Contributions of negatively charged chemical groups to the surface-dependent activation of human plasma by soluble dextran derivatives

Multifunctional Nanoclay-Based Hemostatic Materials for Wound Healing: A Review

Bleeding to death accounts for around 30-40% of all trauma-related fatalities. Current hemostatic materials are mainly mono-functional or have insufficient hemostatic capacity. Nanoclay has been recently shown to accelerate hemostasis, improve wound healing, and provide the resulting multifunctional hemostatic materials antibacterial, anti-inflammatory, and healing-promoting due to its distinctive morphological structure and physicochemical properties. Herein, the chemical design and action mechanism of nanoclay-based hemostatic, antibacterial, and pro-wound healing materials in the context of wound healing are discussed. The physiological processes of hemostasis and wound healing to elucidate the significance of nanoclay for functional wound hemostatic dressing design are outlined. A summary of the features of various nanoclay and product types used in wound hemostatic dressings is provided. Nanoclay can be antimicrobial due to the slow release of metal ions and has an abundant surface charge allowing for high affinity for proteins and cells, which can activate the coagulation reaction or facilitate tissue repair. Nanoclay with a microporous structure can be used as drug carriers to create composites critical for inhibiting bacterial growth on wounds or promoting the regeneration of vascular, muscle, and skin tissues. Directions for further research and innovation of nanoclay-based multifunctional materials for hemostasis and tissue regeneration are explored.

Hemocompatibility of cellulose phosphate aerogel membranes with potential use in bone tissue engineering

Cellulose is an appealing material for tissue engineering. In an attempt to overcome some obstacles with cellulose II cell scaffolding materials related to insufficient biomineralization, lack of micron-size porosity, and deficiency in surface charge, respective solutions have been proposed. These included covalent phosphorylation of different cellulose materials targeting relatively low degrees of substitution (DS 0.18-0.23) and processing these cellulose derivatives into scaffolding materials by a dissolution/coagulation approach employing the hitherto rarely used TBAF/DMSO/H₂O system for cellulose dissolution. Here, we report bioactivity and preliminary hemocompatibility testing of dual-porous cellulose phosphate aerogels (contrasted with the phosphate-free reference) obtained via coagulation (water/ethanol), solvent exchange and scCO₂ drying. Deposition of hydroxyapatite from simulated body fluid (7 days of immersion) revealed good bioactivity (1.5-2.2 mg Ca²⁺ per mg scaffold). Incubation of the scCO₂-dried and rehydrated scaffolding materials in heparin anticoagulated human whole blood was conducted to study selected parameters of hemostasis (prothrombin F1+2 fragment, PF4, count of thrombocyte-leukocyte conjugates) and inflammatory response (C5a fragment, leukocyte activation marker CD11b). Adhesion of leukocytes on the surface of the incubated substrates was assessed by scanning electron and fluorescence microscopy (DAPI staining). The results suggest that phosphorylation at low DS does not increase platelet activation. However, a significant increase in platelet activation and thrombin formation was observed after a certain fraction of the negative surface charges had been compensated by Ca²⁺ ions. The combination of both phosphorylation and calcification turned out to be a potent means for controlling the inflammatory response, which was close to baseline level for some of the studied samples.

Metal oxide surface charge mediated hemostasis

Blood coagulates faster upon contact with polar glasslike surfaces than on nonpolar plastic surfaces; this phenomenon is commonly termed the glass effect. However, the variable hemostatic response that we report here for contact-activated coagulation by different metal oxides, all of which are polar substrates, requires a refinement of this simple polarity model of how inorganic metal oxides activate the intrinsic pathway of blood coagulation. To our knowledge, the role of metal oxide surface charge as determined at the physiological pH and Ca2+ concentration of blood has not been previously investigated. We find that basic oxides with an isoelectric point above the pH of blood are anticoagulant while acidic oxides with an isoelectric point below the pH of blood are procoagulant. Using a thromboelastograph, we find that the onset time for coagulation and rate of coagulation post-initiation depend on both the sign and the magnitude of the initial surface charge density of the metal oxide. This work presents a useful strategy based on a quantifiable material parameter to select metal oxides to elicit a predictable and tunable biological response when they are in contact with blood.

