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Results for “Hydrogels”

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At least 109 records · Page 6Linked to original sources

PubMed2005

Corneal epithelial cell growth over tethered-protein/peptide surface-modified hydrogels.

In this study, we investigated the corneal epithelial cell growth rate and adhesion to novel hydrogels with (1) extracellular matrix proteins [fibronectin, laminin, substance P, and insulin-like growth factor-1 (IGF-1)] and (2) peptide sequences [RGD and fibronectin adhesion-promoting peptide (FAP)] tethered to their surface on poly(ethylene glycol) (PEG) chains. The growth rate to confluence of primary rabbit cornea epithelial cells was compared for plain polymethacrylic acid-co-hydroxyethyl methacrylate (PHEMA/MAA) hydrogels, PHEMA/MAA hydrogels coated with extracellular matrix proteins or peptides, and PHEMA/MAA hydrogels with tethered extracellular matrix proteins or peptides on the surface. The development of focal adhesions by the epithelial cells grown on the surfaces was determined by F-actin staining. Little to no epithelial cell growth occurred on the plain hydrogel surfaces throughout the 15-day culture period. Of the coated hydrogels, only the fibronectin-coated surfaces showed a significant increase in cell growth compared to plain hydrogels (p < 0.009). However, even these surfaces reached a maximum of only 20% confluence. Laminin, fibronectin adhesion-promoting peptide (FAP), and fibronectin/laminin (1:1) tether-modified hydrogels all achieved 100% confluence by the end of the culture period, although the rates at which confluence was reached differed. F-actin staining showed that focal adhesions were formed for the laminin, FAP, and fibronectin/laminin tether-modified surfaces. The results support the hypothesis that tethering certain extracellular matrix proteins and/or peptides to the hydrogel surface enhances epithelial cell growth and adhesion, compared with that seen for protein-coated or plain hydrogel surfaces.

Animals↗

PubMed2006

Thixotrophy property of hydrogels to evaluate the cell growing on the inside of the material bulk (Amber effect).

The realization of injectable hydrogels is one of the most challenging aims of biomedical research. Most injectable hydrogels are obtained by photopolymerization in situ. A hydrogel which is able to pass through a needle without losing its structure once crosslinked would be of great interest for several biomedical applications. In this work, hyaluronane and alginate-based 50% hydrogels were synthesized, their thixotrophic behavior was verified and their mechanical properties (G' and G'') were determined before and after the passage through the needle. A morphological analysis by scanning electron microscopy (SEM) was also performed in order to evaluate the effect of the passage of the hydrogel through the needle on the morphological structure of the material. The thixotrophic property of these hydrogels is used to realize a cell-containing material that supports cell proliferation and growth permitting in vivo engineering of new tissues. In fact, thixotrophic hydrogel can be sucked together with cell suspension and in this way cells remain entrapped inside the hydrogel structure (Amber effect). A comparison of the cell growth using this technique with the classical seeding technique (cell seeding onto the hydrogel) was performed. A different behavior was found between hyaluronane and alginate-based hydrogels.

Humans↗

PubMed2006

Structural analysis of dextran-based hydrogels obtained chemoenzymatically.

This work reports the results of structural analysis in novel dextran-acrylate (dexT70-VA) hydrogels generated chemoenzymatically. Porous structure as well as hydrogel surface and interior morphologies were evaluated by mercury intrusion porosimetry (MIP), nitrogen adsorption (NA), and scanning electron microscopy (SEM) analyses, as a function of the degree of substitution (DS), and initial water content used in the preparation of the hydrogel. MIP analysis showed that the overall networks were clearly macroporous with pore sizes ranging from 0.065 to 10 microm. As expected, the average pore size decreased as DS increased and as initial water content decreased. Moreover, the porosity values ranged from 75 up 90%, which shows that these hydrogels present an interconnected pore structure. Nitrogen adsorption analyses showed that the specific surface area of dexT70-VA hydrogels increased either by increasing the DS or by decreasing the initial water content of the hydrogel. SEM results revealed that the surface of hydrogels with lower DS presented either a porous structure or a polymeric "skin" covering the pores, whereas hydrogels with higher DS were totally porous. Furthermore, the interior morphology varied according to the DS and the initial water content of the hydrogels. Finally, the average pore size was also determined from the swelling of hydrogel using a theoretical model developed by Flory-Rehner. The comparison of the SEM and MIP results with the ones obtained by the equilibrium swelling theory of Flory-Rehner shows that this approach highly underestimates the average pore size.

