Blood compatibility and biodegradability of partially N-acylated chitosan derivatives

Comparison of various mixtures of beta-chitin and chitosan as a scaffold for three-dimensional culture of rabbit chondrocytes

With the use of a recently created chitosan neutral hydrogel, we have been able to create various mixtures of chitin and chitosan without changing their characteristics even at room temperature. The aim of this study was the initial comparison of various mixtures of beta-chitin and chitosan as a scaffold for rabbit chondrocyte culture. We created five types of sponges: pure beta-chitin, pure chitosan, 3:1, 1:1, and 1:3 beta-chitin-chitosan. The absorption efficiencies of chondrocytes in all five types of sponges were found to be around 98%. The mean concentrations of chondroitin sulfate were statistically different neither at week 2 nor at week 4 postculture between the types of sponges. The content of hydroxyproline in the beta-chitin sponge was significantly greater than in other sponges at week 4 postculture. From the histochemical and immunohistochemical findings, the cartilage-like layer in the chondrocytes-sponge composites of all five types of sponges was similar to hyaline cartilage. However, only immunohistochemical staining of type II collagen in the pure beta-chitin sponge was closer to normal rabbit cartilage than other types of sponges. The pure beta-chitin sponge was superior to other sponges concerning the content of extracellular matrices of collagen.

Effect of chitosan molecular weight and deacetylation degree on hemostasis

Comparative studies have been carried out among solid-state chitosan soliquoid, chitosan acetic acid physiological saline solution, and carboxymethyl chitosan physiological saline solution to discover the hemostatic effect of molecular weight (M(w)) and deacetylation degree (DA) of chitosan. It was found that solid-state chitosan and chitosan acetic acid physiological saline solution performed different hemostatic mechanisms. When blood mixed with chitosan acetic acid physiological saline solution, the erythrocytes aggregated and were deformed. The DA, especially a low DA, in the chitosan acetic acid physiological saline solution, had a significant effect on the unusual aggregation and deformation of erythrocytes, compared with the effect of M(w) within a range between 10(5) and 10(6). However, this phenomenon could not be observed in solid-state chitosan soliquoid. Solid-state chitosan with a low DA absorbed more platelets and was more hemostatic. Carboxymethyl chitosan physiological saline solution had nothing to do with the aggregation and deformation of erythrocytes but caused local rouleau. The values of thrombin time (TT), prothrombin time (PT), activated partial thromboplastin time (APTT), and fibrinogen concentration (FIB) were measured after the blood was mixed with solid-state chitosan soliquoid, chitosan acetic acid physiological saline solution, and carboxymethyl chitosan physiological saline solution, separately. The results demonstrated that coagulation factors might not be activated by them.

Chitosan and its derivatives for tissue engineering applications

Tissue engineering is an important therapeutic strategy for present and future medicine. Recently, functional biomaterial researches have been directed towards the development of improved scaffolds for regenerative medicine. Chitosan is a natural polymer from renewable resources, obtained from shell of shellfish, and the wastes of the seafood industry. It has novel properties such as biocompatibility, biodegradability, antibacterial, and wound-healing activity. Furthermore, recent studies suggested that chitosan and its derivatives are promising candidates as a supporting material for tissue engineering applications owing to their porous structure, gel forming properties, ease of chemical modification, high affinity to in vivo macromolecules, and so on. In this review, we focus on the various types of chitosan derivatives and their use in various tissue engineering applications namely, skin, bone, cartilage, liver, nerve and blood vessel.

Structure, depolymerization, and cytocompatibility evaluation of glycol chitosan

Glycol chitosan, a water soluble chitosan derivative being investigated as a new biomaterial, was fractionated via two different methods. Initial characterization of the glycol chitosan with (1)H NMR spectroscopy illustrated the presence of both secondary and tertiary amine groups, contradictory to its widely accepted structure. Fractionation of glycol chitosan with nitrous acid resulted in a significant reduction in the number average molecular weight, specifically, from 170 to approximately 7 kDa for a pH 3 and below. However, the reaction altered its chemical structure, as the secondary amine groups were converted to N-nitrosamines, which are potentially carcinogenic. An increase in the pH of the reaction limited this formation, but not entirely. Free radical degradation initiated with potassium persulfate was not as effective at reducing the molecular weight as the nitrous acid approach, yielding molecular weights around 12 kDa under the same molar ratio of degrading species, but did retain the structural integrity of the glycol chitosan. Additionally, control of the molecular weight appears feasible with potassium persulfate. When assessed in vitro for cytocompatibility, the polymer exhibited no toxicity on monolayer-cultured chondrocytes, and in fact stimulated cell growth at low concentrations.

