Physically crosslinked alginate/N,O-carboxymethyl chitosan hydrogels with calcium for oral delivery of protein drugs

In the study, a complex composed of alginate blended with a water-soluble chitosan (N,O-carboxymethyl chitosan, NOCC) was prepared to form microencapsulated beads by dropping aqueous alginate-NOCC into a Ca(2+) solution. These microencapsulated beads were evaluated as a pH-sensitive system for delivery of a model protein drug (bovine serum albumin, BSA). The main advantage of this system is that all procedures used were performed in aqueous medium at neutral environment, which may preserve the bioactivity of protein drugs. The swelling characteristics of these hydrogel beads at distinct compositions as a function of pH values were investigated. It was found that the test beads with an alginate-to-NOCC weight ratio of 1:1 had a better swelling characteristic among all studied groups. With increasing the total concentration of alginate-NOCC, the effective crosslinking density of test beads increased significantly and a greater amount of drug was entrapped in the polymer chains (up to 77%). The swelling ratios of all test groups were approximately the same ( approximately 3.0) at pH 1.2. At pH 7.4, with increasing the total concentration of alginate-NOCC, the swelling ratios of test beads increased significantly (20.0-40.0), due to a larger swelling force created by the electrostatic repulsion between the ionized acid groups (-COO(-)). It was shown that BSA was uniformly distributed in all test beads. At pH 1.2, retention of BSA in hydrogels may be improved by rinsing test beads with acetone (the amount of BSA released was below 15%). At pH 7.4, the amounts of BSA released increased significantly ( approximately 80%) as compared to those released at pH 1.2. With increasing the total concentration of alginate-NOCC, the release of encapsulated proteins was slower. Thus, the calcium-alginate-NOCC beads with distinct total concentrations developed in the study may be used as a potential system for oral delivery of protein drugs to different regions of the intestinal tract.     

Preparation and antibacterial properties of O-carboxymethyl chitosan/lincomycin hydrogels

In this study, O-carboxymethyl chitosan (O-CMCS) was synthesized from chitosan and monochloroacetic acid. Then O-CMCS hydrogel was prepared by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) in which the lincomycin was packaged. The Fourier transform infrared spectrum and scanning electron microscopy were adopted to characterize the structure and morphology of the product. The influences of dosage of EDC/NHS and concentration of O-CMCS on the swelling properties of the hydrogels were investigated. The hydrogels performed good swelling capacities and obvious pH-sensitive properties. The antibacterial activities of the hydrogels were tested against Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus). Compared with pure O-CMCS hydrogels, the antibacterial activities of O-CMCS/lincomycin hydrogels were significantly improved with the increase in the concentration of lincomycin against E. coli and S. aureus. With the increase in dosage of crosslinking agent or concentration of O-CMCS, the antibacterial activities both decreased gradually against the two bacteria. O-CMCS/lincomycin hydrogel was expected to be used for antibacterial material in view of its significant antibacterial activities.     

Non-cytotoxic, in situ gelable hydrogels composed of N-carboxyethyl chitosan and oxidized dextran

A series of in situ gelable hydrogels were prepared from oxidized dextran (Odex) and N-carboxyethyl chitosan (CEC) without any extraneous crosslinking agent. The gelation readily took place at physiological pH and body temperature. The gelation process was monitored rheologically, and the effect of the oxidation degree of dextran on the gelation process was investigated. The higher the oxidation degree of Odex, the faster the gelation. A highly porous hydrogel structure was revealed under scanning electron microscopy (SEM). Swelling and degradation of the Odex/CEC hydrogels in PBS showed that both swelling and degradation were related to the crosslinking density of the hydrogels. In particular, the hydrogels underwent fast mass loss in the first 2 weeks, followed by a more moderate degradation. The results of long-term cell viability tests revealed that the hydrogels were non-cytotoxic. Mouse fibroblasts were encapsulated in the hydrogels and cell viability was at least 95% within 3 days following encapsulation. Furthermore, cells entrapped inside the hydrogel assumed round shape initially but they gradually adapted to the new environment and spread-out to assume more spiny shapes. Additionally, the results from applying the Odex/CEC system to mice full-thickness transcutaneous wound models suggested that it was capable of enhancing wound healing.     

