Surface modification of chitosan membranes by complexation-interpenetration of anionic polysaccharides for improved blood compatibility in hemodialysis

Development of multifarious carrier materials and impact conditions of immobilised microbial technology for environmental remediation: A review

Microbial technology is the most sustainable and eco-friendly method of environmental remediation. Immobilised microorganisms were introduced to further advance microbial technology. In immobilisation technology, carrier materials distribute a large number of microorganisms evenly on their surface or inside and protect them from external interference to better treat the targets, thus effectively improving their bioavailability. Although many carrier materials have been developed, there have been relatively few comprehensive reviews. Therefore, this paper summarises the types of carrier materials explored in the last ten years from the perspective of structure, microbial activity, and cost. Among these, carbon materials and biofilms, as environmentally friendly functional materials, have been widely applied for immobilisation because of their abundant sources and favorable growth conditions for microorganisms. The novel covalent organic framework (COF) could also be a new immobilisation material, due to its easy preparation and high performance. Different immobilisation methods were used to determine the relationship between carriers and microorganisms. Co-immobilisation is particularly important because it can compensate for the deficiencies of a single immobilisation method. This paper emphasises that impact conditions also affect the immobilisation effect and function. In addition to temperature and pH, the media conditions during the preparation and reaction of materials also play a role. Additionally, this study mainly reviews the applications and mechanisms of immobilised microorganisms in environmental remediation. Future development of immobilisation technology should focus on the discovery of novel and environmentally friendly carrier materials, as well as the establishment of optimal immobilisation conditions for microorganisms. This review intends to provide references for the development of immobilisation technology in environmental applications and to further the improve understanding of immobilisation technology.

Polysaccharide-based layer-by-layer nanoarchitectonics with sulfated chitosan for tuning anti-thrombogenic properties

The development of blood-interacting surfaces is critical to fabricate biomaterials for medical use, such as prostheses, implants, biosensors, and membranes. For instance, thrombosis is one of the leading clinical problems when polymer-based materials interact with blood. To overcome this limitation is necessary to develop strategies that limit platelets adhesion and activation. In this work, hyaluronan (HA)/chitosan (Chi) based-films, recently reported in the literature as platforms for tumor cell capture, were developed and, subsequently, functionalized with sulfated chitosan (ChiS) using a layer-by-layer technique. ChiS, when compared to native Chi, presents the unique abilities to confer anti-thrombogenic properties, to reduce protein adsorption, and also to limit calcification. Film physicochemical characterization was carried out using FTIR and XPS for chemical composition assessment, AFM for the surface morphology, and contact angle for hydrophilicity evaluation. The deposition of ChiS monolayer promoted a decrease in both roughness and hydrophilicity of the HA/Chi films. In addition, the appearance of sulfur in the chemical composition of ChiS-functionalized films confirmed the film modification. Biological assay indicated that the incorporation of sulfated groups limited platelet adhesion, mainly because a significant reduction of platelets adhesion to ChiS-functionalized films was observed compared to HA/Chi films. On balance, this work provides a new insight for the development of novel antithrombogenic biomaterials, opening up new possibilities for devising blood-interaction surfaces.

Properties of a Stable and Sustained-Release Formulation of Recombinant Human Parathyroid Hormone (rhPTH) with Chitosan and Silk Fibroin Microparticles

Background

Parathyroid hormone (PTH) is required for the maintenance of normal bone physiology. This study describes the properties of a sustained-release formulation of recombinant human PTH (rhPTH) using chitosan and silk fibroin microparticles as carriers for drug delivery, developed using a spray-drying method.

Material/Methods

Chitosan, silk fibroin, and chitosan/silk fibroin microparticles loaded with rhPTH were studied with scanning electron microscopy (SEM) to estimate the particle size and surface morphology. The in vitro release of rhPTH was used to assess the developed formulation. The effect of the spray-drying process was assessed by powder X-ray diffraction (PXRD) of the microparticles. Quantification of the released rhPTH was performed by enzyme-linked immune sorbent assay (ELISA). Fourier-transform infrared spectroscopy (FTIR) was used to determine the differences in the absorption frequency of samples.

