Thermo-sensitive injectable hydrogel based on the physical mixing of hyaluronic acid and Pluronic F-127 for sustained NSAID delivery

Smart injectable self-setting bioceramics for dental applications

A thermo-responsive injectable bioactive glass (BAG) that has the ability to set at body temperature was prepared using pluronic F127 and hydroxypropyl methylcellulose as the carrier. The injectable composite has the advantage to fill irregular shape implantation sites and quick setting at body temperature. The structural and morphological analysis of injectable BAG before and after setting was done by using Fourier Transform Infrared spectroscopy (FTIR), and Scanning Electron Microscope (SEM). The effect of an ultrasonic scaler for a quick setting of injectable BAG was also investigated. The ultrasonic scaler sets the BAG formulation three-folds faster than at body temperature and homogenized the dispersion. The in vitro bio-adhesion was studied in the bovine tooth in both artificial saliva and deionized water for periodic time intervals, i.e., day 7, 30, 90, and 180, which confirmed the apatite layer formation. The mineral density analysis was used to differentiate the newly formed apatite with tooth apatite. In the MTT assay, the experimental material showed continuous proliferation and cell growth. This indicated that injectable hydrogel promoted cell growth, facilitated proliferation, and had no cytotoxic effect. The SEM and micro-CT results (performed after in vitro bioactivity testing) showed that the injectable BAG had the ability to regenerate dentin, hence this material has the potential to be used for dental and biomedical applications including tooth and bone regeneration in minimally invasive procedures in future.

Preparation of Injectable Composite Hydrogels by Blending Poloxamers with Calcium Carbonate-Crosslinked Sodium Alginate

The effects of calcium carbonate-crosslinked sodium alginate on poloxamer hydrogels have been investigated. The mechanical strength, degradability, and thermal stability of hydrogels were characterized. The chemical and physical crosslinking in the composite hydrogels has resulted in an improvement of the compressive strength and elasticity of the hydrogels. These mixed hydrogels showed improved mechanical properties, elasticity, and stability as well as environmental responsiveness and injectability.

Formulation strategies to modulate drug release from poloxamer based in situ gelling systems

Introduction: Poloxamer based in situ gelling systems offer numerous advantages in drug delivery; however, their application as prolonged-release delivery platforms is limited mainly due to their weak mechanical properties and the interconnected aqueous network causing fast gel erosion and drug diffusion.Area covered: The focus of this review is to provide an insightful discussion on the formulation strategies that can be employed to sustain/prolong the drug release from poloxamer based in situ gelling systems. The review also outlines the formulation factors, influencing drug release from these systems.Expert opinion: The nature, composition, and concentration of poloxamers are the most critical factors in defining the rate of drug release from an in situ gelling matrix. Hydrophobic gel matrices have compact micellar arrangements resulting in slow diffusion and erosion. Depending on the intended clinical application, gel characteristics can be modulated, either by physical blending or by chemical crosslinking with additive materials, to slow release and improve residence time at the administration site. Incorporating drug-loaded particles into poloxamer gels sustains drug release by creating multiple rate-limiting release barriers. Chemical modification of poloxamers appears to be a promising strategy to obtain prolonged sustained release for parenteral application without compromising the rheological properties of the formulation.

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.

Self-Assemblable Polymer Smart-Blocks for Temperature-Induced Injectable Hydrogel in Biomedical Applications

Self-assembled temperature-induced injectable hydrogels fabricated via self-assembly of polymer smart-blocks have been widely investigated as drug delivery systems and platforms for tissue regeneration. Polymer smart-blocks that can be self-assembly play an important role in fabrication of hydrogels because they can self-assemble to induce the gelation of their copolymer in aqueous solution. The self-assembly occurs in response to an external stimulus change, such as temperature, pH, glucose, ionic strength, light, magnetic field, electric field, or their combination, which results in property transformations like hydrophobicity, ionization, and conformational change. The self-assembly smart-block based copolymers exist as a solution in aqueous media at certain conditions that are suitable for mixing with bioactive molecules and/or cells. However, this solution turns into a hydrogel due to the self-assembly of the smart-blocks under exposure to an external stimulus change in vitro or injection into the living body for a controllable release of loaded bioactive molecules or serving as a biomaterial scaffold for tissue regeneration. This work reports current scenery in the development of these self-assembly smart-blocks for fabrication of temperature-induced injectable physically cross-linked hydrogels and their potential application as drug delivery systems and platforms for tissue engineering.

