Topic 4: Scaffolds in Cellular Systems Engineering
Topic 4: Scaffolds in Cellular Systems Engineering (BME 3303)
Aim
Understand the use and importance of scaffolds in tissue engineering.
Explore the desired properties of scaffolds.
Identify different types of scaffolds.
Scaffolds
Critical Role in Tissue Engineering
Direct the growth of cells, including seeded and migrating cells.
Essential for maintaining mammalian cell growth, as cells are anchorage dependent and require an adhesion substrate, typically provided by scaffold matrices.
Cell Delivery
Scaffolds facilitate high loading and efficient delivery of cells to specific sites.
Diagram Overview
Implantation Process:
Patient receives 3D scaffold containing growth factors and cells.
Growth factors stimulate tissue development through cell isolation and expansion processes.
Scaffolds in Tissue Engineering
Approaches to Scaffold Fabrication:
Top-Down Approach:
Begins with bulk material, which is processed into scaffold structures.
Bottom-Up Approach:
Constructs scaffolds from molecular or cellular components assembled into larger structures.
Material Types:
Biological materials are frequently used to create various scaffold designs including porous scaffolds and 3D printed options.
Types of Scaffolds:
Porous Scaffolds: Facilitate cell migration and nutrient flow.
Bio-printed Scaffolds: Create precise cellular arrangements using bioprinting technologies.
Advantages and Disadvantages
Cell/Molecule-Laden Scaffolds:
Advantages: Offer proper spatial arrangement of cells and mimic the extracellular matrix (ECM) effectively.
Disadvantages: Present lower mechanical properties and slower fabrication speeds compared to other methods.
Desired Properties of Scaffolds
Functional Requirements:
Support and Delivery: Should support and facilitate the delivery of cells.
Tissue Growth Induction: Need to induce, differentiate, and channel tissue growth efficiently.
Cell Adhesion Substrates: Should target specific cellular adhesion substrates to enhance attachment.
Cellular Response Stimulation: Must stimulate appropriate cellular responses.
Material Properties:
Biocompatibility: Should be biocompatible and biodegradable.
Surface-to-Volume Ratio: Ideally, possess a large surface-to-volume ratio for maximized cell interaction.
Mechanical Strength: Must be mechanically strong and structurally stable.
Processable and Malleable: Easy to process and mold into desired shapes.
Sterilizability: Should be capable of sterilization before implantation.
Constructive Remodeling of Functional Tissue Engineered Scaffolds
Key Processes Involved:
Scaffold Degradation: Necessary for natural tissue integration.
Cellular Dynamics: Must allow for cell adhesion, migration, proliferation, and differentiation.
3D Organization: Vital for establishing proper tissue structure at the implant site.
Vascularization: Essential to nourish the tissue with blood supply.
Influential Factors:
Blood supply, pH, oxygen concentration, mechanical stresses, and interactions between the host and the surface of the scaffold significantly control these processes.
Materials for Scaffolds
Natural and Synthetic Polymers: Include the extracellular matrix, natural polymers (like collagen), and synthetic polymers.
Types of Scaffolds
Extracellular Matrix (ECM):
Varied structures (bone, ligaments, tendons, vessels, connective tissues, skin).
Functions:
Provides adhesion, mechanical support, facilitates migration and proliferation, and plays roles in signaling.
Disease Associations:
Related to conditions such as arthritis, atherosclerosis, cancer, and muscular dystrophy.
Specific Functions of ECM:
Cell Anchorage: Provides physical supports for cells.
Cell Orientation and Growth: Aids biological processes essential for tissue development.
Mechanical Integrity: Maintains tissue structure and functionality.
Enviromental Regulation: Contributes to the microenvironment critical for cell differentiation.
Storage of Regulatory Proteins: Sequesters growth factors and other proteins crucial for tissue formation.
Composition of ECM
Three major types of molecules:
Structural Proteins:
Collagen: Most abundant protein in the body, varying types (I to V), location-specific functions (e.g., Type I in bone, Type II in cartilage).
