Injectable hyaluronic acid hydrogel loaded with BMSC and NGF for traumatic brain injury treatment

Glycosaminoglycans' for brain health: Harnessing glycosaminoglycan based biomaterials for treating central nervous system diseases and in-vitro modeling

Dysfunction of the central nervous system (CNS) following traumatic brain injuries (TBI), spinal cord injuries (SCI), or strokes remains challenging to address using existing medications and cell-based therapies. Although therapeutic cell administration, such as stem cells and neuronal progenitor cells (NPCs), have shown promise in regenerative properties, they have failed to provide substantial benefits. However, the development of living cortical tissue engineered grafts, created by encapsulating these cells within an extracellular matrix (ECM) mimetic hydrogel scaffold, presents a promising functional replacement for damaged cortex in cases of stroke, SCI, and TBI. These grafts facilitate neural network repair and regeneration following CNS injuries. Given that natural glycosaminoglycans (GAGs) are a major constituent of the CNS, GAG-based hydrogels hold potential for the next generation of CNS healing therapies and in vitro modeling of CNS diseases. Brain-specific GAGs not only offer structural and biochemical signaling support to encapsulated neural cells but also modulate the inflammatory response in lesioned brain tissue, facilitating host integration and regeneration. This review briefly discusses different roles of GAGs and their related proteoglycan counterparts in healthy and diseases brain and explores current trends and advancements in GAG-based biomaterials for treating CNS injuries and modeling diseases. Additionally, it examines injectable, 3D bioprintable, and conductive GAG-based scaffolds, highlighting their clinical potential for in vitro modeling of patient-specific neural dysfunction and their ability to enhance CNS regeneration and repair following CNS injury in vivo.

Mesenchymal Stem Cell-Loaded Hydrogel Improves Surgical Treatment for Chronic Cerebral Ischemia

Chronic cerebral ischemia (CCI) results in a prolonged insufficient blood supply to the brain tissue, leading to impaired neuronal function and subsequent impairment of cognitive and motor abilities. Our previous research showed that in mice with bilateral carotid artery stenosis, the collateral neovascularization post Encephalo-myo-synangiosis (EMS) treatment could be facilitated by bone marrow mesenchymal stem cells (MSCs) transplantation. Considering the advantages of biomaterials, we synthesized and modified a gelatin hydrogel for MSCs encapsulation. We then applied this hydrogel on the brain surface during EMS operation in rats with CCI, and evaluated its impact on cognitive performance and collateral circulation. Consequently, MSCs encapsulated in hydrogel significantly augment the therapeutic effects of EMS, potentially by promoting neovascularization, facilitating neuronal differentiation, and suppressing neuroinflammation. Furthermore, taking advantage of multi-RNA-sequencing and in silico analysis, we revealed that MSCs loaded in hydrogel regulate PDCD4 and CASP2 through the overexpression of miR-183-5p and miR-96-5p, thereby downregulating the expression of apoptosis-related proteins and inhibiting early apoptosis. In conclusion, a gelatin hydrogel to enhance the functionality of MSCs has been developed, and its combination with EMS treatment can improve the therapeutic effect in rats with CCI, suggesting its potential clinical benefit.

Biomaterial strategies for regulating the neuroinflammatory response

Injury and disease in the central nervous system (CNS) can result in a dysregulated inflammatory environment that inhibits the repair of functional tissue. Biomaterials present a promising approach to tackle this complex inhibitory environment and modulate the mechanisms involved in neuroinflammation to halt the progression of secondary injury and promote the repair of functional tissue. In this review, we will cover recent advances in biomaterial strategies, including nanoparticles, hydrogels, implantable scaffolds, and neural probe coatings, that have been used to modulate the innate immune response to injury and disease within the CNS. The stages of inflammation following CNS injury and the main inflammatory contributors involved in common neurodegenerative diseases will be discussed, as understanding the inflammatory response to injury and disease is critical for identifying therapeutic targets and designing effective biomaterial-based treatment strategies. Biomaterials and novel composites will then be discussed with an emphasis on strategies that deliver immunomodulatory agents or utilize cell-material interactions to modulate inflammation and promote functional tissue repair. We will explore the application of these biomaterial-based strategies in the context of nanoparticle- and hydrogel-mediated delivery of small molecule drugs and therapeutic proteins to inflamed nervous tissue, implantation of hydrogels and scaffolds to modulate immune cell behavior and guide axon elongation, and neural probe coatings to mitigate glial scarring and enhance signaling at the tissue-device interface. Finally, we will present a future outlook on the growing role of biomaterial-based strategies for immunomodulation in regenerative medicine and neuroengineering applications in the CNS.

