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At least 289 records · Page 16Linked to original sources
PubMed2000

Posterior capsular opacification with hydrogel, polymethylmethacrylate, and silicone intraocular lenses: two-year results of a randomized prospective trial.

PURPOSE: To compare the visual outcome, percentage of posterior capsular opacification, and laser capsulotomy rates with polymethylmethacrylate, silicone, and hydrogel intraocular lens implants at 1 and 2 years postoperatively. METHODS: Ninety-three eyes of 93 patients were randomized to receive a polymethylmethacrylate, silicone, or hydrogel intraocular lens implant. A standardized surgical protocol was followed by a single surgeon using phacoemulsification with capsulorhexis; any patients with surgical complications were excluded, and all patients received standardized medication and follow-up. Patients were examined at days 1 and 7, months 1, 3, and 6, and years 1 and 2 after surgery. At each assessment, best-corrected logMAR visual acuity and Pelli-Robson contrast sensitivity were measured. Posterior capsular opacification was objectively assessed by digital retroillumination imaging with the use of a dedicated software program and calculated as the percentage area of opacified capsule. Laser capsulotomy was performed if the eye had lost 2 lines of visual acuity with a clinically opaque capsule. RESULTS: At 2 years postoperatively, the mean percentage area of posterior capsular opacification for hydrogel lenses was 63%; for polymethylmethacrylate, 46%; and for silicone, 17%. Hydrogel intraocular lenses were associated with 17% more posterior capsule opacification than were polymethylmethacrylate lenses (95% confidence interval, 1-33; P =. 037) and 45% more than were silicone lenses (95% confidence interval, 33-58; P <.0001) at 2 years. Polymethylmethacrylate lenses had 28% more posterior capsule opacification than silicone lenses (95% confidence interval, 13-43; P <.0001) at 2 years. Twenty-eight percent of patients with hydrogel intraocular lenses required an Nd:YAG laser posterior capsulotomy at 2 years, compared with 14% with polymethylmethacrylate, whereas no patients with silicone lenses needed a capsulotomy (P =.014). Visual acuity was not significantly different among the three groups, but patients with silicone intraocular lenses had significantly better contrast sensitivity than those with hydrogel lenses (P =.046). CONCLUSIONS: Intraocular lenses made of this specific hydrogel were associated with a significantly higher degree of posterior capsular opacification and more laser capsulotomies than polymethylmethacrylate and silicone intraocular lenses.

Aged↗
PubMed1999

Sealing effect of rapidly curable gelatin-poly (L-glutamic acid) hydrogel glue on lung air leak.

BACKGROUND: Air leak is a problem commonly occurring in lung and thoracic operations. In this study, a rapidly curable hydrogel glue was prepared as the seal for lung air leak. METHODS: Mixing an aqueous solution of gelatin and poly(L-glutamic acid) with a water-soluble carbodiimide produced a hydrogel. The sealing effect on the air leak wound of rat lung was compared with that of conventional fibrin glue. RESULTS: The gelatin-poly(L-glutamic acid) hydrogel glue was solidified as rapidly as the fibrin glue, and was significantly more effective in sealing the lung air leak than the fibrin glue. Approximately 80% of the lungs treated with the hydrogel glue exhibited no air leak at the lung pressure of 50 cm H2O. Urea addition could prevent spontaneous gelatination of the mixed solution at room temperature and did not affect the hydrogel sealing effect. The bonding strength of the hydrogel glue both with and without urea to the lung tissue was significantly higher than that of the fibrin glue. CONCLUSIONS: We concluded that this strong lung adhesion of the gelatin-poly(L-glutamic acid) hydrogel glue resulted in its superior sealing effect.

Animals↗
PubMed2001

Protein release from physically crosslinked hydrogels of the PLA/PEO/PLA triblock copolymer-type.