Elastin and Fibrillin: Important in tissues that require elasticity, stretching, and structural integrity.
Specialized Proteins:
Fibronectin: Facilitates cell attachment through the RGD amino acid sequence that binds to integrins.
Laminin: Involved in cell migration, attachment, and overall tissue organization through integrin binding.
Glycosaminoglycans (GAGs) & Proteoglycans:
GAGs: Long polysaccharides that impart viscosity and biological functions.
Proteoglycans: Composed of GAGs linked to proteins, providing support and property of hydrogels within the ECM.
Examples: Hyaluronic acid, heparin sulfate, chondroitin sulfate, keratin sulfate.
ECM in Tissue Engineering
Utilization:
Harvested ECM is applied in various tissue engineering applications.
Decellularized Scaffolds:
Allogenic or xenogenic ECMs are used because they are well tolerated by the human host.
Decellularization eliminates cellular antigens that could trigger inflammatory responses.
Allows for ready-to-use scaffolds that can be patient-specific with autologous cells seeded prior to implantation.
Goals of Decellularization
Objectives:
Remove all cellular and nuclear components while preserving ECM composition and mechanical and biological properties.
Commercial ECM-Based Products
GraftJacket:
A human dermal collagen matrix that provides supportive reinforcement for tendon and ligament tissues, particularly in foot, ankle, and hand surgeries.
TissueMend:
Fetal bovine skin used for musculotendinous defects.
Zimmer Collagen Repair Patch:
An acellular scaffold made from porcine dermal tissue.
Permacol:
A decellularized and crosslinked porcine dermal collagen implant.
Types of Polymers in Scaffolds
1. Natural Polymers
Derived From: Renewable resources such as plants, animals, and microorganisms.
Properties:
Pseudoplastic behavior, gelation ability, water binding, biodegradability.
Contain functional groups for chemical modifications, facilitating biomolecular conjugation.
Uses: Widely utilized in tissue engineering efforts including vessel, cartilage, and skin regeneration.
Limitations:
Susceptible to degradation by enzymes and possible immune response due to impurities.
2. Synthetic Polymers
Advantages:
Offer uniformity in chemical and mechanical properties, are toxin-free, and can be designed for specific applications.
Examples of Biodegradable Polymers:
Poly(lactic acid), poly(glycolic acid), and poly(caprolactone) which degrade through hydrolysis.
Non-biodegradable Polymers:
Require careful management as they are designed for permanent implants with modifications for safe elimination post-use.
Comparison: Natural versus synthetic polymers:
Natural polymers are obtained directly from biological sources, while synthetic polymers are chemically synthesized and can be adjusted for desired properties, but natural polymers are more variable and difficult to standardize.
Summary
Scaffolds are essential in tissue engineering for directing cell growth and facilitating tissue development.
They possess desired properties that enable successful integration and functionality within the biological environment.
Understanding the various types and properties of scaffolds, including natural and synthetic materials, is crucial for advancing tissue engineering objectives.
Aim
The aim of this topic is to understand the use and importance of scaffolds in tissue engineering, explore the desired properties of scaffolds, and identify different types of scaffolds.
Scaffolds
Scaffolds play a critical role in tissue engineering by directing the growth of cells, including both seeded and migrating cells. They are essential for maintaining mammalian cell growth as cells are anchorage-dependent and require an adhesion substrate, typically provided by scaffold matrices. Additionally, scaffolds facilitate high loading and efficient delivery of cells to specific sites.
Diagram Overview
The implantation process involves a patient receiving a 3D scaffold containing growth factors and cells, with the growth factors stimulating tissue development through cell isolation and expansion processes.
Scaffolds in Tissue Engineering
There are two main approaches to scaffold fabrication: the top-down approach, which begins with bulk material processed into scaffold structures, and the bottom-up approach, where scaffolds are constructed from molecular or cellular components assembled into larger structures. Biological materials are frequently utilized to create various scaffold designs, including porous and 3D printed options. The types of scaffolds include porous scaffolds that facilitate cell migration and nutrient flow, and bio-printed scaffolds that create precise cellular arrangements through bioprinting technologies.