Biocompatible Materials↗

PubMed2004

Preparation and characterization of novel physically cross-linked hydrogels composed of poly(vinyl alcohol) and amine-terminated polyamidoamine dendrimer.

Poly(vinyl alcohol) (PVA) and polyamidoamine (PAMAM) dendrimers are water-soluble, biocompatible and biodegradable polymers, which have been widely applied in biomedical fields. In this paper, novel physically cross-linked hydrogels composed of PVA and amine-terminated PAMAM dendrimer G6-NH(2) were prepared by cyclic freezing/thawing treatment of aqueous solutions containing PVA and G6-NH(2). The FT-IR analysis and elemental analysis indicated that PAMAM dendrimer G6-NH(2) was successfully introduced into the formed hydrogels, possibly via hydrogen bonds among hydroxyl groups, amide groups and amino groups in PVA and PAMAM dendrimer in the process of freezing-thawing cycle. Compared with physically cross-linked PVA hydrogel, PVA/G6-NH(2) hydrogels show higher swelling ratios and faster re-swelling rate due to the higher hydrophilicity of PAMAM dendrimer G6-NH(2). Higher contents of G6-NH(2) in PVA/G6-NH(2) hydrogels resulted in higher swelling ratios and faster re-swelling rates. With increasing freezing/thawing cyclic times, the swelling ratios and re-swelling rates of PVA/G6-NH(2) hydrogels decreased, which is similar to that of physically cross-linked PVA hydrogel. Combining the special host property of polyamidoamine dendrimer, these novel physically cross-linked hydrogels are expected to have potential use in drug delivery, including improving drug-loading amounts in hydrogels and prolonging drug release time. Swelling ratios of physically cross-linked PVA/G6-NH(2)-50 hydrogels prepared by three, six, nine freezing/thawing cycles. The swelling equilibrium experiments were carried out in distilled water at 25 degrees C.

Biocompatible Materials↗

PubMed2004

Long-term retention of endoscopically placed hydrogel prostheses at the lower esophageal sphincter in pigs.

BACKGROUND: Using flexible endoscopic methods, hydrogel prostheses can be safely placed, retained for long periods of time, and removed from the esophageal submucosa of pigs. This new technique may have future applications in the treatment of gastroesophageal reflux disease in selected situations. METHODS: In a controlled, prospective trial, farm pigs ( n = 28) or Sinclair mini-swine ( n = 18) underwent sequential placements of 2-13 pliable, radio-opaque hydrogel prostheses into the submucosa of the esophagus during a single endoscopy session. A novel endoscope-overtube device was used. Followup endoscopy and/or fluoroscopy sessions were video-recorded at 6-week, 12-week, 6-month, and yearly intervals. The endoscopic removal of hydrogels was tested in vivo. Necropsy specimens were inspected for signs of chronic inflammation. RESULTS: Overall, 98% of delivery attempts were successful (288/293). Only three hydrogels were lost after 6 weeks. Short-term animals ( n = 36) retained 88% of hydrogels for periods up to 6 months. Intact hydrogels ( n = 12) were easily removed from four animals at endoscopy. Long-term subjects had two or three hydrogels per animal, using either a beveled-needle device (six pigs) or a trocar design (four pigs). Trocar design: nine of nine prostheses retained at 3 years (100%). Needle design: nine of 10 prostheses retained at 3 years (90%). No significant adverse event occurred. Growth curves were similar between groups. All hydrogels remained pliable to gross inspection upon in vivo removal or necropsy. Pathology showed minimal fibrosis and no chronic inflammation. CONCLUSIONS: A novel endoscopic overtube device allows for the successful delivery of multiple hydrogel prostheses with acceptable safety and long term retention rates. These hydrogel prostheses can also be easily removed from the submucosal space of the esophagus.

