Regenerative medicine strategies for chronic complete spinal cord injury

Spinal cord injury is a condition in which the parenchyma of the spinal cord is damaged by trauma or various diseases.While rapid progress has been made in regenerative medicine for spinal cord injury that was previously untreatable,most research in this field has focused on the early phase of incomplete injury.However,the majority of patients have chronic severe injuries;therefore,treatments for these situations are of fundamental importance.The reason why the treatment of complete spinal cord injury has not been studied is that,unlike in the early stage of incomplete spinal cord injury,there are various inhibitors of neural regeneration.Thus,we assumed that it is difficult to address all conditions with a single treatment in chronic complete spinal cord injury and that a combination of several treatments is essential to target severe pathologies.First,we established a combination therapy of cell transplantation and drug-releasing scaffolds,which contributes to functional recovery after chronic complete transection spinal cord injury,but we found that functional recovery was limited and still needs further investigation.Here,for the further development of the treatment of chronic complete spinal cord injury,we review the necessary approaches to the different pathologies based on our findings and the many studies that have been accumulated to date and discuss,with reference to the literature,which combination of treatments is most effective in achieving functional recovery.

Emergence of the stromal vascular fraction and secretome in regenerative medicine

Recently,we read a mini-review published by Jeyaraman et al.The article explored the optimal methods for isolating mesenchymal stromal cells from adipose tissue-derived stromal vascular fraction(SVF).Key factors include tissue source,processing techniques,cell viability assessment,and the advantages/disadvantages of autologous vs allogeneic use.The authors emphasized the need for standardized protocols for SVF isolation,ethical and regulatory standards for cell-based therapy,and safety to advance mesenchymal stromal cell-based therapies in human patients.This manuscript shares our perspective on SVF isolation in canines.We discussed future directions to potentiate effective regenerative medicine therapeutics in human and veterinary medicine.

Advances in clinical applications of bioceramics in the new regenerative medicine era

In this editorial,we comment on the hard and soft tissue applications of different ceramic-based scaffolds prepared by different mechanisms such as 3D printing,sol-gel,and electrospinning.The new concept of regenerative medicine relies on biomaterials that can trigger in situ tissue regeneration and stem cell recruitment at the defect site.A large percentage of these biomaterials is ceramic-based as they provide the essential requirements of biomaterial principles such as tailored multisize porosity,antibacterial properties,and angiogenic properties.All these previously mentioned properties put bioceramics on top of the hierarchy of biomaterials utilized to stimulate tissue regeneration in soft and hard tissue wounds.Multiple clinical applications registered the use of these materials in triggering soft tissue regeneration in healthy and diabetic patients such as bioactive glass nanofibers.The results were promising and opened new frontiers for utilizing these materials on a larger scale.The same results were mentioned when using different forms and formulas of bioceramics in hard defect regeneration.Some bioceramics were used in combination with other polymers and biological scaffolds to improve their regenerative and mechanical properties.All this progress will enable a larger scale of patients to receive such services with ease and decrease the financial burden on the government.

Mesenchymal stem cell-derived exosomes: Toward cell-free therapeutic strategies in regenerative medicine

Mesenchymal stem cells(MSCs)are multipotent stem cells with marked potential for regenerative medicine because of their strong immunosuppressive and regenerative abilities.The therapeutic effects of MSCs are based in part on their secretion of biologically active factors in extracellular vesicles known as exosomes.Exosomes have a diameter of 30-100 nm and mediate intercellular communication and material exchange.MSC-derived exosomes(MSC-Exos)have potential for cell-free therapy for diseases of,for instance,the kidney,liver,heart,nervous system,and musculoskeletal system.Hence,MSC-Exos are an alternative to MSCbased therapy for regenerative medicine.We review MSC-Exos and their therapeutic potential for a variety of diseases and injuries.

