Tissue Engineered Multicellular Constructs

Tissue Engineered Multicellular Constructs – challenges and opportunities Trusha Bhatt 3rd Year Medical Student LURE Scholar University of Leeds Aims • • • • • • Definition of TE Why TE has developed Uses for TE Challenges The future My work http://www.rcsed.ac.uk/journal/ Tissue Engineering – a definition • Creation of a functional biological substitute using living cells and a matrix to maintain, improve or restore damage to tissues and organs (Atala, A. Engineering tissues, organs and cells. 2007 J Tissue Eng Regen Med 1: 8396) • Bringing together the fields of medicine, biology, engineering and biotechnology http://www.henryfordhealth.org/ http://www.ipeinc.com/l http://rgcb.res.in/ The need for TE • Failing tissues and organs • Shortfalls of current options – Autologous tissues – Allogeneic tissues – Xenogeneic tissues – Synthetic materials www.neverhappened.org http://www.myskin-info.com http://www.stanford.edu/ Autologous tissues • Tissue from the same patient • The ideal option • Biocompatible, no immune response • Natural • Decreasing availability of healthy tissue from patients with disease Atherosclerosis http://commons.wikimedia.org/ Allogeneic tissues • • • • Tissue from another person More practical than autologous harvest Severe shortage of donors Increased immune response to foreign material (Santos, T. et al. TERMIS, NA 2007) • Immunosuppressant drugs required • Unpleasant side effects • Expensive www.edb.utexas.edu Xenogeneic tissues • Tissue harvested from animals • Potentially readily available • Immune response from host to foreign material (Santos, T. et al. TERMIS, NA 2007) • Risk of disease transmission from animal to human e.g. prions and PERVs • Significant ethical considerations http://www.sheppardsoftware.com/ www.wallpaperbase.com TE – in comparison • Biocompatible • made with the patient’s own cells • Engineered to fill the exact role required • Degradation rate, composition, size, mechanical properties • Off-the-shelf availability Making a TE model You will need: – A scaffold • to allow growth and differentiation of cells – Cells of the relevant type and number – Optimum conditions for cell growth • Growth factors • Physical environment (bioreactors) www.bioexpress.com Scaffold • Structural integrity to support cell attachment, growth and differentiation • Correct pore size • Mechanical strength to withstand in vivo compression • Can be natural, synthetic or combined A sheet of small intestinal submucosal scaffold http://www.rcsed.ac.uk/journal/ Cells • Able to cause change and affect structure and function of a graft • Examples: • Skin model: fibroblasts and keratinocytes • Vascular construct: smooth muscle and endothelial cells • Cartilage: chondrocytes • Stem cells – much potential but difficult to direct differentiation and achieve sufficient cell numbers Skin: Ikuta et al Mouse epidermal keratinocytes in three-dimensional organotypic coculture with dermal fibroblasts form a stratified sheet resembling skin. (2006) Bioscience, Biotechnology & Biochemistry. 70(11):2669-75 Vascular: L’heureux et al. A completely biological tissue-engineered human blood vessel. (1998) FASEB J., 12: 47 – 56. Cartilage: Schaefer et al. Tissue-engineered composites for the repair of large osteochondral defects. (2002) Arthrit Rheum 46(9): 2524-2534 Cell sourcing • Ideally autologous • Stem cells – Adult – Embryonic • ‘Immunoprivileged’ • Potentially could differentiate into a wide variety of cell types (Ungrin, M. and Zandstra, P. TERMIS, NA 2007) • Potentially teratogenic/carcinogenic • Ethically, legally and financially questionable www.udel.edu • Difficulties in isolating cells from diseased tissue Environment • Growth factors • Directing cellular activity • Bioreactors • Designed to expose cells to physical stimuli and/or maintain desired conditions • Examples – Bladder urothelium: cyclic strain – Vascular graft: pulsatile flow www.tissuegrowth.com ITEMS Bioreactor: Six Station Vascular Bioreactor Bladder: Kerr et al. The bladder as a bioreactor: urothelium production and secretion of growth hormone into urine.(1998) Nature Biotechnology 16(1):75-9 Vascular: Engbers-Buijtenhuijs et al. Biological characterisation of vascular grafts cultured in a bioreactor. (2006) Biomaterials. 27(11):2390-7 Applications for TE • In surgery • Transplantation of failing tissues/organs • Aiding tissues in the healing process • In the laboratory • Observing immunological, pathological and healing changes in human tissue without harming patients • Drug therapies: efficacy and side effects of drugs Current TE models • Skin – collagen matrix seeded with fibroblasts or keratinocytes Myskin™ http://www.cbte.group.shef.ac.uk/research/ http://www.myskin-info.com/index.php Current TE models • Vascular – small diameter vessels Decellularised Porcine Ureter Mr Chris Derham Current TE models • Heart valves - decellularised http://www.biomed.metu.edu.tr/courses/ www.chir.unizh.ch/ Current TE models •Urethra Atala et al. A novel inert collagen matrix for hypospadias repair. (1999) J Urol. 162(3 pt 2):1148-1151 Current TE models • Bladder Construction of engineered bladder Scaffold seeded with cells (A) and engineered bladder anastamosed to native bladder with running 4–0 polyglycolic sutures (B). Implant covered with fibrin glue and omentum (C). Atala et al. Tissue-engineered autologous bladders for patients needing cystoplasty. (2006) Lancet. 367(9518):1241-6 Current TE models • Kidney Lanza et al. Generation of histocompatible tissues using nuclear transplantation. (2002) Nat Biotechnol. 20(7):689-696. Current TE models • Cartilage Foetal lamb tracheal defects Fuchs et al. Fetal tracheal augmentation with cartilage engineered from bone marrow–derived mesenchymal progenitor cells. (2003) J Pediatr Surg 38: 984–987 news.bbc.co.uk Challenges • Unforeseen hurdles in the creation of multicellular constructs In the laboratory •Supply of nutrients •Removal of waste •Size •Mechanical stability In the patient •Availability •Evidence of efficacy •Safety; graft rejection •Cost Example: Vascular TE • Large diameter grafts (>6mm lumen) – There is already a viable synthetic alternative • Small diameter (<6mm) • PTFE/ePTFE used in large diameter vessels is unsuitable here • Low velocity blood flow in small diameter vessels → thrombus formation • Need confluent endothelium Vascular TE • Availability • Autologous cells needs previous banking • Not useful in emergencies • How do we predict the onset of disease? • Correct choice of animal model to simulate the human body • Benefits over conventional means must outweigh costs The future of TE • Some tissues already in clinical use • Improvements needed to increase availability and safety • For widespread use, reduced cost is essential • Further work should focus on: • vascularisation of new tissue; maintaining nutrient supply to cells in matrix with increasing size • Achieving full potential of stem cells to differentiate into desired cell types Funding for TE • TE has grown considerably since it’s birth • Regulations are comparatively new • Better coordination is required to direct new funding appropriately (Hunziker, R. TERMIS, NA 2007) My Work • • • • • Creation of collagen matrices Containing fibroblasts Seeded with endothelial cells Incorporation of fibrin Novel imaging techniques of tissueengineered constructs • Challenges occur at the most basic level Summary • Tissue Engineering aims to fill the gaps left by conventional methods of tissue sourcing • The tissue engineering triad: – Scaffold – Cells – Optimum growth conditions • Further work is needed regarding biological composition and practicalities of widespread clinical use Acknowledgements • • • • Mr Chris Derham Stacy-Paul Wilshaw Professor Eileen Ingham Professor Shervanthi HomerVanniasinkam Thank you Any Questions?