Receptor targeting drug delivery strategies and prospects in the treatment of rheumatoid arthritis

Rheumatoid arthritis (RA), a chronic inflammatory disease, is characterized by cartilage damage, bone tissue destruction, morphological changes in synovial fluids, and synovial joint inflammation. The inflamed synovial tissue has potential for passive and active targeting because of enhanced permeability and retention effect and the existence of RA synovial macrophages and fibroblasts that selectively express surface receptors such as folate receptor β, CD44 and integrin αVβ. Although there are numerous interventions in RA treatment, they are not safe and effective. Therefore, it is important to develop new drug or drug delivery systems that specifically targets inflamed/swollen joints but attenuates other possible damages to healthy tissues. Recently some receptors such as toll-like receptors (TLRs), the nucleotide-binding oligomerization domain-like receptors, and Fc-γ receptor have been identified in synovial tissue and immune cells that are involved in induction or suppression of arthritis. Analysis of the TLR pathway has moreover suggested new insights into the pathogenesis of RA. In the present paper, we have reviewed drug delivery strategies based on receptor targeting with novel ligand-anchored carriers exploiting CD44, folate and integrin αVβ as well as TLRs expressed on synovial monocytes and macrophages and antigen presenting cells, for possible active targeting in RA. TLRs could not only open a new horizon for developing new drugs but also their antagonists or humanized monoclonal antibodies that block TLRS specially TLR4 and TLR9 signaling could be used as targeting agents to antigen presenting cells and dendritic cells. As a conclusion, common conventional receptors and multifunctional ligands that arte involved in targeting receptors or developing nanocarriers with appropriate ligands for TLRs can provide profoundly targeting drug delivery systems for the effective treatment of RA.

Thermoresponsive Hyalomer intra-articular hydrogels improve monoiodoacetate-induced osteoarthritis in rats

Osteoarthritis (OA) is characterized by degenerative knees, fingers and hip joints. In OA joints, the concentration and polymerization of hyaluronic acid (HA) are changed; affecting the viscosity of the synovial fluid. Replenishing HA synovial fluid content, along with an anti-inflammatory drug could be a cost-effective strategy. As free drugs are rapidly cleared out of the synovial fluid, we aimed to prepare Hyalomer in situ forming gel for intra-articular (IA) injection. Hyalomer contains poloxamer 407 (PX) as thermogelling agent, HA, and diclofenac potassium (DK) as an anti-inflammatory. Hyalomer formulations were prepared and characterized in terms of sol-gel transition, gelation time, in vitro release and 3-month stability. The selected Hyalomer formula was injected IA in OA rat model, in comparison to its individual components. The optimized Hyalomer formulation showed 25% DK release after 24 h and 40% after 4 days. The gelation time was 40 ± 2.08 s and gelation temperature was 26 ± 1.87 °C. Hyalomer maintained the percentage drug release and DK content after 3-months storage. In OA rats, Hyalomer showed the highest anti-nociceptive and anti-edematous effect. Both radiography and histopathology revealed regenerated cartilage profile in Hyalomer-treated group. combining IA HA and diclofenac in thermoresponsive gel represents a promising therapeutic alternative for OA.

A redox-responsive hyaluronic acid-based hydrogel for chronic wound management

Polymer-based hydrogels have been widely applied for chronic wound therapeutics, due to their well-acclaimed wound exudate management capability. At the same time, there is still an unmet clinical need for simple wound diagnostic tools to assist clinical decision-making at the point of care and deliver on the vision of patient-personalised wound management. To explore this challenge, we present a one-step synthetic strategy to realise a redox-responsive, hyaluronic acid (HA)-based hydrogel that is sensitive to wound environment-related variations in glutathione (GSH) concentration. By selecting aminoethyl disulfide (AED) as a GSH-sensitive crosslinker and considering GSH concentration variations in active and non-self-healing wounds, we investigated the impact of GSH-induced AED cleavage on hydrogel dimensions, aiming to build GSH-size relationships for potential point-of-care wound diagnosis. The hydrogel was also found to be non-cytotoxic and aided L929 fibroblast growth and proliferation over seven days in vitro. Such a material offers a very low-cost tool for the visual detection of a target analyte that varies dependent on the status of the cells and tissues (wound detection), and may be further exploited as an implant for fibroblast growth and tissue regeneration (wound repair).

