Characterization of thermosensitive chitosan-based hydrogels by rheology and electron paramagnetic resonance spectroscopy.

Chitosan, an amino-polysaccharide, has been proposed as a promising biopolymer for tissue repair and drug delivery. Chitosan solutions containing glycerol-2-phosphate (beta-GP) have been described as injectable in situ gelling thermosensitive formulations, which undergo sol-gel transition at physiological pH and temperatures. This feature makes them suitable for the parenteral administration of drugs, especially for peptides and proteins. The aim of the present study was to get a deeper insight into the macro- and microstructure of chitosan/beta-GP systems. In addition to oscillating rheology, electron paramagnetic resonance (EPR) spectroscopy was applied to examine the microviscosity and pH inside the gels depending on the beta-GP concentration and to follow the loading and release of spin-labelled Insulin. All chitosan/beta-GP solutions showed a physiological pH ranging from 6.6 to 6.8 that did not change during gelation, irrespective of the proportion of beta-GP. The dynamics of the spin-labelled Insulin and its microviscosity inside the gels and during release were monitored by EPR spectroscopy. The results indicate that the Insulin was incorporated into the aqueous environment of the gel and was released in its native form. The in vitro drug release from the gels was governed by diffusion of drug from the gel matrix. A sustained release of Insulin was observed over a period of 2 weeks. Increasing the proportion of beta-GP increased the amount of released Insulin and the velocity thereof.     

Proprietary Rel-Ease drug delivery technology: opportunity for sustained delivery of peptides, proteins and small molecules

Proprietary Rel-Ease (Praecis Pharmaceuticals) drug delivery technology uses biocompatible polymers as carriers to incorporate a drug into a polymer matrix through opposite charge interaction or complexation. The resulting low solubility complexes can be used to prepare sustained release depot injections or potentially sustained release formulations for oral administration. As a regulatory approved and commercialised drug delivery technology, Rel-Ease is used in abarelix for injectable suspension, a monthly depot injection for the treatment of patients with advanced prostate cancer. The technology offers high drug loading and minimal-to-no initial burst effect in vivo. It uses aqueous processes and is compatible for complexation with many peptide and protein therapeutics; its mechanism can also be applied to many small-molecule therapeutics and offers conventional and alternative methods for sustained release delivery via an oral route.     

Effect of different polymers and their combinations on the release of metoclopramide HCl from sustained-release hydrophilic matrix tablets

Metoclopramide HCl (MTC) is commonly used for the management of gastrointestinal disorders. It has a short biological half-life and is usually administered four times daily to maintain effective concentrations throughout the day. The aim of this study is to develop sustained-release hydrophilic matrix tablet formulations of drug to achieve reproducible and predictable release rates, extended duration of activity, decreased toxicity, reduction of required dose, optimized therapy, and improved patient compliance. Hydroxypropylmethyl cellulose (HPMC), carboxymethylcellulose sodium (NaCMC), chitosan and Carbopol 981 were incorporated in the matrix system separately or in combinations as release controlling factor by direct compression technique. Compatibility among the formulation components was assessed by DSC and FTIR analysis. MTC release from matrix was evaluated by using the US Pharmacopeia dissolution apparatus II. All formulations met the criteria of pharmacopeial requirements. Dissolution studies show that polymer type and concentration are important parameters on drug release. Chitosan, carbopol and NaCMC formulations exhibited pH-dependent drug release profile whereas HPMC did not. All the formulations containing 1:1 ratio of HPMC and chitosan exhibited desired drug release showing that all active substance releases progressively in a period of whole dissolution time and therefore it can be regarded as worthy of consideration for the manufacture of sustained-release MTC product.     

The Role of Chitosan in Drug Delivery

Chitosan, obtained by deacetylation of chitin, is a natural, hydrophilic, nontoxic, biocompatible, and biodegradable polysaccharide suitable for applications in pharmaceutical technology. Its role in drug delivery systems was examined by considering the chemical and biologic properties of the polymer. Chitosan is a nonbranched homopolymer formed by β-(1,4)-linked glucosamine units; hydroxyls and the amino groups are substrates for chemical modifications aimed at obtaining suitable materials for different purposes. Chitosan is soluble at acidic pH, forming gels; hydrogels are also formed in the presence of negatively charged drugs or polyanions, and represent a sustained drug release form. The bioadhesive nature of chitosan can be attributed to the same type of ionic interactions with mucosal membrane components. Mucoadhesive formulations have been developed for ocular, nasal, buccal, gastrointestinal, and vaginal drug administration. Chitosan is able to promote transmucosal absorption of small polar drugs, including peptides, inducing a transient opening of the tight junctions of the cell membrane. Due to its polymeric nature, chitosan has been widely investigated for a variety of microparticulate pharmaceutical forms. Chitosan is also a candidate for potential applications in the delivery of radiopharmaceuticals, genes and peptides.     

