Injectable, Biodegradable Hydrogels for Tissue Engineering Applications

Drug Delivery Based on Nanotechnology for Target Bone Disease

Bone diseases are a serious problem in modern human life. With the coming acceleration of global population ageing, this problem will become more and more serious. Due to the specific physiological characteristics and local microenvironment of bone tissue, it is difficult to deliver drugs to the lesion site. Therefore, the traditional orthopedic medicine scheme has the disadvantages of high drug frequency, large dose and relatively strong side effects. How to target deliver drugs to the bone tissue or even target cells is the focus of the development of new drugs. Nano drug delivery system with a targeting group can realize precise delivery of orthopedic drugs and effectively reduce the systemic toxicity. In addition, the application of bone tissue engineering scaffolds and biomedical materials to realize in situ drug delivery also are research hotspot. In this article, we briefly review the application of nanotechnology in targeted therapies for bone diseases.

New Developments in Medical Applications of Hybrid Hydrogels Containing Natural Polymers

New trends in biomedical applications of the hybrid polymeric hydrogels, obtained by combining natural polymers with synthetic ones, have been reviewed. Homopolysaccharides, heteropolysaccharides, as well as polypeptides, proteins and nucleic acids, are presented from the point of view of their ability to form hydrogels with synthetic polymers, the preparation procedures for polymeric organic hybrid hydrogels, general physico-chemical properties and main biomedical applications (i.e., tissue engineering, wound dressing, drug delivery, etc.).

Alginate-based hydrogels as drug delivery vehicles in cancer treatment and their applications in wound dressing and 3D bioprinting

Hydrogels are a three-dimensional and crosslinked network of hydrophilic polymers. They can absorb a large amount of water or biological fluids, which leads to their swelling while maintaining their 3D structure without dissolving (Zhu and Marchant, Expert Rev Med Devices 8:607-626, 2011). Among the numerous polymers which have been utilized for the preparation of the hydrogels, polysaccharides have gained more attention in the area of pharmaceutics; Sodium alginate is a non-toxic, biocompatible, and biodegradable polysaccharide with several unique physicochemical properties for which has used as delivery vehicles for drugs (Kumar Giri et al., Curr Drug Deliv 9:539-555, 2012). Owing to their high-water content and resembling the natural soft tissue, hydrogels were studied a lot as a scaffold. The formation of hydrogels can occur by interactions of the anionic alginates with multivalent inorganic cations through a typical ionotropic gelation method. However, those applications require the control of some properties such as mechanical stiffness, swelling, degradation, cell attachment, and binding or release of bioactive molecules by using the chemical or physical modifications of the alginate hydrogel. In the current review, an overview of alginate hydrogels and their properties will be presented as well as the methods of producing alginate hydrogels. In the next section of the present review paper, the application of the alginate hydrogels will be defined as drug delivery vehicles for chemotherapeutic agents. The recent advances in the application of the alginate-based hydrogels will be describe later as a wound dressing and bioink in 3D bioprinting.

Bioprinting 101: Design, Fabrication, and Evaluation of Cell-Laden 3D Bioprinted Scaffolds

3D bioprinting is an additive manufacturing technique that recapitulates the native architecture of tissues. This is accomplished through the precise deposition of cell-containing bioinks. The spatiotemporal control over bioink deposition permits for improved communication between cells and the extracellular matrix, facilitates fabrication of anatomically and physiologically relevant structures. The physiochemical properties of bioinks, before and after crosslinking, are crucial for bioprinting complex tissue structures. Specifically, the rheological properties of bioinks determines printability, structural fidelity, and cell viability during the printing process, whereas postcrosslinking of bioinks are critical for their mechanical integrity, physiological stability, cell survival, and cell functions. In this review, we critically evaluate bioink design criteria, specifically for extrusion-based 3D bioprinting techniques, to fabricate complex constructs. The effects of various processing parameters on the biophysical and biochemical characteristics of bioinks are discussed. Furthermore, emerging trends and future directions in the area of bioinks and bioprinting are also highlighted. Graphical abstract [Figure: see text] Impact statement Extrusion-based 3D bioprinting is an emerging additive manufacturing approach for fabricating cell-laden tissue engineered constructs. This review critically evaluates bioink design criteria to fabricate complex tissue constructs. Specifically, pre- and post-printing evaluation approaches are described, as well as new research directions in the field of bioink development and functional bioprinting are highlighted.

Microfluidics-based fabrication of cell-laden microgels

Microfluidic principles have been extensively utilized as powerful tools to fabricate controlled monodisperse cell-laden hydrogel microdroplets for various biological applications, especially tissue engineering. In this review, we report recent advances in microfluidic-based droplet fabrication and provide our rationale to justify the superiority of microfluidics-based techniques over other microtechnology methods in achieving the encapsulation of cells within hydrogels. The three main components of such a system-hydrogels, cells, and device configurations-are examined thoroughly. First, the characteristics of various types of hydrogels including natural and synthetic types, especially concerning cell encapsulation, are examined. This is followed by the elucidation of the reasoning behind choosing specific cells for encapsulation. Next, in addition to a detailed discussion of their respective droplet formation mechanisms, various device configurations including T-junctions, flow-focusing, and co-flowing that aid in achieving cell encapsulation are critically reviewed. We then present an outlook on the current applications of cell-laden hydrogel droplets in tissue engineering such as 3D cell culturing, rapid generation and repair of tissues, and their usage as platforms for studying cell-cell and cell-microenvironment interactions. Finally, we shed some light upon the prospects of microfluidics-based production of cell-laden microgels and propose some directions for forthcoming research that can aid in overcoming challenges currently impeding the translation of the technology into clinical success.