Results

Surface morphology of the final formulation showed the absence of pure crystals of chitosan and silk fibroin in the final formulation and FTIR demonstrated electrostatic interactions between chitosan and silk fibroin, which was supported by PXRD. The chitosan/silk fibroin microparticles loaded with rhPTH showed an entrapment efficiency (EE) that ranged from 60.36–72.99% with a 50% rhPTH release profile at pH 7.5 in 24 hours. There was no particle aggregation in blood and little hemolysis, indicating stability of the rhPTH-loaded microparticles.

Conclusions

A silk fibroin/chitosan microparticle formulation loaded with rhPTH was shown to be stable and to provide sustained-release of rhPTH, supporting a potential role of this formulation in the treatment of bone diseases including osteoporosis and bone fracture.

Hemocompatibility and anti-fouling behavior of multilayer biopolymers immobilized on gold-thiolized drug-eluting cardiovascular stents

To solve the thrombosis and restenosis problem in cardiovascular stent implantation for cardiovascular artery disease, chondroitin 6-sulfate (ChS) with heparin (HEP) have been used as drug carrier layers and alternatively covalently bonded on gold (Au)-dimercaptosuccinic acid (DMSA)-thiolized cardiovascular metallic (SUS316 L stainless steel, SS) stents. Sirolimus, a model drug, was encapsulated in the ChS-HEP alternative layers. The behavior of the drug in releasing and suppressing the growth of smooth-muscle cells (SMCs) was evaluated with 5-layer CHS-HEP coating on the SS stents. Moreover, hemocompatibility of blood clotting time and platelet adhesion was performed. The results showed that the 5-layer ChS-HEP-modified SS stents displayed the greatest hemocompatibility, showing prolonged blood clotting time of the activated partial thrombin time (> 500 s) and less platelet adhesion to reduce thrombosis. Furthermore, sirolimus can be released continuously for more than 40 days with the 5-layer ChS-HEP coating and is beneficial for inhibiting the growth of SMCs; however, it does not affect the proliferation of endothelial cells, which can avoid restenosis formation. Therefore, the multilayers of ChS-HEP grafted onto the Au-DMSA-cardiovascular SS stents provide high potential for use as drug eluting stents.

Biomedical Applications of Chitosan and Its Derivative Nanoparticles

Chitosan is a biodegradable natural polymer with many advantages such as nontoxicity, biocompatibility, and biodegradability. It can be applied in many fields, especially in medicine. As a delivery carrier, it has great potential and cannot be compared with other polymers. Chitosan is extremely difficult to solubilize in water, but it can be solubilized in acidic solution. Its insolubility in water is a major limitation for its use in medical applications. Chitosan derivatives can be obtained by chemical modification using such techniques as acylation, alkylation, sulfation, hydroxylation, quaternization, esterification, graft copolymerization, and etherification. Modified chitosan has chemical properties superior to unmodified chitosan. For example, nanoparticles produced from chitosan derivatives can be used to deliver drugs due to their stability and biocompatibility. This review mainly focuses on the properties of chitosan, chitosan derivatives, and the origin of chitosan-based nanoparticles. In addition, applications of chitosan-based nanoparticles in drug delivery, vaccine delivery, antimicrobial applications, and callus and tissue regeneration are also presented. In summary, nanoparticles based on chitosan have great potential for research and development of new nano vaccines and nano drugs in the future.

Drying-Induced Self-Similar Assembly of Megamolecular Polysaccharides through Nano and Submicron Layering

We propose a self-similar assembly to generate planar orientation of megamolecular polysaccharides on the nanometer scale and submicron scale. Evaporating the aqueous liquid crystalline (LC) solution on a planar air-LC interface induces polymer layering by self-assembly and rational action of macroscopic capillary forces between the layers. To clarify the mechanisms of nanometer- and submicron-scale layering, the polymer films are investigated by electron microscopy.