Schiff Base-Based Hydrogel Embedded with In Situ Generated Silver Nanoparticles Capped by a Hyaluronic Acid-Diethylenetriamine Derivative for Wound Healing Application

In this study, hydrogels were produced using a Schiff base reaction between two hyaluronic acid derivatives: one containing aldehyde groups (HA-Ald) and the other holding a diethylenetriamine with terminal amino groups (HA-DETA). The DETA portion promotes the in situ growth, complexation, and stabilization of silver nanoparticles (AgNPs), eliminating the need for external reducing agents. The reaction between HA-DETA and HA-Ald leads to the formation of imine bonds, which results in dynamically pH-responsive cross-linking. While the DETA capping ability helped in embedding the AgNPs, the on/off pH environmental responsivity of the hydrogel allows for a controlled and on-demand release of the drug, mainly when bacterial infections cause pH variation of the wound bed. The injectable hydrogels resulted in being highly compatible in contact with blood red cells, fibroblasts, and keratinocytes and capable of having a proliferative effect on an in vitro wound scratch model. The pH-responsive hydrogels showed proper antibacterial activity againstPseudomonas aeruginosaandStaphylococcus aureus, common bacterial strains presented in wound infections. Finally, in vivo wound model studies demonstrated an overall speeding up in the wound healing rate and advanced wound conditions in the experimental group treated with the hydrogels compared to control samples.

Strongly Adhesive, Self-Healing, Hemostatic Hydrogel for the Repair of Traumatic Brain Injury

With wide clinical demands, therapies for traumatic brain injury (TBI) are a major problem in surgical procedures and after major trauma. Due to the difficulty in regeneration of neurons or axons after injury, as well as the inhibition of blood vessel growth by the formation of neural scars, existing treatment measures have limited effectiveness in repairing brain tissue. Herein, the biomultifunctional hydrogels are developed for TBI treatment based on the Schiff base reaction of calcium ion (Ca2+)-cross-linked oxidized sodium alginate (OSA) and carboxymethyl chitosan (CMCS). The obtained COCS hydrogel exhibits excellent adhesion to wet tissues, self-repair capability, and antimicrobial properties. What's particularly interesting is that the addition of Ca2+ increases the hydrogel's extensibility, enhancing its hemostatic capabilities. Biological assessments indicate that the COCS hydrogel demonstrates excellent biocompatibility, hemostatic properties, and the ability to promote arterial vessel repair. Importantly, the COCS hydrogel promotes the growth of cerebral microvessels by upregulating CD31, accelerates the proliferation of astrocytes, enhances the expression of GFAP, and stimulates the expression of neuron-specific markers such as NEUN and β-tubulin. All of these findings highlight that the strongly adhesive, self-healing, hemostatic hydrogel shows great potential for the repair of traumatic brain injury and other tissue repair therapy.

Injectable Bombyx mori (B. mori) silk fibroin/MXene conductive hydrogel for electrically stimulating neural stem cells into neurons for treating brain damage

Brain damage is a common tissue damage caused by trauma or diseases, which can be life-threatening. Stem cell implantation is an emerging strategy treating brain damage. The stem cell is commonly embedded in a matrix material for implantation, which protects stem cell and induces cell differentiation. Cell differentiation induction by this material is decisive in the effectiveness of this treatment strategy. In this work, we present an injectable fibroin/MXene conductive hydrogel as stem cell carrier, which further enables in-vivo electrical stimulation upon stem cells implanted into damaged brain tissue. Cell differentiation characterization of stem cell showed high effectiveness of electrical stimulation in this system, which is comparable to pure conductive membrane. Axon growth density of the newly differentiated neurons increased by 290% and axon length by 320%. In addition, unfavored astrocyte differentiation is minimized. The therapeutic effect of this system is proved through traumatic brain injury model on rats. Combined with in vivo electrical stimulation, cavities formation is reduced after traumatic brain injury, and rat motor function recovery is significantly promoted.

Injectable Hydrogels for Nervous Tissue Repair-A Brief Review

The repair of nervous tissue is a critical research field in tissue engineering because of the degenerative process in the injured nervous system. In this review, we summarize the progress of injectable hydrogels using in vitro and in vivo studies for the regeneration and repair of nervous tissue. Traditional treatments have not been favorable for patients, as they are invasive and inefficient; therefore, injectable hydrogels are promising for the treatment of damaged tissue. This review will contribute to a better understanding of injectable hydrogels as potential scaffolds and drug delivery system for neural tissue engineering applications.

An oxidized dextran-composite self-healing coated magnesium scaffold reduces apoptosis to induce bone regeneration

Self-healing coatings have shown promise in controlling the degradation of scaffolds and addressing coating detachment issues. However, developing a self-healing coating for magnesium (Mg) possessing multiple biological functions in infectious environments remains a significant challenge. In this study, a self-healing coating was developed for magnesium scaffolds using oxidized dextran (OD), 3-aminopropyltriethoxysilane (APTES), and nano-hydroxyapatite (nHA) doped micro-arc oxidation (MHA), named OD-MHA/Mg. The results demonstrated that the OD-MHA coating effectively addresses coating detachment issues and controls the degradation of Mg in an infectious environment through self-healing mechanisms. Furthermore, the OD-MHA/Mg scaffold exhibits antibacterial, antioxidant, and anti-apoptotic properties, it also promotes bone repair by upregulating the expression of osteogenesis genes and proteins. The findings of this study indicate that the OD-MHA coated Mg scaffold possessing multiple biological functions presents a promising approach for addressing infectious bone defects. Additionally, the study showcases the potential of polysaccharides with multiple biological functions in facilitating tissue healing even in challenging environments.