Advantages and Disadvantages
Cell/molecule-laden scaffolds have advantages such as offering proper spatial arrangements of cells and effectively mimicking the extracellular matrix (ECM), but they also present lower mechanical properties and slower fabrication speeds compared to other methods.
Desired Properties of Scaffolds
Several functional requirements are essential for scaffolds, including the ability to support and deliver cells, induce tissue growth, and enhance cell adhesion. Additionally, scaffolds must stimulate appropriate cellular responses.
In terms of material properties, scaffolds should be biocompatible and biodegradable, possess a large surface-to-volume ratio for maximal cell interaction, and be mechanically strong and stable. Furthermore, they should be easy to process and sterilizable before implantation.
Constructive Remodeling of Functional Tissue Engineered Scaffolds
Key processes involved in this area include scaffold degradation, which is necessary for natural tissue integration; cellular dynamics, which must allow for adhesion, migration, proliferation, and differentiation; the establishment of 3D organization critical for tissue structure; and vascularization to nourish the tissue with blood supply. Several influential factors, such as blood supply, pH, oxygen concentration, mechanical stresses, and interactions between the host and scaffold surface, significantly control these processes.
Materials for Scaffolds
Materials used in scaffolds include both natural and synthetic polymers, encapsulating the extracellular matrix and other biological materials.
Types of Scaffolds
Extracellular Matrix (ECM): ECM is characterized by varied structures such as bones, ligaments, tendons, vessels, connective tissues, and skin. Its primary functions include providing adhesion, mechanical support, facilitating cell migration and proliferation, and playing important roles in signaling, with disease associations including arthritis, atherosclerosis, cancer, and muscular dystrophy.
Specific Functions of ECM: ECM assists in cell anchorage, growth orientation, and environmental regulation critical to tissue development while also storing regulatory proteins necessary for tissue formation.
Composition of ECM
The ECM consists of three major types of molecules:
Structural Proteins: This includes collagen, the most abundant protein in the body, and others like elastin and fibrillin that are crucial for elasticity and structural integrity.
Specialized Proteins: Proteins such as fibronectin and laminin are involved in cell attachment and tissue organization.
Glycosaminoglycans (GAGs) & Proteoglycans: These extend the essential biological functions of the ECM, with GAGs imparting viscosity and proteoglycans providing structural support. Examples include hyaluronic acid and chondroitin sulfate.
ECM in Tissue Engineering
The harvested ECM is applied in various tissue engineering applications, notably in decellularized scaffolds. Both allogenic and xenogenic ECMs are used as they are well accepted by the human host, and decellularization removes cellular antigens that could incite inflammatory responses. This process results in ready-to-use scaffolds that can be patient-specific with autologous cells seeded prior to implantation.
Goals of Decellularization
The objectives of decellularization are to remove all cellular and nuclear components while preserving the ECM’s composition and mechanical properties.
Commercial ECM-Based Products
Some examples of ECM-based products include GraftJacket, which is a human dermal collagen matrix for tendon and ligament tissues; TissueMend, which is fetal bovine skin used for musculotendinous defects; the Zimmer Collagen Repair Patch, an acellular scaffold from porcine dermal tissue; and Permacol, a decellularized and crosslinked porcine dermal collagen implant.
Types of Polymers in Scaffolds
Natural Polymers: These are derived from renewable resources and possess properties such as biodegradability and the ability to bind water. They have limitations, including degradation by enzymes.
Synthetic Polymers: Synthetic polymers offer uniformity in properties, are toxin-free, and allow for design specificity. They include biodegradable options such as poly(lactic acid) and poly(glycolic acid), which degrade through hydrolysis. In contrast, non-biodegradable polymers require careful management for use in permanent implants.
Summary
Scaffolds are essential in tissue engineering, directing cell growth and facilitating tissue development. They possess properties that aid in successful integration and functionality within biological environments. Understanding the types and properties of scaffolds, including both natural and synthetic materials, is crucial for advancing tissue engineering objectives.