Tissue Engineering Notes

Tissue engineering is an interdisciplinary field using engineering and life science principles.
It develops biological substitutes to restore, maintain, or improve tissue functions.
Often involves in vitro cultivation of tissues for therapeutic or research purposes.

Applies biology and engineering principles to develop functional substitutes for damaged tissue.
The TE triad: cells, scaffold, and signals.
Multidisciplinary fields combining biology, chemistry, engineering, medicine, and material science.

Key component for successful tissue engineering.
Used to create or replace new tissue.
Can be used alone or with support matrices.
Cell Source Considerations:
- Adequate environment crucial.
- Cell manipulation creates new avenues.
- Scaffold design influences environment.

Artificial 3D structures mimicking extracellular matrix.
Provide support for cell attachment, growth, and tissue formation.
Key Characteristics:
- Biocompatible and biodegradable.
- Highly porous with interconnected network.
- Suitable surface chemistry.
- Mechanical properties matching target tissue.
Fabrication Techniques:
- Lyophilization, freeze casting, gas foaming.
- Solvent casting, compression molding.
- 3D printing, electrospinning.
Considerations:
- Cell distribution and penetration.
- Degradation rate matching tissue growth.
- Incorporation of growth factors or bioactive cues.

Definition: Bioactive molecules regulating cellular processes.
Types of signals:
- Soluble factors: Growth factors, hormones, small molecules.
- Insoluble cues: ECM stiffness, mechanical stimulation, fluid flow.
Key growth factors:
- VEGF, FGF: Promote endothelial cell migration and proliferation.
- PDGF-BB: Stimulates pericyte adhesion and blood vessel maturation.
- BMP-2: Induces bone formation.
- TGF-β: Regulates cell growth and differentiation.
Challenges:
- Short half-life and rapid inactivation.
- Need for controlled delivery.

The scientists created an ear-like scaffold of porous, biodegradable polyester fabric and then distributed human cartilage cells throughout this form. The entire construct was then implanted onto the back of the nude mouse.
Develop Biocompatible Artificial Tissues and Organs.

Key components of the study:
- Scaffold – nonwoven poly(glycolic acid) (PGA)/poly(lactic acid) (PLA) mesh, shaped within a plaster mold of an ear.
- Cells – Calf chondrocytes (cartilage cells) harvested from the articular surfaces of a calf, which were seeded onto scaffold.
- Signals - In vitro and in vivo maturation: After 12 weeks in the back of athymic mice, cell seeded scaffolds supported extensive cartilage formation.

Any manufactured device or system that supports a biologically active environment.
Applications of bioreactors in tissue engineering
- Cell seeding and expansion
- Vascularization
- 3D tissue construction
- Mimicking physiological conditions
- Scaling up production

Replication: increase in the number of cells
Differentiation: change in gene expression to reflect particular functions
Death: controlled cell death
Motion: control of the motion of the cell in a structure
Adhesion: binding of the cell to the environment (other cell, extracellular matrix, artificial surface

Simple example of tissue engineering.
Skin is made of Dermis and Epidermis -> both can be easily cultured
Skin grafts are used for generating new skin from skin of another part of the body

Undifferentiated or partially differentiated cells that can:
- Replicate indefinitely
- Change into various cell types
Embryonic: acquired from fertilized eggs, somatic cell nuclear transfer
Adult: acquired from bone marrow, cord blood or specific tissue

Adult
- Restricted in ability to differentiate
- No issues of rejection
- Can be easily acquired
Embryonic
- Pluripotent cell, can differentiate into any tissue
- Ethical concerns