Biomaterials and Tissue Engineering PDF

Biomaterials and Tissue engineering Expected Learning outcomes Understand the basis of tissue engineering Identify the different components of the tissue engineering process Types and functions of each of the components Understand the applications and challenges of tissue engineering Introduction Th...

Biomaterials and Tissue engineering Expected Learning outcomes Understand the basis of tissue engineering Identify the different components of the tissue engineering process Types and functions of each of the components Understand the applications and challenges of tissue engineering Introduction There is a need for effective regenerative treatments due to the rapidly aging population, environmental factors, and growing lifestyle disorders such as stress, obesity & diabetes, and growth in trauma cases Tissue engineering is an interdisciplinary field that applies methods of bioengineering, material science, and life sciences toward the assembly of biologic substitutes that will restore, maintain, and improve tissue functions following damage either by disease or traumatic processes. refers to the practice of combining scaffolds, cells, and biologically active molecules into functional tissues. create functional three-dimensional (3D) tissues combining scaffolds, cells and/or bioactive molecules. The most key application segments of tissue engineering are Cancer Cord blood & cell banking Dental Urology Musculoskeletal Orthopaedics Spine Cardiology & vascular Neurology Biomaterials Biomaterials form an integral component in Tissue Engineering. They are either used for therapeutic or diagnostic purposes. A biomaterial is said to be an ideal one which fulfils the following requirements: injectability synthetic manufacture biocompatibility non-immunogenicity transparency nano-scale fibers low concentration resorption rates Scaffolds Scaffolds are materials engineered for the formation of new functional tissues and used for medical purposes. A scaffold must mimic the ECM by exhibiting the biological, chemical, and mechanical cues that influence cell phenotype and tissue formation. It must recreate the in-vivo environment that is provided by the extracellular matrix. Depending on its origin, Scaffolds are classified into two types. Natural scaffolds take part in the process of morphogenesis and function acquisition of different cell types in the in-vivo environment. The composition of these scaffolds depends on animal origin, isolation and purification procedures, and assays. Synthetic scaffolds are made to mimic specific ECM (Extra Cellular Matrix) properties under controlled conditions. Uses of scaffolds include cell attachment and migration retention of cells and biochemical factors allowance for the diffusion of vital cell products and expressed products modification of the behavior of cell phase by exerting biological and mechanical influences. Scaffolds need to fulfil specific requirements for tissue engineering An adequate pore size with high porosity for facilitating cell seeding and diffusion into the whole structure. Biodegradability The scaffold should provide structural integrity while cells are fabricating their natural matrix structure around themselves. It should break down as soon as the new tissue forms. The degradation has to coincide with the rate of tissue formation. The three types of biomaterials that are used for fabrication of scaffolds are: Ceramics– They have excellent biocompatibility because of their chemical and structural similarity. They constitute high mechanical stiffness and very low elasticity. Examples include- hydroxyapatite (HA) and tri-calcium phosphate (TCP), for bone regeneration applications. Synthetic polymers– They exhibit controlled degradation characteristics and are easy to be fabricated with a tailored architecture. These include- polystyrene, poly-l-lactic acid (PLLA), polyglycolic acid (PGA) and poly-dl-lactic-co-glycolic acid (PLGA). Natural polymers– They are biologically active and allow host cells to produce their own extracellular matrix and replace the degraded scaffold. Biomaterials of human origin are frequently used as therapeutics in medicine or as potential building blocks From tissue/organ transplantation to the use of either naturally occurring biopolymers or biomimetic materials are used in tissue engineering and regenerative medicine. ECM, extracellular matrix; GAGs, glycosaminoglycans; HA, hyaluronic acid; HS, heparin sulfate; CS, chondroitin sulfate; PRP, platelet-rich plasma; PRF, platelet-rich fibrin; PL, platelet lysate; BMC, bone marrow concentrate; SVF, stromal vascular fraction PCL –polycaprolactone , PLA- Poly Lactic Acid, PGA- polyglycolic acid, PLGA- poly ( lactic –co- glycolic)acid. Biomaterials Schematic representation of pivotal factors (structural, mechanical, biochemical and biological) involved in the design of biomaterials for tissue engineering that coax cells to behave in the same or a similar manner as their natural in vivo counterparts Crosstalk between stem cells and niche cells is mediated by soluble ECM growth factors and the properties of the surrounding ECM The design of new advance biomaterials must consider these functions of the native ECM to mimic the natural environment/ to regulate stem cell fate decisions Through cell membrane, growth factor receptors and a complex signal transduction network, instructions are conveyed to the stem cells, resulting in specific biological cellular responses and functionalities, such as cell differentiation and gene expression. The ECM also affects cells via its architecture and overall biological and mechanical properties Soluble and matrix-binding factors