In vitro and in vivo biocompatibility of chitosan-xanthan polyionic complex

In vitro and in vivo evaluation on the bioactivity of ZnO containing nano-hydroxyapatite/chitosan cement

A ZnO containing nano-hydroxyapatite/chitosan (n-HA/CS) cement was developed and its bone formation ability was investigated in vitro and in vivo. The physico-chemical properties of the cement were determined in terms of pH variation during and after setting, injectability and wettability. The results indicated that, the pH varied from 7.04 to 7.12 throughout the soaking of the cement in distilled water. The injectability was excellent during the first 4 min, but the cement became less injectable or even not injectable at all after 7 min setting. The static contact angle of the cement against water was 53.5 +/- 2.7 degrees . The results of immersion tests in simulated body fluid (SBF) indicated that the cement exhibited excellent bone-like apatite forming ability. In vivo studies, involving the installation of the cement of tibial-bone defects in rabbit tibia revealed an inflammatory response around the cement at 3 days of implantation. After 4 weeks, the inflammation began to disappear and the cement had bound to the surrounding host bone. Radiological examination also confirmed that the ZnO containing n-HA/CS cement significantly induced new bone formation. These results suggest that the ZnO containing n-HA/CS cement may be beneficial to enhance bone regeneration in osseous defect sites.

Complex nanoparticles based on chitosan and ionic/nonionic strong polyanions: formation, stability, and application

Interpolyelectrolyte complex (IPEC) nanoparticles formed between chitosan having different molar masses (470, 670, and 780 kDa) and two random copolymers of 2-(acrylamido)-2-methylpropanesulfonate (AMPS) with tert-butylacrylamide (TBA) [P(AMPS(54)-co-TBA(46)) and P(AMPS(37)-co-TBA(63))] were prepared by the dropwise addition of polyanion onto the chitosan solution. The effect of polyelectrolyte characteristics and the molar ratio between charges on the morphology of the complex nanoparticles and on their colloidal stability was deeply investigated by turbidimetric titration (optical density at 500 nm), dynamic light scattering, and atomic force microscopy. It was found that the lowest sizes of the IPEC nanoparticles were obtained, with both polyanions, when the chitosan having the lowest molar mass (470 kDa) was used as a major component. In this case, the particle sizes varied in a narrow range, even after the complex stoichiometry; i.e., when the polyanion was added in excess, the colloidal stability of these IPEC dispersions was very high. A mechanism of complex formation as a function of the ratio between charges was proposed. According to this mechanism, the nonstoichiometric complex nanoparticles formed at molar ratios between charges, n(-)/n+, lower than 0.2, i.e., far from the complex stoichiometry, would have a high density of positive charges in excess not only because of the chitosan in excess, which forms the shell, but also because of the mismatch of opposite charges, due to both the differences in the flexibility of complementary polyions and the presence of the hydrophobic comonomer, TBA, in the polyanion structure. Nonstoichiometric IPECs prepared at n(-)/n+ around 0.2 proved to be more efficient than chitosan in the destabilization of kaolin from a model suspension, with a lower optimum concentration flocculation and a much larger flocculation window being found compared with chitosan.

In vitro models in biocompatibility assessment for biomedical-grade chitosan derivatives in wound management

One of the ultimate goals of wound healing research is to find effective healing techniques that utilize the regeneration of similar tissues. This involves the modification of various wound dressing biomaterials for proper wound management. The biopolymer chitosan (beta-1,4-D-glucosamine) has natural biocompatibility and biodegradability that render it suitable for wound management. By definition, a biocompatible biomaterial does not have toxic or injurious effects on biological systems. Chemical and physical modifications of chitosan influence its biocompatibility and biodegradability to an uncertain degree. Hence, the modified biomedical-grade of chitosan derivatives should be pre-examined in vitro in order to produce high-quality, biocompatible dressings. In vitro toxicity examinations are more favorable than those performed in vivo, as the results are more reproducible and predictive. In this paper, basic in vitro tools were used to evaluate cellular and molecular responses with regard to the biocompatibility of biomedical-grade chitosan. Three paramount experimental parameters of biocompatibility in vitro namely cytocompatibility, genotoxicity and skin pro-inflammatory cytokine expression, were generally reviewed for biomedical-grade chitosan as wound dressing.

