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PubMed2006

Enhanced bone regeneration at a segmental bone defect by controlled release of bone morphogenetic protein-2 from a biodegradable hydrogel.

The objective of this study is to investigate the feasibility of a biodegradable hydrogel of gelatin as the controlled release carrier of bone morphogenetic protein-2 (BMP-2) suitable for enhancement of bone regeneration at a segmental bone defect. Hydrogels with three different water contents were prepared through glutaraldehyde crosslinking of gelatin with an isoelectric point of 9.0 under varied reaction conditions. Segmental critical-sized defects (20 mm) were created at the ulnar bone of skeletally mature New Zealand white rabbits, and gelatin hydrogels incorporating BMP-2 (17 microg/hydrogel) were implanted into the defects. When bone regeneration was evaluated by soft x-ray observation and bone mineral density (BMD) measurement, the gelatin hydrogels incorporating BMP- 2 exhibited significantly high osteoinduction activity compared with that of free BMP-2, although the activity depended on the water content of the hydrogels. Significantly higher BMD enhancement was observed in the gelatin hydrogel with a water content of 97.8 wt% than that with the lower or higher water content. We concluded that the biodegradable gelatin hydrogel is a promising controlled release carrier of BMP-2 for bone regeneration at the segmental bone defect.

Absorbable Implants↗
PubMed2006

Fabrication of 3D hepatic tissues by additive photopatterning of cellular hydrogels.

We have fabricated a hepatic tissue construct using a multilayer photopatterning platform for embedding cells in hydrogels of complex architecture. We first explored the potential of established hepatocyte culture models to stabilize isolated hepatocytes for photoencapsulation (e.g., double gel, Matrigel, cocultivation with nonparenchymal cells). Using photopolymerizable PEG hydrogels, we then tailored both the chemistry and architecture of the hydrogels to further support hepatocyte survival and liver-specific function. Specifically, we incorporated adhesive peptides to ligate key integrins on these adhesion-dependent cells. To identify the appropriate peptides for incorporation, the integrin expression of cultured hepatocytes was monitored by flow cytometry and their functional role in cell adhesion was assessed on full-length extracellular matrix (ECM) molecules and their adhesive peptide domains. In addition, we modified the hydrogel architecture to minimize barriers to nutrient transport for these highly metabolic cells. Viability of encapsulated cells was improved in photopatterned hydrogels with structural features of 500 microm in width over unpatterned, bulk hydrogels. Based on these findings, we fabricated a multilayer photopatterned PEG hydrogel structure containing the adhesive RGD peptide sequence to ligate the alpha5beta1 integrin of cocultured hepatocytes. Three-dimensional photopatterned constructs were visualized by digital volumetric imaging and cultured in a continuous flow bioreactor for 12 d where they performed favorably in comparison to unpatterned, unperfused constructs. These studies will have impact in the field of liver biology as well as provide enabling tools for tissue engineering of other organs.

Animals↗
PubMed1999

Antibiotic hydrogel coated Foley catheters for prevention of urinary tract infection in a rabbit model.

PURPOSE: We developed an antibiotic liposome (ciprofloxacin liposome) containing hydrogel for external coating of silicone Foley catheters and evaluated its efficacy in a rabbit model. Our goal was to create a catheter that would hinder the development of catheter associated nosocomial urinary tract infections. MATERIALS AND METHODS: We inserted either an untreated, liposomal hydrogel coated or a liposome hydrogel with ciprofloxacin coated 10F silicone Foley catheter into New Zealand White rabbits. We challenged the system with 5x10(6) virulent Escherichia coli at the urethral meatus twice daily for 3 days. Urine cultures were evaluated twice daily for 7 days. When urine cultures became positive, the rabbits were sacrificed and urine, urethral catheter and urethral tissue were cultured. RESULTS: The time to bacteriuria detection in 50% of the specimens was double for hydrogel with ciprofloxacin coated catheters versus untreated and hydrogel coated catheters. A significant (p = 0.04) improvement in average time to positive urine culture from 3.5 to 5.3 days and a 30% decrease in the bacteriuria rate for hydrogel with ciprofloxacin coated catheters were noted compared to untreated catheters. CONCLUSIONS: A significant benefit was realized by coating the extraluminal catheter surface with a ciprofloxacin liposome impregnated hydrogel. We believe this procedure will provide a significant clinical advantage, while reducing health care costs substantially.

Animals↗
PubMed1996

An apparent pH-induced effect on extended wear hydrogel lens water content.

