Regenerative medicine as applied to solid organ transplantation: current status and future challenges

In the last two decades, regenerative medicine has shown the potential for “bench‐to‐bedside” translational research in specific clinical settings. Progress made in cell and stem cell biology, material sciences and tissue engineering enabled researchers to develop cutting‐edge technology which has lead to the creation of nonmodular tissue constructs such as skin, bladders, vessels and upper airways. In all cases, autologous cells were seeded on either artificial or natural supporting scaffolds. However, such constructs were implanted without the reconstruction of the vascular supply, and the nutrients and oxygen were supplied by diffusion from adjacent tissues. Engineering of modular organs (namely, organs organized in functioning units referred to as modules and requiring the reconstruction of the vascular supply) is more complex and challenging. Models of functioning hearts and livers have been engineered using “natural tissue” scaffolds and efforts are underway to produce kidneys, pancreata and small intestine. Creation of custom‐made bioengineered organs, where the cellular component is exquisitely autologous and have an internal vascular network, will theoretically overcome the two major hurdles in transplantation, namely the shortage of organs and the toxicity deriving from lifelong immunosuppression. This review describes recent advances in the engineering of several key tissues and organs.     

The Next Generation of Burns Treatment: Intelligent Films and Matrix, Controlled Enzymatic Debridement, and Adult Stem Cells

We describe a novel technology based on nanoengineered multifunctional acellular biologic scaffolds combined with wound dressings and films of the same kind. This method allows selective delivery and release of shielded biomaterials and bioactive substances to a desired wound or damaged tissue while stimulating the selective anchoring and adhesion of endogenous circulating repairing cells, such as mesenchymal stem cells, to obtain a faster and more physiologic healing process. We also present a new controlled enzymatic debridement process for more effective burned tissue scarolysis. In light of our preliminary in vitro and in vivo data, we are convinced that these approaches can include the use of other kinds of adult stem cells, such as endometrial regenerative cells, to improve the vascularization of the constructs, with great potential in the entire tissue and organ regeneration field but especially for the treatment of severely burned patients, changing the way these lesions may be treated in the future.     

Application of stem cells for cardiovascular grafts tissue engineering

Congenital and acquired heart diseases are leading causes of morbidity and mortality world-wide. Currently, the synthetic materials or bioprosthetic replacement devices for cardiovascular surgery are imperfect and subject patients to one or more ongoing risks including thrombosis, limited durability and need for reoperations due to lack of growth in children and young adults. Suitable replacement grafts should have appropriate characteristics, including resistance to infection, low immunogenicity, good biocompatability and thromboresistance, with appropriate mechanical and physiological properties. Tissue engineering is a new scientific field aiming at fabrication of living, autologous grafts having structure or function properties that can be used to restore, maintain or improve tissue function. The use of autologous stem cells in cardiovascular tissue engineering is quite promising due to their capacity of self-renewal, high proliferation, and differentiation into specialized progeny. Progress has been made in engineering the various components of the cardiovascular system, including myocardial constructs, heart valves, and vascular patches or conduits with autologous stem cells. This paper will review the current achievements in stem cell-based cardiovascular grafts tissue engineering, with an emphasis on its clinical or possible clinical use in cardiovascular surgery.     

Recent advances in head and neck cancer reconstruction

Treatment of cancer is race against time! Following radical excision, breathing, speech, mastication and swallowing are hampered. Face is invariably involved. Beside functional normalcy, excellent cosmetic restoration is necessary for patient''s life quality. Primary wound healing, quick resumption of adequate oral intake, prompt initiation of chemo-radiotherapy has direct bearing on cure. Primary reconstruction with pedicle or free flap is the choice of treatment in most protocols. Composite defects are requiring bone, muscle and skin restrict choice of donor site and may have shortfalls in aesthetic and functional requirements. To improve further newer, and newer modalities are being developed and used to give best aesthetic and functions. Navigation, use of three-dimensional imaging, stereo lithic model and custom made implant for reconstruction are recommended as they promise improvement in aesthetics. Robotic surgeries allow access for resection of tumours and reconstruction with free flap in deep oropharynx obviating need of doing mandibulotomy. Researchers in stem cell and tissue engineering are looking forward to regenerating tissues and avoid the need of autologous tissue flaps. Desired tissue combination across counter may be available in the future. Excellent immunosuppressant drugs have made it possible to reconstruct composite facial anatomical units with allotransplant in a single surgery, along sensory and motor recovery! Mythological heterogenic head transplant like clone Ganesha, will be a reality in the near future!!KEY WORDS: Head, mandible, reconstruction, transplant     

Regenerative medicine in orthopaedic surgery.

