Polyethylene glycol in spinal cord injury repair: a critical review

Harnessing the potential of hydrogels for advanced therapeutic applications: current achievements and future directions

The applications of hydrogels have expanded significantly due to their versatile, highly tunable properties and breakthroughs in biomaterial technologies. In this review, we cover the major achievements and the potential of hydrogels in therapeutic applications, focusing primarily on two areas: emerging cell-based therapies and promising non-cell therapeutic modalities. Within the context of cell therapy, we discuss the capacity of hydrogels to overcome the existing translational challenges faced by mainstream cell therapy paradigms, provide a detailed discussion on the advantages and principal design considerations of hydrogels for boosting the efficacy of cell therapy, as well as list specific examples of their applications in different disease scenarios. We then explore the potential of hydrogels in drug delivery, physical intervention therapies, and other non-cell therapeutic areas (e.g., bioadhesives, artificial tissues, and biosensors), emphasizing their utility beyond mere delivery vehicles. Additionally, we complement our discussion on the latest progress and challenges in the clinical application of hydrogels and outline future research directions, particularly in terms of integration with advanced biomanufacturing technologies. This review aims to present a comprehensive view and critical insights into the design and selection of hydrogels for both cell therapy and non-cell therapies, tailored to meet the therapeutic requirements of diverse diseases and situations.

Developing preclinical dog models for reconstructive severed spinal cord continuity via spinal cord fusion technique

Background

Spinal cord injury (SCI) is a severe impairment of the central nervous system, leading to motor, sensory, and autonomic dysfunction. The present study investigates the efficacy of the polyethylene glycol (PEG)-mediated spinal cord fusion (SCF) techniques, demonstrating efficacious in various animal models with complete spinal cord transection at the T10 level. This research focuses on a comparative analysis of three SCF treatment models in beagles: spinal cord transection (SCT), vascular pedicle hemisected spinal cord transplantation (vSCT), and vascularized allograft spinal cord transplantation (vASCT) surgical model.

Methods

Seven female beagles were included in the SCT surgical model, while four female dogs were enrolled in the vSCT surgical model. Additionally, twelve female dogs underwent vASCT in a paired donor-recipient setup. Three surgical model were evaluated and compared through electrophysiology, imaging and behavioral recovery.

Results

The results showed a progressive recovery in the SCT, vSCT and vASCT surgical models, with no statistically significant differences observed in cBBB scores at both 2-month and 6-month post-operation (both P>0.05). Neuroimaging analysis across the SCT, vSCT and vASCT surgical models revealed spinal cord graft survival and fiber regrowth across transection sites at 6 months postoperatively. Also, positive MEP waveforms were recorded in all three surgical models at 6-month post-surgery.

Conclusion

The study underscores the clinical relevance of PEG-mediated SCF techniques in promoting nerve fusion, repair, and motor functional recovery in SCI. SCT, vSCT, and vASCT, tailored to specific clinical characteristics, demonstrated similar effective therapeutic outcomes.

Neural stem cell therapies for spinal cord injury repair: an update on recent preclinical and clinical advances

Traumatic spinal cord injury (SCI) is a leading cause of lifelong disabilities. Permanent sensory, motor and autonomic impairments after SCI are substantially attributed to degeneration of spinal cord neurons and axons, and disintegration of neural network. To date, minimal regenerative treatments are available for SCI with an unmet need for new therapies to reconstruct the damaged spinal cord neuron-glia network and restore connectivity with the supraspinal pathways. Multipotent neural precursor cells (NPCs) have a unique capacity to generate neurons, oligodendrocytes and astrocytes. Due to this capacity, NPCs have been an attractive cell source for cellular therapies for SCI. Transplantation of NPCs has been extensively tested in preclinical models of SCI in the past two decades. These studies have identified opportunities and challenges associated with NPC therapies. While NPCs have the potential to promote neuroregeneration through various mechanisms, their low long-term survival and integration within the host injured spinal cord limit the functional benefits of NPC-based therapies for SCI. To address this challenge, combinatorial strategies have been developed to optimize the outcomes of NPC therapies by enriching SCI microenvironment through biomaterials, genetic and pharmacological therapies. In this review, we will provide an in-depth discussion on recent advances in preclinical NPC-based therapies for SCI. We will discuss modes of actions and mechanism by which engrafted NPCs contribute to the repair process and functional recovery. We will also provide an update on current clinical trials and new technologies that have facilitated preparation of medical-grade human NPCs suitable for transplantation in clinical studies.

