Types of Hydrogels Flashcards
How is alginate made?
- naturally occurring brown seaweed is extracted from brown algae.
- extract is filtered
- sodium or calcium chloride is added to filtrate to precipitate alginate
How is alginic acid made?
alginate salt treated with dilute HCl
How is sodium alginate powder produced?
after further purification and conversion
Is alginate low or high cost to produce?
low cost
Describe alginate’s structure
linear copolymers containing blocks of M and G residues
What is the unique trait of G-blocks in alginates?
participate in intermolecular cross-linking with divalent cations (Ca^2+) to form hydrogels.
What 4 factors affect the physical properties of alginate and resultant hydrogel?
- composition (M/G ratio)
- sequence
- G-block length
- molecular weight
How are the mechanical properties of alginate gels enhanced?
by increasing the length of G-block and molecular weight
What are the properties of alginate?
- biocompatible
- low toxicity
What are the medical applications of alginate?
- wound healing
- delivery of bioactive agents
What are the pharmaceutical applications of alginate?
- thickening, gel-forming, and stabilizing agents
- delivery of low MW drugs
- drug release overtime in alginate gels
The physiochemical properties of alginate are highly dependent on what 4 things?
- molecular weight
- chemical composition
- cross-linking type
- cross-linking density
What types of cross-linking affect the properties of alginate?
- ionic
- covalent
- cell
What is debated about alginate?
biocompatibility
What is the structure of hyaluronic acid (HA)?
long unbranched polysaccharide chain, composed of twin sugar units
Where is hyaluronic acid found?
- extracellular matrix of skin, cartilage, vitreous humor, and other body tissue
- umbilical cord
- rooster combs
What was the first medical use for hyaluronic acid in late 1950s?
vitreous substitution/replacement during eye surgery
Hyaluronic acid is a ____________ naturally occurring in all organisms
carbohydrate
When hyaluronic acid binds to water it gives it a more ___________ consistency similar to jello
viscous
What are the 4 biological functions of HA?
- join synovial fluid
- vitreous fluid
- control of tissue hydration
- water transport
What is HA’s function in the body?
to bind water and to lubricate moveable parts of the body such as joints and muscles
What are the properties of hyaluronic acid?
- high density of negative charges
- hygroscopic
- high viscosity
- high capacity for lubrication, water absorption and retention
What does the high capacity of lubrication, water absorption/retention allow for in hyaluronic acids?
allows the migration, adhesion and proliferation of cells to function
In the body hyaluronic acid occurs in the ________ form, called ____________.
salt
hyaluronate
List the 5 medical applications of HA
- ophthalmic
- reduces nerve impulses and sensitivity associated with pain
- enhances chondrocyte HA and proteoglycan synthesis
- reduces production of pro-inflammatory mediators and matrix metalloproteinases
- alters the behavior of immune cells
- orthopedic
Describe the 3 orthopedic applications of HA
- development of cartilage
- maintenance of synovial fluid
- regeneration of tendons
What 2 characteristics of HA make it optimal for orthopedics?
- viscoelastic nature
- ability to form highly hydrated matrices
In the joint, HA acts as the _______ and the __________.
lubricant and shock absorber
What is HA particularly useful for in ophthalmic applications?
space-filling matrix in the eye so intraocular injection of HA is used to maintain shape of anterior chamber
HA solutions serve as ___________ of eye drops and as a __________ to eye tissue repair
viscosity-enhancing component and adjuvant
Both HA and enzyme that eliminates HA, hyaluronidases, correlate with _______ progression
cancer
Expression of HA synthases increases HA levels which leads to acceleration of __________ growth and _________.
tumor growth and metastasis