Superporous hydrogels containing poly(acrylic acid-co-acrylamide)/O-carboxymethyl chitosan interpenetrating polymer networks

Superporous hydrogels containing poly(acrylic acid-co-acrylamide)/O-carboxymethyl chitosan interpenetrating polymer networks (SPH-IPNs) were prepared by cross-linking O-carboxymethyl chitosan (O-CMC) with glutaraldehyde (GA) after superporous hydrogel (SPH) was synthesized. The structures of the SPH-IPNs were characterized with FT-IR, 13C-NMR and DSC. SEM, CLSM and light images revealed that the SPH-IPNs possessed both the IPN network and large numbers of pores and the cross-linked O-CMC molecules were located on the peripheries of these pores. The swelling behavior of SPH-IPNs was dependent on the O-CMC content, GA amount and cross-linking time. Due to the cross-linked O-CMC network, in vitro muco-adhesive force and mechanical properties, including compression and tensile modulus, of the SPH-IPN were greatly improved when compared with the CSPH. An enhanced loading capacity for insulin could be obtained by the SPH-IPNs as compared to non-porous hydrogel and CSPH, and more than 90% of the insulin was released within 1 h. With the improved mechanical properties, in vitro muco-adhesive force and loading capacities, the SPH-IPN may be used as a potential muco-adhesive system for peroral delivery of peptide and protein drugs.     

Polyelectroylte complex composed of chitosan and sodium alginate for wound dressing application.

Drug-impregnated polyelectrolyte complex (PEC) sponge composed of chitosan and sodium alginate was prepared for wound dressing application. The morphological structure of this wound dressing was observed to be composed of a dense skin outer layer and a porous cross-section layer by scanning electron microscopy (SEM). Equilibrium water content and release of silver sulfadiazine (AgSD) could be controlled by the number of repeated in situ PEC reactions between chitosan and sodium alginate. The release of AgSD from AgSD-impregnated PEC wound dressing in PBS buffer (PH = 7.4) was dependent on the number of repeated in situ complex formations for the wound dressing. The antibacterial capacity of AgSD-impregnated wound dressing was examined in agar plate against Pseudomonas aeruginosa and Staphylococcus aureus. From the behavior of antimicrobial release and the suppression of bacterial proliferation, it is thought that the PEC wound dressing containing antimicrobial agents could protect the wound surfaces from bacterial invasion and effectively suppress bacterial proliferation. In the cytotoxicity test, cellular damage was reduced by the controlled released of AgSD from the sponge matrix of AgSD-medicated wound dressing. In vivo tests showed that granulation tissue formation and wound contraction for the AgSD plus dihydroepiandrosterone (DHEA) impregnated PEC wound dressing were faster than any other groups.     

Degradation behavior of dextran hydrogels composed of positively and negatively charged microspheres

This paper reports on the degradation behavior of in situ gelling hydrogel matrices composed of positively and negatively charged dextran microspheres. Rheological analysis showed that, once the individual microspheres started to degrade, the hydrogel changed from a mainly elastic to a viscoelastic network. It was shown with gels composed of equal amounts of cationic and anionic microspheres, that both a higher crosslink density of the particles and a decrease in water content of the hydrogels resulted in a slower degradation, ranging from 65 to 140 days. Dispersions containing cationic, neutral or anionic microspheres completely degraded within 30, 55 or 120 days, respectively. The microspheres were loaded with rhodamine-B-dextran and degradation was studied with confocal microscopy and fluorescence spectroscopy. After a lag time of 3 days rhodamine-B-dextran started to release from the positive microspheres with a 50% release after 16 days. In contrast, release of rhodamine-B-dextran from the negative microspheres started after 10 days with a 50% release after 36 days. The faster degradation of the positively charged microspheres as compared to the negatively charged microspheres is attributed to stabilization of the transition state in the hydrolysis process by the protonated tertiary amine groups present in the cationic microspheres. On the other hand, the presence of negatively charged groups causes repulsion of hydroxyl anions resulting in a slower degradation. Combining the oppositely charged microspheres in different ratios makes it possible to tailor the network properties and the degradation behavior of these hydrogels, making them suitable for various applications in drug delivery and tissue engineering.     