Sulfonated chitosan and dopamine based coatings for metallic implants in contact with blood

Thrombosis and calcification constitute the main clinical problems when blood-interacting devices are implanted in the body. Coatings with thin polymer layers represent an acknowledged strategy to modulate interactions between the material surface and the blood environment. To ensure the implant success, at short-term the coating should limit platelets adhesion and delay the clot formation, and at long-term it should delay the calcification process. Sulfonated chitosan, if compared to native chitosan, shows the unique ability to reduce proteins adsorption, decrease thrombogenic properties and limit calcification. In this work, stainless steel surfaces, commonly used for cardiovascular applications, were coated with sulfonated chitosan, by using dopamine and PEG as anchors, and the effect of these grafted surfaces on platelet adhesion, clot formation as well as on calcification were investigated. Surface characterization techniques evidenced that the coating formation was successful, and the sulfonated chitosan grafted sample exhibited a higher roughness and hydrophilicity, if compared to native chitosan one. Moreover, sulfonated surface limited platelet activation and the process of clot formation, thus confirming its high biological performances in blood. Calcium deposits were also lower on the sulfonated chitosan sample compared to the chitosan one, thus showing that calcification was minimal in presence of sulfonate groups. In conclusion, this sulfonated-modified surface has potential to be as blood-interacting material.

Gel Beads Composed of Chitosan and Polyacids and Their Blood Compatibility

Chitosan gel beads were prepared as a model for new chitosan materials and their blood compatibility was evaluated in vitroin human pool plasma and in human whole blood. The one-stage method for the preparation of monolithic beads consisted of performing a template polymerization of 2-acryloylamido-2-methylpropanesulfonic acid (AMPS) or copolymerization of AMPS and acrylic acid. Monolithic beads of semi-interpenetrating networks chitosan/copolymer were prepared in the presence of a cross-linking agent. The equilibrium degree of swelling of the beads was dependent on the composition. Reservoir-type beads consisting of a chitosan core and a coating of polyelectrolyte complex with anticoagulant activity and chitosan were also prepared. The reservoir-type beads and the monolithic beads showed improved compatibility with blood in comparison with the uncoated chitosan beads.

Similarities and differences in coatings for magnesium-based stents and orthopaedic implants

Magnesium (Mg)-based biodegradable materials are promising candidates for the new generation of implantable medical devices, particularly cardiovascular stents and orthopaedic implants. Mg-based cardiovascular stents represent the most innovative stent technology to date. However, these products still do not fully meet clinical requirements with regards to fast degradation rates, late restenosis, and thrombosis. Thus various surface coatings have been introduced to protect Mg-based stents from rapid corrosion and to improve biocompatibility. Similarly, different coatings have been used for orthopaedic implants, e.g., plates and pins for bone fracture fixation or as an interference screw for tendon-bone or ligament-bone insertion, to improve biocompatibility and corrosion resistance. Metal coatings, nanoporous inorganic coatings and permanent polymers have been proved to enhance corrosion resistance; however, inflammation and foreign body reactions have also been reported. By contrast, biodegradable polymers are more biocompatible in general and are favoured over permanent materials. Drugs are also loaded with biodegradable polymers to improve their performance. The key similarities and differences in coatings for Mg-based stents and orthopaedic implants are summarized.

Hematotoxicological analysis of surface-modified and -unmodified chitosan nanoparticles

The increasing interest in using chitosan nanoparticles for controlled drug delivery is hampered by its blood incompatibility, especially for intravenous applications. This study investigated the effects of processing solvents (acetic acid/lactic acid), dispersing media (acidic medium/saline), and surface modifiers (polyethylene glycol, polyvinyl alcohol, and ethylenediaminetetraacetatic acid) on the hemocompatibility of chitosan. Blood compatibility of chitosan nanoparticles prepared by ionotropic gelation with altered surface chemistry was evaluated by assessing their hemolytic activity, platelet aggregation, coagulation, and cytokine induction. It was observed that nanoparticles prepared in lactic acid and dispersed in saline did not show hemolysis, platelet aggregation, or coagulation, whereas nanoparticles prepared in acetic acid showed strong hemolysis. Surface modifiers were not observed to significantly affect blood compatibility, with the exception of EDTA, which delayed blood clotting times. Thus, chitosan nanoparticles prepared in lactic acid and dispersed in saline may be an ideal nanocarrier for parenteral applications.

