Cell and Tissue Engineering #1

Tissue

A group of similar cells, along with their extracellular matrix (ECM), that work together to perform a specific biological function.

: A tissue is composed of similar cells and the __________ __________ that supports and surrounds them.

Extracellular matrix (ECM)

Different tissues are specialized to perform specific functions in the body. (T/F)

True

Why is the extracellular matrix (ECM) considered a critical part of a tissue in tissue engineering?

Because the ECM provides structural support and biochemical cues that regulate cell behavior such as adhesion, migration, proliferation, and differentiation.

Extracellular Matrix (ECM)

A complex, non-cellular network of proteins and polysaccharides surrounding cells that provides structural support and biochemical signals regulating cell behavior.

A non-cellular network of proteins and polysaccharides that surrounds cells and regulates their behavior.

Extracellular matrix

Why is the extracellular matrix critical in tissue engineering?

Because it controls cell adhesion, migration, proliferation, and differentiation, guiding tissue formation and function.

Is the extracellular matrix considered living tissue?

No — it is non-cellular, but it is biologically active and essential for tissue function.

What happens to a tissue with increased extracellular matrix (ECM) content?

The tissue generally becomes stiffer, less cellular, and more load-bearing, with altered cell signaling.

Does more ECM mean more cells?

No — more ECM usually means fewer cells per volume.

As ECM content increases, tissue stiffness __________ and cell density typically __________.

Increases; decreases

Tissue-Engineered Medical Products (TEMPs)

Medical products that use cells, scaffolds, and/or biologically active molecules to repair, replace, or regenerate damaged tissues or organs.

Tissue-engineered medical products typically involve __________, __________, and signaling molecules.

Cells; scaffolds

Are TEMPs the same as medical devices?

No — TEMPs often involve living cells and biological function, not just hardware.

Goal of Tissue Engineering

To restore, maintain, or improve tissue function by combining cells, biomaterials, and biological cues to regenerate functional tissue.

The primary goal of tissue engineering is to restore __________, not just tissue __________.

Function; structure

Biomaterial

A natural or synthetic material designed to interact with biological systems for medical purposes, such as tissue repair, replacement, or regeneration.

A biomaterial may be __________ or __________ and is used to interact with biological systems.

Natural; synthetic

Biomaterials must be biocompatible to be used safely in the body.

True

Name three common classes of biomaterials.

Polymers; ceramics; metals (also acceptable: composites)

What role do biomaterials play in tissue engineering?

They act as scaffolds that support cells and provide mechanical and biochemical cues.

Autologous

Originating from the same individual who will receive the treatment.

Allogeneic

Derived from a different individual of the same species as the recipient.

Allogeneic cells come from a __________ donor of the same __________.

Different; species

Xenogeneic

Derived from a different species than the recipient.

Why are xenogeneic materials sometimes used in tissue engineering?

They are readily available and can be processed (e.g., decellularized) to reduce immune response.

How are biomaterials different from Tissue-Engineered Medical Products (TEMPs)?

Biomaterials are materials that interact with tissue, while TEMPs are biological products that use cells ± biomaterials to regenerate tissue function.

How are donor organs different from Tissue-Engineered Medical Products (TEMPs)?

Donor organs are fully formed tissues taken from a human donor, while TEMPs are engineered constructs designed to regenerate or restore tissue function.

What are the main types of TEMPs?

Cell-based, scaffold-based, and cell-scaffold combined products.

Hybrid biomaterials

Biomaterials that combine two or more material types (e.g., natural + synthetic) to achieve improved biological and mechanical performance.

Give an example of a hybrid biomaterial.

Collagen–polymer composite scaffold (e.g., collagen + PLA).

Chemical and Mechanical Stimulation

External biochemical signals and physical forces applied to cells or tissues to regulate cell behavior and promote tissue development.

Cell sources

The origin of cells used in tissue engineering, defined by where the cells come from and their biological characteristics.

Common cell sources in tissue engineering include __________, __________, and __________ cells.

Autologous; allogeneic; xenogeneic

Heart transplant

Donor organ transplantation

Titanium hip replacement

Biomaterial / medical device

Injection of stem cells into damaged heart tissue

Cell-based TEMP

Acellular biodegradable scaffold implanted to promote tissue regrowth

Scaffold-based TEMP

Skin substitute with living cells seeded on a scaffold

Cell–scaffold combined TEMP

Drug therapy to reduce inflammation

Medical (pharmacological) treatment

Why is a skin graft with living cells considered a TEMP but a metal implant is not?