Hydrogels as Potential Nano-, Micro- and Macro-Scale Systems for Controlled Drug Delivery

This review is an extensive evaluation and essential analysis of the design and formation of hydrogels (HGs) for drug delivery. We review the fundamental principles of HGs (their chemical structures, physicochemical properties, synthesis routes, different types, etc.) that influence their biological properties and medical and pharmaceutical applications. Strategies for fabricating HGs with different diameters (macro, micro, and nano) are also presented. The size of biocompatible HG materials determines their potential uses in medicine as drug carriers. Additionally, novel drug delivery methods for enhancing treatment are discussed. A critical review is performed based on the latest literature reports.

Autologous protein-based scaffold composed of platelet lysate and aminated hyaluronic acid

This study describes a protein-based scaffold using platelet rich plasma (PRP), aminated hyaluronic acid (HA-NH₂) and Genipin for potential use in regenerative applications as an autologous tissue engineering scaffold. Human PRP was subjected to three freeze-thaw cycles for obtaining platelet lysates (PL). HA-NH₂ was synthesized from hyaluronic acid. PL/HA-NH₂ scaffolds were fabricated using different concentrations of genipin (0.05, 0.1 and 0.2%) and HA-NH₂ (10, 20 and 30 mg/mL). Mechanical, physical, and chemical properties of the scaffolds were comprehensively investigated. The compressive test findings revealed that crosslinking with 0.1 and 0.2% genipin improved the mechanical properties of the scaffolds. SEM evaluations showed that the scaffolds exhibited an interconnected and macroporous structure. Besides, porosimetry analysis indicated a wide distribution of the scaffold pore-size. Rheological findings demonstrated that the G' values were higher than the G″ values, indicating that PL/HA-NH₂ scaffolds had typical viscoelastic properties. In vitro biocompatibility studies showed that the scaffolds were both cytocompatible and hemocompatible. Alamar Blue test indicated that human adipose mesenchymal stem cells (hASCs) were able to attach, spread and proliferate on the scaffolds for 21 days-duration. Our findings clearly indicate that PL/HA-NH₂ can be a promising autologous candidate scaffold for tissue engineering applications.

Production of reactive species in alginate hydrogels for cold atmospheric plasma-based therapies

In the last years, great advances have been made in therapies based in cold atmospheric plasmas (CAP). CAP generate reactive oxygen and nitrogen species (RONS) which can be transferred to liquids. These CAP activated liquids display the same biological efficacy (i.e. on killing cancer cells) as CAP themselves, opening the door for minimally invasive therapies. However, injection of a liquid in the body results in fast diffusion due to extracellular fluids and blood flow. Therefore, the development of efficient vehicles which allow local confinement and delivery of RONS to the diseased site is a fundamental requirement. In this work, we investigate the generation of RONS (H2O2, NO2-, short-lived RONS) in alginate hydrogels by comparing two atmospheric pressure plasma jets: kINPen and a helium needle, at a range of plasma treatment conditions (time, gas flow, distance to the sample). The physic-chemical properties of the hydrogels remain unchanged by the plasma treatment, while the hydrogel shows several-fold larger capacity for generation of RONS than a typical isotonic saline solution. Part of the RONS are quickly released to a receptor media, so special attention has to be put on the design of hydrogels with in-situ crosslinking. Remarkably, the hydrogels show capacity for sustained release of the RONS. The plasma-treated hydrogels remain fully biocompatible (due the fact that the species generated by plasma are previously washed away), indicating that no cytotoxic modifications have occurred on the polymer. Moreover, the RONS generated in alginate solutions showed cytotoxic potential towards bone cancer cells. These results open the door for the use of hydrogel-based biomaterials in CAP-associated therapies.

Fabrication of pH-responsive TA-keratin bio-composited hydrogels encapsulated with photoluminescent GO quantum dots for improved bacterial inhibition and healing efficacy in wound care management: In vivo wound evaluations

Wounds origins serious complications of lives of human beings which may leads to death. The important issue for the problem is infection during wound care management which delays wound healing process. These kinds of infections may be caused by the overuse or misuse of antibiotics, antidotes, usage of new drugs, not properly sterilized surgical instruments, not appropriate for pH level and imperfect wound dressing etc. during or after surgery. Hence in this report, antimicrobial action of pH responsive TA/KA composited hydrogel crosslinked with GO-QDs (TA/KA-GOQDs) using citric acid as cross-linker has been reported by demonstrating in-vitro and in-vivo studies for wound care management. The prepared samples of GOQDs, TA/KA hydrogel and TA/KA-GOQDs were characterized using FT-IR, XRD, SEM and TEM techniques. pH responsive hydrogel property of TA/KA was evaluated by swelling studies. In-vitro antibacterial studies was carried out by direct contact test method. Further, the prepared samples were tested in a wound healing model of rate with the wound of size 1.5 cm² for in-vivo studies. After 16 days of treatment, the prepared samples for wound healing causes 100% wound areas closure. Histological observations were made by MT and HE staining process which proves keratinocytes proliferation by biocompatible and biocomposited TA/KA-GOQDs. The pH responsive TA/KA-GOQDs proved as efficient wound healing agent by faster keratinocytes proliferation within a compact period.

