Thermosensitive hydrogels for drug delivery

Aqueous Phase Separation Behavior of Highly Syndiotactic, High Molecular Weight Polymers with Densely Packed Hydroxy-Containing Side Groups

Herein we describe the Rh-catalyzed C1 polymerization of silyl-protected diazoacetates of the general formula HC(=N₂)C(=O)O(CH₂) _x OSiR₃, where x = 2-5. After polymerization and subsequent desilylation, syndiotactic polymers bearing a hydroxy-containing side group on every backbone carbon are obtained. The molecular weight of the desired polymers can be controlled via chain transfer with methanol during the polymerization. The produced polymers are compared to atactic analogues formed by [(η³-C₃H₅)PdCl]-catalyzed polymerization of silyl-protected diazoacetates with the same general formula. While the polymers produced by the Rh and Pd catalysts have the same hydrophilic/hydrophobic balance, the stereoregularity of the polymers formed by the Rh catalyst was found to be of influence on the thermoresponsive behavior of the polymer. The effect of this stereoregularity on the thermoresponsive phase separation behavior of the produced polymers in aqueous solution was investigated.

PEO-PPO-PEO Tri-Block Copolymers for Gene Delivery Applications in Human Regenerative Medicine-An Overview

Lineal (poloxamers or Pluronic^®) or X-shaped (poloxamines or Tetronic^®) amphiphilic tri-block copolymers of poly(ethylene oxide) and poly(propylene oxide) (PEO-PPO-PEO) have been broadly explored for controlled drug delivery in different regenerative medicine approaches. The ability of these copolymers to self-assemble as micelles and to undergo sol-to-gel transitions upon heating has endowed the denomination of “smart” or “intelligent” systems. The use of PEO-PPO-PEO copolymers as gene delivery systems is a powerful emerging strategy to improve the performance of classical gene transfer vectors. This review summarizes the state of art of the application of PEO-PPO-PEO copolymers in both nonviral and viral gene transfer approaches and their potential as gene delivery systems in different regenerative medicine approaches.

Investigation of nanoscale zerovalent iron-based magnetic and thermal dual-responsive composite materials for the removal and detection of phenols

In this study, well-defined magnetic and thermal dual-responsive nanomaterials were synthesized, which contained ultrafine core-shell Fe@SiO₂ nanoparticles as magnetic core and poly(N-isopropylacrylamide) (PNIPAM) as thermosensitive outer shell. The fabricated nanoparticles were characterized and investigated for the adsorption of four phenolic compounds, including bisphenol A (BPA), tetrabromobisphenol A (TBBPA), 4-tert-octylphenol (4-OP) and 4-n-nonylphenol (4-NP). The experimental results demonstrated that the excellent adsorption rates were attributed to hydrophobic effect, hydrogen-bonding interaction, and electrostatic attraction. The adsorption process followed pseudo-second-order kinetics model and nonlinear isotherms, indicating heterogeneous adsorption process. The adsorption efficiency of 4-NP using Fe@SiO₂@PNIPAM was more than 90% under optimized condition within 2 h. The determined maximum adsorption amounts of BPA, TBBPA, 4-OP and 4-NP were 2.43, 6.83, 24.75, and 49.34 mg g^-1, respectively. Meanwhile, a magnetic solid phase extraction (MSPE) method with Fe@SiO₂@PNIPAM was established to determine these four compounds simultaneously. Under the optimal conditions, the linearity ranges were in the range of 2-200, 2-300, 2-100 and 2-100 μg L^-1 for BPA, 4-OP, TBBPA, and 4-NP, respectively, and the detection limits were in the range of 0.58-0.76 μg L^-1, respectively. The applicability of the proposed method was evaluated by analyzing three fresh water samples, and satisfactory spiked recoveries in the range 70.9-119.9% were achieved. It was proved that these adsorbents could be easily collected and recycled owing to the appropriate magnetism. The results also demonstrated that the as-prepared adsorbents had promising potential in the enrichment and analysis of detrimental organic pollutants from water.