Modulation of cellular responses on engineered polyurethane implants

An in vivo rat cage implant system was used to study the effect of polyurethane surface chemistries on protein adsorption, macrophage adhesion, foreign-body giant cell formation (FBGCs), cellular apoptosis, and cytokine response. Polyurethanes with zwitterionic, anionic, and cationic chemistries were developed. The changes in the surface topography of the materials were determined using atomic force microscopy and the wettability by dynamic contact angle measurements. The in vitro protein adsorption studies revealed higher protein adsorption on cationic surfaces when compared with the base, while adsorption was significantly reduced on zwitterionic (**p < 0.01) and anionic (*p < 0.05) polyurethanes. Analysis of the exudates surrounding the materials revealed no differences between surfaces in the types or levels of cells present. Conversely, the proportion of adherent cells undergoing apoptosis, as determined by annexin V-FITC staining, increased significantly on anionic followed by zwitterionic surfaces (60 + 5.0 and 38 + 3.7%) when compared with the base. Additionally, zwitterionic and anionic substrates provided decreased rates of macrophage adhesion and fusion into FBGCs, whereas cationic surfaces promoted macrophage adhesion and FBGC formation. Visualization of the F-actin cytoskeleton by Alexa Fluor 488 phalloidin showed a significant delay in the cytoskeletal fusion response on zwitterionic and the anionic surfaces. The real-time polymerase chain reaction (PCR) analysis of proinflammatory cytokines (tumor necrosis factor (TNF)-α and interleukin (IL)-10) and pro-wound healing cytokines (IL-4 and TGF-β) revealed differential cytokine responses. Cationic substrates that triggered stimulation of TNF-α and IL-4 were associated with more spread cells and higher FBGCs, whereas zwitterionic and anionic substrates that suppressed these cytokines levels were associated with less spread cells and few FBGCs. These studies have revealed that zwitterionic and anionic polyurethane surface chemistries can not only reduce nonspecific adhesion, fusion, and inflammatory events but also effectively promote cellular apoptosis in vivo.

Sub-micron tailoring of bi-soft segment asymmetric polyurethane membrane surfaces with enhanced hemocompatibility properties

Enhancement of membrane hemocompatibility is achieved through the control of the surface morphology. Bi-soft segment integrally skinned poly(ester urethane urea) (PEUU) membranes containing polycaprolactone (PCL) as a second soft segment are synthesized with PCL-diol ranging from 0% to 15% (w/w). Scanning electron microscopy and atomic force microscopy characterized membrane asymmetry and sub-micron roughnesses, R(a), of top dense surfaces as major assets to the development of platelet/membrane surface interactions. Here we show that the top dense surfaces of asymmetric PEUU membranes can be tailored with different morphologies when the ratio of the two soft segments PPO/PCL varies. A strong correlation between the top surface roughnesses, R(a) and platelet deposition is identified. The membrane with 15% (w/w) of PCL-diol, PEUU 85, shows the smoothest top dense layer with a R(a) as low as 1 nm which is 5 times below the characteristic value of the PEUU membrane with a single soft segment. The PEUU 85 asymmetric membrane displayed minimal platelet deposition and inhibition of extreme stages of platelet activation.