Clinical evaluation of bioadhesive hydrogels for topical delivery of hexylaminolevulinate to Barrett's esophagus

Fluorescence diagnosis following oral administration of 5-aminolevulinic acid (5-ALA) has shown to enable the sensitive visualization of intestinal metaplasia, dysplasia and early carcinoma in Barrett's esophagus. Once being established, this technique will be a potential alternative to today's standard diagnosis, i.e. four-quadrant random biopsies which are taken every 1-2 cm of the esophagus for histopathological analysis. In order to further improve this methodology, topical application of lipophilic 5-ALA esters to the esophagus could be advantageous in terms of fluorescence contrast and fluorescence intensity in the target tissue, adverse side effects, as well as application time. Therefore, the aim of this study was to develop a bioadhesive formulation loaded with hexylaminolevulinate (HAL) targeting the esophageal lining. In the present study, different mucoadhesive gels including poloxamer 407, cross-linked polyacrylic acid, hydroxypropylmethylcellulose, sodium carboxymethylcellulose and chitosan have been evaluated with respect to bioadhesion to the esophagus using an ex vivo rat model and a clinical study on healthy volunteers. In order to visualize the mucoadhesive properties of the formulations, a blue dye was incorporated as contrast agent. Chitosan has shown the best esophageal adhesion both in vitro and in vivo. Furthermore, using the in vitro release profiles from chitosan loaded with 40 mM of HAL, one can estimate that after a residence time of 10 min on the esophageal wall, the amount of HAL delivered to the epithelium will be sufficient to perform fluorescence diagnosis of Barrett's esophagus following swallowing of this formulation.

Evaluation of in vitro enzymatic degradation of various thiomers and cross-linked thiomers

The aim of this study was to examine the biodegradability of thiomers and cross-linked thiomers in comparison with unmodified polymers. Disulfide-cross-linked conjugates were prepared by air oxidation at room temperature. Thiomers were investigated by viscosity measurements and spectrophotometric assays. The influence of different factors on the hydrolysis rate, such as the degree of modification of thiomers, structure of the conjugates, pH value of the reaction medium, and the impact of the process of cross-linking were evaluated. Due to the modification, thiolated chitosans degraded 12.9-24.7% less than unmodified chitosan in the framework of viscosity measurements. In addition, the hydrolysis degree of thiolated alginates and modified carboxymethylcelluloses was 25.6-32.4% and 18.4-27.0% lower, respectively, in comparison to the corresponding unmodified polymers. Conjugates with higher coupling rate of thiol groups were degraded even more slowly. Moreover, the cross-linking process via disulfide bonds additionally reduced the rate of thiomer degradation. The range of degradation rates achieved in vitro could be modified by alterations of the contents of thiol and disulfide groups, as well as by suitable design of the polymer structure and ligands used. These results represent helpful basic information for the development of mucoadhesive drug delivery systems, implantable delivery systems and tissue engineering constructs.

Cell-based cardiac pumps and tissue-engineered ventricles

Mortalities resulting from cardiovascular disorders remain high, with an urgent need to develop novel treatment modalities. Tissue-engineering therapies aim to provide cell-based alternatives to conventional options. Significant technological advancements have occurred during the last decade towards the fabrication of functional 3D heart muscle in vitro. More recent research has focused on the development of cell-based cardiac pumps and tissue-engineered ventricles. The global objective of this collective work is to simulate the functional performance of the left ventricle, utilizing completely cell-based options. Current prototypes have shown several physiological performance metrics, including the ability of these devices to generate intraluminal pressure upon electrical stimulation. This review will highlight the transition from tissue engineering 3D heart muscle to cell-based cardiac pumps/ventricles.

Controlled release of PEI/DNA complexes from mannose-bearing chitosan microspheres as a potent delivery system to enhance immune response to HBV DNA vaccine

A novel approach involving the preparation of mannose-bearing chitosan microspheres with entrapping complexes of HBV DNA and PEI was developed to improve the delivery of DNA into antigen-presenting cells (APCs) after intramuscular (i.m.) injection. Compared with the traditional chitosan microspheres, the microspheres could quickly release intact and penetrative PEI/DNA complexes. What's more, chitosan was modified with mannose to target the primary APCs such as dendritic cells (DCs) owing to the high density of mannose receptors expressing on the surface of immature DCs. After i.m. immunization, the microspheres induced significantly enhanced serum antibody and cytotoxic T lymphocyte (CTL) responses in comparison to naked DNA.

Evaluation and modification of N-trimethyl chitosan chloride nanoparticles as protein carriers

N-Trimethyl chitosan chloride (TMC) nanoparticles were prepared by ionic crosslinking of TMC with tripolyphosphate (TPP). Two model proteins with different pI values, bovine serum albumin (BSA, pI=4.8) and bovine hemoglobin (BHb, pI=6.8), were used to investigate the loading and release features of the TMC nanoparticles. TMC samples with different degrees of quaternization were synthesized to evaluate its influence on the physicochemical properties and release profiles of the nanoparticles. Sodium alginate was used to modify the TMC nanoparticles to reduce burst release. The results indicated that the TMC nanoparticles had a high loading efficiency (95%) for BSA but a low one (30%) for BHb. The particle size and zeta potential were significantly affected by the BSA concentration but not by the BHb concentration. Nanoparticles of TMC with a lower degree of quaternization showed an increase in particle size, a decrease in zeta potential and a slower drug-release profile. As for the alginate-modified nanoparticles, a smaller size and lower zeta potential were observed and the burst release of BSA was reduced. These studies demonstrated that TMC nanoparticles are potential protein carriers, and that their physicochemical properties and release profile could be optimized by means of various modifications.