Construction and evaluation of BSA-CaP nanomaterials with enhanced transgene performance via biocorona-inspired caveolae-mediated endocytosis

Non-viral nanovectors have attracted much attention owing to their ability to condense genetic materials and their ease of modification. However, their poor stability, low biocompatibility and gene degradation in endosomes or lysosomes has significantly hampered their application in vivo and in the clinic. In an attempt to overcome these difficulties a series of bovine serum albumin (BSA)-calcium phosphate (CaP) nanoparticles were constructed. The CaP condenses with DNA to form nanocomplexes coated with a biomimetic corona of BSA. Such complexes may retain the inherent endocytosis profile of BSA, with improved biocompatibility. In particular the transgene performance may be enhanced by stimulating the cellular uptake pathway via caveolae-mediated endocytosis. Two methods were employed to construct and optimize the formulation of BSA-CaP nanomaterials. The optimized BSA-CaP-50-M2 nanoparticles prepared by our second method exhibited good stability, negligible cytotoxicity and enhanced transgene performance with long-term expression for 72 h in vivo even with a single dose. Determination of the cellular uptake pathway and Western blot revealed that cellular uptake of the designed BSA-CaP-50-M2 nanoparticles was mainly via caveolae-mediated endocytosis in a non-degradative pathway in which the biomimetic uptake profile of BSA was retained.

Self-assembled thermoresponsive nanostructures of hyaluronic acid conjugates for osteoarthritis therapy

Under pathological conditions, joints and skin are often affected by an imbalance in the breakdown and production of hyaluronic acid (HA). The unique biochemical and biomechanical properties provided by HA must be restored for the long-term lubrication and cushioning effects. To overcome the inconvenience of repeated injections and the rapid degradation of exogenous HA treatments, HA is conjugated to a thermosensitive polymer, enabling the spontaneous formation of nanoparticles (HA Nano) at body temperature. Three HA Nano preparations are tested for their injectability, sensitivity to enzymatic degradation and cytocompatibility. One of them is delivered via subcutaneous and intra-articular injections to healthy mice and tested in a murine osteoarthritis (OA) model. It is found to be biocompatible, to offer a prolonged residence time at the injection site, have the ability to protect cartilage, to reduce pro-inflammatory cytokines and to preserve epiphysis thickness. In this study, HA Nano spontaneously forms nanoparticles at body temperature in vivo and is a promising candidate for the next generation of the sustainable/long-lasting treatment of OA and potentially also dermatological conditions.

Thermogelling, ABC Triblock Copolymer Platform for Resorbable Hydrogels with Tunable, Degradation-Mediated Drug Release

Clinical application of injectable, thermoresponsive hydrogels is hindered by lack of degradability and controlled drug release. To overcome these challenges, a family of thermoresponsive, ABC triblock polymer-based hydrogels has been engineered to degrade and release drug cargo through either oxidative or hydrolytic/enzymatic mechanisms dictated by the "A" block composition. Three ABC triblock copolymers are synthesized with varying "A" blocks, including oxidation-sensitive poly(propylene sulfide), slow hydrolytically/enzymatically degradable poly(ε-caprolactone), and fast hydrolytically/enzymatically degradable poly(D,L-lactide-co-glycolide), forming the respective formulations PPS135-b-PDMA152-b-PNIPAAM225 (PDN), PCL85-b-PDMA150-b-PNIPAAM150 (CDN), and PLGA60-b-PDMA148-b-PNIPAAM152 (LGDN). For all three polymers, hydrophilic poly(N,N-dimethylacrylamide) and thermally responsive poly(N-isopropylacrylamide) comprise the "B" and "C" blocks, respectively. These copolymers form micelles in aqueous solutions at ambient temperature that can be preloaded with small molecule drugs. These solutions quickly transition into hydrogels upon heating to 37 °C, forming a supra-assembly of physically crosslinked, drug-loaded micelles. PDN hydrogels are selectively degraded under oxidative conditions while CDN and LGDN hydrogels are inert to oxidation but show differential rates of hydrolytic/enzymatic decomposition. All three hydrogels are cytocompatible in vitro and in vivo, and drug-loaded hydrogels demonstrate differential release kinetics in vivo corresponding with their specific degradation mechanism. These collective data highlight the potential cell and drug delivery use of this tunable class of ABC triblock polymer thermogels.