Neurogenic Cell Behavior in 3D Culture Enhanced Within a Highly Compliant Synthetic Hydrogel Platform Formed via Competitive Crosslinking

Purpose

Scaffold materials that better support neurogenesis are still needed to improve cell therapy outcomes for neural tissue damage. We have used a modularly tunable, highly compliant, degradable hydrogel to explore the impacts of hydrogel compliance stiffness on neural differentiation. Here we implemented competitive matrix crosslinking mechanics to finely tune synthetic hydrogel moduli within soft tissue stiffnesses, a range much softer than typically achievable in synthetic crosslinked hydrogels, providing a modularly controlled and ultrasoft 3D culture model which supports and enhances neurogenic cell behavior.

Methods

Soluble competitive allyl monomers were mixed with proteolytically-degradable poly(ethylene glycol) diacrylate derivatives and crosslinked to form a matrix, and resultant hydrogel stiffness and diffusive properties were evaluated. Neural PC12 cells or primary rat fetal neural stem cells (NSCs) were encapsulated within the hydrogels, and cell morphology and phenotype were investigated to understand cell-matrix interactions and the effects of environmental stiffness on neural cell behavior within this model.

Results

Addition of allyl monomers caused a concentration-dependent decrease in hydrogel compressive modulus from 4.40 kPa to 0.26 kPa (natural neural tissue stiffness) without influencing soluble protein diffusion kinetics through the gel matrix. PC12 cells encapsulated in the softest hydrogels showed significantly enhanced neurite extension in comparison to PC12s in all other hydrogel stiffnesses tested. Encapsulated neural stem cells demonstrated significantly greater spreading and elongation in 0.26 kPa alloc hydrogels than in 4.4 kPa hydrogels. When soluble growth factor deprivation (for promotion of neural differentiation) was evaluated within the neural stiffness gels (0.26 kPa), NSCs showed increased neuronal marker expression, indicating early enhancement of neurogenic differentiation.

Conclusions

Implementing allyl-acrylate crosslinking competition reduced synthetic hydrogel stiffness to provide a supportive environment for 3D neural tissue culture, resulting in enhanced neurogenic behavior of encapsulated cells. These results indicate the potential suitability of this ultrasoft hydrogel system as a model platform for further investigating environmental factors on neural cell behavior.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-024-00794-2.

Traumatic Human Spinal Cord Injury: Are Single Treatments Enough to Solve the Problem?

Traumatic spinal cord injury (SCI) results in partial or complete motor deficits, such as paraplegia, tetraplegia, and sphincter control, as well as sensory disturbances and autonomic dysregulation such as arterial hypotension, lack of sweating, and alterations in skin lability. All this has a strong psychological impact on the affected person and his/her family, as well as costs to healthcare institutions with an economic burden in the short, medium, and long terms. Despite at least forty years of experimental animal studies and several clinical trials with different therapeutic strategies, effective therapy is not universally accepted. Most of the published works on acute and chronic injury use a single treatment, such as medication, trophic factor, transplant of a cell type, and so on, to block some secondary injury mechanisms or promote some mechanisms of structural/functional restoration. However, despite significant results in experimental models, the outcome is a moderate improvement in muscle strength, sensation, or eventually in sphincter control, which has been considered non-significant in human clinical trials. Here we present a brief compilation of successful individual treatments that have been applied to secondary mechanisms of action. These studies show limited neuroprotective or neurorestorative approaches in animal models and clinical trials. Thus, the few benefits achieved so far represent a rationale to further explore other strategies that seek better structural and functional restoration of the injured spinal cord.

Stem Cell Scaffolds for the Treatment of Spinal Cord Injury-A Review

Spinal cord injury (SCI) is a profoundly debilitating yet common central nervous system condition resulting in significant morbidity and mortality rates. Major causes of SCI encompass traumatic incidences such as motor vehicle accidents, falls, and sports injuries. Present treatment strategies for SCI aim to improve and enhance neurologic functionality. The ability for neural stem cells (NSCs) to differentiate into diverse neural and glial cell precursors has stimulated the investigation of stem cell scaffolds as potential therapeutics for SCI. Various scaffolding modalities including composite materials, natural polymers, synthetic polymers, and hydrogels have been explored. However, most trials remain largely in the preclinical stage, emphasizing the need to further develop and refine these treatment strategies before clinical implementation. In this review, we delve into the physiological processes that underpin NSC differentiation, including substrates and signaling pathways required for axonal regrowth post-injury, and provide an overview of current and emerging stem cell scaffolding platforms for SCI.

Applications of drug delivery systems, organic, and inorganic nanomaterials in wound healing

The skin is known to be the largest organ in the human body, while also being exposed to environmental elements. This indicates that skin is highly susceptible to physical infliction, as well as damage resulting from medical conditions such as obesity and diabetes. The wound management costs in hospitals and clinics are expected to rise globally over the coming years, which provides pressure for more wound healing aids readily available in the market. Recently, nanomaterials have been gaining traction for their potential applications in various fields, including wound healing. Here, we discuss various inorganic nanoparticles such as silver, titanium dioxide, copper oxide, cerium oxide, MXenes, PLGA, PEG, and silica nanoparticles with their respective roles in improving wound healing progression. In addition, organic nanomaterials for wound healing such as collagen, chitosan, curcumin, dendrimers, graphene and its derivative graphene oxide were also further discussed. Various forms of nanoparticle drug delivery systems like nanohydrogels, nanoliposomes, nanofilms, and nanoemulsions were discussed in their function to deliver therapeutic agents to wound sites in a controlled manner.