Preparation of alginate hydrogels through solution extrusion and the release behavior of different drugs

Homogeneous alginate hydrogels were facilely fabricated through solution extrusion process. CaCO₃ and D-glucono-δ-lactone (GDL) were used as the gelation agents. The slow gelation of alginate was realized by the in-situ release of Ca²⁺ from CaCO₃ particles induced by hydrolysis of GDL to reduce pH. Slight gelation during the extrusion caused the enhanced strength of the alginate solutions, leading to the extrudability of the blends. This method enables to produce alginate hydrogels in a single step via extrusion, which is economically advantageous to conventional lab-scale preparation for mass production. Three different drugs, ibuprofen, acetaminophen, and methylthionine chloride, were used as model drugs to evaluate the drug release behavior of the alginate hydrogels. It was demonstrated that the drug release behavior was significantly adjusted by both the drug solubility and the ionic interaction between alginate and the drug molecule. It was shown that solution extrusion process is a feasible method to produce alginate-based drug delivery systems.     

The tensile properties of alginate hydrogels

Alginate hydrogels are currently being employed and explored for a broad range of medical applications including cell encapsulation, drug delivery, and tissue engineering. In these capacities, knowledge of the mechanical and material properties of the hydrogels and the properties that govern and influence them is necessary to adequately design and effectively use these systems. Although much is known about the mechanical properties of alginate in compression and shear, little is known about the tensile characteristics. Thus, an extensive tensile assessment of alginate hydrogels was completed as a function of alginate type, formulation, gelling conditions, incubation, and strain rate. In general, the initial tensile behavior and properties of alginate hydrogels were highly dependent on the choice of the alginate polymer and how it was processed. Specifically, high guluronic acid containing alginate polymers yielded stronger, more ductile hydrogels than high mannuronic acid containing alginates. The ultimate stress, ultimate strain, and tensile modulus were decreased by increased phosphate concentrations, solution reconstitution with phosphate buffered saline instead of culture media, and peptide modification. Incubation of hydrogels for at least 7 days diminished many of the initial tensile property differences associated with formulation and gelling conditions. Overall, by controlling the specific alginate polymer and processing methods, a wide range of tensile properties are available from these hydrogels.     

Adipose tissue engineering using injectable, oxidized alginate hydrogels

Current treatment modalities for soft tissue augmentation which use autologous grafting and commercially available fillers present a number of challenges and limitations, such as donor site morbidity and volume loss over time. Adipose tissue engineering technology may provide an attractive alternative. This study investigated the feasibility of a degradable alginate hydrogel system with commercially available cryopreserved human adipose stem cells (hADSCs) to engineer adipose tissue. hADSCs were differentiated into adipogenic cells, and encapsulated in alginate hydrogels made susceptible to hydrolysis by partial periodate oxidation of the polymer chains. Cell laden gels were subcutaneously injected into the chest wall of male nude mice, and a cell suspension without alginate served as control. After 10 weeks, specimens were harvested and analyzed morphologically, histologically, and with immunoblotting of tissue extractions. Newly generated tissues were semitransparent and soft in all experimental mice, grossly resembling adipose tissue. Analysis using confocal live imaging, immunohistochemisty and western blot analysis revealed that the newly generated tissue was adipose tissue. This study demonstrates that degradable, injectable alginate hydrogels provide a suitable delivery vehicle for preconditioned cryopreserved hADSCs to engineer adipose tissue.     

Synthesis of pH-sensitive inulin hydrogels and characterization of their swelling properties

In this study, pH-responsive inulin hydrogels were prepared by radical copolymerization of methacrylated inulin (MA-inulin) with acrylic acid (AAc) in aqueous solution using ammonium peroxydisulfate (APS) and N,N,N',N'-tetramethylethylenediamine (TMEDA) as an initiation system. The AAc content in hydrogels was evaluated by FTIR spectroscopy. The covalent bridging of AAc among MA moieties of MA-inulins was observed by a significant increase in the effective network density of hydrogels and further confirmed by TGA studies. While, at a low content of AAc, the hydration of hydrogels at pH 7.4 decreased owing to the increased crosslinking density, the swelling subsequently increased with further increasing AAc as a consequence of the increased ionic osmotic pressure within hydrogels. The change in swelling of hydrogels in response to pH change between 7.4 and 2.2 was therefore enlarged when the AAc content increased.     