Thermosensitive Hydrogel Containing Doxycycline Exerts Inhibitory Effects on Abdominal Aortic Aneurysm Induced By Pancreatic Elastase in Mice

Doxycycline (DOX) is reported to exert therapeutic effects against abdominal aortic aneurysm (AAA), a severe degenerative disease. In this study, a DOX hydrogel formulation of DOX/PECT^gel is studied, and its phase transition behavior and in vitro release profiles are explored. In addition, the anti-AAA effects and bioavailability of DOX/PECT^gel are evaluated in an elastase induced AAA mouse model. The results show that the phase transition temperature of 30% poly(e-caprolactone-co-1,4,8-trioxa[4.6]spiro-9-undecanone) (PECT) solution is above 34 °C. In vitro release profiles of DOX/PECT^gel indicate a fast release of DOX at the first two days, followed by a slow and sustained release for 14 d. In vivo single-dose single subcutaneous injection of DOX/PECT^gel containing 8.4 or 4.2 mg mL^-1 DOX presents comparatively preventive effects on AAA, compared to intraperitoneal injections of DOX alone at a dose of 15 mg kg^-1 for seven injections, while DOX bioavailability of the DOX/PECT^gel treated groups is 1.39 times or 1.19 times of the DOX alone treated group, respectively.

Basic concepts and recent advances in nanogels as carriers for medical applications

Nanogels in biomedical field are promising and innovative materials as dispersions of hydrogel nanoparticles based on crosslinked polymeric networks that have been called as next generation drug delivery systems due to their relatively high drug encapsulation capacity, uniformity, tunable size, ease of preparation, minimal toxicity, stability in the presence of serum, and stimuli responsiveness. Nanogels show a great potential in chemotherapy, diagnosis, organ targeting and delivery of bioactive substances. The main subjects reviewed in this article concentrates on: (i) Nanogel assimilation in the nanomedicine domain; (ii) Features and advantages of nanogels, the main characteristics, such as: swelling capacity, stimuli sensitivity, the great surface area, functionalization, bioconjugation and encapsulation of bioactive substances, which are taken into account in designing the structures according to the application; some data on the advantages and limitations of the preparation techniques; (iii) Recent progress in nanogels as a carrier of genetic material, protein and vaccine. The majority of the scientific literature presents the multivalency potential of bioconjugated nanogels in various conditions. Today's research focuses over the overcoming of the restrictions imposed by cost, some medical requirements and technological issues, for nanogels' commercial scale production and their integration as a new platform in biomedicine.

Development and characterization dual responsive magnetic nanocomposites for targeted drug delivery systems

A drug delivery system based on dual responsive units was developed. An appealing pH- and thermo-responsive triblock terpolymer as the drug carrier was synthesized by RAFT polymerization of N-isopropyl acrylamide and methacrylic acid monomers using PEG-RAFT agent. The Fe₃O₄ magnetic nanoparticles were synthesized by co-precipitation of Fe salts. Synthesized samples were characterized by FT-IR, XRD, GPC, SEM and TEM. The dual responsive behaviour and self-assembly of the triblock terpolymers in aqueous solution were investigated using UV-vis transmittance and DLS. Based on the results of DLS and TEM, the average size of micelles was 170, 125 and 30 nm. The triblock terpolymer was used as a chemotherapy drug carrier and doxorubicin as a model drug. The release rate of the drug at two different temperatures (37 °C and 42 °C) and pHs (5.8 and 7.4) was studied. The in vitro cytotoxicity assay of free doxorubicin and drug-loaded magnetic nanoparticles was studied. The MTT assay exhibited that these polymers are biocompatible and no toxicity. As well, IC₅₀ of the DOX-loaded triblock terpolymer in MTT test demonstrated that these systems could be suitable for the treatment of cancer.

Two-step volume phase transition mechanism of poly(N-vinylcaprolactam) hydrogel online-tracked by two-dimensional correlation spectroscopy

The volume phase transition of PVCL hydrogel was online-tracked by 2D correlation FTIR spectroscopy, and a two-step mechanism was proposed.

Topical drug delivery systems: a patent review

INTRODUCTION

Topical administration is the favored route for local delivery of therapeutic agents due to its convenience and affordability. The specific challenge of designing a therapeutic system is to achieve an optimal concentration of a certain drug at its site of action for an appropriate duration.