Hyaluronic acid/corn silk extract based injectable nanocomposite: A biomimetic antibacterial scaffold for bone tissue regeneration

Injectable hydrogels have revealed the great potential for use as scaffolds in cartilage and bone tissue engineering. Here, thermosensitive and injectable hydrogels containing β-tricalcium phosphate, hyaluronic acid, and corn silk extract-nanosilver (CSE-Ag NPs) were synthesized for their potential use in bone tissue regeneration applications. Spherical nanoparticles of silver were biosynthesized through microwave-assisted green approach using CSE in organic solvent-free medium. Rheological experiments demonstrated that the thermosensitive hydrogels have gelification temperature (T_gel) close to body temperature. The samples containing Ag NPs showed antibacterial activity toward gram-positive (Bacillus Subtilis, Staphylococcus Aureus) and gram-negative (Pseudomonas Aeruginosa, Escherichia Coli) bacteria along without cytotoxicity after 24 h. Mesenchymal stem cells seeded in the nanocomposite exhibited high bone differentiation which indicate that thay could be a good candidate as a potential scaffold for bone tissue regeneration.

Dual Thermo- and pH-Responsive Behavior of Double Zwitterionic Graft Copolymers for Suppression of Protein Aggregation and Protein Release

Graft copolymers consisting of two different zwitterionic blocks were synthesized via reversible addition fragmentation chain transfer polymerization. These polymers showed dual properties of thermo- and pH-responsiveness in an aqueous solution. Ultraviolet-visible spectroscopy and dynamic light scattering were employed to study the phase behavior under varying temperatures and pH values. Unlike the phase transition temperatures of other graft copolymers containing nonionic blocks, the phase transition temperature of these polymers was easily tuned by changing the polymer concentration. Owing to the biocompatible and stimuli-responsive nature of the polymers, this system was shown to effectively release proteins (lysozyme) while simultaneously protecting them against denaturation. The positively charged lysozyme was shown to bind with the negatively charged polymer at the physiological pH (pH 7.4). However, it was subsequently released at pH 3, at which the polymer exhibits a positive charge. Protein aggregation studies using a residual enzymatic activity assay, circular dichroism, and a Thioflavin T assay revealed that the secondary structure of the lysozyme was retained even after harsh thermal treatment. The addition of these polymers helped the lysozyme retain its enzymatic activity and suppressed its fibrillation. Both polymers showed excellent protein protection properties, with the negatively charged polymer exhibiting slightly superior protein protection properties to those of the neutral polymer. To the best of the authors' knowledge, this is the first study to develop a graft copolymer system consisting of two different zwitterionic blocks that shows dual thermo- and pH-responsive properties. The presence of the polyampholyte structure enables these polymers to act as protein release agents, while simultaneously protecting the proteins from severe stress.

Smart polymers for cell therapy and precision medicine

Soft materials have been developed very rapidly in the biomedical field over the past 10 years because of advances in medical devices, cell therapy, and 3D printing for precision medicine. Smart polymers are one category of soft materials that respond to environmental changes. One typical example is the thermally-responsive polymers, which are widely used as cell carriers and in 3D printing. Self-healing polymers are one type of smart polymers that have the capacity to recover the structure after repeated damages and are often injectable through needles. Shape memory polymers are another type with the ability to memorize their original shape. These smart polymers can be used as cell/drug/protein carriers. Their injectability and shape memory performance allow them to be applied in bioprinting, minimally invasive surgery, and precision medicine. This review will describe the general materials design, characterization, as well as the current progresses and challenges of these smart polymers.