Chitosan-glycerol phosphate/blood implants elicit hyaline cartilage repair integrated with porous subchondral bone in microdrilled rabbit defects

OBJECTIVE

We have previously shown that microfractured ovine defects are repaired with more hyaline cartilage when the defect is treated with in situ-solidified implants of chitosan-glycerol phosphate (chitosan-GP) mixed with autologous whole blood. The objectives of this study were (1) to characterize chitosan-GP/blood clots in vitro, and (2) to develop a rabbit marrow stimulation model in order to determine the effects of the chitosan-GP/blood implant and of debridement on the formation of incipient cartilage repair tissue.

METHODS

Blood clots were characterized by histology and in vitro clot retraction tests. Bilateral 3.5 x 4 mm trochlear defects debrided into the calcified layer were pierced with four microdrill holes and filled with a chitosan-GP/blood implant or allowed to bleed freely as a control. At 1 day post-surgery, initial defects were characterized by histomorphometry (n=3). After 8 weeks of repair, osteochondral repair tissues between or through the drill holes were evaluated by histology, histomorphometry, collagen type II expression, and stereology (n=16).

RESULTS

Chitosan-GP solutions structurally stabilized the blood clots by inhibiting clot retraction. Treatment of drilled defects with chitosan-GP/blood clots led to the formation of a more integrated and hyaline repair tissue above a more porous and vascularized subchondral bone plate compared to drilling alone. Correlation analysis of repair tissue between the drill holes revealed that the absence of calcified cartilage and the presence of a porous subchondral bone plate were predictors of greater repair tissue integration with subchondral bone (P<0.005), and of a higher total O'Driscoll score (P<0.005 and P<0.01, respectively).

CONCLUSIONS

Chitosan-GP/blood implants applied in conjunction with drilling, compared to drilling alone, elicited a more hyaline and integrated repair tissue associated with a porous subchondral bone replete with blood vessels. Concomitant regeneration of a vascularized bone plate during cartilage repair could provide progenitors, anabolic factors and nutrients that aid in the formation of hyaline cartilage.

Development of a new calcium sulphate-based composite using alginate and chemically modified chitosan for bone regeneration

In this work we developed a novel calcium sulphate-based composite in which the hemihydrate calcium sulphate (CHS) can be encapsulated in a polymeric biodegradable and biocompatible matrix, in order to retain the structural integrity and decrease the bioresorption rate in bone regeneration applications. Two polymers were employed to realize this system: chitosan (Ch) and sodium alginate (Alg), both already widely used in biotechnological and biomedical applications. Chitosan was modified in order to obtain a water soluble polymer, the N-succinylchitosan (sCh). The reaction was performed with succinic anhydride in presence of pyridine and confirmed by FT-IR and NMR analyses. Finely ground Alg and sCh powders were mixed in different compositions with CHS and by adding water to the powder mixture it was obtained a mouldable paste that sets in few hours. Thermogravimetric analyses coupled with solvent extraction performed on the composite proved the alginate crosslinking in the presence of CHS. Mechanical studies carried out on composites of different compositions demonstrated that the blend of the two polymeric components causes a substantial synergistic reinforcement of composites. The presence of carboxylic groups on sCh chain in addition to those of alginate could enhance the chelating power of polysaccharide mixture. The results obtained with morphological analyses (SEM) further confirmed the hypotesis of the synergistic effect between alginate and N-succinylchitosan in presence of calcium sulphate. In vitro cytotoxicity tests proved that the developed system was not cytotoxic.

N-Trimethyl chitosan (TMC) nanoparticles loaded with influenza subunit antigen for intranasal vaccination: Biological properties and immunogenicity in a mouse model

In this study, the potential of N-trimethyl chitosan (TMC) nanoparticles as a carrier system for the nasal delivery of a monovalent influenza subunit vaccine was investigated. The antigen-loaded nanoparticles were prepared by mixing a solution containing TMC and monovalent influenza A subunit H3N2 with a tripolyphosphate (TPP) solution, at ambient temperature and pH 7.4 while stirring. The nanoparticles had an average size of about 800 nm with a narrow size distribution and a positive surface charge. The nanoparticles showed a loading efficiency of 78% and a loading capacity of 13% (w/w). It was shown that more than 75% of the protein remained associated with the TMC nanoparticles upon incubation of the particles in PBS for 3h. The molecular weight and antigenicity of the entrapped hemagglutinin was maintained as shown by polyacrylamide gel electrophoresis and Western blotting, respectively. Single i.n. or i.m. immunization with antigen-loaded TMC nanoparticles resulted in strong hemagglutination inhibition and total IgG responses. These responses were significantly higher than those achieved after i.m. administration of the subunit antigen, whereas the IgG1/IgG2a profile did not change substantially. The i.n. administered antigen-TMC nanoparticles induced higher immune responses compared to the other i.n. antigen formulations, and these responses were enhanced by i.n. booster vaccinations. Moreover, among the tested formulations only i.n. administered antigen-containing TMC nanoparticles induced significant IgA levels in nasal washes of all mice. In conclusion, these findings demonstrate that TMC nanoparticles are a potent new delivery system for i.n. administered influenza antigens.