Regenerative medicine holds great promise for orthopaedic surgery. As surgeons continue to face challenges regarding the healing of diseased or injured musculoskeletal tissues, regenerative medicine aims to develop novel therapies that will replace, repair, or promote tissue regeneration. This review article will provide an overview of the different research areas involved in regenerative medicine, such as stem cells, bioinductive factors, and scaffolds. The potential use of stem cells for orthopaedic tissue engineering will be addressed by presenting the current progress with skeletal muscle-derived stem cells. As well, the development of a revascularized massive allograft will be described and will serve as a prototypic model of orthopaedic tissue engineering. Lastly, we will describe current approaches used to design cell instructive materials and how they can be used to promote and regulate the formation of bony tissue.     

Cellular strategies for enhancement of fracture repair

Tissue engineering seeks to translate scientific knowledge into tangible products to advance the repair, replacement, or regeneration of organs and tissues. Current tissue engineering strategies have progressed recently from a historical approach that is based primarily on biomaterials to a cell and tissue-based approach that includes understanding of cell-sourcing and bioactive stimuli. New options include methods for harvest and transplantation of tissue-forming cells, bioactive matrix materials that act as tissue scaffolds, and delivery of bioactive molecules within scaffolds. These strategies are already benefiting patients, and they place increasing demands on orthopaedic surgeons to have a solid foundation in the contemporary concepts and principles of cell-based tissue engineering. Essentially all orthopaedic tissue engineering strategies can be distilled to a strategy or combination of strategies that seek to increase the number or relative performance of bone-forming cells. The global term connective tissue progenitors has been used to define the heterogeneous populations of stem and progenitor cells that are found in native tissue and that are capable of differentiating into one or more connective tissue phenotypes. These stem or progenitor populations are found in various tissue sources, with varying degrees of ability to differentiate along connective tissue lineages. Available cell-based strategies include targeting local cells with use of scaffolds or bioactive factors, or transplantation of autogenous connective tissue progenitor cells derived from bone marrow or other tissues, with or without processing to change their concentration or prevalence. The future may include means of homing circulating connective tissue progenitor cells with use of intrinsic chemokine systems, or modifying the biological performance of connective tissue progenitor cells by means of genetic modifications.     

Nonoperative and Operative Bone and Cartilage Regeneration and Orthopaedic Biologics of the Hip: An Orthoregeneration Network (ON) Foundation Hip Review

Orthoregeneration is defined as a solution for orthopaedic conditions that harnesses the benefits of biology to improve healing, reduce pain, improve function, and, optimally, provide an environment for tissue regeneration. Options include drugs, surgical intervention, scaffolds, biologics as a product of cells, and physical and electromagnetic stimuli. The goal of regenerative medicine is to enhance the healing of tissue after musculoskeletal injuries as both isolated treatment and adjunct to surgical management, using novel therapies to improve recovery and outcomes. Various orthopaedic biologics (orthobiologics) have been investigated for the treatment of pathology involving the hip, including osteonecrosis (aseptic necrosis) involving bone marrow, bone, and cartilage, and chondral injuries involving articular cartilage, synovium, and bone marrow. Promising and established treatment modalities for osteonecrosis include nonweightbearing; pharmacological treatments including low molecular-weight heparin, prostacyclin, statins, bisphosphonates, and denosumab, a receptor activator of nuclear factor-kB ligand inhibitor; extracorporeal shock wave therapy; pulsed electromagnetic fields; core decompression surgery; cellular therapies including bone marrow aspirate comprising mesenchymal stromal cells (MSCs aka mesenchymal stem cells) and bone marrow autologous concentrate, with or without expanded or cultured cells, and possible addition of bone morphogenetic protein-2, vascular endothelial growth factor, and basic fibroblast growth factor; and arterial perfusion of MSCs that may be combined with addition of carriers or scaffolds including autologous MSCs cultured with beta-tricalcium phosphate ceramics associated with a free vascularized fibula. Promising and established treatment modalities for chondral lesions include autologous platelet-rich plasma; hyaluronic acid; MSCs (in expanded or nonexpanded form) derived from bone marrow or other sources such as fat, placenta, umbilical cord blood, synovial membrane, and cartilage; microfracture or microfracture augmented with membrane containing MSCs, collagen, HA, or synthetic polymer; mosaicplasty; 1-stage autologous cartilage translation (ACT) or 2-stage ACT using 3-dimensional spheroids; and autologous cartilage grafting; chondral flap repair, or flap fixation with fibrin glue. Hip pain is catastrophic in young patients, and promising therapies offer an alternative to premature arthroplasty. This may address both physical and psychological components of pain; the goal is to avoid or postpone an artificial joint.Level of EvidenceLevel V, expert opinion.     

