Synthesis,properties, and permeation of solutes through hydrogels based on poly(ethylene glycol)-co-poly(lactones) diacrylate macromers and chitosan

Triblock copolymers from poly(ethylene glycol) (PEG) and D,L -lactide or ε-caprolactone were synthesized to prepare semi-interpenetrating polymer networks (semi-IPNs) with chitosan by ultraviolet (UV) irradiation method. Then, the solute permeation through these semi-IPNs hydrogels were investigated. The structures of semi-IPNs were confirmed by Fourier transform infrared (FTIR) spectroscopy and wide-angle X-ray diffractometer (WAXD). The equilibrium water content (EWC) of these hydrogels was in the range of 67–75%. The crystallinity, thermal properties, and mechanical properties of semi-IPNs hydrogels were studied. All the hydrogels revealed a remarkable decrease in crystallinity as compared with the PEG macromer itself. The tensile strengths of semi-IPNs hydrogels in a dry state were rather high, but those of hydrogels in a wet state decreased drastically. The permeabilities of solutes of hydrogels followed the swelling behaviors and were regulated by solute size. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2151–2158, 1999     

Phase behavior,in vitro drug release,and antibacterial activity of thermoresponsive poloxamer–polyvinyl alcohol hydrogel-loaded mupirocin nanoparticles

This research was designed to develop thermoresponsive poloxamer (P407)–polyvinyl alcohol (PVA) hydrogels to deliver mupirocin nanoparticles for wound healing. The mupirocin nanoparticles containing drug and gelatin or poly (acrylic acid) were prepared by spray drying. The hydrogel phases were evaluated by small-angle X-ray scattering. An in vitro drug release study was performed and the antibacterial activity of mupirocin nanoparticles-loaded hydrogel (MLH) was evaluated. Fourier transform infrared and proton nuclear magnetic resonance spectrum spectra of the mupirocin nanoparticles indicated a weak interaction between mupirocin and the carriers of carbopol and gelatin. The mupirocin molecules were surrounded by the carrier molecules. The MLH appeared to exhibit single diamond (Fd3m) phase behavior similar to P407 and the hydrogel base. The release of MLH in vitro indicated first-order kinetics (R² = .9839–.8868). The MLH showed lower minimum inhibitory concentrations and minimum bactericidal concentrations against Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, and Escherichia coli than mupirocin ointment.     

In situ gel forming systems of poloxamer 407 and hydroxypropyl cellulose or hydroxypropyl methyl cellulose mixtures for controlled delivery of vancomycin

Poloxamers are a family of triblock copolymers consisting of two hydrophilic blocks of polyoxyethylene separated by a hydrophobic block of polyoxypropylene, which form micelles at low concentrations and form clear thermally reversible gels at high concentrations. The objective of this study was to develop an in situ gel forming drug delivery system for vancomycin using the minimum possible ratio of poloxamer 407 (P407). Decreasing the concentration of poloxamer could reduce the risk of hypertriglyceridemia induction. Different additives were added to the poloxamer formulations. It was observed that among different additives, hydroxypropyl methyl cellulose (HPMC) and hydroxypropyl cellulose (HPC) can decrease poloxamer concentration required to form in situ gelation from 18 to 10%. The dynamic viscoelastic properties of the samples were determined. Both the storage modulus and the loss modulus of the samples increased abruptly as the temperature passed a certain point. The gelling temperature was in the order of P407 : HPC (10 : 10 w/w) < P407 : HPMC (10 : 10 w/w) < P407 : HPMC (15 : 5 w/w) < P407 : HPC (15 : 5 w/w). Drug release rate could be controlled by changing the type and ratio of additives as well as the amount of drug loaded. It can be concluded that combining P407 and cellulose derivatives could be a promising strategy for preparation of thermally reversible in situ gel forming delivery systems with low poloxamer concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Kinetics of sol-to-gel transition for poloxamer polyols