Numerous studies have examined the separate issues of precorneal tearfilm pH and hydrogel lens water content. None have examined the two issues in an associated, clinical fashion. Earlier research by this author has shown that stabilized hydrogel lens anterior surface pH correlates with established values for the precorneal tearfilm pH. This technique was therefore paired with two different methods of hydrogel lens water content assessment to determine if there was a predictable tear pH-related effect on soft lens hydration. Sixty-five volunteer subjects were fitted with either 38% (polymacon) or 58% (etafilcon A) water content hydrogel lenses on an extended-wear basis. The in situ hydrogel lens anterior surface pH was measured with a flat-surfaced, self-referenced pH electrode 5 min after initial fitting, and on subsequent extended wear follow-up examinations. On each follow-up, associated lens water content was determined by gravimetric and/or refractive analysis, yielding a total of 517 paired data points over a 33 month period. While the anterior lens surface pH increased in a nonlinear fashion with immediate duration of extended lens wear [p < 0.001 analysis of variance (ANOVA) by number of days extended lens wear], the water content decreased in a nonlinear fashion under the same conditions (p < 0.001 by ANOVA). Correlation of these two nonlinear functions yielded a negatively sloped linear regression (r = 0.99 and 0.97) for each material. The slopes of the resultant linear functions were significantly different (p < 0.01) by t-test; the higher water content material exhibited a greater sensitivity to pH. The routine labeling of pH-induced water content changes by hydrogel lens manufacturers would provide an objective model for clinical lens behavior, and assist in lens type and parameter selection when fitting extended-wear soft lenses. Additionally, as other lens materials are characterized, it may be possible to model the "ideal" hydrogel material in terms of apparent pH-dependent or-independent behavior.

Contact Lenses, Extended-Wear↗
PubMed2003

Mucin balls with wear of conventional and silicone hydrogel contact lenses.

PURPOSE: To compare the frequency of mucin balls in subjects wearing conventional and high-Dk silicone hydrogel lenses during 12 months of extended-wear and to determine whether mucin balls are associated with any lens or subject characteristics. METHODS: This study used data from a clinical trial where subjects wore either conventional hydrogel (N = 69, 6-night extended-wear) or silicone hydrogel (N = 70, 30-night extended-wear) contact lenses for 12 months. The number of mucin balls and other physiological responses, lens fit and performance, and subjective patient responses to lens wear were rated at each scheduled visit. RESULTS: Subjects in the silicone hydrogel group had significantly greater numbers of mucin balls compared with subjects in the conventional hydrogel group over time (p < 0.001), but there were no significant differences in the percentage of subjects with mucin balls between the two groups. Increasing lens wettability, back surface deposits, and time of lens wear were associated with higher numbers of mucin balls in the conventional hydrogel group (p < 0.05); steeper corneal curvature and increasing lens wettability, back surface deposits, and number of microcysts were associated with higher numbers of mucin balls in the silicone hydrogel group (p < 0.05). CONCLUSIONS: This study indicates that a subset of the population is predisposed to develop mucin balls irrespective of the soft contact lens type worn, but lens type influences the degree of mucin ball formation. The relationship between lens wettability, back surface deposits, and steeper corneal curvature with mucin balls supports the hypothesis that the mechanical interaction of a lens with the surface layer of the epithelium and the tear film in association with the blinking forces of the lid is involved in mucin ball formation.

Adult↗
PubMed2006

Oxygen transmissibility of piggyback systems with conventional soft and silicone hydrogel contact lenses.

PURPOSE: To investigate the apparent oxygen transmissibility of various piggyback systems using conventional and silicone hydrogel soft contact lenses of different water content and permeability, rigid poly(methyl methacrylate), and rigid gas-permeable lenses of medium, high, and ultrahigh oxygen permeability. The aim of the study was to establish which material (rigid or hydrogel) is more representative of the resulting oxygen performance of piggyback systems. METHODS: The apparent oxygen transmissibility of 66 piggyback systems was measured with an electrochemical method. Eighteen of these combinations involved the use of silicone hydrogel contact lenses currently available. One hyperpermeable rigid gas-permeable contact lens (tisilfocon A) was also included in the study. RESULTS: Measured apparent transmissibility correlates with rigid lens permeability (r = 0.403; SE = +/-3.03 barrer/cm; P < 0.001) and hydrogel lens permeability (r = 0.334; SE = +/-3.2 barrer/cm; P < 0.001). As expected, a linear model comprising permeability values from both rigid and soft materials gave a more precise estimation of the piggyback transmissibility (r = 0.736; SE = +/-2.02 barrer/cm; P < 0.001). The highest values of apparent oxygen transmissibility were found for the combination of tisilfocon A rigid material with any of the 3 silicone hydrogel lenses. Tisilfocon A material significantly improved the transmissibility of all piggyback systems even when conventional hydrogels are involved. CONCLUSION: The combination of hypertransmissible rigid gas permeable lenses with silicone hydrogel soft materials should result in normal corneal function under daily wear conditions. When fitting piggyback systems, clinicians must be aware of material selection to optimize oxygen performance. This is of particular importance in already compromised corneas.

