Formulation optimization of photocrosslinked polyacrylic acid modified with 2-hydroxyethyl methacrylate hydrogel as an adhesive for a dermatological patch

Chain-Extendable Crosslinked Hydrogels Using Branching RAFT Modification

Functional crosslinked hydrogels were prepared from 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AA). The acid monomer was incorporated both via copolymerization and chain extension of a branching, reversible addition–fragmentation chain-transfer agent incorporated into the crosslinked polymer gel. The hydrogels were intolerant to high levels of acidic copolymerization as the acrylic acid weakened the ethylene glycol dimethacrylate (EGDMA) crosslinked network. Hydrogels made from HEMA, EGDMA and a branching RAFT agent provide the network with loose-chain end functionality that can be retained for subsequent chain extension. Traditional methods of surface functionalization have the downside of potentially creating a high volume of homopolymerization in the solution. Branching RAFT comonomers act as versatile anchor sites by which additional polymerization chain extension reactions can be carried out. Acrylic acid grafted onto HEMA–EGDMA hydrogels showed higher mechanical strength than the equivalent statistical copolymer networks and was shown to have functionality as an electrostatic binder of cationic flocculants.

Wound dressing adherence: a review

Wound dressing adherence is an important problem that is frequently encountered in wound care, and is associated with both clinical and economic burdens. However, only a few review articles have focused on this issue. The objective of this review was to present a comprehensive discussion of wound dressing adherence, including the mechanism of dressing adherence, adverse consequences (clinical burdens and economic burdens), factors affecting adherence (dressing-, patient- and wound-related factors, and factors related to the wound care procedure), tests to assess dressing adherence (in vitro assay, in vivo assay and clinical trials), and reduction of wound adherence (modification of dressing adherence and special care in particular patients). Accordingly, this review article emphasises an awareness of dressing adherence, and is intended to be an informative source for the development of new dressings and for wound management.

Controlled evaporation-induced phase separation of droplets containing nanogels and salt molecules

Droplets without protection from surfactants or surfactant-like objects normally experience merging or a coalescence process since it is thermodynamically favored. However, division or replication of droplets is thermodynamically unfavored and comparably more difficult to realize. Herein, we demonstrate that a population of droplets that are composed of nanogels and salt spontaneously undergo a separation process under a slow solvent evaporation condition. Each individual droplet underwent changes in size, shape and eventually developed into two domains, which was caused by the screening effect due to the increased salt concentration as a result of solvent evaporation. The two domains gradually separated into nanogel-rich and salt-rich parts. These two parts eventually evolved into nanogel aggregates and branched structures, respectively. This separation was mainly due to the salting out effect and dewetting. Comparison studies indicate that both the nanogels and salt are indispensable ingredients for the phase separation. These discoveries may have profound applications in the fields of biomimetics and offer new routes for self-replication systems.

An individual droplet containing nanogels and salts can evolve into gel-rich and salt-rich two separate parts upon evaporation.

The Usefulness of Definitive Screening Design for a Quality by Design Approach as Demonstrated by a Pharmaceutical Study of Orally Disintegrating Tablet

Definitive screening design (DSD) is a new class of small three-level experimental design that is attracting much attention as a technical tool of a quality by design (QbD) approach. The purpose of this study is to examine the usefulness of DSD for QbD through a pharmaceutical study on the preparation of ethenzamide-containing orally disintegrating tablet. Model tablets were prepared by directly compressing the mixture of the active pharmaceutical ingredient (API) and excipients. The five evaluated factors assigned to DSD were: the contents of API (X1) and lubricant (X2), and the compression force (X3) of the tableting process, the mixing time (X4), and the filling ratio of powder in the V-type mixer (X5). After tablet preparation, hardness and disintegration time were measured. The same experiments were performed by using the conventional design of experiments [i.e., L8 and L16 orthogonal array designs and central composite design (CCD)]. Results showed that DSD successfully clarified how various factors contribute to tablet properties. Moreover, the analysis result from DSD agreed well with those from the L8 and L16 experiments. In additional experiments, response surfaces for tablet properties were created by DSD. Compared with the response surfaces created by CCD, DSD could produce reliable response surfaces for its smaller number of experiments. We conclude that DSD is a powerful tool for implementing pharmaceutical studies including the QbD approach.

