Spinal Cord Injury Management through the Combination of Stem Cells and Implantable 3D Bioprinted Platforms

3D bioprinting approaches for spinal cord injury repair

Regenerative healing of spinal cord injury (SCI) poses an ongoing medical challenge by causing persistent neurological impairment and a significant socioeconomic burden. The complexity of spinal cord tissue presents hurdles to successful regeneration following injury, due to the difficulty of forming a biomimetic structure that faithfully replicates native tissue using conventional tissue engineering scaffolds. 3D bioprinting is a rapidly evolving technology with unmatched potential to create 3D biological tissues with complicated and hierarchical structure and composition. With the addition of biological additives such as cells and biomolecules, 3D bioprinting can fabricate preclinical implants, tissue or organ-like constructs, andin vitromodels through precise control over the deposition of biomaterials and other building blocks. This review highlights the characteristics and advantages of 3D bioprinting for scaffold fabrication to enable SCI repair, including bottom-up manufacturing, mechanical customization, and spatial heterogeneity. This review also critically discusses the impact of various fabrication parameters on the efficacy of spinal cord repair using 3D bioprinted scaffolds, including the choice of printing method, scaffold shape, biomaterials, and biological supplements such as cells and growth factors. High-quality preclinical studies are required to accelerate the translation of 3D bioprinting into clinical practice for spinal cord repair. Meanwhile, other technological advances will continue to improve the regenerative capability of bioprinted scaffolds, such as the incorporation of nanoscale biological particles and the development of 4D printing.

Biomedical applications of engineered heparin-based materials

Heparin is a negatively charged polysaccharide with various chain lengths and a hydrophilic backbone. Due to its fascinating chemical and physical properties, nontoxicity, biocompatibility, and biodegradability, heparin has been extensively used in different fields of medicine, such as cardiovascular and hematology. This review highlights recent and future advancements in designing materials based on heparin for various biomedical applications. The physicochemical and mechanical properties, biocompatibility, toxicity, and biodegradability of heparin are discussed. In addition, the applications of heparin-based materials in various biomedical fields, such as drug/gene delivery, tissue engineering, cancer therapy, and biosensors, are reviewed. Finally, challenges, opportunities, and future perspectives in preparing heparin-based materials are summarized.

Improving Efficiency of Direct Pro-Neural Reprogramming: Much-Needed Aid for Neuroregeneration in Spinal Cord Injury

Spinal cord injury (SCI) is a medical condition affecting ~2.5-4 million people worldwide. The conventional therapy for SCI fails to restore the lost spinal cord functions; thus, novel therapies are needed. Recent breakthroughs in stem cell biology and cell reprogramming revolutionized the field. Of them, the use of neural progenitor cells (NPCs) directly reprogrammed from non-neuronal somatic cells without transitioning through a pluripotent state is a particularly attractive strategy. This allows to "scale up" NPCs in vitro and, via their transplantation to the lesion area, partially compensate for the limited regenerative plasticity of the adult spinal cord in humans. As recently demonstrated in non-human primates, implanted NPCs contribute to the functional improvement of the spinal cord after injury, and works in other animal models of SCI also confirm their therapeutic value. However, direct reprogramming still remains a challenge in many aspects; one of them is low efficiency, which prevents it from finding its place in clinics yet. In this review, we describe new insights that recent works brought to the field, such as novel targets (mitochondria, nucleoli, G-quadruplexes, and others), tools, and approaches (mechanotransduction and electrical stimulation) for direct pro-neural reprogramming, including potential ones yet to be tested.

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.

Cell Encapsulation and 3D Bioprinting for Therapeutic Cell Transplantation

The promise of cell therapy has been augmented by introducing biomaterials, where intricate scaffold shapes are fabricated to accommodate the cells within. In this review, we first discuss cell encapsulation and the promising potential of biomaterials to overcome challenges associated with cell therapy, particularly cellular function and longevity. More specifically, cell therapies in the context of autoimmune disorders, neurodegenerative diseases, and cancer are reviewed from the perspectives of preclinical findings as well as available clinical data. Next, techniques to fabricate cell-biomaterials constructs, focusing on emerging 3D bioprinting technologies, will be reviewed. 3D bioprinting is an advancing field that enables fabricating complex, interconnected, and consistent cell-based constructs capable of scaling up highly reproducible cell-biomaterials platforms with high precision. It is expected that 3D bioprinting devices will expand and become more precise, scalable, and appropriate for clinical manufacturing. Rather than one printer fits all, seeing more application-specific printer types, such as a bioprinter for bone tissue fabrication, which would be different from a bioprinter for skin tissue fabrication, is anticipated in the future.