Protamine sulfate/poly(L-aspartic acid) polyionic complexes self-assembled via electrostatic attractions for combined delivery of drug and gene

In this study, a series of self-assembled polyionic complexes (PICs) were prepared via electrostatic attraction between protamine sulfate (PS) and poly(L-aspartic acid) (PASP) or doxorubicin (DOX)-conjugated PASP (DOX-PASP). The size of the PICs measured by Nano-ZS ZEN3600 was around 200-300 nm at different weight ratios of PS/PASP. Transmission electron microscopy (TEM) showed that PS/PASP PICs displayed a regular spherical shape and no aggregation was observed. The cytotoxicity study indicated that the PICs did not exhibit apparent cytotoxicity in comparison with that of 25 kDa polyethylenimine (PEI). Gel retardation assay indicated that the PICs were able to bind DNA completely when weight ratio of PS/PASP was higher than 2:1. Luciferase assay and green fluorescent protein (GFP) detection were used to confirm that the PICs could be used as efficient non-viral gene vectors and they exhibited comparable transfection efficiency with the one of 25 kDa PEI. Furthermore, confocal laser scanning microscopy as well as suppression activity of DOX-conjugated PICs (DOX-PICs) showed that they could quickly release the loaded DOX into HeLa cells, indicating that PICs can be also used as carriers for combined delivery of drug and gene.

Hydrogels for tissue engineering and delivery of tissue-inducing substances

This manuscript presents hydrogels (HGs) from a tissue engineering perspective being especially written for those who are approaching this field by offering a concise but inclusive review of hydrogel synthesis, properties, characterization methods, and applications.

Properties of sustained release hot-melt extruded tablets containing chitosan and xanthan gum

The aim of this study was to investigate the influence of pH, buffer species and ionic strength on the release mechanism of chlorpheniramine maleate (CPM) from matrix tablets containing chitosan and xanthan gum prepared by a hot-melt extrusion process. Drug release from hot-melt extruded (HME) tablets containing either chitosan or xanthan gum was pH and buffer species dependent and the release mechanisms were controlled by the solubility and ionic properties of the polymers. All directly compressed (DC) tablets prepared in this study also exhibited pH and buffer species dependent release. In contrast, the HME tablets containing both chitosan and xanthan gum exhibited pH and buffer species independent sustained release. When placed in 0.1N HCl, the HME tablets formed a hydrogel that functioned to retard drug release in subsequent pH 6.8 and 7.4 phosphate buffers even when media contained high ionic strength, whereas tablets without chitosan did not form a hydrogel to retard drug release in 0.1N HCl. The HME tablets containing both chitosan and xanthan gum showed no significant change in drug release rate when stored at 40 degrees C for 1 month, 40 degrees C and 75% relative humidity (40 degrees C/75% RH) for 1 month, and 60 degrees C for 15 days.

Biocompatibility of elastin-like polymer poly(VPAVG) microparticles:in vitro andin vivo studies

Poly(L-valine-L-proline-L-alanine-L-valine-L-glycine) (VPAVG) is a new kind of proteinaceous polymer belonging to the Elastin-like family. These polymers are based on the recurrence of certain short peptide monomers that are considered as "building blocks" in the natural elastin. This smart thermoresponsive polymer has the ability to self-associate at physiological temperature to form aggregates with about 60% in water. This ability can be harnessed to prepare microparticles loaded with an active substance. The aim of this report is to evaluate, from the results of the experiment conducted, the biocompatibility of microparticles prepared from poly(VPAVG). We have studied the cytotoxic effects of microparticles, edema formation after subcutaneous injection (1 and 2.5 mg) in rats (n = 6), and also intraocular tolerance after the intravitreal injection of 2.5 mg of poly(VPAVG) microparticles into pigmented rabbits (n = 12). The polymer did not induce any cytotoxicity or nonspecific depression of cellular respiration on macrophages under the range of polymer concentrations investigated in this study (20, 30, 40, and 60 mg/mL). We observed no inflammatory response to microparticles after subcutaneous injection in the hind-paw of rats, with no significant differences between the control group (PBS) and experimental groups. Anterior and posterior segment signs were evaluated after intraocular injection of poly(VPAVG) microparticles. Only a few eyes (2/11) of the experimental group presented inflammation signs at day 28 postinjection. Nevertheless, 45% (5/11) of the eyes receiving microparticles showed tractional retinal detachment. The results observed in this work suggested certain fibroblastic activity induced by poly(VPAVG) microparticles after their intraocular injection.