Gadolinium diethylenetriaminopentaacetic acid-loaded chitosan microspheres for gadolinium neutron-capture therapy

In order to provide a suitable device that would contain water-soluble drugs, highly water-soluble gadolinium diethylenetriaminopentaacetic acid-loaded chitosan microspheres (CMS-Gd-DTPA) were prepared by the emulsion method using glutaraldehyde as a cross-linker and Span 80 as a surfactant for gadolinium neutron-capture therapy of cancer. The gadolinium content and the mass median diameter of CMS-Gd-DTPA were estimated. The size and morphology of the CMS-Gd-DTPA were strongly influenced by the initial applied weight ratio of Gd-DTPA:chitosan. FTIR spectra showed that the electrostatic interaction between chitosan and Gd-DTPA accelerated the formation of gadolinium-enriched chitosan microspheres. Sufficient amounts of glutaraldehyde and Span 80 were necessary for producing discrete CMS-Gd-DTPA. The CMS-Gd-DTPA having a mass median diameter 11.7microm and 11.6% of gadolinium could be used in Gd-NCT following intratumoral injection.

Processing and Characterization of Porous Structures from Chitosan and Starch for Tissue Engineering Scaffolds

Natural biodegradable polymers were processed by different techniques for the production of porous structures for tissue engineering scaffolds. Potato, corn, and sweet potato starches and chitosan, as well as blends of these, were characterized and used in the experiments. The techniques used to produce the porous structures included a novel solvent-exchange phase separation technique and the well-established thermally induced phase separation method. Characterization of the open pore structures was performed by measuring pore size distribution, density, and porosity of the samples. A wide range of pore structures ranging from 1 to 400 microm were obtained. The mechanisms of pore formation are discussed for starch and chitosan scaffolds. Pore morphology in starch scaffolds seemed to be determined by the initial freezing temperature/freezing rate, whereas in chitosan scaffolds the shape and size of pores may have been determined by the processing route used. The mechanical properties of the scaffolds were assessed by indentation tests, showing that the indentation collapse strength depends on the pore geometry and the material type. Bioactivity and degradation of the potential scaffolds were assessed by immersion in simulated body fluid.

Cell mimetic monolayer supported chitosan-haemocompatibility studies

Chitosan is a natural polymer, widely explored for biomedical and tissue engineering applications. However the thrombogenic nature limits their application in blood contacting devices and implants. Here, we have attempted to understand the haemocompatibility of chitosan by immobilizing a monolayer of cell mimetic lipid compositions. The phosphatidylcholine/cholesterol/galactocerebroside lipid composition (PC/Chol/GalC, 1:0.35:0.125) was deposited onto the chitosan films. Characterization of the modified surface was done by sessile drop contact angle measurement. The contact angle of the chitosan film reduced from 80.65 +/- 1.4 to 23.5 +/- 1.9 after the surface modification. Swelling nature of chitosan seemed to influence the orientation and packing of the lipid monolayer. In vitro calcification studies with metastable salt solution indicated increased calcification on the modified surface. This may be due to formation of nuclei for calcification on the expanding monolayer. The preliminary haemocompatibility studies with washed platelets, leukocytes and erythrocytes showed overall reduction in blood cell adhesion to the modified surfaces. Scanning electron microscopy was used for morphological characterization of platelet adhesion and activation on the surfaces. On the bare chitosan surface, fully spread platelets with extending pseudopodia indicated platelet activation. The smooth surface of the modified film did not activate platelets. These studies showed that, though the lipid monolayer on chitosan film is able to reduce the over all blood cell adhesion and platelet activation it is prone to calcification.

Inflammatory response on injection of chitosan/GP to the brain

Chitosan is a well-known biomaterial that, with the addition of glycerophosphate salt (GP), gels at physiological temperatures and therefore is useful for tissue engineering purposes. This study examines the procedure of injecting chitosan/ GP to the brain in order to form a gel track. The gel system and surgical technique were successful in this endeavour; however, on examining the inflammatory response to the material it was found that the chitosan/GP was wholly engulfed by macrophages within 7 days. This was determined by staining for both the gel and the macrophages, an important technique for localising injected material. The chitosan/GP-containing macrophages formed a neat tract at the lesion site, but after 45 days no chitosan/GP was found. It was concluded that, although chitosan/GP is present after implantation, it is not available for direct scaffolding in the brain.