Cell outer membrane mimetic modification of a cross-linked chitosan surface to improve its hemocompatibility

A novel strategy has been developed to improve the hemocompatibility of chitosan surface by cell outer membrane mimetic structure able to reduce protein adsorption and cell adhesion. Phosphorylcholine dichloride was synthesized and grafted onto a glutaraldehyde-cross-linked chitosan (CS-GA) film surface to prepare phosphorylcholine-coated CS-GA film (CS-GA-PC) through a heterogeneous reaction process. The spectroscopic and contact angle characterization show that a cell outer membrane mimetic structure was formed on the cross-linked chitosan surface, and the significantly improved hemocompatibility of the modified surface was shown by a suppression of 94% on platelet adhesion, a suppression of 60-70% for bovine plasma fibrinogen and bovine serum albumin adsorptions. These results demonstrated that this cell outer membrane mimetic surface modification with phosphorylcholine dichloride is a promising strategy to improve the hemocompatibility of chitosan.

Surface modification of poly(tetramethylene adipate-co-terephthalate) membrane via layer-by-layer assembly of chitosan and dextran sulfate polyelectrolyte multiplayer

The improvement of hydrophilicity and hemocompatibility of poly(tetramethylene adipate-co-terephthalate) (PTAT) membrane was developed via polyelectrolyte multilayers (PEMs) immobilization. The polysaccharide PEMs included chitosan (CS, as a positive-charged and antibacterial agent) and dextran sulfate (DS, as a negative-charged and anti-adhesive agent) were successfully prepared using the aminolyzed PTAT membrane in a layer-by-layer (LBL) self-assembly manner. The obtained results showed that the contact angle of as-modified PTAT membranes reached to the steady value after four bilayers of coating, hence suggesting that the full coverage was achieved. It could be found that the PTAT-PEMs membranes with DS as the outmost layer could resist the platelet adhesion and human plasma fibrinogen (HPF) adsorption, thereby prolonging effectively the blood coagulation times. According to L929 fibroblast cell growth inhibition index, the as-prepared PTAT membranes exhibited non-cytotoxic. Overall results demonstrated that such an easy, valid and shape-independent processing should be potential for surface modification of PTAT membrane in the application of hemodialysis devices.

Construction of antithrombogenic polyelectrolyte multilayer on thermoplastic polyurethane via layer-by-layer self-assembly technique

The improvement of hydrophilicity and hemocompatibility of thermoplastic polyurethane (TPU) film was developed using surface modification of polyelectrolyte multilayers (PEMs) deposition. The polysaccharide PEMs included chitosan (CS, as a positive-charged agent) and dextran sulfate (DS, as a negative-charged and an antiadhesive agent) that were successfully prepared on the aminolyzed TPU film in a layer-by-layer (LBL) self-assembly manner. X-ray photoelectron spectroscopy (XPS), field-emission scanning electronic microscopy (FE-SEM), and atomic force microscopy (AFM) data will verify the progressive buildup of the PEMs film. The obtained results showed that the contact angle and Zeta-potential reached the steady value after four bilayers of coating, hence proving that the full coverage of coating with PEM layers was achieved. It could be found that the PEMs-deposited TPU films with DS as the outmost layer could resist the platelet adhesion and human plasma fibrinogen (HPF) adsorption, thereby prolonging effectively the blood coagulation times. Besides, the results of growth inhibition index (GI) of L929 fibroblast proliferation suggested that the as-fabricated TPU films were noncytotoxic. Overall results demonstrated that such an easy, valid, shape-independent, and noncytotoxic processing should be potential for the ion of TPU substrate in the application of hemodialysis or cardiovascular devices.

Polysaccharide-based polymer blends: Methods of their production

The existing methods of preparing polymer blends of cellulose, chitin and chitosan with natural and synthetic polymers and their applications are reviewed. The methods of solid-phase blending of these polymers under conditions of joint action of high pressure and shear deformation are discussed. Normally, under these conditions the processes of dispersion of polymer particles, amorphization, mixing at different levels, depolymerization as well as a chemical interaction resulting in formation of branched and crosslinked structures can take place. The probability and intensity of these processes depend in many respects on the type and magnitude of the external force, but the properties of the polymers are of higher importance. The advantages of the method of joint action of high pressure and shear deformation compared to the conventional techniques of polysaccharides mixtures production are shown.

