In situ-forming hydrogels--review of temperature-sensitive systems

Local Riluzole Release from a Thermosensitive Hydrogel Rescues Injured Motoneurons through Nerve Root Stumps in a Brachial Plexus Injury Rat Model

The C5-C6 nerve roots are usually spared from avulsion after brachial plexus injury (BPI) and can thus be used as donors for nerve repair. A BPI rat model with C5-C6 nerve root stumps has been established in our previous work. The aim of this study was to test whether riluzole loaded into a thermosensitive hydrogel could applied locally in the nerve root stumps of this BPI rat model, thus increasing the reparative effect of the nerve root stumps. Nile red (a hydrophobic dye) was used as a substitute for riluzole since riluzole itself does not emit light. Nile red, loaded into a thermosensitive hydrogel, was added to the nerve root stumps of the BPI rat model. Additionally, eighteen rats, with operation on right brachial plexus, were evenly divided into three groups: control (Con), thermosensitive hydrogel (Gel) and thermosensitive hydrogel loaded with riluzole (Gel + Ri) groups. Direct nerve repair was performed after local riluzole release for two weeks. Functional and electrophysiological evaluations and histological assessments were used to evaluate the reparative effect 8 weeks after nerve repair. Nile red was slowly released from the thermosensitive hydrogel and retrograde transport through the nerve root stumps to the motoneurons, according to immunofluorescence. Discernible functional recovery began earlier in the Gel + Ri group. The compound muscle action potential, ChAT-expressing motoneurons, positivity for neurofilaments and S100, diameter of regenerating axons, myelin sheath thickness and density of myelinated fibers were markedly increased in the Gel + Ri group compared with the Con and Gel groups. Our results indicate that the local administration of riluzole could undergo retrograde transportation through C5-C6 nerve root stumps, thereby promoting neuroprotection and increasing nerve regeneration.

Ultrasmall AgNP-Impregnated Biocompatible Hydrogel with Highly Effective Biofilm Elimination Properties

Ultrasmall silver nanoparticles (AgNPs; size < 3 nm) have attracted a great deal of interest as an alternative to commercially available antibiotics due to their ability to eliminate a wide range of microbial pathogens. However, most of these ultrasmall AgNPs are highly reactive and unstable, as well as susceptible to fast oxidation. Therefore, both the stability and toxicity remain major shortcomings for their clinical application and uptake. To circumvent these problems, we present a novel strategy to impregnate ultrasmall AgNPs into a biocompatible thermosensitive hydrogel that enables controlled release of silver alongside long-term storage stability and highly potent antibacterial activity. The advantage of this strategy lies in the combination of a homogenous dispersion of AgNPs in a hydrogel network, which serves as a sustained-release reservoir, and the unique feature of ultrasmall AgNP size, which provides an improved biofilm eradication capacity. The superior biofilm dispersion properties of the AgNP hydrogel is demonstrated in both single-species and multispecies biofilms, eradicating ∼80% of established biofilms compared to untreated controls. Notably, the effective antibacterial concentration of the formulation shows minimal toxicity to human fibroblasts and keratinocytes. These findings present a promising novel strategy for the development of AgNP hydrogels as an efficient antibacterial platform to combat resistant bacterial biofilms associated with wound infections.

Recent Advances in the Development of In Situ Gelling Drug Delivery Systems for Non-Parenteral Administration Routes

In situ gelling drug delivery systems have gained enormous attention over the last decade. They are in a sol-state before administration, and they are capable of forming gels in response to different endogenous stimuli, such as temperature increase, pH change and the presence of ions. Such systems can be administered through different routes, to achieve local or systemic drug delivery and can also be successfully used as vehicles for drug-loaded nano- and microparticles. Natural, synthetic and/or semi-synthetic polymers with in situ gelling behavior can be used alone, or in combination, for the preparation of such systems; the association with mucoadhesive polymers is highly desirable in order to further prolong the residence time at the site of action/absorption. In situ gelling systems include also solid polymeric formulations, generally obtained by freeze-drying, which, after contact with biological fluids, undergo a fast hydration with the formation of a gel able to release the drug loaded in a controlled manner. This review provides an overview of the in situ gelling drug delivery systems developed in the last 10 years for non-parenteral administration routes, such as ocular, nasal, buccal, gastrointestinal, vaginal and intravesical ones, with a special focus on formulation composition, polymer gelation mechanism and in vitro release studies.

Enhanced proliferation and differentiation of neural stem cells by peptide-containing temperature-sensitive hydrogel scaffold

Hydrogel has attracted great attention in the past few years as a widely used material for repairing central nerve damage. However, conventional hydrogel bio-scaffold, such as chitosan, gelatin, and sodium alginate, lack sufficient biological activity and have limited nerve repair capabilities. Therefore, to explore biologically active and intelligent hydrogel materials is particularly important and necessary for central nerve repair. Herein, we developed a temperature-sensitive hydrogel grafted with a bioactive peptide IKVAV (Ile-Lys-Val-Ala-Val, IKVAV). The hydrogel was prepared by copolymerization of N-propan-2-ylprop-2-enamide (NIPAM) and AC-PEG-IKVAV copolymers via reversible addition-fracture chain transfer (RAFT) polymerization, using polyethylene glycol (PEGDA) and N, N'-Methylenebisacrylamide (BISAM) as cross-linking agents. The prepared hydrogel scaffold demonstrates a series of excellent properties such as rapid (de)swelling performance, good biocompatibility, regular three-dimensional porous structure, and in particular good biological activity, which can guide cell fate and mediate neuron's differentiation. Therefore, the developed peptide hydrogel scaffold provides a new strategy for designing biomaterials that are widely used in tissue engineering for central nervous system injury.

Optimization and in Vitro Evaluation of Injectable Sustained-Release of Levothyroxine Using PLGA-PEG-PLGA

Purpose

In situ-forming gels (semi-solid state) (ISFGs) are widely used as sustained drug delivery, but they show a high burst release as well. The purpose of the current study is to make triblock that can make a quick gel on injection with a minimum burst release.