Application of Conductive Hydrogels on Spinal Cord Injury Repair: A Review

Spinal cord injury (SCI) causes severe motor or sensory damage that leads to long-term disabilities due to disruption of electrical conduction in neuronal pathways. Despite current clinical therapies being used to limit the propagation of cell or tissue damage, the need for neuroregenerative therapies remains. Conductive hydrogels have been considered a promising neuroregenerative therapy due to their ability to provide a pro-regenerative microenvironment and flexible structure, which conforms to a complex SCI lesion. Furthermore, their conductivity can be utilized for noninvasive electrical signaling in dictating neuronal cell behavior. However, the ability of hydrogels to guide directional axon growth to reach the distal end for complete nerve reconnection remains a critical challenge. In this Review, we highlight recent advances in conductive hydrogels, including the incorporation of conductive materials, fabrication techniques, and cross-linking interactions. We also discuss important characteristics for designing conductive hydrogels for directional growth and regenerative therapy. We propose insights into electrical conductivity properties in a hydrogel that could be implemented as guidance for directional cell growth for SCI applications. Specifically, we highlight the practical implications of recent findings in the field, including the potential for conductive hydrogels to be used in clinical applications. We conclude that conductive hydrogels are a promising neuroregenerative therapy for SCI and that further research is needed to optimize their design and application.

Oligo (Poly (Ethylene Glycol) Fumarate)-Based Multicomponent Cryogels for Neural Tissue Replacement

Synthetic hydrogels provide a promising platform to produce neural tissue analogs with improved control over structural, physical, and chemical properties. In this study, oligo (poly (ethylene glycol) fumarate) (OPF)-based macroporous cryogels were developed as a potential next-generation alternative to a non-porous OPF hydrogel previously proposed as an advanced biodegradable scaffold for spinal cord repair. A series of OPF cryogel conduits in combination with PEG diacrylate and 2-(methacryloyloxy) ethyl-trimethylammonium chloride (MAETAC) cationic monomers were synthesized and characterized. The contribution of each component to viscoelastic and hydration behaviors and porous structure was identified, and concentration relationships for these properties were revealed. The rheological properties of the materials corresponded to those of neural tissues and scaffolds, according to the reviewed data. A comparative assessment of adhesion, migration, and proliferation of neuronal cells in multicomponent cryogels was carried out to optimize cell-supporting characteristics. The results show that OPF-based cryogels can be used as a tunable synthetic scaffold for neural tissue repair with advantages over their hydrogel counterparts.

Heterogeneous pHPMA hydrogel promotes neuronal differentiation of bone marrow derived stromal cellsin vitroandin vivo

Synthetic hydrogels composed of polymer pore frames are commonly used in medicine, from pharmacologically targeted drug delivery to the creation of bioengineering constructions used in implantation surgery. Among various possible materials, the most common are poly-[N(2-hydroxypropyl)methacrylamide] (pHPMA) derivatives. One of the pHPMA derivatives is biocompatible hydrogel, NeuroGel. Upon contact with nervous tissue, the NeuroGel's structure can support the chemical and physiological conditions of the tissue necessary for the growth of native cells. Owing to the different pore diameters in the hydrogel, not only macromolecules, but also cells can migrate. This study evaluated the differentiation of bone marrow stromal cells (BMSCs) into neurons, as well as the effectiveness of using this biofabricated system in spinal cord injuryin vivo. The hydrogel was populated with BMSCs by injection or rehydration. After cultivation, these fragments (hydrogel + BMSCs) were implanted into the injured rat spinal cord. Fragments were immunostained before implantation and seven months after implantation. During cultivation with the hydrogel, both variants (injection/rehydration) of the BMSCs culture retained their viability and demonstrated a significant number of Ki-67-positive cells, indicating the preservation of their proliferative activity. In hydrogel fragments, BMSCs also maintained their viability during the period of cocultivation and were Ki-67-positive, but in significantly fewer numbers than in the cell culture. In addition, in fragments of hydrogel with grafted BMSCs, both by the injection or rehydration versions, we observed a significant number up to 57%-63.5% of NeuN-positive cells. These results suggest that the heterogeneous pHPMA hydrogel promotes neuronal differentiation of bone marrow-derived stromal cells. Furthermore, these data demonstrate the possible use of NeuroGel implants with grafted BMSCs for implantation into damaged areas of the spinal cord, with subsequent nerve fiber germination, nerve cell regeneration, and damaged segment restoration.