Contact Lenses, Hydrophilic↗
PubMed2004

Posterior capsule opacification after implantation of a hydrogel intraocular lens.

AIM: To compare the degree of posterior capsule opacification (PCO) in eyes with a hydrophilic hydrogel intraocular lens (IOL) with that in eyes with a hydrophobic acrylic IOL. METHODS: Ninety five patients underwent a hydrogel IOL implantation in one eye and an acrylic IOL implantation in the opposite eye. The PCO value of these patients was measured using the Scheimpflug videophotography system at 1, 6, 12, 18, and 24 months postoperatively. The rate of neodymium:YAG (Nd:YAG) laser posterior capsulotomy and visual acuity were also evaluated. RESULTS: The mean PCO value in the hydrogel group increased significantly (p<0.0001), while that in the acrylic group did not show significant change. The PCO value in the hydrogel group was significantly greater than that in the acrylic group throughout the follow up period. Kaplan-Meier survival analysis determined that the Nd:YAG capsulotomy rate in the hydrogel group was significantly higher than that in the acrylic group (p<0.0001). Mean visual acuity in the hydrogel group decreased significantly with time (p<0.0001), and became significantly worse than that in the acrylic group at 18 and 24 months postoperatively. CONCLUSION: Posterior capsule opacification in eyes with a hydrophilic hydrogel IOL is significantly more extensive than that in eyes with a hydrophobic acrylic IOL, and results in a significant impairment of visual acuity.

Acrylates↗
PubMed2002

pH-modulated release of insulin entrapped in a spontaneously formed hydrogel system composed of two water-soluble phospholipid polymers.

To develop a polypeptide drug carrier through oral administration, a polymer hydrogel has been found that is very easy to prepare by mixing two water-soluble phospholipid polymers. The polymers having 2-methacryloyloxyethyl phosphorylcholine (MPC) moieties spontaneously formed a hydrogel, which showed controllable dissociation via pH changes. In this study, the MPC polymer hydrogel was prepared from aqueous solutions containing water-soluble poly[MPC-co-methacrylic acid (MA)] (PMA) and poly[MPC-co-n-butyl methacrylate (BMA)] (PMB), and the applicability of the hydrogel as an oral drug delivery carrier was examined. The gelation process from the two MPC polymers is spontaneous, requiring no chemical reactions and/or no physical stimuli. PMB has a hydrophobic domain, which is suitable for loading hydrophobic drugs. Insulin could be very easily loaded to almost 100% in the hydrogel. PMA also has carboxyl groups, which are well known for pH sensitivity. At pH 1.8, the swelling continued for 8 h, with complete dissociation after 16 h. At pH 6.8, the hydrogel completely dissociated within 4 h. The hydrogel remained stable at pH 1.8 and released all the insulin at pH 6.8. The release rate was approximately four times faster at pH 6.8. After release, the insulin did not show any denaturing tendency.

Drug Delivery Systems↗
PubMed2003

Effect of drying history on swelling properties and cell attachment to oligo(poly(ethylene glycol) fumarate) hydrogels for guided tissue regeneration applications.