Calming the Nerves via the Immune Instructive Physiochemical Properties of Self-Assembling Peptide Hydrogels

Current therapies for the devastating damage caused by traumatic brain injuries (TBI) are limited. This is in part due to poor drug efficacy to modulate neuroinflammation, angiogenesis and/or promoting neuroprotection and is the combined result of challenges in getting drugs across the blood brain barrier, in a targeted approach. The negative impact of the injured extracellular matrix (ECM) has been identified as a factor in restricting post-injury plasticity of residual neurons and is shown to reduce the functional integration of grafted cells. Therefore, new strategies are needed to manipulate the extracellular environment at the subacute phase to enhance brain regeneration. In this review, potential strategies are to be discussed for the treatment of TBI by using self-assembling peptide (SAP) hydrogels, fabricated via the rational design of supramolecular peptide scaffolds, as an artificial ECM which under the appropriate conditions yields a supramolecular hydrogel. Sequence selection of the peptides allows the tuning of these hydrogels' physical and biochemical properties such as charge, hydrophobicity, cell adhesiveness, stiffness, factor presentation, degradation profile and responsiveness to (external) stimuli. This review aims to facilitate the development of more intelligent biomaterials in the future to satisfy the parameters, requirements, and opportunities for the effective treatment of TBI.

Hydrogel-Based Growth Factor Delivery Platforms: Strategies and Recent Advances

Growth factors play a crucial role in regulating a broad variety of biological processes and are regarded as powerful therapeutic agents in tissue engineering and regenerative medicine in the past decades. However, their application is limited by their short half-lives and potential side effects in physiological environments. Hydrogels are identified as having the promising potential to prolong the half-lives of growth factors and mitigate their adverse effects by restricting them within the matrix to reduce their rapid proteolysis, burst release, and unwanted diffusion. This review discusses recent progress in the development of growth factor-containing hydrogels for various biomedical applications, including wound healing, brain tissue repair, cartilage and bone regeneration, and spinal cord injury repair. In addition, the review introduces strategies for optimizing growth factor release including affinity-based delivery, carrier-assisted delivery, stimuli-responsive delivery, spatial structure-based delivery, and cellular system-based delivery. Finally, the review presents current limitations and future research directions for growth factor-delivering hydrogels.

A ROS-responsive loaded desferoxamine (DFO) hydrogel system for traumatic brain injury therapy

Traumatic brain injury (TBI) produces excess iron, and increased iron accumulation in the brain leads to lipid peroxidation and reactive oxygen species (ROSs), which can exacerbate secondary damage and lead to disability and death. Therefore, inhibition of iron overload and oxidative stress has a significant role in the treatment of TBI. Functionalized hydrogels with iron overload inhibiting ability and of oxidative stress inhibiting ability will greatly contribute to the repair of TBI. Herein, an injectable, post-traumatic microenvironment-responsive, ROS-responsive hydrogel encapsulated with deferrioxamine mesylate (DFO) was developed. The hydrogel is rapidly formed via dynamic covalent bonding between phenylboronic acid grafted hyaluronic acid (HA-PBA) and polyvinyl alcohol (PVA), and phenylboronate bonds are used to respond to and reduce ROS levels in damaged brain tissue to promote neuronal recovery. The release of DFO from HA-PBA/PVA hydrogels in response to ROS further promotes neuronal regeneration and recovery by relieving iron overload and thus eradicating ROS. In the Feeney model of Sprague Dawley rats, HA-PBA/PVA/DFO hydrogel treatment significantly improved the behavior of TBI rats and reduced the area of brain contusion in rats. In addition, HA-PBA/PVA/DFO hydrogel significantly reduced iron overload to reduce ROS and could effectively promote post-traumatic neuronal recovery. Its effects were also explored, and notably, HA-PBA/PVA/DFO hydrogel can reduce iron overload as well as ROS, thus protecting neurons from death. Thus, this injectable, biocompatible and ROS-responsive drug-loaded hydrogel has great potential for the treatment of TBI. This work suggests a novel method for the treatment of secondary brain injury by inhibiting iron overload and the oxidative stress response after TBI.

Biomaterials and Cell Therapy Combination in Central Nervous System Treatments

Current pharmacological and surgical therapies for the central nervous system (CNS) show a limited capacity to reduce the damage progression; that together with the intrinsic limited capability of the CNS to regenerate greatly reduces the hopes of recovery. Among all the therapies proposed, the tissue engineering strategies supplemented with therapeutic stem cells remain the most promising. Neural tissue engineering strategies are based on the development of devices presenting optimal physical, chemical, and mechanical properties which, once inserted in the injured site, can support therapeutic cells, limiting the effect of a hostile environment and supporting regenerative processes. Thus, this review focuses on the employment of hydrogel and nanofibrous scaffolds supplemented with stem cells as promising therapeutic tools for the central and peripheral nervous systems in preclinical and clinical applications.

