in Fg, vitronectin (Vn), fibronectin (Fn), or von Willebrand's factor (vWf) will be reviewed. These studies clearly showed a major role for Fg in platelet adhesion under static conditions and both Fg and vWf for adhesion from flowing suspensions, but no significant role for Vn or Fn. However, it was also shown that platelet adhesion was poorly correlated with the total amount of adsorbed Fg, but very well correlated with the binding of antibodies specific to the cell binding domains of Fg. A brief overview of nonfouling surfaces for prevention of Fg adsorption will be given. A more extensive discussion of structural changes in Fg after its adsorption is included, including changes detected with both physicochemical and biological methods. A short discussion of the state of the art of structural determination of adsorbed proteins with computational methods is also given. A final section identifies Fg adsorption as the single most important event determining the biocompatibility of implants in soft tissue and in blood. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2777-2788, 2018.

Surface Engineered Polymeric Biomaterials with Improved Biocontact Properties

We present many examples of surface engineered polymeric biomaterials with nanosize modified layers, controlled protein adsorption, and cellular interactions potentially applicable for tissue and/or blood contacting devices, scaffolds for cell culture and tissue engineering, biosensors, biological microchips as well as approaches to their preparation.

Investigation of the activation of a human serum complement protein, C3, by orthopedic prosthetic particulates

Myriad molecular, cellular, and physiological processes underlie the inflammatory and osteolytic processes induced by particles of biomaterials resulting from the wear of implants such as total joint replacement prostheses. The objective this study was to investigate the role that the complement system may be playing in these phenomena. The aim was to evaluate the degree to which particles of selected orthopaedic materials--high density and ultrahigh molecular weight polyethylene, polymethylmethacrylate, and commercially pure titanium--cause the elevation of a key complement molecule, C3a, in an in vitro assay that directly measured the concentration of C3a. The results demonstrated that HDPE particles, at high concentration, are capable of causing the elevation of C3a in the in vitro assay. This finding is discussed in the context of other work and the mechanics of the complement system as it may affect the osteolytic process.

The preparation of the chronic hyper-endotoxemia experimental animal model by means of a drug delivery system

A drug delivery system (DDS) consisting of lipopolysaccharide (LPS) as a drug and 2-hydroxyethyl methacrylate (HEMA)-diethylene glycol dimethacrylate (2G) or -polyethylene glycol dimethacrylate (4G, 9G) copolymer was prepared, and used for the efficient preparation of an experimental animal model of chronic hyper-endotoxemia. The release profiles of LPS in the in-vitro test were greatly influenced by the composition of HEMA-2G, 4G, 9G in the copolymer. It was found that LPS release from the DDS continued gradually and constantly throughout 2 weeks. In the in-vivo experiment with rats, the DDS maintained a high blood concentration level of LPS for 3 days. These results strongly suggest the possibility of convenient and reproducible preparation of a chronic hyper-endotoxemia animal model.

Adsorption of plasma proteins to DMAA hydrogels obtained by ionizing radiation and its relationship with blood compatibility

The interaction of plasma proteins such as albumin, gamma-globulin, and fibrinogen with the surface of graft copolymers DMAA-G-PTFE, DMAA-G-PETFE, and DMAA-G-PE obtained by radiation graft polymerization was studied. The adsorption of serum proteins was affected by the hydrophilicity of the graft copolymers. Increased albumin adsorption and decreased fibrinogen and gamma-globulin adsorption with increasing grafting levels was shown. A certain range of degrees of grafting showed an improved blood compatibility of the polymeric surfaces due to the existence of a hydrophilic/hydrophobic balance on the polymers. The results suggest that the DMAA-G-PTFE, DMAA-G-PETFE, and DMAA-G-PE graft copolymers can be used as biomaterials for long-term use in cardiovascular systems.

Experimental study of the antithrombogenic behavior of Dacron vascular grafts coated with hydrophilic acrylic copolymers bearing salicylic acid residues

The objective of the present work was study of the behavior of active coatings of hydrophilic acrylic polymers bearing salicylic acid residues linked covalently to the macromolecular chains, after their application to woven and knitted Dacron vascular grafts. In vitro tests were carried out under dynamic flow conditions using equipment especially designed to reproduce physiologic conditions, to determine the retention of the coating using a saline solution. Ex vivo tests were carried out in an extracorporeal circuit using the dog as an animal model. The study of the deposition of platelets was followed by labeling of autologous platelets with 111In-oxine, as well as by analysis of the surfaces of the prostheses by scanning electron microscopy. An application of thin coatings of hydrophilic acrylic copolymers improves the antithrombogenicity of the vascular grafts with respect to the uncoated prosthesis. The presence of relatively small amounts of units bearing salicylic acid residues in the copolymer chains (5-20 wt %) gives good results when they are applied to woven and knitten Dacron meshes which have been quantified by analysis of the percentage of radiotracer on the surface of the vascular grafts tested in ex vivo experiments. The salicylic acid residues are released slowly to the medium by hydrolysis of the reversible covalent bonds of this compound to the acrylic macromolecular chains, which provides an additional antiaggregating effect for platelets. The polymeric coating forms a thin active film which improves the antithrombogenic properties of the surface of woven or knitted Dacron vascular grafts in ex vivo experiments.