A series of PLA/PEO/PLA triblock copolymers was prepared by ring opening polymerization of rac-lactide in the presence of various di-hydroxyl poly (ethylene glycol)s, using CaH2 as a biocompatible initiator. Hydrogels were prepared by a phase separation method consisting of introducing small amounts of water over solutions of the copolymers in a biocompatible organic solvent, namely tetraglycol [poly(ethylene glycol monotetrahydrofurfuryl ether)]. The resulting hydrogels appeared much more hydrophilic than the rather tough hydrogels formed by swelling of dry tablets or films processed from the same copolymers. The phase separation-derived hydrogels were soft enough to be injected through a trochar. Two proteins, namely bovine serum albumine (BSA) and fibrinogen, were physically entrapped in these hydrogels by mixing with the polymer solutions before gel formation. This procedure appeared to be protein-respecting according to circular dichroism analysis on the released BSA. Dramatically different release profiles were obtained for the two proteins. In the case of BSA, the release depended on the quantity of protein incorporated in the hydrogel and presented a parabolic-type profile, in agreement with the behaviors of diffusion-controlled monolitic drug delivery devices. In contrast, almost linear release profiles were observed in the case of fibrinogen, the hydrogels behaving like a reservoir drug delivery system. These findings are tentatively interpreted in terms of gel-protein compatibility in the case of BSA and gel-protein incompatibility in the case of fibrinogen.

Hydrogels↗
PubMed2002

Assessment of the cytotoxicity of photocrosslinked dextran and hyaluronan-based hydrogels to vascular smooth muscle cells.

The cytotoxicity of polysaccharide-based hydrogels and solutions was studied in vitro after 48h of indirect exposure of the materials with vascular smooth muscle cells. Dextran and/or hyaluronan were derivatized using glycidyl methacrylate, and hydrogels were formed in the presence of photoinitiators and ultraviolet radiation in multiwell inserts to avoid direct contact with cell monolayers. Observation of cell morphology indicated that dextran hydrogels, a blend of non-derivatized hyaluronan into dextran hydrogel. and a hyaluronan solution were highly cytocompatible. However, hydrogels made of derivatized hyaluronan were cytotoxic when compared to unexposed sham controls that contained multiwell inserts but no hydrogels. Results from quantitative assays for proliferation and viability corroborated the qualitative observations, and scrape wound assays revealed a significant increase in smooth muscles cell migration/proliferation after indirect exposure to several of the polysaccharide-based materials. Results from this study demonstrate that hydrogels made of dextran and hyaluronan solution show good cytocompatibility in vitro. making these degradable matrices interesting candidates for drug delivery purposes.

Animals↗
PubMed2002

Photopolymerizable hydrogels for tissue engineering applications.

Photopolymerized hydrogels are being investigated for a number of tissue engineering applications because of the ability to form these materials in situ in a minimally invasive manner such as by injection. In addition, hydrogels, three-dimensional networks of hydrophilic polymers that are able to swell large amounts of water, can be made to resemble the physical characteristics of soft tissues. Hydrogel materials also generally exhibit high permeability and good biocompatibility making, these materials attractive for use in cell encapsulation and tissue engineering applications. A number of hydrogel materials can be formed via photopolymerization processes mild enough to be carried out in the presence of living cells. This allows one to homogeneously seed cells throughout the scaffold material and to form hydrogels in situ. This review presents advantages of photopolymerization of hydrogels and describes the photoinitiators and materials in current use. Applications of photopolymerized hydrogels in tissue engineering that have been investigated are summarized.

Animals↗
PubMed2002

Hyaluronic acid hydrogel in the treatment of osteoarthritis.