An Optimized and Feasible Preparation Technique for the Industrial Production of Hydrogel Patches

For hydrogel patches, the laboratory tests could not fully reveal the existing problems of full scale of industrial production, and there are few studies about the preparation technique for the industrial manufacturing process of hydrogel patches. So, the purpose of this work was to elucidate the effects of mainly technological operation and its parameters on the performance of hydrogel patches at the industrial-scale production. The results revealed the following: (1) the aqueous phase was obtained by polyvinylpyrrolidone (PVP) along with tartaric acid dissolved in purified water, then feeding this into a vacuum mixer as a whole in one batch, thus extended the crosslinking reaction time of hydrogel paste (matrix) and allowed the operation of coating/cutting-off to be carried out easily, and there was no permeation of backing layer; (2) the gel strength of the hydrogel patches increased with the increase of working temperature, however, once the temperature exceeded 35 ± 2 °C, the hydrogel paste would lose water severely and the resultant physical crosslinking structure which has lower gel/cohesive strength would easily bring gelatinization/residues during application; (3) the relative humidity (RH) of the standing-workshop was dynamically controlled (namely at 35 ± 2 °C, keeping the RH at 55 ± 5% for 4 days, then 65 ± 5% for 2 days), which would make patches with satisfactory characteristics such as better flexibility, higher adhesive force, smooth flat matrix surface, and without gelatinization/residues and warped edge during the using process; (4) the aging of the packaged hydrogel patches was very sensitive to storage temperature, higher temperature, higher gel strength and lower adhesiveness. The storage temperature of 10 ± 2 °C could effectively prevent matrix aging and adhesion losing, which would also facilitate the expiration date of patches extended obviously. In conclusion, this work provides an optimized and feasible preparation technique for the industrial production of the hydrogel patches and establishes the hydrogel patches as a novel carrier for transdermal drug delivery.

Preparation of a mixed-matrix hydrogel of vorinostat for topical administration on the rats as experimental model

Oral vorinostat has the remarkable curative effect on aggravated and recurrent cutaneous T-cell lymphoma (CTCL), but is accompanied by serious adverse effects. Therefore, oral vorinostat is not applicable to the treatment of early stage CTCL. The aim of this study is to develop a novel vorinostat formulation which is effective for early stage CTCL and free of the serious adverse effects. A mixed-matrix hydrogel of vorinostat was prepared and characterized as a potential topical skin delivery system. Moisture retention, swelling behavior, viscosity, real-time morphology and differential scanning calorimeter analysis (DSC) of hydrogel were evaluated to select the solvent, matrix and humectant. The optimal HPMC/HPC ratio, pH, additive, dose and drug loading of vorinostat hydrogel were determined by evaluating the cumulative vorinostat amount of skin retention and transdermal amount of vorinostat through the skin in vitro. The optimal hydrogel presented a low transdermal amount of vorinostat through the skin, suggesting that the hydrogel reduced the amount of vorinostat that was absorbed in the systemic circulation. More importantly, in vivo percutaneous permeation experiments were also performed to evaluate the permeation behavior of vorinostat into the skin. The topical application with a much lower dose showed higher AUC (the cumulative vorinostat amount of skin retention) than oral application and the hydrogel achieved a sustained permeation of vorinostat in the skin for 24h in vivo. It indicated that a higher relative bioavailability for hydrogel was achieved compared with oral vorinostat. Moreover, there was no damage, inflammation or cell swelling of the skin after administration. Thus, the mixed-matrix vorinostat hydrogel prepared in this study could deliver vorinostat into local skin more efficiently than oral administration.

Study of the contribution of the state of water to the gel properties of a photocrosslinked polyacrylic acid hydrogel using magnetic resonance imaging

Photocrosslinked polyacrylic acid (PAA-HEMA) hydrogels are a promising candidate for use in dermatological patch adhesives. To gain further knowledge about the properties of this gel, we investigated the T1 relaxation time and the diffusion coefficient (D) of water in the hydrogels using magnetic resonance (MR) imaging. Hydrogels with different formulations and process factors were prepared and tested. The observed data were analyzed by ANOVA, which clarified the mode of action of the formulation and process factors based on these MR parameters. Various gel properties (i.e., gel fraction, swelling capacity, gel strength, and water-retention ability) were also measured, followed by a Bayesian network (BN) analysis. The BN allowed us to summarize well the relationships between the formulation and process factors, MR parameters, and gel properties. T1 was associated with the swelling and water-retention properties of the hydrogel, whereas D was associated with gel formation and gel strength. Furthermore, this study clarified that T1 and D mostly represented the hydration and water-compartmentalization effects of the hydrogel, respectively. In conclusion, the state of water seems to play an important role in the properties of the PAA-HEMA hydrogel.