Methods

In this study, to control the release of levothyroxine from ISFG, PLGA-PEG-PLGA (triblock) polymer was used. The melting method was employed to synthesize the triblock via ring-opening polymerization (ROP). Different weight percentages of triblock in the formulation were investigated to reach the minimum initial burst release of levothyroxine from ISFGs. Furthermore, the results of the in-situ forming implant (solid-state) (ISFI) of levothyroxine prepared from PLGA 504 H polymers were compared with ISFG.

Results

The melting method employed in this study showed a successful ROP of the triblock. As the % triblock concentration was increased from 30 to 50%, the initial burst release decreased significantly. The initial burst release levothyroxine from ISFG (6.52 ± 0.30%) was much lower than the amount of levothyroxine released from ISFI (14.15 ± 0.79%). No cytotoxicity was observed for the sustained-release formulation containing ISFG 50% according to the MTT assay.

Conclusion

The results indicated that this formulation was safe to be administered subcutaneously. As the synthesized triblock has thermosensitive properties, and also has the hydrogen bonding between the N-methyl pyrrolidone molecules and PEG, therefore, these properties make ISFG formulation to have a smaller initial burst release compared to ISFI formulation.

Stimuli-responsive In situ gelling system for nose-to-brain drug delivery

The diagnosis and treatment of neurological ailments always remain an utmost challenge for research fraternity due to the presence of BBB. The intranasal route appeared as an attractive and alternative route for brain targeting of therapeutics without the intrusion of BBB and GI exposure. This route directly and effectively delivers the therapeutics to different regions of the brain via olfactory and trigeminal nerve pathways. However, shorter drug retention time and mucociliary clearance curtail the efficiency of the intranasal route. The in situ mucoadhesive gel overthrow the limitations of direct nose-to-brain delivery by not only enhancing nasal residence time but also minimizing the mucociliary clearance and enzymatic degradation. This delivery system further improves the nasal absorption as well as bioavailability of drugs in the brain. The in situ mucoadhesive gel is a controlled and sustained release system that facilitates the absorption of various proteins, peptides and other larger lipophilic and hydrophilic moieties. Owing to multiple benefits, in situ gelling system has been widely explored to target the brain via nasal route. However, very few review works are reported which explains the application of in situ nasal gel for brain delivery of CNS acting moieties. Hence, in this piece of work, we have initially discussed the global statistics of neurological disorders reported by WHO and other reputed organizations, nasal anatomy, mechanism and challenges of nose-to-brain drug delivery. The work mainly focused on the use of different stimuli-responsive polymers, specifically thermoresponsive, pH-responsive, and ion triggered systems for the development of an effective and controlled dosage form, i.e., in situ nasal gel for brain targeting of bioactives. We have also highlighted the origin, structure, nature and phase transition behavior of the smart polymers found suitable for nasal administration, including poloxamer, chitosan, EHEC, xyloglucan, Carbopol, gellan gum and DGG along with their application in the treatment of neurological disorders. The article is aimed to gather all the information of the past 10 years related to the development and application of stimuli-responsive in situ nasal gel for brain drug delivery.

Bioresponsive nanostructured systems for sustained naltrexone release and treatment of alcohol use disorder: Development and biological evaluation

In this study, microemulsions capable of transforming into nanostructured hexagonal phase gels in vivo upon uptake of biological fluids for naltrexone prolonged release were investigated as a strategy for management of alcohol use disorder (AUD). Microemulsions were prepared using monoolein, tricaprylin, water and propylene glycol; after preliminary characterization, one formulation was selected, which contained 55% of monoolein-tricaprylin (M-55). This microemulsion displayed size below 200 nm and Newtonian rheological behavior. Liquid crystalline gels formed in vitro upon 8 h of contact with water following a second order kinetics. After 120 h, <50% of naltrexone was released in vitro independently on drug loading (5 or 10%). In vivo, gels formed within 24 h of M-55 subcutaneous administration, and persisted locally for over 30 days providing slow release of the fluorescent marker Alexa fluor compared to a solution. Using the conditioned place preference paradigm, a test used to measure drug's rewarding effects, a single dose of M-55 containing 5% naltrexone reduced the time spent in the ethanol-paired compartment by 1.8-fold compared to saline; this effect was similar to that obtained with daily naltrexone injections, demonstrating the formulation efficacy and its ability to reduce dosing frequency. A more robust effect was observed following administration of M-55 containing 10% of naltrexone, which was compatible with aversion. These results support M-55 as a platform for sustained release of drugs that can be further explored for management of AUD to reduce dosing frequency and aid treatment adherence.

Formulation, characterization and in vitro anti-leishmanial evaluation of amphotericin B loaded solid lipid nanoparticles coated with vitamin B12-stearic acid conjugate

Despite the advancement of new anti-leishmanials, amphotericin B (AmB) prevails as one of the most potent agent in the treatment of visceral leishmaniasis (VL), a neglected tropical disease affecting mostly poverty ridden and underdeveloped regions of the globe. Nonetheless, many patients display intolerance to parenteral AmB, notably at higher dosages. Also, conventional AmB presents an apparently poor absorption. Therefore, to improve AmB bioavailability and overcome multiple barriers for oral delivery of AmB, we fabricated a promising vitamin B₁₂-stearic acid (VBS) conjugate coated solid lipid nanoparticles (SLNs) encapsulated with AmB (VBS-AmB-SLNs) by a combination of double emulsion solvent evaporation and thermal sensitive hydrogel techniques. VBS-AmB-SLNs showed a particle size of 306.66 ± 3.35 nm with polydispersity index of 0.335 ± 0.08 while the encapsulation efficiency and drug loading was observed to be 97.99 ± 1.6% and 38.5 ± 5.6% respectively. In vitro drug release showed a biphasic release pattern and chemical stability of AmB was ensured against simulated gastrointestinal fluids. Cellular uptake studies confirmed complete internalization of the formulation. Anti-leishmanial evaluation against intramacrophage amastigotes showed an enhanced efficacy of 94% which was significantly (P < 0.01) higher than conventional AmB without showing any toxic effects on J774A.1 cells. VBS-AmB-SLNs could serve as a potential therapeutic strategy against VL.