In these experiments, the effects of the drying history of hydrogels made from a novel polymer, oligo(poly(ethylene glycol) fumarate) (OPF) with two different poly(ethylene glycol) (PEG) molecular weights (approximately 920 (1K) and 9110 (10K) g/mol), were investigated. The hydrogels were either formed, dried and then swelled, representing what may occur in the case of a pre-formed membrane for guided tissue regeneration, or were formed and swelled immediately, as may occur with an injectable material for such applications. Subsequently, swelling properties, sol fraction and polymer network structure (as indicated by differential scanning calorimetry), as well as attachment of human dermal fibroblasts to these hydrogels at 4 and 24 h was examined. It was found that drying before swelling caused a significant reduction in final fold swelling of OPF hydrogels, regardless of OPF formulation or method of drying (air-dried or vacuum-dried) (e.g. PEG 10K swollen first: 13.94 +/- 0.35 vs. vacuum first: 6.53 +/- 0.12; PEG 1K swollen first: 8.99 +/- 0.47 vs. vacuum first: 2.26 +/- 0.08). This decreased swelling correlated to significantly higher cell attachment (% seeded) to these hydrogels at 24 h (PEG 10K vacuum first: 21.1 +/- 4.7% vs. swollen first: 7.1 +/- 5.5%; PEG 1K vacuum first: 58.2 +/- 2% vs. swollen first: 7.4 +/- 2.2%). LIVE/DEAD staining followed by microscopic analysis revealed attached cells were viable, yet rounded, and that, in the case of the PEG 1K dried-first samples, undulations in the surface visible in the hydrated state may have affected cell adhesion. Regardless of treatment, all hydrogels showed significantly less cell attachment than the tissue culture polystyrene control after 24 h (104.9 +/- 4.4%). These results suggest that, by altering the PEG molecular weight used in synthesis, OPF hydrogels may be tailored to produce desired swelling properties and reduce non-specific cell adhesion for either injectable or pre-formed applications, thus providing a potential alternative material for use in guided tissue regeneration procedures.

Calorimetry, Differential Scanning↗
PubMed2005

2-methacryloyloxyethyl N-butylcarbamate: a new co-monomer for synthesis of polyurethane hydrogels with improved mechanical properties for biomedical applications.

Hydrogels with tunable hydrophilic and mechanical properties were synthesized by the free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) and 2-methacryloyloxyethyl N-butylcarbamate. The resulting hydrogels were investigated for their equilibrium water content, sessile drop water contact angles, gel fraction, mechanical properties and protein adsorption. Results indicated that co-polymer hydrogels have good hydrophilicity and that, with the incorporation of the 2-methacryloyloxyethyl N-butylcarbamate, mechanical properties could be improved significantly. without affecting other important properties. Lysozyme and albumin adsorption experiments demonstrated that, similar to most hydrogel materials, the co-polymer hydrogels adsorb more lysozyme than albumin and that the adsorption was dependent on hydrophilicity. The control poly(HEMA) hydrogels were found to adsorb more protein than the co-polymer hydrogels; this is thought to be primarily a consequence of protein absorption rather than protein adsorption.

Calorimetry, Differential Scanning↗
PubMed2006

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.

Acrylic Resins↗
PubMed1998

The modulation of cellular responses to poly(2-hydroxyethyl methacrylate) hydrogel surfaces: phosphorylation decreases macrophage collagenase production in vitro.

We examined the regulation of collagenase production by the monocyte/macrophage THP-1 cell line when these cells were exposed to poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel surfaces with different chemistries and morphologies. Tissue culture modified polystyrene (TCP), used as a control surface, induced the maximum collagenase response. Copolymer hydrogels containing 2-ethoxyethyl methacrylate (EMA) or methyl methacrylate (MMA) also induced a high response, while PHEMA hydrogels induced a low level response and the phosphorylated hydrogel induced no response. This pattern was altered when the morphology of the hydrogels was changed to that of a sponge. The overall enzyme response to the sponge hydrogels was lower than that to the homogeneous hydrogels. Sponges containing EMA and MMA produced low level response relative to the TCP control. PHEMA and phosphorylated sponges produced little and no response respectively. The dramatically reduced enzyme response to phosphorylated surfaces was not a consequence of cell death, and may be a phenomenon related to changes in cell surface charge.

Biocompatible Materials↗
PubMedDate not supplied

Comparing the use of hydrogel dressings to lanolin ointment with lactating mothers.