A novel chitosan oligosaccharide-stearic acid micelles for gene delivery: properties and in vitro transfection studies

Stearic acid (SA) grafted chitosan oligosaccharide (CSO) (CSO-SA), which was synthesized by an 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)-mediated coupling reaction, was demonstrated to form micelle like structure by self-aggregation in aqueous solution. The critical micelle concentration (CMC) of CSO-SA with 15.4% amino substituted degree of CSO was about 0.035 mg/ml. The micelles with 1mg/ml CSO-SA concentration had 70.6 nm volume average hydrodynamic diameter with a narrow size distribution and 46.4+/-0.1 mV surface potential. Due to the cationic property, the micelles could compact the plasmid DNA to form micelle/DNA complexes nanoparticles, which can efficiently protect the condensed DNA from enzymatic degradation by DNase I. The volume average hydrodynamic diameter of CSO-SA micelle/DNA complex increased from 203 nm to 318 nm and decreased to 102 nm due to the variation of zeta potential when the N/P ratio increased from 0.25 to 3.6 and from 3.6 to 58. The IC(50) value of the CSO-SA micelle against A549 cells was 543.16 microg/ml, while the IC(50) of Lipofectamine 2000 was about 6 microg/ml. The in vitro transfection efficiency of CSO-SA micelles was investigated by using plasmid DNA (pEGFP-C1). The transfection efficiency with CSO-SA/DNA (N/P ratio is 29) was increased with the post-transfection time (in 76h), while the optimal transfection of Lipofectamine 2000/DNA was obtained at 24h. The transfection of CSO-SA was not interfered in the presence of 10% fetal bovine serum, which showed remarkable enhancement effect. The optimal transfection efficiency of CSO-SA micelles in A549 cells was about 15%, which was higher than that of CSO (about 2%) and approach to that of Lipofectamine 2000 (about 20%). The low cytotoxic biodegradable CSO-SA micelles could be used as an effective DNA condensation carrier for gene delivery system.

Preparation and characterization of protein-loaded N-trimethyl chitosan nanoparticles as nasal delivery system

In this study, the potential of N-trimethyl chitosan (TMC) nanoparticles as a carrier system for the nasal delivery of proteins was investigated. TMC nanoparticles were prepared by ionic crosslinking of TMC solution (with or without ovalbumin) with tripolyphosphate, at ambient temperature while stirring. The size, zeta-potential and morphology of the nanoparticles were investigated as a function of the preparation conditions. Protein loading, protein integrity and protein release were studied. The toxicity of the TMC nanoparticles was tested by ciliary beat frequency measurements of chicken embryo trachea and in vitro cytotoxicity assays. The in vivo uptake of FITC-albumin-loaded TMC nanoparticles by nasal epithelia tissue in rats was studied by confocal laser scanning microscopy. The nanoparticles had an average size of about 350 nm and a positive zeta-potential. They showed a loading efficiency up to 95% and a loading capacity up to 50% (w/w). The integrity of the entrapped ovalbumin was preserved. Release studies showed that more than 70% of the protein remained associated with the TMC nanoparticles for at least 3 h on incubation in PBS (pH 7.4) at 37 degrees C. Cytotoxicity tests with Calu-3 cells showed no toxic effects of the nanoparticles, whereas a partially reversible cilio-inhibiting effect on the ciliary beat frequency of chicken trachea was observed. In vivo uptake studies indicated the transport of FITC-albumin-associated TMC nanoparticles across the nasal mucosa. In conclusion, TMC nanoparticles are a potential new delivery system for transport of proteins through the nasal mucosa.

Preparation and characterization of novel hybrid of chitosan-g-lactic acid and montmorillonite

The utilization of biopolymers and the development of organic-inorganic hybrids are ever increasing interest of material science researchers around the globe for various applications. The present attempt is intended to prepare nanocomposites of lactic acid grafted chitosan and layered silicates. Nanocomposites were prepared by dissolving chitosan and dispersing sodium montmorillonite in aqueous solution of L-lactic acid with subsequent heating and film casting. They were characterized by conventional techniques such as Fourier transform infrared spectroscopy, X-ray diffractometry, thermogravimetric analysis, energy dispersive X-ray spectroscopy, and elemental analysis. The results from polar optical and transmission electron microscopic measurements are also discussed. Sorption behavior of samples has been followed by measuring swelling degree and contact angle. The films have shown enhanced hydrophilicity when compared with polylactic acid (PLA). Issues on the interactions of polycationic chitosan with clay are also discussed. It is observed that nanocomposites are exhibiting better thermal and physical properties than neat chitosan-g-LA and PLA.

Biopolymer-based biomaterials as scaffolds for tissue engineering

Biopolymers as biomaterials and matrices in tissue engineering offer important options in control of structure, morphology and chemistry as reasonable substitutes or mimics of extracellular matrix systems. These features also provide for control of material functions such as mechanical properties in gel, fiber and porous scaffold formats. The inherent biodegradability of biopolymers is important to help regulate the rate and extent of cell and tissue remodeling in vitro or in vivo. The ability to genetically redesign these polymer systems to bioengineer appropriate features to regulate cell responses and interactions is another important feature that offers both fundamental insight into chemistry-structure-function relationships as well as direct utility as biomaterials. Biopolymer matrices for biomaterials and tissue engineering can directly influence the functional attributes of tissues formed on these materials and suggest they will continue play an increasingly important role in the field.