Cefepime loaded O-carboxymethyl chitosan microspheres with sustained bactericidal activity and enhanced biocompatibility

Cefepime (CFP) is a frequently used antibiotic for prevention of post-surgery infection. Systemic delivery of CFP in a bulk dose usually shows effective therapeutic effects, while cytotoxicity can also be generated. To avoid the drawback of systemic delivery of antibiotic, local and controlled administration of drug is being employed to prolong therapeutic effects and reduce cytotoxicity by sustaining drug release and minimizing drug exposure. In this work, CFP loaded polymer O-carboxymethyl chitosan (OCMC) microspheres (CFP-OCMC-MPs) were fabricated and their antimicrobial activity against Staphylococcus aureus as well as biocompatibility were evaluated. The microspheres possessed the spherical surface with diameter approximately 7 μm. Fourier transforms infrared spectral and wide-angle X-ray diffraction analysis showed that CFP was steadily incorporated. The drug loading content and encapsulation efficiency of the microspheres were 21.4 ± 0.5% and 42.3 ± 0.7%, respectively. The drug release profiles were found to be biphasic with an initial burst release followed by a gradual release phase, following the Higuchi model. In addition, the CFP-OCMC-MPs were able to kill all the bacteria cultured in suspension within 24 h and exhibited long-lasting bactericidal activity as demonstrated by inhibition zone study. Compared to CFP, CFP-OCMC-MPs showed a milder toxicity toward osteoblast-like cells over an 8 day period. All these results suggest that CFP-OCMC-MPs are endowed with sustained treatment of bacterial infection and enhanced biocompatibility.     

The calcium silicate/alginate composite: Preparation and evaluation of its behavior as bioactive injectable hydrogels

In this study, an injectable calcium silicate (CS)/sodium alginate (SA) hybrid hydrogel was prepared using a novel material composition design. CS was incorporated into an alginate solution and internal in situ gelling was induced by the calcium ions directly released from CS with the addition of d-gluconic acid δ-lactone (GDL). The gelling time could be controlled, from about 30 s to 10 min, by varying the amounts of CS and GDL added. The mechanical properties of the hydrogels with different amounts of CS and GDL were systematically analyzed. The compressive strength of 5% CS/SA hydrogels was higher than that of 10% CS/SA for the same amount of GDL. The swelling behaviors of 5% CS/SA hydrogels with different contents of GDL were therefore investigated. The swelling ratios of the hydrogels decreased with increasing GDL, and 5% CS/SA hydrogel with 1% GDL swelled by only less than 5%. Scanning electron microscopy (SEM) observation of the scaffolds showed an optimal interconnected porous structure, with the pore size ranging between 50 and 200 μm. Fourier transform infrared spectroscopy and SEM showed that the CS/SA composite hydrogel induced the formation of hydroxyapatite on the surface of the materials in simulated body fluid. In addition, rat bone mesenchymal stem cells (rtBMSCs) cultured in the presence of hydrogels and their ionic extracts were able to maintain the viability and proliferation. Furthermore, the CS/SA composite hydrogel and its ionic extracts stimulated rtBMSCs to produce alkaline phosphatase, and its ionic extracts could also promote angiogenesis of human umbilical vein endothelial cells. Overall, all these results indicate that the CS/SA composite hydrogel efficiently supported the adhesion, proliferation and differentiation of osteogenic and angiogenic cells. Together with its porous three-dimensional structure and injectable properties, CS/SA composite hydrogel possesses great potential for bone regeneration and tissue engineering applications.     