Kinetics of gelation for aqueous solutions of poloxamers 407 and 288 were determined using pulse shearometry. The principle of this method for determining the shear modulus of a semisolid was based on generation of a torsional force that is transmitted through the poloxamer sample at discrete time intervals. Three distinct linear phases were observed for the log dynamic shear modulus (G′) vs. time profiles as poloxamer 407 and 288 solutions of varying concentrations were allowed to passively warm at room temperature to a temperature exceeding the sol-to-gel transition temperature, T_m. The beginning of the second exponential phase coincided with the onset of the gelation process as determined by visual observation. Although gelation appeared visually to be complete at the beginning of the third exponential phase of the log G′ vs. time profiles, this last exponential phase may indicate the rate of formation of the polymer network. A comparison of poloxamer 407 [30% (w/w); T_m = 10.9°C] and poloxamer 288 [37% (w/w); T_m = 11.1°C] would suggest that the concentration of poloxamer required to achieve approximately the same gelation temperature for poloxamers having a similar ratio of poly(oxypropylene):poly(oxyethylene) units decreases with increasing molecular weight of the poly(oxypropylene) hydrophobe contained in the copolymer. Results of these preliminary studies suggest that the gelation process was significantly (p < .05) more rapid for poloxamer 407 at a 30% (w/w) concentration compared to a 30% (w/w) solution of poloxamer 288 when the poloxamer solutions were allowed to passively warm at room temperature. In addition, it appears that the rate of gelation for the poloxamer solutions studied was dependent on the rate of heat transfer through the polymer solution.     

Development of a poloxamer analogs/bioadhesive polymers‐based in situ gelling ophthalmic delivery system for tiopronin

The purpose of this study was to develop a poloxamer analogs/bioadhesive polymers‐based in situ gelling ophthalmic delivery system aiming at enhancing bioavailability and anticataract effect. The effect of poloxamer 407 (P407), poloxamer 188 (P188), carbopol 934P (C934), and sodium hyaluronate (NaHA) concentration on the gelation temperature (GT) was examined. The GT of P407 based in situ gel increased with an increase in the P188 concentration. NaHA and C934 lowered the GT of poloxamer analogs based in situ gel. Correlation analysis demonstrated that in vitro drug release from in situ gel was controlled by gel dissolution and followed zero‐order kinetics. Tiopronin in vitro transcorneal transit accorded with zero‐order kinetics. Twenty‐two percent P407 and 6% P188 containing 0.2% NaHA based formulation can be chosen as in situ gel matrix of tiopronin because of proper GT and sustained releasing ability. In vivo study showed that the area under the aqueous humor–concentration time curve of tiopronin increased by 1.6 folds for in situ gel, compared with tiopronin aqueous solution. High‐dose tiopronin in situ gel and solution delayed the development of selenite cataract 6 d and 4 d, respectively. The results showed that tiopronin in situ gel exhibits higher bioavailability and therapeutical effect. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Swelling characteristics and in vitro drug release study with pH‐ and thermally sensitive hydrogels based on modified chitosan

The grafting of a poly(ethylene glycol) diacrylate macromer onto a chitosan backbone was carried out with different macromer concentrations. The grafting was achieved by (NH₄)₂Ce(NO₃)₆‐induced free‐radical poly merization. Biodegradable, pH‐ and thermally responsive hydrogels of poly(ethylene glycol)‐g‐chitosan crosslinked with a lower amount of glutaraldehyde were prepared for controlled drug release studies. Both the graft copolymers and the hydrogels were characterized with Fourier transform infrared, elemental analysis, and scanning electron microscopy. The obtained hydrogels were subjected to equilibrium swelling studies at different temperatures (25, 37, and 45°C) in buffer solutions of pHs 2.1 and 7.4 (similar to those of gastric and intestinal fluids, respectively). 5‐Fluorouracil was entrapped in these hydrogels, and equilibrium swelling studies were carried out for the drug‐entrapped gels at pHs 2.1 and 7.4 and 37°C. The in vitro release profile of the drug was established at 37°C and pHs 2.1 and 7.4. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 977–985, 2006     

Solute and solvent effects on the thermorheological properties of poly(oxyethylene)–poly(oxypropylene) block copolymers: Implications for pharmaceutical dosage form design