In order to overcome the problem of rapid clearance of the polysaccharide hyaluronic acid (Hyal) in the treatment of osteoarthritis (OA), a 50% cross-linked Hyal hydrogel (Hyal 50%) was synthesised. The 50% refers to the amount of COOH groups of the polysaccharide involved in the cross-linking reaction. i.e. 50% of the total amount. The rheological behaviour of the Hyal 50% hydrogel, and in particular the possibility to inject it through a needle, was studied. The results obtained demonstrated that the hydrogel injected through the needle still behaved like a gel, although it showed a reduction of the dynamic moduli. The most appropriate sterilisation technique for this kind of hydrogel was also evaluated. Liophilised Hyal 50% samples were sterilised by steam, Ethylene Oxide (EtO) and gamma-rays. EtO and gamma-rays did not modify the characteristics of the hydrogel in terms of swellability and morphology. Lastly, the in vivo effect of Hyal 50% hydrogel in the treatment of chondral defect in rabbit knee was also studied. The results obtained showed the Hyal 50% injections improved chondrocytes density and matrix appearance. Furthermore, the permanence in situ of the hydrogel was longer than that of the linear Hyal.

3T3 Cells↗
PubMed1998

Effect of charged groups on the adsorption and penetration of proteins onto and into carboxymethylated poly(HEMA) hydrogels.

A range of carboxymethylated poly(hydroxyethyl methacrylate) (CM-PHEMA) hydrogels with varying degrees of carboxymethylation was synthesized for a systematic study of the effects of ionized groups ('charge') on the uptake by hydrogel matrices of the proteins, lysozyme and human serum albumin (HSA). Using a radiolabel-tracer technique, X-ray photoelectron spectroscopy, and laser scanning confocal microscopy, we attempted to differentiate between protein molecules that were irreversibly adsorbed onto the hydrogel surface and those that penetrated into the hydrogel matrix. The effective pore size of the CM-PHEMA hydrogels was modelled and compared with the known molecular dimensions of the two proteins. The effects of the presence of varying amounts of ionized groups in the hydrogel matrix differed for the two proteins. For lysozyme, increased uptake was observed at higher carboxymethylation; this is interpreted as resulting from a combination of electrostatic attraction and increasing ease of penetration of the protein into the more porous hydrogel matrix. For HSA, on the other hand, the uptake was primarily by surface adsorption, with little diffusive penetration into the matrix.

Adsorption↗
PubMed2000

Cross-linked hyaluronic acid hydrogel films: new biomaterials for drug delivery.

A new hyaluronic acid (HA)-based hydrogel film was prepared and evaluated for use in drug delivery. This biocompatible material crosslinks and gels in minutes, and the dried film swells and rehydrates to a flexible hydrogel in seconds. HA was first converted to the adipic dihydrazide derivative and then crosslinked with the macromolecular homobifunctional reagent poly(ethylene glycol)-propiondialdehyde to give a polymer network. After gelation, a solvent casting method was used to obtain a HA hydrogel film. The dried film swelled sevenfold in volume in buffer, reaching equilibrium in less than 100 s. Scanning electron microscopy (SEM) of the hydrogel films showed a condensed and featureless structure before swelling, but a porous microstructure when hydrated. The thermal behavior of the hydrogel films was characterized by differential scanning calorimetry. The enzymatic degradation of the HA hydrogel films by hyaluronidase was studied using both SEM and a spectrophotometric assay. Drug release from the hydrogel film was evaluated in vitro using selected anti-bacterial and anti-inflammatory drugs. This novel biomaterial can be employed for controlled release of therapeutic agents at wound sites.

Anti-Infective Agents↗
PubMed2001

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.

Algorithms↗
PubMed2002

Preparation of theophylline hydrogels of atactic poly(vinyl alcohol)/NaCl/H2O system for drug delivery system.