Strategies for Hyaluronic Acid-Based Hydrogel Design in Drug Delivery

Hyaluronic acid (HA) is a natural, linear, endogenous polysaccharide that plays important physiological and biological roles in the human body. Nowadays, among biopolymers, HA is emerging as an appealing starting material for hydrogels design due to its biocompatibility, native biofunctionality, biodegradability, non-immunogenicity, and versatility. Since HA is not able to form gels alone, chemical modifications, covalent crosslinking, and gelling agents are always needed in order to obtain HA-based hydrogels. Therefore, in the last decade, different strategies for the design of physical and chemical HA hydrogels have been developed, such as click chemistry reactions, enzymatic and disulfide crosslinking, supramolecular assembly via inclusion complexation, and so on. HA-based hydrogels turn out to be versatile platforms, ranging from static to smart and stimuli-responsive systems, and for these reasons, they are widely investigated for biomedical applications like drug delivery, tissue engineering, regenerative medicine, cell therapy, and diagnostics. Furthermore, the overexpression of HA receptors on various tumor cells makes these platforms promising drug delivery systems for targeted cancer therapy. The aim of the present review is to highlight and discuss recent advances made in the last years on the design of chemical and physical HA-based hydrogels and their application for biomedical purposes, in particular, drug delivery. Notable attention is given to HA hydrogel-based drug delivery systems for targeted therapy of cancer and osteoarthritis.

LDH hybrid thermosensitive hydrogel for intravaginal delivery of anti-HIV drugs

Microbicides based on hydrogel have become an effective way to prevent the HIV replication and transmission because of their convenience and prolonging drug release. In this study, a hybrid thermo-sensitive hydrogel constituted by nanosized layered double hydroxides and poloxamer 407 (P407) was constructed and co-loaded with both hydrophobic and hydrophilic drug. The LDH-P407 hydrogel could achieve sol-gel transition at body temperature. The in vivo experiment showed that LDH-P407 hydrogel can achieve controlled release of theaflavin and Nile red (hydrophobic drug model) into blood by vaginal drug delivery, meanwhile the hydrogel showed barely mucosal irritation. In addition, ex vivo experiment showed that the nifeviroc-loaded LDH-P407 hydrogel was able to specifically bind co-receptor CCR5 of DCs cells. Therefore, the LDH-P407 hydrogel would be a promising carrier for intravaginal delivery of anti-HIV drugs.

Recent advances in musculoskeletal local drug delivery

Musculoskeletal disorders are a significant burden on the global economy and public health. Advanced drug delivery plays a key role in the musculoskeletal field and holds the promise of enhancing the repair of degenerated and injured musculoskeletal tissues. Ideally, drug delivery should have the ability to directly deliver therapeutic agents to the diseased/injured sites with a desirable drug level over a period of time. Here, we present a mini-review of the current state-of-the-art research associated with local drug delivery and its use for the treatment of musculoskeletal disorders. First, an overview of drug delivery strategies, with a focus on issues related to musculoskeletal pathology, potential therapeutic strategies, conventional and non-conventional drugs, and various delivery systems, is introduced. Then, we highlight recent advances in the emerging fields of musculoskeletal local drug delivery, involving therapeutic drugs (e.g., genes, small molecule therapeutics, and stem cells), novel delivery vehicles (e.g., 3D printing and tissue engineering techniques), and innovative delivery approaches (e.g., multi-drug delivery and smart stimuli-responsive delivery). The review concludes with future perspectives and associated challenges for developing local drug delivery for musculoskeletal applications. STATEMENT OF SIGNIFICANCE: Three important aspects are highlighted in this manuscript: 1) The advanced musculoskeletal drug delivery is introduced from the aspects ranging from musculoskeletal disorders, potential therapeutic solutions, and various drug delivery systems. 2) The recent advances in the emerging fields of musculoskeletal local drug delivery, involving therapeutic drugs (e.g., genes, small molecule therapeutics, and stem cells), novel delivery vehicles (e.g., 3D printing and tissue engineering technique), and innovative delivery approaches (e.g., multi-drug delivery and smart stimuli-responsive delivery), are highlighted. 3) The challenges and perspectives of future research directions in the development of musculoskeletal local drug delivery are presented.