Chitosan-glycerol phosphate/blood implants improve hyaline cartilage repair in ovine microfracture defects

BACKGROUND

Microfracture is a surgical procedure that is used to treat focal articular cartilage defects. Although joint function improves following microfracture, the procedure elicits incomplete repair. As blood clot formation in the microfracture defect is an essential initiating event in microfracture therapy, we hypothesized that the repair would be improved if the microfracture defect were filled with a blood clot that was stabilized by the incorporation of a thrombogenic and adhesive polymer, specifically, chitosan. The objectives of the present study were to evaluate (1) blood clot adhesion in fresh microfracture defects and (2) the quality of the repair, at six months postoperatively, of microfracture defects that had been treated with or without chitosan-glycerol phosphate/blood clot implants, using a sheep model.

METHODS

In eighteen sheep, two 1-cm2 full-thickness chondral defects were created in the distal part of the femur and treated with microfracture; one defect was made in the medial femoral condyle, and the other defect was made in the trochlea. In four sheep, microfracture defects were created bilaterally; the microfracture defects in one knee received no further treatment, and the microfracture defects in the contralateral knee were filled with chitosan-glycerol phosphate/autologous whole blood and the implants were allowed to solidify. Fresh defects in these four sheep were collected at one hour postoperatively to compare the retention of the chitosan-glycerol phosphate/blood clot with that of the normal clot and to define the histologic characteristics of these fresh defects. In the other fourteen sheep, microfracture defects were made in only one knee and either were left untreated (control group; six sheep) or were treated with chitosan-glycerol phosphate/blood implant (treatment group; eight sheep), and the quality of repair was assessed histologically, histomorphometrically, and biochemically at six months postoperatively.

RESULTS

In the defects that were examined one hour postoperatively, chitosan-glycerol phosphate/blood clots showed increased adhesion to the walls of the defects as compared with the blood clots in the untreated microfracture defects. After histological processing, all blood clots in the control microfracture defects had been lost, whereas chitosanglycerol phosphate/blood clot adhered to and was partly retained on the surfaces of the defect. At six months, defects that had been treated with chitosan-glycerol phosphate/blood were filled with significantly more hyaline repair tissue (p < 0.05) compared with control defects. Repair tissue from medial femoral condyle defects that had been treated with chitosan-glycerol phosphate/blood contained more cells and more collagen compared with control defects and showed complete restoration of glycosaminoglycan levels.

CONCLUSIONS

Solidification of a chitosan-glycerol phosphate/blood implant in microfracture defects improved cartilage repair compared with microfracture alone by increasing the amount of tissue and improving its biochemical composition and cellular organization.

The enzymatic degradation and swelling properties of chitosan matrices with different degrees of N-acetylation

In the design of chitosan-based drug delivery systems and implantable scaffolds, the biodegradation rate of the chitosan matrix represents a promising strategy for drug delivery and the function of carriers. In this study, we have investigated the degradation of chitosan with different degrees of N-acetylation, with respect to weight loss, water absorption, swelling behavior, molecular weight loss of bulk materials, and reducing sugar content in the media. Chitosan matrices were prepared by compression molding. The results revealed that the initial degradation rate, equilibrium water absorption, and swelling degree increased with decreasing degree of deacetylation (DD) and a dramatic rise began as DD of the chitosan matrix decreased to 62.4%. Chitosan matrices with DD of 52.6%, 56.1%, and 62.4% had the weight half-life of 9.8, 27.3, and more than 56 days, respectively, and the weight half-life of average molecular weight 8.4, 8.8, and 20.0 days, respectively. For chitosan matrices with DD of 71.7%, 81.7%, and 93.5%, both types of half-life exceeded 84 days because of the much slower degradation rate. The dimension of chitosan matrices during degradation was determined by the process of swelling and degradation. These findings may help to design chitosan-based biomedical materials with predetermined degradation timed from several days to months and proper swelling behaviors.

Preparation of γ-PGA/chitosan composite tissue engineering matrices

Gamma-poly(glutamic acid) (gamma-PGA), a hydrophilic and biodegradable polymer, was chosen to modify chitosan matrices to produce a gamma-PGA/chitosan composite biomaterial. Three types of both dense and porous composite matrices containing different amounts of gamma-PGA were fabricated. Chitosan and gamma-PGA matrices were also prepared as controls. Fluorescence staining indicated that chitosan and gamma-PGA were evenly distributed in the composite matrices. SEM micrographs showed that an interconnected porous structure with a pore size of 30-100 microm was present in all porous matrices except the gamma-PGA ones. By increasing the percentage of gamma-PGA from 0% to 20%, the swelling ratio of the matrices was enhanced from 1.6 to 3.2. Similarly, the contact angle of the matrices decreased from 113 degrees to 94 degrees . These data suggested that the surface hydrophilicity, water absorption rate, and swelling ratio were improved by adding gamma-PGA to the matrices. Additionally, the mechanical strength of the porous gamma-PGA/chitosan matrices was about 25-50%, higher than that of the unmodified chitosan matrices. The composite matrices were also examined and found to be an appropriate environment for cell attachment and proliferation. The cell density on the 20% gamma-PGA-modified matrices was almost triple that on the unmodified chitosan matrices on day 5. In summary, the gamma-PGA/chitosan composite matrices, due to their better hydrophilic, cytocompatible, and mechanical properties, are very promising biomaterials for tissue engineering applications.