Tissue reactions of in situ formed dextran hydrogels crosslinked by stereocomplex formation after subcutaneous implantation in rats

In this study, the in vivo biocompatibility of physically crosslinked dextran hydrogels was investigated. These hydrogels were obtained by mixing aqueous solutions of dextran grafted with L-lactic acid oligomers and dextran grafted with D-lactic acid oligomers. Gelation occurs due to stereocomplex formation of the lactic acid oligomers of opposite chirality. Since gelation takes some time, in situ gel formation is possible with this system. A number of sterilization methods was evaluated for their effect on the chemical and physical properties of the hydrogel. It was shown that of the investigated options (filtration, gamma irradiation, dry-heat and autoclaving) dry-heat sterilization was the preferred method to prepare sterile gels suitable for in vivo evaluations. Two types of stereocomplex gels were prepared and implanted subcutaneously in rats. The tissue reaction was evaluated over a period of 30 days. A mild ongoing foreign body reaction was observed characterized by infiltration of macrophages. Giant cells were only scarcely formed and the low numbers of lymphocytes showed that priming of the immune system is hardly involved. Importantly, the gels fully degraded in vivo within 15 days, which is in good agreement with the in vitro degradation behaviour of these gels. In conclusion, stereocomplexed dextran-oligolactic gels showed good biocompatibility which makes them suitable candidates for the design of controlled release devices for pharmaceutically active proteins.

Synthesis and characterization of thermosensitive chitosan copolymer as a novel biomaterial

Novel water-soluble thermosensitive chitosan copolymers were prepared by graft polymerization of N-isopropylacrylamide (NIPAAm) onto chitosan using cerium ammonium nitrate (CAN) as an initiator. The physicochemical properties of the resulting chitosan-g-NIPAAm copolymers were characterized by Fourier transform infrared (FT-IR) spectroscopy, 1H-nuclear magnetic resonance, X-ray diffraction measurement, thermogravimetric analysis (TGA) and solubility test. Sol-gel transition behavior was investigated by the cloud point measurement of the chitosan-g-NIPAAm aqueous solution. The gelling temperature was examined using the vial inversion method. The percentage of grafting (%) and efficiency of grafting (%) were investigated according to concentrations of monomer and initiator. The maximum grafted chitosan copolymer was obtained with 0.4 M NIPAAm and 6 x 10(-3) M CAN. Water-soluble chitosan-g-NIPAAm copolymers were prepared successfully and they formed thermally reversible hydrogel, which exhibits a lower critical solution temperature (LCST) around 32 degrees C in aqueous solutions. A preliminary in vitro cell study showed nontoxic and biocompatible properties. These results suggest that chitosan-g-NIPAAm copolymer could be very useful in biomedical and pharmaceutical applications as an injectable material for cell and drug delivery.

In situ crosslinked biodegradable hydrogels loaded with IL-2 are effective tools for local IL-2 therapy

We investigated the therapeutic efficacy of recombinant human interleukin-2 (rhIL-2)-loaded, in situ gelling, physically crosslinked dextran hydrogels, locally applied to SL2 lymphoma in mice. The physical crosslinking was established by stereocomplex formation between d-lactic acid oligomers and l-lactic acid oligomers grafted separately to dextrans. The stereocomplex hydrogel as described in our manuscript has several favourable characteristics, which enables its use as system for the controlled release of pharmaceutically active proteins. Firstly, the hydrogel system is a physically crosslinked system. In physically crosslinked gels, the use of chemical crosslinking agents is avoided. Such agents can potentially inactivate the protein and can covalently link the protein to the hydrogel network. Secondly, the hydrogel formation takes place at room temperature and physiological pH, and, importantly, in an all-aqueous environment. All factors are important to preserve the three-dimensional structure, and thus the biological activity, of the protein to be entrapped and released from the gels. Thirdly, the gel formation does not occur instantaneously. This means that a liquid formulation can be injected which solidifies after injection (in situ gel formation is possible). Fourthly, no pH drop during degradation is expected during degradation. As a control, free rhIL-2 was administered locally in either a single injection or at five consecutive days. All mice received the same total dose of rhIL-2. The rhIL-2-loaded hydrogels released most IL-2 over a period of about 5 days. The biocompatibility and biodegradability of the gels were excellent, as there were no acute or chronic inflammatory reaction and as the gels were replaced completely by fibroblasts after 15 days. The therapeutic efficacy of rhIL-2-loaded in situ gelled hydrogels is very good, as was demonstrated in DBA/2 mice bearing SL2. The therapeutic effect of a single application of gels loaded with 1 x 10(6) IU rhIL-2 is at least comparable to the therapeutic effect of injection of an equal dose of free rhIL-2. All mice cured with rhIL-2-loaded hydrogels survived a subsequent challenge, rejecting 10(6) intraperitoneal (i.p.) injected SL2 cells. In conclusion, this study demonstrates that in situ gelling, physically crosslinked dextran hydrogels slowly release encapsulated rhIL-2 in such a way that it is intact and biologically and therapeutically active. These hydrogels may greatly enhance the clinical applicability of rhIL-2 immunotherapy as only a single treatment is required and as these hydrogels are completely biodegradable.