Because TEMPs involve biological regeneration, while metal implants are passive replacements.

Integrins

Transmembrane proteins that connect cells to the ECM and transmit signals.

Collagen

Primary structural protein in the ECM providing tensile strength. (Example: Tendon, Bone)

Elastin

ECM protein that allows tissues to stretch and recoil.

Glycosaminoglycans (GAGs)

Long, negatively charged polysaccharides that retain water.

Proteoglycans

Core protein with attached GAG chains that resist compression.

Hyaluronic Acid

Non-sulfated GAG involved in lubrication and hydration.

Fibronectin

ECM glycoprotein involved in cell adhesion and migration.

Laminin

ECM protein in the basal lamina that supports epithelial cells.

Tissue Dynamics

Continuous changes in tissue structure and function over time.

Tissue Homeostasis

Maintenance of stable tissue structure and function.

Tissue Development

Process by which tissues form during growth and maturation.

Tissue Repair

Restoration of tissue after injury.

Fate Processes

Cellular decisions determining survival, death, or function.

Adhesion

Attachment of cells to other cells or ECM.

Proliferation

Increase in cell number through division.

Migration

Directed movement of cells through tissue or ECM.

Differentiation

Process by which cells become specialized.

Apoptosis

Programmed cell death

Soluble

Able to dissolve in fluid.

Insoluble

Not dissolved; structural components.

Epithelial Cells

Cells that line surfaces and form barriers.

Apical

Surface of epithelial cells facing the lumen or outside.

Basal

Surface of epithelial cells attached to basal lamina.

Mesenchymal Cells

Migratory, multipotent cells that form connective tissues.

Basal Lamina

Thin ECM layer supporting epithelial cells.

Connective Tissue

Tissue that supports, binds, or protects other tissues.

Epithelial Tissue

Tissue that covers surfaces and lines cavities.

Cell fate processes

biological mechanisms that guide how an unspecialized cell becomes a specific, functional cell type during development.

Differentiation

The process by which a cell develops specialized structure and function.

Proliferation

The process by which cells divide and increase in number.

Migration

The movement of cells from one location to another during development.

Apoptosis

Programmed cell death that removes unnecessary or damaged cells and helps shape developing tissues.

Integrins

Transmembrane proteins that connect cells to the extracellular matrix and help transmit mechanical and chemical signals.

Cadherins

Calcium‑dependent adhesion proteins that help cells stick to each other in tissues.

Desmosome

A strong cell–cell junction that anchors intermediate filaments and resists mechanical stress.

Hemidesmosome

A junction that anchors cells to the extracellular matrix rather than to other cells.

Actin filaments

Thin cytoskeletal fibers involved in cell shape, movement, and muscle contraction.

Intermediate filaments

Cytoskeletal fibers that provide mechanical strength and structural stability

Genotype vs Phenotype

Genotype = genetic makeup; Phenotype = observable traits resulting from genes + environment.

Transdifferentiation

Direct conversion of one differentiated cell type into another without going through a stem‑cell state.

Gene expression

The process of using DNA information to produce RNA and proteins.

Transcription

The synthesis of RNA from a DNA template.

Translation

The process of building a protein from an mRNA sequence.

RNA polymerase

The enzyme that synthesizes RNA during transcription.

General transcription factors

Proteins required for RNA polymerase to bind the promoter and start transcription.

Promoter

A DNA sequence where transcription begins and RNA polymerase binds.

RNA‑seq

A technique that sequences all RNA in a cell to measure gene expression.

Housekeeping gene

A gene expressed in all cells because it performs essential basic functions.

Transcription regulators: activators vs repressors

Activators increase gene expression; repressors decrease it.

cis‑regulatory sequences (operator)

DNA regions that control transcription by binding regulatory proteins.

Induced pluripotent stem cells (iPS cells)

Adult cells reprogrammed to a pluripotent, embryonic‑like state.

Cell memory

The ability of cells to maintain their identity through stable gene expression patterns.

Autonomous specification

Cell fate determined by internal factors inherited during division.

Conditional specification

Cell fate determined by signals from neighboring cells.

Lamellipodia

Sheet‑like actin‑rich protrusions used for cell movement.

Focal adhesion

Sites where cells attach to the extracellular matrix and transmit mechanical signals.

Myosin motors

Motor proteins that move along actin filaments to generate force

Mitosis

The process of dividing a cell’s nucleus to produce two genetically identical daughter cells.

Meiosis

A type of cell division that produces four genetically diverse haploid cells for sexual reproduction.