Dexamethasone release from hyaluronic acid microparticle and proanthocyanidin-gelatin hydrogel in sciatic tissue regeneration

Biodegradable microparticles are useful vehicles for the controlled release of bioactive molecules in drug delivery, tissue engineering and biopharmaceutical applications. We developed dexamethasone (Dex) encapsulation into tyramine-substituted hyaluronic acid microparticles (Dex-HA-Tyr Mp) mediated by horseradish peroxidase (HRP) crosslinking using a microfluidic device and infollowing crosslinked gelatin (Gela) with proanthocyanidin (PA) as a semi-confined bed hydrogel for the repair of sciatic tissue injury. It was found that the simultaneous use of Dex-HA-Tyr Mp and cross-linked Gela-PA hydrogel improved the physical properties of the hydrogel, including mechanical strength and degradability. The designed composite also provided a sustained release system for Dex delivery to the surrounding sites, demonstrating the applicability of the fabricated hydrogel composite for sciatic nerve tissue engineering and regeneration. The encapsulated cells were viable and showed adequate growth ability and morphogenesis during prolonged incubation in Gela-PA/HA-Tyr Mp hydrogel compared to control conditions. Interestingly, histological analysis revealed a significant increase in the number of axons in the injured sciatic nerve following treatment with Dex-HA-Tyr Mp and injectable Gela-PA hydrogel compared to other control groups. In conclusion, the results demonstrated that fabricated Dex-loaded MPs and injectable hydrogel from biomimetic components are suitable systems for sustained delivery of Dex with adequate biocompatibility and the approach may have potential therapeutic applications in peripheral nerve regeneration.

Biomaterials in Traumatic Brain Injury: Perspectives and Challenges

Traumatic brain injury (TBI) is a leading cause of mortality and long-term impairment globally. TBI has a dynamic pathology, encompassing a variety of metabolic and molecular events that occur in two phases: primary and secondary. A forceful external blow to the brain initiates the primary phase, followed by a secondary phase that involves the release of calcium ions (Ca2+) and the initiation of a cascade of inflammatory processes, including mitochondrial dysfunction, a rise in oxidative stress, activation of glial cells, and damage to the blood-brain barrier (BBB), resulting in paracellular leakage. Currently, there are no FDA-approved drugs for TBI, but existing approaches rely on delivering micro- and macromolecular treatments, which are constrained by the BBB, poor retention, off-target toxicity, and the complex pathology of TBI. Therefore, there is a demand for innovative and alternative therapeutics with effective delivery tactics for the diagnosis and treatment of TBI. Tissue engineering, which includes the use of biomaterials, is one such alternative approach. Biomaterials, such as hydrogels, including self-assembling peptides and electrospun nanofibers, can be used alone or in combination with neuronal stem cells to induce neurite outgrowth, the differentiation of human neural stem cells, and nerve gap bridging in TBI. This review examines the inclusion of biomaterials as potential treatments for TBI, including their types, synthesis, and mechanisms of action. This review also discusses the challenges faced by the use of biomaterials in TBI, including the development of biodegradable, biocompatible, and mechanically flexible biomaterials and, if combined with stem cells, the survival rate of the transplanted stem cells. A better understanding of the mechanisms and drawbacks of these novel therapeutic approaches will help to guide the design of future TBI therapies.

Nrf2 enhances the therapeutic efficiency of adipose-derived stem cells in the treatment of neurogenic erectile dysfunction in a rat model

BACKGROUND

Erectile dysfunction (ED) caused by intraoperative nerve injury is a major complication of pelvic surgery. Adipose-derived stem cells (ADSCs) have presented therapeutic potential in a rat model of bilateral cavernous nerve injury (BCNI), while inadequate in vivo viability has largely limited their application. Nuclear factor-E2-related Factor (Nrf2) is a key transcription factor that regulates cellular anti-oxidative stress. In this work, we investigated the effect of Nrf2 expression regulation on the viability of ADSCs, and explore its repair potential in a BCNI rat model.

RESULTS

The survival time of tert-Butylhydroquinone (tBHQ)-ADSCs in BCNI model increased obviously. In addition, the tBHQ-ADSCs group presented better restoration of major pelvic ganglion (MPG) nerve contents and fibers, better improvement of erectile function, and less penile fibrosis than the other groups. Moreover, the expression of Nrf2 and superoxide dismutase 1 (SOD1) were higher than those of other groups.

CONCLUSION

Nrf2 could enhance the anti-oxidative stress ability of ADSCs, so as to improve the therapeutic effect of ADSCs on BCNI rat model.

Hyaluronic Acid Conjugated with 17β-Estradiol Effectively Alleviates Estropause-Induced Cognitive Deficits in Rats

Women are at a higher risk of cognitive impairments and Alzheimer's disease (AD), particularly after the menopause, when the estrous cycle becomes irregular and diminishes. Numerous studies have shown that estrogen deficiency, especially estradiol (E2) deficiency, plays a key role in this phenomenon. Recently, a novel polymeric drug, hyaluronic acid-17β-estradiol conjugate (HA-E2), has been introduced for the delivery of E2 to brain tissues. Studies have indicated that HA-E2 crosses the blood-brain barrier (BBB) and facilitates a prolonged E2 release profile while lowering the risk of estrogen-supplement-related side effects. In this study, we used ovariohysterectomy (OHE) rats, a postmenopausal cognitive deficit model, to explore the effect of a 2-week HA-E2 treatment (210 ng/kg body weight, twice a week) on the cholinergic septo-hippocampal innervation system, synaptic transmission in hippocampal pyramidal neurons and cognitive improvements. Our study revealed an 11% rise in choline acetyltransferase (ChAT) expression in both the medial septal nucleus (MS nucleus) and the hippocampus, along with a 14-18% increase in dendritic spine density in hippocampal pyramidal neurons, following HA-E2 treatment in OHE rats. These enhancements prompted the recovery of cognitive functions such as spatial learning and memory. These findings suggest that HA-E2 may prevent and improve estrogen-deficiency-induced cognitive impairment and AD.