Stem Cell Strategies in Promoting Neuronal Regeneration after Spinal Cord Injury: A Systematic Review

Spinal cord injury (SCI) is a devastating condition with a significant medical and socioeconomic impact. To date, no effective treatment is available that can enable neuronal regeneration and recovery of function at the damaged level. This is thought to be due to scar formation, axonal degeneration and a strong inflammatory response inducing a loss of neurons followed by a cascade of events that leads to further spinal cord damage. Many experimental studies demonstrate the therapeutic effect of stem cells in SCI due to their ability to differentiate into neuronal cells and release neurotrophic factors. Therefore, it appears to be a valid strategy to use in the field of regenerative medicine. This review aims to provide an up-to-date summary of the current research status, challenges, and future directions for stem cell therapy in SCI models, providing an overview of this constantly evolving and promising field.

Anti-Caspr-conjugated gold nanoparticles emergence as a novel approach in the treatment of EAE animal model

Multiple sclerosis (MS) is a chronic autoimmune disorder of central nervous system which is increasing worldwide. Although immunosuppressive agents are used for the treatment of MS disease, nevertheless the lack of non-toxic and efficient therapeutic method is perceptible. Hence, this study aims to evaluate the effect of Contactin-associated protein (Caspr) antibody-, poly ethylene glycol (PEG)- and exosome combined gold nanoparticles (GNPs) in comparison to Glatiramer acetate as a selective treatment of MS disease in the experimental autoimmune encephalomyelitis (EAE) mouse model. EAE was induced in female C57BL/6 mice and 25-day treatment with anti-Caspr-, PEG- and exosome combined GNPs was evaluated. Histopathological examination of spinal cord, regulatory T cells as well as inflammatory pathway including IFN-ɣ and IL-17 and mir-326 were investigated. The results showed the severity of MS symptoms was significantly decreased in all treated groups. Histological examination of the spinal cord indicated the reduced demyelination and immune cell infiltration. Besides, regulatory T cells were significantly increased following all treatments. Remarkably, the cytokine levels of IFN-ɣ and IL-17 as well as mir-326 is altered in treated groups. Taken together, the obtained findings demonstrate that the administration of anti-Caspr-, PEG- and exosome combined GNPs can be considered a potential treatment in MS disease.

AM1241-Loaded Poly(ethylene glycol)–Dithiothreitol Hydrogel Repairs Cranial Bone Defects by Promoting Vascular Endothelial Growth Factor and COL-1 Expression

Objective: To explore the repair effect of the prepared drug-loaded AM1241 poly(ethylene glycol)–dithiothreitol (PEG-DTT) hydrogel on cranial bone defects in SD rats.

Methods: The PEG-DTT hydrogel under borax catalysis was quickly prepared, and the characterization of the material was observed by a scanning electron microscope. The effect of AM1241 on cell activity and bone tissue differentiation was tested. The SD rat model of cranial bone defect was established, and the defect was repaired by injecting the prepared hydrogel into the defect. The defect was divided into four groups, namely, sham group, blank group, PEG-DTT group, and PEG-DTT + AM1241 group. The rats were euthanized, and whole cranial bone was taken out for micro-CT and histological observation.

Results: The prepared hydrogel is porous; it is liquid when heated to 80°C and a hydrogel when cooled to 25°C. 5–10 μM AM1241 increased osteoblast activity. A moderate amount of AM1241 can promote osteogenic differentiation. Both the PEG-DTT group and PEG-DTT + AM1241 group showed obvious new bone tissue formation, but the PEG-DTT + AM1241 group had a better effect. In addition, the new bone tissue in the PEG-DTT + AM1241 group was significantly more than that in the other groups.

Conclusion: The prepared AM1241-loaded PEG-DTT hydrogel showed a good repair effect on SD rats with cranial bone defects. It can be used as materials for cranial bone repair in SD rats with cranial bone defects, but the repair effect is weaker than that of normal bone. These results provide a theoretical and practical basis for its further clinical application.

Reverse Adverse Immune Microenvironments by Biomaterials Enhance the Repair of Spinal Cord Injury

Spinal cord injury (SCI) is a severe and traumatic disorder that ultimately results in the loss of motor, sensory, and autonomic nervous function. After SCI, local immune inflammatory response persists and does not weaken or disappear. The interference of local adverse immune factors after SCI brings great challenges to the repair of SCI. Among them, microglia, macrophages, neutrophils, lymphocytes, astrocytes, and the release of various cytokines, as well as the destruction of the extracellular matrix are mainly involved in the imbalance of the immune microenvironment. Studies have shown that immune remodeling after SCI significantly affects the survival and differentiation of stem cells after transplantation and the prognosis of SCI. Recently, immunological reconstruction strategies based on biomaterials have been widely explored and achieved good results. In this review, we discuss the important factors leading to immune dysfunction after SCI, such as immune cells, cytokines, and the destruction of the extracellular matrix. Additionally, the immunomodulatory strategies based on biomaterials are summarized, and the clinical application prospects of these immune reconstructs are evaluated.