Temperature-Dependent Solubilization of the Hydrophobic Antiepileptic Drug Lamotrigine in Different Pluronic Micelles-A Spectroscopic, Heat Transfer Method, Small-Angle Neutron Scattering, Dynamic Light Scattering, and in Vitro Release Study

Pluronics (tri-block copolymers) have a significant role in the pharmaceutical industry and are being used to enhance the solubility and delivery of hydrophobic drugs in different marketed formulations. However, instability and unsatisfactory drug-loading capacity are the major weak spots of these pluronic micelles. The present research work is designed to solve the existing issues by the solubilization study of hydrophobic drugs in different pluronic micelles at variable temperatures. The solubilization of the hydrophobic antiepileptic drug lamotrigine (LAM) in five different pluronic micelles viz. P84, P85, F127, F108, and F68 was studied at different temperatures, 37, 47, and 57 °C, using UV-visible spectroscopy. The solubilization of LAM in pluronic micelles increased with the increase in temperature. Small-angle neutron scattering (SANS) measurements were used to observe the morphological and structural changes taking place in pluronics by increasing the temperature. The SANS results showed the morphological changes of spherical P84 micelles to prolate ellipsoidal micelles at 57 °C due to remarkable increase in the aggregation number. This morphological conversion was further confirmed by the heat transfer method (HTM) and dynamic light scattering (DLS) measurements. DLS measurements confirmed that LAM-loaded micelles showed a greater hydrodynamic diameter (D h) compared to unloaded micelles, assuring LAM solubilization in the pluronic micelles. The rate of controlled release of LAM from five different pluronic micelles was accessed by using different kinetic models to evaluate the in vitro release profile. This is the first report in which HTM measurements are established for the analysis of morphological changes in the thermoresponsive pluronic micelles in real time. The present work corroborates how we can control the drug-loading capacity, morphological structure of the drug carrier, as well as drug release by simply changing the temperature of pluronic micellar media.

Sterilization Procedure for Temperature-Sensitive Hydrogels Loaded with Silver Nanoparticles for Clinical Applications

Hydrogels (HG) have recognized benefits as drug delivery platforms for biomedical applications. Their high sensitivity to sterilization processes is however one of the greatest challenges regarding their clinical translation. Concerning infection diseases, prevention of post-operatory related infections is crucial to ensure appropriate patient recovery and good clinical outcomes. Silver nanoparticles (AgNPs) have shown good antimicrobial properties but sustained release at the right place is required. Thus, we produced and characterized thermo-sensitive HG based on Pluronic^® F127 loaded with AgNPs (HG-AgNPs) and their integrity and functionality after sterilization by dry-heat and autoclave methods were carefully assessed. The quality attributes of HG-AgNPs were seriously affected by dry-heat methods but not by autoclaving methods, which allowed to ensure the required sterility. Also, direct sterilization of the final HG-AgNPs product proved more effective than of the raw material, allowing simpler production procedures in non-sterile conditions. The mechanical properties were assessed in post mortem rat models and the HG-AgNPs were tested for its antimicrobial properties in vitro using extremely drug-resistant (XDR) clinical strains. The produced HG-AgNPs prove to be versatile, easy produced and cost-effective products, with activity against XDR strains and an adequate gelation time and spreadability features and optimal for in situ biomedical applications.

Non-Anticoagulant Heparin Prodrug Loaded Biodegradable and Injectable Thermoresponsive Hydrogels for Enhanced Anti-Metastasis Therapy

Metastasis is a pathogenic spread of cancer cells from the primary site to surrounding tissues and distant organs, making it one of the primary challenges for effective cancer treatment and the major cause of cancer mortality. Heparin-based biomaterials exhibit significant inhibition of cancer cell metastasis. In this study, a non-anticoagulate heparin prodrug is developed for metastasis treatment with a localized treatment system using temperature sensitive, injectable, and biodegradable (poly-(ε-caprolactone-co-lactide)-b-poly(ethylene glycol)-b-poly(ε-caprolactone-co-lactide) polymeric hydrogel. The drug molecule (heparin) is conjugated with the polymer via esterification, and its sustained release is ensured by hydrolysis and polymeric biodegradation. An aqueous solution of the polymer could be used as an injectable solution at below 25 °C and it achieves gel formation at 37 °C. The anti-metastasis effect of the hydrogels is investigated both in vitro and in vivo. The results demonstrated that local administration of injectable heparin-loaded hydrogels effectively promote an inhibitory effect on cancer metastasis.