Amino acid-induced rapid gelation and mechanical reinforcement of hydrogels with low-hysteresis and self-recoverable and fatigue-resistant properties

Hydrogels with rapid gelation ability and robust mechanical properties are highly desirable for nascent applications in biomedical, wearable electronic, industrial and agricultural fields. However, current rapid-gelation hydrogels are compromised by poor mechanical properties, complex design of precursor molecular structures and limited precursor species. Herein, we propose a facile and universal strategy to achieve rapid gelation, strengthening and toughening of free-radical polymerized hydrogels by introducing cheap and accessible amino acids. Amino acids not only activate persulfate to quickly produce free radicals and thus induce fast free radical polymerization, but also can form strong hydrogen bonds with the network chains to strengthen and toughen the hydrogels. For example, with the presence of L-serine, the acrylamide (AM) monomer shows rapid gelation within tens of seconds, and moreover the resulting hydrogel reaches a tensile strength of 0.45 MPa and a breaking strain of 2060%. More importantly, owing to the extremely dynamic feature of the hydrogen bonds between L-serine molecules and network chains, the hydrogel possesses the advantages of low hysteresis, rapid self-recovery capability and outstanding fatigue resistance. Furthermore, this strategy is general to a wide range of amino acids and monomers. We also demonstrate that this rapid, controllable and universal strategy for the fabrication of mechanically robust hydrogels holds tremendous potential for diverse practical applications, such as flexible electronic sensors and ultraviolet (UV)-blocking artificial skins.

Treatment strategies for intrauterine adhesion: focus on the exosomes and hydrogels

Intrauterine adhesion (IUA), also referred to as Asherman Syndrome (AS), results from uterine trauma in both pregnant and nonpregnant women. The IUA damages the endometrial bottom layer, causing partial or complete occlusion of the uterine cavity. This leads to irregular menstruation, infertility, or repeated abortions. Transcervical adhesion electroreception (TCRA) is frequently used to treat IUA, which greatly lowers the prevalence of adhesions and increases pregnancy rates. Although surgery aims to disentangle the adhesive tissue, it can exacerbate the development of IUA when the degree of adhesion is severer. Therefore, it is critical to develop innovative therapeutic approaches for the prevention of IUA. Endometrial fibrosis is the essence of IUA, and studies have found that the use of different types of mesenchymal stem cells (MSCs) can reduce the risk of endometrial fibrosis and increase the possibility of pregnancy. Recent research has suggested that exosomes derived from MSCs can overcome the limitations of MSCs, such as immunogenicity and tumorigenicity risks, thereby providing new directions for IUA treatment. Moreover, the hydrogel drug delivery system can significantly ameliorate the recurrence rate of adhesions and the intrauterine pregnancy rate of patients, and its potential mechanism in the treatment of IUA has also been studied. It has been shown that the combination of two or more therapeutic schemes has broader application prospects; therefore, this article reviews the pathophysiology of IUA and current treatment strategies, focusing on exosomes combined with hydrogels in the treatment of IUA. Although the use of exosomes and hydrogels has certain challenges in treating IUA, they still provide new promising directions in this field.

Prospects for Nerve Regeneration and Gene Therapy in the Treatment of Traumatic Brain Injury

Traumatic brain injury (TBI) is a prevalent neurological disorder and a leading cause of death and disability worldwide. The high mortality rates result in a tremendous burden on society and families in terms of public health and economic costs. Despite advances in biomedical research, treatment options for TBI still remain limited, and there is no effective therapy to restore the structure and function of the injured brain. Regrettably, due to the excessive heterogeneity of TBI and the lack of objective and reliable efficacy evaluation indicators, no proven therapeutic drugs or drugs with clear benefits on functional outcomes have been successfully developed to date. Therefore, it is urgent to explore new therapeutic approaches to protect or regenerate the injured brain from different perspectives. In this review, we first provide a brief overview of the causes and current status of TBI and then summarize the preclinical and clinical research status of cutting-edge treatment methods, including nerve regeneration therapy and gene therapy, with the aim of providing valuable references for effective therapeutic strategies for TBI.

Toward a New Generation of Bio-Scaffolds for Neural Tissue Engineering: Challenges and Perspectives

Neural tissue engineering presents a compelling technological breakthrough in restoring brain function, holding immense promise. However, the quest to develop implantable scaffolds for neural culture that fulfill all necessary criteria poses a remarkable challenge for material science. These materials must possess a host of desirable characteristics, including support for cellular survival, proliferation, and neuronal migration and the minimization of inflammatory responses. Moreover, they should facilitate electrochemical cell communication, display mechanical properties akin to the brain, emulate the intricate architecture of the extracellular matrix, and ideally allow the controlled release of substances. This comprehensive review delves into the primary requisites, limitations, and prospective avenues for scaffold design in brain tissue engineering. By offering a panoramic overview, our work aims to serve as an essential resource, guiding the creation of materials endowed with bio-mimetic properties, ultimately revolutionizing the treatment of neurological disorders by developing brain-implantable scaffolds.