OBJECTIVE: To evaluate the use of hydrogel dressings for the prevention and treatment of nipple soreness in lactating women as compared with the common intervention of lanolin ointment. The hypothesis was as follows: Participants using hydrogel dressings as a preventive measure for nipple soreness will experience greater pain relief and a lower rate of nipple wounds as compared with the control group. The secondary hypothesis was that the reduction of nipple soreness in the treatment group would produce a longer duration of breastfeeding as compared with the control group. DESIGN: A multicentered, prospective, randomized controlled clinical trial evaluating a sample of 106 lactating mothers. SETTING: Study sites were the University of Alabama Medical Center at Birmingham (an inner-city teaching hospital) and Northeast Health System (a community hospital in Beverly, Massachusetts). PARTICIPANTS: Participants were older than age 18, fluent in English, and had an operational telephone in the residence. Other inclusion criteria were singleton, vaginal deliveries; no prior breastfeeding experience; and written informed consent. INTERVENTIONS: Participants were randomized to either the lanolin ointment or the hydrogel dressings group and received instructions specific to their assignment. All participants received breastfeeding education provided by a board-certified lactation consultant. MAIN OUTCOME MEASURES: During the initial 12 study days, participants identified pain intensity using a numeric pain intensity scale and verbal descriptor scale. Subjective data were collected via self-reported skin assessments of the bilateral breasts, nipples, and areolae. Breastfeeding duration was established by a follow-up telephone call at 2 months. RESULTS: The hydrogel dressings group had significantly greater reduction in pain score mean values at baseline, on study Day 10, and on study Day 12 in comparison to the control group. Participants using the hydrogel dressings discontinued treatment sooner than participants in the lanolin ointment group. The lanolin ointment group had eight breast infections, whereas the hydrogel dressings group had none. CONCLUSION: Hydrogel dressings are a safe, available treatment that provided more effective pain management for nipple soreness than the common intervention of lanolin ointment.

Breast Feeding↗
PubMedDate not supplied

Implantation of collagen IV/poly(2-hydroxyethyl methacrylate) hydrogels containing Schwann cells into the lesioned rat optic tract.

Poly (2-hydroxyethylmethacrylate) (PolyHEMA) hydrogels, when combined with extracellular matrix molecules and infiltrated with cultured Schwann cells, have the capability to induce CNS axonal regrowth after injury. We have further investigated these PolyHEMA hydrogels and their potential to bridge CNS injury sites. Collagen IV-impregnated hydrogels containing Schwann cells were implanted into the lesioned optic tract in 14 rats. On examination 2-4 months later, there was good adherence between the implants and CNS tissue, and large numbers of viable Schwann cells (S100+, GFAP+, Laminin+, and LNGFR+) were seen within the hydrogel matrices. Immunohistochemical analysis showed that the collagen IV-impregnated PolyHEMA hydrogels preferentially supported the transplanted Schwann cells and not host glial cells such as astrocytes (GFAP+) or oligodendroglia (CAII+). Macrophages (ED1+) were also seen within the sponge structure. Eighty-three percent of the implanted hydrogels contained RT97+ axons within their trabecular networks. Regrowing axons were associated with the transplanted Schwann cells and not with the small number of infiltrating astrocytes. RT97+ axons were traced up to 510 microm from the nearest host neuropil. These axons were sometimes myelinated by the transplanted Schwann cells and expressed the peripheral myelin marker Po+. WGA/HRP-labeled retinal axons were seen within transplanted hydrogel sponges, with 40% of the cases growing for distances up to 350-450 microm within the polymer network. The data indicate that impregnating PolyHEMA sponges with collagen IV can modify the host glial reaction and support the survival of transplanted Schwann cells. This study thus provides new information on how biomaterials could be used to modify and bridge CNS injury sites.

Animals↗
PubMed2000

In-vivo drug delivery of 5-fluorouracil using poly(2-hydroxyethyl methacrylate-co-acrylamide) hydrogels.

Poly(2-hydroxyethyl methacrylate-co-acrylamide) hydrogels crosslinked with ethylen glycol dimethacrylate were used as devices for the in-vivo drug release of 5-fluorouracil (5-FU). Drug-loaded hydrogels were subcutaneously implanted in the back of Wistar rats. All hydrogel discs reached an equilibrium swelling degree, which was slightly larger than that determined in-vitro. After 30 days of implantation, the hydrogel discs were transparent, and without fracture or apparent degradation. In addition, a fibrous capsule was not detected around the hydrogels that had greater hydration degrees. Release of 5-FU from these hydrogels allows the drug to remain in the plasma from 1 to 5 days, in spite of its short plasma half-life (15 min). This was an improvement of up to 98-times compared with the intraperitoneal drug administration. Administration of 5-FU by implantation of 2-hydroxyethylmethacrylate-co-acrylamide copolymeric hydrogels seems to be a good candidate for 5-FU therapy, since the drug released results in a therapeutically suitable plasma concentration of 5-FU for an extended period of time, despite the short half-life of the drug.

Animals↗
PubMed2005

Characterization of crosslinking effects on the physicochemical and drug diffusional properties of cationic hydrogels designed as bioactive urological biomaterials.

