Properties of biodegradable hydrogels prepared by γ irradiation of microbial poly(ϵ-lysine) aqueous solutions

Poly(?-lysine) (PL) hydrogels have been prepared by means of γ irradiation of PL produced by Streptomyces albulus in aqueous solutions. When the dosage of γ irradiation was 70 kGy or more and the concentration of PL in water was 1–7 wt %, transparent hydrogels (opaque hydrogels for 1–3 wt % PL concentration) could be produced. In the case of 70 kGy of γ irradiation and 5 wt % PL concentration, the specific water content (wt of absorbed water/wt of dry hydrogel) of the PL hydrogel was approximately 160. Specific water contents of PL hydrogels decreased markedly with an increase in the dosage of γ irradiation. The specific water contents were increased with an increase in PL concentration in the irradiated solution. This result indicates the presence of a radical scavenger in the PL solution. Swelling equilibria of PL hydrogels were measured in water or in aqueous solutions of various pHs or concentrations of NaCl, Na₂SO₄, and CaCl₂. Under acid conditions, the PL hydrogel swelled due to the ionic repulsion of the protonated amino groups in the PL molecules. The degree of deswelling in electrolyte solution was smaller than that of other ionic hydrogels [poly(γ-glutamic acid), poly(acrylic acid) etc.]. In addition, the enzymatic degradations of PL hydrogel were studied at 40°C and pH 7.0 in an aqueous solution of the neutral protease [Protease A (Amano)] produced from Aspergillus oryzae. The rate of enzymatic degradation of the respective PL hydrogels was much faster than the rate of simple hydrolytic degradation. The rate of enzymatic degradation decreased with the increase in γ-irradiation dose during preparation of the PL hydrogel. © 1995 John Wiley & Sons, Inc.     

Thermally crosslinked anionic hydrogels composed of poly(vinyl alcohol) and poly(γ‐glutamic acid): Preparation,characterization, and drug permeation behavior

pH‐sensitive anionic hydrogels composed of poly(vinyl alcohol) (PVA) and poly(γ‐glutamic acid) (γ‐PGA) were prepared by the freeze drying method and thermally crosslinked to suppress hydrogel deformation in water. The physical properties, swelling, and drug‐diffusion behaviors were characterized for the hydrogels. In the equilibrium swelling study, PVA/γ‐PGA hydrogels shrunk in pH regions below the pK_a (2.27) of γ‐PGA, whereas they swelled above the pK_a. In the drug‐diffusion study, the drug permeation rates of the PVA/γ‐PGA hydrogels were directly proportional to their swelling behaviors. The cytocompatibility test showed no cytotoxicity of the PVA/γ‐PGA hydrogels for the 3T3 fibroblast cell lines. The results of these studies suggest that hydrogels prepared from PVA and γ‐PGA could be used as orally administrable drug‐delivery systems. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Characterization of poly(N‐(hydroxymethyl)methacrylamide‐ATU) hydrogels synthesized by γ radiation

Poly(N‐(hydroxymethyl)methacrylamide‐1‐allyl‐2‐thiourea), (poly(NHMMA‐ATU)) hydrogels were synthesized by γ radiation, using ⁶⁰Co γ source at different radiation doses, to change the porosity and crosslinking density of the hydrogels. The percent of 1‐allyl‐2‐thiourea (ATU) in the monomer mixture before the irradiation was varied between 2.5% and 10.0%, to increase the content of ATU, which was involved in some different applications in the hydrogels. Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), elemental analysis, and the swelling experiments were used to characterize the poly(NHMMA‐ATU) hydrogels synthesized in this study. Characterization results of hydrogels showed that crosslinking density of the hydrogels was increased by the increasing radiation dose and ATU content in the irradiated mixture. Swellability of these hydrogels was found to be high enough to allow the metal ions and biomolecules getting inside the hydrogels to interact with all active groups on/in the hydrogels in the adsorption applications. Equilibrium swelling ratio of the hydrogels at pH 0.5 is at least half of the equilibrium swelling ratio of the hydrogels at pH 7.0. Oscillatory swelling behavior of poly(NHMMA‐ATU) hydrogels between pH 0.5 and pH 7.0 showed that the hydrogels are quite stable at different pH conditions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1657–1664, 2006     

In situ injectable poly(γ‐glutamic acid) based biohydrogel formed by enzymatic crosslinking