Despite their widespread use as platforms for topical drug delivery systems, there is a relative lack of information concerning the thermorheological and viscoelastic properties of poloxamer systems and the effects of formulation components on these properties. To address this deficit, we examined the effects of the poloxamer concentration (25 and 35% w/w), molecular weight blend (poloxamer 407 and poloxamer 188), cosolvents (ethanol, propylene glycol, and glycerol), and presence of inorganic and organic electrolytes (sodium chloride and tetracaine hydrochloride, respectively) on these properties. The rheological properties were examined with a rheometer (4‐cm‐diameter, stainless steel, parallel‐plate geometry) in either thermal sweep (0.5 Hz) or frequency sweep (0.01–1.0 Hz and 37°C) modes. Increasing the poloxamer concentration increased the elasticity [i.e., increased the storage modulus (G′) and reduced the loss tangent (tan δ)] and reduced the sol–gel transition temperature (T_m) of all the formulations. Decreasing the ratio (407:188) increased T_m and reduced the elasticity of all the formulations. Increasing the concentration of ethanol, propylene glycol, or glycerol in the solvent reduced T_m. The presence of ethanol reduced G′ and increased tan δ in a concentration‐dependent fashion, whereas the viscoelastic properties of the poloxamers were more tolerant of glycerol (in particular) and propylene glycol. The elasticity of the formulations containing up to 10% glycerol and 5% propylene glycol was increased with respect to their aqueous counterparts. The presence of sodium chloride reduced T_m and, at lower concentrations (1 and 3%), increased G′ and reduced tan δ for aqueous poloxamer systems. Conversely, the addition of a model therapeutic agent, tetracaine hydrochloride (5 and 7% w/w), significantly increased T_m and altered the viscoelastic character of the poloxamer system, notably reducing G′ and increasing the loss modulus and tan δ. Alterations in the viscoelastic and thermorheological properties of aqueous poloxamer systems will have implications for their clinical performance. This study, therefore, has highlighted the need for the rational selection of components in the formulation of poloxamer systems as platforms for topical drug delivery. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1016–1026, 2003     

Novel polyurethane‐based thermosensitive hydrogels as drug release and tissue engineering platforms: design and in vitro characterization

Poloxamer P407 (P407) is a Food and Drug Administration approved triblock copolymer; its hydrogels show fast dissolution in aqueous environment and weak mechanical strength, limiting their in vivo application. In this work, an amphiphilic poly(ether urethane) (NHP407) was synthesized from P407, an aliphatic diisocyanate (1,6‐hexanediisocyanate) and an amino acid derived diol (N‐Boc serinol). NHP407 solutions in water‐based media were able to form biocompatible injectable thermosensitive hydrogels with a lower critical gelation temperature behavior, having lower critical gelation concentration (6% w/v versus 18% w/v), superior gel strength (G′ at 37 °C about 40 000 Pa versus 10 000 Pa), faster gelation kinetics (<5 min versus 15–30 min) and higher stability in physiological conditions (28 days versus 5 days) compared to P407 hydrogels. Gel strength and PBS absorption at 37 °C increased whereas dissolution rate (in phosphate‐buffered saline (PBS) at 37 °C) and permeability to nutrients (studied using fluorescein isothiocyanate–dextran model molecule) decreased as a function of NHP407 hydrogel concentration from 10% to 20% w/v. By varying the concentration, NHP407 hydrogels were thus prepared with different properties which could suit specific applications, such as in situ drug/cell delivery or bioprinting of scaffolds. Moreover, deprotected amino groups in NHP407 could be exploited for the grafting of bioactive molecules obtaining biomimetic hydrogels. © 2016 Society of Chemical Industry     

Thermoplastic hydrogel based on pentablock copolymer consisting of poly(γ‐benzyl L‐glutamate) and poloxamer