Silk Sericin Semi-interpenetrating Network Hydrogels Based on PEG-Diacrylate for Wound Healing Treatment

Silk sericin (SS) from the Bombyx mori silk cocoons has received much attention from biomedical scientists due to its outstanding properties, such as antioxidant, antibacterial, UV-resistant, and ability to release moisturizing factors. Unmodified SS does not self-assemble strongly enough to be used as a hydrogel wound dressing. Therefore, there is a need for suitable stabilization techniques to interlink the SS peptide chains or strengthen their structural cohesion. Here, we reported a method to form a silk semi-interpenetrating network (semi-IPN) structure through reacting with the short-chain poly(ethylene glycol) diacrylate (PEGDA) in the presence of a redox pair. Various hydrogels were prepared in aqueous media at the final SS/PEGDA weight percentages of 8/92, 15/85, and 20/80. Results indicated that all semi-IPN samples underwent a sol-gel transition within 70 min. The equilibrium water content (EWC) for all samples was found to be in the range of 70-80%, depending on the PEGDA content. Both the gelation time and the sol fraction decreased with the increased PEGDA content. This was due to the tightened network structure formed within the hydrogel matrices. Among all hydrogel samples, the 15/85 (SS/PEGDA) hydrogel displayed the maximum compressive strength (0.66 MPa) and strain (7.15%), higher than those of pure PEGDA. This implied a well-balanced molecular interaction within the SS/PEGDA/water systems. Based on the direct and indirect MTS assay, the 15/85 hydrogel showed excellent in vitro biocompatibility towards human dermal fibroblasts, representing a promising material for biomedical wound dressing in the future. A formation of a semi-IPN structure has thus proved to be one of the best strategies to extend a practical limit of using SS hydrogels for wound healing treatment or other biomedical hydrogel matrices in the future.

Injectable and thermosensitive nanofibrous hydrogel for bone tissue engineering

The use of injectable hydrogels is currently restricted by the challenge of achieving fast gelation, good mechanical strength, and cytocompatibility. Polymeric self-assembly is a potent tool for generating functional materials that combine multiple characteristics and can react to external factors. In this study, we have developed fiber-reinforced composite hydrogels that exhibits significantly enhanced mechanical strength, reduced gelling time, and excellent cytocompatibility. The practicability of developing a chitosan-based thermogelling solution using hydroxyapatite and polyelectrolyte complex (PEC) self-assembled fibers were evaluated. The effect of βGP concentration on gelation time was studied by varying the concentration of βGP added to the chitosan solution. Various combinations were tested to create a suitable hydrogel environment for cell encapsulation, growth, and proliferation at physiological pH and temperature. Determination of Young modulus revealed that PEC fibers reinforced hydrogel was three times stiffer than chitosan-βGP gels. The gelation time was reduced to 3 min, and the hydrogels had porous structures and gels at physiological pH, temperature, and showed >80% viability for MTT assay to MG63 cells. Moreover, confocal imaging of PEC fiber reinforced hydrogels showed noticeable viability and proliferation. The molecular interactions between gelling agents, polyelectrolytes, and hydroxyapatite were studied using FTIR. We investigated interfacial bonding between PEC fibers with βGP, NaHCO_3, and HAp. The combination of hydroxyapatite and polymer self-assembly technique improved the efficiency of injectable hydrogels that are helpful in minimally invasive applications.

Injectable and fast self-healing protein hydrogels

Injectable hydrogels are adapted to irregularities in the desired location by injection as a liquid and gelation in situ. However, traditional slow-gelling injectable hydrogels may result in loss of cargo (cells/drugs) as well as diffusion at the target site, and extremely rapid gelation may lead to undesired premature coagulation. These practical problems can be solved by using self-healing hydrogels. Herein, through the reduction of disulfide bonds in BSA protein by using a reducing agent, the disulfide bonds between the individual BSA protein molecules are re-matched to form a network structure, thereby forming a protein hydrogel. This hydrogel shows an efficient and rapid self-healing property, and the broken protein hydrogel can be fast repaired within 1-2 minutes in response to H₂O₂ stimulation, and the repair efficiency reached up to 100%. The hydrogel can be extruded using only a pinhole syringe, and cytotoxicity experiments have demonstrated excellent biocompatibility of the protein hydrogel. This non-toxic, injectable, fast self-healing protein hydrogel is expected to be widely used in biomedical, tissue engineering, injectable gel, 3D bioprinting, and other applications.

An Injectable Self-Healing Protein Hydrogel with Multiple Dissipation Modes and Tunable Dynamic Response

Hydrogels with dynamic mechanical properties are of special interest in the field of tissue engineering and drug delivery. However, it remains challenging to tailor the dynamic mechanical response of hydrogels to simultaneously meet diverse application needs. Here, we report a hetero-coiled-coil complex cross-linked protein hydrogel exhibiting unusual multiple energy dissipation modes and tunable dynamic response. Such unique features confer on the hydrogel responsiveness to mechanical stimuli in a broad range of frequencies. Therefore, the hydrogels are injectable due to their shearing-thinning properties at low shear rates of 0.8 rad s^-1 and can fully recover their mechanical properties within a few seconds due to the intrinsic fast dynamics of the cross-linkers. Moreover, the dynamic response of these hydrogels can be fine-tuned by the temperature and the hydrogel network structures. We anticipate that these hydrogels are promising candidates for delivering therapeutic drugs, biological molecules, and cells in a broad spectrum of biomedical applications.

Functional Hydrogels and Their Application in Drug Delivery, Biosensors, and Tissue Engineering

Hydrogel is a new class of functional polymer materials with a promising potential in the biomedical field. The purpose of this article is to review recent advancements in several types of biomedical hydrogels, including conductive hydrogels, injectable hydrogels, double network hydrogels, responsive hydrogels, nanocomposite hydrogels, and sliding hydrogels. In comparison with traditional hydrogels, these advanced hydrogels exhibit significant advantages in structure, mechanical properties, and applications. The article focuses on different methods used to prepare advanced biomedical hydrogels and their diversified applications as drug delivery systems, wound dressings, biosensors, contact lenses, and tissue replacement. These advances are rapidly overcoming current limitations of hydrogels, and we anticipate that further research will lead to the development of advanced hydrogels with ubiquitous roles in biomedicine and tissue replacement and regeneration.