Controlling cell adhesion and degradation of chitosan films by N-acetylation

As part of our ongoing effort to develop a biodegradable nerve guidance channel based on chitin/chitosan, we conducted a systematic in vitro study on the biodegradation and neural cell compatibility of chitosan and N-acetylated chitosan. The in vitro degradation (pH 7.4, 37 degrees C) in the presence of 1.5 microg/ml lysozyme showed a progressive mass loss to greater than 50% within 4 weeks for films with 30-70% acetylation. In contrast, the degradation of samples with very low or high acetylation was minimal over the 4-week period. Neural cell compatibility of chitosan and N-acetylated chitosan was tested using primary chick dorsal root ganglion (DRG) neurons. All chitosan-based films showed DRG cell adhesion after 2 days of culture. However, cell viability decreased with increasing acetylation. Chitosan that was 0.5% acetylated had the greatest cell viability, which was approximately 8 times higher than that of chitosan that was 11% acetylated. Chitosan with 0.5% and 11% acetylation showed more and longer neurites than the other samples studied. Thus chitosan amine content can be tuned for optimal biodegradation and cell compatibility, which are important for tissue engineering in the nervous system.

Chitosan adhesive for laser tissue repair: in vitro characterization

BACKGROUND AND OBJECTIVES

Laser tissue repair usually relies on hemoderivate protein solders, based on serum albumin. These solders have intrinsic limitations that impair their widespread use, such as limited tensile strength of repaired tissue, poor solder solubility, and brittleness prior to laser denaturation. Furthermore, the required activation temperature of albumin solders (between 65 and 70 degrees C) can induce significant thermal damage to tissue. In this study, we report on the design of a new polysaccharide adhesive for tissue repair that overcomes some of the shortcomings of traditional solders.

STUDY DESIGN/MATERIALS AND METHODS

Flexible and insoluble strips of chitosan adhesive (elastic modulus approximately 6.8 Mpa, surface area approximately 34 mm2, thickness approximately 20 microm) were bonded onto rectangular sections of sheep intestine using a diode laser (continuous mode, 120 +/- 10 mW, lambda = 808 nm) through a multimode optical fiber with an irradiance of approximately 15 W/cm2. The adhesive was based on chitosan and also included indocyanin green dye (IG). The temperature between tissue and adhesive was measured using a small thermocouple (diameter approximately 0.25 mm) during laser irradiation. The repaired tissue was tested for tensile strength by a calibrated tensiometer. Murine fibroblasts were cultured in extracted media from chitosan adhesive to assess cytotoxicity via cell growth inhibition in a 48 hours period.

RESULTS

Chitosan adhesive successfully repaired intestine tissue, achieving a tensile strength of 14.7 +/- 4.7 kPa (mean +/- SD, n = 30) at a temperature of 60-65 degrees C. Media extracted from chitosan adhesive showed negligible toxicity to fibroblast cells under the culture conditions examined here.

CONCLUSION

A novel chitosan-based adhesive has been developed, which is insoluble, flexible, and adheres firmly to tissue upon infrared laser activation.

Chitosan based surfactant polymers designed to improve blood compatibility on biomaterials

We developed chitosan based surfactant polymers that could be used to modify the surface of existing biomaterials in order to improve their blood compatibility. These polymers consist of a chitosan backbone, PEG side chains to repel non-specific protein adsorption, and hexanal side chains to facilitate adsorption and proper orientation onto a hydrophobic substrate via hydrophobic interactions. Since chitosan is a polycationic polymer, and it is thrombogenic, the surface charge was altered to determine the role of this charge in the hemocompatibility of chitosan. Charge had a notable effect on platelet adhesion. The platelet adhesion was greatest on the positively charged surface, and decreased by almost 50% with the neutralization of this charge. A chitosan surface containing the negatively charged SO(3)(-) exhibited the fewest number of adherent platelets of all surfaces tested. Coagulation activation was not altered by the neutralization of the positive charge, but a marked increase of approximately 5-6 min in the plasma recalcification time (PRT) was displayed with the addition of the negatively charged species. Polyethylene (PE) surfaces were modified with the chitosan surfactant resulting in a significant improvement in blood compatibility, which correlated to the increasing PEG content within the polymer. Adsorption of the chitosan surfactants onto PE resulted in approximately an 85-96% decrease in the number of adherent platelets. The surfactant polymers also reduced surface induced coagulation activation, which was indicated by the PEG density dependent increase in PRTs. These results indicate that surface modification with our chitosan based surfactant polymers successfully improves blood compatibility. Moreover, the inclusion of either negatively charged SO(3)(-) groups or a high density of large water-soluble PEG side chains produces a surface that may be suitable for cardiovascular applications.

Efficacy of an intratumoral controlled release formulation of clusterin antisense oligonucleotide complexed with chitosan containing paclitaxel or docetaxel in prostate cancer xenograft models

PURPOSE

To develop and evaluate an injectable, controlled release delivery system for a phosphorothioate antisense oligonucleotide (ASO) based on complexed ASO:chitosan dispersed in a biodegradable polymeric paste for intratumoral treatment of solid tumors.