Synthesis and characterization of a pH-sensitive hydrogel made of pyruvic-acid-modified chitosan

Pyruvic-acid-type chitosan (PA-CS) was prepared by the reaction of an amine group on chitosan with a carbonyl group on pyruvic acid. Then, a novel hydrogel film was obtained via cross-linking of poly(ethylene glycol) diglycidyl ether (PEGDE) with PA-CS. 1H-NMR and FT-IR spectrometry were applied for the verification of the CS and PA-CS structure. The degree of swelling was studied by changing the molar ratio of PEGDE and PA-CS. Moreover, the swelling ratio of cross-linked membrane in different pH buffer solutions was measured. The result showed that the swelling of hydrogel exhibited obvious pH-sensitivity. The swelling ratio was higher at pH 1-4 and pH 7-12, but lower at pH 5-6.     

Performance and biocompatibility of extremely tough alginate/polyacrylamide hydrogels

Although hydrogels now see widespread use in a host of applications, low fracture toughness and brittleness have limited their more broad use. As a recently described interpenetrating network (IPN) of alginate and polyacrylamide demonstrated a fracture toughness of ∼9000 J/m², we sought to explore the biocompatibility and maintenance of mechanical properties of these hydrogels in cell culture and in vivo conditions. These hydrogels can sustain a compressive strain of over 90% with minimal loss of Young's Modulus as well as minimal swelling for up to 50 days of soaking in culture conditions. Mouse mesenchymal stem cells exposed to the IPN gel-conditioned media maintain high viability, and although cells exposed to conditioned media demonstrate slight reductions in proliferation and metabolic activity (WST assay), these effects are abrogated in a dose-dependent manner. Implantation of these IPN hydrogels into subcutaneous tissue of rats for 8 weeks led to mild fibrotic encapsulation and minimal inflammatory response. These results suggest the further exploration of extremely tough alginate/PAAM IPN hydrogels as biomaterials.     

Dynamic and equilibrium swelling behaviour of pH-sensitive hydrogels containing 2-hydroxyethyl methacrylate

The equilibrium and dynamic swelling behaviour of hydrogels containing methacrylic acid or various acrylamides was studied as a function of copolymer composition. In all cases, the comonomer was 2-hydroxyethyl methacrylate, methyl methacrylate or N-vinyl-2-pyrrolidone. It is shown that pH-sensitive behaviour with a wide range of swelling ratios could be obtained using a range of compositional changes. The dynamic swelling behaviour was a function of the acidity of the buffered solution.     

药物控释用海藻酸钠、壳聚糖、明胶的研究进展

由于许多药物如肽或蛋白质药物,物理化学性质不稳定,在胃肠道中极易降解.因此,在口服释药设计中,pH敏感水凝胶如海藻酸钠、壳聚糖和明胶作为药物控制释放载体日益引起人们的关注.将针对三种天然高分子材料的来源、结构、性能及共混改性展开讨论.     

Preparation,characterization, and in vitro cytotoxicity of chitosan hydrogels containing silver nanoparticles

Hydrogels, chitosan as well as silver nanoparticles become in recent years materials characterized by a great interest. In present paper hydrogel based on chitosan and containing mentioned type of nano-sized particles have been synthesized by means of photopolymerization. Sorption capacity in selected liquids as well as behavior in simulated body fluid (such as Ringer’s liquid) have been determined. Particularly attention was paid to the studies on toxicity of the hydrogels in relation to the epidermal cells as well as on their impact on growth of selected strain of bacteria (Escherichia coli). Furthermore, impact of introduction of nanosilver into hydrogel matrix on its properties has also been defined. Surface morphology of attained hydrogels by means of SEM analysis and chemical structure using spectroscopy have been checked. The most interesting conclusion is the fact that proposed chitosan based hydrogels modified with nanosilver do not affect negatively on epidermal cells. However, they inhibit a growth of E. coli. These two observations make them very interesting from the medical point of view.     