Enzymatic crosslinking was developed to prepare in situ forming poly(γ‐glutamic acid) (γ‐PGA) based hydrogel in this study. First, the precursor of poly(γ‐glutamic acid)–tyramine (γ‐PGA–Ty) was synthesized through the reaction of carboxyl groups from a γ‐PGA backbone with tyramine. The structure of the grafted precursor was confirmed by ¹H‐NMR and Fourier transform infrared spectroscopy. After that, the crosslinking of the phenol‐containing γ‐PGA–Ty precursor was triggered by horseradish peroxidase in the presence of H₂O₂; this resulted in the formation of the γ‐PGA–Ty hydrogels. The equilibrium water content, morphology, enzymatic degradation rate, and mechanical properties of the hydrogels were characterized in detail. The data revealed that the well‐interconnected hydrogels had tunable water contents, mechanical properties, and degradability through adjustments of the composition. Furthermore, cell experiments proved the biocompatibility of the hydrogels by 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay. These characteristics provide an opportunity for the in situ formation of injectable biohydrogels as potential candidates in cell encapsulation and drug delivery. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42301.     

Polyelectrolyte complex hydrogel composed of chitosan and poly(γ‐glutamic acid) for biological application: Preparation,physical properties,and cytocompatibility

Polyelectrolyte complex (PEC) hydrogels composed of chitosan as a cationic polyelectrolyte and poly (γ‐glutamic acid) (γ‐PGA) as an anionic polyelectrolyte were prepared from PEC dispersions based on a chitosan solution to which different amounts of γ‐PGA solutions were added to charge equivalency. The chemical structures of the PEC hydrogels were investigated by Fourier transform infrared spectroscopy. The physical properties, fixed charge concentration, crystallinity, mechanical properties, micromorphology, and swelling properties of the PEC hydrogels were also investigated. The total fixed charge concentration of the PEC hydrogels varied as a function of pH on the pK intervals between chitosan (pK = 6.5) and γ‐PGA (pK = 2.27). The isoelectric points (IEP) were shifted to a lower pH with a higher weight ratio of γ‐PGA to chitosan. The elastic modulus was decreased with the weight ratio increasing from 0 : 1 to 1 : 1 (γ‐PGA/chitosan) by ionic crosslinking between the amino groups of chitosan and the carboxyl groups of γ‐PGA. The results of the swelling study showed that the swelling properties of PEC hydrogels were more affected by the change in the elastic restoring force than by the change in the fixed charge concentration depending on the pH. Also, the cytotoxicity of the PEC hydrogels was investigated using normal human dermal fibroblast (NHDF) cell lines, and the results showed the PEC hydrogels were not toxic. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:386–394, 2007     

Poly(γ-glutamic acid) hydrogel prepared from microbial poly(γ-glutamic acid) and alkanediamine with water-soluble carbodiimide

Poly(γ-glutamic acid) (PGA) hydrogels have been prepared from microbial PGA produced by Bacillus subtilis F-02-1, water-soluble carbodiimide (WSC), and alkanediamines such as 1,3-propanediamine (1,3-PD), 1,4-butanediamine (1,4-BD), and 1,6-hexanediamine (1,6-HD) in aqueous medium. The carboxyl groups of PGA were activated by the addition of WSC in deionized water, and the PGA-WSC adduct was produced. PGA hydrogels could be produced after the mixing of PGA-WSC and alkanediamine in deionized water. This alkanediamine to which both amino groups reacted with the carboxyl groups of PGA plays the role of a crosslinking point. When the amount of PGA was 100 mg, WSC was 50 mg or more, and 1,3-PD was 25 μL or more in 2 mL of deionized water, PGA hydrogels could be produced. Specific water contents (weight of absorbed water/weight of dry gel) ranged from 300 to 1,993 g/g in the case of 1,3-PD. If the PGA-WSC adduct was freeze-dried, the yield of the PGA hydrogel became higher than that when PGA-WSC was not freeze-dried. The highest yield of the PGA hydrogel from 100 mg of PGA, 100 mg of WSC, and 100 μL of 1,3-PD in 2 mL of deionized water using the freeze-dry method was 39.9 mg of dry PGA hydrogel with a 650 g/g specific water content. The order of yield was 1,6-HD > 1,4-BD > 1,3-PD from 100 mg of PGA-100 mg of WSC in 2 mL of deionized water. The order of the specific water content was 1,3-PD (462 g/g) > 1,4-BD (234 g/g) > 1,6-HD (199 g/g). This order may be due to the higher reaction probability between the activated carboxyl groups in the PGA-WSC and both amino groups in the alkanediamine with longer methylene chains, indicating that the crosslinking density of the PGA hydrogel is higher and the specific water content is lower. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1889–1896, 1997     