MMP-responsive in situ forming hydrogel loaded with doxorubicin-encapsulated biodegradable micelles for local chemotherapy of oral squamous cell carcinoma

The complex construction within the oral cavity causes incomplete surgical resection of oral squamous cell carcinoma (OSCC) that may enhance the risk of recurrence and metastasis in the treatment. In situ forming injectable hydrogels with minimally invasive procedures, encapsulation stability and stimuli-responsive degradation have emerged as promising carriers for local drug delivery. In this study, doxorubicin (DOX) was first encapsulated in biodegradable poly(d,l-lactide)-poly(ethylene glycol)-poly(d,l-lactide) (PDLLA-PEG-PDLLA) micelles and then loaded into an in situ injectable hyaluronic acid (HA) hydrogel, which was cross-linked by a matrix metalloproteinase-2 (MMP-2)-responsive peptide (GCRDGPQGIWGQDRCG) through a Michael addition reaction. In vitro studies demonstrated that the HA hydrogel had a sensitive MMP-2-responsive drug release profile. Investigations including MTT, live-dead, apoptosis, and wound healing assays illustrated that DOX micelle-loaded HA hydrogels exhibited outstanding cytotoxicity against squamous carcinoma cells (SCC-15). Furthermore, by in vivo studies, we also proved that HA hydrogels degraded faster in the tumor site than in normal tissue, which led to a local sustained release of DOX-loaded micelles and tumor growth inhibition of oral squamous cell carcinoma (OSCC) without any damage to the organs. Therefore, this work provides a remarkable drug delivery platform for local chemotherapy and other applications.

Impact of Counter Ions of Cationic Monomers on the Production and Characteristics of Chitosan-Based Hydrogel

Chitosan-based hydrogel has received considerable interests because of its appealing properties and applications in many areas. The primary objective of this work was to produce novel cationic chitosan-based hydrogels via polymerizing chitosan with two cationic monomers of the same structure but with different counter ions [2-(methacryloyloxy)ethyl]trimethylammonium methyl sulfate (METMS) and [2-(methacryloyloxy)ethyl]trimethylammonium chloride (METAC). Polymerization of chitosan with the cationic monomers performed under the conditions of 50 °C, 5 h, 7 pH, and 2/1 mol/mol monomer/chitosan led to chitosan-METMS and -METAC with the cationic charge densities of 3.22 and 2.88 mequiv/g, respectively. Elemental analysis, gel permeation chromatography, Fourier transform infrared, X-ray diffraction, and differential scanning calorimetry analyses were used to confirm the impact of counter ions of cationic monomers (i.e., polarizability of monomers) on their polymerization performance and the characteristics of induced chitosan-based hydrogels. Also, the results of this work postulated that the counter ions associated with the monomers could dramatically impact the water uptake and swelling properties of the generated chitosan-based hydrogels as well as their performance in adsorbing an anionic dye from a simulated solution.

Enhanced dual network hydrogels consisting of thiolated chitosan and silk fibroin for cartilage tissue engineering

Thiolated chitosan (CS-NAC) was synthesized and the selected CS-NAC was used together with silk fibroin (SF) to produce dual network CS-NAC/SF hydrogels. The CS-NAC/SF solutions with formulated compositions were able to form hydrogels at physiological temperature and pH. Rheological measurements showed that elastic modulus of some CS-NAC/SF gels could reach around 3 kPa or higher and was much higher than their respective viscous modulus, indicating that they behaved like strong gels. Deformation measurements verified that CS-NAC/SF gels had well-defined elasticity. The optimized CS-NAC/SF gels exhibited jointly enhanced properties in terms of strength, stiffness and elasticity when compared to the gels resulted from either CS-NAC or SF. Examinations of dry CS-NAC/SF gels revealed that they were highly porous with well-interconnected pore features. Cell culture demonstrated that CS-NAC/SF gels supported the growth of chondrocytes while effectively maintaining their phenotype. Results suggest that these dual network gels have promising potential in cartilage repair.

Induction of zonal-specific cellular morphology and matrix synthesis for biomimetic cartilage regeneration using hybrid scaffolds

Cartilage is anisotropic in nature and organized into distinct zones. Our goal was to develop zonal-specific three-dimensional hybrid scaffolds which could induce the generation of zonal-specific cellular morphology and extracellular matrix (ECM) composition. The superficial and middle zones comprised two layers of hyaluronic acid (HA) hydrogel which enveloped specifically orientated or randomly arranged polylactic acid nanofibre meshes. The deep zone comprised a HA hydrogel with multiple vertical channels. Primary bovine chondrocytes were seeded into the individual zonal scaffolds, cultured for 14 days and then the ECM was analysed. The aligned nanofibre mesh used in the superficial zone induced an elongated cell morphology, lower glycosaminoglycan (GAG) and collagen II production, and higher cell proliferation and collagen I production than the cells in the middle zone scaffold. Within the middle zone scaffold, which comprised a randomly orientated nanofibre mesh, the cells were clustered and expressed more collagen II. The deep zone scaffold induced the highest GAG production, the lowest cell proliferation and the lowest collagen I expression of the three zones. Assembling the three zones and stabilizing the arrangement with a HA hydrogel generated aligned, randomly aggregated and columnar cells in the superficial, middle and deep zones. This study presents a method to induce zonal-specific chondrocyte morphology and ECM production.

Autoclavable and Injectable Cryogels for Biomedical Applications

Prior to any clinical application, terminal sterilization of biomaterials is a critical process imposed by the Food and Drug Administration. Of all the methods available for sterilization, high-pressure steam sterilization such as autoclaving is the most widely used. While autoclave sterilization minimizes pathogen contamination, it can dramatically impact both structural and biological properties of biomaterials. It has recently been reported that injectable cryogels with shape memory properties hold great promises as 3D macroporous biomimetic scaffolds for biomedical applications including tissue engineering. In this study, the impact of autoclave sterilization on properties of a series of cryogels is measured. Unlike conventional hydrogels, cryogels made of natural polymers demonstrate a strong resilience to autoclave sterilization. This process does not alter either their macrostructural or unique physical properties including syringe injectability. The scaffolds' bioactive sites are preserved and autoclaved cryogels retain their excellent cytological compatibility post-autoclaving. Furthermore, autoclaved cryogels do not trigger a notable activation of primary murine bone marrow-derived dendritic cells suggesting a minimal risk for biomaterial-induced inflammation, which is further confirmed by an in vivo histologic analysis. In summary, these results further demonstrate the huge potential of cryogels in the biomedical field and their capacity to be translated into clinical applications.

