Poly(2-hydroxyethyl methacrylate) film as a drug delivery system for pilocarpine

Designing temperature-responsive biocompatible copolymers and hydrogels based on 2-hydroxyethyl(meth)acrylates

Free-radical copolymerization of 2-hydroxyethyl methacrylate with 2-hydroxyethyl acrylate can be successively utilized for the synthesis of water-soluble polymers and hydrogels with excellent physicochemical properties, thus showing promise for pharmaceutical and biomedical applications. In the work presented it has been demonstrated that water-soluble copolymers based on 2-hydroxyethyl methacrylate and 2-hydroxyethyl acrylate exhibit lower critical solution temperature in aqueous solutions, whereas the corresponding high molecular weight homopolymers do not have this unique property. The temperature-induced transitions observed upon heating the aqueous solutions of these copolymers proceed via liquid-liquid phase separation. The hydrogels were also synthesized by copolymerizing 2-hydroxyethyl methacrylate and 2-hydroxyethyl acrylate in the absence of a bifunctional cross-linker. The cross-linking of these copolymers during copolymerization is believed to be due to the presence of bifunctional admixtures or transesterification reactions. Transparency, swelling behavior, mechanical properties, and porosity of the hydrogels are dependent upon the monomer ratio in the copolymers. Hydrogel samples containing more 2-hydroxyethyl methacrylate are less transparent, have lower swelling capacity, higher elastic moduli, and pores of smaller size. The assessment of the biocompatibility of the copolymers using the slug mucosal irritation test revealed that they are also less irritant than poly(acrylic acid).

Characterization of the rheological, mucoadhesive, and drug release properties of highly structured gel platforms for intravaginal drug delivery

This investigation describes the formulation and characterization of rheologically structured vehicles (RSVs) designed for improved drug delivery to the vagina. Interactive, multicomponent, polymeric platforms were manufactured containing hydroxyethylcellulose (HEC, 5% w/w) polyvinylpyrrolidone (PVP, 4% w/w), Pluronic (PL, 0 or 10% w/w), and either polycarbophil (PC, 3% w/w) or poly(methylvinylether-co-maleic anhydride) (Gantrez S97, 3% w/w) as a mucoadhesive agent. The rheological (torsional and dynamic), mechanical (compressional), and mucoadhesive properties were characterized and shown to be dependent upon the mucoadhesive agent used and the inclusion/exclusion of PL. The dynamic rheological properties of the gel platforms were also assessed following dilution with simulated vaginal fluid (to mimic in vivo dilution). RSVs containing PC were more rheologically structured than comparator formulations containing GAN. This trend was also reflected in formulation hardness, compressibility, consistency, and syringeability. Moreover, formulations containing PL (10% w/w) were more rheologically structured than formulations devoid of PL. Dilution with simulated vaginal fluids significantly decreased rheological structure, although RSVs still retained a highly elastic structure (G' > G'' and tan delta < 1). Furthermore, RSVs exhibited sustained drug release properties that were shown to be dependent upon their rheological structure. It is considered that these semisolid drug delivery systems may be useful as site-retentive platforms for the sustained delivery of therapeutic agents to the vagina.

Design and evaluation of novel fast forming pilocarpine-loaded ocular hydrogels for sustained pharmacological response

Fast forming hydrogels prepared by crosslinking a poly(ethylene glycol) (PEG)-based copolymer containing multiple thiol (SH) groups were evaluated for the controlled ocular delivery of pilocarpine and subsequent pupillary constriction. Physical properties of the hydrogels were characterized using UV-Vis spectrophotometry, transmission electron microscopy (TEM), rheometry, and swelling kinetics. Pilocarpine loading efficiency and release properties were measured in simulated tear fluid. The hydrogel formulations exhibited high drug loading efficiency (approximately 74%). Pilocarpine release was found to be biphasic with release half times of approximately 2 and 94 h, respectively, and 85-100% of the drug was released over 8-days. Pilocarpine-loaded (2% w/v) hydrogels were evaluated in a rabbit model and compared to a similar dose of drug in aqueous solution. The hydrogels were retained in the eye for the entire period of the study with no observed irritation. Pilocarpine-loaded hydrogels sustained pupillary constriction for 24 h after administration as compared to 3 h for the solution, an 8-fold increase in the duration of action. A strong correlation between pilocarpine release and pupillary response was observed. In conclusion, the current studies demonstrate that in situ forming PEG hydrogels possess the viscoelastic, retention, and sustained delivery properties required for an efficient ocular drug delivery system.

