In-Depth Notes on Advanced Biomaterials and Tissue Engineering

Tissue Engineering Overview

• Interdisciplinary field combining engineering and life sciences to create biological substitutes for tissue and organ restoration.

• Aims to address organ transplantation challenges by regenerating patient's organs.

• There are different needs while looking at this: such as scafholding and surface coating and more

• Applications include: skin for burn victims, nerve repair for paralyzed individuals.

Basic Principles

• Utilizes living cells to repair or regrow damaged tissues or organs.

• Techniques focus on optimizing regeneration processes.

• Regenerative medicine includes tissue engineering and broader strategies for cell/tissue regeneration.

Bioartificial Tissues

• Critical features of biomaterials:

  • Biocompatibility: Must not trigger inflammation or immune responses.

  • Biodegradability: Should break down safely in the body.

  • Design Variability: Must match the biomechanical needs of specific anatomical scenarios.

  • Ensure: adequate cell distribution, matrix formation, and tissue integration. NOT all made of the same material, could be made out of different materials or have different treatments on the finishes.

  • Functionalization: Involves surface modifications to enhance interactions with biological systems, such as promoting cell adhesion or preventing thrombosis.

  • Stem cells are the MOST favorable to use for tissue engineering.

  • By adding Growth factors to material will attract specific type of cells. Could be done if it is made of polymers, on the coating or in the pores

Methodology in Tissue Engineering(Listed out 1→4 )

1. Cell Harvesting: Obtain progenitor cells (e.g., osteoblasts for bones).

2. Cell Seeding: Place cells onto a 3D scaffold.

3. Environment Placement: Introduce cell constructs to environments (in vitro/in vivo) conducive to tissue formation.

4. Implantation: Deliver engineered tissues into the patient to replace damaged areas.

Tools for Tissue Engineering

• Cells: Living tissue components providing function and reparative properties.

• Scaffolds: Structural support for cells, facilitating attachment and growth; ideally biodegradable.

• Help with proliferation of the cell, produce extracellular matrix, and form tissue, the cell needs a carrier and structural support, Changes in pore size, uniformity, where the pores led to. There are many different types of pores.

• Growth Factors: Proteins that signal and enhance cell behaviors like proliferation and differentiation.

Types of Scaffolds

• Material Composition:

  • Polymers: Biodegradable and biocompatible options.

  • Ceramics: Strong and inert options for load-bearing tissues.

  • Natural Biomaterials: Include collagen, gelatin, alginate, etc.

Assessment of Medical Need

• Type of Tissue: Load-bearing tissues need durable scaffolds capable of withstanding stress (e.g., bone, ligaments).

• Can be done by bone vascularized and experience compression and torsion.

• Ligaments are loaded primarily un tension

• Articular cartilage is avascular and experiences compression and shear.

• Extent of Damage: Strategies vary for different tissue types and damage severity.

• involves repairing both a vascularized tissue bone and an avascular tissue and their interface

• repair a non-load bearing bone defects in the skull requires different strategies than those used for regenerating bone in a femur.

  SUMMARY:

  This underscores the importance of tailoring biomaterial choices and cell therapies to the specific mechanical and biological properties of each tissue type.

Tissue Engineering Approaches

1. Scaffold-based: Scaffold without any cells are used to fill a tissue defect- types of scaffold: porous structures, native cells can infiltrate the scaffold from the surrounding tissue. Depending on its location, a variety of cells types can migrate to the scaffold. Advantageous if the migrating cells are the kind required for the regeneration of that specific tissue.

   Biochemical molecules can be attached to/released form the scaffold to encourage cell attachment.

   Scaffolds are used to fill tissue defects, allowing native cells to infiltrate.

2. Cell-based: Cells introduced without scaffolds; success depends on surrounding matrix support.

   Cells can be different levels of development

   -stem cells

   -Differentiated cells

   -Successful when cells are introduced into an area where there is existing matrix to support them introduction of health myocytes into the cells

3. Cell-loaded Scaffolds: Scaffolds preloaded with cells with possible delivery of biological signals.

   • most current methods use these scaffolds biological signals can also be delivered this way

Inflammatory Response Post-Implantation/ Scaffold placing

• Classic wound healing involving bleeding and macrophage activity, leading to granulation and potential scar formation.(could be : Initial bleeding , Hemorrhaging/excessive bleeding, Formation of fibrinous clot. )

• release of biological signals results in clean up(gradual reaporpstion)

  • Challenge: Prevent unwanted scar tissue, fostering functional tissue regeneration.