Biomaterial–Related Cell Microenvironment in Tissue Engineering and Regenerative Medicine

An appropriate cell microenvironment is key to tissue engineering and regenerative medicine.Revealing the factors that influence the cell microenvironment is a fundamental research topic in the fields of cell biology,biomaterials,tissue engineering,and regenerative medicine.The cell microenvironment consists of not only its surrounding cells and soluble factors,but also its extracellular matrix(ECM)or nearby external biomaterials in tissue engineering and regeneration.This review focuses on six aspects of bioma-terial-related cell microenvironments:①chemical composition of materials,②material dimensions and architecture,③material-controlled cell geometry,④effects of material charges on cells,⑤matrix stiff-ness and biomechanical microenvironment,and⑥surface modification of materials.The present chal-lenges in tissue engineering are also mentioned,and eight perspectives are predicted.

Nanofat: A therapeutic paradigm in regenerative medicine

Adipose tissue is a compact and well-organized tissue containing a heterogeneous cellular population of progenitor cells,including mesenchymal stromal cells.Due to its availability and accessibility,adipose tissue is considered a“stem cell depot.”Adipose tissue products possess anti-inflammatory,anti-fibrotic,antiapoptotic,and immunomodulatory effects.Nanofat,being a compact bundle of stem cells with regenerative and tissue remodeling potential,has potential in translational and regenerative medicine.Considering the wide range of applicability of its reconstructive and regenerative potential,the applications of nanofat can be used in various disciplines.Nanofat behaves on the line of adipose tissuederived mesenchymal stromal cells.At the site of injury,these stromal cells initiate a site-specific reparative response comprised of remodeling of the extracellular matrix,enhanced and sustained angiogenesis,and immune system modulation.These properties of stromal cells provide a platform for the usage of regenerative medicine principles in curbing various diseases.Details about nanofat,including various preparation methods,characterization,delivery methods,evidence on practical applications,and ethical concerns are included in this review.However,appropriate guidelines and preparation protocols for its optimal use in a wide range of clinical applications have yet to be standardized.

Regenerative medicine in China:main progress in different fields

Regenerative medicine(RM) is an emerging interdisciplinary field of research and China has developed the research quickly and impressed the world with numerous research findings in stem cells,tissue engineering,active molecules and gene therapy.Important directions are induced differentiation of induced pluripotent stem and embryo stem cells as well as somatic stem cell differentiation potential and their application in trauma,burns,diseases of aging and nerve regeneration.The products Activ Skin and bone repair scaffolds have been approved and are applied in the clinic,and similar products are being studied.About 10 engineered growth-factor drugs for repair and regeneration have been approved and are used in the clinic.Gene therapy,therapeutic cloning and xenotransplantation are some of the strategies being studied.However,China needs to develop standards,regulations and management practices suitable for the healthy development of RM.Aspects that should be strengthened include sound administrative systems,laws,and technical specifications and guidelines;conservation of stem cell resources;emphasis on training and retention of talented stem cell researchers;and reasonable allocation of resources,diversification of investment and breakthroughs in key areas.Finally,broad and deep international cooperation is necessary.

Stem cells, a two-edged sword: Risks and potentials of regenerative medicine

The recent advancements in stem cell (SC) biology have led to the concept of regenerative medicine, which is based on the potential of SC for therapies aimed to facilitate the repair of degenerating or injured tissues. Nonetheless, prior to large scale clinical appli- cations, critical aspects need to be further addressed, including the long-term safety, tolerability, and efficacy of SC-based treatments. Most problematic among the risks of SC-based therapies, in addition to the pos- sible rejection or loss of function of the infused cells, is their potential neoplastic transformation. Indeed, SCs may be used to cure devastating diseases, but their specific properties of self-renewal and clonogenicity may render them prone to generate cancers. In this respect, ‘Stemness’ might be seen as a two-edged sword, its bright side being represented by normal SCs, its dark side by cancer SCs. A better understand- ing of SC biology will help fulfill the promise of regen- erative medicine aimed at curing human pathologies and fighting cancer from its roots.