Swelling behaviour of poly(α‐hydroxyacrylic acid) gel

Poly(α‐hydroxy acrylic acid) (PHA) and poly(acrylicacid) (PAA) gels were prepared by irradiating the respective 15 wt% aqueous solutions with γ‐rays. Swelling ratios for PHA gel were measured as a function of pH and divalent cation (Mg²⁺, Ca²⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺) concentration C₂ in the external solution to provide a comparison with the results for PAA gels. It was found that the swelling ratio of PHA gel steeply increases between pH 2 and 4, followed by a gradual swelling in the higher pH region. The corresponding steep swelling of PAA gel was observed at pH 3–6. Cation specificity in the equilibrium swelling ratio at a lower C₂ value (1.0 × 10⁻³ M) was approximately consistent with the binding selectivity in the solution system. Typically, the swelling ratio of PHA gel in the presence of Ca²⁺ was significantly lower than in the Mg²⁺ system, while the difference was slight for PAA gel. The response of the swelling ratio to changes in pH and C₂ was analysed as a first order relaxation to estimate the time constants. The (de)swelling kinetics measured by both the pH and C₂ jump were qualitatively interpreted in terms of main‐chain stiffness and intermolecular hydrogen bonding in the respective polymers. © 2000 Society of Chemical Industry     

γ‐Irradiation preparation of poly(acrylic acid)–chitosan hydrogels for in vitro drug release

Biocompatible and biodegradable pH‐responsive hydrogels based on poly(acrylic acid) and chitosan were prepared for controlled drug delivery. These interpolymeric hydrogels were synthesized by a γ‐irradiation polymerization technique. The degree of gelation was over 96% and increased as the chitosan or acrylic acid (AAc) content increased. The equilibrium swelling studies of hydrogels prepared under various conditions were carried out in an aqueous solution, and the pH sensitivity in a range of pH 1–12 was investigated. The AAc/chitosan hydrogels showed the highest water content when 30 vol % AAc and 0.1 wt % chitosan were irradiated with a 30 kGy dose of radiation. In addition, an increase of the degree of swelling with an increase in the pH was noticed and it had the highest value at pH 12. The drug 5‐fluorouracil was loaded into these hydrogels and the release studies were carried out in simulated gastric and intestinal fluids. The in vitro release profiles of the drugs showed that more than 90% of the loaded drugs were released in the first 1 h at intestinal pH and the rest of the drug was released slowly. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3270–3277, 2003     

Preparation and characterization by radiation of poly(vinyl alcohol) and poly(N‐vinylpyrrolidone) hydrogels containing aloe vera

In these studies, hydrogels for wound dressings were made from a mixture of aloe vera and poly(vinyl alcohol) (PVA)/poly(N‐vinylpyrrolidone) (PVP) by freezing and thawing, γ‐Ray irradiation, or a two‐step process of freezing and thawing and γ‐ray irradiation. We examined the physical properties, including gelation, water absorptivity, gel strength, and degree of water evaporation, to evaluate the applicability of these hydrogels for wound dressings. The PVA:PVP ratio was 6:4, the dry weight of aloe vera was in the range 0.4–1.2 wt %, and the solid concentration of the PVA/PVP/aloe vera solution was 15 wt %. We used γ radiation doses of 25, 35, and 50 kGy to expose mixtures of PVA/PVP/aloe vera to evaluate the effect of radiation dose on the physical properties of the hydrogels. Gel content and gel strength increased as the concentration of aloe vera in the PVA/PVP/aloe vera gels decreased and as radiation dose increased and the number of freeze–thaw cycles was increased. The swelling degree was inversely proportional to the gel content and gel strength. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1477–1485, 2003     

Hydrogels composite of poly(acrylamide‐co‐acrylate) and rice husk ash. I. Synthesis and characterization