Animals↗

PubMed2006

Bone marrow stem cells and polymer hydrogels--two strategies for spinal cord injury repair.

1. Emerging clinical studies of treating brain and spinal cord injury (SCI) led us to examine the effect of autologous adult stem cell transplantation as well as the use of polymer scaffolds in spinal cord regeneration. We compared an intravenous injection of mesenchymal stem cells (MSCs) or the injection of a freshly prepared mononuclear fraction of bone marrow cells (BMCs) on the treatment of an acute or chronic balloon-induced spinal cord compression lesion in rats. Based on our experimental studies, autologous BMC implantation has been used in a Phase I/II clinical trial in patients (n=20) with a transversal spinal cord lesion. 2. MSCs were isolated from rat bone marrow by their adherence to plastic, labeled with iron-oxide nanoparticles and expanded in vitro. Macroporous hydrogels based on derivatives of 2-hydroxyethyl methacrylate (HEMA) or 2-hydroxypropyl methacrylamide (HPMA) were prepared, then modified by their copolymerization with a hydrolytically degradable crosslinker, N,O-dimethacryloylhydroxylamine, or by different surface electric charges. Hydrogels or hydrogels seeded with MSCs were implanted into rats with hemisected spinal cords. 3. Lesioned animals grafted with MSCs or BMCs had smaller lesions 35 days postgrafting and higher scores in BBB testing than did control animals and also showed a faster recovery of sensitivity in their hind limbs using the plantar test. The functional improvement was more pronounced in MSC-treated rats. In MR images, the lesion populated by grafted cells appeared as a dark hypointense area and was considerably smaller than in control animals. Morphometric measurements showed an increase in the volume of spared white matter in cell-treated animals. In the clinical trial, we compared intraarterial (via a. vertebralis, n=6) versus intravenous administration of BMCs (n=14) in a group of subacute (10-33 days post-SCI, n=8) and chronic patients (2-18 months, n=12). For patient follow-up we used MEP, SEP, MRI, and the ASIA score. Our clinical study revealed that the implantation of BMCs into patients is safe, as there were no complications following cell administration. Partial improvement in the ASIA score and partial recovery of MEP or SEP have been observed in all subacute patients who received cells via a. vertebralis (n=4) and in one out of four subacute patients who received cells intravenously. Improvement was also found in one chronic patient who received cells via a. vertebralis. A much larger population of patients is needed before any conclusions can be drawn. The implantation of hydrogels into hemisected rat spinal cords showed that cellular ingrowth was most pronounced in copolymers of HEMA with a positive surface electric charge. Although most of the cells had the morphological properties of connective tissue elements, we found NF-160-positive axons invading all the implanted hydrogels from both the proximal and distal stumps. The biodegradable hydrogels degraded from the border that was in direct contact with the spinal cord tissue. They were resorbed by macrophages and replaced by newly formed tissue containing connective tissue elements, blood vessels, GFAP-positive astrocytic processes, and NF-160-positive neurofilaments. Additionally, we implanted hydrogels seeded with nanoparticle-labeled MSCs into hemisected rat spinal cords. Hydrogels seeded with MSCs were visible on MR images as hypointense areas, and subsequent Prussian blue histological staining confirmed positively stained cells within the hydrogels. 4. We conclude that treatment with different bone marrow cell populations had a positive effect on behavioral outcome and histopathological assessment after SCI in rats; this positive effect was most pronounced following MSC treatment. Our clinical study suggests a possible positive effect in patients with SCI. Bridging the lesion cavity can be an approach for further improving regeneration. Our preclinical studies showed that macroporous polymer hydrogels based on derivatives of HEMA or HPMA are suitable materials for bridging cavities after SCI; their chemical and physical properties can be modified to a specific use, and 3D implants seeded with different cell types may facilitate the ingrowth of axons.