Poly (acrylic acid) chitosan interpolymer complexes for stomach controlled antibiotic delivery

The aim of this study was to develop a stomach-specific drug delivery system to increase the efficacy of amoxicillin against Helicobacter pylori. Polyacrylic acid (PAA), chitosan (CS), and amoxicillin (A) were employed to obtain polyionic complexes. The design of the hydrogel delivery system was based on the swellable approach; with a floating feature to prolong the Gastric Residence Time (GRT). The polyionic complex (PAA:CS:A 2.5:5:2) showed a sustained drug release profile in enzyme-free simulated gastric fluid (SGF) and pH 4.0. A pH independent swelling-eroding pattern with adequate maximum swelling ratios of 17.76 and 13.42 was obtained at in SGF and pH 4.0, respectively, with similar eroding profiles in both pH media. This network carrier provides an amoxicillin protective effect towards the hydrolytic degradation in SGF. The in vivo study was performed on healthy volunteers, using the [13C] octanoic acid breath test. The proposed hydrogel showed a prolonged GRT of up to 3 h. The preliminary results from this study suggest that amoxicillin polyionic complexes have potential for improving local antibiotic therapy against H. pylori.

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.

In vitro cytotoxicity evaluation of a 50.8% NiTi single crystal

To our knowledge, the biocompatibility of nickel-titanium (NiTi) single crystals has not been reported. Yet certain orientations of single crystals present several advantages over the polycrystalline form in terms of maximal strain, fatigue resistance, and temperature range of superelasticity. Therefore we tested the in vitro biocompatibility of 50.8% NiTi single crystals in the orientation <001> after four different heat treatments in a helium atmosphere followed by mechanical polishing. The study was performed on the material extracts after immersion of the specimens in cell culture medium (DMEM) for 7 days at 37 degrees C. Cytotoxicity studies were performed on L-929 mouse fibroblasts using the MTT assay. J-774 macrophages were used to assess the potential inflammatory effect of the extracts by IL1-beta and TNF-alpha dosages (sandwich ELISA method). Exposure of L-929 to material extracts did not affect cell viability. In addition, IL1-beta and TNF-alpha secretion was not stimulated after incubation with NiTi extracts compared to the negative controls. These results were predictable since atomic absorption spectroscopy did not detect nickel ions in the extracts with a resolution of 1 ppm. Within the limits of in vitro testing, our results demonstrate that the TiNi(50.8%) single crystals do not trigger a cytotoxic reaction.

Biocompatibility of thermosensitive chitosan-based hydrogels: an in vivo experimental approach to injectable biomaterials

Chitosan, an amino-polysaccharide obtained from the alkaline deacetylation of chitin, presents an interest as a drug vehicle. Indeed, chitosan solutions containing glycerol-2-phosphate (beta-GP) undergo sol-gel transition at a temperature close to 37 degrees C, which make them suitable for the parenteral administration of drugs. However, before using these chitosan derivatives for biomedical applications, it is important to evaluate their biocompatibility, and particularly to test their inflammatory effects. When injected in the hindpaw of the rat, we have shown that: (i) four chitosan/beta-GP solutions tested triggered a non-specific response, with solutions prepared with chitosans of higher deacetylation degrees yielding a lesser inflammatory reaction and (ii) systemic pretreatment of animals with icatibant, apafant and diphenhydramine did not significantly diminish this response; dexamethasone practically abolished it for all solutions and ketanserine only slightly decreased it in one preparation at two different times. In conclusion, it appears that a higher degree of deacetylation of the chitin chain is desirable for superior biocompatibility.