Adhesive properties: a critical issue in transdermal patch development

INTRODUCTION

Transdermal patches and medicated plasters (patch) represent well-established prolonged release dosage forms. Even if satisfactory adhesion to the skin is strictly linked to the efficacy and safety of the therapeutic treatment, nowadays numerous reports of in vivo 'adhesion lacking' are still addressed to regulatory agencies. The adhesive properties of a patch should be characterized considering i) the ability to form a bond with the surface of another material on brief contact and under light pressure (tack); ii) the resistance of the adhesive to flow (shear adhesion); and iii) the force required to peel away a patch from a surface (peel adhesion).

AREAS COVERED

In this manuscript, the most widely used methods to measure adhesive properties during development studies are described, along with the quality control of patches. The influence of formulative variables on patch adhesive properties, and their possible relationship with the in vivo adhesion performances, is also discussed.

EXPERT OPINION

The Pharmacopoeias should consider the opportunity of introducing compendial testing to assay the quality of adhesive patch properties, and regulatory agencies should issue proper guidelines to evaluate these features during development.

Biosensors for phenolic compounds by immobilization of tyrosinase in photocurable methacrylic-acrylic membranes of varying hydrophilicities

Electrochemical biosensors for phenolic compound determination were developed by immobilization of tyrosinase enzyme in a series of methacrylic-acrylic based biosensor membranes deposited directly using a photocuring method. By modifying the hydrophilicity of the membranes using different proportions of 2-hydroxyethyl methacrylate (HEMA) and butyl acrylate (nBA), we developed biosensor membranes of different hydrophilic characters. The differences in hydrophilicity of these membranes led to changes in the sensitivity of the biosensors towards different phenolic compounds. In general biosensors constructed from the methacrylic-acrylic based membranes showed the poorest response to catechol relative to other phenolic compounds, which is in contrast to many other biosensors based on tyrosinase. The decrease in hydrophilicity of the membrane also allowed better selectivity towards chlorophenols. However, phenol biosensors constructed from the more hydrophilic membrane materials demonstrated better analytical performance towards phenol compared with those made from less hydrophilic ones. For the detection of phenols, these biosensors with different membranes gave detection limits of 0.13-0.25 microM and linear response range from 6.2-54.2 microM phenol. The phenol biosensors also showed good phenol recovery from landfill leachate samples (82-117%).

Novel approaches to neural and evolutionary computing in pharmaceutical formulation: challenges and new possibilities

The development of commercial pharmaceutical formulations can involve extensive experimentation that generates a large amount of data. Understanding such data and discovering the key relationships within them can be a complex process, adding considerably to the time and expense taken to get a product to market. However, new computational techniques such as neural and evolutionary computing have the potential to accelerate the mining and modeling of data, and these methodologies are now being packaged in a way that makes them readily accessible to the product formulator. This article outlines the basis of these technologies and reviews their use in pharmaceutical formulation, showing that they have gained acceptance as practical research tools, especially when integrated with complementary optimization and visualization tools. Neural and evolutionary computing are gaining widespread acceptance in the field of pharmaceutical formulation, with results being comparable with, or better than, those from traditional statistical methods.

Formulation optimization of an indomethacin-containing photocrosslinked polyacrylic acid hydrogel as an anti-inflammatory patch

Photocrosslinked polyacrylic acid hydrogel, made from polyacrylic acid (PAA) modified with 2-hydroxyethyl methacrylate (HEMA), is a promising candidate adhesive for dermatological patches. In this study, we investigated the further availability of hydrogel as an adhesive for dermatological patches using a hydrogel containing indomethacin (IDM) as a model anti-inflammatory patch. From an orthogonal experimental study, we clarified the relationships between formulation factors and characteristics of model formulation. Formulations with a lower degree of swelling were prepared by increasing the degree of HEMA modification and the addition of Tween 80. Apparent permeation rate was increased by addition of L-menthol and Tween 80. A tendency for higher HEMA modification to be accompanied by the prolongation of the lag time of IDM was observed. To obtain an applicable anti-inflammatory patch, we conducted a formulation optimization study using a novel optimization method, a response-surface method incorporating multivariate spline interpolation (RSM-S). Consequently, a highly functional anti-inflammatory patch in terms of its adhesive properties and bioavailability was successfully obtained. Since a wide range of functions can be fully controlled by manipulating the formulation factors, photocrosslinked polyacrylic acid hydrogel is an attractive candidate adhesive for dermatological patches.