Carbodiimide cross-linked hyaluronic acid hydrogels as cell sheet delivery vehicles: characterization and interaction with corneal endothelial cells

It was reported that cell-adhesive gelatin discs have been successfully used as delivery vehicles for intraocular grafting of bioengineered corneal endothelial cell sheets. Development of alternative biomaterials to bovine-based gelatin vehicles can potentially eliminate the risk of bovine spongiform encephalopathy. In the present work, to investigate whether it was appropriate for use as cell sheet delivery vehicles, 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) cross-linked hyaluronic acid (HA) hydrogels were studied by determinations of morphological characteristic, mechanical and thermal property, water content, in vitro degradability and cytocompatibility. Glutaraldehyde (GTA) cross-linked HA samples were used for comparison. It was found that HA discs after cross-linking significantly increased its tensile stress but reduced its tensile strain, water uptake and enzymatic degradability. The results of differential scanning calorimetry demonstrated that cross-linking could lead to the alteration of polymer structure. In addition, the EDC-cross-linked HA discs had a smoother surface structure, a faster degradation rate and a relatively lower cytotoxicity as compared to the GTA cross-linked counterparts. It is concluded that EDC can be successfully applied for HA cross-linking to fabricate structurally stable, mechanically reinforced, readily deformable, transparent and cytocompatible HA hydrogel discs with the potential to be applied as delivery vehicles for corneal endothelial cell therapy.

Functionalized chitosan/NIPAM (HEMA) hybrid polymer networks as inserts for ocular drug delivery: Synthesis,in vitro assessment, andin vivo evaluation

A series of hybrid polymeric hydrogels, prepared by the reaction of acrylic acid-functionalized chitosan with either N-isopropylacrylamide or 2-hydroxyethyl methacrylate monomers, were synthesized, pressed into minitablets, and investigated for their ability to act as controlled release vehicles for ophthalmic drug delivery. For comparison, interpolymeric complex analogues synthesized using the same monomers and pure, unfunctionalized chitosan were examined by means of an identical characterization protocol. The effects of network structure and composition upon the swelling properties, adhesion behavior, and drug release characteristics were investigated. Comparative in vitro studies employing chloramphenicol, atropine, norfloxacin, or pilocarpine informed the selection of drug-specific carrier compositions for the controlled delivery of these compounds. In addition, in vivo (rabbit model) experiments involving the delivery of pilocarpine indicated that chitosan-based hybrid polymer networks containing 2-hydroxyethyl methacrylate are useful carriers for the delivery of this therapeutic agent.

Soft Nanotechnology with Soft Nanoparticles

The last decade of research in the physical sciences has seen a dramatic increase in the study of nanoscale materials. Today, "nanoscience" has emerged as a multidisciplinary effort, wherein obtaining a fundamental understanding of the optical, electrical, magnetic, and mechanical properties of nanostructures promises to deliver the next generation of functional materials for a wide range of applications. While this range of efforts is extremely broad, much of the work has focused on "hard" materials, such as Buckyballs, carbon nanotubes, metals, semiconductors, and organic or inorganic dielectrics. Meanwhile, the soft materials of current interest typically include conducting or emissive polymers for "plastic electronics" applications. Despite the continued interest in these established areas of nanoscience, new classes of soft nanomaterials are being developed from more traditional polymeric constructs. Specifically, nanostructured hydrogels are emerging as a promising group of materials for multiple biotechnology applications as the need for advanced materials in the post-genomic era grows. This review will present some of the recent advances in the marriage between water-swellable networks and nanoscience.

Initiated chemical vapor deposition of linear and cross-linked poly(2-hydroxyethyl methacrylate) for use as thin-film hydrogels