Effect of solvent mixture on the properties of temperature- and pH-sensitive polysaccharide-based hydrogels

Novel partially biodegradable, temperature- and pH-sensitive polysaccharide-based hydrogels (NDF) were synthesized from modified dextran (dextran-maleic acid, Dex-MA) and N-isopropylacrylamide precursors over a wide range of mixed solvent ratios of dimethyl formamide (DMF) to water. N-Isopropylacrylamide monomers were chosen to impart thermo-responsive capability to Dex-MA, while Dex-MA was chosen to impart pH-responsive capability to N-isopropylacrylamide. The pH-sensitive precursor (Dex-MA) was synthesized by reacting dextran with maleic anhydride in the presence of triethylamine catalyst. To fabricate multi-stimuli hybrid hydrogel networks, both Dex-MA and N-isopropylarylamide precursors were photo-cross-linked via UV at a fixed Dex-MA to N-isopropylarylamide feed ratio over a wide range of DMF to water mixed solvent ratios. The newly synthesized PNIPAAm/Dex-MA hybrid hydrogels (NDF) were characterized by Fourier transform infrared spectroscopy for chemical structure determination, differential scanning calorimetry for thermal analysis and scanning electron microscopy for morphological study. The properties of the hybrid hydrogels, such as thermo-induced deswelling, pH-sensitivity, ionic strength sensitivity and thermo-reversibility, were also examined. The swelling data obtained clearly showed that newly synthesized multi-stimuli NDF hydrogels exhibited multi-responsive capability to external stimuli like temperature and pH. The morphological data obtained showed that this new class of PNIPAAm/Dex-MA hybrid hydrogels had a wide range of unique three-dimensional porous network structures that depended on the composition ratio of the mixed DMF/water solvent during cross-linking reaction. This unique but versatile 3D porous network structures of NDF hydrogels were correlated to the data from thermo-induced swelling behavior, thermo-reversibility, pH-dependent swelling and ionic strength sensitivity.     

Designing alginate hydrogels to maintain viability of immobilized cells

Hydrogel-forming materials have been widely utilized as an immobilization matrix and transport vehicle for cells. Success in these applications is dependent upon maintaining cell viability through the gel preparation process. We hypothesized that the high viscosity of pre-gelled solutions typically used in these applications may decrease cell viability due to the high shear forces required to mix cells with these solutions. Further, we proposed this harmful effect could be mediated by decreasing the molecular weight (Mw) of the polymer used to form the gel, while maintaining its gel-forming ability. To investigate this hypothesis, alginate was used as model system, as this copolymer consists of cross-linkable guluronic acid (G) blocks and non-cross-linkable blocks. Decreasing the Mw of alginate using irradiation (e.g., irradiating at dose of 2 Mrad) decreased the low shear viscosity of 2% (w/w) pre-gelled solutions from 1000 to 4 cP, while maintaining high elastic moduli, once cross-linked to form a gel. Importantly, the immobilization of cells with these polymer hydrogels increased cell viability from 40% to 70%, as compared to using high Mw polymer chains to form the gels. Furthermore, the solids concentration of gels formed with the low Mw alginate could be raised to further increase the moduli of gels without significantly deteriorating the viability of immobilized cells. This was likely due to the limited increase in the viscosity of these solutions. This material design approach may be useful with a variety of synthetic or naturally occurring block copolymers used to immobilize cells.     

Photocrosslinked alginate hydrogels with tunable biodegradation rates and mechanical properties

Photocrosslinked and biodegradable alginate hydrogels were engineered for biomedical applications. Photocrosslinkable alginate macromers were prepared by reacting sodium alginate and 2-aminoethyl methacrylate in the presence of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride and N-hydroxysuccinimide. Methacrylated alginates were photocrosslinked using ultraviolet light with 0.05% photoinitiator. The swelling behavior, elastic moduli, and degradation rates of photocrosslinked alginate hydrogels were quantified and could be controlled by varying the degree of alginate methacrylation. The methacrylated alginate macromer and photocrosslinked alginate hydrogels exhibited low cytotoxicity when cultured with primary bovine chondrocytes. In addition, chondrocytes encapsulated in these hydrogels remained viable and metabolically active as demonstrated by Live/Dead cell staining and MTS assay. These photocrosslinked alginate hydrogels, with tailorable mechanical properties and degradation rates, may find great utility as therapeutic materials in regenerative medicine and bioactive factor delivery.