combine with cell–matrix adhesion, cell–cell contact and signalling gradients to determine and control the most fundamental behaviours and characteristics of stem cells, including polarity, adhesion, anchorage, proliferation, migration, differentiation and apoptosis. Schematic representation of the extracellular matrix (ECM) functions and crosstalk at the cell–cell and cell–matrix interfaces. Schematic representation of tissue-specific stem cell niches and their cellular and extracellular matrix (ECM) components. (A) Hematopoietic stem cell (HSC) niche; (B) hair follicle stem cell niche; (C) satellite cell niche; and (D) neural stem cell niche (SVZ). Decellularized matrices from tissues (e.g., small intestinal submucosa (SIS)) or organs (e.g., kidney, heart and liver)that have native-like extracellular matrix (ECM) microstructures, compositions and biomechanical properties. These decellularized ECMs may maintain the shapes of the original tissues and organs when used as scaffolding materials in tissue engineering approaches for new tissue/organ regeneration. Decellularized matrices derived from tissues and organs can be made into different types, such as a patch or particle, for tissue engineering scaffolding biomaterials or can be designed as an injectable gel for cell culture substrates The production of extracellular matrix (ECM) products for targeted biomedical use is influenced by many factors – the properties of the donor tissue or organ (e.g., tissue type, architecture, cellularity and dimension), the method, agent and protocol for decellularization (e.g., chemical, enzymatic and physical treatments) and the desired biological and geometric properties of the post-processed product. Every cell decellularization treatment will alter the ECM composition, damage the biochemical features and disrupt the native ultrastructure and architecture to some degree; the selection of an appropriate strategy for the decellularization of a particular tissue/organ for a target application is important to minimize these undesirable effects. Uptake of growth factors or other therapeutic agents via biomaterials engineering (A) adsorption or embedding. (B) Non-covalent immobilization (e.g., forming ionic complexes with the polymer backbone). (C) Covalent immobilization (e.g., tethering of cues to the polymer chains by linking via cleavable bonds). (D) Pre-encapsulation into a well-defined particulate system. Schematic representation of the distinct and crucial challenges related to the production and application of extracellular matrix (ECM)-based biomaterials in regenerative medicine and tissue engineering Preparation of human-derived bone marrow concentrate (BMC) for cell therapy and tissue engineering applications. BMC is a rich source of the regenerative cells needed for bone formation and angiogenesis, including The use of BMC offers the potential to bridge the gap between stem cells and signalling factors in a traditional tissue engineering triad. The SVF is the product of a lipoaspirate, which is obtained from liposuction of excess adipose tissue. The SVF contains a large population of mature cells, progenitors and stem cells. Adipose-derived stem cells (ASCs) share many similarities with bone marrow-derived stem cells, including self-renewal and multilineage differentiation capacity. Mesenchymal stem cells (MSCs, which convert to osteoblasts in support of new bone formation), Hematopoietic stem cells (HSCs, which orchestrate bone formation) and Endothelial progenitor cells (EPCs, which stimulate angiogenesis). In addition, BMC includes platelets, which mediate cell-to-cell adhesion via the release of multiple growth factors; Lymphocytes, which support the migration and proliferation of EPCs; and granulocytes, which release vascular endothelial growth factors (VEGFs) in support of angiogenesis. Schematic representation of several cell culture methods frequently used for the preparation of cell-formed decellularized extracellular matrices (ECMs) that satisfy specific application needs Use of decellularized tissue (organ) as a tissue engineering biomaterial Decellularized tissue (organ) is obtained by the decellularization of living tissue (organ). The resulting cell-free ECM can be modified (e.g., by heparin crosslinking and growth factor binding) before implantation. The ECM scaffold is reseeded with ex vivo-cultured cells that “prime” the biomaterial (e.g., to enhance its ability in vascularization or remodeling) and/or “get primed” toward a specific cell fate decision (e.g., to proliferate or differentiate). Such a cell–matrix construct induce tissue regeneration by the combined action of seeded and recruited cells in a functionalized native matrix. Modified ECM can be directly transplanted into a patient without cell seeding. In this case, tissue regeneration entirely relies on the capacity of the ECM material to instruct resident cells toward target recruitment, specific differentiation and subsequent tissue formation (endogenous tissue regeneration). Schematic representation of tissue grafts and organs of human origin for clinical therapeutics Autologous tissue grafts include soft tissues, such as free gingival grafts; fat, fascial, skin (partial-thickness or full-thickness) and myocutaneous flaps; and bone grafts, including block bone and cancellous bone. Allogenic tissues for transplantation include corneal grafts; skin grafts; and certain composite (organ-level) tissues, such as a full hand or a near-total face transplant. In addition, organ allotransplantation is often performed for the kidney, liver, lung and heart, among others. Bone grafting materials and dentin matrix can be produced from the bone and teeth of human