Composite hydrogels of poly(acrylamide‐co‐acrylate) with rice husk ash (RHA) were synthesized and studies of the swelling variables were accomplished comparatively with commercial polyacrylamide gel and PAMACRYL, a poly(acrylamide‐co‐acrylate) hydrogel without RHA. FT‐IR and WAXS were the techniques employed for characterizing a series of hydrogel obtained by varying the percentage of RHA (1, 2, 5, 10, and 20 wt %) and the amount of crosslinking agent (0.05, 0.1, and 0.2 mol %) relative to sum of AAm and AAc. Superabsorbent hydrogel with W_eq > 800 g H₂O/g gel was obtained with percentage of 10 wt % of RHA and 0.1 of crosslinking agent mol %. The hydrogel showed to be sensitive to the pH variation and to the presence of salts. The hydrogels, even though submitted through cycles of drying and swelling, preserved their superabsorbent characteristics and demonstrated better water absorbance properties when compared with commercial polyacrylamide gel. The composite hydrogels of poly(acrylamide‐co‐acrylate) with RHA presented good characteristics to be applied as soil conditioner for using in agriculture. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation of alginate/poly(N‐isopropylacrylamide) semi‐interpenetrating and fully interpenetrating polymer network hydrogels with γ‐ray irradiation and their swelling behaviors

Semi‐interpenetrating polymer network (semi‐IPN) and fully interpenetrating polymer network (full‐IPN) hydrogels composed of alginate and poly(N‐isopropylacrylamide) were prepared with γ‐ray irradiation. The semi‐IPN hydrogels were prepared through the irradiation of a mixed solution composed of alginate and N‐isopropylacrylamide (NIPAAm) monomer to simultaneously achieve the polymerization and self‐crosslinking of NIPAAm. The full‐IPN hydrogels were formed through the immersion of the semi‐IPN film in a calcium‐ion solution. The results for the swelling and deswelling behaviors showed that the swelling ratio of semi‐IPN hydrogels was higher than that of full‐IPN hydrogels. A semi‐IPN hydrogel containing more alginate exhibited relatively rapid swelling and deswelling rates, whereas a full‐IPN hydrogel showed an adverse tendency. All the hydrogels with NIPAAm exhibited a change in the swelling ratio around 30–40°C, and full‐IPN hydrogels showed more sensitive and reversible behavior than semi‐IPN hydrogels under a stepwise stimulus. In addition, the swelling ratio of the hydrogels continuously increased with the pH values, and the swelling processes were proven to be repeatable with pH changes. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4439–4446, 2006     

Hydrolytic degradation of nonoriented poly(β-propiolactone)

The hydrolytic degradation of poly(β-propiolactone) with a molecular weight M_w of 32,000 has been studied in a buffered salt solution (pH 7.2) at 37°C. Within 42 days, the embrittlement of the samples made tensile strength measurement impossible, which is due to the rapid reduction of molecular weight, 50% reduction after 49 days. The maximum weight due to water absorption was measured to 1.2 wt %, reached after 2 days. The absorbed water acts as a plasticizer in poly(β-propiolactone) observed by the displacement in the maxima of the tan δ_α peak. A fast increase of crystallinity in the samples has been observed during the first 50 days of degradation, with the increase continued up until 190 days, after which a decline of the crystallinity can be observed, indicating hydrolityc degradation of the crystalline part of the samples. The mass loss of the samples becomes prominent after 150 days of immersion and reached a value of 14.6% after 260 days.     

Preparation and swelling characterization of poly (n‐isopropylacrylamide)‐based porous hydrogels

Nine different poly(n‐isopropylacrylamide)‐based hydrogels, including nonionic, cationic, and anionic hydrogels, were synthesized in with and without the addition of pore‐forming agents. The synthesized hydrogels were characterized with dry gel density measurements, scanning electron microscopy observations, and the determination of the swelling ratio swelling kinetics. All the results showed that the cationic hydrogels had faster swelling kinetics than the anionic and nonionic hydrogels. The addition of pore‐forming agents (NaHCO₃ and carboxymethylcellulose) during the synthesis process led to porous hydrogels with lower dry densities, swelling ratios, and swelling kinetic parameter values. An empirical equation was developed to successfully correlate the swelling kinetic parameter with the hydrogel swelling ratio. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3651–3658, 2004     

β‐cyclodextrin/poly(vinyl alcohol) hydrogels containing phenylpropionic acid and naphthylamine: dual pH‐sensitive release