Animals↗

PubMed2006

Thermoresponsive gelatin/monomethoxy poly(ethylene glycol)-poly(D,L-lactide) hydrogels: formulation, characterization, and antibacterial drug delivery.

PURPOSE: The primary objective of this study was to prepare novel thermoresponsive binary component hydrogels composed of gelatin and monomethoxy poly(ethylene glycol)-poly(D,L-lactide) (MPEG-PDLLA) diblock copolymer and to obtain optimal formulations capable of forming gels upon a narrow temperature range between body temperature and room temperature. METHODS: MPEG-PDLLA diblock copolymers with a lower critical solution temperature (LCST) feature were synthesized by using a ring-opening polymerization method. The starting weight ratio of MPEG/DLLA was varied to obtain a series of copolymers with a wide range of molecular weight and hydrophilicity. The copolymers were characterized by 1H nuclear magnetic resonance (1H NMR) and thermogravimetric analysis. MPEG (2K)-PDLLA (1:4) was chosen to construct hydrogels with gelatin. To obtain optimal thermoresponsive formulation, various hydrogels were formulated and quantified in terms of sol-gel phase transition kinetics and rheological properties. Selected hydrogels were studied as drug carrier for gentamicin sulfate. RESULTS: Gelatin/MPEG-PDLLA hydrogels underwent gelation in less than 15 min when 30 wt.% MPEG (2K)-PDLLA (1:4) was mixed with 10, 50, or 100 mg/mL gelatin. Hydrogels showed rapid gelation when 100 mg/mL gelatin was mixed with 15, 20, or 25 wt.% MPEG-PDLLA as temperature fell from 37 degrees C to room temperature. The viscosity of hydrogels depended on the frequency applied in the rheological tests, the environment temperature, and the concentration of both polymer components. The time needed for 50% gentamicin sulfate release was 5 days or longer at room temperature, and the release lasted up to 40 days. 1H NMR confirmed that MPEG-PDLLA hydrolyzed under in vitro situations. CONCLUSIONS: The incorporation of a second polymer component MPEG-PDLLA into the gelatin hydrogel could modify the thermal characteristic of gelatin and the resulting binary component hydrogels obtained different thermal characteristics from the individual polymer components. Formulation of gelatin/MPEG-PDLLA hydrogels could be varied for obtaining such gels that can undergo gelation promptly upon a narrow temperature change.

Anti-Bacterial Agents↗

PubMed2006

Biological functionalization and surface micropatterning of polyacrylamide hydrogels.

Hydrogels are useful for linking proteins to solid surfaces because their hydrophilic nature and porous structure help them to maintain these labile molecules in the native functional state. We have developed a method for creating surface-patterned, biofunctionalized hydrogels on glass or silicon, using polyacrylamide and the disulfide-containing polyacrylamide crosslinker, bis(acryloyl)cystamine. Treatment with a reducing agent created reactive sulfhydryl (-SH) groups throughout these hydrogels that were readily conjugated to iodoacetyl biotin and streptavidin (SA). Immobilization efficiency was approximately 1-2% of the total potential binding capacity of the hydrogel. Porosity of the hydrogel was not a limiting factor for SA immobilization, as determined using fluorescence confocal microscopy. Rather, steric hindrance due to the binding of SA decreased the effective porosity near the surface of the hydrogel, restricting access to the rest of the gel. Using microcontact printing, we indirectly patterned SA on the surface of the hydrogel, generating well-resolved feature sizes of 2 microm in width. Through repeated rounds of microcontact printing, multiple, adjacent protein patterns were generated on the surface of the hydrogel. Biotinylated immune complexes and lipid vesicles readily bound to SA-functionalized hydrogels, demonstrating the feasibility of using this hydrogel system to generate complex biofunctionalized surfaces.

Acrylic Resins↗

PubMed2006

Enzyme-degradable phosphorylcholine porous hydrogels cross-linked with polyphosphoesters for cell matrices.