Theophylline (TH) was loaded in an a-PVA/NaCl/H2O hydrogels system by one cycle gelation only at -20 degrees C. However, it developed some unwanted crystal-like structure surrounding the hydrogels while kept at room temperature. The physical, chemical and thermal analyses of this crystal-like structure indicated TH embedded with thin hydrogels of a-PVA/NaCl. Later during dissolving of feed-mixture at least 3 h heat treatment with proper mixing at high temperature contributed hydrogels of almost no crystal-like structure. 3% of TH was successfully loaded by this way. This type of hydrogels showed Fickian type drug release (Higuchi Model) and it showed a more sustained effect than that of traditional cyclic FT. Comparatively lower release rate, diffusion coefficient and kinetic constant values of this system prevail over other systems studied here. A DSC thermogram revealed that apparently homogeneous microgel junctions might play the key role behind the above properties. Moreover the a-PVA/TH/NaCl/H2O system depresses the freezing point at -30 degrees C instead of above this temperature. The hydrogels of this system were also prepared by freezing at -30 degrees C for 16 h as one cycle. Three cycles were done in cyclic FT (freezing at -30 degrees C for 16 h and thawing at room temperature for 8 h). Drug release was studied for a total of 750 min. Up to the asymptotic value, 10.5 h TH release from the hydrogel matrices of the a-PVA/NaCl/H2O system (gelation at -20 degrees C) and 6.5 h from those of a-PVA/NaCl/H2O (freezing at -30 degrees C) and a-PVA/H2O systems (cyclic FT) were found.

Calorimetry, Differential Scanning↗
PubMed2000

Synthesis and characterization of superporous hydrogel composites.

Recently, we synthesized superporous hydrogels which swell fast with high swelling ratios for development of gastric retention devices. Due to their superabsorbent nature, superporous hydrogels are too mechanically weak for gastric retention application. The mechanical strength of superporous hydrogels was substantially increased by making superporous hydrogel composites. The composite materials used were hydrophilic particulate materials commonly used as disintegrants in pharmaceutical tablets. In this study, Ac-Di-Sol was used as a model composite material. Addition of Ac-Di-Sol resulted in significant improvement in the properties of superporous hydrogels. The dried superporous hydrogels maintained interconnected channels even after drying in the air. Thus, the swelling kinetics and the swelling ratio were not affected by air drying, which normally would have resulted in partial or total collapse of the interconnected pores. The presence of Ac-Di-Sol also increased the mechanical strength substantially. Scanning electron microscopic examination showed that the composite material increased the physical crosslinking density which provided high mechanical strength and prevented polymer chains from collapsing during air drying. The superporous hydrogel composites possess properties suitable for gastric retention.

Chemical Phenomena↗
PubMed2000

Controlled release of terbinafine hydrochloride from pH sensitive poly(acrylamide/maleic acid) hydrogels.

Adsorption and controlled release of terbinafine hydrochloride (TER-HCl) to and from pH sensitive poly(acrylamide/maleic acid) (P(AAm/MA)) hydrogels were investigated. P(AAm/MA) hydrogels were prepared by irradiating the ternary mixtures of AAm/MA/and water by gamma-rays at ambient temperature. Antifungal drug, TER-HCl containing hydrogels, at different drug to polymer ratios, was prepared by direct adsorption method. The influence of MA content in the gel on the adsorption capacities of hydrogel and the effect of pH on the releasing behavior of TER-HCl from gel matrix were investigated. Terbinafine adsorption capacity of hydrogels are found to increase from 2 to 38 mg TER-HCl per g dry gel with increasing amount of MA in the gel system. In vitro drug release studies in different buffer solutions show that the basic parameters affecting the drug release behavior of hydrogel are the pH of the solution and MA content of hydrogel.

Acrylic Resins↗
PubMed2000

Self-assembled hydrogel nanoparticles composed of dextran and poly(ethylene glycol) macromer.