Complement activation by angiographic catheters in vitro

PURPOSE

Four different polymers used in commercial angiographic catheters were compared in vitro with respect to their ability to activate the complement system.

MATERIALS AND METHODS

Commercially available angiographic catheters made from one of the following plastics were used: polyamide, polyethylene, polyurethane, and polytetrafluoroethylene. Silicone-coated latex urinary catheters served as the reference standard. Each catheter was cut into 20-mm segments, immersed in a polypropylene tube containing fresh serum from a volunteer donor, and incubated at 37 degrees C. Samples were drawn at 15 minutes, 1 hour, and 6 hours; C3 activation products (C3AP) and the terminal complement complex (TCC) content were estimated with enzyme immunoassays.

RESULTS

By 1 hour, a significant increase in C3AP and TCC concentrations was observed with all angiographic catheters relative to controls (P < .01-.001). The time-concentration plots for both C3AP and TCC were steepest for polyamide. C3AP concentrations relative to controls were significantly higher with exposure to polyamide compared with polyurethane at 1 hour (P < .01), and with both polyethylene and polyurethane at 6 hours (P < .01). Polytetrafluoroethylene induced larger amounts of C3AP formation by 6 hours than polyethylene and polyurethane (P < .05). However, polytetrafluoroethylene was associated with the lowest relative median concentrations of TCC; the difference with polyamide was significant at 6 hours (P < .001). As with C3AP, differences in TCC generation between polyethylene and polyurethane were marginal at all observation points (P > .05).

CONCLUSIONS

All the polymers tested activated the complement system. Activation was most prominent with exposure to polyamide and least marked with polyurethane.

Protein adsorption onto poly(ether urethane ureas) containing Methacrol 2138F: a surface-active amphiphilic additive

Surface characterization and protein adsorption studies were carried out on a series of additive dispersed and additive coated poly(ether urethane ureas), PEUUs, to characterize early events in the blood compatibility of these materials. A hypothesis that is based on surface hydrophilicity, surface flexibility, and adsorption media has been developed to understand the modulated adsorption of plasma proteins by PEUU additives. Electron spectroscopy for chemical analysis (ESCA) and contact angle analysis were performed on two PEUU formulation as well as on PEUU formulations modified with Methacrol 2138F (co[diisopropylaminoethyl methacrylate (DIPAM)/decyl methacrylate (DM)][3/1]) or acrylate or methacrylate polymer or copolymer analogs of Methacrol 2138F. Methacrol 2138F is a commercially used amphiphilic copolymethacrylate. ESCA showed that the PEUUs loaded with Methacrol 2138F or with its hydrophilic component, homopoly (DIPAM) (h-(DIPAM)), had a higher percentage of nitrogen at their surfaces than did the base PEUUs. Contact angle analysis also showed that the air side of PEUU formulations loaded with Methacrol 2138F were more hydrophobic than was the air side of base PEUUs when films were cast from dimethylacetamide. However, during contact angle testing, the air side of PEUU films loaded with Methacrol 2138F rapidly became more hydrophilic than did the air side of the base PEUU films. A radioimmunoassay and whole or diluted human plasma were also used to characterize the presence of the proteins fibrinogen, immunoglobulin G, factor VIII/von Willebrand factor, Hageman factor (factor XII), and albumin, on the surface of the same PEUUs as analyzed by ESCA and contact angle. The protein adsorption assay showed that PEUU films loaded or coated with Methacrol 2138F, with a copolyacrylate analog of Methacrol 2138F (co(diisopropylaminoethyl acrylate [DIPAA]/decyl acrylate [DA]) [3/1]), or with the hydrophilic polyacrylate or polymethacrylate component analogs of Methacrol 2138F (h-DIPAM or h-DIPAA) adsorbed significantly lower amounts of the proteins than did either the base PEUU formulations or the homopoly(decyl methacrylate) (h-DM) or homopoly(decyl acrylate) (h-DA) coated or loaded PEUUs.

Adsorption of coagulation proteins from whole blood on to polymer materials: relation to platelet activation

A combination of methods, immunoassays of plasma proteins and platelet release of beta-thromboglobulin and chromogenic substrates for enzymatically active coagulation factors, was used to measure the reactions of coagulation proteins upon contact between whole blood and artificial surfaces as a function of time and surface material. Four types of well-known polymer surfaces, polyvinylchloride, polytetrafluoroethylene, polyurethane and silicone rubber, were investigated to elucidate if a simple and fast in vitro experimental set-up can be of guidance in the selection of materials for use in vivo. Platelets were activated at the polymer surfaces whereas the coagulation enzymes showed little activity on the polymer surfaces tested. There was a correlation between the adsorption of adhesins (fibrinogen, fibronectin and factor VIII-related antigen) at the surfaces and the release of beta-thromboglobulin from platelets, suggesting that adsorption of adhesins is a major determinant of blood compatibility of polymer materials. Significant differences between the surfaces were seen--polyurethane being the surface with the least protein adsorbed and least platelet activation initiated. This study shows that it is possible to make a first in vitro choice of possible blood compatible artificial surfaces before expensive and cumbersome in vivo experiments.