In situ thermo-co-electroresponsive mucogel for controlled release of bioactive agent

The purpose of this work was to develop an in situ thermosensitive electro-responsive mucoadhesive gel loaded with bioactive agent (nanocomposite) meant for nose to brain delivery in a controllable manner when electric stimulation is applied. Nanocomposite was developed using a combinatorial blending of chitosan, hydroxypropylmethylcellulose, pluronic F127 and polyaniline which was then loaded with BCNU-Nano-co-Plex (the bioactive agent). The nanocomposite was a liquid at room temperature but formed an in situ mucogel at a temperature of 27.5 ± 0.5 °C. Furthermore, the nanocomposite possessed a redox element which makes it responsive to electrical stimulation (ES). The stimuli responsiveness enabled the formulation to release the bioactive agent when electrical potential was applied and demonstrated a desired 10.28% release of nanoparticles per application cycle. The results further revealed pore formation within the formulation which accommodated the loaded nanoparticles. The release profile also demonstrated a pulsatile release of the bioactive material when subjected to ES. This formulation may therefore be useful as a nose to brain drug delivery system that can be modulated to deliver bioactive agents to the brain via electro-actuation in an "on-off" drug release kinetics by means of an external ES for a controlled nose-to-brain delivery.

Recent advances in functional nanostructured materials for bone-related diseases

Bone-related diseases seriously threaten people's health and research studies have been dedicated towards searching for new and effective treatment methods. Nanotechnologies have opened up a new field in recent decades and nanostructured materials, which exist in a variety of forms, are considered to be promising materials in this field. This article reviews the most recent progress in the development of nanostructured materials for bone-related diseases, including osteoporosis, osteoarthritis, bone metastasis, osteomyelitis, myeloma, and bone defects. We highlight the advantages and functions of nanostructured materials, including sustained release, bone targeting, scaffolding in bone tissue engineering, etc., in bone-related diseases. We also include the remaining challenges of these emerging materials.

Drug-Loaded Biocompatible Nanocarriers Embedded in Poloxamer 407 Hydrogels as Therapeutic Formulations

Hydrogels are three-dimensional networks of hydrophilic polymers able to absorb and retain a considerable amount of water or biological fluid while maintaining their structure. Among these, thermo-sensitive hydrogels, characterized by a temperature-dependent sol–gel transition, have been massively used as drug delivery systems for the controlled release of various bioactives. Poloxamer 407 (P407) is an ABA-type triblock copolymer with a center block of hydrophobic polypropylene oxide (PPO) between two hydrophilic polyethyleneoxide (PEO) lateral chains. Due to its unique thermo-reversible gelation properties, P407 has been widely investigated as a temperature-responsive material. The gelation phenomenon of P407 aqueous solutions is reversible and characterized by a sol–gel transition temperature. The nanoencapsulation of drugs within biocompatible delivery systems dispersed in P407 hydrogels is a strategy used to increase the local residence time of various bioactives at the injection site. In this mini-review, the state of the art of the most important mixed systems made up of colloidal carriers localized within a P407 hydrogel will be provided in order to illustrate the possibility of obtaining a controlled release of the entrapped drugs and an increase in their therapeutic efficacy as a function of the biomaterial used.

In situ photocrosslinked hyaluronic acid and poly (γ-glutamic acid) hydrogels as injectable drug carriers for load-bearing tissue application

Due to the syringeability of precursor solution and convenience of open surgical treatment, injectable hydrogels have gained growing attention in drug delivery application. For load-bearing tissue, the excellent mechanical property is an important requirement for delivery vehicles to resist external stress and loads. Herein, we prepared mechanically robust injectable hydrogels (HA/γ-PGA hydrogels for short) using methacrylate-functionalized hyaluronic acid and poly (γ-glutamic acid) via photopolymerization. The HA/γ-PGA hydrogels showed outstanding anti-compression ability and could suffer a more than 80% strain. Meanwhile, after 5 cycles of compression, HA/γ-PGA hydrogels could still recover quickly against external stress, showing excellent shape recovery capability. Moreover, the mechanical properties could be modulated easily by changing the molar ratio of HA to γ-PGA. The drug release behavior was also evaluated and the drug-loaded HA/γ-PGA hydrogels showed a weak burst release and sustained release behavior. Additionally, HA/γ-PGA hydrogels also exhibited superior biocompatibility. Therefore, HA/γ-PGA hydrogels have great potential as injectable drug carriers for load-bearing tissue application.