Future of fat as raw material for tissue regeneration

Tissue replacement traditionally requires use of autologous tissue and is associated with the attendant morbidity of donor site harvest. In the case of allograft transplantation, there are concerns, similar to those associated with organ transplantation, of rejection and immunosuppression. For these reasons, emphasis has been placed on the development of tissue-engineered substitutes that incorporate autologous stem cells into tissue-engineered scaffolds. The authors' laboratory has characterized a population of cells obtained from processed lipoaspirate (PLA), which have the capacity in vitro to differentiate into osteoblasts, chondrocytes, myocytes, adipocytes, and neuron-like cells. Adipose tissue is an abundant, expendable, and easily obtained tissue that may prove to be an ideal source of autologous stem cells for engineering tissues.     

Tissue Engineering mit mesenchymalen Stammzellen zur Knorpel- und Knochenneubildung

Tissue engineering offers the possibility to fabricate living substitutes for tissues and organs by combining histogenic cells and biocompatible carrier materials. Pluripotent mesenchymal stem cells are isolated and subcultured ex vivo and then their histogenic differentiation is induced by external factors. The fabrication of bone and cartilage constructs, their combinations and gene therapeutic approaches are demonstrated. Advantages and disadvantages of these methods are described by in vitro and in vitro testing. The proof of histotypical function after implantation in vivo is essential. The use of autologous cells and tissue engineering methods offers the possibility to overcome the disadvantages of classical tissue reconstruction--donor site morbidity of autologous grafts, immunogenicity of allogenic grafts and loosening of alloplastic implants. Furthermore, tissue engineering widens the spectrum of surgical indications in bone and cartilage reconstruction.     

Healing,Inflammation, and Fibrosis: Radiation-Induced Tissue Damage: Clinical Consequences and Current Treatment Options

Radiation therapy is a valuable tool in the treatment of numerous malignancies but, in certain cases, can also causes significant acute and chronic damage to noncancerous neighboring tissues. This review focuses on the pathophysiology of radiation-induced damage and the clinical implications it has for plastic surgeons across breast reconstruction, osteoradionecrosis, radiation-induced skin cancers, and wound healing. The current understanding of treatment modalities presented here include hyperbaric oxygen therapy, autologous fat grafting and stem cells, and pharmaceutical agents.     

Heart valve tissue engineering

Valvular heart disease is a significant cause of morbidity and mortality world-wide. Classical replacement surgery involves the implantation of mechanical valves or biological valves (xeno- or homografts). Tissue engineering of heart valves represents a new experimental concept to improve current modes of therapy in valvular heart surgery. Various approaches have been developed differing either in the choice of scaffold (synthetic biodegradable polymers, decellularised xeno- or homografts) or cell source for the production of living tissue (vascular derived cells, bone marrow cells or progenitor cells from the peripheral blood). The use of autologous bone marrow cells in combination with synthetic biodegradable scaffolds bears advantages over other tissue engineering approaches: it is safe, it leads to complete autologous prostheses and the cells are more easily obtained in the clinical routine. Even though we demonstrated the feasibility to construct living functional tissue engineered heart valves from human bone marrow cells, so far their general potential to differentiate into non-hematopoietic cell lineages is not fully exploited for tissue engineering applications.     

Biodegradable and plasma‐treated electrospun scaffolds coated with recombinant Olfactomedin‐like 3 for accelerating wound healing and tissue regeneration

Three‐dimensional biomimetic scaffolds resembling the native extracellular matrix (ECM) are widely used in tissue engineering, however they often lack optimal bioactive cues needed for acceleration of cell proliferation, neovascularization, and tissue regeneration. In this study, the use of the ECM‐related protein Olfactomedin‐like 3 (Olfml3) demonstrates the importance and feasibility of fabricating efficient bioactive scaffolds without in vitro cell seeding prior to in vivo implantation. First, in vivo proangiogenic properties of Olfml3 were shown in a murine wound healing model by accelerated wound closure and a 1.4‐fold increase in wound vascularity. Second, subcutaneous implantation of tubular scaffolds coated with recombinant Olfml3 resulted in enhanced cell in‐growth and neovascularization compared with control scaffolds. Together, our data indicates the potential of Olfml3 to accelerate neovascularization during tissue regeneration by promoting endothelial cell proliferation and migration. This study provides a promising concept for the reconstruction of damaged tissue using affordable and effective bioactive scaffolds.     