Temperature-sensitive gel-loaded composite nanomedicines for the treatment of cervical cancer by vaginal delivery

In this study, toad venom (TV) and realgar were loaded into a poloxamer 188/407 (F127/F188)-based temperature-sensitive in situ gel (TISG) and encapsulated in solid lipid nanoparticles (TV-SLN) or ground nano-realgar (NR) to improve drug release and reduce local irritation after vaginal administration. The combination of TV-SLN and NR (TV-SLN/NR) greatly enhanced the inhibition of tumor cell proliferation and was most effective at a dose ratio of 2:3 (w/w). After TV-SLN/NR treatment, S and G0/G1 phase arrest were observed in HeLa and SKOV-3 cells and the inhibitory effects on proliferation were stronger than those in the conventional powder group. The gelation temperature of TV-SLN and NR-loaded TISG (TV-SLN/NR-TISG) using the selected formulation was 33 ± 0.91 °C. The cumulative release of the drug increased as the dissolution of gel progressed, showing a linear relationship (r > 0.99). TV-SLN/NR-TISG enabled the sustained release of cargo by adhesion to the vaginal mucosa and showed excellent biocompatibility during continuous administration for 7 days. We specifically demonstrated the effectiveness of the TISG for the vaginal delivery of TV-SLN and NR, supporting its important clinical implications for the treatment of cervical cancer.

Poloxamer: A versatile tri-block copolymer for biomedical applications

Poloxamers, also called Pluronic, belong to a unique class of synthetic tri-block copolymers containing central hydrophobic chains of poly(propylene oxide) sandwiched between two hydrophilic chains of poly(ethylene oxide). Some chemical characteristics of poloxamers such as temperature-dependent self-assembly and thermo-reversible behavior along with biocompatibility and physiochemical properties make poloxamer-based biomaterials promising candidates for biomedical application such as tissue engineering and drug delivery. The microstructure, bioactivity, and mechanical properties of poloxamers can be tailored to mimic the behavior of various types of tissues. Moreover, their amphiphilic nature and the potential to self-assemble into the micelles make them promising drug carriers with the ability to improve the drug availability to make cancer cells more vulnerable to drugs. Poloxamers are also used for the modification of hydrophobic tissue-engineered constructs. This article collects the recent advances in design and application of poloxamer-based biomaterials in tissue engineering, drug/gene delivery, theranostic devices, and bioinks for 3D printing. STATEMENT OF SIGNIFICANCE: Poloxamers, also called Pluronic, belong to a unique class of synthetic tri-block copolymers containing central hydrophobic chains of poly(propylene oxide) sandwiched between two hydrophilic chains of poly(ethylene oxide). The microstructure, bioactivity, and mechanical properties of poloxamers can be tailored to mimic the behavior of various types of tissues. Moreover, their amphiphilic nature and the potential to self-assemble into the micelles make them promising drug carriers with the ability to improve the drug availability to make cancer cells more vulnerable to drugs. However, no reports have systematically reviewed the critical role of poloxamer for biomedical applications. Research on poloxamers is growing today opening new scenarios that expand the potential of these biomaterials from "traditional" treatments to a new era of tissue engineering. To the best of our knowledge, this is the first review article in which such issue is systematically reviewed and critically discussed in the light of the existing literature.

Thermally Tunable Dynamic and Static Elastic Properties of Hydrogel Due to Volumetric Phase Transition

The temperature dependence of the mechanical properties of polyvinyl alcohol-based poly n-isopropyl acrylamide (PVA-PNIPAm) hydrogel was studied from the static and dynamic bulk modulus of the material. The effect of the temperature-induced volumetric phase transition on Young’s Modulus, Poisson’s ratio, and the density of PVA-PNIPAm was experimentally measured and compared with a non-thermo-responsive Alginate hydrogel as a reference. An increase in the temperature from 27.5 to 32 °C results in the conventional temperature-dependent de-swelling of the PVA-PNIPAm hydrogel volume of up to 70% at the lower critical solution temperature (LCST). However, with the increase in temperature, the PVA-PNIPAm hydrogel showed a drastic increase in Young’s Modulus and density of PVA-PNIPAm and a corresponding decrease in the Poisson’s ratio and the static bulk modulus around the LCST temperature. The dynamic bulk modulus of the PVA-PNIPAm hydrogel is highly frequency-dependent before the LCST and highly temperature-sensitive after the LCST. The dynamic elastic properties of the thermo-responsive PVA-PNIPAm hydrogel were compared and observed to be significantly different from the thermally insensitive Alginate hydrogel.

Smart Hydrogels - Synthetic Stimuli-Responsive Antitumor Drug Release Systems

Among modern drug formulations, stimuli-responsive hydrogels also called "smart hydrogels" deserve a special attention. The basic feature of this system is the ability to change their mechanical properties, swelling ability, hydrophilicity, bioactive molecules permeability, etc., influenced by various stimuli, such as temperature, pH, electromagnetic radiation, magnetic field and biological factors. Therefore, stimuli-responsive matrices can be potentially used in tissue engineering, cell cultures and technology of innovative drug delivery systems (DDSs), releasing the active substances under the control of internal or external stimuli. Moreover, smart hydrogels can be used as injectable DDSs, due to gel-sol transition connected with in situ cross-linking process. Innovative smart hydrogel DDSs can be utilized as matrices for targeted therapy, which enhances the effectiveness of tumor chemotherapy and subsequently limits systemic toxicity. External stimulus sensitivity allows remote control over the drug release profile and gel formation. On the other hand, internal factors provide drg accumulation in tumor tissue and reduce the concentration of active drug form in healthy tissue. In this report, we summarise the basic knowledge and chemical strategies for the synthetic smart hydrogel DDSs applied in antitumor therapy.

Chitosan hydrogels for sustained drug delivery

Sustainable and controlled delivery of drugs is at the centre of a huge amount of undertaken researches. The ability of hydrogels, high water content materials, to achieve a local and delayed-delivery has already been demonstrated for a wide variety of therapeutic agents and various polymer natures. In particular, chitosan, a natural polymer, stands out as a first choice material for hydrogels elaboration in biomedical, cosmetic, and health related applications, owing to its interesting properties (as biocompatibility, biodegradability, antimicrobial capacity, and mucoadhesivity). Moreover, chitosan also allows drugs to go easier through biological barriers. The main objective of this review is to report the various uses of chitosan hydrogels as drug delivery devices to control and/or delay the release of drugs loaded into their three dimensional matrix. A wide spectrum of corresponding biomedical applications of these systems can be encountered in the literature, whatever the physicochemical nature of drugs (hydrophilic, hydrophobic, macromolecular), as detailed in this review.