Designing the Slide-Ring Polymer Network with both Good Mechanical and Damping Properties via Molecular Dynamics Simulation

Through coarse-grained molecular dynamics simulation, we have successfully designed the chemically cross-linked (fixed junction) and the slide-ring (SR) systems. Firstly, we examine the dynamic properties such as the mean-square displacement, the bond, and the end-to-end autocorrelation functions as a function of the cross-linking density, consistently pointing out that the SR system exhibits much lower mobility compared with the fixed junction one at the same cross-linking density. This is further validated by a relatively higher glass transition temperature for the SR system compared with that of the fixed junction one. Then, we calculated the effect of the cross-linking density on the stretch-recovery behavior for the SR and fixed junction systems. Although the chain orientation of the SR system is higher than that of the fixed-junction system, the tensile stress is smaller than the latter. We infer that much greater chain sliding can occur during the stretch, because the movable ring structure homogeneously sustains the external force of the SR system, which, therefore, leads to much larger permanent set and higher hysteresis during the recovery process compared with the fixed-junction one. Based on the stretch-recovery behavior for various cross-linking densities, we obtain the change of the hysteresis loss, which is larger for the SR system than that of the fixed junction system. Lastly, we note that the relatively bigger compressive stress for the SR system results from the aggregation of the rigid rings compared with the fixed junction system. In general, compared with the traditionally cross-linked system, a deep molecular-level insight into the slide-ring polymer network is offered and thus is believed to provide some guidance to the design and preparation of the slide-ring polymer network with both good mechanical and damping properties.

Multifunctional smart hydrogels: potential in tissue engineering and cancer therapy

In recent years, clinical applications have been proposed for various hydrogel products. Hydrogels can be derived from animal tissues, plant extracts and/or adipose tissue extracellular matrices; each type of hydrogel presents significantly different functional properties and may be used for many different applications, including medical therapies, environmental pollution treatments, and industrial materials. Due to complicated preparation techniques and the complexities associated with the selection of suitable materials, the applications of many host-guest supramolecular polymeric hydrogels are limited. Thus, improvements in the design and construction of smart materials are highly desirable in order to increase the lifetimes of functional materials. Here, we summarize different functional hydrogels and their varied preparation methods and source materials. The multifunctional properties of hydrogels, particularly their unique ability to adapt to certain environmental stimuli, are chiefly based on the incorporation of smart materials. Smart materials may be temperature sensitive, pH sensitive, pH/temperature dual sensitive, photoresponsive or salt responsive and may be used for hydrogel wound repair, hydrogel bone repair, hydrogel drug delivery, cancer therapy, and so on. This review focuses on the recent development of smart hydrogels for tissue engineering applications and describes some of the latest advances in using smart materials to create hydrogels for cancer therapy.

Photothermally triggered disassembly of a visible dual fluorescent poly(ethylene glycol)/α-cyclodextrin hydrogel

The real-time tracking and adjustment of the disassembly and status of hydrogels in vivo are important challenges to accurate and precise assessment. In this article, a photothermally controllable, visible, dual fluorescent thermosensitive hydrogel was designed and developed based on a porphyrin-poly(ethylene glycol)/IR-820-α-cyclodextrin hydrogel. Due to the photothermal effect and fluorescence emission of IR-820, it can exert the dual functions of photothermal control and fluorescence imaging tracking. The IR-820 conjugated hydrogel can regulate the hydrogel disassembly by the photothermal effect of IR-820. Furthermore, each component of the hydrogel can be tracked by the fluorescence of IR-820 and porphyrin. Fluorescence imaging tracking and remote photothermal control were merged into the visible and controlled hydrogel disassembly after subcutaneous injection using mice as models. The dual fluorescence imaging visualization of cyclodextrin/poly(ethylene glycol) hydrogels revealed the disassembly process by tracking each component, and the hydrogel disassembly can be efficiently accelerated under laser irradiation with the photothermal effect of IR-820. This affords an important basis for understanding the disassembly process of the poly(ethylene glycol)/α-cyclodextrin hydrogel.