A tissue sealant based on reactive multifunctional polyethylene glycol

A rapidly gelling synthetic tissue sealant was developed from tetra-succinimidyl and tetra-thiol-derivatized polyethylene glycol (PEG). The two reagents were dissolved in aqueous buffers at 20% (w/v) solids and sprayed on the tissue site, with the use of a sprayer/mixer device. Good adhesion to collagen membranes, PTFE grafts, and carotid artery was observed in vitro. In a burst test on collagen membranes with a 2-mm orifice defect, the gel sustained fluid pressures of 125 +/- 36 mm Hg (n = 18), fivefold greater than capillary blood pressure and one-half that observed in hypertension. On 0.4-mm-diameter puncture defects in PTFE grafts, pressures of 390-490 mm Hg were sustained, and on 0.6-0.9-mm puncture defects in carotid arteries, pressures of 490 to 840 mm Hg were sustained. In vitro data corresponded to results in vivo, where bleeding in rabbit arteries was stopped immediately in five out of six trials. A significant reduction in time to hemostasis and blood loss, compared to controls, was observed. Carotid artery and subcutaneous implant data in rabbits showed that the formula was compatible with biological tissue. Rapid gelling and effective sealing were dependent on the presence of active succinimidyl ester and thiol groups on PEG. HPLC and chemical substitution methods were useful in predicting whether batches of derivatized PEG would perform satisfactorily.

In vivo biocompatibility and degradability of a novel injectable-chitosan-based implant

A novel injectable-chitosan-based delivery system with low cytotoxicity was fabricated in the study. The chitosan microspheres with small particle size, low crystallinity and good sphericity were prepared by a spray-drying method followed by treating with a crosslinker. In the study, a naturally occurring crosslinking reagent (genipin), which has been used in herbal medicine and in the production of food dyes, was used to crosslink the chitosan microspheres. The glutaraldehyde-crosslinked counterparts were used as a control. Histological study of the genipin-crosslinked chitosan microspheres injected intramuscularly into the skeletal muscle of a rat model showed a less inflammatory reaction than its glutaraldehyde-crosslinked counterparts. The results of the scanning electron microscopic examination indicated that the glutaraldehyde-crosslinked chitosan microspheres retrieved at 12-week postoperatively were already degraded into a loose and porous structure. However, the degradation of the genipin-crosslinked chitosan microspheres was not significant after 20 weeks of implantation. The results of the study demonstrated that the genipin-crosslinked chitosan microspheres have a superior biocompatibility and a slower degradation rate than the glutaraldehyde-crosslinked chitosan microspheres. Accordingly, the genipin-crosslinked chitosan microspheres may be a suitable polymeric carrier for long-acting injectable drug delivery.

Physically crosslinked dextran hydrogels by stereocomplex formation of lactic acid oligomers: degradation and protein release behavior

Hydrogels, physically crosslinked through stereocomplex formation, were obtained by mixing aqueous solutions of dextran with L-lactic acid grafts and dextran with D-lactic acid grafts. Protein-loaded hydrogels were simply prepared by dissolving the protein in these dextran solutions prior to mixing. It was shown that under physiological conditions the gels are fully degradable. When the gels were exposed to an aqueous buffer solution, they first showed a swelling phase in which their weight increased 2-3 times due to absorption of water, followed by a dissolution phase. The degradation time depended on the composition of the hydrogel, i.e., the number of lactate grafts, the length and polydispersity of the grafts and the initial water content, and varied from 1 to 7 days. Most likely, the degradation of the stereocomplex hydrogel started with hydrolysis of the carbonate ester, which links the lactate graft to dextran. The gels showed a release of the entrapped model proteins (IgG and lysozyme) over 6 days and the kinetics depended on the gel characteristics, such as the polydispersity of the lactate grafts and the initial water content. Lysozyme was mainly released by Fickian diffusion, indicating that its hydrodynamic diameter is smaller than the hydrogel mesh size. On the other hand the release of IgG was governed by diffusion as well as swelling/degradation of the hydrogel. Importantly, the proteins were quantitatively released from the gels and with full preservation of the enzymatic activity of lysozyme, emphasizing the protein-friendly preparation method of the protein-loaded stereocomplex hydrogel.