AREAS COVERED

This review summarizes innovations from the past 3 years (2012-2015) in the field of topical drug delivery for the treatment of local infections of the vagina, nose, eye and skin. The review also throws some light on the anatomy and physiology of these organs and their various defensive barriers which affect the delivery of drugs administered topically.

EXPERT OPINION

Topical administration has been gaining attention over the last few years. However, conventional topical drug delivery systems suffer from drawbacks such as poor retention and low bioavailability. The successful formulation of topical delivery products requires the careful manipulation of defensive barriers and selection of a soluble drug carrier. Extensive research is required to develop newer topical drug delivery systems aiming either to improve the efficacy or to reduce side effects compared to current patented systems.

Improving Cell Engraftment in Cardiac Stem Cell Therapy

Myocardial infarction (MI) affects millions of people worldwide. MI causes massive cardiac cell death and heart function decrease. However, heart tissue cannot effectively regenerate by itself. While stem cell therapy has been considered an effective approach for regeneration, the efficacy of cardiac stem cell therapy remains low due to inferior cell engraftment in the infarcted region. This is mainly a result of low cell retention in the tissue and poor cell survival under ischemic, immune rejection and inflammatory conditions. Various approaches have been explored to improve cell engraftment: increase of cell retention using biomaterials as cell carriers; augmentation of cell survival under ischemic conditions by preconditioning cells, genetic modification of cells, and controlled release of growth factors and oxygen; and enhancement of cell survival by protecting cells from excessive inflammation and immune surveillance. In this paper, we review current progress, advantages, disadvantages, and potential solutions of these approaches.

Modulation of wound healing and scar formation by MG53 protein-mediated cell membrane repair

Cell membrane repair is an important aspect of physiology, and disruption of this process can result in pathophysiology in a number of different tissues, including wound healing, chronic ulcer and scarring. We have previously identified a novel tripartite motif family protein, MG53, as an essential component of the cell membrane repair machinery. Here we report the functional role of MG53 in the modulation of wound healing and scarring. Although MG53 is absent from keratinocytes and fibroblasts, remarkable defects in skin architecture and collagen overproduction are observed in mg53(-/-) mice, and these animals display delayed wound healing and abnormal scarring. Recombinant human MG53 (rhMG53) protein, encapsulated in a hydrogel formulation, facilitates wound healing and prevents scarring in rodent models of dermal injuries. An in vitro study shows that rhMG53 protects against acute injury to keratinocytes and facilitates the migration of fibroblasts in response to scratch wounding. During fibrotic remodeling, rhMG53 interferes with TGF-β-dependent activation of myofibroblast differentiation. The resulting down-regulation of α smooth muscle actin and extracellular matrix proteins contributes to reduced scarring. Overall, these studies establish a trifunctional role for MG53 as a facilitator of rapid injury repair, a mediator of cell migration, and a modulator of myofibroblast differentiation during wound healing. Targeting the functional interaction between MG53 and TGF-β signaling may present a potentially effective means for promoting scarless wound healing.

Classification, processing and application of hydrogels: A review

This article aims to review the literature concerning the choice of selectivity for hydrogels based on classification, application and processing. Super porous hydrogels (SPHs) and superabsorbent polymers (SAPs) represent an innovative category of recent generation highlighted as an ideal mould system for the study of solution-dependent phenomena. Hydrogels, also termed as smart and/or hungry networks, are currently subject of considerable scientific research due to their potential in hi-tech applications in the biomedical, pharmaceutical, biotechnology, bioseparation, biosensor, agriculture, oil recovery and cosmetics fields. Smart hydrogels display a significant physiochemical change in response to small changes in the surroundings. However, such changes are reversible; therefore, the hydrogels are capable of returning to its initial state after a reaction as soon as the trigger is removed.

Injectable hydrogels based on poly(ethylene glycol) and derivatives as functional biomaterials

The design criteria for injectable, in situ-gelling hydrogels are reviewed in conjunction with highlights on recent progress in the preparation of injectable PEG and PEG-analogue poly(oligoethylene glycol methacrylate) (POEGMA) hydrogels.