Evaluation of the Reliability of Nonlinear Optimal Solutions in Pharmaceuticals Using a Bootstrap Resampling Technique in Combination With Kohonen's Self‐Organizing Maps

The response surface method incorporating multivariate spline interpolation (RSM-S) is a powerful technique for the formulation optimization of pharmaceuticals. However, no satisfactory method has been developed to evaluate the reliability of the optimal solution. We integrated bootstrap (BS) resampling and Kohonen's self-organizing maps (SOM) into RSM-S using the formulation optimization of theophylline tablets as the model experiment. The hardness and the 63.2% drug-release times of the tablets were measured as response variables. Based on the data set obtained, the simultaneous optimal solution was estimated using RSM-S. Leave-one-out cross-validation showed the optimal solution to be reliable. Concurrently, a large number of BS samples were generated from the original data set using BS resampling, and simultaneous optimal solutions for each BS sample (BS optimal solutions) were estimated. The distribution of the BS optimal solutions was far from a normal distribution, suggesting a mixture of global and local optimal solutions. SOM clustering was used to identify the set of global optimal solutions. SOM clustering divided the BS optimal solutions into several clusters, and the reliability of the optimal solution was evaluated from the cluster that included the optimal solution. This study offers a promising method for evaluating the reliability of nonlinear optimal solutions. .

Key functions in polymer carriers for intestinal absorption of insulin

This work aimed to clarify the relationship between polymer function and insulin absorption, and to evaluate the optimized preparative formulation predicted from this relationship. Insulin-loaded polymer (ILP) carrier systems were prepared following a two-factor composite second-order spherical experimental design. To investigate the polymer function, we evaluated its insulin release, bioadhesiveness, and protective effect. Each ILP was administered intestinally, and glucose reduction was monitored as the pharmacological effect. Based on these data, an optimized formulation was predicted and how the polymer function affects insulin absorption was clarified by multivariate spline (MVS) interpolation. A greater pharmacological effect was apparent in ILPs with a smaller particle size and loaded with more insulin. The pharmacological effect predicted by MVS after the administration of ILP made under optimized preparative conditions was almost identical to the observed effect. Moreover, MVS clarified the relationship between the polymer function and the pharmacological effect. These results supported that MVS can be an effective tool with which to approximate the relationship between the function of a dosage form and its absorption, and to explore the optimized preparative conditions.

Importance of evaluating the consolidation of granules manufactured by high shear mixer

The effects of the process parameters of high shear wet granulation on the granule properties and dissolution properties of mefenamic acid from tablets have been studied, and the importance of evaluating the consolidation of granules has been considered. The process parameters selected for investigation were the amount of water added, the impeller rotation speed and the kneading time. Increases in the amount of water and the kneading time led to increases in the particle diameter of the granules and to decreases in the mean pore diameter. The mean pore diameter decreased with increases in the impeller rotation speed, while the particle diameters were independent of the impeller rotation speed. The process parameters affected the surface morphology and the internal morphology of the granules. The mean particle diameter and the mean pore diameter of the granules basically correlated with the dissolution properties of the tablets. The contribution of the mean pore diameter to this correlation was higher than that of mean particle diameter. Therefore, it was concluded that evaluation of the granule consolidated state, such as the mean pore diameter, was important in order to assure the dissolution properties of drug products.

Synthesis and Characterization of Degradable p(HEMA) Microgels: Use of Acid-Labile Crosslinkers

New divinyl-functionalized acetal-based crosslinkers were synthesized as building elements to form acid-labile microgel particles for controlled-release applications. The synthesized crosslinkers underwent hydrolysis at slightly acidic pHs in less than 1 h while they were stable at neutral pHs for longer times. HEMA was copolymerized with the crosslinkers via an inverse emulsion polymerization technique using a redox initiator system at room temperature to form crosslinked, colloidal p(HEMA) microgels. Microgels in diameters ranging from 150 to 475 nm with narrow distribution could be produced. The crosslinking density and the diameter of the microgels were found to be controlled by monomer/crosslinker feed ratio. The microgels demonstrated a pH-dependent cleavage behavior that mimicked the pH-dependent hydrolysis profile of the acid-labile crosslinkers. Model biomacromolecules, i.e., Rhodamine B-labeled dextran and BSA were efficiently loaded into the microgels. The release of the biomolecules from p(HEMA) microgels was also found to be controllable by the pH of the environment similar to the particle degradation. The protein released from the microgels was observed to retain its structural stability.