Biodegradable hydrogel nanoparticles were prepared from glycidyl methacrylate dextran (GMD) and dimethacrylate poly(ethylene glycol) (DMP). GMD was synthesized by coupling of glycidyl methacrylate to dextran in the presence of 4-(N,N-dimethylamino)pyridine (DMAP) using dimethylsulfoxide (DMSO) as an aprotic solvent. DMP was synthesized from poly(ethylene glycol) (PEG) and methacryloyl chloride. GMD/DMP (abbreviated as DP) hydrogel was prepared by radical polymerization of GMD and DMP using ammonium peroxydisulfate (APS) as an initiator and UV curing. DP hydrogel nanoparticles were obtained by diafiltration method using DMSO solution. The GMD and DMP were characterized by fourier transform infrared spectroscopy. Fluorescence probe technique was used to investigate the self-assembly of DP in water using pyrene as a hydrophobic probe. The critical association concentration (CAC) was determined to be 5.6 x 10(-2) g/l. The shape of DP hydrogel nanoparticles was spherical when observed by transmission electron microscope (TEM). The size range of DP hydrogel nanoparticles was about 20 approximately 50 nm. The hydrodynamic size of DP hydrogel nanoparticles was measured by photon correlation spectroscopy (PCS) and gradually increased with time in PBS (0.1 M, pH 7.4). Drug release study was performed using clonazepam (CNZ) as a hydrophobic model drug. In vitro release rate of CNZ from the DP hydrogel nanoparticles was dependent on the existence of dextranase and the pH of the release medium.

Anticonvulsants↗
PubMed2001

In vitro and in vivo evaluations of topically applied capsaicin and nonivamide from hydrogels.

The purpose of this study was designed to investigate the in vitro and in vivo skin absorption of capsaicin and nonivamide from hydrogels. Various commercialized creams of capsaicin were also compared with hydrogels. Both skin stripping technique and Mexameter were applied to evaluate the level of capsaicin and nonivamide retained in stratum corneum (SC) and skin erythema in vivo. The partition of drug between skin and the hydrogel matrix was considered to play an important role in the permeation process. The in vitro permeation of capsaicin from hydrogels depends on the physicochemical nature and the concentration of the polymer used. The incorporation of nonionic Pluronic F-127 polymer into hydrogels resulted in a retarded release of capsaicin. On the other hand, the in vitro capsaicin permeation showed higher levels in cationic chitosan and anionic carboxymethyl cellulose (CMC) hydrogels than cream bases. The permeation of nonivamide was retarded at the late stage of in vitro application. The inter-subject variation was more significant in the in vivo study than in vitro skin permeation experiments. The cream induced in vivo skin erythema depending on the drug concentration, however, the dose-dependence was not observed in hydrogels. Nonivamide-treated skin showed stronger erythema than capsaicin-treated skin. The present study indicates that there is a moderate correlation between in vitro skin permeation and in vivo erythema responses of topically applied capsaicin and nonivamide. The correlation between drug amount in SC and skin erythema test in vivo was also observed.

Administration, Topical↗
PubMed2001

Controlled release of antifungal drug terbinafine hydrochloride from poly(N-vinyl 2-pyrrolidone/itaconic acid) hydrogels.

Adsorption and controlled release of terbinafine hydrochloride (TER-HCl) to and from pH-sensitive poly(N-vinyl 2-pyrrolidone/itaconic acid) P(VP/IA) hydrogels were investigated. P(VP/IA) hydrogels were prepared by irradiating the ternary monomer mixtures of N-vinyl 2-pyrrolidone/itaconic acid/ethylene glycol dimethacrylate in aqueous solution by gamma-rays at ambient temperature. Hydrogels containing antifungal drug TER-HCl, at different drug-to-polymer ratios, were prepared by direct adsorption method. The influence of IA content in the gel on the adsorption capacities of hydrogels and the effect of pH on the releasing behavior of TER-HCl from the gel matrix were investigated. Terbinafine adsorption capacity of hydrogels was found to increase from 6 to 82 mg of TER-HCl per gram of dry gel with increasing drug concentration and amount of IA in the gel system. In-vitro drug-release studies in different buffer solutions showed that the basic parameters affecting the drug-release behavior of hydrogels are the pH of the solution and the IA content of the hydrogel.

Algorithms↗
PubMed2001

Posterior continuous curvilinear capsulorhexis with hydrogel and silicone intraocular lens implantation: development of capsulorhexis size and capsule opacification.