Injectable hydrogels in central nervous system: Unique and novel platforms for promoting extracellular matrix remodeling and tissue engineering

Repairing central nervous system (CNS) is difficult due to the inability of neurons to recover after damage. A clinically acceptable treatment to promote CNS functional recovery and regeneration is currently unavailable. According to recent studies, injectable hydrogels as biodegradable scaffolds for CNS tissue engineering and regeneration have exceptionally desirable attributes. Hydrogel has a biomimetic structure similar to extracellular matrix, hence has been considered a 3D scaffold for CNS regeneration. An interesting new type of hydrogel, injectable hydrogels, can be injected into target areas with little invasiveness and imitate several aspects of CNS. Injectable hydrogels are being researched as therapeutic agents because they may imitate numerous properties of CNS tissues and hence reduce subsequent injury and regenerate neural tissue. Because of their less adverse effects and cost, easier use and implantation with less pain, and faster regeneration capacity, injectable hydrogels, are more desirable than non-injectable hydrogels. This article discusses the pathophysiology of CNS and the use of several kinds of injectable hydrogels for brain and spinal cord tissue engineering, paying particular emphasis to recent experimental studies.

Functional hydrogels for the repair and regeneration of tissue defects

Tissue defects can be accompanied by functional impairments that affect the health and quality of life of patients. Hydrogels are three-dimensional (3D) hydrophilic polymer networks that can be used as bionic functional tissues to fill or repair damaged tissue as a promising therapeutic strategy in the field of tissue engineering and regenerative medicine. This paper summarises and discusses four outstanding advantages of hydrogels and their applications and advances in the repair and regeneration of tissue defects. First, hydrogels have physicochemical properties similar to the extracellular matrix of natural tissues, providing a good microenvironment for cell proliferation, migration and differentiation. Second, hydrogels have excellent shape adaptation and tissue adhesion properties, allowing them to be applied to a wide range of irregularly shaped tissue defects and to adhere well to the defect for sustained and efficient repair function. Third, the hydrogel is an intelligent delivery system capable of releasing therapeutic agents on demand. Hydrogels are capable of delivering therapeutic reagents and releasing therapeutic substances with temporal and spatial precision depending on the site and state of the defect. Fourth, hydrogels are self-healing and can maintain their integrity when damaged. We then describe the application and research progress of functional hydrogels in the repair and regeneration of defects in bone, cartilage, skin, muscle and nerve tissues. Finally, we discuss the challenges faced by hydrogels in the field of tissue regeneration and provide an outlook on their future trends.

Hyaluronan-based hydrogel integrating exosomes for traumatic brain injury repair by promoting angiogenesis and neurogenesis

With wide clinical demands, therapies for traumatic brain injury (TBI) are far from satisfactory. Combining the merits of stem cells but avoiding the risk of immunologic rejection, bone marrow mesenchymal stem cell-derived exosomes (BME) attract increasing interests and have been proved effective for TBI repair by intravenous or in situ injection. However, difficulties in sustained delivery or aggregation in lesion sites remain obstacle to using BME for TBI. Inspired by that hydrogels are promising to bridge the destroyed neural gap and provide neural niches, we raised a novel strategy of incorporating BME into hyaluronan-collagen hydrogel (DHC-BME) to achieve both mimicking of brain matrix and steady release of exosomes, and thus realizing TBI repair. External characterizations proved that the BME and DHC synergistically promoted neural stem cells (NSCs) differentiation into neurons and oligodendrocytes while inhibited astrocytes differentiation. DHC-BME induced angiogenesis and neurogenesis, from endogenous NSC recruitment to neuronal differentiation and vascularization to synergistically promote axonal regeneration, remyelination, synapse formation and even brain structural remodeling, and lastly, neurological functional recovery of TBI.

Hyaluronic acid-based hydrogels: As an exosome delivery system in bone regeneration

Exosomes are extracellular vesicles (EVs) containing various ingredients such as DNA, RNA, lipids and proteins, which play a significant role in intercellular communication. Numerous studies have demonstrated the important role of exosomes in bone regeneration through promoting the expression of osteogenic-related genes and proteins in mesenchymal stem cells. However, the low targeting ability and short circulating half-life of exosomes limited their clinical application. In order to solve those problems, different delivery systems and biological scaffolds have been developed. Hydrogel is a kind of absorbable biological scaffold composed of three-dimensional hydrophilic polymers. It not only has excellent biocompatibility and superior mechanical strength but can also provide a suitable nutrient environment for the growth of the endogenous cells. Thus, the combination between exosomes and hydrogels can improve the stability and maintain the biological activity of exosomes while achieving the sustained release of exosomes in the bone defect sites. As an important component of the extracellular matrix (ECM), hyaluronic acid (HA) plays a critical role in various physiological and pathological processes such as cell differentiation, proliferation, migration, inflammation, angiogenesis, tissue regeneration, wound healing and cancer. In recent years, hyaluronic acid-based hydrogels have been used as an exosome delivery system for bone regeneration and have displayed positive effects. This review mainly summarized the potential mechanism of HA and exosomes in promoting bone regeneration and the application prospects and challenges of hyaluronic acid-based hydrogels as exosome delivery devices in bone regeneration.