Tail nerve electrical stimulation promoted the efficiency of transplanted spinal cord-like tissue as a neuronal relay to repair the motor function of rats with transected spinal cord injury

Following transected spinal cord injury (SCI), there is a critical need to restore nerve conduction at the injury site and activate the silent neural circuits caudal to the injury to promote the recovery of voluntary movement. In this study, we generated a rat model of SCI, constructed neural stem cell (NSC)-derived spinal cord-like tissue (SCLT), and evaluated its ability to replace injured spinal cord and repair nerve conduction in the spinal cord as a neuronal relay. The lumbosacral spinal cord was further activated with tail nerve electrical stimulation (TNES) as a synergistic electrical stimulation to better receive the neural information transmitted by the SCLT. Next, we investigated the neuromodulatory mechanism underlying the action of TNES and its synergism with SCLT in SCI repair. TNES promoted the regeneration and remyelination of axons and increased the proportion of glutamatergic neurons in SCLT to transmit brain-derived neural information more efficiently to the caudal spinal cord. TNES also increased the innervation of motor neurons to hindlimb muscle and improved the microenvironment of muscle tissue, resulting in effective prevention of hindlimb muscle atrophy and enhanced muscle mitochondrial energy metabolism. Tracing of the neural circuits of the sciatic nerve and tail nerve identified the mechanisms responsible for the synergistic effects of SCLT transplantation and TNES in activating central pattern generator (CPG) neural circuits and promoting voluntary motor function recovery in rats. The combination of SCLT and TNES is expected to provide a new breakthrough for patients with SCI to restore voluntary movement and control their muscles.

The application of 3D-bioprinted scaffolds for neuronal regeneration after traumatic spinal cord injury - A systematic review of preclinical in vivo studies

BACKGROUND

The implantation of 3D-bioprinted scaffolds represents a promising therapeutic approach for traumatic Spinal Cord Injury (SCI), currently investigating in preclinical in vivo studies. However, a systematic review of the relevant literature has not been performed to date. Hence, we systematically reviewed the outcomes of the application of 3D-bioprinted implants in the treatment of SCI based on studies conducted on experimental animal models.

METHODS

We searched PubMed, Scopus, Web of Science, and Cochrane Library databases. Manuscripts in other designs than in vivo preclinical study and written in other languages than English were excluded. A risk of bias assessment was performed using SYRCLE's tool. The quality of included articles was assessed by ARRIVE guidelines. Extracted data were synthesized only qualitatively because the data were not suitable for conducting the meta-analysis.

RESULTS

Overall, eleven animal studies reporting on the transection SCI rat model were included. Six of included studies investigated 3D-bioprinted scaffolds enriched with stem cells, two studies - 3D-bioprinted scaffolds combined with growth factors, and three studies - stand-alone 3D-bioprinted scaffolds. In all included studies the application of 3D-bioprinted scaffolds led to significant improvement in functional scores compared with no treated SCI rats. The functional recovery corresponded with the changes observed at the injury site in histological analyses. Seven studies demonstrated medium, three studies - high, and one study - low risk of bias. Moreover, some of the included studies were conducted in the same scientific center. The overall quality assessment ratio amounted to 0.60, which was considered average quality.

CONCLUSION

The results of our systematic review suggest that 3D-bioprinted scaffolds may be a feasible therapeutic approach for the treatment of SCI. Further evidence obtained on other experimental SCI models is necessary before the clinical translation of 3D-bioprinted scaffolds.

Molecular Mechanisms and Clinical Application of Multipotent Stem Cells for Spinal Cord Injury

Spinal Cord Injury (SCI) is a common neurological disorder with devastating psychical and psychosocial sequelae. The majority of patients after SCI suffer from permanent disability caused by motor dysfunction, impaired sensation, neuropathic pain, spasticity as well as urinary complications, and a small number of patients experience a complete recovery. Current standard treatment modalities of the SCI aim to prevent secondary injury and provide limited recovery of lost neurological functions. Stem Cell Therapy (SCT) represents an emerging treatment approach using the differentiation, paracrine, and self-renewal capabilities of stem cells to regenerate the injured spinal cord. To date, multipotent stem cells including mesenchymal stem cells (MSCs), neural stem cells (NSCs), and hematopoietic stem cells (HSCs) represent the most investigated types of stem cells for the treatment of SCI in preclinical and clinical studies. The microenvironment of SCI has a significant impact on the survival, proliferation, and differentiation of transplanted stem cells. Therefore, a deep understanding of the pathophysiology of SCI and molecular mechanisms through which stem cells act may help improve the treatment efficacy of SCT and find new therapeutic approaches such as stem-cell-derived exosomes, gene-modified stem cells, scaffolds, and nanomaterials. In this literature review, the pathogenesis of SCI and molecular mechanisms of action of multipotent stem cells including MSCs, NSCs, and HSCs are comprehensively described. Moreover, the clinical efficacy of multipotent stem cells in SCI treatment, an optimal protocol of stem cell administration, and recent therapeutic approaches based on or combined with SCT are also discussed.