PURPOSE: To evaluate the influence of primary posterior continuous curvilinear capsulorhexis (PCCC) on capsule opacification development and capsular bag changes within the first year after cataract surgery with 2 intraocular lenses (IOLs) of comparable design but different material. SETTING: Department of Ophthalmology, University of Vienna, Medical School, Vienna, Austria. METHODS: Thirty-seven patients with age-related cataract had bilateral small incision cataract surgery with a PCCC performed after capsular tension ring insertion. One eye was randomly assigned to receive a hydrogel IOL and the other eye, a silicone IOL. Standardized digital retroillumination photographs were taken 1 day, 1 week, and 1, 3, 6, and 12 months after surgery to evaluate changes in the dimensions of the anterior and posterior capsulorhexis opening area and the presence of anterior and posterior capsule opacification. RESULTS: The area of the anterior continuous curvilinear capsulorhexis (ACCC) opening was significantly reduced during the first 6 postoperative months. The shrinkage was more pronounced (-25%) in the silicone IOL group than in the hydrogel IOL group. Ten percent of eyes with a silicone IOL had marked shrinkage of the ACCC. The area of the PCCC did not change in eyes with a hydrogel IOL but was larger (+20%) in eyes with a silicone IOL. Anterior ongrowth was observed in 60% in the hydrogel group and in no eye in the silicone group. Anterior capsule fibrosis was observed in 90% in the silicone group and in 20% in the hydrogel group. Total closure of the PCCC was not observed within the first year, but posterior ongrowth was observed in 40% in the hydrogel group and 10% in the silicone group. CONCLUSIONS: Anterior capsulorhexis shrinkage with concomitant posterior capsulorhexis enlargement was observed in eyes with a silicone IOL. The hydrogel IOL induced more ongrowth on the anterior and posterior IOL surfaces, whereas the silicone IOL induced more anterior capsule fibrosis. Total closure of the PCCC was not observed within the first year after surgery.

Aged↗
PubMed2004

Structure and interactions in covalently and ionically crosslinked chitosan hydrogels for biomedical applications.

This review presents a critical analysis of covalently and ionically crosslinked chitosan hydrogels and related networks for medical or pharmaceutical applications. The structural basis of these hydrogels is discussed with reference to the specific chemical interactions, which dictate gel formation. The synthesis and chemistry of these hydrogels is discussed using specific pharmaceutical examples. Covalent crosslinking leads to formation of hydrogels with a permanent network structure, since irreversible chemical links are formed. This type of linkage allows absorption of water and/or bioactive compounds without dissolution and permits drug release by diffusion. pH-controlled drug delivery is made possible by the addition of another polymer. Ionically crosslinked hydrogels are generally considered as biocompatible and well-tolerated. Their non-permanent network is formed by reversible links. Ionically crosslinked chitosan hydrogels exhibit a higher swelling sensitivity to pH changes compared to covalently crosslinked chitosan hydrogels. This extends their potential application, since dissolution can occur in extreme acidic or basic pH conditions.

Biomedical Technology↗
PubMed2001

Thermo-responsive peptide-modified hydrogels for tissue regeneration.

Loosely cross-linked hydrogels consisting of N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc) were synthesized, characterized, and used as model scaffolds for studying cell-material interactions in three-dimensions (3D). The AAc groups were functionalized with peptides containing the -RGD- and -FHRRIKA- sequences found in bone sialoprotein. Chemical modification of the hydrogels was verified via solid-state (1)H nuclear magnetic resonance spectroscopy, lower critical solution temperature studies, and volume change studies. The peptide-modified hydrogels were pliable at 22 degrees C and could be injected through a small-diameter aperture. Rat calvarial osteoblasts (RCO) seeded into the peptide-modified hydrogels were viable for at least 21 days of in vitro culture. The RCO spread more and demonstrated significantly greater proliferation when cultured within the peptide-modified hydrogels, as compared to control hydrogels. These peptide-modified P(NIPAAm-co-AAc) hydrogels serve as useful tools for studying cell-material interactions within 3D structures and have the potential to be used as injectable scaffolds for tissue engineering applications.

Acrylamides↗