The Application of Hydrogels Based on Natural Polymers for Tissue Engineering

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Hydrogels are known as polymer-based networks with the ability to absorb water and other body fluids. Because of this, the hydrogels are used to preserve drugs, proteins, nutrients or cells. Hydrogels possess great biocompatibility, and properties like soft tissue, and networks full of water, which allows oxygen, nutrients, and metabolites to pass. Therefore, hydrogels are extensively employed as scaffolds in tissue engineering. Specifically, hydrogels made of natural polymers are efficient structures for tissue regeneration, because they mimic natural environment which improves the expression of cellular behavior.

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Producing natural polymer-based hydrogels from collagen, hyaluronic acid (HA), fibrin, alginate, and chitosan is a significant tactic for tissue engineering because it is useful to recognize the interaction between scaffold with a tissue or cell, their cellular reactions, and potential for tissue regeneration. The present review article is focused on injectable hydrogels scaffolds made of biocompatible natural polymers with particular features, the methods that can be employed to engineer injectable hydrogels and their latest applications in tissue regeneration.

Investigating the Potential to Deliver and Maintain Plasma and Brain Levels of a Novel Practically Insoluble Methuosis Inducing Anticancer Agent 5-Methoxy MOMIPP Through an Injectable In Situ Forming Thermoresponsive Hydrogel Formulation

A new indole based chalcone molecule MOMIPP induced methuosis mediated cell death in gliobastoma and other cancer cell lines. But the drug was insoluble in water and had a very short plasma half-life. The purpose of this work was to develop a formulation that can provide sustained levels of MOMIPP in vivo. Initial studies established drug solubility in various solvents. N-methyl pyrrolidone (NMP) was determined as an excellent solvent for the drug. Subsequently a poloxamer-407 based thermoreversible gel containing NMP was used to develop the formulation. Rheological studies were performed via oscillatory temperature mode, continuous shear analysis, and oscillatory frequency mode experiments. The mechanical properties of the formulations were tested using a texture profile analyzer. The gelation temperature and time of formulations increased with increasing amounts of NMP. However, the viscosity at 20 °C and storage modulus decreased as the amount of NMP increased. Characterization studies helped to identify the gel formulation that was used to administer the drug orally, sub-cutaneously, and intra-peritoneally. When the gel was given intraperitoneally the target plasma and brain levels of over 5 μM was maintained for about 8 h. Thus, a thermoreversible gel formulation that can deliver MOMIPP in animal studies was successfully developed.

Injectable thermosensitive chitosan/gelatin-based hydrogel carried erythropoietin to effectively enhance maxillary sinus floor augmentation in vivo

OBJECTIVE

Maxillary sinus floor augmentation (MSFA) is commonly used to increase the alveolar bone height in the posterior maxilla before implant placement. In the present study, we evaluated if the injectable thermosensitive chitosan/β-sodium glycerophosphate disodium salt hydrate/gelatin (CS/GP/GA) hydrogel carried erythropoietin (EPO) could enhance the new bone formation for MSFA in vivo.

METHODS

EPO-CS/GP/GA hydrogel was prepared by ionic crosslinking. Then, characteristics of EPO-CS/GP/GA were evaluated by morphology, injectable property and pH on the gelling time (GT). The release profile of EPO was evaluated by enzyme linked immunosorbent assay (ELISA), and effects of EPO on proliferation and osteoblastic differentiation of bone marrow stromal cells (BMSC) were analyzed by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) and reverse transcription quantitative real-time PCR (RT-qPCR), respectively. Finally, EPO-CS/GP/GA was injected into the maxillary sinus floor of the rabbit to test the potential application for MSFA.

RESULTS

Results showed that GT was decreased with the increase of pH value. The GT was 110±15s at pH 7.0. SEM images showed that the CS/GP/GA hydrogel had a sponge network structure. Results from ELISA assay revealed that the cumulative release of EPO from the EPO-CS/GP/GA hydrogel reached 67% at 4h, and 94% at 15 days. MTT assay showed that EPO within EPO-CS/GP/GA hydrogel could significantly promote proliferation of BMSCs compared to control group (p<0.001) . Results of RT-qPCR assays demonstrated that the expression of Sp7, Runx2, Col I and Alp were significantly increased from EPO-CS/GP/GA group compared to control group on day 14 (p<0.001). Importantly, EPO-CS/GP/GA hydrogel could significantly induce bone formation (81.98mm³) compared with control group (43.11mm³) after 12 weeks post-implantation in vivo. The calculation of thickness of mesenchymal condensation indicated that thickness of mesenchymal condensation was significantly increased from EPO-CS/GP/GA group (∼121.4μm) compared to control group (∼37μm) resulting in enhancing intramembranous ossification.

SIGNIFICANCE

The EPO-CS/GP/GA hydrogel provides a novel strategy for MSFA with a minimally invasive way.

Dynamic crosslinked and injectable biohydrogels as extracellular matrix mimics for the delivery of antibiotics and 3D cell culture

Antibiotics are widely used in clinical medicine. As an important member, vancomycin often plays an irreplaceable role in some serious infections but for its use, there is still a lack of suitable carriers and effective formulations. To find a vancomycin carrier with potential for clinical applications, a new class of poly(γ-glutamic acid)/dextran-based injectable hydrogels have been constructed through dynamic covalent hydrazone linkages. Adipic dihydrazide (ADH)-grafted poly(γ-glutamic acid) (PGAADH) and sodium periodate-oxidized dextran (OD) precursors were synthesized; then, the hydrogels were formed by blending PGAADH and OD buffer solutions without any additives under physiological conditions. The newly formed precursor structures, mechanical properties, morphologies, hydrogel degradation profiles, and the interaction between the drug and precursors were investigated with FTIR spectroscopy, 1H NMR spectroscopy, rheological experiments, compression tests, SEM, and isothermal titration calorimetric (ITC) measurements. The resulting hydrogels exhibited excellent antibacterial ability and ideal variable performances. Moreover, the hydrogels exhibited different drug release kinetics and mechanisms and were applied effectively towards the controlled release of vancomycin. Significantly, benefitting from the reversibly cross-linked systems and the excellent biocompatibility, the hydrogels can work as the ideal material for HeLa cell culture, leading to encapsulated cells with higher viability and capacity that is proliferative. Therefore, the injectable PGAADH/OD hydrogels demonstrated attractive properties for future applications in pharmaceutics and tissue engineering.