Lipid polymer hybrid as emerging tool in nanocarriers for oral drug delivery

The oral route for drug delivery is a widely accepted route. For that reason, many researchers are currently working to develop efficient oral drug delivery systems. Use of polymeric nanoparticles (NPs) and lipid carrier systems, including liposomes, solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLC), has limitations such as drug leakage and high water content of dispersions. Thus, lipid polymer hybrid nanoparticles (LPNs) have been explored by the researchers to provide a better effect using properties of both polymers and lipids. The present review is focused on the challenges, possibilities, and future perspectives of LPNs for oral delivery.

PEG-g-chitosan thermosensitive hydrogel for implant drug delivery: cytotoxicity, in vivo degradation and drug release

Thermosensitive hydrogels based on chitosan are of great interests for injectable implant drug delivery. The poly(ethylene glycol)-grafted-chitosan (PEG-g-CS) hydrogel was reported as a potential thermosensitive system. The objective of the present study is to evaluate the cytotoxicity, in vivo degradation and drug release of PEG-g-CS hydrogel. Cytotoxicity was evaluated using L929 murine fibrosarcoma cell line. Degradation and drug release in vivo were investigated by subcutaneous injection of the hydrogel into Sprague-Dawley rats. PEG-g-CS polymer exhibits no significant cytotoxicity when its concentration is less than 3 mg mL(-1). After being implanted, PEG-g-CS hydrogel maintains its integrity for two weeks and collapses, merging into the tissue, in the third week. It causes moderate inflammatory response but no fibrous encapsulation around the hydrogel is found. The hydrogel presents a three-week sustained release of cyclosporine A with no significant burst release in vitro and produces the effective drug concentration in blood for more than five weeks in vivo, performing almost the same bioavailability to chitosan/glycerophosphate hydrogel. Further modifications of PEG-g-CS hydrogel might be necessary to modulate the degradation and to mitigate the fluctuations in blood drug concentration.

rhEGF-containing thermosensitive and mucoadhesive polymeric sol–gel for endoscopic treatment of gastric ulcer and bleeding

Gastrointestinal endoscopy is a standard diagnostic tool for gastrointestinal ulcers and cancer. In this study, we have developed recombinant human epidermal growth factor-containing ulcer-coating polymeric sol–gel for endoscopic application. Chitosan and pluronic F127 were employed for their thermoresponsive and bioadhesive properties. At temperatures below 21℃, polymeric sol–gel remains liquid during endoscopic application and transforms to gel at body temperature after application on ulcers. In an in vitro cellular wounding assay, recombinant human epidermal growth factor sol–gel significantly enhanced the cell migration and decreased the wounding area (68%) compared to nontreated, recombinant human epidermal growth factor solution, and sol–gel without recombinant human epidermal growth factor (42, 49, and 32 % decreased at day 1). The in vivo ulcer-healing study was performed in an acetic acid-induced gastric ulcer rat model and proved that our recombinant human epidermal growth factor endoscopic sol–gel facilitated the ulcer-healing process more efficiently than the other treatments. Ulcer sizes in the recombinant human epidermal growth factor sol–gel group were decreased 2.9- and 2.1-fold compared with those in the nontreated group on days 1 and 3 after ulceration, respectively. The mucosal thickness in the recombinant human epidermal growth factor sol–gel group was significantly increased compared to that in the nontreated group (3.2- and 6.9-fold on days 1 and 3 after ulceration, respectively). In a gastric retention study, recombinant human epidermal growth factor sol–gel stayed on the gastric mucosa more than 2 h after application. The present study suggests that recombinant human epidermal growth factor sol–gel is a prospective candidate for treating gastric ulcers via endoscopic application.