A thermoplastic hydrogel based on a pentablock copolymer composed of poly(γ‐benzyl L ‐glutamate) (PBLG) and poloxamer was synthesized by polymerization of BLG N‐carboxyanhydride, which was initiated by diamine‐terminated groups located at the ends of poly(ethylene oxide) (PEO) chains of the poloxamer, to attain a new pH‐ and temperature‐sensitive hydrogel for drug delivery systems. Circular dichroism measurements in solution and IR measurements in the solid state revealed that the polypeptide block existed in the α‐helical conformation, as in the PBLG homopolymer. The intensity of the wide‐angle X‐ray diffraction patterns of the polymers depended on the poloxamer content in the copolymer and showed basically similar reflections to the PBLG homopolymer. The melting temperature (T_m) of the poloxamer in the copolymer was reduced with an increase of the PBLG block in comparison with the T_m of the poloxamer, which is indicative of a thermoplastic property. The water contents of the copolymers were dependent on the poloxamer content in the copolymers, for example, those for the GPG‐2 (48.7 mol % poloxamer) and GPG‐1 (57.5 mol % poloxamer) copolymers were 31 and 41 wt %, respectively, indicating characteristics of a polymeric hydrogel. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2649–2656, 2003     

Preparation and properties of modified PHEMA hydrogel with sulfonated PEG graft

A novel poly(ethylene glycol) (PEG) macromer with a methacryloyl and sulfonic acid group at each end of the chain was prepared. Modified hydroxyethyl methacrylate (HEMA) based hydrogels were synthesized by crosslinking polymerization of HEMA in the presence of the above‐mentioned PEG macromer. The effect of the sulfonated PEG graft was examined by comparing the swelling properties with those of a pure poly(hydroxyethyl methacrylate) (PHEMA) hydrogel. The modified PHEMA hydrogel exhibited increasing water absorbency with increasing sulfonated PEG content up to 15 wt %. These hydrogels with the sulfonated PEG graft exhibited a more hydrophilic character than the pure PHEMA gel. Also the swelling degree varied slightly with pH, showing increased swelling at higher pH probably due to the presence of the anionic sulfonate group on the PEG end chain. In addition, the protein adsorption test showed a lower level of fibrinogen adsorption from the sulfonated poly(ethylene glycol) (SPEG) modified gel than on the homo PHEMA hydrogel. Interestingly, scanning electron microscopy showed that the porous and rather uniform morphology of the gels changed with increasing sulfonated PEG content in PHEMA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2484–2489, 2007     

Preparation of semi‐interpenetrating polymer networks composed of silk fibroin and poly(ethylene glycol) macromer

Semi‐interpenetrating polymer networks (SIPNs) composed of silk fibroin (SF) and a poly(ethylene glycol) (PEG) diacrylate macromer were synthesized and characterized. The conformation of SF in SIPNs was changed from a random coil to a β‐sheet structure by formation of SIPNs with PEG, while the crystalline structures of SF and PEG in SIPNs was not changed. The decomposition temperature of SF in the SIPNs was inner‐shifted, an indication of SIPN formation between the SF and the PEG macromer. The tensile strength and elongation of the SIPNs were much higher than were those of SF itself or the SF/PEG blend and increased with an increase of the PEG content. The equilibrium water content of SF was remarkably increased by formation of SIPNs with PEG due to the hydrophilic property of PEG. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1848–1853, 2001     

Syntheses of hydroxypropyl methylcellulose phthalate hydrogels in Na2CO3 aqueous solutions with electron‐beam irradiation

Novel cellulose ether hydrogels were prepared by the radiation‐induced crosslinking of hydroxypropyl methylcellulose phthalate (HPMCP) in a solution of Na₂CO₃. The effects of several factors, such as the HPMCP concentration, Na₂CO₃ concentration, absorbed dose, and dose rate, on the crosslinking of HPMCP were investigated in detail. An increase in the HPMCP concentration resulted in an increasing content of the gel fraction, and this meant that the crosslinking probability increased as well. Na₂CO₃ was essential for dissolving HPMCP in water, and a 4–5% Na₂CO₃ aqueous solution was optimal for the crosslinking of HPMCP. The dose rate also affected the radiation crosslinking of HPMCP; hydrogels with higher gel fractions and transparency could be formed at lower dose rates. The ratio of degradation to crosslinking of the gel was calculated according to the Charlesby–Rosiak equation, and it showed good agreement with the experimental results. Some important properties, such as the swelling kinetics, ion and ionic strength dependence, and pH dependence, of the HPMCP hydrogels were also investigated. The HPMCP hydrogels possessed excellent swelling rates and swelling ratios in some solvents, such as water and methanol, with a high hydrogen‐bonding parameter. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2123–2130, 2003     