3D printed scaffold design for bone defects with improved mechanical and biological properties

Bone defect treatment is still a challenge in clinics, and synthetic bone scaffolds with adequate mechanical and biological properties are highly needed. Adequate waste and nutrient exchange of the implanted scaffold with the surrounded tissue is a major concern. Moreover, the risk of mechanical instability in the defect area during regular activity increases as the defect size increases. Thus, scaffolds with better mass transportation and mechanical properties are desired. This study introduces 3D printed polymeric scaffolds with a continuous pattern, ZigZag-Spiral pattern, for bone defects treatments. This pattern has a uniform distribution of pore size, which leads to uniform distribution of wall shear stress which is crucial for uniform differentiation of cells attached to the scaffolds. The mechanical, mass transportation, and biological properties of the 3D printed scaffolds are evaluated. The results show that the presented scaffolds have permeability similar to natural bone and, with the same porosity level, have higher mechanical properties than scaffolds with conventional lay-down patterns 0-90° and 0-45°. Finally, human mesenchymal stem cells are seeded on the scaffolds to determine the effects of geometrical microstructure on cell attachment and morphology. The results show that cells in scaffold with ZigZag-Spiral pattern infilled pores gradually, while the other patterns need more time to fill the pores. Considering mechanical, transportation, and biological properties of the considered patterns, scaffolds with ZigZag-Spiral patterns can mimic the properties of cancellous bones and be a better choice for treatments of bone defects.

The Time Sequence of Gene Expression Changes after Spinal Cord Injury

Gene expression changes following spinal cord injury (SCI) are time-dependent, and an accurate understanding of these changes can be crucial in determining time-based treatment options in a clinical setting. We performed RNA sequencing of the contused spinal cord of rats at five different time points from the very acute to chronic stages (1 hour, 1 day, 1 week, 1 month, and 3 months) following SCI. We identified differentially expressed genes (DEGs) and Gene Ontology (GO) terms at each time point, and 14,257 genes were commonly expressed at all time points. The biological process of the inflammatory response was increased at 1 hour and 1 day, and the cellular component of the integral component of the synaptic membrane was increased at 1 day. DEGs associated with cell activation and the innate immune response were highly enriched at 1 week and 1 month, respectively. A total of 2841 DEGs were differentially expressed at any of the five time points, and 18 genes (17 upregulated and 1 downregulated) showed common expression differences at all time points. We found that interleukin signaling, neutrophil degranulation, eukaryotic translation, collagen degradation, LGI–ADAM interactions, GABA receptor, and L1CAM-ankyrin interactions were prominent after SCI depending on the time post injury. We also performed gene–drug network analysis and found several potential antagonists and agonists which can be used to treat SCI. We expect to discover effective treatments in the clinical field through further studies revealing the efficacy and safety of potential drugs.

Combination Therapy Using Nanomaterials and Stem Cells to Treat Spinal Cord Injuries

As a part of the central nervous system, the spinal cord (SC) provides most of the communications between the brain and other parts of the body. Any damage to SC interrupts this communication, leading to serious problems, which may remain for the rest of their life. Due to its significant impact on patients' quality of life and its exorbitant medical costs, SC injury (SCI) is known as one of the most challengeable diseases in the world. Thus, it is critical to introduce highly translatable therapeutic platforms for SCI treatment. So far, different strategies have been introduced, among which utilizing various types of stem cells is one of the most interesting ones. The capability of stem cells to differentiate into several types of cell lines makes them promising candidates for the regeneration of injured tissues. One of the other interesting and novel strategies for SCI treatment is the application of nanomaterials, which could appear as a carrier for therapeutic agents or as a platform for culturing the cells. Combining these two approaches, stem cells and nanomaterials, could provide promising therapeutic strategies for SCI management. Accordingly, in this review we have summarized some of the recent advancements in which the applications of different types of stem cells and nanomaterials, alone and in combination forms, were evaluated for SCI treatment.