Regulation mechanism of the serine protease activity of plasma hyaluronan binding protein

The inhibitor for the serine protease activity of plasma hyaluronan binding protein (PHBP) was purified from human plasma by polyethylene glycol (PEG) fractionation, diethylaminoethyl (DEAE)-Sephacel ion-exchange chromatography, Phenyl Toyopearl 650M hydrophobic chromatography, Bio Gel A-0.5 m gel-filtration and hydroxyapatite chromatography. The serine protease activity of PHBP was measured with Boc-Phe-Ser-Arg-methylcoumarine amide (MCA) as the synthetic substrate of PHBP. The results of the amino acid sequence analyses of the purified PHBP inhibitor indicated that it was C1 inhibitor of the serpin family. C1 inhibitor formed a complex with PHBP, suggesting that it is the actual inhibitor of PHBP in human plasma. On the other hand, dextran sulfate and phosphatidylethanolamine enhanced the auto-fragmentation and the serine protease activity of pro-PHBP, but kaolin did not. These results suggested that the serine protease activity of PHBP was regulated in a similar manner to that of factor XII of the coagulation system.

Vascular endothelial cell responses to different electrically charged poly(vinylidene fluoride) supports under static and oscillating flow conditions

We investigated the effect of electrically charged surface copolymers on endothelialization of four types of poly(vinylidene fluoride) (PVDF) copolymer surface films with different electrical characteristics. PVDF films without a surface charge, with a remanent surface (5 and 7 microC) and with piezoelectric characteristics were studied through the secretion by an endothelial cell (EC) line culture, under static and oscillating flow conditions of prostacyclin (PGI2) and thromboxane (TXA2), two metabolites which have directly opposing actions on platelet function. The surface electrical properties of PVDF are suitable for promoting cell adhesion. Secretion of thrombomodulatory mediators varied, depending on the surface electrical charge and on the molecular structure of the PVDF substrate. Under static conditions the ECs respond to the substrates by a similar increase of PGI2. Under oscillating flow conditions, the ratio of PGI2 to TXA2 is higher with the piezoelectric PVDF film. The piezoelectricity generated from shear stress along the entire length of the fibres may be appropriate in vivo to keep the [PGI2]/[TXA2] ratio at a level which could counteract the build-up of surface deposits which could be at the origin of thrombosis.

Explicit constants for the dextran-sulfate-mediated activation and autoactivation of purified human factor XII (Hageman factor)

The autoactivation kinetics of purified factor XII (FXII) in the presence of dextran sulfate of 500000 Da was reexamined assuming the existence of two preceding activation steps. Kinetics were numerically simulated by using rate and equilibrium constants related to surface-bound species. Relevant feature parameters related to the polymer (number of binding sites and concentration, dissociation constant of FXII from the surface) and the zymogen (concentration. Michaelis-Menten constant of the autoactivation reaction, catalytic rate constant) were accordingly introduced in the mechanisms. Depending on the rate-limiting step i.e. whether the polymer or FXII predominates, numerical simulation analysis led to obtain for the observed autoactivation rate constant (kobs) two explicit expressions which included the contributing variables. One of the two proposed models was in good accordance with the experimental data obtained in this study and with others published previously. We were able to estimate the mean number of the FXII-activating sites supported by the polymer chains (220) and the equilibrium dissociation constant of FXII from the surface (1 microM). Further treatment led us to determine surface-concentration-independent constants (K(m) = 2510 nM and kcat = 0.01 s-1), as well as the rate constant (k1 = 1.6 x 10(-4) s-1) of the postulated first-order activation rate aimed at explaining the formation of the first trace amounts of FXIIa via an intramolecular mechanism. Overall, the treatment applied to the dextran sulfate case offers a quantitative tool by which data determined in the presence of other activating materials can be rationalized.