Poly(dimethylsiloxane)-poly(ethylene oxide)-heparin block copolymers. II: Surface characterization and in vitro assessments

Amphiphilic block copolymers containing poly(dimethylsiloxane), poly(ethylene oxide), as well as heparin-coated glass beads and tubes were evaluated for the amounts and activities of surface-immobilized heparin. Because the amphiphilic copolymer system is thermodynamically predicted to demonstrate low-energy phase enrichment on the surfaces of air-cast films, studies were also undertaken to understand the in vitro results. Solvent-cast copolymer films have a heterogeneous microphase-separated structure according to transmission electron micrographs. Wilhelmy plate contact angle analysis indicates significant surface restructuring occurs upon hydration. Attenuated total reflectance infrared spectroscopy studies of the desiccated and hydrated films at two different sampling depths show compositional heterogeneity as a function of depth, as well as near surface restructuring allowing surface enrichment of the high-energy segments following contact with water. Significant concentrations of heparin are detected on the surface of these coatings by toluidine blue assays. In addition, a portion of the surface-bound heparin maintains its original bioactivity as determined by recalcification times, thrombin times, and Factor Xa assays. These substrates were also tested for platelet adhesion and activation reactions in vitro using polymer-coated beads in rabbit platelet-rich plasma. Heparinized polymers promoted low levels of platelet adhesion and serotonin release. Surface concentrations of heparin from bioactivity assays were then correlated with platelet adhesion and the extent of platelet release to assess the efficacy of this heparin-immobilized copolymer as a blood-compatible material or coating.

Bulk, surface, and blood-contacting properties of polyetherurethanes modified with polyethylene oxide

The bulk, surface, and blood-contacting properties of a series of polyether polyurethanes based on polyethylene oxide (PEO) (MW = 1450), polytetramethylene oxide (PTMO) (MW = 1000), and mixed PEO/PTMO soft segments were evaluated. The effect of varying the weight percentage of PEO, and thus the overall polarity of the mixed soft segment phase, was investigated. Two polymer blends prepared from a PTMO-based and a PEO-based polyurethane were also studied. Differential scanning calorimetry (DSC) and dynamic mechanical analysis indicated that the polyurethanes based on either the PEO or the PTMO soft segments are relatively phase mixed. The degree of phase mixing in the polymers increased with increasing weight fraction of PEO. As expected, water absorption and the hydrophilicity of the polymer increased with increasing PEO soft segment content. In vacuum, the PEO-rich polymers have a lower concentration of soft segment at the surface, possibly due to the migration of the polar PEO segments away from the polymer/vacuum interface. The blood-contacting results indicated that the higher PEO-containing polymers were more thrombogenic than the pure PTMO-based polyurethane. A threshold concentration of PEO in the polyurethane appeared to be required before the blood-contacting properties were significantly affected.

Covalent coupling of polysaccharides to silicon and silicon rubber surfaces

A method to produce a hydrogel by covalently coupling dextran polysaccharide to silicon and silicon rubber surfaces is described. A bifunctional epoxysilane was used as coupling mediator and the conditions for the reaction were optimized. Coupling of the silane to silicon rubber was possible only after oxidation of the surface by plasma etching. The reaction between the epoxy-group and dextran was concentration dependent and required high concentrations of dextran. The turnover rate of fibrinogen in solution at the hydrophilic surface was found to be high when measured by ellipsometry.

Platelet adhesion onto microcapsule membranes with different degrees of sulfonation

Microcapsules having different numbers of sulfonic acid groups on their surfaces were prepared by the interfacial polycondensation method. Platelets adhered to these capsules, and the rate and degree of platelet adhesion were found to be remarkable on those microcapsules that had high surface charge compared to those with low surface charge. This trend was strengthened by the coating of the capsules with plasma, while the electrophoretic mobilities of the plasma-coated capsules showed a considerable reduction and no appreciable difference between the respective mobilities could be observed. This trend suggest that the adsorption of plasma components on microcapsules, and not their surface negative charge, affected platelet adhesiveness directly. In connection with the glycosyl transferase hypothesis, the adsorption pattern and its effect on platelet adhesion of albumin, gamma-globulin, and fibrinogen were examined. The protein adsorption pattern varied depending on both the type of protein and the magnitude of negative charge on the microcapsule surface, but its effect on platelet adhesion was not fully consistent with the glycosyl transferase hypothesis. It was concluded from the findings that the surface negative charge of the capsules strongly affected the composition, molecular orientation, and/or configuration of the adsorbed plasma components, which probably induced the differences in platelet adhesiveness depending on the magnitude of surface negative charge of the microcapsules.

Pressurized polymerization for reaction casting of poly(2-hydroxyethyl methacrylate)

Homopolymers of the hydrogel poly(2-hydroxyethyl methacrylate) are produced with no observable bubbles trapped in the lattice by performing the free radical initiated polymerization reaction under pressure (700 kPa). Implantable hydrogel structures of intricate and exact geometry, such as nipples for ureteral anastomoses in the prosthetic urinary bladder, can be made using this technique.