Novel Strategies for Spinal Cord Regeneration

A spinal cord injury (SCI) is one of the most devastating lesions, as it can damage the continuity and conductivity of the central nervous system, resulting in complex pathophysiology. Encouraged by the advances in nanotechnology, stem cell biology, and materials science, researchers have proposed various interdisciplinary approaches for spinal cord regeneration. In this respect, the present review aims to explore the most recent developments in SCI treatment and spinal cord repair. Specifically, it briefly describes the characteristics of SCIs, followed by an extensive discussion on newly developed nanocarriers (e.g., metal-based, polymer-based, liposomes) for spinal cord delivery, relevant biomolecules (e.g., growth factors, exosomes) for SCI treatment, innovative cell therapies, and novel natural and synthetic biomaterial scaffolds for spinal cord regeneration.

Photopolymerized Features via Beam Pen Lithography as a Novel Tool for the Generation of Large Area Protein Micropatterns

A cantilever-free scanning probe lithography (CF-SPL)-based method for the rapid polymerization of nanoscale features on a surface via crosslinking and thiol-acrylate photoreactions is described, wherein the nanoscale position, height, and diameter of each feature can be finely and independently tuned. With precise spatiotemporal control over the illumination pattern, beam pen lithography (BPL) allows for the photo-crosslinking of polymers into ultrahigh resolution features over centimeter-scale areas using massively parallel >160 000 pen arrays of individually addressable pens that guide and focus light onto the surface with sub-diffraction resolution. The photoinduced crosslinking reaction of the ink material, which is composed of photoinitiator, diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide, poly(ethylene glycol) diacrylate, and thiol-modified functional binding molecules (i.e., thiol-PEG-biotin or 16-mercaptohexanoic acid), proceeds to ≈80% conversion with UV exposure (72 mW cm^-2 ) for short time periods (0.5 s). Such polymer patterns are further reacted with proteins (streptavidin and fibronectin) to yield protein arrays with feature arrangements at high resolution and densities controlled by local UV exposure. This platform, which combines polymer photochemistry and massive arrays of scanning probes, constitutes a new approach to making biomolecular microarrays in a high-throughput and high-yielding manner, opening new routes for biochip synthesis, bioscreening, and cell biology research.

Anisotropy and Nanomechanics of Cellulose Nanocrystals/Polyethylene Glycol Composite Films

The influence of shear flow on the nanomechanical properties of cellulose nanocrystal (CNC)/polyethylene glycol (PEG) composite films and the distribution of anisotropic phases are investigated at various CNC/PEG ratios. Here, the drying process of CNC/PEG mixed suspensions is systematically traced by rheology, followed by the spatial mapping of local mechanical properties of CNC/PEG films by nanoindentation. The detailed study of the morphology of CNC/PEG films by polarized optical microscopy (POM) and image analysis revealed the link between the mechanical properties and the influence of shear flow. A comparison of the data obtained for shear-dried films with nonsheared films showed the improved reduced Young's modulus (E_r) and hardness (H), and suppression of microphase separation in the shear-dried films. Based on this experimental evidence, a mechanism is proposed to explain the microstructural transition during the shear-drying process leading to the generation of the anisotropic domains containing the shear-induced assembled structure of CNC particles coexisting with the elongated PEG microphases.

Construction of ferritin hydrogels utilizing subunit-subunit interactions

Various proteins form nanostructures exhibiting unique functions, making them attractive as next-generation materials. Ferritin is a hollow spherical protein that incorporates iron ions. Here, we found that hydrogels are simply formed from concentrated apoferritin solutions by acid denaturation and subsequent neutralization. The water content of the hydrogel was approximately 80%. The apoferritin hydrogel did not decompose in the presence of 1 M HCl, 2-mercaptoethanol, or methanol but was dissolved in the presence of 1 M NaOH, by heating at 80°C, or by treatment with trypsin or 6 M guanidine hydrochloride. The Young’s modulus of the hydrogel was 20.4 ± 12.1 kPa according to local indentation experimentes using atomic force microscopy, indicating that the hydrogel was relatively stiff. Transition electron microscopy measurements revealed that a fibrous network was constructed in the hydrogel. The color of the hydrogel became yellow-brown upon incubation in the presence of Fe³⁺ ions, indicating that the hydrogel adsorbed the Fe³⁺ ions. The yellow-brown color of the Fe³⁺-adsorbed hydrogel did not change upon incubation in pure water, whereas it became pale by incubating it in the presence of 100 mM ethylenediaminetetraacetic acid (EDTA). The apoferritin hydrogel also adsorbed Co²⁺ and Cu²⁺ ions and released them in the presence of EDTA, while it adsorbed less Ni²⁺ ions; more Fe³⁺ ions adsorbed to the apoferritin hydrogel than other metal ions, indicating that the hydrogel keeps the iron storage characteristic of ferritin. These results demonstrate a new property of ferritin: the ability to form a hydrogel that can adsorb/desorb metal ions, which may be useful in designing future biomaterials.