METHODS

Clusterin ASO was complexed with chitosan particles and incorporated into a paste based on a 60:40 blend of methoxy-poly(ethylene glycol) (MePEG) and triblock copolymer of poly(D: ,L: -lactic acid-co-caprolactone)-PEG-(D: ,L: -lactic acid-co-caprolactone). In vitro release profiles of clusterin ASO into phosphate-buffered saline at 37 degrees C were obtained under sink conditions and assayed by anionic exchange high-performance liquid chromatography. In vivo efficacy studies were carried out in human prostate PC-3 and LNCaP tumors grown subcutaneously in mice. Paste formulations of clusterin ASO with or without paclitaxel or docetaxel were injected intratumorally and tumor volumes and serum prostate specific antigen (PSA) levels were measured.

RESULTS

Controlled release of clusterin ASO was obtained over several weeks. The rate and extent of ASO release was proportional to the ratio of ASO to chitosan in the paste. Treatment of mice bearing PC-3 tumors with clusterin ASO plus paclitaxel or docetaxel paste had reduced mean tumor volume by greater than 50% at 4 weeks. Treatment of mice bearing LNCaP tumors with clusterin ASO plus paclitaxel reduced mean tumor volume and serum PSA level by more than 50% and 70%, respectively.

CONCLUSIONS

Complexation of clusterin ASO with chitosan and incorporation into polymeric paste with paclitaxel or docetaxel produced in vitro controlled release of the ASO and in vivo efficacy over 4 weeks following a single intratumoral injection in solid human prostate tumors in mice.

Formation of Polyelectrolyte Complex Particles from Self-Complexation of N-Sulfated Chitosan

This work investigated the elaboration of biocompatible nanoparticles from the pH-induced self-complexation of the amphoteric polysaccharide N-sulfated chitosan. The acidification of aqueous solutions of chitosan having a degree of acetylation of 24% and a degree of sulfation of 34% or 56% was followed stepwise by turbidimetry, dynamic light scattering, and electrophoresis. With the highest sulfated chitosan, no turbidity was recorded between pH = 7.8 and 2.0, traducing a high apparent solubility of the polymer chains in this domain of pH. With the lowest sulfated chitosan, a steady increase in turbidity was monitored from pH = 6.90 to 6.15 followed by the flocculation of the polymer at pH approximately 6.0. In this range of pH, the polymer phase separated to yield particles having hydrodynamic diameters decreasing from 350 to 260 nm and an almost constant negative charge. These particles were assembled by electrostatic interactions between the protonated amino residues and the sulfate functions and stabilized by an excess of surface sulfate groups. The particles could be separated from the reaction medium and concentrated by centrifugation-redispersion cycles without alteration of their structure.

Effects of the chemical structure and the surface properties of polymeric biomaterials on their biocompatibility

Polymeric biomaterials have extensively been used in medicinal applications. However, factors that determine their biocompatibility are still not very clear. This article reviews various effects of the chemical structure and the surface properties of polymeric biomaterials on their biocompatibility, including protein adsorption, cell adhesion, cytotoxicity, blood compatibility, and tissue compatibility. Understanding these aspects of biocompatibility is important to the improvement of the biocompatibility of existing polymers and the design of new biocompatible polymers.

Chitin-based tubes for tissue engineering in the nervous system

The purpose of this study was to investigate chitin and chitosan as potential materials for biodegradable nerve guides. Transparent chitin hydrogel tubes were synthesized, for the first time, from chitosan solutions using acylation chemistry and mold casting techniques. Alkaline hydrolysis of chitin tubes resulted in chitosan tubes, with the extent of hydrolysis controlling the resulting amine content. This, in turn, impacted compressive strength and cell adhesion. Chitosan tubes were mechanically stronger than their chitin origins, as measured by the transverse compressive test, where tubes having degrees of acetylation of 1%, 3%, 18% (i.e. chitosan) and 94% (i.e. chitin) supported loads at a 30% displacement of 40.6 +/- 4.3, 25.3 +/- 4.5, 10.6 +/- 0.8, and 8.7 +/- 0.4 g, respectively. However, the chitin processing methodology could be optimized for compressive strength, by either incorporating reinforcing coils in the tube wall, or air-drying the hydrogel tubes. Chitin and chitosan supported adhesion and differentiation of primary chick dorsal root ganglion neurons in vitro. Chitosan films showed significantly enhanced neurite outgrowth relative to chitin films, reflecting the dependence of nerve cell affinity on the amine content in the polysaccharide: neurites extended 1794.7 +/- 392.0 microm/mm(2) on chitosan films vs. 140.5 +/- 41.6 microm/mm(2) on chitin films after 2 days of culture. This implies that cell adhesion and neurite extension can be adjusted by amine content, which is important for tissue engineering in the nervous system. The methods for easy processing and modification of chitin and chitosan described herein, allow the mechanical properties and cyto-compatibility to be controlled and provide a means for a broader investigation into their use in biomedical applications.