Recent Advances in Biomaterials-Based Therapies for Alleviation and Regeneration of Traumatic Brain Injury

Traumatic brain injury (TBI), a major public health problem accompanied with numerous complications, usually leads to serve disability and huge financial burden. The adverse and unfavorable pathological environment triggers a series of secondary injuries, resulting in serious loss of nerve function and huge obstacle of endogenous nerve regeneration. With the advances in adaptive tissue regeneration biomaterials, regulation of detrimental microenvironment to reduce the secondary injury and to promote the neurogenesis becomes possible. The adaptive biomaterials could respond and regulate biochemical, cellular, and physiological events in the secondary injury, including excitotoxicity, oxidative stress, and neuroinflammation, to rebuild circumstances suitable for regeneration. In this review, the development of pathology after TBI is discussed, followed by the introduction of adaptive biomaterials based on various pathological characteristics. The adaptive biomaterials carried with neurotrophic factors and stem cells for TBI treatment are then summarized. Finally, the current drawbacks and future perspective of biomaterials for TBI treatment are suggested.

3D printing of injury-preconditioned secretome/collagen/heparan sulfate scaffolds for neurological recovery after traumatic brain injury in rats

BACKGROUND

The effects of traumatic brain injury (TBI) can include physical disability and even death. The development of effective therapies to promote neurological recovery is still a challenging problem. 3D-printed biomaterials are considered to have a promising future in TBI repair. The injury-preconditioned secretome derived from human umbilical cord blood mesenchymal stem cells showed better stability in neurological recovery after TBI. Therefore, it is reasonable to assume that a biological scaffold loaded with an injury-preconditioned secretome could facilitate neural network reconstruction after TBI.

METHODS

In this study, we fabricated injury-preconditioned secretome/collagen/heparan sulfate scaffolds by 3D printing. The scaffold structure and porosity were examined by scanning electron microscopy and HE staining. The cytocompatibility of the scaffolds was characterized by MTT analysis, HE staining and electron microscopy. The modified Neurological Severity Score (mNSS), Morris water maze (MWM), and motor evoked potential (MEP) were used to examine the recovery of cognitive and locomotor function after TBI in rats. HE staining, silver staining, Nissl staining, immunofluorescence, and transmission electron microscopy were used to detect the reconstruction of neural structures and pathophysiological processes. The biocompatibility of the scaffolds in vivo was characterized by tolerance exposure and liver/kidney function assays.

RESULTS

The excellent mechanical and porosity characteristics of the composite scaffold allowed it to efficiently regulate the secretome release rate. MTT and cell adhesion assays demonstrated that the scaffold loaded with the injury-preconditioned secretome (3D-CH-IB-ST) had better cytocompatibility than that loaded with the normal secretome (3D-CH-ST). In the rat TBI model, cognitive and locomotor function including mNSS, MWM, and MEP clearly improved when the scaffold was transplanted into the damage site. There is a significant improvement in nerve tissue at the site of lesion. More abundant endogenous neurons with nerve fibers, synaptic structures, and myelin sheaths were observed in the 3D-CH-IB-ST group. Furthermore, the apoptotic response and neuroinflammation were significantly reduced and functional vessels were observed at the injury site. Good exposure tolerance in vivo demonstrated favorable biocompatibility of the scaffold.

CONCLUSIONS

Our results demonstrated that injury-preconditioned secretome/collagen/heparan sulfate scaffolds fabricated by 3D printing promoted neurological recovery after TBI by reconstructing neural networks, suggesting that the implantation of the scaffolds could be a novel way to alleviate brain damage following TBI.

Role of 3D Printing in the Development of Biodegradable Implants for Central Nervous System Drug Delivery

Increased life expectancy has led to a rise in age-related disorders including neurological diseases such as Alzheimer's disease and Parkinson's disease. Limited progress has been made in the development of clinically translatable therapies for these central nervous system (CNS) diseases. Challenges including the blood-brain barrier, brain complexity, and comorbidities in the elderly population are some of the contributing factors toward lower success rates. Various invasive and noninvasive ways are being employed to deliver small and large molecules across the brain. Biodegradable, implantable drug-delivery systems have gained lot of interest due to advantages such as sustained and targeted delivery, lower side effects, and higher patient compliance. 3D printing is a novel additive manufacturing technique where various materials and printing techniques can be used to fabricate implants with the desired complexity in terms of mechanical properties, shapes, or release profiles. This review discusses an overview of various types of 3D-printing techniques and illustrative examples of the existing literature on 3D-printed systems for CNS drug delivery. Currently, there are various technical and regulatory impediments that need to be addressed for successful translation from the bench to the clinical stage. Overall, 3D printing is a transformative technology with great potential in advancing customizable drug treatment in a high-throughput manner.