Macrophage polarization in vitro and in vivo modified by contact with fragmented chitosan hydrogel

We have previously shown that implantation of a fragmented chitosan hydrogel suspension (chitosan-FPHS) into a traumatic spinal cord lesion in adult rats led to significant axon regrowth and functional recovery, which was associated to a modulation of inflammation. Using an in vitro culture system, we show here that polarization of bone marrow-derived macrophages is indeed modified by direct contact with chitosan-FPHS. Reducing the degree of acetylation (DA) and raising the concentration of chitosan (Cp, from 1.5% to 3%), favors macrophage polarization toward anti-inflammatory subtypes. These latter also migrate and adhere efficiently on low, but not high DA chitosan-FPHS, both in vitro and in vivo, while inflammatory macrophages rarely invade a chitosan-FPHS implant in vivo, no matter the DA. Our in vitro model setup should prove a valuable tool for screening diverse biomaterial formulations and combinations thereof for their inflammatory potential prior to implantation in vivo.

A Review of Biomaterials and Scaffold Fabrication for Organ-on-a-Chip (OOAC) Systems

Drug and chemical development along with safety tests rely on the use of numerous clinical models. This is a lengthy process where animal testing is used as a standard for pre-clinical trials. However, these models often fail to represent human physiopathology. This may lead to poor correlation with results from later human clinical trials. Organ-on-a-Chip (OOAC) systems are engineered microfluidic systems, which recapitulate the physiochemical environment of a specific organ by emulating the perfusion and shear stress cellular tissue undergoes in vivo and could replace current animal models. The success of culturing cells and cell-derived tissues within these systems is dependent on the scaffold chosen; hence, scaffolds are critical for the success of OOACs in research. A literature review was conducted looking at current OOAC systems to assess the advantages and disadvantages of different materials and manufacturing techniques used for scaffold production; and the alternatives that could be tailored from the macro tissue engineering research field.

Recent trends in the development of peptide and protein-based hydrogel therapeutics for the healing of CNS injury

Traumatic brain injury (TBI) and spinal cord injury (SCI) cause millions of deaths and permanent or prolonged physical disabilities around the globe every year. It generally happens due to various incidents, such as accidents during sports, war, physical assault, and strokes which result in severe damage to brain and spinal cord. If this remains untreated, traumatic CNS injuries may lead to early development of several neurodegenerative diseases like Alzheimer's, Parkinson, multiple sclerosis, and other mental illnesses. The initial physical reaction, which is also termed as the primary phase, includes swelling, followed by inflammation as a result of internal haemorrhage causing damage to indigenous tissue, i.e., axonal shear injury, rupture of blood vessels, and partial impaired supply of oxygen and essential nutrients in the neurons, thereby initiating a cascade of events causing secondary injuries such as hypoxia, hypotension, cognitive impairment, seizures, imbalanced calcium homeostasis and glutamate-induced excitotoxicity resulting in concomitant neuronal cell death and cumulative permanent tissue damage. In the modern era of advanced biomedical technology, we are still living with scarcity of the clinically applicable comparative non-invasive therapeutic strategies for regeneration or functional recovery of neurons or neural networks after a massive CNS injury. One of the key reasons for this scarcity is the limited regenerative ability of neurons in CNS. Growth-impermissive glial scar and the lack of a synthetic biocompatible platform for proper neural tissue engineering and controlled supply of drugs further retard the healing process. Injectable or implantable hydrogel materials, consisting majorly of water in its porous three-dimensional (3D) structure, can serve as an excellent drug delivery platform as well as a transplanted cell-supporting scaffold medium. Among the various neuro-compatible bioinspired materials, we are limiting our discussion to the recent advancement of engineered biomaterials comprising mainly of peptides and proteins due to their growing demand, low immunogenicity and versatility in the fabrication of neuro regenerative medicine. In this article, we try to explore all the recent scientific avenues that are developing gradually to make peptide and peptide-conjugated biomaterial hydrogels as a therapeutic and supporting scaffold for treating CNS injuries.