Synthesis, characterization, biodegradability and biocompatibility of a temperature-sensitive PBLA-PEG-PBLA hydrogel as protein delivery system with low critical gelation concentration

Temperature-sensitive hydrogels were designed using a series of A-B-A triblock copolymers consisting of poly (ethylene glycol) (PEG) with different molecular weights as the hydrophilic block B and poly (β-butyrolactone-co-lactic acid)(PBLA) with varying block lengths and composition as the hydrophobic block A. The triblock copolymers were synthesized by ring-opening polymerization (ROP) of β-BL and LA in bulk using PEG as an initiator and Sn(Oct)2 as the catalyst. Their chemical structure and molecular characteristics were determined by NMR, GPC and DSC, and the relationship between structure and phase behaviors in aqueous solutions was investigated as well. It was found that the phase behaviors in aqueous solutions including critical micelle concentration (CMC), sol-gel-sedimentation phase transition temperature, gel window width and critical gelation concentration (CGC) are largely dependent on the molecular weight and block length ratio of PEG/PBLA. Most importantly, they show a very low CGC ranging from 4 to 8 wt% because of the introduction of β-BL. Furthermore, the biodegradability and biocompatibility of the hydrogels were evaluated. Finally, lysozyme as a model protein was used to evaluate the ability to deliver protein drugs in a sustained release manner and biologically active form. All results demonstrated that the temperature-sensitive in situ forming hydrogel has a promising potential as sustained delivery system for protein drugs.

Temperature-sensitive polymers for drug delivery

The ability to undergo rapid changes in response to subtle environmental cues make stimuli- responsive materials attractive candidates for minimally invasive, targeted and personalized drug delivery applications. This special report aims to highlight and provide a brief description of several of the significant natural and synthetic temperature-responsive materials that have clinical relevance for drug delivery applications. This report examines the advantages and disadvantages of natural versus synthetic materials and outlines various scaffold architectures that can be utilized with temperature-sensitive drug delivery materials. The authors provide a commentary on the current state of the field and provide their insight into future expectations for temperature-sensitive drug delivery, emphasizing the importance of the emergence of dual and multiresponsive systems capable of responding precisely to an expanding set of stimuli, thereby allowing the development of disease-specific drug delivery vehicles.

Nitric oxide donors for cardiovascular implant applications

In an era of increased cardiovascular disease burden in the ageing population, there is great demand for devices that come in to contact with the blood such as heart valves, stents, and bypass grafts that offer life saving treatments. Nitric oxide (NO) elution from healthy endothelial tissue that lines the vessels maintains haemostasis throughout the vasculature. Surgical devices that release NO are desirable treatment options and N-diazeniumdiolates and S-nitrosothiols are recognized as preferred donor molecules. There is a keen interest to investigate newer methods by which NO donors can be retained within biomaterials so that their release and kinetic profiles can be optimized. A range of polymeric scaffolds incorporating microparticles and nanomaterials are presenting solutions to current challenges, and have been investigated in a range of clinical applications. This review outlines the application of NO donors for cardiovascular therapy using biomaterials that release NO locally to prevent thrombosis and intimal hyperplasia (IH) and enhance endothelialization in the fabrication of next generation cardiovascular device technology.

Reversibly crosslinked nanocarriers for on-demand drug delivery in cancer treatment

Polymer micelles have proven to be one of the most versatile nanocarriers for anticancer drug delivery. However, the in vitro and in vivo stability of micelles remains a challenge due to the dynamic nature of these self-assembled systems, which leads to premature drug release and nonspecific biodistribution in vivo. Recently, reversibly crosslinked micelles have been developed to provide solutions to stabilize nanocarriers in blood circulation. Increased stability allows nanoparticles to accumulate at tumor sites efficiently via passive and/or active tumor targeting, while cleavage of the micelle crosslinkages, through internal or external stimuli, facilitates on-demand drug release. In this review, various crosslinking chemistries as well as the choices for reversible linkages in these nanocarriers will be introduced. Then, the development of reversibly crosslinked micelles for on-demand drug release in response to single or dual stimuli in the tumor microenvironment is discussed, for example, acidic pH, reducing microenvironment, enzymatic microenvironment, photoirradiation and the administration of competitive reagents postmicelle delivery.