Application of mesenchymal stem cells derived from human pluripotent stem cells in regenerative medicine

Mesenchymal stem cells(MSCs)represent the most clinically used stem cells in regenerative medicine.However,due to the disadvantages with primary MSCs,such as limited cell proliferative capacity and rarity in the tissues leading to limited MSCs,gradual loss of differentiation during in vitro expansion reducing the efficacy of MSC application,and variation among donors increasing the uncertainty of MSC efficacy,the clinical application of MSCs has been greatly hampered.MSCs derived from human pluripotent stem cells(hPSC-MSCs)can circumvent these problems associated with primary MSCs.Due to the infinite selfrenewal of hPSCs and their differentiation potential towards MSCs,hPSC-MSCs are emerging as an attractive alternative for regenerative medicine.This review summarizes the progress on derivation of MSCs from human pluripotent stem cells,disease modelling and drug screening using hPSC-MSCs,and various applications of hPSC-MSCs in regenerative medicine.In the end,the challenges and concerns with hPSC-MSC applications are also discussed.

Protecting the delivery of heart failure: Regenerative Medicine/Stem Cell Therapeutics:Potential protections afforded by the Department of Health and Human Services and Health Resources Service Administration’s Bureau of Special Programs

Advances in stem cell science and potential clinical applications have brought clinical medicine closer to the actualization of Regenerative Medicine—an extension of transplantation of organs and cells and implantation of bioprosthetics and biodevices. The goal of such therapeutics will be intervention prior to onset of severe individual disability, enhance organ function and enhance patient performance status without incurring the economic impacts of standard organ transplantation. Regenerative Medicine is already demonstrating proof of principle or efficacy in restora- tion of myocardial contractility, joint mobility and function, immune competence, pulmonary function, immunologic self- tolerance, motor function and normal hemoglobin production with the next targets—diabetes mellitus (type I and type II), neurologic injury, hepatic dysfunction preparing to enter trials. Expenditures on health care needs of an aging U.S. citizenry approximate 20-25% ($3 trillion) of U.S. GDP currently and may to grow to 40% of U.S. GDP by 2025. As the potential of Regenerative Medicine is clinically realized, the societal impact and economic benefits will be disproportionately magnified in the economies of industrialized nations. The experi- ence of the Department of Health and Human Services (HHS), United Network for Organ Sharing (UNOS), the National Bone Marrow Donor Registry (NBMDR), and the National Vaccine Injury Compensation Programs (NVICP) can help ensure that as Regenerative Medicine strives to achieve clinical benefits while avoiding decimation of therapeutic options by product liability and medical malpractice concerns—concerns that crippled the U.S. vaccine manufacturing industry until the creation of the NVICP. The first 50 years of organ/cell/tissue transplantation demonstrates that clinical reality of allogeneic and autologous transplantation can antedate complete understanding of the basic science underlying successful transplantation. Product liability and medical malpractice liability have not impeded the development and growth of organ/cell/tissue transplanta- tion despite increased risks of infection, malignancy and cardiovascular disease in transplant recipients. Currently, human transplantation is only performed using FDA/CBER-approved, non-embryonic stem cells from peripheral blood, bone marrow or umbilical cord blood. Federal legislation passed in 2005 (HR2520 and S1317: The Bone Marrow and Cord Blood Cell Transplantation Program) authorizes the Secretary of Health and Human Services acting through the Director of HRSA to ensure uniform stem cell units distribution and outcomes monitoring via the federally-designated C.W. Bill Young Cell Transplant Program. Historically in the U.S., human biological therapies (vaccines, organ transplant and stem cell transplant) have re- quired federal protections to ensure continued distribution, fair access and avoidance of inhibitory product liability via protections afforded under the “stewardship” of the Secretary of Health and Human Services. The National Childhood Vaccine Injury Act of 1986 established the NVICP to equitably and expeditiously compensate individuals, or families of individuals, who have been declared injured by vaccines, thereby stabilizing a once imperiled vaccine supply by substan-tially reducing the threat of liability for vaccine companies, physicians, and other health care professionals who administer vaccines. Vaccines were the first biologics administered to U.S. citizens en masse and presage stem cell therapeutics (which may similarly be administered to millions) will similarly necessitate that a Stem Cell Injury Compensation Program (SCICP) will also need to be in place to demonstrate an intention to do good, an understanding that industry may do well, but that the health care consumer has a right of protection—all recognized from the outset. The Federal Tort Claims Act (FTCA) addresses liability claims via the Executive, Judicial and Legislative branches of Government, providing an um- brella of liability protection to other participants in the stem cell unit “chain of custody” under the FTCA—similar to the protection from product liability seen in organ and stem cell transplantation for the past 40-50 years. Efficacious development of regenerative medicine capabilities will mandate controlled access must first be provided for individuals with life-threatening diseases without therapeutic options or unable to benefit from or receive proven therapeutic options (ALS, cardiomyopathy and deemed not a candidate for heart transplantation, IDDM with hypoglyce- mic unawareness and no allogeneic source of traditional islet cell replacement available via HRSA) and mandates the prompt adoption of business and legal principles to ensure that the fate of the vaccine manufacturing industry does not become the fate of the stem cell therapeutics industry. If legal and regulatory concerns consume an increasing percentage of health care dollars that could be focused upon innovation, the Regenerative Medicine model will have not realized its full potential. The Diabetes Transplantation/Regenerative Medicine Model is the first organ to cell transplant model outside of oncology to demonstrate the regenerative medicine paradigm. Since all human tissues can be already recapitulated by human stem cells and key patent holders already exist, outlet or distribution of “more-than-minimally-manipulated stem cell units” as an IND approved under FDA/CBER guidelines can be accomplished via the current HHS/HRSA/Dept of Trans- plant methodology. As cardiovascular stem cell researchers develop human therapeutics utilizing more-than-minimally- manipulated stem cell products, they could be afforded protections from product liability historically enjoyed by the transplant community. Extending the Diabetes Transplant/Regenerative Medicine Model to the more than 5 million Americans with chronic heart failure, cell-based therapies to regenerate myocardial contractility could fill an existing void and be delivered in conjunction with and consistent with existing distribution of organs and tissues via HRSA/Department of Transplantation.