Enzymatic Degradation Behaviour of Starch Conjugated Phosphorylated Chitosan

Phosphorylated chitosan (P-chitosan) was synthesized by means of graft copolymerization technique. The conjugate membranes were prepared from oxidised starch and Pchitosan using reductive alkylation crosslinking. The synthesized membranes were characterised by FT-IR. In order to characterize degradation behaviour of this conjugated system, the membranes were incubated in enzyme solutions of alpha-amylase and lysozyme as well as a physiological saline solution (PBS) used as control solution. In PBS, low starch containing membranes (0.16-0.38 weight (starch)/weight (P-chitosan), (ws/wc)) and control membranes have not showed significant change in their weight during two months of incubation. High starch containing membranes (0.73-1.04 ws/wc) indicated less than 20 % weight loss after this period. After α-amylase incubation, a distinct degradation behaviour was observed from starch-P-chitosan membranes. The degradation of the conjugate membranes was found to be fast with increasing starch content. Weight losses between 20 to 55 % were detected for the lowest (0.16 ws/wc) starch and highest (1.04 ws/wc) starch containing membranes, respectively. In the lysozyme degradation study, the conjugate membranes were not degraded by enzymatic activity and the weights of membranes were seen to be increased about 20 % because of swelling. The control membranes showed gradual weight loss in enzyme solutions. These results indicated the lysozyme degradation of starch-free P-chitosan membranes and inhibition of degradation P-chitosan by highly conjugated starch molecules.

Biodegradable membrane-covered stent from chitosan-based polymers

Membrane-covered devices could help treat disease of the vasculature such as aneurysm, rupture, and fistulas. They are also investigated to reduce embolic complication associated with revascularization of saphenous vein graft. The aim of this study is to design a clinically applicable biodegradable membrane-covered stent based on the natural polysaccharide chitosan, which has been developed. The mechanical properties of the membrane is optimized through blending with polyethylene oxide (70:30% Wt CH:PEO). The membrane was able to sustain the mechanical deformation of the supporting self-expandable metallic stents during its deployment. The membrane was demonstrated to resist physiological transmural pressure (burst pressure resistance >500 mm Hg) and presented a high-water permeation resistance (1 mL/cm(2) min(-1) at 120 mmHg). The CH-PEO membrane showed a good hemocompatibility in an ex vivo assay. Heparin and hyaluronan surface complexation with the membrane further reduced platelet adhesion by 50.1 and 63% (p = 0.05). The ability of the membrane-covered devices to be used as a drug reservoir was investigated using the nitric oxide donor sodium nitroprusside (SNP). SNP-loaded membranes displayed significantly reduced platelet adhesion.

In-Vitro Hemocompatibility Evaluation of a Thermoplastic Polyurethane Membrane with Surface-Immobilized Water-Soluble Chitosan and Heparin

The surface of a thermoplastic polyurethane (TPU) membrane was treated with low temperature plasma (LTP) and was then grafted with poly(acrylic acid) (PAA), followed by the grafting of water-soluble chitosan (WSC) and heparin (HEP). The surface was characterized with static contact-angle and X-ray photoelectron spectroscopy (XPS). The results showed that the surface densities of peroxides and PAA reached a maximum when treated with LTP for 90 s. A higher pH of the reacting solution led to higher graft densities of WSC and HEP. After WSC and HEP grafting, the hydrophilicity of the TPU membrane was increased. The adsorption of proteins on HEP-grafted TPU membranes was effectively curtailed. In addition, HEP grafting also reduced platelet adhesion, elevated thrombin inactivation, and prolonged the blood coagulation time. According to the L929 fibroblast cell growth inhibition index, the HEP-grafted TPU membranes exhibited non-cytotoxicity. Overall results demonstrated that the HEP immobilization could not only improve the hydrophilicity but also the hemocompatibility of the TPU membrane, while maintaining the ascendant biocompatibility.