Tissue Engineering von Sehnen- und Ligamentgewebe Eine neue Herausforderung

Injuries to ligaments and tendons heal by formation of inferior repair tissue. This may result in severe joint dysfunction. Because of an increased occurrence of sports-related injuries, musculoskeletal disorders may become one of the major burden of health care. Tissue engineering offers the potential to improve the quality of ligament and tendon tissues during the healing process and may provide a more effective approach to the treatment of injuries to ligaments and tendons than traditional methods. Application of growth factors, gene transfer techniques, cell therapy and cell-matrix composites have shown to affect the process of ligament and tendon healing. The benefits of using mesenchymal stem cells on a three dimensional biological matrix have been shown recently. Tissue engineering will also include mechanical manipulation of tissue environments to accelerate cell differentiation and to improve matrix formation. Fibroblast-seeded polymer scaffolds could be useful in ligament and tendon replacement in which autogenous fibroblasts would be obtained through biopsy, cultured and seeded onto a scaffold.     

Nanofibrous structured biomimetic strategies for skin tissue regeneration

Mimicking porous topography of natural extracellular matrix is advantageous for successful regeneration of damaged tissues or organs. Nanotechnology being one of the most promising and growing technology today shows an extremely huge potential in the field of tissue engineering. Nanofibrous structures that mimic the native extracellular matrix and promote the adhesion of various cells are being developed as tissue‐engineered scaffolds for skin, bone, vasculature, heart, cornea, nervous system, and other tissues. A range of novel biocomposite materials has been developed to enhance the bioactive or therapeutic properties of these nanofibrous scaffolds via surface modifications, including the immobilization of functional cell‐adhesive ligands and bioactive molecules such as drugs, enzymes, and cytokines. In skin tissue engineering, usage of allogeneic skin is avoided to reestablish physiological continuity and also to address the challenge of curing acute and chronic wounds, which remains as the area of exploration with various biomimetic approaches. Two‐dimensional, three‐dimensional scaffolds and stem cells are presently used as dermal regeneration templates for the treatment of full‐thickness skin defects resulting from injuries and severe burns. The present review elaborates specifically on the fabrication of nanofibrous structured strategies for wound dressings, wound healing, and controlled release of growth factors for skin tissue regeneration.     

Advances in tissue engineering of blood vessels and other tissues

Tissue engineering is a new and rapidly expanding field, in which techniques are being developed for culturing a variety of tissues both in vitro and in vivo using polymer ‘scaffolds’ to support tissue growth. Polymer scaffolds used in tissue engineering are generally biodegradable, often involving compounds which are already approved for human implantation. In some cases, these polymers may be chemically modified to exhibit selective cell adhesion properties, which enhance cell attachment and subsequent tissue growth. Many cell types have been successfully cultured on these scaffolds, including smooth muscle cells, endothelial cells, hepatocytes and chondrocytes.Tissue engineering holds the potential for the in vitro development of autologous or allogeneic transplantable vascular conduits. Each year in the USA, there are approximately 1.4 million procedures performed which require arterial prostheses. Most of these procedures are in small calibre (<6 mm) vessels, for which synthetic graft materials are not generally suitable. While autologous venouos or arterial vessels are generally used, not all patients possess adequate conduit for revascularization.Tubular scaffolds have been specially designed for culturing small calibre arteries in vitro. Bovine aortic vascular cells were seeded and cultured on these polymer scaffolds, and grown under conditions of pulsatile pressure and intra-luminal flow. To minimize contamination during the weeks of tissue culture required to produce an arterial prosthesis, a sterile incubator system was developed. Preliminary studies have achieved good cell densities of both smooth muscle cells and endothelial cells on biodegradable polymer scaffolds.     

Constructive soft tissue remodelling with a biologic extracellular matrix graft: overview and review of the clinical literature

The extracellular matrix directs all phases of healing following trauma or disease and is therefore nature's ideal scaffold material. When used strategically to induce the repair and restoration of soft tissues following surgery, exogenous extracellular matrix scaffolds interact with surrounding tissues and cells to form a permanent repair without leaving behind a permanent material that can result in chronic inflammation or infection. Biomaterials derived from natural extracellular matrix, such as Surgisis (Cook Medical Incorporated, Bloomington, IN, USA), provide the extracellular components necessary to direct the healing response, allow for the reconstruction of new, healthy tissue and restore mechanical and functional integrity to the damaged site. The 3-dimensional organization of these extracellular components distinguishes the Surgisis mesh from synthetic materials and is associated with better long-term repairs. The tissue response to this biologic mesh is discussed in the context of recent reports on successful clinical applications.     