How regenerative medicine and tissue engineering may complement the available armamentarium in gastroenterology?

The increasing shortage of donors and the adverse effects of immunosuppression have restricted the impact of solid organ transplantation.Despite the initial promising developments in xenotransplantation,roadblocks still need to be overcome and this form of organ support remains a long way from clinical practice.While hepatocyte transplantation may be effectively correct metabolic defects,it is far less effective in restoring liver function than liver transplantation.Tissue engineering,using extracellular matrix scaffolds with an intact but decellularized vascular network that is repopulated with autologous or allogeneic stem cells and/or adult cells,holds great promise for the treatment of failure of organs within gastrointestinal tract,such as endstage liver disease,pancreatic insufficiency,bowel failure and type 1 diabetes.Particularly in the liver field,where there is a significant mortality of patients awaiting transplant,human bioengineering may offer a source of readily available organs for transplantation.The use of autologous cells will mitigate the need for long term immunosuppression thus removing a major hurdle in transplantation.

VEGF in the nervous system: an important target for research in neurodevelopmental and regenerative medicine

Vascular endothelial growth factor（VEGF）in neurodevelopment and regeneration：VEGF is a well-known factor that promotes vascularization and angiogenesis.Besides this it participates in the pathogenesis of several diseases,such as colorectal carcinoma,lung cancer or diabetic retinopathy.Within the last decade,VEGF has been successfully integrated into the treatment of such diseases,for example as a therapy for colorectal cancer with the VEGF-receptor （VEGFR）-inhibitor axitinib.