Initiated chemical vapor deposition (iCVD) is able to synthesize linear and cross-linked poly(2-hydroxyethyl methacrylate) (PHEMA) thin films, in one step, from vapors of 2-hydroxyethyl methacrylate (HEMA), ethylene glycol diacrylate (EGDA), and tert-butyl peroxide (TBPO) without using any solvents. This all-dry technique also allows control of the cross-link density by adjusting the partial pressure of the cross-linking agent EGDA in the vapor phase. Films with specific cross-link densities and hence thermal, wetting, and swelling properties can be created in one single vacuum processing step. Through selective thermal decomposition of the initiator TBPO, films with well-defined chemical structures and full functionality retention can be deposited, which is evident in the Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses. These spectroscopic methods also facilitate determination of EGDA incorporation in the cross-linked films based on the fact that HEMA contains a hydroxyl group but EGDA does not. For the linear PHEMA depositions, the growth rate was found to be nonlinear in the partial pressure of HEMA, possibly due to nonlinear multilayer adsorption and/or primary termination. The EGDA/HEMA ratio in the films systematically increased from 0.00 to 0.46 as the EGDA partial pressure was raised. The onset temperatures of decomposition were between 270 and 302 degrees C for the linear and the most cross-linked films, respectively. Thermal annealing at approximately 430 degrees C resulted in minuscule amounts of residue for all films, linear or cross-linked. The most cross-linked film had approximately 99.50% thickness removed after annealing. The contact angle was found to increase with increasing cross-link density. Significant contact-angle hysteresis was observed, indicating surface reconfiguration, and the lowest receding angle was 17 degrees for the linear film. Swelling measurements using spectroscopic ellipsometry showed that the degree of swelling decreased with increasing EGDA incorporation. The water content decreased from 35% (v/v) for the linear film to below 10% (v/v) for the most cross-linked film. These results show that iCVD is able to produce PHEMA thin films that function as hydrogels when soaked in water. The spectroscopic results, the contact-angle results, and the swelling analysis altogether prove the retention of the hydrophilic pendant groups in the iCVD process.

Poly(2-hydroxyethyl methacrylate) wound dressing containing ciprofloxacin and its drug release studies

An improved wound dressing with a long-term drug diffusion-efficacy has been developed by UV-radiation technique. It involves incorporation of ciprofloxacin (CIP), at the concentration of 0.5-2.0% (w/v), into a water mixture of 2-hydroxymethacrylate (HEMA) monomer, benzoin isobutyl ether (BIE) initiator and different content of ethylene glycol dimethacrylate (EGDMA) cross-linker. Increasing the concentration of EGDMA would reduce the releasing ratio of CIP from pHEMA. T1/2 is increased from 2.64 to 45.67 h when the EGDMA is added from 1 to 8%. In the ranges of 0< or = F < or = 0.6, the n value of 1%CIP-pHEMA membranes is increased from 0.48 to 0.81. It indicates that the mechanism of drug release falls between the Fickian and Case II diffusion model. The antibacterial activity of the drug impregnated into the membrane was evaluated by in vitro drug kinetic agar plate method. Higher concentration of EGDMA, up to 8% of the cross-linker, extends the drug release. Comparison with the drug-soaked membranes, the newly synthesized 1% CIP-pHEMA membrane (cross-linked with 4% EGDMA) sustains the release of the entrapped drug and maintains the antibacterial activity up to 12 days.

Novel carboxymethylcellulose-based microporous hydrogels suitable for drug delivery

Several materials capable of acting as structures for controlled release were analysed for the fabrication of matrices. Among those used, hydrophilic polysaccharides appeared to be the most suitable materials. Carboxymethylcellulose (a semi-synthetic polysaccharide) was chemically cross-linked with a 60% and 90% cross-linking degree in order to obtain hydrogels and utilised as matrix for the realisation of controlled drug release systems. The morphology of the gels was changed in order to obtain a microporous structure with different porosity (14, 30 and 40 microm). The obtained porous matrices were characterised in terms of pore density, dimension and swelling behaviour. The influence of both the pore dimension and technique of loading on the release kinetics was analysed. By increasing the pore dimension the release of ibuprofen-lysin was slower. Inducing the microporous structure after the loading of the hydrogel with the drug resulted in a slower release.

One-side-coated insert as a unique ophthalmic drug delivery system

We newly prepared a unique one-side-coated insert that releases drug from only uncoated side. The purpose of this study is to determine whether ocular and systemic absorption of ophthalmic drug could be altered by an inserting direction of the insert in rabbit eyes. One-side-coated insert was prepared by attaching a polypropylene tape on the one side of the polymer disc of poly(2-hydroxypropyl methacrylate) (HPM) containing tilisolol as a model ophthalmic drug. The insert was applied in the lower conjunctival cul-de-sac of albino rabbits with the uncoated side facing bulbar conjunctiva/sclera (SC insert) or palpebral conjunctiva (CJ insert). At the adequate intervals, the tear fluid, plasma, aqueous humor, conjunctiva, and sclera were collected and the drug concentrations were determined by an HPLC. A release of tilisolol from the one-side-coated insert was twice slower than from the uncoated insert. Ocular application of the one-side-coated insert produced the constant concentrations of tilisolol in the tear fluid over 180 min. SC insert showed higher drug concentrations in the aqueous humor and sclera, and lower drug concentrations in the plasma and conjunctiva than CJ insert.The one-side-coated insert can alter the ocular and systemic absorption of drug by an inserting direction.