Hydrogel composed of β‐cyclodextrin (β‐CD) and poly(vinyl alcohol) was prepared in a strong alkaline condition using epichlorohydrin as a crosslinker. Phenylpropionic acid (PPA) and naphthylamine (NA) were loaded in the cavities of β‐CD residues to endow the hydrogel with a dual pH‐sensitive characteristic. In release experiments using fluorescein isothiocyanate‐dextran (FITC‐dextran) as a dye, PPA/NA‐loaded hydrogel exhibited an extensive release not only in acidic conditions (e.g. pH 3.0) but also in alkaline conditions (e.g. pH 9.0). PPA and NA will be highly ionized at the alkaline and the acidic pH and they could promote swelling of the hydrogel, causing an extensive release at those pH values. However, the release was suppressed at mid pH values (e.g. pH 5.0 and pH 7.4), possibly due to the formation of salt bridges between PPA^? and NA⁺. In fact, the degree of swelling at mid pH was lower than that observed at strong acidic pH and alkaline pH. According to SEM images, the pore size and the texture compactness of hydrogels which had been subjected to swelling at different pH values could also account for the dual pH‐sensitive releases. The hydrogels exhibited dual pH sensitivities in terms of FITC‐dextran release and swelling. These hydrogels might be used as a pH‐sensitive vehicle for water‐soluble drugs. © 2013 Society of Chemical Industry     

Preparation and swelling behavior of biodegradable hydrogels based on α,β‐poly(N‐2‐hydroxyethyl‐DL‐aspartamide)

Biodegradable polymers and the hydrogels have been increasingly applied in a variety of biomedical fields and pharmaceutics. α,β‐Poly(N‐2‐hydroxyethyl‐DL ‐aspartamide), PHEA, one of poly(amino acid)s with hydroxyethyl pendants, are known to be biodegradable and biocompatible, and has been studied as an useful biomaterial, especially for drug delivery, via appropriate structural modification. In this work, hydrogels based on PHEA were prepared by two‐step reaction, that is, the crosslinking of polysuccinimide, the precursor polymer, with oligomeric PEG or PEI‐diamines and the following nucleophilic ring‐opening reaction by ethanolamine. Soft hydrogels possessing varying degrees of gel strength could be prepared easily, depending on the amount of different crosslinking reagents. The swelling degrees, which were in the range of 10–40 g–water/dry gel, increased somewhat at higher temperature, and also at alkaline pH of aqueous solution. A typical hydrogel remained almost unchanged for 1 week, at 37°C in phosphate buffer of pH 7.4, and then seemed to degrade slowly as time. A porous scaffold could be fabricated by the freeze drying of water‐swollen gel. The PHEA‐based hydrogels have potential for useful biomaterial applications including current drug delivery system. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3741–3746, 2003     

Delivery of bupivacaine included in poly(acrylamide‐co‐monomethyl itaconate) hydrogels as a function of the pH swelling medium

Copolymeric hydrogels of poly(acrylamide‐co‐monomethyl itaconate) (A/MMI) crosslinked with N,N′‐methylenbisacrylamide (NBA) were synthesized as devices for the controlled release of bupivacaine (Bp). Two compositions of the copolymer, 60A/40MMI and 75A/25MMI, were studied. A local anesthetic was included in the feed mixture of polymerization (2–8 mg Bp/tablet) and by immersion of the copolymeric tablets in an aqueous solution of the drug. A very large amount of Bp (36–38 mg Bp/tablet) was included in the gels by sorption due to interactions between the drug and the side groups of the hydrogels. Swelling and drug release were in accordance with the second Fick's law at the first stages of the processes. The swelling behavior of these copolymers depended on the pH of the medium. The equilibrium swelling degree (W_∞) was larger at pH 7.5 (W_∞ ≈ 90 wt %) than at pH 1.5 (W_∞ ≈ 52–64 wt %) due to the ionization of the side groups of the copolymer. Release of the drug also depended on the pH of the swelling medium; at pH 7.5, about 60% of the included drug was released, and at pH 1.5, about 80% was released. Bp release was controlled by the comonomer composition of the gels, their drug‐load, and the pH of the swelling medium. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 327–334, 2002     

Synthesis and properties of hydrogels of poly(acrylic‐co‐acroloyl β‐cyclodextrin)