Evaluation of RGD peptide hydrogel in the posterior segment of the rabbit eye

The aim of this study was to evaluate the biocompatibility and biodegradability of RGD peptide hydrogel in the posterior segment of the eye as a biomaterial potentially useful for sustained drug delivery systems. RGD peptide hydrogel was injected into the vitreous cavity and suprachoroidal space of rabbit eyes. Clinical follow-up and histological observation were performed up to four weeks. The biodegradability was also evaluated by the lifetime of the hydrogel which was defined by ophthalmoscopic observation or ultrasonography. The results showed that RGD peptide hydrogel was well tolerated in the vitreous cavity and suprachoroidal space, and disappeared from the injection sites progressively. As for suprachoroidal injection, the hydrogel was clearly identified by ultrasound echography and was confirmed innoxious to the retinal vessels by fluorescein angiography. Histological observations showed that the structures of retina, choroid and other tissues around the injection site remained normal after the injection. The lifetime of the hydrogel was 25.7 ± 2.65 days and 14.3 ± 3.3 days in the vitreous cavity and suprachoroidal space, respectively. The results obtained demonstrated that RGD peptide hydrogel, which showed excellent biocompatibility and favorable biodegradability in the posterior segment of rabbit eyes, appears to be a promising biomaterial to deliver drugs focally to the choroid and the retina.

Adjustable degradation and drug release of a thermosensitive hydrogel based on a pendant cyclic ether modified poly(ε-caprolactone) and poly(ethylene glycol)co-polymer

The convenient and precise fabrication of drug-hydrogel formulations with satisfactory degradability and a well-controlled drug release profile are crucial factors for injectable hydrogel formulations in clinical applications. Here a new injectable thermosensitive hydrogel formed from poly(ε-caprolactone) (PCL)-poly(ethylene glycol)-poly(ε-caprolactone) amphiphilicco-polymers with 1,4,8-trioxa[4.6]spiro-9-undecanone (TOSUO) moieties incorporated in the poly(ε-caprolactone) (PCL)block (PECT) was constructed to provide a route to tailor the degradation and drug release behavior. The effect of hydrophilic cyclic ether moieties on the degradation of and drug release by PECT hydrogels were evaluated in vitro and in vivo. The results indicated that a freeze-dried powder of paclitaxel-loaded PECT nanoparticles rapidly dissolved in water at ambient temperature with slightly shaking and formed a stable injectable in situ drug-hydrogel formulation at body temperature, which is convenient for clinical operations because it avoids the need for pre-quenching or long-term incubation. The paclitaxel distribution was also more quantitative and homogeneous on entrapping paclitaxel in PECT nanoparticles. Further, the small number of pendant cyclic ether groups in PCL could decrease the cystallinity and hydrophobicity and, as a result, the in vitro and in vivo retention time of PECT hydrogels and the release of entrapped paclitaxel could be tuned from a few weeks to months by varying the amount of PTOSUO in the hydrophobic block. Significantly, paclitaxel-loaded PECT nanoparticles and free paclitaxel could be simultaneously released during the in vitro paclitaxel release from PECT hydrogels. A histopathological evaluation indicated that in vivo injected PECT hydrogels produced only a modest inflammatory response. Thus pendant cyclic ether modification of PCL could be an effective way to achieve the desired degradation and drug release profiles of amphiphilicco-polymer thermosensitive hydrogels and PECT hydrogels may be suitable for local drug delivery.

Advancement in stimuli triggered in situ gelling delivery for local and systemic route

INTRODUCTION

Current research efforts focused on the design and evaluation of drug delivery systems that are easy to administer require decreased administration frequency, and provide sustained drug release in order to increase clinical efficacy and compliance of the patients. The gel forming smart polymeric formulations offer numerous applications resemble sustained and prolonged action in contrast to conventional drug delivery systems.

AREAS COVERED

Article summarizes type of bioactive, sol-gel triggering factors, dose, rationales, and polymers involved in gelation with respect to their route of administration. A lot of work has been done with smart polymeric gelling system taking the advantage of stimuli (temperature and pH) triggered sol-gel phase-transition in the administered area that have great prospective in biomedical and pharmaceutical applications, particularly in target-specific controlled drug delivery systems.

EXPERT OPINION

Although the principle of gelation is so attractive, key issues remain to be solved which include (i) variability of the drug release, (ii) avoidance of burst release in case of depot formulation, and (iii) issues related to toxicity. Unfortunately, till now area concerning the detailed processes of the gelling formation is still not much explored. Despite this proclamation, many efforts are made in industry and institutions to improve concerned approaches. New materials and approaches enter the preclinical and clinical phases and one can be sure that this strategy will gain further clinical importance within the next years. Thus, this review article will assuredly serve as an informative tool for the innovators working in the concern area.