Thermosensitive hydrogels a versatile concept adapted to vaginal drug delivery

Vaginal drug delivery represents an attractive strategy for local and systemic delivery of drugs otherwise poorly absorbed after oral administration. The rather dense vascular network, mucus permeability and the physiological phenomenon of the uterine first-pass effect can all be exploited for therapeutic benefit. However, several physiological factors such as an acidic pH, constant secretion, and turnover of mucus as well as varying thickness of the vaginal epithelium can impact sustained drug delivery. In recent years, polymers have been designed to tackle challenges mentioned above. In particular, thermosensitive hydrogels hold great promise due to their stability, biocompatibility, adhesion properties and adjustable drug release kinetics. Here, we discuss the physiological and anatomical uniqueness of the vaginal environment and how it impacts the safe and efficient vaginal delivery and also reviewed several thermosensitive hydrogels deemed suitable for vaginal drug delivery by addressing specific characteristics, which are essential to engage the vaginal environment successfully.     

Comparison of chitosan nanoparticles and chitosan hydrogels for vaccine delivery

In this work the potential of chitosan nanoparticles (CNP) and thermosensitive chitosan hydrogels as particulate and sustained release vaccine delivery systems was investigated. CNP and chitosan hydrogels were prepared, loaded with the model protein antigen ovalbumin (OVA) and characterised. The immunostimulatory capacity of these vaccine delivery systems was assessed in‐vitro and in‐vivo. Particle sizing measurements and SEM images showed that optimised OVA‐loaded CNP had a size of approximately 200 nm, a polydispersity index < 0.2, and a positive zeta‐potential of approximately 18 mV. The amount of OVA adsorbed onto CNP was high with an adsorption efficacy of greater than 96%. Raman spectroscopy indicated conformational changes of OVA when adsorbed onto the surface of CNP. Uptake of the dispersions and immunological activation of murine dendritic cells in‐vitro could be demonstrated. Investigation of the release of fluorescently‐labelled OVA (FITC‐OVA) from CNP and chitosan hydrogels in‐vitro showed that approximately 50% of the total protein was released from CNP within a period of ten days; release of antigen from chitosan gel occurred in a more sustained manner, with < 10% of total protein being released after 10 days. The slow release from gel formulations may be explained by the strong interactions of the protein with chitosan. While OVA‐loaded CNP showed no significant immunogenicity, formulations of OVA in chitosan gel were able to stimulate both cell‐mediated and humoral immunity in‐vivo.     

Local drug delivery using poly(lactic-co-glycolic acid) nanoparticles in thermosensitive gels for inner ear disease treatment

Intratympanic (IT) therapies have been explored to address several side effects that could be caused by systemic administration of steroids to treat inner ear diseases. For effective drug delivery to the inner ear, an IT delivery system was developed using poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) and thermosensitive gels to maintain sustained release. Dexamethasone (DEX) was used as a model drug. The size and zeta potential of PLGA NPs and the gelation time of the thermosensitive gel were measured. In vitro drug release was studied using a Franz diffusion cell. Cytotoxicity of the formulations was investigated using SK-MEL-31 cells. Inflammatory responses were evaluated by histological observation of spiral ganglion cells and stria vascularis in the mouse cochlea 24 h after IT administration. In addition, the biodistribution of the formulations in mouse ears was observed by fluorescence imaging using coumarin-6. DEX-NPs showed a particle size of 150.0 ± 3.2 nm in diameter and a zeta potential of −18.7 ± 0.6. The DEX-NP-gel showed a gelation time of approximately 64 s at 37 °C and presented a similar release profile and cytotoxicity as that for DEX-NP. Furthermore, no significant inflammatory response was observed after IT administration. Fluorescence imaging results suggested that DEX-NP-gel sustained release compared to the other formulations. In conclusion, the PLGA NP-loaded thermosensitive gel may be a potential drug delivery system for the inner ear.     