Biodegradable highly porous hydrogels composed of poly [2-methacryloyloxyethyl phosphorylcholine (MPC)] cross-linked with polyphosphoesters have been prepared as novel cellular matrices. Well-controlled porous hydrogels were fabricated by using potassium hydrogen carbonate as a porogen salt for forming gas. This process enabled the homogeneous expansion of pores within the polymer hydrogel matrices, leading to well-interconnected high porosity. The mechanical properties of the hydrogels were influenced by the cross-linking density and porous structure. Hydrolysis and enzymatic digestion of the hydrogels were determined under basic conditions. The cross-linking density and porosity influenced the rate of degradation of the hydrogels. Acceleration of the degradation with alkaline phosphatase was also observed. Cultivation of mouse osteoblastic cell (MC3T3-E1) was performed in the highly porous hydrogels and cell viability was well maintained. The rate of cell proliferation also was relatively increased with an increase in the amount of polyphosphoesters in the hydrogel. Basic fibroblast growth factor (bFGF) was physically absorbed by the hydrogels and effectively induced cell proliferation. In conclusion, the porous hydrogels prepared in this study contributed a suitable environment for three-dimensional cell cultivation and may be useful for cell and tissue matrices.

3T3 Cells↗

PubMed2004

In vivo anti-tumor effect of dual release of cisplatin and adriamycin from biodegradable gelatin hydrogel.

The objective of this paper is to investigate the in vivo anti-tumor effect by dual release of cisplatin (CDDP) and adriamycin (ADM) from a biodegradable hydrogel. Hydrogels with different water contents were prepared through the chemical crosslinking of gelatin by various concentrations of glutaraldehyde. Aqueous solution of CDDP, ADM or their mixture (CDDP+ADM) was impregnated into the freeze-dried hydrogel, followed by air-drying to obtain the dried hydrogel incorporating the corresponding drug. Irrespective of the hydrogel water content, 8-20% of CDDP incorporated and 60-80% of ADM was released from the hydrogel in the phosphate-buffered saline solution (PBS) at 37 degrees C within the initial 6 h and thereafter little release was observed. When intratumorally applied into mice carrying a mass of Meth-AR-1 tumor cells, the hydrogel incorporating CDDP+ADM showed significant higher anti-tumor effect on the tumor growth suppression and on survival period than other drug applications. Combination effect assay revealed that the hydrogel incorporating CDDP+ADM showed a synergistic effect between the CDDP and ADM, while the solution form showed antagonistic. The concentration of CDDP and ADM in the tumor tissue maintained at higher levels over 14 days after application. The time course of in vivo CDDP retention was in a good accordance with that of hydrogel remaining, whereas ADM was released faster, followed by the sustained release for 14 days. No practically problematic change in the mouse body and blood biochemical parameters was observed by application of the hydrogel incorporating CDDP+ADM. We conclude that dual sustained release of CDDP and ADM attached to the tumor synergistically enhanced their in vivo anti-tumor effect through the trans-tissue delivery.

Animals↗

PubMed2003

Quantification of ligand surface concentration of bulk-modified biomimetic hydrogels.

This study describes a method for the quantification of active ligand surface concentration for bulk-modified hydrogels. Two poly(propylene fumarate-co-ethylene glycol) (P(PF-co-EG)) block copolymers were synthesized with terminal poly(ethylene glycol) (PEG) chains of number average molecular weight 1960 and 5190 g/mol. Hydrogels were synthesized with bulk-modified biotin as a model ligand, making use of a PEG spacer arm with a molecular weight of 3400 g/mol. Bulk concentration of biotin was calculated from the initial concentration of biotin, sol fraction, equilibrium water content, and relative incorporation of the polymers to the hydrogel. Surface concentration of biotin bulk-modified hydrogels was quantified with an enzyme linked immunosorbent assay using mouse monoclonal anti-biotin antibody (IgG), horseradish peroxidase-conjugated anti-mouse IgG, and a chemiluminescent substrate. The larger size of the IgG relative to the mesh size of the hydrogels allowed for the quantification of the active biotin at the surface of the hydrogels. Luminescent imaging was used to qualitatively show the isolation of the horseradish peroxidase-conjugated antibodies to the surface of the bulk-modified hydrogel. The active biotin ligands at the surface of hydrogels synthesized with terminal PEG chains of 1960 g/mol were at the top 7.2 nm while for those synthesized with terminal PEG chains of 5190 g/mol were at the top 4.4 nm of the bulk-modified hydrogel. The relationship between bulk ligand concentration and the active ligand concentration at the surface was dependent on the hydrogel composition. The relative magnitude of the PEG spacer arm of the ligand compared to the PEG block length of the copolymer affected the surface availability of the ligand. The results suggest that steric hindrances caused by mobile PEG chains of the copolymer of molecular weight greater than that of the PEG spacer arm contributed to the decreased surface concentration of ligand. This work relates the bulk concentration of a ligand to its surface concentration, an important parameter for the adhesion, migration, and function of anchorage dependent cells.

