Question

Provide an overview of Tissue Engineering focusing on scaffolds and in particular hydrogel scaffolds. Your answer should include:

a)Main components of “Tissue Engineering”

b)List the 3 categories of scaffolds.

c) What are functions of a scaffold?

d) List two different ways Hydrogels can be made and describe the stability of each type.

e) List advantages and disadvantages of Ionic crosslinking as relevant to hydrogels.

f) Discuss how you make an alginate hydrogel with the D-Glucono-d-lactone (i.e., GDL) system.

g) What does Rheology tell you about scaffolds?

h) Although this Labster lab does not discuss how to add cells to the hydrogel, how do you think you could add cells to the hydrogel?

Answer 1

Tissue Engineering :

As stated by Langer and Vacanti tissue culture is an interdisciplinary field that applies the principles of Engineering and life sciences towards the development of biological substitutes that restore, maintain or improve function of biological tissue or whole organ.

In other words it is to create an artificial fully alive tissue or organ which can replace old one or improve the function.

Scaffolds : are artificial structures that support the tissue formation. Cells are implanted on scaffold. Scaffolds help in cell attachmentband migration. Help in diffusion of nutrients.

Steps of tissue Engineering :

1. Take tissue samples from the body of patients. Tissues are broken down using enzymes. They require scaffold as structure for support, to provide nutrients, and oxygen.

2. Growing cells into new tissue, scaffold:

Without scaffold cells are free floating. They are not connected to each other. Scaffolds dissolve once structure of cell is formed. Bathe the scaffolds with growth factors. Cells multiply and fill up the scaffold and grow into 3 dimensional tissue.

3. Implantation in the body: cells recreate their functions inside the body. Blood vessels attach to the new tissue. Then the scaffold dissolves. This new tissue blends with the surroundings and does its function.

From fluid tissues like blood cells are extracted by centrifugation or apheresis. Extraction is more diff from solid tissues. First the tissue is minced. Then digested with enzymes trypsin or collagenase to dissolve the extra cellular matrix.After that cells are extracted using centrifugation or apheresis.

So the 3 main components of tissue Engineering are the scaffolds, cells which are the basic unit of tissue and the growth factors which are poly peptides that regulate the activities of cells.

Polymers like PLA, PCA, PEG etc or Bioactive ceramic s Ha or TCP, or natural polymers collagen, GAGs, chitosan may be used for scaffold formation.

Hydrogel scaffolds:

Cells are suspended within or adhered to the 3D Hydrogel framework during or after formulation as scaffolds.

Inclusion of RGD domains in Hydrogels improved cellular migration, proliferation and growth and organisation in tissue regeneration application.

(RGD : arginine-glycine-aspartic acid adhesion peptide sequence)

Cells like endothelial cells, smooth muscle cells, fibroblasts, chondrocytes, osteoblasts, favourably bind to RGD Hydrogels. scaffold

Homopoleric Hydrogels are derived from single species of monomers.

Copolymeric Hydrogels are derived from two or more different monomer species. One hydrophilic group arranged in a random, block, or alternating configuration along the chain of polymer network.

Multipolymer Hydrogels made of two independent Cross linked synthetic or natural polymer component in a network form.

Three ways to synthesise physically cross linked hydrogels:

1. By hydrogen bonds:

Hydrogen bond formation between oxygen of poly ethylene glycol and carboxylic group of polyacrylic acid or polymethaacrylic acid.

2. Hydrophobic modification :

From polysaccharides dextran, chitosan, pullulan, carboxy methyl curdlan physically crosslinked Hydrogels can be made by hydrophobic modification.

3. Crystallisation:

Crystallisation in homopolymer system. Aqueous solution of poly vinyl alcohol stored at room temperature forms gels with little mechanical strength. This polyvinyl alcohol aqueous solution when subjected to freeze thaw process a tough, greatly elastic gel is produced.

Alginate hydrogel preparation using D glucono D lactone: by solution extrusion process.

Caco3 and D glucono d lactone are used as gelatin agents. There is release of ca from Caco3 induced by hydrolysis of GDL cause slow gelation of alginate.