Biomaterials Processing Lecture 1

3 Types of Tissues

Epithelia, Basement Membrane and Connective Tissue (Make up almost all organs)

Epithelia

• Epithelial layer covers all surfaces, tubes, and cavities of the body

• Avascular (no blood vessels)

• No significant amount of extracellular matrix (ECM). The ECM is the extracellular part of tissue

• 100% cells

• Can regenerate spontaneously (ex. the epidermis in skin)

Avascular

No blood vessels

Basement Membrane

• Acellular, avascular, continous layer of ECM separates the epithelial layer and the connective tissue

• No cells, no blood vessels, 100% matrix

• Regenerates spontaneously on the connective tissue

Connective Tissue

• Cellular, contains ECM, heavily vascularized, and provides a reservoir for nutrient uptake to and waste removal from basement membrane and epithelia

• Has cells, matrix, and blood vessels

• Has limited ability to regenerate spontaneously (ex. dermis in skin)

Regeneration vs. Repair

• Microscopic defects in connective tissues can regenerate with or without being treated by pharmaceuticals, vitamins, hormones and antibiotics

• Organ-scale defects (large defects, mm or cm-scale) in connective tissues caused by disease or by an acute or chronic insult can’t regenerate

• Adult mammals don’t typically exhibit spontaneous regeneration after severe organ injuries

• Adult mammals undergo repair following severe organ injuries—closure of the wound by cell-mediated contraction and scar tissue formation

Regeneration

The synthesis of a physiological (normal, functional) replacement rissue in the wound site that’s structurally and functionally similar to the original tissue. Some connective tissues have capability to regenerate themselves, like skin, and some can’t effectively regenerate, like the heart. Some connective tissues that can self regenerate can’t effectively regenerate because it takes a long time, is a larg defect, a scar, etc.

Autograft

Tissue harvested from one location of the patient’s body and transplanted into another part of the same patient

Allograft

Tissue or organ harvested from donor and then transplanted into the patient

Xenograft

Tissue or organ from an animal is transplanted into a human recipient

Man-made Implants

Replacement of tissue with implants to replicate, augment and extend functions performed by biologoical systems.

Examples: Artifiical hearts, heart valves, prosthetic joints, and breast implants

Tissue Engineering/Regenerative Medicine

A multidiscipinary field involving the life, physicial and engineering sciences that seeks to develop functional cell, tissue, and organ substitutes to repair, replace or enhance biological function that has been lost due to congenital abnormalities, injury, disease, or aging.

OR

An interdisciplinary field that applies the principles of engineering and the life sciences towards the development of biological substitutes that restore, maintain or improve tissue function.

Tissue Engineering Strategies

(Paper Notes)

• Cells + Biomaterials → Tissue → Implantation

• Cells + Biomaterials → Implantation

• Cells → Implantation

• Biomaterials → Implantation

Tissue Regeneration Elements

• Scaffold: Structural and mechanical support for cells

• Cell: Source, cell type (cells can’t assemble by themselves to become the desired tissue)

• Regulators: Growth factor (regulates cell behavior such as division), mechanical loading (mechanical stimuli; should have similar properties as the native tissue)

Scaffold

The structural and mechanical support for cells (typically are 3D since most tissues are 3D). Must have sufficient mechanical properties for proper support (should have the exact same mechanical properties as the tissue being engineered).

Roles of Scaffolds

1. Serve as a matrix for cell adhesion to facilitate or regulate cellular processes such as growth, migration (most cells need to attach to a matrix in order to survive since they normally adhere to the ECM)

2. Maintain the shape of the defect and prevent distortion of surrounding tissue

3. Serve as a barrier to the surrounding tissue that may impede the process of regeneration

4. Serve as a delivery vehicle for cells, growth factors and genes

5. Facilitate cell-matrix interactions that are involved with tissue regeneration by providing the appropriate sites for cell interaction

6. Growth factors/genes can be loaded into the scaffolds (how they can be used for cells)

Scaffolding Materials

• Inorganic Materials: Ceramics and Bioglass

• Synthetic Polymers (are organic but man-made): Polyesters and Polyurethanes

• Natural Polymers (organic): Collagen, Albumin, Cellulose (most abundant natural polymer’ found in tress), and Chitosan (derived from chitin, 2nd most abundant natural polymer)

Collagen

• Type 1: Most abundant type in the skin and throughout the body

• Type 2: More localized

Ratio between the two vary depending on the tissue

Scaffold Types

• Hydrogel (used because has similar characterisitcs to tissue)

• Decellularized Tissue (gets rid of the risk of an immune response happening → risk is slim)

• Porous scaffold (cells can proliferate, grow, and migrate into other pores

Core Scaffold Properties for Tissue Regeneration

1. Mechanical properties

2. Pore size, pore geometry, and pore size distribution (all three are equally important for the scaffold). The pores should be highly interconnected to allow for easy cell migration.

3. Interconnectivitiy and porosity (% of void space)

4. Cell/scaffold interactions (scaffold surface properties)

5. Controlled release of active molecules

6. Biodegradation (rate, mechanics vs time, cytocompatibility). [Slowly degrades overtime till whole tissue is regenerated, if too fast, leads to gaps, too slow leads to delayed regeneration)