Biomimetic Materials↗

PubMed2003

Degradation of phospholipid polymer hydrogel by hydrogen peroxide aiming at insulin release device.

The purpose of this study is to ascertain the applicable possibility of H(2)O(2) degradable hydrogel for fabrication of insulin release system synchronized with the change in the glucose concentration in the medium. The hydrogel was prepared by using 2-methacryloyloxyethyl phosphorylcholine (MPC) and crosslinker. The favorable characteristic of the hydrogel was H(2)O(2) concentration responsive degradation. The H(2)O(2) was utilized and produced by enzymatic reaction between glucose oxidase and glucose. Poly(MPC) (PMPC) was easily degraded in H(2)O(2) aqueous solution, and the PMPC hydrogel was also degraded in H(2)O(2) aqueous solution. The degradation mechanism was considered to be main chain scission of PMPC. The degradation profile was evaluated by using weight swelling ratio and volume swelling ratio. The weight swelling ratio of PMPC hydrogel firstly increased due to the reduction of crosslink density, then the ratio decreased to zero (complete degradation). The degradation profile was proportional to the H(2)O(2) concentration. Furthermore, volume swelling ratio also increased, and complex elastic modulus decreased with degradation in H(2)O(2) aqueous solution. These results indicated that the hydrogel was degraded by hydroxy and/or hydroperoxy radicals which was produced by H(2)O(2), the crosslink density and mechanical property decreased. The release profile from the hydrogel was estimated by using lipid microsphere (LM) as an insulin model. The LM was released with the degradation of PMPC hydrogel. Taking these results into account, the PMPC hydrogel was available for H(2)O(2) degradable hydrogel for synchronization with glucose concentration by using enzymatic reaction.

Absorbable Implants↗

PubMed2003

In vivo release and gene expression of plasmid DNA by hydrogels of gelatin with different cationization extents.

The objective of this paper is to investigate the in vivo release and gene expression of lacZ plasmid DNA (pSV-lacZ) by the hydrogels of cationized gelatin. Gelatin with different cationization extents was prepared by changing the amount of ethylenediamine added to aminize the carboxyl groups of gelatin with a water-soluble carbodiimide. The cationized gelatin prepared was crosslinked by various concentrations of glutaraldehyde (GA) to obtain cationized gelatin hydrogels with different cationization extents as the release carrier of plasmid DNA. When the cationized gelatin hydrogels incorporating 125I-labeled pSV-lacZ were implanted into the femoral muscle of mice, the radioactivity remaining decreased with time and the retention period was prolonged with an increase in the concentration of GA used for hydrogel preparation. In vivo experiments with 125I-labeled cationized gelatin hydrogels revealed that the higher the GA concentration, the longer the in vivo retention period of radioactivity remaining for every cationized gelatin hydrogel. Only for the hydrogels prepared from gelatin with the aminized percentages of 29.7, 41.6, and 47.8 mol.%, the time profile of pSV-lacZ retention correlated well with that of hydrogel retention. The gene expression by the cationized gelatin hydrogels incorporating pSV-lacZ depended on the aminized percentage of gelatin and was significant at the percentage of 41.6 mol.% or higher. It is possible that the pSV-lacZ was complexed with the degraded fragments of cationized gelatin and released with a positive charge, resulting in enhanced gene expression. We conclude that gelatin with a cationization extent of at least 41.6 mol.% is needed for the enhanced in vivo gene expression of plasmid DNA by the hydrogel release system.