Chitosan based bioactive materials in tissue engineering applications-A review

In recent years, there have been increasingly rapid advances of using bioactive materials in tissue engineering applications. Bioactive materials constitute many different structures based upon ceramic, metallic or polymeric materials, and can elicit specific tissue responses. However, most of them are relatively brittle, stiff, and difficult to form into complex shapes. Hence, there has been a growing demand for preparing materials with tailored physical, biological, and mechanical properties, as well as predictable degradation behavior. Chitosan-based materials have been shown to be ideal bioactive materials due to their outstanding properties such as formability into different structures, and fabricability with a wide range of bioactive materials, in addition to their biocompatibility and biodegradability. This review highlights scientific findings concerning the use of innovative chitosan-based bioactive materials in the fields of tissue engineering, with an outlook into their future applications. It also covers latest developments in terms of constituents, fabrication technologies, structural, and bioactive properties of these materials that may represent an effective solution for tissue engineering materials, making them a realistic clinical alternative in the near future.

Comparison of thermosensitive in situ gels and drug-resin complex for ocular drug delivery: In vitro drug release and in vivo tissue distribution

Conventional ophthalmic eye drops are limited by their rapid elimination rate and short time of action. Ion exchange resin has been used to achieve sustained ocular drug delivery but the high selectivity of drug molecules restricts its broad application. In situ gel system seems to be a good strategy to address these problems but the influence of in situ gel type on the sustained release behavior and tissue distribution after ocular application is unclear. Therefore, in this study, using betaxolol hydrochloride as a model drug, poloxamer 407 and methylcellulose as the carriers, two thermosensitive in situ gel systems were prepared and characterized. Influence of formulation composition type and concentration on in vitro drug release was studied. Tissue distribution after ocular delivery of two different thermosensitive in situ gels was studied and compared with commercial BH eye drop (Betoptic S®). In vitro studies demonstrated that addition of 4% HPMC 606W in 15% P407 solution and 5% PEG4000 in 2% MC solution obtained gels with appropriate gelation temperature and similar sustained drug release rate. In vivo tissue distribution study indicated that they presented similar drug concentration in cornea, iris-ciliary and aqueous humor irrespective of gel type, with higher drug concentration achieved after 4 h compared to the commercial resin suspension eye drops. The AUC and MRT of the two in situ gel eye drops were 2 times higher than that of the commercial resin suspension eye drops in cornea. In conclusion, the two thermosensitive in situ gels have prolonged drug release after ocular drug delivery compared with ion exchange resin eye drops, implying their potential applications in clinic with broad drug adoptability.

Intranasal delivery system of bacterial antigen using thermosensitive hydrogels based on a Pluronic-Gantrez conjugate

Thermosensitive hydrogels have been studied as feasible needle-avoidance alternative to vaccine delivery. In this work, we report the development of a new thermal-sensitive hydrogel for intranasal vaccine delivery. This delivery system was formulated with a combination of the polymer Gantrez® AN119 and the surfactant Pluronic® F127 (PF127), with a high biocompatibility, biodegradability and immunoadjuvant properties. Shigella flexneri outer membrane vesicles were used as the antigen model. A stable and easy-to-produce thermosensitive hydrogel which allowed the incorporation of the OMV-antigenic complex was successfully synthetized. A rapid gel formation was achieved at body temperature, which prolonged the OMV-antigens residence time in the nasal cavity of BALB/c mice when compared to intranasal delivery of free-OMVs. In addition, the bacterial antigens showed a fast release profile from the hydrogel in vitro, with a peak at 30 min of incubation at 37 °C. Hydrogels appeared to be non-cytotoxic in the human epithelial HeLa cell line and nose epithelium as well, as indicated by the absence of histopathological features. Immunohistochemical studies revealed that after intranasal administration the OMVs reached the nasal associated lymphoid tissue. These results support the use of here described thermosensitive hydrogels as a potential platform for intranasal vaccination.

Thermoresponsive Poly(ε-Caprolactone)-Poly(Ethylene/Propylene Glycol) Copolymers as Injectable Hydrogels for Cell Therapies

Injectable, thermoresponsive hydrogels are promising candidates for the delivery, maintenance and controlled release of adoptive cell therapies. Therefore, there is significant interest in the development of cytocompatible and biodegradable thermoresponsive hydrogels with appropriate gelling characteristics. Towards this end, a series of thermoresponsive copolymers consisting of poly(caprolactone) (PCL), poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) segments, with various PEG:PPG ratios, were synthesised via ring-opening polymerisation (ROP) of ε-caprolactone and epoxy-functionalised PEG and PPG derivatives. The resultant PCL-PEG-PPG copolymers were characterised via proton nuclear magnetic resonance (1H NMR) spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The thermoresponsive characteristics of the aqueous copolymer solutions at various concentrations was investigated using the inversion method. Whilst all of the copolymers displayed thermoresponsive properties, the copolymer with a ratio of 1:2 PEG:PPG exhibited an appropriate sol-gel transition (28 °C) at a relatively low concentration (10 wt%), and remained a gel at 37 °C. Furthermore, the copolymers were shown to be enzymatically degradable in the presence of lipases and could be used for the encapsulation of CD4+ T-cell lymphocytes. These results demonstrate that the thermoresponsive PCL-PEG-PPG hydrogels may be suitable for use as an adoptive cell therapy (ACT) delivery vehicle.