Hydrogel patch with pretreated stem cells accelerates wound closure in diabetic rats

Delay in wound healing is a diabetes mellites resulting disorder causing persistent microbial infections, pain, and poor quality of life. This disorder is treated by several strategies using natural biomaterials, growth factors and stem cells molded into various scaffolds which possess the potential to accelerate the closure of impaired diabetic wounds. In this study, we developed a hydrogel patch using chitosan (CS) and polyethylene glycol (PEG) with laden bone marrow-derived mesenchymal stem cells (BMSCs) that were pretreated with fibroblast growth factor 21 (FGF21). The developed hydrogel patches were characterized by scanning electron microscopy and fourier transform infrared (FTIR) spectroscopy. After studying the swelling behavior, growth factor (FGF21) was used to modulate BMSC in the hyperglycemic environment. Later, FGF21 treated BMSC were embedded in CS/PEG hydrogel patch and their wound closure effect was assessed in diabetic rats. The results showed that CS/PEG hydrogel patches have good biocompatibility and possess efficient BMSC recruiting properties. The application of CS/PEG hydrogel patches accelerated wound closure in diabetic rats as compared to the control groups. However, the use of FGF21 pretreated BMSCs laded CS/PEG hydrogel patches further increased the therapeutic efficacy of wound closure in diabetic rats. This study demonstrated that the application of a hydrogel patch of CS/PEG with FGF21 pretreated BMSCs improves diabetic wound healing, but further studies are needed on larger animals before the use of these dressings in clinical trials.

Donors for nerve transplantation in craniofacial soft tissue injuries

Neural tissue is an important soft tissue; for instance, craniofacial nerves govern several aspects of human behavior, including the expression of speech, emotion transmission, sensation, and motor function. Therefore, nerve repair to promote functional recovery after craniofacial soft tissue injuries is indispensable. However, the repair and regeneration of craniofacial nerves are challenging due to their intricate anatomical and physiological characteristics. Currently, nerve transplantation is an irreplaceable treatment for segmental nerve defects. With the development of emerging technologies, transplantation donors have become more diverse. The present article reviews the traditional and emerging alternative materials aimed at advancing cutting-edge research on craniofacial nerve repair and facilitating the transition from the laboratory to the clinic. It also provides a reference for donor selection for nerve repair after clinical craniofacial soft tissue injuries. We found that autografts are still widely accepted as the first options for segmental nerve defects. However, allogeneic composite functional units have a strong advantage for nerve transplantation for nerve defects accompanied by several tissue damages or loss. As an alternative to autografts, decellularized tissue has attracted increasing attention because of its low immunogenicity. Nerve conduits have been developed from traditional autologous tissue to composite conduits based on various synthetic materials, with developments in tissue engineering technology. Nerve conduits have great potential to replace traditional donors because their structures are more consistent with the physiological microenvironment and show self-regulation performance with improvements in 3D technology. New materials, such as hydrogels and nanomaterials, have attracted increasing attention in the biomedical field. Their biocompatibility and stimuli-responsiveness have been gradually explored by researchers in the regeneration and regulation of neural networks.

Applications and Mechanisms of Stimuli-Responsive Hydrogels in Traumatic Brain Injury

Traumatic brain injury (TBI) is a global neurotrauma with high morbidity and mortality that seriously threatens the life quality of patients and causes heavy burdens to families, healthcare institutions, and society. Neuroinflammation and oxidative stress can further aggravate neuronal cell death, hinder functional recovery, and lead to secondary brain injury. In addition, the blood–brain barrier prevents drugs from entering the brain tissue, which is not conducive to the recovery of TBI. Due to their high water content, biodegradability, and similarity to the natural extracellular matrix (ECM), hydrogels are widely used for the delivery and release of various therapeutic agents (drugs, natural extracts, and cells, etc.) that exhibit beneficial therapeutic efficacy in tissue repair, such as TBI. Stimuli-responsive hydrogels can undergo reversible or irreversible changes in properties, structures, and functions in response to internal/external stimuli or physiological/pathological environmental stimuli, and further improve the therapeutic effects on diseases. In this paper, we reviewed the common types of stimuli-responsive hydrogels and their applications in TBI, and further analyzed the therapeutic effects of hydrogels in TBI, such as pro-neurogenesis, anti-inflammatory, anti-apoptosis, anti-oxidation, and pro-angiogenesis. Our study may provide strategies for the treatment of TBI by using stimuli-responsive hydrogels.

Novel Trends into the Development of Natural Hydroxyapatite-Based Polymeric Composites for Bone Tissue Engineering

In recent years, the number of people needing bone replacements for the treatment of defects caused by chronic diseases or accidents has continuously increased. To solve these problems, tissue engineering has gained significant attention in the biomedical field, by focusing on the development of suitable materials that improve osseointegration and biologic activity. In this direction, the development of an ideal material that provides good osseointegration, increased antimicrobial activity and preserves good mechanical properties has been the main challenge. Currently, bone tissue engineering focuses on the development of materials with tailorable properties, by combining polymers and ceramics to meet the necessary complex requirements. This study presents the main polymers applied in tissue engineering, considering their advantages and drawbacks. Considering the potential disadvantages of polymers, improving the applicability of the material and the combination with a ceramic material is the optimum pathway to increase the mechanical stability and mineralization process. Thus, ceramic materials obtained from natural sources (e.g., hydroxyapatite) are preferred to improve bioactivity, due to their similarity to the native hydroxyapatite found in the composition of human bone.