This study examined the effects of concentration and type of crosslinker (tetraethyleneglycol diacrylate, TEGDA; diethyleneglycol dimethacrylate, DEGDMA; and polyethyleneglycol dimethacrylate, PEGDMA) on the mechanical and drug diffusional properties of hydrogels that had been selected as candidate coatings for bioactive medical devices. Hydrogels (dimethylaminoethylmethacrylate-co-vinylpyrrolidone; 1:1) were prepared by free radical polymerization and characterized using tensile analysis, dynamic contact angle analysis and analysis of swelling at pH 6.0. The release of fusidic acid and chlorhexidine was evaluated using buffered medium at pH 6.0 and, in addition, using dissolution medium that had been buffered to pH 9 in the presence and absence of elevated concentrations of calcium, representative of urinary encrustation. Crosslinker concentration, but not type, affected the advancing and receding contact angles. Conversely, both crosslinker type and concentration affected the mechanical and swelling properties of the hydrogels. Maximum swelling and elongation at break were associated with the PEGDMA-crosslinked hydrogels whereas TEGDA-crosslinked hydrogels exhibited the maximum ultimate tensile strength and Young's modulus. Drug release from all systems occurred by diffusion. The mass of chlorhexidine and fusidic acid released was dependent on crosslinker type and concentration, with hydrogels crosslinked with PEGDMA offering the greatest mass of drug released at each sampling period. The mass of fusidic acid but not chlorhexidine released at pH 9.0 in a calcium augmented medium was lower than that released in the same medium devoid of elevated calcium, due to the formation of the poorly soluble calcium salt. In conclusion, this study has uniquely examined the effects of crosslinker type and concentration on physicochemical and drug release properties essential to the clinical and non-clinical performance of bioactive hydrogels for medical device application.

Anti-Infective Agents↗
PubMed1998

Kinetic modeling for macromolecule loading into crosslinked polyacrylamide hydrogel matrix by swelling.

A kinetic model was proposed to characterize the swelling phenomenon of polyacrylamide hydrogel and to quantify and predict the loading of insulin into the hydrogel by swelling. Polyacrylamide hydrogel and porcine insulin were used in the study. During swelling, the insulin concentration in the hydrogel was found to be higher than that in the loading solution, which could be attributed to ionization of the ionic networks, Donnan exclusion, and the possible ionic interactions between the anionic carboxylic pendants and cationic insulin. The experimental results demonstrated that the proposed kinetic model was able to describe the swelling kinetics of polyacrylamide hydrogel and the loading kinetics of insulin by using only two constants [input rate (Kin) and output rate (Kout)]. The experimental values of Kin and Kout were found to highly depend on the concentration of HCl. As medium pH declined (because of the addition of HCl), the degree of swelling decreased and the insulin loading amount in the hydrogel was reduced. A linear log-log function was observed between Kin and the volume fraction of HCl. The Kout values also decreased with the addition of HCl, but remained constant after more than 1% (v/v) of HCl (0.01 N) was added. The proposed model was able to characterize the swelling kinetics of polyacrylamide and predict the loading dose of insulin in the polyacrylamide hydrogel by swelling.

Acrylic Resins↗
PubMedDate not supplied

Evaluation of properties microcrystalline chitosan as a drug carrier. Part 1. In vitro release of diclofenac from mictocrystalline chitosan hydrogel.

The influence of microcrystalline chitosan hydrogel, alone (MCCh) as well as in combination with methylcellulose (MC) or Carbopol (CP), on the release of diclofenac free acid (DA) and its salt (DS) was studied in vitro. Commercial Olfen gel (Mepha Ltd., Switzerland) was applied as a reference preparation. The influence of hydrophilizing agents (1,2-propylene glycol and glycerol) and methycellulose hydrogel on the rheological properties of the vehicle and on the release of drug from modified MCCh hydrogel was studied. The quantity of the released substance was determined by UV-spectroscopy. The results confirmed that release was dependent on the chemical character of the drug and on the type of vehicle. The process of diclofenac release from MCCh hydrogels as well as from Carbopol hydrogels runs in two phases. The first phase is characterised by rapid release whereas in the second phase the release is much slower. The most suitable basis for diclofenac is microcrystalline chitosan hydrogel with addition glycerol, 1,2-propylene glycol, and methylcellulose hydrogel.

Anti-Inflammatory Agents, Non-Steroidal↗