Biomimetic cartilage scaffold with orientated porous structure of two factors for cartilage repair of knee osteoarthritis

A dual-layer biomimetic cartilage scaffold was prepared by mimicking the structural design, chemical cues and mechanical characteristics of mature articular cartilage. The surface layer was made from collagen (COL), chitosan (CS) and hyaluronic acid sodium (HAS). The transitional layer with microtubule array structure was prepared with COL, CS and silk fibroin (SF). The PLAG microspheres containing kartogenin (KGN) and the polylysine-heparin sodium nanoparticles containing TGF-β1 (TPHNs) were constructed for the surface, transitional layer, respectively. The SEM result showed that the dual-layer composite scaffold had a double structure similar to natural cartilage. The vitro biocompatibility experiment showed that the biomimetic cartilage scaffold with orientated porous structure was more conducive to the proliferation and adhesion of BMSCs. A rabbit KOA cartilage defect model was established and biomimetic cartilage scaffolds were implanted in the defect area. Compared with the surface layer and transitional layer scaffolds group, the results of dual-layer biomimetic cartilage scaffold group showed that the defects had been completely filled, the boundary between new cartilage and surrounding tissue was difficult to identify, and the morphology of cells in repair tissue was almost in accordance with the normal cartilage after 16 weeks. All those results indicated that the biomimetic cartilage scaffold could effectively repair the defect of KOA, which is related to the fact that the scaffold could guide the morphology, orientation, and proliferation and differentiation of BMSCs. This work could potentially lead to the development of multilayer scaffolds mimicking the zonal organization of articular cartilage.

Hydrogels Based Drug Delivery Synthesis, Characterization and Administration

Hydrogels represent 3D polymeric networks specially designed for various medical applications. Due to their porous structure, they are able to swollen and to entrap large amounts of therapeutic agents and other molecules. In addition, their biocompatibility and biodegradability properties, together with a controlled release profile, make hydrogels a potential drug delivery system. In vivo studies have demonstrated their effectiveness as curing platforms for various diseases and affections. In addition, the results of the clinical trials are very encouraging and promising for the use of hydrogels as future target therapy strategies.

Codelivery of paclitaxel and temozolomide through a photopolymerizable hydrogel prevents glioblastoma recurrence after surgical resection

A photopolymerizable hydrogel-based local drug delivery system was developed for the postsurgical treatment of glioblastoma (GBM). We aimed for a local drug combination therapy with paclitaxel (PTX) and temozolomide (TMZ) within a hydrogel to synergistically inhibit tumor growth. The in vitro cytotoxicity of TMZ was assessed in U87MG cells. We demonstrated the synergistic effect of PTX and TMZ on U87MG cells by clonogenic assay. Treatment with TMZ did not induce O6-methylguanine-DNA methyltransferase related drug resistance in tumor-bearing mice. PTX had sustained release for at least 1 month in vivo in healthy mice brains. The drug combination was tolerable and suppressed tumor growth more efficiently than the single drugs in the U87MG orthotopic tumor model. The PTX and TMZ codelivery hydrogel showed superior antitumor effects and can be considered a promising approach for the postsurgical treatment of GBM.

Sequential Delivery of Dual Growth Factors from Injectable Chitosan-Based Composite Hydrogels

Local administration of platelet-derived growth factor-BB (PGDF-BB) and bone morphogenetic protein-2 (BMP-2) in a sequential release manner could substantially promote bone healing. To achieve this goal, a delivery system that could sustain the release of PGDF-BB and BMP-2 by way of temporal separation was developed. One type of PGDF-BB-encapsulated alginate microsphere and another type of BMP-2-encapsulated microsphere with a core-shell structure were respectively produced using emulsification methods. These two types of microspheres were then embedded into chitosan/glycerophosphate hydrogel for constructing composite gels. Some of them were found to be injectable at ambient temperature and had thermo-sensitive features near physiological temperature and pH. The optimally formulated composite gels showed the ability to control the release of PGDF-BB and BMP-2 in a sequential fashion in which PDGF-BB was released earlier than BMP-2. In vitro release patterns indicated that the release rates could be significantly regulated by varying the embedded amount of the factor-encapsulated microspheres, which can in turn mediate the temporal separation release interval between PGDF-BB and BMP-2. The released PDGF-BB and BMP-2 were detected to be bioactive based on their respective effects on Balb/c 3T3 and C2C12 cells. These results suggest that the presently developed composite gels have the potential for bone repair by synergistically utilizing the early chemotactic effect of PDGF-BB and the subsequent osteogenic and angiogenic functions of PDGF-BB and BMP-2.

Scaffolding Strategies for Tissue Engineering and Regenerative Medicine Applications

During the past two decades, tissue engineering and the regenerative medicine field have invested in the regeneration and reconstruction of pathologically altered tissues, such as cartilage, bone, skin, heart valves, nerves and tendons, and many others. The 3D structured scaffolds and hydrogels alone or combined with bioactive molecules or genes and cells are able to guide the development of functional engineered tissues, and provide mechanical support during in vivo implantation. Naturally derived and synthetic polymers, bioresorbable inorganic materials, and respective hybrids, and decellularized tissue have been considered as scaffolding biomaterials, owing to their boosted structural, mechanical, and biological properties. A diversity of biomaterials, current treatment strategies, and emergent technologies used for 3D scaffolds and hydrogel processing, and the tissue-specific considerations for scaffolding for Tissue engineering (TE) purposes are herein highlighted and discussed in depth. The newest procedures focusing on the 3D behavior and multi-cellular interactions of native tissues for further use for in vitro model processing are also outlined. Completed and ongoing preclinical research trials for TE applications using scaffolds and hydrogels, challenges, and future prospects of research in the regenerative medicine field are also presented.