Gene Delivery to the Epidermal Cells of Human Skin Explants Using Microfabricated Microneedles and Hydrogel Formulations

Purpose Microneedles disrupt the stratum corneum barrier layer of skin creating transient pathways for the enhanced permeation of therapeutics into viable skin regions without stimulating pain receptors or causing vascular damage. The cutaneous delivery of nucleic acids has a number of therapeutic applications; most notably genetic vaccination. Unfortunately non-viral gene expression in skin is generally inefficient and transient. This study investigated the potential for improved delivery of plasmid DNA (pDNA) in skin by combining the microneedle delivery system with sustained release pDNA hydrogel formulations. Materials and Methods Microneedles were fabricated by wet etching silicon in potassium hydroxide. Hydrogels based on Carbopol polymers and thermosensitive PLGA-PEG-PLGA triblock copolymers were prepared. Freshly excised human skin was used to characterise microneedle penetration (microscopy and skin water loss), gel residence in microchannels, pDNA diffusion and reporter gene (β-galactosidase) expression. Results Following microneedle treatment, channels of approximately 150–200 μm depth increased trans-epidermal water loss in skin. pDNA hydrogels were shown to harbour and gradually release pDNA. Following microneedle-assisted delivery of pDNA hydrogels to human skin expression of the pCMVβ reporter gene was demonstrated in the viable epidermis proximal to microchannels. Conclusions pDNA hydrogels can be successfully targeted to the viable epidermis to potentially provide sustained gene expression therein.     

Ocular application of chitosan

INTRODUCTION: A major problem in ocular therapeutics with classical formulations is the maintenance of an effective drug concentration at the site of action for a long period of time. Enhancement of ocular bioavailability with increased dose penetration and longer retention time at desired sites can be achieved by recent formulations. Chitosan stands out with its unique structural advantageous characteristics for different types of formulations like in situ gelling systems, micro- and nanoparticles, inserts, etc. AREAS COVERED: In this review, the authors focus on ocular therapeutics and the characteristics that make chitosan more acceptable in ocular applications. EXPERT OPINION: Chitosan seems to be one of the most promising polymeric carriers for both hydrophilic and lipophilic drugs for ocular application.     

Proprietary Rel-Ease™ drug delivery technology: opportunity for sustained delivery of peptides,proteins and small molecules

Proprietary Rel-Ease? (Praecis Pharmaceuticals) drug delivery technology uses biocompatible polymers as carriers to incorporate a drug into a polymer matrix through opposite charge interaction or complexation. The resulting low solubility complexes can be used to prepare sustained release depot injections or potentially sustained release formulations for oral administration. As a regulatory approved and commercialised drug delivery technology, Rel-Ease is used in abarelix for injectable suspension, a monthly depot injection for the treatment of patients with advanced prostate cancer. The technology offers high drug loading and minimal-to-no initial burst effect in vivo. It uses aqueous processes and is compatible for complexation with many peptide and protein therapeutics; its mechanism can also be applied to many small-molecule therapeutics and offers conventional and alternative methods for sustained release delivery via an oral route.     

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

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

The physicodynamic properties of mucoadhesive polymeric films developed as female controlled drug delivery system

Phenoporlamine hydrochloride is a novel compound that is used for the treatment of hypertension. The purpose of this study was to develop a sustained release tablet for phenoporlamine hydrochloride because of its short biological half-life. Three floating matrix formulations of phenoporlamine hydrochloride based on gas forming agent were prepared. Hydroxypropyl methylcellulose K4M and Carbopol 971P NF were used in formulating the hydrogel drug delivery system. Incorporation sodium bicarbonate into matrix resulted in the tablet floating over simulated gastric fluid for more than 6 h. The dissolution profiles of all tablets showed non-Fickian diffusion in simulated gastric fluid. Moreover, release of the drug from these tablets was pH-dependent. In vivo evaluations of these formulations of phenoporlamine hydrochloride were conducted in six healthy male human volunteers to compare the sustained release tablets with immediate release tablets. Data obtained in these studies demonstrated that the floating matrix tablet containing more Carbopol was capable of sustained delivery of the drug for longer periods with increased bioavailability and the relative bioavailability of formulation (containing 25% Carbopol 971P NF, 8.3% HPMC K4M) showed the best bioequivalency to the reference tablet (the relative bioavailability was 1.11 ± 0.19).     