Animals↗

PubMedDate not supplied

Biodegradable polymers from renewable sources: rheological characterization of hemicellulose-based hydrogels.

Hemicellulose-based hydrogels were prepared by radical polymerization of 2-hydroxyethyl methacrylate or poly(ethylene glycol) dimethacrylate with oligomeric hydrosoluble hemicellulose modified with well-defined amounts of methacrylic functions. The polymerization reaction was carried out in water at 40 degrees C using a redox initiator system. The hydrogels were in general elastic, soft, and easily swellable in water. Their viscoelastic properties were determined by oscillatory shear measurements on 2 mm thick hydrogels under a slight compression to avoid slip, over the frequency range 10(-1) to 10(2). The rheological characterization indicated that the elastic response of the hydrogels was stronger than the viscous response, leading to the conclusion that the hydrogel systems displayed a predominantly solid-like behavior. The curves showed an increase in shear storage modulus with increasing cross-linking density. The nature of the synthetic comonomer in the hemicellulose-based hydrogels also influenced the shear storage modulus. Comparison of hemicellulose-based hydrogels with pure poly(2-hydroxyethyl methacrylate) hydrogels showed that their behaviors were rather similar, demonstrating that the synthetic procedure made it possible to prepare hemicellulose-based hydrogels with properties similar to those of pure poly(2-hydroxyethyl methacrylate) hydrogels.

Biodegradation, Environmental↗

PubMed2005

Fibrous crystalline hydrogels formed from polymers possessing a linear poly(ethyleneimine) backbone.

Novel thermoreversible physical hydrogels formed from polymers with linear and star architectures possessing a linear poly(ethyleneimine) (PEI) backbone have been investigated. The hydrogelation occurred simply upon natural cooling of hot aqueous solutions of PEIs to room temperature. The X-ray diffraction and differential scanning calorimetry measurements for the resultant hydrogels unambiguously indicated that the hydrogelation originated from the formation of dihydrate crystalline structures of PEI. These crystalline hydrogels are structurally unique and hierarchical. Microscopic images revealed that the morphologies of the crystalline hydrogels depend on their molecular architectures. The linear PEI resulted in branched fibrous bundles organized by unit crystalline nanofibers with a width of ca. 5-7 nm. The six-armed star with benzene ring core produced fanlike fibrous bundles while the four-armed star with porphyrin core assembled into asterlike aggregates. The critical concentration of gelation (C(G)) was low (about 0.2 approximately 0.3%) and the thermoreversible gel-sol transition temperatures (T(G)) were controllable from approximately 43 to approximately 79 degrees C. The hydrogels formed in the presence of the various aqueous additives including organic solvents, hydrophilic polymers, physical cross-linker, chemical cross-linker, and base enabling modification and functionalization during synthesis. The mechanical properties of the hydrogels could be improved by chemical cross-linking of preformed hydrogels by glutaraldehyde. Physically and physical/chemical cross-linked hydrogels served as excellent template roles in biomimetic silicification, which produced silica-PEI hybrid powder or monolith constructed by nanofibers.

Ammonia↗

PubMedDate not supplied

Polyacrylamide-chitosan hydrogels: in vitro biocompatibility and sustained antibiotic release studies.

