Tissue Engineering and ECM

Tissue

• group of cells, usually with common embryonic origin, function together to carry out specialized activities (similar cells form a tissue)

Types of Tissues

• Epithelial

  • covers surfaces, lines cavities, forms glands

• Muscle

  • enables movement

  • skeletal, smooth, cardiac

• Connective

  • supports, binds, protects other tissues

  • bone, cartilage, tendons, fat

• Nervous

  • sends/receives signals

Epithelial Tissue

• Protection, support, regulation, secretion, separation, etc

• All substances that enter body must cross epithelium

• Form linings and secretion glands

  • Tightly packed

  • Avascular

  • Apical and basolateral surfaces (apical top faces outside or external cavity, basal connected to bottom surface)

  • self-renewal

Connective Tissue

• ECM gives tissue structural integrity

• fibroblasts, chondrocytes, osteoblasts

• Transport

• Energy storage

• Immune protection

ECM

• composed of network of proteins, sugars, signaling molecules, water

• Proteoglycans, elastin, collagen

• regulates cell functions like growth, movement, differentiation, communication

Collagen

Distribution in Human Body

• 85% tendons

• 75% skin

• 90% bones

• 70% joint cartilage

• 70% ligaments

• 6% tendinous muscles

Function: enables flexible deformation while providing high mechanical strength to collagenous tissues such as tendons

• Forms long, triple helical fibers, collagen fibers composed of collagen fibrils, collagen molecules are triple helices of a-chains with amino acids

Pathological States:

• Osteogenesis Imperfecta: brittle bone disease

Elastin

Mainly found in:

• Aorta

• Mouse carotid artery

• skin

• lung alveoli

Function:

• Gives tissues elasticity, allowing them to stretch and return to original shape

Disorders:

• marfan syndrome: reduced cross linking of elastin, fibers too weak or too few

  • long limbs, lens dislocation, abnormal spine curvature, protruding backbones

• Loss of elastin in arteries results in stiffness (Atherosclerosis)

Proteoglycan

• Highly glycosylated monomer

• Negatively charged

• brush-like

• Function:

  • lubricants, shock absorbers space fillers

  • PG highly negatively charged GAG chains attract and trop water (like gel), hydrating, lubricating, and resisting/absorbing mechanical load in tissues.

• Pathological states:

  • Osteoarthritis: reduced joint cushioning

Decellularization

• Leaves behind a scaffold that can be used for potential clinical applications

  • implants, tissue repair, cardiac repair

• Can be used to understand drug testing and disease modeling