cadavers. Cells Source – is important for tissue engineering. Stem cells ( Embryonic or Adult Stem Cells) have emerged as promising alternative cell sources. ASC’s are more appropriate for Tissue Engineering as they have a more limited capacity to differentiate than ESCs. Biomolecules– Signalling molecules are much as important as the scaffolds and cell source. These signals are unique to each organ and are tightly controlled. The presence of factors such as growth factors, chemokines, and cytokines play an important role in biological phenomena. The use of the signalling molecules can be in two ways (1) addition to the culture media in-vitro or (2) attachment to the scaffold by covalent and non-covalent interactions. Regenerative Medicine repair damaged tissues and organs. They stimulate the body’s own repair mechanisms to heal previously irreparable tissues or organs. If the body cannot heal itself, the tissues or organs can be grown in the laboratory and then implanted. Regenerative Medicine involves the use of stem cells or progenitor cells obtained through directed differentiation. The process begins with the creation of scaffolds and introducing cells into it. A tissue develops once it gets the right environment. In some cases, self-assembly occurs which involves the mixing of all the cells, scaffolds, and growth factors together. The applications of Tissue Engineering have been helpful in overcoming problems of damaged tissues Bone Tissue Engineering- Bones are composed of collagen and have the property to regenerate, repair in response to an injury. Bone graft is required for large bone defects occurring after trauma, infection, tumour resection or skeletal abnormalities. Producing the features of bones in-vitro is very challenging. So, to obtain an ideal scaffold for bone tissue regeneration is also difficult. 3D porous scaffolds with similar composition to the bone and, for better compatibility are developed. Bio ceramic scaffolds are used. The osteo-inducive scaffolds make use of biomolecular signalling and progenitor cells for new bone formation. In the bone defect models, the nanoparticles designed for the release of osteogenic factors showed increased in-vitro and in-vivo osteogenic differentiation. Cartilage tissue engineering- Cartilage is a connective tissue found in elbows, knees, and ankles. Several scaffolds have been used for cartilage repair but, the most relevant are the synthetic scaffolds like polyurethane, Poly (Ethylene Glycol) (PEG), elastin-based polymers. Cartilage is composed of chondrocytes so, an ideal donor cell type for cartilage repair is autologous chondrocytes. They are difficult to obtain and require invasive techniques. Mesenchymal Stem Cells (MSCs) collected from different sources, such as adipose tissue or bone marrow have been used as an alternative source. They can be easily cultured in-vitro and have the ability to proliferate and differentiate towards osteogenic, adipogenic, chondrogenic and myogenic lineages. Certain other TE applications include cardiac tissue engineering, pancreas tissue engineering, vascular tissue engineering In-Vitro Human Models for Tissue Engineering Creation of In-Vitro Human Models for Tissue Engineering is another application to analyse the role of different chemical, mechanical and/or physical factors in a simple system. Cancer- To recreate the process of tumor progression, an accurate modelling of tumour microenvironment is required. This is possible through 3D cultures that can provide the micro-environmental conditions that control tumorigenesis. The 3D cultures are based on combining cells, scaffolds, and biomolecules. Both natural and synthetic biomaterials have been used to model cancer. Drug Discovery- For effective drug screening, 3D cultures are introduced to analyse the effect of drug action. Hepatocytes regained their morphology and expression of key-liver proteins when cultured in 3D culture. Tissue Engineering is expensive. Allografts and transplants face risks of getting rejected by the patient’s system. However, advances in areas of bone, cartilage, heart, pancreas, and vasculature have taken tissue Engineering to a new level. Functional Biomaterials for Tissue Engineering The design and development of multifunctional smart biomaterials compatible to human physiology is crucial to achieve the required biological function with a reduced negative biological response. Several medical bioimplants have been tested to boost life expectancy and better-quality life. The concept of biocompatibility focuses on body acceptance and no harmful effects after implantation, which require modulating the properties of materials during synthesis, surface functionalization, and bio-functionality. Such developed bioactive and biodegradable materials including bio-mimic materials, biomaterials, self-assembly biomaterials, bioprinting functional hydrogels and hybrid synthetic–natural hydrogels have been utilized to achieve the required function at a specific period and sustainability ; to withstand the surrounding tissues; for treating severe injuries and diseases. The greatest challenges facing the field of organ transplantation are a shortage of organs, the lack of available organ donors, high cost of transplantation, and morbidity and mortality of consequent life-long immunosuppression. Tissue engineering (TE) has opened a new window of opportunity for supplying organ substitutes. Highly specialized structures with the well-interconnected network should be maintained by newly designed tissueengineered constructs. The basic type of biomaterials can be synthetic polymers, such as polyanhydrides, and naturally occurring polymers, such as complex sugars (hyaluronan and chitosan), and other inorganics (hydroxyapatite). They are also classified based on functions such as hydrogels, injectables , capable of drug delivery, surface modified, and by other specific features. The successful outcome of organs made from tissue engineering principally depends on delivery of sufficient nutrients, especially oxygen to cells for the initial period of the formation of microvasculature in the construct. Without proper mimicking of highly organized architectures of tissues and organs, channelizing an adequate amount of nutrient transfer, oxygen transport, and other biological function can be critical. An emerging approach is using 3D scaffolds made from oxygen-generating biomaterials to tackle transport limitations deep within the engineered tissues. This class of biomaterials address the challenges associated with ischemia occurring within large tissue constructs. Hence, advance biomaterials are important in the emerging role of tissue engineering (TE), and it is mandatory to have deep knowledge about the targeted site. Strategies of various bioengineering techniques for generating functionally mature organoids Since organoids produced by conventional culture methods are not functionally mature, a variety of bioengineering approaches have been considered for improving the functional maturation of organoids. On-chip technology and 3D printing technology can provide 3D microenvironments for organoids that mimic the in vivo environment. Microfluidic chip technology enables spatial and temporal control of soluble or insoluble factors, gradient generation, and microenvironmental effects, resulting in regulated organoid morphogenesis and development. Bioreactors, which provide media flow to facilitate nutrient and oxygen absorption, can create organoids that exhibit more homogeneous characteristics. Using co-culture systems with supporting cell types and functional biomaterials for enhanced stem cell differentiation, organoids can be further differentiated into more mature phenotypes. Co-culture systems with stromal cell types, such as endothelial cells, immune cells, and peripheral nerve cells as well as functional biomaterials and physiological stimulation that provide an in vivo-like environment to organoids can boost the development of in vitro organoid systems, enabling them to be similar to in vivo organ systems. Strategies of various bioengineering techniques for generating functionally mature organoids Challenges of TE Body tissues possess a highly organized structure and unique composition that help in providing mechanical and transport support to regulate biological and cellular function. Owing to tissue injury, disease, malfunctioning, or aging, there is a need for natural biodegradable, and biocompatible materials that can be mimicked to actual tissue architecture and structural organization. These tissue-engineered constructs can be helpful in restoring and repairing malfunctioned tissues and organs. It is also challenging to incorporate these bioengineered materials due to limitations of onsite target and side effects such as cell toxicity, interfering with immune systems, and transporting mechanisms. Also, designing and developing a system based on biological features such as mechanical stress at the targeted site, strength, complex viscoelastic, nonlinear, and anisotropic mechanical features have constantly been an area of consideration. Salient features of biomaterials required for TE (A) combination of biomaterials, cell, and growth factors (signaling) associated with tissue engineering (B) integration of smart biomaterials with specific salient features, which facilitate osteo function and regulation. Challenges of TE The TE involving human stem cells along with various approaches for bio-scaffold generation offers new avenues for basic research in the field of biology, physiology, HTS (high-throughput screening) for the pharmaceutical industry, pharmacokinetics and others as well. There exists clinically successful implantations of acellular bio-scaffold with host cell growth. Significant challenges in vivo applications are the low survival rate of the donors or autologous cells in vivo that are initially grown in tissue culture, and improper vascularisation of the implanted tissue/organ. The use of acellular scaffolds, providing shelter to host cells has expanded the clinical application of TE many folds. The 3D printing of scaffolds with desired cells for tissue preparation has advanced the construction of biomimetic living tissues. A very balanced and keen optimization and evaluation of various newer techniques along with ethical considerations are required to promote its potential clinical applications. The primary clinical obstacles relate to problems with the transfer of living cells from the culture conditions into the human body; this applies to many isolated cells; tissue constructs and artificially engineered organs. Additionally, the vascularisation of implanted tissues/organs is very challenging. While the rapid and creative advances in tissue bioengineering hold great promise for the future of regenerative medicine, balanced and critical evaluation of these new technologies is required for potential clinical applications. Tissue Engineering Strategies for Organ Development Source and isolation of stem cells/cells, usually autologous. 3D scaffolds, where oxygen-generating biomaterials may enhance the formation of the microvasculature. Growth factors, peptides, or stimulation to enhance cell proliferation and integration to the surrounding tissue. Constructs can be placed in bioreactors in vitro or inside patients in vivo prior to transplantation Any Questions ?