In situ forming oxidized salecan/gelatin injectable hydrogels for vancomycin delivery and 3D cell culture

Antibiotics are widely used in clinical medicine. As an important member, vancomycin often plays an irreplaceable role in some serious infections, but its use still lacks suitable carriers and effective formulations. In order to find a vancomycin carrier with potential for clinical application, a new class of oxidized salecan/gelatin based injectable hydrogels are constructed through dynamic covalent Schiff base reaction. The sodium periodate oxidized salecan (OS) precursor was synthesized, and then the gelatin/oxidized salecan (GS) hydrogels are formed by blending gelatin and OS buffer solutions without any additives under physiological condition. The chemical structure, as well as internal morphologies, mechanical properties, In vitro enzymatic degradation profile of hydrogels are investigated with proton nuclear magnetic resonance (¹H NMR), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), compression test and rheological experiments. The resulted hydrogels exhibit excellent antibacterial ability and variable characteristics. Moreover, the hydrogels display ideal drug release kinetics and mechanisms, and are applied successfully to the controlled release of vancomycin. Importantly, benefitting from the excellent biocompatibility and the reversibly crosslinked networks, GS hydrogels can function as suitable three dimensional (3D) extracellular matrix for HeLa cells, leading to the encapsulated cells maintaining a high viability and proliferative capacity. Therefore, the injectable GS hydrogels demonstrated attractive properties for future application in pharmaceutics and tissue engineering.

Network-supported, metal-mediated catalysis: progress and perspective

This minireview focuses on recent developments of network-supported catalysts to improve the performance of a wide range of metal-mediated catalytic reactions.

Dual responsive oligo(lysine)-modified Pluronic F127 hydrogels for drug release of 5-fluorouracil

Peptide-containing hydrogels have become a research hotspot due to their unique secondary structure and biocompatibility. Herein, we used amino-terminated F127 as a macroinitiator to initiate the ring-opening polymerization of l-lysine(z)-NCA, and the obtained oligo(lysine)-modified F127 (FL) had degrees of polymerization of lysine of 2, 5, and 8. The results showed that the FL hydrogels had reversible temperature-dependent sol–gel transitions, and the introduction of lysine increased the critical gel temperature. In the dilute solution of FL, the micelle size increased and aggregated as the pH increased; the micelle grew into a rod-like shape under alkaline conditions. Scanning electron micrographs showed that the interior of the FL hydrogel had a more complete porous structure. The FL-2 hydrogel loaded with 5-fluorouracil exhibited an approximately linear release trend within 12 h and has good biocompatibility. Therefore, FL hydrogels have potential applications in the field of biomedicine.

Oligo(lysine)-F127 hydrogels have a temperature-responsive sol–gel transition and pH-responsive micelle morphology.

Thermo-responsive Fluorescent Nanoparticles for Multimodal Imaging and Treatment of Cancers

Theranostic systems capable of delivering imaging and therapeutic agents at a specific target are the focus of intense research efforts in drug delivery. To overcome non-degradability and toxicity concerns of conventional theranostic systems, we formulated a novel thermo-responsive fluorescent polymer (TFP) and conjugated it on the surface of iron oxide magnetic nanoparticles (MNPs) for imaging and therapeutic applications in solid tumors. Methods: TFP-MNPs were synthesized by copolymerizing poly(N-isopropylacrylamide), allylamine and a biodegradable photoluminescent polymer, and conjugating it on MNPs via a free radical polymerization reaction. Physicochemical properties of the nanoparticles were characterized using Fourier transform infrared spectroscopy, dynamic light scattering, and vibrational sample magnetometry. Nanoparticle cytocompatibility, cellular uptake and cytotoxicity were evaluated using in vitro cell assays. Finally, in vivo imaging and therapeutic efficacy studies were performed in subcutaneous tumor xenograft mouse models. Results: TFP-MNPs of ~135 nm diameter and -31 mV ζ potential maintained colloidal stability and superparamagnetic properties. The TFP shell was thermo-responsive, fluorescent, degradable, and released doxorubicin in response to temperature changes. In vitro cell studies showed that TFP-MNPs were compatible to human dermal fibroblasts and prostate epithelial cells. These nanoparticles were also taken up by prostate and skin cancer cells in a dose-dependent manner and exhibited enhanced killing of tumor cells at 41°C. Preliminary in vivo studies showed theranostic capabilities of the nanoparticles with bright fluorescence, MRI signal, and therapeutic efficacy under magnetic targeting after systemic administration in tumor bearing mice. Conclusion: These results indicate the potential of TFP-MNPs as multifunctional theranostic nanoparticles for various biological applications, including solid cancer management.

Injectable hydrogels based on MPEG–PCL–RGD and BMSCs for bone tissue engineering

The aim of this study was to investigate the osteogenic potential of BMSCs seeded on RGD-conjugated methoxy polyethylene glycol-polycaprolactone (MP–RGD) in vitro and in vivo.

Tunable swelling and deswelling of temperature- and light-responsive graphene oxide-poly(N-isopropylacrylamide) composite hydrogels

Swelling and deswelling behaviors of graphene oxide-poly(N-isopropylacrylamide) composite hydrogels can be tuned by the concentrations of a chemical crosslinker and graphene oxide, and the rate of the external temperature change.

Printability of 3D Printed Hydrogel Scaffolds: Influence of Hydrogel Composition and Printing Parameters

Extrusion-based bioprinting of hydrogel scaffolds is challenging due to printing-related issues, such as the lack of capability to precisely print or deposit hydrogels onto three-dimensional (3D) scaffolds as designed. Printability is an index to measure the difference between the designed and fabricated scaffold in the printing process, which, however, is still under-explored. While studies have been reported on printing hydrogel scaffolds from one or more hydrogels, there is limited knowledge on the printability of hydrogels and their printing processes. This paper presented our study on the printability of 3D printed hydrogel scaffolds, with a focus on identifying the influence of hydrogel composition and printing parameters/conditions on printability. Using the hydrogels synthesized from pure alginate or alginate with gelatin and methyl-cellulose, we examined their flow behavior and mechanical properties, as well as their influence on printability. To characterize the printability, we examined the pore size, strand diameter, and other dimensions of the printed scaffolds. We then evaluated the printability in terms of pore/strand/angular/printability and irregularity. Our results revealed that the printability could be affected by a number of factors and among them, the most important were those related to the hydrogel composition and printing parameters. This study also presented a framework to evaluate alginate hydrogel printability in a systematic manner, which can be adopted and used in the studies of other hydrogels for bioprinting.