ECM based injectable thermo-sensitive hydrogel on the recovery of injured cartilage induced by osteoarthritis

Intra-articular injection of anti-inflammatory drugs can be a promising strategy for recovery of injured articular cartilage. We prepared a series of injectable thermo-sensitive composite hydrogels, composed of Pluronic F127, glycosaminoglycan (GAG) and bone morphogenetic protein (BMP-2), which was designed to mimic extracellular matrix (ECM). The rheological properties and dissolution rate of composite hydrogels containing chondroitin sulfate or with different hyaluronic acid molecular mass (10k, 90k, 800k) were investigated. Meanwhile, bovine serum albumin (BSA) or FITC-BSA was chosen as model drug loaded into PF/GAG hydrogels to study their sustained release behavior in vitro. The results showed that hydrogels could maintain shapes for more than 16 days and the release rate of BSA in PF/GAG composite gels was much slower than in PF127 gels, due to the affinity between BSA and GAG. Furthermore, increasing the molecular weight of hyaluronic acid correspondingly increased hydrogel dissolution rate and BSA release in the hydrogels. Subsequently, MTT experiments were performed to investigate the toxicity of the hydrogels on mouse pre-osteoblast cell MC3T3-E1. In vivo anti-inflammation results showed that PF/GAG@BMP-2 composite hydrogels had the most efficient efficacy on recovery of injured cartilage, which is induced by osteoarthritis, compared to the control groups (PF127@BMP-2 or BMP-2 saline solution).

Injectable hydrogels based on the hyaluronic acid and poly (γ-glutamic acid) for controlled protein delivery

Injectable hydrogels have great potential in minimally invasive delivery. In this work, novel injectable hydrogels were prepared via self-crosslinking of aldehyde hyaluronic acid (HA-CHO) and hydrazide-modified poly (γ-glutamic acid) (γ-PGA-ADH) for proteins delivery. The HA/γ-PGA hydrogels could be formed in situ as fast as 9s with high swelling ratios. Rheological properties illustrated a wide processing range and good mechanical properties, which were reflected by broad linear viscoelastic region and higher threshold shear stress (σ_c) and storage modulus (G'). Meanwhile, the gelation time, swelling ratio, rheological properties, as well as the protein release behavior could be modulated conveniently. Bovine serum albumin (BSA) was designed as a model drug to study the release behavior. We found that the release mechanisms were either diffusion or Case-II relaxation depending on the different hydrogel components. The HA/γ-PGA hydrogels also showed good biocompatibility. Therefore, the HA/γ-PGA hydrogels have great potential as promising injectable biomaterials for controlled protein delivery.

Hydrogel Based Biosensors for In Vitro Diagnostics of Biochemicals, Proteins, and Genes

Hydrogel-based biosensors have drawn considerable attention due to their various advantages over conventional detection systems. Recent studies have shown that hydrogel biosensors can be excellent alternative systems to detect a wide range of biomolecules, including small biochemicals, pathogenic proteins, and disease specific genes. Due to the excellent physical properties of hydrogels such as the high water content and stimuli-responsive behavior of cross-linked network structures, this system can offer substantial improvement for the design of novel detection systems for various diagnostic applications. The other main advantage of hydrogels is the role of biomimetic three-dimensional (3D) matrix immobilizing enzymes and aptamers within the detection systems, which enhances their stability. This provides ideal reaction conditions for enzymes and aptamers to interact with substrates within the aqueous environment of the hydrogel. In this review, we have highlighted various novel detection approaches utilizing the outstanding properties of the hydrogel. This review summarizes the recent progress of hydrogel-based biosensors and discusses their future perspectives and clinical limitations to overcome.