Novel acrylic monomers (β‐CD‐A and β‐CD‐6‐EA) containing β‐cyclodextrin (β‐CD) with different extent of substitution were prepared by using dicyclohexylcarbodiimide (DCC) as a condensation agent at room temperature. Two kinds of functional hydrogels were also synthesized by copolymerization of β‐CD‐A and β‐CD‐6‐EA with acrylic acid (AAc) using a redox initiator system in aqueous solution. The nuclear magnetic resonance (¹H NMR), infrared spectroscopy (IR), thermogravimetric analysis (TGA) were employed to character the molecular structures of β‐CD modified monomers and their copolymers. The swelling experiments indicate that the hydrogels with different equilibrium swelling ratio (ESR) possess obvious pH‐sensitivity and distinct dynamic swelling behavior. Using an anti‐cancer drug, chlorambucil (CHL), able to form complexes with β‐CD in water, as a model compound, the controlled drug release behaviors of these hydrogels were investigated. The release behavior of CHL from two kinds of hydrogels synthesized reveals that the release rate of CHL can be effectively controlled by pH values, cross‐linking density, and β‐CD content. In addition, it is found that the β‐CD with the proper frame and concentration can increase release efficiency of CHL from the hydrogels. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Heterogeneous and homogeneous structure dextran–poly(methacrylic acid) interpenetrating network hydrogels: synthesis and an application study

pH‐sensitive dextran–poly(methacrylic acid) (Dext–pMeAc) full interpenetrating network hydrogels (INHs) were prepared by simultaneous radical polymerization of methacrylic acid monomer (MeAc) and Dext polymer chains in the presence of N,N‐methylenebisacrylamide (MBA) as crosslinker in aqueous solution. These hydrogels were investigated as a drug carrier. The influence of MeAc and MBA contents in the network hydrogels on the swelling behaviour and mechanical strength of prepared Dext–pMeAc INHs was evaluated. Dext–pMeAc INHs were characterized by Fourier transform IR spectroscopy, and kinetic swelling measurements were carried out in deionized water and in simulated gastric fluids (pH 1.1 and pH 7.4). Dext–pMeAc/1‐1, Dext–pMeAc/3‐1 and Dext–pMeAc/5‐1 hydrogels with molar ratios of n_Dext/n_MeAc = 10 and n_MBA/n_Dext = 10, 30 and 50 respectively showed a core–shell structure when they swelled. This phenomenon was not observed in Dext–pMeAc/5‐2, Dext–pMeAc/5‐3 and Dext–pMeAc/5‐5 hydrogels containing a higher amount of Dext in the gels. The swelling data proved the formation of INHs with pH‐sensitive behaviour. A drug release study was performed using Rhodamine 6G fluorescent dye as a model hydrophilic bioactive molecule. The in vitro release rate of Rhodamine 6G from Dext–pMeAc/5‐3 hydrogel was dependent on the pH of the release medium. Copyright © 2012 Society of Chemical Industry     

Biodegradable polymers for use in surgery — poly(glycolic)/poly(Iactic acid) homo and copolymers: 2. In vitro degradation

The degradation mechanism of a series of polyglycolic/polylactic acid, (PGA/PLA), homo and copolymers synthesized as in Part 1¹, has been studied _vitro. An in vitro test model similar to that described in a previous study⁹, was used. The effects of time, temperature and pH on the rate and mechanism of degradation were elucidated. The degree of degradation was monitored molecularly by gel permeation chromatography (g.p.c.), tensile strength determination and mass loss measurements. The mechanism of degradation is shown to be by hydrolysis. The copolymers of PGA and PLA are shown to have a wide range of degradation rates governed by the hydrophilic/hydrophobic balance and crystallinity of the respective copolymer. The effect of the glass transition temperature (T_g) of PGA on its sensitivity to degradation is also demonstrated.     

Temperature and pH‐response swelling behavior of poly(2‐ethyl‐2‐oxazoline)/chitosan interpenetrating polymer network hydrogels

Interpenetrating polymer network (IPN) hydrogels composed of poly(2‐ethyl‐2‐oxazoline) (PEtOz) and chitosan (CS) were prepared with radical polymerization and were characterized for their swelling properties. Sample OC11 (hydrogel weight ratio PEtOz/CS = 1/1) swelled more than samples OC21 (PEtOz/CS = 2/1) and OC31 (PEtOz/CS =3/1), exhibiting a swelling ratio of about 2000 wt % in deionized water; the swelling ratios of the other samples were about 1000 and 700 wt %. The swelling behavior of the IPN hydrogels was observed under various pH and temperature conditions. The swelling ratios of the samples ranged from about 2000 to 6500 wt % at lower pHs, with a maximum swelling ratio of about 6500 wt % in a pH 2 aqueous solution. They exhibited low critical solution temperature behavior, with sample OC31 more sensitive to temperature and sample OC11 more sensitive to pH. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1100–1103, 2006