In vitro topical application and in vivo pharmacodynamic evaluation of nonivamide hydrogels using Wistar rat as an animal model

Nonivamide, a so-called synthetic capsaicin, is a substitute for capsaicin which has a similar chemical structure and pharmacological activities as those of capsaicin. The purposes of this study were to explore the in vivo pharmacodynamic responses of nonivamide in hydrogels using Wistar rat as an animal model and to correlate the in vivo results with in vitro topical application. The incorporation of Pluronic F-127 polymer into hydrogels resulted in retarded release of nonivamide. Chitosan and carboxymethylcellulose hydrogels produced higher levels of in vitro nonivamide permeation and skin distribution. The in vivo effects of nonivamide on skin perturbation and vasodilation were found to differ depending on dose and duration after topical application. Quantification of transepidermal water loss was demonstrated to correlate with the measured in vitro skin distribution of nonivamide. The various doses of nonivamide in the hydrogels did not markedly influence erythematous reactions of skin as determined by colorimetric measurements. Hydrogel formulations of nonivamide delivered more drug to the skin and produced greater pharmacodynamic activities than did cream bases of capsaicin.     

Biodegradable thermosensitive copolymer hydrogels for drug delivery

Biodegradable thermogelling copolymer hydrogels have great applicative potential in areas such as sustained drug release, gene delivery and tissue engineering. These injectable materials can be implanted in the human body with minimal surgical intervention. The thermosensitive copolymers have been incorporated with a variety of biocompatible and biodegradable components such as poly(D,L-lactic acid-co-glycolic acid), poly(L-lactic acid), poly (L-carprolactone), poly([R]-3-hydroxybutyrate), poly(organophosphazene), poly(peptide), poly(propylene fumarate), poly(propylene phosphate), polyacetal and poly(ortho ester). Various formulations consisting of the copolymers and therapeutic agents have been developed and the sustained release of these agents has been demonstrated. This review aims to provide a comprehensive summary of the recent developments in this field of study and highlights the most recent intellectual property and research papers.     

注射用姜黄素温敏凝胶在实体瘤内滞留时间的研究

目的:研究注射用姜黄素温敏凝胶在小鼠实体瘤内的滞留时间。方法:复制小鼠实体瘤模型,以亚甲蓝温敏凝胶和亚甲蓝水溶液为模型药物,直观考察温敏凝胶是否可延长滞留时间,确定所用方法的可行性。通过反相高效液相色谱法测定注射用姜黄素温敏凝胶于不同时间点时在小鼠实体瘤内的剩余量,从而确定其滞留时间,并与同浓度的注射用姜黄素混悬液对比。结果:亚甲蓝水溶液注射进入瘤体后会沿着针孔外渗,而亚甲蓝温敏凝胶无此现象。注射用姜黄素温敏凝胶在实体瘤内的滞留时间为43.02h,显著长于姜黄素混悬液的滞留时间(P<0.01)。结论:注射用姜黄素温敏凝胶在小鼠实体瘤内滞留时间较长,显示其具有一定的缓释作用。     

Thermosensitive hydrogels for drug delivery

INTRODUCTION: Controlled drug delivery has been widely applied in areas such as cancer therapy and tissue regeneration. Thermosensitive hydrogel-based drug delivery systems have increasingly attracted the attention of the drug delivery community, as the drugs can be readily encapsulated and released by the hydrogels. AREAS COVERED: Thermosensitive hydrogels that can serve as drug carriers are discussed in this paper. Strategies used to control hydrogel properties, in order to tailor drug release kinetics, are also reviewed. This paper also introduces applications of the thermosensitive hydrogel-based drug delivery systems in cancer therapy and tissue regeneration. EXPERT OPINION: When designing a drug delivery system using thermosensitive hydrogels, one needs to consider what type of thermosensitive hydrogel needs to be used, and how to manipulate its properties to meet the desired drug release kinetics. For material selection, both naturally derived and synthetic thermosensitive polymers can be used. Various methods can be used to tailor thermosensitive hydrogel properties in order to achieve the desired drug release profile.     