Thermally triggered injectable chitosan/silk fibroin/bioactive glass nanoparticle hydrogels for in-situ bone formation in rat calvarial bone defects

Copper-containing bioactive glass nanoparticles (Cu-BG NPs) with designed compositions and sizes were synthesized and incorporated into chitosan (CH)/silk fibroin (SF)/glycerophosphate (GP) composites to prepare injectable hydrogels for cell-free bone repair. The resulting Cu-BG/CH/SF/GP gels were found to exhibit well-defined injectability and to undergo rapid gelation at physiological temperature and pH. They were highly porous and showed the ability to administer Si, Ca and Cu ions at their respective safe doses in a sustained and controlled manner. In vitro studies revealed that the gels supported the growth of seeded MC3T3-E1 and human umbilical vein endothelial cells, and effectively induced them toward osteogenesis and angiogenesis, respectively. In vivo bone repair based on a critical-size rat calvarial bone defect model demonstrated that the optimal Cu-BG/CH/SF/GP gel was able to fully restore the bone defect with formation of vascularized bone tissue and mineralized collagen deposition during a treatment period of 8 weeks without utilization of any cells and/or growth factors. The results suggest that the presently developed Cu-BG/CH/SF/GP composite hydrogels have great potential and translation ability for bone regeneration owing to their thermo-sensitive properties, cell-free bioactivity, and cost-effectiveness. STATEMENT OF SIGNIFICANCE: Hydrogels loaded with cells and/or growth factors exhibit potential in bone repair. However, they have been facing obstacles related to the clinic translation. Here, a novel type of hydrogel system consisting of copper-containing bioactive glass nanoparticles and chitosan/silk fibroin composite was developed. These gels showed injectability and thermally triggered in situ gelation properties and were able to administer the release of ions at safe but effective doses in a controlled manner while inducing the seeded cells toward osteogenesis and angiogenesis. The optimal gel showed the ability to fully repair critical-size rat calvarial bone defects without involving time consuming cell processing and/or the use of expensive growth factors, confirming that this novel hydrogel system has great potential for translation to the clinic.

Fabrication and properties of an injectable sodium alginate/PRP composite hydrogel as a potential cell carrier for cartilage repair

Three-dimensional scaffolds like hydrogels can be employed as cell carriers for in vitro or in vivo colonization and have become a major research topic to replace damaged tissue. In the current study, a novel composite hydrogel composed of sodium alginate (SA) and platelet-rich-plasma (PRP) varying in blending ratios, cross-linked with calcium ions, released from calcium carbonate-D-Glucono-d-lactone (CaCO₃ -GDL) was successfully prepared. It was found that addition of PRP changed largely the physical properties and biological performance of the composite hydrogels, which was depending on the blending ratio. The gelation rate and swelling ratio of alginate hydrogels were significantly reduced by the addition of PRP, which produced also a more homogeneous gel structure. Field emission scanning electron microscopy (FE-SEM) investigation confirmed the incorporation of PRP-derived proteins in the hydrogel, where a porous structure with a pore size of 200-300 μm was found. On the other hand, an increase in surface roughness was observed after the addition of PRP. The compressive mechanical strength of SA/PRP composite hydrogel was enhanced in comparison to the pure SA gel. The composite hydrogels with the highest PRP content exhibited at a maximum compressive stress of 0.26 MPa a maximum strain of 55%, while the maximum compressive strain of pure SA hydrogels was only 45% at a stress of 0.08 MPa. It was also found that the in vitro degradation of the alginate gel was accelerated by the addition of PRP. In terms of cellular responses, all gels exhibited an excellent cytocompatibility. Indeed, the composite hydrogels supported bone marrow-derived mesenchymal stem cells proliferation and their chondrogenesis with up-regulation of chondrogenic marker genes Sox9 and Aggrecan. Overall, the present study suggests a great potential of SA/PRP composite hydrogels as cell carriers for cartilage tissue engineering.

Chitosan-Based Hydrogels Embedded with Hyaluronic Acid Complex Nanoparticles for Controlled Delivery of Bone Morphogenetic Protein-2

Chitosan(CH)-poly(dioxanone) (CH-PDO) copolymers containing varied amounts of PDO and having free amino groups at their CH backbone were synthesized using a group protection method. The selected CH-PDO with soluble characteristics in aqueous media was used together with hyaluronic acid (HA) to prepare HA/CH-PDO polyelectrolyte complex nanoparticles (NPs) via an ionotropic gelation technique, and such a type of HA/CH-PDO NPs was employed as a carrier for delivering bone morphogenetic protein-2 (BMP-2). The optimal BMP-2-encapsulated HA/CH-PDO NPs with high encapsulation efficiency were embedded into CH/glycerophosphate composite solutions to form different hydrogels in order to achieve long-term BMP-2 release. The formulated gels were found to be injectable at room temperature and had its thermosensitive phase transition near physiological temperature and pH. They also showed abilities to administer the release of BMP-2 in approximately linear manners for a few weeks while effectively preserving the bioactivity of the encapsulated BMP-2. In view of their fully biocompatible and biodegradable components, the presently developed gel systems have promising potential for translation to the clinic use in bone repair and regeneration where the sustained and controlled stimuli from active signaling molecules and the stable biomechanical framework for housing the recruited cells are often concurrently needed.