Cell Sourcing and Classification

1. Autologous: From Patient's own cells, minimizing rejection risk.

   • Do not cause immune response

   • Most often used for tissue engineering

2. Allogenic: From Cells from other individuals of the same species.

3. Syngeneic: From Genetically identical donor cells (e.g., twins).

4. Xenogenic: From Cells from different species.

Stem Cells

• Embryonic Stem Cells: Pluripotent; can differentiate into any cell type.

• Adult Stem Cells: Limited differentiated potential; found in various tissues.(Somatic: multipotent, can form many different cells)

• Trans-differentiation cells: can differentiate into cells that are different from their own lineage, brain stem cells can produce blood cells

• Induced Pluripotent Stem Cells (iPSCs): Adult cells reprogrammed to a pluripotent state.

Cell Bio-preservation Techniques

• Optimum cooling rate: most critical parameter for cryopreservation

• fasting cooling rate possible that would not form intracellular ice

• cooling rate change with cell type

• cell membrane permeability and the cell initial surface to volume ratio predict the optimal cooling rate required to minimize ice crystal formation and maintain cell viability after thawing. This requires careful consideration of the cryoprotectant used and its concentration, as these factors can significantly influence both the cooling dynamics and overall cell survival post-thaw.

• Cryopreservation: Freeze cells for later use; critical cooling rates prevent damage.

• Anhydrobiotic Preservation: Drying cells without freezing.

• Vitrification: Rapidly freezing cells to avoid ice formation.

Scaffold Properties and Fabrication

• Important scaffold properties: biocompatibility, biodegradability, mechanical strength, and porosity for cell growth.

• Fabrication Techniques: Include solvent casting, electrospinning, and solid free form fabrication technologies.

- Alternative methods for cell Bio-Preservation:

• Anhydrobiotic Preservation: Preserve the cells in a dried but not metabolically active state, which allows for long-term storage without compromising cell viability.

• Properties of Scaffolds: Biocompatibility: ability to be removed in vitro, or be biodegradable, Biodegradation/remodeling should be synchronized with tissue regeneration, High permeability to enable diffusion of nutrients for the cell

• Porous to provide the cells space to proliferate and form the extracellular matrix, the pore size should be optimum for the cell in use,

• Mechanical properties similar to surrounding native tissue

• Ability to encourage and promote the formation of extracellular matrix and tissue ingrowth by providing suitable biochemical signals that direct cellular behavior and enhance cell adhesion.

• Polymer Scaffold fabrication: Polymer scaffolds are solid state or hydrogels, choice of scaffolding depends on the function

• Porous solid state scaffolds, Application Bone tissue engineering, Material properties, Solid and stable porous structures, does not melt under in vitro tissue culture condition or when implants in vivo degrade

• Solvent casting and particulate leaching -

• Dissolution of polymer in an organic solvent, mixing porogen particles into the solution

• Removal of the solvent via material

• Removal of the solvent via evaporation

• Immersion of the resulting polymer particle composite in water to dissolve and extract the porogen particles

• Electro-spinning: Dissolution of polymer in an organic solvent

• ejection of the solution through a fine needle

• application of a high voltage between the needle and cell

Measurement Techniques

• Porosity Measurement: Mercury intrusion porosimetry; gravimetry for overall scaffold assessment.

• Pore Size and Permeability: Micro-CT for 3D imaging; fluid flow analysis through scaffolds.

Bioreactors for Enhanced Tissue Engineering

• Static and Dynamic Culturing: Utilizing bioreactors to improve nutrient diffusion and cellular activity.

• Types of Bioreactors:

  • Spinner Flask, Rotating Wall Vessel, Hollow Fiber, Direct Perfusion.

Properties and Evaluations of Cells in Scaffolds

• Assess cell proliferation by microscopy and metabolic assays (e.g., AlamarBlue).

• Immunostaining and mechanical testing assess tissue properties.

Challenges in Tissue Engineering

• Vascularization: Need to regenerate blood supply alongside tissue.

• Scaling Up: Larger scaffolds present diffusion challenges.

• Growth Factors Supply: Timing and delivery method critical for effective tissue regeneration.