Polysaccharides in Ocular Drug Delivery

Polysaccharides, such as cellulose, hyaluronic acid, alginic acid, and chitosan, as well as polysaccharide derivatives, have been successfully used to augment drug delivery in the treatment of ocular pathologies. The properties of polysaccharides can be extensively modified to optimize ocular drug formulations and to obtain biocompatible and biodegradable drugs with improved bioavailability and tailored pharmacological effects. This review discusses the available polysaccharide choices for overcoming the difficulties associated with ocular drug delivery, and it explores the reasons for the dependence between the physicochemical properties of polysaccharide-based drug carriers and their efficiency in different formulations and applications. Polysaccharides will continue to be of great interest to researchers endeavoring to develop ophthalmic drugs with improved effectiveness and safety.

Expert design and desirability function approach for the development of diazepam thermally sensitive rectal gel

Aim: The aim of the present work was to develop an in situ thermosensitive rectal gel for diazepam by using Expert-design for improving three factors and a three-level process was formed by using a cold method. Methods & materials: Response surface design was utilized to investigate the effect of independent variables like sodium chloride (NaCl, X1), poloxamer 407 (F-127, X2) and diazepam (X3), on different dependent variables such as gelation temperature, mucoadhesive strength, drug content, along with permeation and stability. Results: The obtained results revealed that the addition of diazepam enhanced the gelation temperature of hydrogel while it decreased the gel strength and mucoadhesive force. Conclusion: It is suggested that in situ hydrogels may be suitable candidates for rectal delivery.

A thermo-sensitive injectable hydroxypropyl chitin hydrogel for sustained salmon calcitonin release with enhanced osteogenesis and hypocalcemic effects

Pharmacotherapy towards hypercalcemia treatment mainly caused by osteoporosis and bone tumor is an effective method to regulate in vivo calcium equilibrium. As a clinical therapeutic peptide, salmon calcitonin (sCT) is considered as a quick-acting medicine but it is limited by the short half-life. To address this challenge, we designed an injectable thermo-sensitive hydrogel based on hydroxypropyl chitin (HPCH) and incorporated the complex of sCT and hyaluronic acid (HA) (sCT-HA) with high association efficiency up to 96.84 ± 7.25%. This composite hydrogel showed a tunable biodegradable property. In vitro sCT release profiles revealed that this hydrogel can achieve long-term sustained sCT release (28 days) with considerable structure stability. The cellular study illustrated outstanding compatibility and osteoconductive potential of this multi-component hydrogel according to the higher ALP activity (2.10-fold), calcium expression (2.30-fold) and extracellular calcium deposition (1.10-fold) compared to that of the sCT group. In vivo sCT release confirmed that this hydrogel system realized sustained sCT release and a continuous hypocalcemic effect for as long as 28 days, and there were no inflammation and immune responses according to the histological evaluations (H&E and IgG staining). These findings demonstrate that this osteoconductive hydrogel system can provide a promising method for therapy of bone related disease.

Impact of Different Mucoadhesive Polymeric Nanoparticles Loaded in Thermosensitive Hydrogels on Transcorneal Administration of 5-Fluorouracil

In a previous paper a thermosensitive hydrogel formulation based on chitosan or its derivatives (TSOH), containing medicated chitosan nanoparticles (Ch NP) for transcorneal administration of 5-fluorouracil (5-FU) was described. The Ch NP-containing TSOH allowed a time-constant 5-FU concentration in the aqueous for 7 h from instillation. The aim of the present work was to study the impact of the surface characteristics of new NP contained in TSOH on ocular 5-FU bioavailability. The Ch derivatives used to prepare NP were quaternary ammonium-Ch conjugate (QA-Ch), S-protected derivative thereof (QA-Ch-S-pro), and a sulphobutyl chitosan derivative (SB-Ch). All NP types had 300–400 nm size, 16–18% encapsulation efficiency, and retained the entrapped drug for at least 15 h. Drug release from TSOH containing NP based on QA-Ch or QA-Ch-S-pro was virtually equal, whereas with TSOH containing NP based on SB-Ch was significantly slower. Instillation, in rabbit eyes, of NP-containing TSOH based on QA-Ch or SB-Ch led to a plateau in the aqueous concentration vs. time plot in the 1–10 h range with significantly enhanced area under curve (AUC). Negative charges on the NP surface slowed down 5-FU release from TSOH while positive charges increased NP contact with the negatively charged ocular surface. Either results in enhanced ocular bioavailability.

An In Situ Gelling System for the Local Treatment of Inflammatory Bowel Disease (IBD). The Loading of Maqui (Aristotelia Chilensis) Berry Extract as an Antioxidant and Anti-Inflammatory Agent

The aim of the present work was the development of an innovative in situ gelling system, to be applied on the mucosa of the distal colon via rectal route. The system consisted of three polymers having different functions: gellan (GG), able to jellify in presence of ions; methylcellulose (MC), a thermosensitive polymer with a gelation temperature close to 50 °C; and hydroxypropylcellulose (HPC), a mucoadhesive polymer. The three polymers were able to act synergistically, increasing the permanence of the vehicle on the mucosa and forming a protective gel layer. A DoE approach, "simplex centroid mixture design," was used to identify the optimal quantitative composition of the vehicle. The response variables considered were: vehicle viscosity at room temperature; increase in vehicle viscosity on increasing temperature (from room to physiological value) and upon dilution with simulated colonic fluid (SCF); and viscoelastic behavior, thixotropic area, and mucoadhesion properties of the gel formed at 37 °C upon dilution in SCF. The optimized vehicle was loaded with maqui berry extract (MBE), known for its antioxidant and anti-inflammatory properties. MBE loading (0.5% w/w) into the vehicle improved rheological and mucoadhesive properties of the formulation. Both MBE and the optimized vehicle were not cytotoxic towards human fibroblasts and Caco-2 cells. Moreover, the optimized vehicle did not affect MBE antioxidant properties.