Effect of gamma irradiation on the physicochemical and rheological properties of enzyme-catalyzed tragacanth-based injectable hydrogels

In the present study, gamma irradiation was applied to promote the mechanical properties of enzyme- mediated in situ forming hydrogels prepared with tyramine-functionalized gum tragacanth (TA-GT). For this purpose, after gamma irradiation of powder or hydrocolloid solution of gum tragacanth (GT), the physiochemical and rheological properties of GT solution, and resultant hydrogel was investigated. In situ forming hydrogels were prepared via horseradish peroxidase catalyzed coupling reaction of TA-GT in the presence of hydrogen peroxide. Gamma irradiation led to a decrease in GT molecular weight and solution viscosity. Also, the solubility of GT improved and the separation of water soluble/swellable part of gum samples became easier, using gamma irradiation. In addition, by gamma irradiation of GT powder at doses of 5–15 kGy, a polymeric solution with higher concentration could be prepared that resulted in the promotion of hydrogels storage modulus. Further increase of irradiation dose did not improve storage modulus due to the extra decrease of gum molecular weight.

Effects of concentration variation on the physical properties of alginate-based substrates and cell behavior in culture

Nowadays alginate capsules exhibit good biocompatibility and high permeability for nutrients and metabolic wastes making them appealing biomaterial for therapeutic cell encapsulation. Further study of the characteristics of alginate beads which are highly dependent on various environmental conditions to create an optimum microenvironment for cells is also critical. Thus, in this study, the effect of concentration variation on the physical properties of alginate-based beads and entrapped-cells behavior was analyzed. Results showed that the increase of Ca ions concentration brought about the decrease of the average diameter, prolongation of dissolution time, reduction of permeability and swelling, and a rise of crosslinking extent and shrinkage of capsules; while raising sodium alginate concentration had an opposite effect on the diameter and shrinkage. Moreover, the addition of gelatin enhanced the penetration and swelling and slowed down the shrinkage of capsules. And MC3T3-E1 cells enclosed in the particles in which the concentration of calcium chloride, sodium alginate and gelatin was 2.5%, 2.0% and 0.5% (w/v %) had preferable abilities of proliferation and higher expression of alkaline phosphatase. Overall, the ability to tailor this system to support in vitro growth of MC3T3-E1 cells might have significance for the future use of other cell types in regenerative medicine.

Polyelectrolyte Complexes of Natural Polymers and Their Biomedical Applications

Polyelectrolyte complexes (PECs), composed of natural and biodegradable polymers, (such as positively charged chitosan or protamine and negatively charged glycosaminoglycans (GAGs)) have attracted attention as hydrogels, films, hydrocolloids, and nano-/micro-particles (N/MPs) for biomedical applications. This is due to their biocompatibility and biological activities. These PECs have been used as drug and cell delivery carriers, hemostats, wound dressings, tissue adhesives, and scaffolds for tissue engineering. In addition to their comprehensive review, this review describes our original studies and provides an overview of the characteristics of chitosan-based hydrogel, including photo-cross-linkable chitosan hydrogel and hydrocolloidal PECs, as well as molecular-weight heparin (LH)/positively charged protamine (P) N/MPs. These are generated by electrostatic interactions between negatively charged LH and positively charged P together with their potential biomedical applications.

Injectable Hydrogels Based on Pluronic/Water Systems Filled with Alginate Microparticles for Biomedical Applications

A (model) composite system for drug delivery was developed based on a thermoresponsive hydrogel loaded with microparticles. We used Pluronic F127 hydrogel as the continuous phase and alginate microparticles as the dispersed phase of this composite system. It is well known that Pluronic F127 forms a gel when added to water in an appropriate concentration and in a certain temperature range. Pluronic F127 hydrogel may be loaded with drug and injected, in its sol state, to act as a drug delivery system in physiological environment. A rheological characterization allowed the most appropriate concentration of Pluronic F127 (15.5 wt%) and appropriate alginate microparticles contents (5 and 10 wt%) to be determined. Methylene blue (MB) was used as model drug to perform drug release studies in MB loaded Pluronic hydrogel and in MB loaded alginate microparticles/Pluronic hydrogel composite system. The latter showed a significantly slower MB release than the former (10 times), suggesting its potential in the development of dual cargo release systems either for drug delivery or tissue engineering.

Injectable chitosan/gelatin/bioactive glass nanocomposite hydrogels for potential bone regeneration: In vitro and in vivo analyses

The present work describes in vitro and in vivo behaviors of thermosensitive composite hydrogels based on polymers/bioactive glass nanoparticles. Assays in SBF (simulated body fluid) solution showed that loss of hydrogel mass in vitro was decreased by 4.3% when bioactive glass nanoparticles (nBG) were incorporated, and confirmed the bioactivity of nBG containing hydrogels. In vitro assays demonstrated the cytocompatibility of the hydrogels with encapsulated rat bone marrow mesenchymal stem cells (BMSC). Crystal violet assays showed a 27% increase in cell viability when these cells were seeded in hydrogels containing nBG. In vivo biocompatibility was examined by injecting hydrogels into the dorsum of Swiss rats. The results indicated that the prepared hydrogels were nontoxic upon subcutaneous injection, and could be candidates for a safe in situ gel-forming system. Injection of the hydrogels into a rat tibial defect allowed preliminary evaluation of the hydrogels' regenerative potential. Micro Computed Tomography analysis suggested that more new tissue was formed in the defects treated with the hydrogels. Taken together, our data suggest that the developed injectable composite hydrogels possess properties which make them suitable candidates for use as temporary injectable matrices for bone regeneration.