Can the venerated silk be the next generation nanobiomaterialfor biomedical device designing, regenerative medicine and drugdelivery? Prospects and hitches

Of late, the relevance of silk in a myriad of material science and biotechnological realms has been realized, as attested by the incessantly clambering number of reports and patents in the scienti fic repositories. The write-up is geared off with a scrutiny into the pertinence of the basic nano-structural features of silk, christened as the ‘queen of textile’ for exemplary bioengi- neering applications including designing and fabrication of devices for micro fluidics, opto fluidics, chemo/bio sensing, etc. Then, the major thrust of this short review is directed towards comprehending the prospects of using silk-based biomaterials (e.g. sca ffolds, electrospun membranes, films, hydrogels, bioinks) for tissue engineering and regenerative medicine as well as targeted delivery of various biomolecular cargoes/therapeutic agents, etc., as vouched by few avant-garde endeavours of the recent years. The write-up is entwined with a discussion on the various factors that could plausibly hinder the realization of silk as the next-generation nanobiomaterial, suggestions for some approaches to dodge and deal with the practical snags and what lies ahead!

Adipose stromal/stem cells in regenerative medicine:Potentials and limitations

This article presents the stem and progenitor cells from subcutaneous adipose tissue,briefly comparing them with their bone marrow counterparts,and discussing their potential for use in regenerative medicine.Subcutaneous adipose tissue differs from other mesenchymal stromal/stem cells(MSCs)sources in that it contains a pre-adipocyte population that dwells in the adventitia of robust blood vessels.Pre-adipocytes are present both in the stromal-vascular fraction(SVF;freshly isolated cells)and in the adherent fraction of adipose stromal/stem cells(ASCs;in vitro expanded cells),and have an active role on the chronic inflammation environment established in obesity,likely due their monocyticmacrophage lineage identity.The SVF and ASCs have been explored in cell therapy protocols with relative success,given their paracrine and immunomodulatory effects.Importantly,the widely explored multipotentiality of ASCs has direct application in bone,cartilage and adipose tissue engineering.The aim of this editorial is to reinforce the peculiarities of the stem and progenitor cells from subcutaneous adipose tissue,revealing the spheroids as a recently described biotechnological tool for cell therapy and tissue engineering.Innovative cell culture techniques,in particular 3D scaffold-free cultures such as spheroids,are now available to increase the potential for regeneration and differentiation of mesenchymal lineages.Spheroids are being explored not only as a model for cell differentiation,but also as powerful 3D cell culture tools to maintain the stemness and expand the regenerative and differentiation capacities of mesenchymal cell lineages.

The impact of graphene on neural regenerative medicine

There is increasing interest in studying carbon-based nanomaterials（CBNs）for use in regenerative medicine.Some carbon crystalline structures,such as graphene,carbon nanotubes/nanofibers,boron nitride nanosheets/nanotubes and fullerenes,as well as disordered structures,such as diamond-like carbon,glasslike carbon,and amorphous carbon,are now being considered as promising scaffolds（Ferreira et al.,2015;Kabiri et al.,2015）,

Regenerative medicine using dental pulp stem cells for liver diseases

Acute liver failure is a refractory disease and its pro-gnosis, if not treated using liver transplantation, is extremely poor. It is a good candidate for regenerative medicine, where stem cell-based therapies play a central role. Mesenchymal stem cells(MSCs) are known to differentiate into multiple cell lineages including hepatocytes. Autologous cell transplant without any foreign gene induction is feasible using MSCs, thereby avoiding possible risks of tumorigenesis and immune rejection. Dental pulp also contains an MSC population that differentiates into hepatocytes. A point worthy of special mention is that dental pulp can be obtained from deciduous teeth during childhood and can be subsequently harvested when necessary after deposition in a tooth bank. MSCs have not only a regenerative capacity but also act in an anti--inflammatory manner via paracrine mechanisms. Promising efficacies and difficulties with the use of MSC derived from teeth are summarized in this review.