Controlled release of Mitomycin C from modified cellulose based thermo-gel prevents post-operative de novo peritoneal adhesion

The complications from surgery associated peritoneal adhesion can be alleviated by combination of physical isolation and pharmaceutical treatment. This work aims to develop thermo-sensitive hydrogel barrier by combining mitomycin C (MMC) with modified tempo oxidized nanocellulose (cTOCN) through EDC/NHS-chemical conjugation followed by integration with methyl cellulose (MC). The MMC was successfully combined with cTOCN and ensured controlled release of MMC from hydrogel throughout 14 days. Amount of MC (1.5, 2.5, 3.5% w/v) was proportional to gelation time and inversely proportional to degradation of hydrogel. The optimized hydrogel (C2.5T1M0.2) needed only 30 s for thermoreversible sol-gel (4℃-37℃) phenomenon and did not show in vitro fibroblast cells toxicity as well as ensured complete adhesion prevention efficacy, reperitonealization in rat side wall-cecal abrasion model. Overall, the developed C2.5T1M0.2 thermo-gel advances state-of-the-art in view of cytocompatibility, mechanical stability, optimum degradation, good injectability, sustain drug release from surgical sites, and satisfactory de novo anti-adhesion capacity.

Arabinoxylan/Cellulose Nanocrystal Hydrogels with Tunable Mechanical Properties

Hydrogels are three-dimensional networks of hydro-soluble polymers containing a large amount of water that have found a wide panel of applications in many sectors. The need for eco-friendly and nontoxic materials for the elaboration of sustainable hydrogels is obvious, and materials derived from biomass can easily meet these requirements. Cellulose nanocrystals (CNC) and arabinoxylans (AX) are abundant, biobased, hydrophilic, and renewable nanoparticles and polymers that interact together. In this study, we have built fully biobased hydrogels using CNC and AX. First, as revealed by Quartz Crystal Microbalance with Dissipation (QCM-D) experiments, AX adsorbs almost instantly on cellulosic surfaces in an irreversible manner. Nevertheless, gelation kinetics is not instantaneous and shows temperature dependence. The determination of phase diagrams using the inverted tube method leads to the conclusion that high AX/CNC ratios are needed for gel formation. The mechanical properties of CNC-AX hydrogels were investigated by measuring storage and loss moduli (G', G'') as a function of concentrations and hydrogel reformation after submission to high shear rates. Hydrogel properties were also tuned by increasing the ionic strength and the enzymatic removal of arabinose moieties from AX. In light of the obtained results, we hypothesize that gel formation occurs in two steps, i.e., AX adsorption followed by gelation of the complexes, and is due to the formation of reversible and tunable interactions between CNC/AX complexes interacting with each other, offering a wide panel of physicochemical tools to tune and trigger the final properties of hydrogels.

Development of a Mucoadhesive in Situ Gelling Formulation for the Delivery of Lactobacillus gasseri into Vaginal Cavity

Local administration of vaginal probiotics, especially lactobacilli, has been recently proposed as an effective prevention strategy against candidosis recurrences, which affect 40-50% of women. In this context, the aim of the present work was the development of a mucoadhesive in situ gelling formulation for the vaginal administration of Lactobacillus gasseri. Mixtures of poloxamer 407 (P407) and methylcellulose (MC), two thermosensitive polymers, were prepared and subjected to rheological analyses for the assessment of their sol/gel transition temperature. The association of P407 (15% w/w) with MC (1.5% w/w) produced an increase in gelation extent at 37 °C even after dilution in simulated vaginal fluid (SVF). The presence of 0.5% w/w pectin (PEC) produced a reduction of vehicle pH and viscosity at 25 °C that is the vehicle resistance to flow during administration. The presence of a low concentration of xyloglucan (XYL) (0.25% w/w) increases the mucoadhesive properties and the capability to gelify at 37 °C of the formulation after dilution with SVF. A three-component (P407/MC/PEC; 3cM) and a four-component (P407/MC/PEC/XYL; 4cM) mixture were selected as promising candidates for the delivery of L. gasseri to the vaginal cavity. They were able to preserve L. gasseri viability and were cytocompatible towards the HeLa cell line.

Application of a Thermosensitive In Situ Gel of Chitosan-Based Nasal Spray Loaded with Tranexamic Acid for Localised Treatment of Nasal Wounds

The integrity of the nasal epithelium plays a crucial role in the airway defence mechanism. The nasal epithelium may be injured as a result of a large number of factors leading to nose bleeds, also known as epistaxis. However, local measures commonly used to treat epistaxis and improve wound healing present several side effects and patient discomfort. Hence, this study aims to address some of these drawbacks by developing a new formulation for nasal epithelial wound healing. Chitosan, a biodegradable and biocompatible polymer, was used to develop a thermosensitive nasal formulation for the delivery of tranexamic acid (TXA), one of the most effective pharmacological options to control bleeding with cost and tolerability advantages. The in situ gelation properties of the formulation upon administration in the nasal cavity were investigated in terms of gelation time and temperature. It was found that the developed formulation can undergo rapid liquid-to-gel phase change within approximately 5 min at 32°C, which is well within the human nasal cavity temperature range. The spray pattern, deposition and droplet size generated by the nasal spray was also characterised and were found to be suitable for nasal drug delivery. It was also observed that the in situ gelation of the formulation prevent nasal runoff, while the majority of drug deposited mainly in the anterior part of the nose with no lung deposition. The developed formulation was shown to be safe on human nasal epithelium and demonstrated six times faster wound closure compared to the control TXA solution.

Temperature-Dependent Rheological and Viscoelastic Investigation of a Poly(2-methyl-2-oxazoline)-b-poly(2-iso-butyl-2-oxazoline)-b-poly(2-methyl-2-oxazoline)-Based Thermogelling Hydrogel

The synthesis and characterization of an ABA triblock copolymer based on hydrophilic poly(2-methyl-2-oxazoline) (pMeOx) blocks A and a modestly hydrophobic poly(2-iso-butyl-2-oxazoline) (piBuOx) block B is described. Aqueous polymer solutions were prepared at different concentrations (1-20 wt %) and their thermogelling capability using visual observation was investigated at different temperatures ranging from 5 to 80 °C. As only a 20 wt % solution was found to undergo thermogelation, this concentration was investigated in more detail regarding its temperature-dependent viscoelastic profile utilizing various modes (strain or temperature sweep). The prepared hydrogels from this particular ABA triblock copolymer have interesting rheological and viscoelastic properties, such as reversible thermogelling and shear thinning, and may be used as bioink, which was supported by its very low cytotoxicity and initial printing experiments using the hydrogels. However, the soft character and low yield stress of the gels do not allow real 3D printing at this point.