Controlled drug delivery is gaining importance over the conventional methods of drug administration because of its inherent benefits. Self-regulated release from the delivery vehicle may enhance drug potency with a sustained action. The present study describes a novel hydrogel blend of polyacrylamide with chitosan for controlled delivery of antibiotics. Hydrogel was synthesized by cross-linking acrylamide-chitosan mixture (8:2 v/v) with N,N' methylene bisacrylamide. Hydrogel was characterized for surface morphology, hydrophilicity, pH-dependent swelling properties, cytotoxicity, and control release properties. Scanning electron microscopy (SEM) revealed the macroporous surface morphology of the matrix with average pore size at 104 +/- 7.61 mu. Hydrogel was found to be highly hydrophilic as assessed by octane contact angle (154.5 + 0.572) measurement. Hydrogel showed no cytotoxic effects on NIH3T3 and HeLa cells up to 40% of extract concentrations as determined by MTT and neutral red assay. This showed hydrogel biocompatibility and thus absence of deleterious effects of the hydrogel on cell viability and functionality. Hydrogels did not show any pH-dependent swelling profile, and they swelled considerably to achieve a swelling ratio of approximately 16.0 at the end of 24 hr. Amoxicillin was incorporated in the hydrogel matrix as a candidate antibiotic for release studies. In vitro release studies of amoxicillin revealed the sustained nature of delivery and matrix released 56.47 + 1.12% and 77.096 + 1.72% of amoxicillin at the end of 24 and 75 hr, respectively. Although in vivo studies are awaited, the present study provides enough documentation to consider polyacrylamide-chiotsan hydrogel as a possible candidate for controlled delivery of antibiotics.

3T3 Cells↗

PubMed1977

Bile salts secretion in cirrhosis.

The bile salts secretion was studied in ten normal subjects and sixteen patients with alcoholic cirrhosis, in a basal period and during 60 minutes after Secretin injection. Total bile salts were measured by a modification of the enzymatic method of Iwata and Yamasaki and the individual bile salts were separated by silica gel thin-layer chromatography. During the 60 minutes after Secretin the mean concentration was 2.88 +/- 2.58 muM/ml in normals and 1.96 +/- 1.25 muM/ml in cirrhotics. The difference is not significant. During the first 20 minutes however the concentration was higher than 3 muM/ml in 8 out of 10 normals and lower than 2 muM/ml in 10 out 16 cirrhotics. The ratios of tri-to dihydroxy bile salts was similar in both groups. The ratios between bile salts conjugated with glycine and with taurine was higher in normals, and the ratio between free to conjugated bile salts was higher in cirrhotics. The lower concentration of total bile salts immediatly after Secretin, the higher proportion of taurin conjugates and of free bile salts could be important factors in the difficulties of fact digestion and absorption frequently found in patients with alcoholic cirrhosis.

Adult↗

PubMedDate not supplied

Acceleration of wound healing in healing-impaired db/db mice with a photocrosslinkable chitosan hydrogel containing fibroblast growth factor-2.

Application of ultraviolet light irradiation to a photocrosslinkable chitosan (Az-CH-LA) aqueous solution including fibroblast growth factor-2 (FGF-2) results within 30 seconds in an insoluble, flexible hydrogel. The FGF-2 molecules retained in the chitosan hydrogel remain biologically active and are released from the chitosan hydrogel upon in vivo biodegradation of the hydrogel. To evaluate the accelerating effect on wound healing of this hydrogel, full-thickness skin incisions were made in the backs of healing-impaired diabetic (db/db) mice and their normal (db/+) littermates. The mice were later killed, and histological sections of the wound were prepared. The degree of wound healing was evaluated using several histological parameters such as the rate of contraction, epithelialization, and tissue filling. Application of the chitosan hydrogel significantly advanced the rate of contraction on Days 0 to 2 in db/db and db/+ mice. Although the addition of FGF-2 into the chitosan hydrogel in db/+ mice had little effect, application of the chitosan hydrogel-containing FGF-2 further accelerated the adjusted tissue filling rate (Days 2 to 4 and Days 4 to 8) in db/db mice. Furthermore, the chitosan hydrogel-containing FGF-2 markedly increased the number of CD-34-positive vessels in the wound areas of db/db mice on Day 4. Thus, the application of chitosan hydrogel-containing FGF-2 onto a healing-impaired wound induces significant wound contraction and accelerates wound closure and healing.

Administration, Topical↗