Current Approaches to the Management of Acute Thoracolumbar Disc Extrusion in Dogs

Intervertebral disc extrusion (IVDE) is one of the most common neurologic problems encountered in veterinary clinical practice. The purpose of this manuscript is to provide an overview of the literature related to treatment of acute canine thoracolumbar IVDE to help construct a framework for standard care of acute canine thoracolumbar IVDE where sufficient evidence exists and to highlight opportunities for future prospective veterinary clinical research useful to strengthen care recommendations in areas where evidence is low or non-existent. While there exist a number of gaps in the veterinary literature with respect to standards of care for dogs with acute thoracolumbar IVDE, recommendations for standard care can be made in some areas, particularly with respect to surgical decompression where the currently available evidence supports that surgery should be recommended for dogs with nonambulatory paraparesis or worse. While additional information is needed about the influence on timing of decompression on outcome in dogs that are deep pain negative for longer than 48 h duration, there is no evidence to support treatment of the 48 h time point as a cut off beyond which it becomes impossible for dogs to achieve locomotor recovery. Surgical decompression is best accomplished by either hemilaminectomy or mini-hemilaminectomy and fenestration of, at a minimum, the acutely ruptured disc. Adjacent discs easily accessed by way of the same approach should be considered for fenestration given the evidence that this substantially reduces future herniation at fenestrated sites. Currently available neuroprotective strategies such as high does MPSS and PEG are not recommended due to lack of demonstrated treatment effect in randomized controlled trials, although the role of anti-inflammatory steroids as a protective strategy against progressive myelomalacia and the question of whether anti-inflammatory steroids or NSAIDs provide superior medical therapy require further evaluation.

A GelMA-PEGDA-nHA Composite Hydrogel for Bone Tissue Engineering

A new gelatin methacrylamine (GelMA)-poly (ethylene glycol) diacrylate (PEGDA)-nano hydroxyapatite (nHA) composite hydrogel scaffold was developed using UV photo-crosslinking technology. The Ca²⁺ from nHA can form a [HO]Ca²⁺ [OH] bridging structure with the hydroxyl group in GelMA, thereby enhancing the stability. Compared with GelMA-PEGDA hydrogel, the addition of nHA can control the mechanical properties of the composite hydrogel and reduce the degradation rate. In vitro cell culture showed that osteoblast can adhere and proliferate on the surface of the hydrogel, indicating that the GelMA-PEGDA-nHA hydrogel had good cell viability and biocompatibility. Furthermore, GelMA-PEGDA-nHA has excellent injectability and rapid prototyping properties and is a promising 3D printed bone repair scaffold material.

Promising Role of Nano-Encapsulated Drugs for Spinal Cord Injury

Nanomaterials have been utilized for the drug delivery in the central nervous system (CNS), and many research investigators are currently focussing on this specified area. There has been a lot of advancement in the nanoparticle-mediated drug delivery to the brain. Neuronal injuries including spinal cord injury (SCI) and their targeted therapies are still in its infancy on this planet. SCI has been known to cause axonal damage followed by the loss of communication between CNS and other non-neuronal systems. SCI has been critically associated with prolonged inflammation, sensory dysfunction, and motor impairment in SCI patients. There has been a critical crosstalk in SCI and blood brain barriers (BBBs) for drug absorption and distribution in patients. There is a paucity of possible therapies for proper intervention of SCI due to selective permeability of the drugs across BBB. Nanomaterials are contemplated in the drug delivery system for SCI. In addition, self-assembled nanomicelles, lipid nanoparticles, and other co-polymers have now been explored for neuronal injuries. This review focuses on the promising approach and/or role of nanodrug delivery to target SCI in both in vitro and in vivo models.

Design of hydrogel-based scaffolds for the treatment of spinal cord injuries

Hydrogel-based scaffold design approaches for the treatment of spinal cord injuries.

Anti-PEG antibodies: Properties, formation, testing and role in adverse immune reactions to PEGylated nano-biopharmaceuticals

Conjugation of polyethylene glycols (PEGs) to proteins or drug delivery nanosystems is a widely accepted method to increase the therapeutic index of complex nano-biopharmaceuticals. Nevertheless, these drugs and agents are often immunogenic, triggering the rise of anti-drug antibodies (ADAs). Among these ADAs, anti-PEG IgG and IgM were shown to account for efficacy loss due to accelerated blood clearance of the drug (ABC phenomenon) and hypersensitivity reactions (HSRs) entailing severe allergic symptoms with occasionally fatal anaphylaxis. In addition to recapitulating the basic information on PEG and its applications, this review expands on the physicochemical factors influencing its immunogenicity, the prevalence, features, mechanism of formation and detection of anti-PEG IgG and IgM and the mechanisms by which these antibodies (Abs) induce ABC and HSRs. In particular, we highlight the in vitro, animal and human data attesting to anti-PEG Ab-induced complement (C) activation as common underlying cause of both adverse effects. A main message is that correct measurement of anti-PEG Abs and individual proneness for C activation might predict the rise of adverse immune reactions to PEGylated drugs and thereby increase their efficacy and safety.