Selective adhesion of platelets on a polyion complex composed of phospholipid polymers containing sulfonate groups and quarternary ammonium groups

We investigated the effects of electrical charges on cell-polymer interactions of poly[2-methacryloyloxyethyl phosphorylcholine(MPC)-co-n-butyl methacrylate (BMA)] (PMB) having excellent blood compatibility, by copolymerizing anionic or cationic methacrylates with MPC and BMA. A polyion complex (PIC) composed of anionic and cationic MPC copolymers was also prepared. When the cell adhesion on these polymer surfaces from rabbit whole blood was evaluated, we observed a considerable reduction in cell adhesion on the MPC copolymers compared with that on poly(BMA), even when the MPC copolymer was electrically charged. On the other hand, many platelets selectively adhered to the PIC surface from whole blood, but the adherent platelets maintained a discoid shape. The amount of adenosine triphosphate (ATP) in platelets adherent on the PMB or the PIC from a platelet-rich plasma (PRP) was more than 75% of that in the original PRP, which indicated that the activity of these platelets remained high. However, in the platelets adherent to poly(BMA), only a small amount of ATP remained. Protein adsorption on the polymer surface from human plasma was investigated using a gold-colloid-labeled immunoassay against albumin gamma-globulin, and fibrinogen. Many of these proteins adsorbed on poly(BMA), whereas a small amount of protein was observed on the MPC copolymers that had an electrical charge. Albumin adsorption and suppression of gamma-globulin and fibrinogen adsorption were found on the PIC. Therefore, the introduction of electrical charges in the PMB did not have an adverse effect on cell adhesion and protein adsorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution and tissue uptake of poly(ethylene glycol) with different molecular weights after intravenous administration to mice

After intravenous (iv) injection of 125I-labeled poly(ethylene glycol) (PEG) with different molecular weights to mice, the radioactivity of the organs was measured to pharmacokinetically analyze the body distribution of PEG according to a two-compartment model. High molecular weight PEGs were retained in the blood circulation for a longer period than low molecular weight PEGs. The terminal half-life of PEG in the circulation extended from 18 min to 1 day as the PEG molecular weight increased from 6000 to 190,000. PEG tended to accumulate in the tissues/organs such as muscle, skin, bone, and the liver to a higher extent than the other organs, irrespective of the molecular weight. The time dependence of tissue accumulation was based on the vascular permeability. The results of pharmacokinetic analysis suggested that small PEG tended to freely translocate from the circulation to extravascular tissues and to return to the blood circulation again by diffusion, whereas large PEG translocated more slowly to extravascular tissues. Urinary clearance decreased with increasing PEG molecular weight, similar to the tissue clearance, whereas liver clearance increased with the increasing PEG molecular weight, after passing a minimum around the molecular weight of 50,000. PEG uptake by Kupffer cells was enhanced as the molecular weight became > 50,000.

Autoactivation of human blood coagulation factor XII on dextran derivatives of different molecular weight

We prepared a derivative of dextran T40 (average M(r) 43,000) from which fractions of different M(r) but with equal charge density were obtained and tested for their ability to promote autoactivation of human blood coagulation factor XII. The mechanism of autoactivation appeared dependent upon the M(r) of the polymer used. Thus, with polymers of 38,000 M(r) or higher only alpha-factor XIIa was formed and the reaction could be completely described in terms of a simple second-order mechanism of autoactivation. With smaller polymer molecules beta-factor XIIa became a major reaction product and as a result of this the autoactivation kinetics did not adhere to the second-order mechanisms thus far described.

Molecular weight-dependent contact activation of plasma induced by soluble polystyrene and dextran derivatives

The surface dependent contact activation of human plasma was studied as a function of the molecular weight of several synthetic macromolecular and watersoluble derivatives: polystyrene sulphonates, dextran methyl-benzylamide sulphonate/carboxylates as well as dextran sulphates as reference materials. Extent of the contact activation was determined by the amidolytic activities generated from cold activation of plasma in the presence of dilutions of the polymers for varying incubation times. The activating properties of the materials have been rationalized by means of a parameter calculated from the shapes of the amidolytic rates vs. incubation time variations. It was found that all the studied polymers behave similarly: contact stimulating properties begin to increase sharply passed a molecular weight of 25,000 and thereafter gradually reach a limiting plateau for Mw = 100,000. Activating capacities estimated for these limiting values have been expressed in term of specific capacities unrelated to Mw effects. These parameters were also compared to that of standard heparin estimated in the same conditions.