Effect of macromer synthesis time on the properties of the resulting poly(β‐amino ester) degradable hydrogel

Poly(β‐amino ester) biodegradable hydrogels are common in biomedical applications because of their tunable properties and similarities to natural soft tissue. Previous work has shown property adjustments through the choice of monomers, the ratio between monomers and the addition of a crosslinking component. Here, we show that the reaction time for the creation of the macromer can affect the resulting hydrogel properties, and thus provides another method of tuning properties. Macromer was created through the reaction of isobutylamine with poly(ethylene glycol) diacrylate (n = 400). The reaction progress was analyzed using IR and GPC analysis. Hydrogels were created through UV photopolymerization from macromers synthesized for 24, 36, and 48 h. The degradation, compressive moduli, and swelling were measured in an aqueous solution. All showed significant differences between hydrogels of different macromer synthesis times. These differences likely stem from the incomplete macromer synthesis reaction and resulting PEG‐rich regions in hydrogels from shorter synthesis times. These regions will not readily degrade, but do increase the mechanical properties and extent of swelling. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Study of poly(acrylamide‐co‐2‐acrylamido‐2‐methylpropane sulfonic acid) hydrogels made using gamma radiation initiation

Poly(acrylamide‐co‐2‐acrylamido‐2‐methylpropane sulfonic acid) hydrogels were synthesized using gamma‐radiation‐initiated polymerization. The progress of copolymerization and crosslinking was observed by viscosity measurement on reaction mixtures subjected to varying radiation doses. The copolymer gels were characterized by differential scanning calorimetry, X‐ray diffraction, scanning electron microscopy, infrared spectroscopy, and elemental analysis. The swelling behavior and other properties of the gels were found to be very similar to those of poly(acrylamide‐co‐2‐acrylamido‐2‐methylpropane sulfonic acid) hydrogels synthesized using conventional free‐radical initiation in the presence of crosslinkers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1322–1330, 2003     

Thermosensitive and ampholytic hydrogels for salt solution

A series of N‐isopropylacrylamide/[[3‐(methacryloylamino)propyl]dimethy(3‐sulfopropyl)ammonium hydroxide] (NIPAAm/MPSA) copolymer hydrogels were prepared with various compositions. Swelling of the hydrogels in water, aqueous NaCl, KCl, CaCl₂, and MgCl₂ solutions was studied. NIPAAm/MPSA hydrogels have a higher degree of swelling in water and salt solutions than that of poly(N‐isopropylacrylamide) (PNIPAAm). Also, NIPAAm/MPSA hydrogels are more salt resistant when deswelling in salt solutions. For <7 mol % MPSA, the formed hydrogels retain both temperature reversibility and high swelling. A higher content of MPSA (>11 mol %) leads to better salt resistance but a decrease in thermosensitivity. The swelling of NIPAAm/MPSA hydrogel in 0.05M NaCl is non‐Fickian. In NaCl and KCl aqueous solutions, the zwitterionic hydrogels do not show obvious antipolyelectrolyte swelling behavior, whereas in divalent salt CaCl₂ and MgCl₂ solutions, the swelling ability of NIPAAm/MPSA hydrogels is enhanced at low salt concentration, then decreases with further increase in salt concentration. The lower critical solution temperatures of NIPAAm/MPSA hydrogels are also affected by concentrated salt solution. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2032–2037, 2003     

New route to the preparation of carboxymethylchitosan hydrogels

A new method to prepare CM–chitosan hydrogels was introduced with the use of steam. The procedure was simple and economical, with no toxic chemicals involved. The steam‐induced crosslinking of CM–chitosan sodium salt involved the –NH₂ and –COONa groups, forming amide linkages (–CONH–), evidently supported by FTIR spectroscopy and other techniques. The hydrogels instantly imbibed a great deal of water. The degree of swelling (DS) of the hydrogels was found to be up to 36, depending on the harshness of steaming conditions used. Likewise, the coloration of the samples increased from light beige to brown with increasing temperature and duration of steam exposure. The overall efficiency of the steam method for the crosslinking of CM–chitosan sodium salt was quite high. The percentage weight loss was found to be less than 10 to obtain hydrogels with DS values around 20. No weight loss in the dry weight of the fractionated hydrogels was observed when the samples were steamed at 115°C or higher for 15 min or longer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 4016–4020, 2003     