Blood compatibility of thermoplastic polyurethane membrane immobilized with water-soluble chitosan/dextran sulfate

Water-soluble chitosan (WSC)/dextran sulfate (DS) was immobilized onto the surface of thermoplastic polyurethane (TPU) membrane after ozone-induced graft polymerization of poly(acrylic acid) (PAA). The surface was characterized with contact angle measurement and X-ray photoelectron spectroscopy (XPS). The adsorption of human plasma fibrinogen (HPF) followed the Langmuir adsorption isotherm. The results showed that the surface density of peroxides generated and poly(acrylic acid) (PAA) grafted reached the maximum value at 20 min of ozone treatment. It was found that the WSC- and DS-immobilized amount increased with pH and the molecular weight of WSC. The membrane/water interfacial free energy increased with PAA-grafting and WSC/DS-immobilization, indicating the increasing wettability of TPU membrane. The adsorption of HPF on TPU-WSC/DS membranes could be effectively curtailed and exhibited unfavorable adsorption. Moreover, WSC/DS immobilization could effectively reduce platelet adhesion and prolong the blood coagulation time, thereby membrane improving blood compatibility of TPU membrane. In addition, the in vitro cytotoxicity test of PEC modification was non-cytotoxic according to much low growth inhibition of L929 fibroblasts. Furthermore, TPU-WSC/DS membranes exhibited higher cell viability than native TPU membrane.

Hemocompatibility and anaphylatoxin formation of protein-immobilizing polyacrylonitrile hemodialysis membrane

Plasma proteins were covalently immobilized onto polyacrylonitrile (PAN) membrane to evaluate the hemocompatibility and anaphylatoxin formation. This is used as a model to study the effect of protein-adsorption on the blood-contacting response of hemodializing membranes. The proteins used were either platelet-adhesion-promoting collagen (COL) or platelet-adhesion-inhibiting human serum albumin (HSA). The microstructure and characterization of the protein-immobilizing PAN membranes were evaluated by Coomassie dye assay, atomic force microscopy, X-ray photoelectron spectroscopy and water contact angle measurement. PAN-HSA membrane improved not only hemocompatibility including less platelet adhesion, longer blood coagulation times, and higher thrombin inactivity level, but also induced lower complement activation. On the other hand, PAN-COL membrane exhibited blood incompatibility, although induced less increase of C3, C4 antigens of serum. Overall results of this study demonstrated that the immobilization of HSA onto the surface of PAN membrane would be beneficial to improve the hemocompatibility and to reduce the anaphylatoxin formation during hemodialysis.

A chitosan-arginine conjugate as a novel anticoagulation biomaterial

Chitosan (CS) was modified with arginine using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) as coupling agents. FTIR and 13C NMR spectra showed that arginine was chemically coupled to CS to form a chitosan-arginine conjugate (CS-ArgC). The substitution degree of arginine in CS estimated from elemental analysis was 20.1%. The circular dichroism spectra indicated that the incorporation of arginine significantly altered the conformation of thrombin; while no obvious variation in the conformation of thrombin was observed with the addition of CS. The anticoagulation activity of glucose aldehyde crosslinked CS-ArgC and CS membranes was evaluated by assaying prothrombin time (PT), thrombin time (TT) and activated partial thromboplastin time (APTT). The APTT of CS-ArgC membrane was prolonged two times as that of CS counterpart, suggesting that the CS-ArgC is a promising candidate as an anticoagulation biomaterial.