Current concepts and applications in the musculoskeletal and peripheral nervous systems

Biotechnology and tissue engineering have broad applications over several medical disciplines. The advances in the fields of biotechnology and tissue engineering offer new possibilities in the repair or regeneration of tissue lost to disease or injury. Consequently, a major portion of the research effort has focused on applications in orthopaedics with emphasis on the development of techniques for developing bone, articular cartilage, ligaments, tendons and nerve. Tissue engineering represents a multidisciplinary approach to solving some of the most demanding medical problems, particularly the creation of new tissues similar to those in the living organism. These new technical approaches include strategies in using new synthetic polymer formulations and various alternatives in tissue regeneration. This paper will examine the possible impact of biomolecular medicine in areas critical to the future of hand surgery, including tissue replacement, tissue regeneration, wound healing, and bone, tendon, cartilage, ligament and nerve repair.     

Optimization of bone tissue engineering in goats: a peroperative seeding method using cryopreserved cells and localized bone formation in calcium phosphate scaffolds

BACKGROUND: Bone tissue engineering by combining cultured bone marrow stromal cells with a porous scaffold is a promising alternative for the autologous bone graft. Drawbacks of the technique include the delay necessary for cell culture and the complicated logistics. We investigated methods to bypass these drawbacks. Furthermore, we investigated the localization of bone formation inside the scaffold. METHODS: Bone marrow stromal cells from seven goats were culture expanded and cryopreserved. One week before surgery, some of the cells were thawed, cultured, and seeded on porous calcium phosphate scaffolds. The constructs were cultured for another week until implantation. The remaining cryopreserved cells were thawed just before implantation and peroperatively resuspended in plasma before combining with the scaffold. Scaffolds impregnated with fresh bone marrow, devitalized cultured constructs, and empty scaffolds served as controls. All samples were implanted in the back muscles of the goats for 9 weeks. RESULTS: Histologic examination showed minimal (<1%) bone in the empty and devitalized scaffolds, 4.2 +/- 5.1 bone area percent in the bone marrow samples, and significantly more bone in both the cultured and peroperatively seeded constructs (11.7 +/- 2.5 and 14.0 +/- 2.0%). The peripheral 350 microm of the implants contained significantly less bone. CONCLUSION: Peroperative preparation of osteogenic constructs with cryopreserved cells is feasible. These constructs yield substantially more bone than the scaffolds alone or scaffolds impregnated with fresh bone marrow. Bone deposition is much less on the scaffold periphery.     

Tissue engineering with chondrocytes

Tissue engineering of cartilage, using chondrocytes based on the use of synthetic biodegradable polymer cell delivery vehicles (scaffolds), is an alternate treatment modality for replacing missing cartilage. Cartilage tissue engineering has an important role to play in the generation of graft material for head and neck reconstruction. It is an approach to fabricate cartilage constructs in vitro, which could be used in reconstructive surgery. Methods involve (1) harvesting septal cartilage during septoplasty, (2) isolating chondrocytes through enzymatic digestion of the septal cartilage, (3) expanding the cell number in a two-dimensional monolayer culture, using serum-free media, (4) seeding the cells onto a biodegradable polymer scaffold, and (5) cultivating the seeded scaffolds in a rotating bioreactor. In this article we briefly outline the methodology and clinical applications of cartilage grown ex vivo.     

Stem cells used for cardiovascular tissue engineering

Stem cell research and tissue engineering have become leading fields in basic research worldwide. Especially in cardiovascular medicine, initial reports on the potential of using stem cells to recover cardiac function and replace organ subunits such as heart valves seemed to offer the promise of widespread clinical use in the near future. However, the broad application of this new therapy failed due to safety and efficacy concerns. Due in part to the initial reports, major basic research efforts were undertaken to explore the specific cell types in greater detail and identify their mechanisms of supporting function, resulting in remarkable new findings in stem cell biology. For example, the notion of resident human cardiac stem cells has disproved the earlier supposition that the human heart is a finitely differentiated organ without the intrinsic potential for regeneration. Furthermore, new technologies emerged to produce pluripotent cells without the ethical and immunological drawbacks of embryonic stem cells (for instance by nuclear transfer). Other autologous cell sources are presently under investigation in myocardial tissue engineering. For tissue engineering of heart valves and small calibre vessels, the use of autologous endothelial (precursor) cells may be the optimal means of seeding a biological or artificial scaffold. It is important that ongoing basic and clinical research in cardiovascular surgery might explore the potential of different cell types either using tissue engineering constructs or in cell transplantation approaches.