Synthesis and properties of amphiphilic copolymers of butyl acrylate and methyl methacrylate with uniform polyoxyethylene grafts

Amphiphilic copolymers of butyl acrylate (BA) and methyl methacrylate (MMA) with uniform polyoxyethylene (PEO) grafts were synthesized by the copolymerization of BA and MMA with a methacrylate‐terminated PEO macromer in benzene with azobisisobutyronitrile as an initiator. The effects of various copolymerization conditions on the grafting efficiency and molecular weight of the copolymers, as well as the effect of the copolymerization time on the conversions of the macromer and the monomers, were reported. The copolymers, with uniform PEO grafts, were purified by successive extractions with water and ether/acetone (3/7) to remove unreacted macromer and ungrafted copolymers of MMA and BA, respectively. The purified graft copolymers were characterized with IR, ¹H‐NMR, membrane osmometry, gel permeation chromatography, and differential scanning calorimetry. The highest grafting efficiency was about 90%, and molecular weight of the copolymers varied around 10⁵. The average grafting number of the copolymer was about 10. A study of the crystalline properties, emulsifying properties, phase‐transfer catalytic ability, and mechanical properties of the graft copolymers showed that the emulsifying volume decreased with the increasing molecular weight of the PEO grafts but increased with the PEO content. The conversion of potassium phenolate in the Williamson solid–liquid reaction obviously increased with an increasing PEO content of the graft copolymers. The crystallinity of the graft copolymers increased with the PEO content of the graft copolymers or the molecular weight of the macromer used. The copolymers, prepared under certain conditions, behaved as thermoplastic elastomers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2982–2988, 2003     

Controlled Release from Crosslinked Poloxamer Hydrogels

Chemically modified derivatives of the copolymeric poloxamer surfactants have been polymerised to form crosslinked, swelling hydrogels. Mixtures of derivatives of poloxamers 188 and 181 form gels which show increased swelling with increased content of the more hydrophilic poloxamer 188. The rate of release of benzoic and p-hydroxybenzoic acids also increases with increasing content of poloxamer 188. Release rate data have been analysed in terms of the swelling controlled release model for these hydrogels.     

Thermal degradation of poly(ethylene oxide-propylene oxide-ethylene oxide) triblock copolymer: comparative study by SEC/NMR, SEC/MALDI-TOF-MS and SPME/GC-MS

By comparing size exclusion chromatography/matrix assisted laser desorption ionisation (SEC/MALDI) and SEC/NMR spectra from virgin poly(ethylene oxide-propylene oxide-ethylene oxide) triblock copolymer, we were able to understand the bimodal distribution observed in poloxamer 407. Propylene oxide, isomerised to allyl alcohol during polymerisation, eventually forms a Poly(ethylene oxide-propylene oxide) diblock copolymer when EO is added to the feed. The oxidative thermal degradation of poloxamer 407 at 80°C in air was studied. We found by MALDI that degradation starts after 21 days in the PPO block of the copolymer. This result was confirmed by solid phase microextraction/gas chromatography-mass spectrometry (SPME/GC-MS): The first volatile degradation product to appear is 1,2-propanediol,1-acetate,2-formate. The structure of this molecule suggests that a six-ring intramolecular decomposition reaction of the PPO chain occurs at the very beginning of the polymer breakdown. Thus, the secondary hydroperoxide formed on the PPO chain plays a major role on the thermoxidation of poloxamer materials.     

Chemically treated hard gelatin capsules for colon‐targeted drug delivery: A novel approach

Hard gelatin capsules, containing riboflavin‐loaded poly (N‐viny1–2‐pyrrolidone)‐polyacrylamide cylindrical hydrogels, were modified chemically by treating with an aqueous formaldehyde solution for the purpose of delayed release of drug along the gastrointestinal tract. The t_dis (disintegration time) of capsules was studied as a function of concentration of formaldehyde solution and the treatment time. The dynamic release of vitamin B₂ was studied as a function of crosslinking ratio of the hydrogels. The device studied seems to have potential to be used for colon‐targeted drug delivery. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2277–2282, 2003