In Situ Generated Medical Devices

Medical devices play a major role in all areas of modern medicine, largely contributing to the success of clinical procedures and to the health of patients worldwide. They span from simple commodity products such as gauzes and catheters, to highly advanced implants, e.g., heart valves and vascular grafts. In situ generated devices are an important family of devices that are formed at their site of clinical function that have distinct advantages. Among them, since they are formed within the body, they only require minimally invasive procedures, avoiding the pain and risks associated with open surgery. These devices also display enhanced conformability to local tissues and can reach sites that otherwise are inaccessible. This review aims at shedding light on the unique features of in situ generated devices and to underscore leading trends in the field, as they are reflected by key developments recently in the field over the last several years. Since the uniqueness of these devices stems from their in situ generation, the way they are formed is crucial. It is because of this fact that in this review, the medical devices are classified depending on whether their in situ generation entails chemical or physical phenomena.

One-pot green synthesis of polymeric nanocomposite: Biodegradation studies and application in sorption-degradation of organic pollutants

The research work proposes the synthesis of a nanocomposite hydrogel which is a dual combination of binary interpenetrating network (BIPN) and bismuth ferrite nanoparticles. BIPN synthesized from binary graft copolymer (BGC) used as starting material. The cross-linked network of BGC is interpenetrating the newly synthesized cross-linked network of poly(acrylic acid) and the product is named as BIPN. Binary graft copolymer had been synthesized from grafting of guggul aqueous extract with copolymeric chains of acrylamide (primary monomer) and acrylic acid (secondary monomer) crosslinked by N,N'-methylene bisacrylamide (MBA). The maximum percentage swelling was evaluated for BGC through optimization of various reaction parameters: amount of water, binary ratio of acrylamide to acrylic acid, concentrations of MBA, ammonium persulphate, pH, temperature and time. Considering pre-optimized parameters for BGC synthesis, BIPN formation required optimization of only acrylic acid. Maximum percentage swelling obtained was 1497.79% and 308.15% for BGC and BIPN, respectively. Maximum percentage biodegradation of 90.64% and 82.38% were calculated for BGC and BIPN, respectively using composting method. Degradation efficiency of brilliant blue (BB) and fuchsin basic (FB) dyes was in the order: Nanocomposite ≫ BIPN > BGC. Maximum percentage degradation observed in case of nanocomposite was 94.1% and 99.3% in sunlight for BB and FB, respectively. The interaction of dyes with the nanocomposite involved mainly ionic interactions. The adsorption models Freundlich and Langmuir were applicable to overall adsorption and degradation process of BB and FB, respectively. Maximum adsorption capacities corresponding to minimum concentration i.e. 10 mg L^-1 for BB and FB were calculated as 0.409 mg g^-1 and 0.439 mg g^-1, respectively. Second order and first order kinetics were found to be suitable for BB and FB adsorption-degradation pathways, respectively. Intraparticle diffusion mechanism was favorable to both dyes and adsorption followed three steps. Gas chromatography coupled with mass spectrometric analysis could give the degraded products which was helpful in drawing degradation pathway. The degradation process involved active radical species (O₂^-., OH^.) and they carry out oxidation-reduction reactions on dyes to give decolorized solution containing mineral ions.

A Biocompatible Therapeutic Catheter-Deliverable Hydrogel for In Situ Tissue Engineering

Hydrogels have emerged as a diverse class of biomaterials offering a broad range of biomedical applications. Specifically, injectable hydrogels are advantageous for minimally invasive delivery of various therapeutics and have great potential to treat a number of diseases. However, most current injectable hydrogels are limited by difficult and time-consuming fabrication techniques and are unable to be delivered through long, narrow catheters, preventing extensive clinical translation. Here, the development of an easily-scaled, catheter-injectable hydrogel utilizing a polymer-nanoparticle crosslinking mechanism is reported, which exhibits notable shear-thinning and self-healing behavior. Gelation of the hydrogel occurs immediately upon mixing the biochemically modified hyaluronic acid polymer with biodegradable nanoparticles and can be easily injected through a high-gauge syringe due to the dynamic nature of the strong, yet reversible crosslinks. Furthermore, the ability to deliver this novel hydrogel through a long, narrow, physiologically-relevant catheter affixed with a 28-G needle is highlighted, with hydrogel mechanics unchanged after delivery. Due to the composition of the gel, it is demonstrated that therapeutics can be differentially released with distinct elution profiles, allowing precise control over drug delivery. Finally, the cell-signaling and biocompatibility properties of this innovative hydrogel are demonstrated, revealing its wide range of therapeutic applications.

The Investigation of LRP5-Loaded Composite with Sustained Release Behavior and Its Application in Bone Repair

Low-density lipoprotein receptor-related protein 5 (LRP5) plays a vital role in bone formation and regeneration. In this study, we developed an injectable and sustained-release composite loading LRP5 which could gelatinize in situ. The sustained release of the composite and its efficacy in bone regeneration were evaluated. Sodium alginate, collagen, hydroxyapatite, and LRP5 formed the composite LRP5-Alg/Col/HA. It was found that the initial setting time and final setting time of LRP5-Alg/Col/HA containing 4% alginate were suitable for surgical operation. When the composite was loaded with 40 μg/mL LRP5, LRP5-Alg/Col/HA did not exhibit a burst-release behavior and could sustainably release LRP5 up to 21 days. Up to 18 days, LRP5 released from LRP5-Alg/Col/HA still present the binding activity with DKK1 (Wnt signaling pathway antagonist) and could increase the downstream β-catenin mRNA in bone marrow mesenchymal stem cells. Moreover, LRP5-Alg/Col/HA was found to significantly increase bone mineral density in the defect area after 6 weeks’ implantation of LRP5-Alg/Col/HA into the rats’ calvarial defect area. H&E staining detection demonstrated that LRP5-Alg/Col/HA could mediate the formation of a new bone tissue. Therefore, we concluded that Alg/Col/HA was a suitable sustained-release carrier for LRP5 and LRP5-Alg/Col/HA had a significant effect on repairing bone defects and could be a good bone regeneration material.