Graphene platform for neural regenerative medicine

Graphene is a material composed of a single layer of carbon atoms arranged in a two-dimensional honeycomb lattice. The unique elec- trical, optical, thermal, and mechanical properties of graphene are extensively exploited for various applications in electronics, energy, and sensors.

The prospects of regenerative medicine combined with rehabilitative approaches for chronic spinal cord injury animal models

Regenerative medicine has opened a window for functional recovery in acute-to-subacute phase spinal cord injury（SCI）.By contrast,there are still only a few studies have focused on the treatment of the chronically injured spinal cord,in which cell-based regenerative medicine seems less effective.Since the majority of SCI patients are in the chronic phase,representing a major challenge for the clinical application of cellbased regenerative medicine.Although combined therapies for the treatment of chronic SCI have attracted attention of researchers and its potential importance is also widely recognized,there had been very few studies involving rehabilitative treatments to date.In a recent study,we have demonstrated for the first time that treadmill training combined with cell transplantation significantly promotes functional recovery even in chronic SCI,not only in additive but also in synergistic manner.Even though we have succeeded to outline the profiles of recovery secondary to the combination therapy,the mechanism underlying the effects remain unsolved.In this review article,we summarize the present progress and consider the prospect of the cell-based regenerative medicine particularly combined with rehabilitative approaches for chronic SCI animal models.

Dental-derived stem cells and biowaste biomaterials:What’s next in bone regenerative medicine applications

The human teeth and oral cavity harbor various populations of mesenchymal stem cells(MSCs),so called dental-derived stem cells(D-dSCs)with self-renewing and multilineage differentiation capabilities.D-dSCs properties involves a strong paracrine component resulting from the high levels of bioactive molecules they secrete in response to the local microenvironment.Altogether,this viewpoint develops a general picture of current innovative strategies to employ D-dSCs combined with biomaterials and bioactive factors for regenerative medicine purposes,and offers information regarding the available scientific data and possible applications.

Calcium channels and their role in regenerative medicine

Stem cells hold indefinite self-renewable capability that can be differentiated into all desired cell types.Based on their plasticity potential,they are divided into totipotent(morula stage cells),pluripotent(embryonic stem cells),multipotent(hematopoietic stem cells,multipotent adult progenitor stem cells,and mesenchymal stem cells[MSCs]),and unipotent(progenitor cells that differentiate into a single lineage)cells.Though bone marrow is the primary source of multipotent stem cells in adults,other tissues such as adipose tissues,placenta,amniotic fluid,umbilical cord blood,periodontal ligament,and dental pulp also harbor stem cells that can be used for regenerative therapy.In addition,induced pluripotent stem cells also exhibit fundamental properties of self-renewal and differentiation into specialized cells,and thus could be another source for regenerative medicine.Several diseases including neurodegenerative diseases,cardiovascular diseases,autoimmune diseases,virus infection(also coronavirus disease 2019)have limited success with conventional medicine,and stem cell transplantation is assumed to be the best therapy to treat these disorders.Importantly,MSCs,are by far the best for regenerative medicine due to their limited immune modulation and adequate tissue repair.Moreover,MSCs have the potential to migrate towards the damaged area,which is regulated by various factors and signaling processes.Recent studies have shown that extracellular calcium(Ca^(2+))promotes the proliferation of MSCs,and thus can assist in transplantation therapy.Ca^(2+)signaling is a highly adaptable intracellular signal that contains several components such as cell-surface receptors,Ca^(2+)channels/pumps/exchangers,Ca^(2+)buffers,and Ca^(2+)sensors,which together are essential for the appropriate functioning of stem cells and thus modulate their proliferative and regenerative capacity,which will be discussed in this review.