Hemocompatibility of polyacrylonitrile dialysis membrane immobilized with chitosan and heparin conjugate

Chitosan (CS)/heparin (HEP) polyelectrolyte complex (PEC) was covalently immobilized onto the surface of polyacrylonitrile (PAN) membrane. The effect of surface modification on the protein adsorption and platelet adhesion, metabolites permeation and anticoagulation activity of the resulting membrane was investigated. Surface characterization such as water contact angle, and X-ray photoelectron spectroscope were performed. The immobilization of PEC caused the water contact angle to reduce, thereby indicating the increase in the hydrophilicity. Protein adsorption, platelet adhesion, and thrombus formation were all reduced by the immobilization of HEP. Anticoagulant activity was evaluated with activated partial thrombin time (APTT), prothrombin time (PT), fibrinogen time, and thrombin time (TT). The results revealed that PEC-immobilizing membrane can improve antithrombogenicity of PAN membrane. In addition, the PEC-immobilized membranes can suppress the proliferation of Pseudomonas aeruginosa. In vitro cytotoxicity test showed leachable substance released was below cytotoxic level. The pure water permeability results show little variation due to PEC-immobilization. Thus PEC-immobilization can endow the PAN membrane hemocompatibility and antibacterial activity while retaining the original permeability.

Enzyme immobilization in novel alginate–chitosan core-shell microcapsules

Alginate-chitosan core-shell microcapsules were prepared in order to develop a biocompatible matrix for enzyme immobilization, where the protein is retained either in a liquid or solid core and the shell allows permeability control over substrates and products. The permeability coefficients of different molecular weight compounds (vitamin B2, vitamin B12, and myoglobin) were determined through sodium tripolyphosphate (Na-TPP)-crosslinked chitosan membrane. The microcapsule core was formed by crosslinking sodium alginate with either calcium or barium ions. The crosslinked alginate core was uniformly coated with a chitosan layer and crosslinked with Na-TPP. In the case of calcium alginate, the phosphate ions of Na-TPP were able to extract the calcium ions from alginate and liquefy the core. A model enzyme, beta-galactosidase, was immobilized in the alginate core and the catalytic activity was measured with o-nitrophenyl-beta-D-galactopyranoside (ONPG). Change in the activity of free and immobilized enzyme was determined at three different temperatures. Na-TPP crosslinked chitosan membranes were found to be permeable to solutes of up to 17,000Da molecular weight. The enzyme loading efficiency was higher in the barium alginate core (100%) as compared to the calcium alginate core (60%). The rate of ONPG conversion to o-nitrophenol was faster in the case of calcium alginate-chitosan microcapsules as compared to barium alginate-chitosan microcapsules. Barium alginate-chitosan microcapsules, however, did improve the stability of the enzyme at 37 degrees C relative to calcium alginate-chitosan microcapsules or free enzyme. This study illustrates a new method of enzyme immobilization for biotechnology applications using liquid or solid core and shell microcapsule technology.

Structure and interactions in chitosan hydrogels formed by complexation or aggregation for biomedical applications

The aim of this review was to provide a detailed overview of physical chitosan hydrogels and related networks formed by aggregation or complexation, which are intended for biomedical applications. The structural basis of these systems is discussed with particular emphasis on the network-forming interactions, the principles governing their formation and their physicochemical properties. An earlier review discussing crosslinked chitosan hydrogels highlighted the potential negative influence on biocompatibility of covalent crosslinkers and emphasised the need for alternative hydrogel systems. A possible means to avoid the use of covalent crosslinkers is to prepare physical chitosan hydrogels by direct interactions between polymeric chains, i.e. by complexation, e.g. polyelectrolyte complexes (PEC) and chitosan/poly (vinyl alcohol) (PVA) complexes, or by aggregation, e.g. grafted chitosan hydrogels. PEC exhibit a higher swelling sensitivity towards pH changes compared to covalently crosslinked chitosan hydrogels, which extends their potential application. Certain complexed polymers, such as glycosaminoglycans, can exhibit interesting intrinsic properties. Since PEC are formed by non-permanent networks, dissolution can occur. Chitosan/PVA complexes represent an interesting alternative for preparing biocompatible drug delivery systems if pH-controlled release is n/ot required. Grafted chitosan hydrogels are more complex to prepare and do not always improve biocompatibility compared to covalently crosslinked hydrogels, but can enhance certain intrinsic properties of chitosan such as bacteriostatic and wound-healing activity.