Evaluating Suspension Formulations of Theophylline Cocrystals With Artificial Sweeteners

Pharmaceutical cocrystals have garnered significant interest as potential solids to address issues associated with formulation development of drug substances. However, studies concerning the understanding of formulation behavior of cocrystals are still at the nascent stage. We present results of our attempts to evaluate suspension formulations of cocrystals of an antiasthmatic drug, theophylline, with 2 artificial sweeteners. Stability, solubility, drug release, and taste of the suspension formulations were evaluated. Suspension that contained cocrystal with acesulfame showed higher drug release rate, while a cocrystal with saccharin showed a significant reduction in drug release rate. The cocrystal with saccharin was found stable in suspension for over 9 weeks at accelerated test condition; in contrast, the cocrystal with acesulfame was found unstable. Taste analysis using an electronic taste-sensing system revealed improved sweetness of the suspension formulations with cocrystals. Theophylline has a narrow therapeutic index with a short half-life which necessitates frequent dosing. This adversely impacts patient compliance and enhances risk of gastrointestinal and cardiovascular adverse effects. The greater thermodynamic stability, sweetness, and sustained drug release of the suspension formulation of theophylline-saccharin could offer an alternative solution to the short half-life of theophylline and make it a promising formulation for treating asthmatic pediatric and geriatric patients.     

Chitosan-based hydrogels for controlled, localized drug delivery

Hydrogels are high-water content materials prepared from cross-linked polymers that are able to provide sustained, local delivery of a variety of therapeutic agents. Use of the natural polymer, chitosan, as the scaffold material in hydrogels has been highly pursued thanks to the polymer's biocompatibility, low toxicity, and biodegradability. The advanced development of chitosan hydrogels has led to new drug delivery systems that release their payloads under varying environmental stimuli. In addition, thermosensitive hydrogel variants have been developed to form a chitosan hydrogel in situ, precluding the need for surgical implantation. The development of these intelligent drug delivery devices requires a foundation in the chemical and physical characteristics of chitosan-based hydrogels, as well as the therapeutics to be delivered. In this review, we investigate the newest developments in chitosan hydrogel preparation and define the design parameters in the development of physically and chemically cross-linked hydrogels.     

瘤内注射用醋酸奥曲肽温敏凝胶的质量评价

目的:评价自制瘤内注射用醋酸奥曲肽(OA)温敏凝胶的质量。方法:测定醋酸奥曲肽温敏凝胶的胶凝温度、黏度,采用反相高效液相色谱法测定样品中OA含量并考察其体外释放情况。结果:醋酸奥曲肽温敏凝胶的胶凝温度为(37.1±0.2)℃,在此温度下黏度为(4750±13)mPa·s,含量为5.1mg·mL-1,96h在磷酸盐缓冲液释放介质(pH=7.2)中体外累积释药率为(85.7±1.67)%。结论:醋酸奥曲肽温敏凝胶质量合格。     

Design and development of an injectable in situ forming drug delivery system of methotrexate for the treatment of rheumatoid arthritis

Methotrexate (MTX) is the drug of choice for the treatment of rheumatoid arthritis (RA). At present there exists a lacuna in delivering methotrexate in suitable dosage form to maintain optimum plasma concentration to achieve therapeutic efficacy during the treatment period. Exposure of MTX at higher concentrations resulted in severe side effects. Moreover, the treatment modality (initial and maintenance dose) of RA is not clinically uniform. Biodegradable injectable in situ gels offer versatility in delivering drug at predetermined rates, and maintaining plasma concentration with a possibility of dose adjustment. They can be developed to optimize the therapeutic properties of a drug product, render them safe, effective and reliable during therapy. The aim of the present study was to formulate a biodegradable injectable in situ gel system for methotrexate sodium in the treatment of rheumatoid arthritis. The formulations were prepared by "cold technique" using thermosensitive polymer, Pluronic F-127 (20 %) and varying concentration of co-polymers, Pluronic F-68 (2–6 %) and Carbopol 934 (1.0-1.5 %). The prepared in situ gels were evaluated in vitro for drug interactions by FT-IR, sterility, gelation characteristics, content uniformity, viscosity, syringeability and in vitro drug release. MTX was evenly distributed in all formulations, which were sterile and syringeable through an 18 gauze needle. The gels were thermosensitive and thermoresponsive, and were dependent on the concentration of co-polymers. Drug release from in situ gels was sustained for 96 h to 120 h, and influenced by the type and concentration of co-polymers employed. Drug release was significantly higher in dynamic diffusion state in comparison with static state as ascertained by student t-test. The drug release was by non-fickian diffusion mechanism and followed first-order kinetics. These findings suggested that in situ gels can be effectively used to achieve controlled drug release; are easy to administer, are effective with reduced frequency of dosage, and result in increased patient compliance and comfort. It may be concluded that methotrexate in situ gels are ideally suitable in the treatment of RA.