In situ injectable hydrogels for spinal cord regeneration: advances from the last 10 years

Spinal cord injury (SCI) is a tremendously devastating disorder with no effective therapy. Neuroprotective strategies have been applied aiming to prevent secondary cell death but no successful and robust effects have been observed. Recently, combinatorial approaches using biomaterials with cells and/or growth factors have demonstrated promising therapeutic effects because of the improvement of axonal growth and in vivo functional recovery in model organisms. In situ injectable hydrogels are a particularly attractive neuroregenerative approach to improve spinal cord repair and regeneration since they can be precisely injected into the lesion site filling the space prior to gelification, decrease scarring and promote axon growth due to the hydrogel's soft structure. Important advances regarding the use of hydrogels as potential therapeutic approaches has been reported during the last 10 years. Injectable alginate hydrogel loaded with GDNF, thermoresponsives heparin-poloxamer loaded with NGF and imidazole-poly(organophosphazenes) hydrogels are just three examples of biomaterials that can promote neurite, axon growth and improve functional recovery in hemisected and resected rats. Here we will review the status of in situ injectable hydrogels for spinal cord regeneration with special focus in the advantages of using hydrogel scaffolds, the ideal polymers to be used, the gelification process and the cells or growth factors combined. The in vitro and in vivo results reported for those biomaterials will be presented, compared and discussed.

LINGO-1 deficiency promotes nerve regeneration through reduction of cell apoptosis, inflammation, and glial scar after spinal cord injury in mice

Leucine-rich repeat and immunoglobulin domain-containing protein 1 (LINGO-1) is a transmembrane protein that negatively regulates neural regeneration in the central nervous system. LINGO-1 expression is up-regulated after central nerve injury, and is accompanied by cell death. Both LINGO-1 and cell death in the injury microenvironment are thought to limit neural regeneration, but the relationship between LINGO-1 and cell death has not been characterized. To investigate whether LINGO-1 deletion improves the spinal cord microenvironment after spinal cord injury (SCI) and contributes to cell survival, we generated LINGO-1 knockout (KO) mice. These mice and wild-type control mice were subjected to spinal cord transection. Fourteen days after spinal cord transection, cell apoptosis, inflammation, glial scar, and growth of nerve fibers were evaluated by immunostaining. The results showed that LINGO-1 KO mice demonstrated a profound reduction in expression of caspase-3, transferase-mediated deoxyuridine triphosphate biotin nick end labeling (TUNEL), ionized calcium binding adapter molecule 1 (IBA1), glial fibrillary acidic protein (GFAP), and chondroitin sulfate proteoglycans (CSPGs) compared to controls. In contrast, expression of neurofilament (NF) at the SCI site in LINGO-1 KO mice was markedly increased compared to that in wild-type mice. These results suggested that LINGO-1 plays a critical role in the injury microenvironment in processes such as cell death, inflammatory response, and glial scar formation. Importantly, LINGO-1 deletion and a positive microenvironment may exert synergistic effects to promote nerve fiber regeneration. Therefore, inhibition of LINGO-1 may be a therapeutic strategy to promote neural regeneration following SCI.

Reconstruction of the spinal cord of spinal transected dogs with polyethylene glycol

Background:

Our study shows that a membrane sealant/fiber fusogen polyethylene glycol (PEG) applied immediately on a sharp section of the spinal cord can mend the cord and lead to exceptional levels of motor recovery, with some animals almost normal.

Materials and Methods:

Before deploying such technology in man, long-term data in large mammals that exclude delayed complications (e.g., central pain), confirm the stability of motor recovery, and provide histological evidence of fiber regrowth are necessary. Here, we provide such evidence in dogs followed up over 6 months and in 2 cases up to 1 year along with imaging and histologic data.

Results:

We show that dogs whose dorsal cord has been fully transected recover locomotion after immediate treatment with a fusogen (PEG). No pain syndrome ensued over the long term. Diffusion tensor imaging magnetic resonance and histological, including immunohistochemical, data confirmed the re-establishment of anatomical continuity along with interfacial axonal sprouting.

Conclusions:

This study proves that a form of irreversible spinal cord injury (SCI) can effectively be treated and points out a way to treat SCI patients.

Bridging the gap: Spinal cord fusion as a treatment of chronic spinal cord injury

Despite decades of animal experimentation, human translation with cell grafts, conduits, and other strategies has failed to cure patients with chronic spinal cord injury (SCI). Recent data show that motor deficits due to spinal cord transection in animal models can be reversed by local application of fusogens, such as Polyethylene glycol (PEG). Results proved superior at short term over all other treatments deployed in animal studies, opening the way to human trials. In particular, removal of the injured spinal cord segment followed by PEG fusion of the two ends along with vertebral osteotomy to shorten the spine holds the promise for a cure in many cases.