Polymers used in bio-medical application

Macromolecular compound obtained from natural origin. Chemical nature - polysaccharides, protein and bacterial polyesters Flexibility; Resistance to biochemical attack; Good biocompatibility; Light weight; Available in a wide variety of compositions with adequate physical and mechanical properties and can be easily manufactured into products with the desired shape.

Classification Biomedical Polymers

1. Natural Polymers 2 Synthetic Polymers

Natural polymers, or polymers, derived from living creatures, are of great interest in the

biomaterials field. Properties of natural polymers: Biodegradable; Non-toxic/ non-inflammatory; Mechanically similar to the tissue to be replaced; Highly porous; Natural polymers .Encouraging of cell attachments and growth; Easy and cheap to manufacture Capable of attachment with other molecules ( to potentially increase scaffold interaction with normal tissue).

Example of natural polymers ;- Collagen , Cellulose , Alginates , . Dextrans and Chitosan .

Collagen .

It is the main structural protein in the extracellular space in the various connective tissues in animal bodies. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole-body protein content. Collagen consists of amino acids wound together to form triple-helices to form of elongated fibrils. It is mostly found in fibrous tissues such as tendons, ligaments and skin. Depending upon the degree of mineralization, collagen tissues may be rigid (bone), compliant (tendon), or have a gradient from rigid to compliant (cartilage) It Consist of three intertwined protein chains, helical structure . Collagen is .non-toxic, minimal immune response .Can be processed into a variety formats –Porous sponges, Gels, and Sheets .

Applications –Surgery, Drug delivery, Prosthetic implants and tissue-engineering of multiple organs .

Derived from chitin, It present in hard exoskeletons of shellfish like shrimp and crab Chitosan desirable properties Minimal foreign body reaction ,Controllable mechanical biodegradation properties Applications .In the engineering of cartilage, nerve, and liver tissue, wound dressing and drug delivery devices Chitosan

Alginate

A polysaccharide derived from brown seaweed . Can be processed easily in water . Non-toxic, Biodegradable , Controllable porosity

· Forms a solid gel under mild processing conditions

· Applications in Liver, nerve, heart, cartilage & tissue- engineering

Synthetic Polymers

Advantages of Synthetic Polymers, Ease of manufacturability ,process ability ,reasonable cost , The Required Properties , Biocompatibility , Sterilizability, Physical Property , Manufacturability

Applications:.Medical disposable supplies, Prosthetic materials, Dental materials, implants, dressings, polymeric drug delivery, tissue engineering products

Example of Synthetic Polymers : (PTFE) Polytetrafluoroethylene ,Polyethylene, (PE) , Polypropylene, (PP) ,Poly (methyl methacrylate) PMMA – it is a Material used in maxillofacial prosthetic

Classifications

Biostable, Bioerodible, Water soluble ,

Polymers that are sufficiently biostable to allow their long term use in artificial organs blood pumps,

blood vessel prostheses, heart valves, skeletal joints, kidney prostheses.

A polymer must fulfill certain critical requirements if it is to be used in an artificial organ. It must be physiologically inert .The polymer itself should be stable during many years of exposure to hydrolytic or oxidative conditions at body temperature Biostable Polymers

It must be strong and resistant to impact (when it is used as structural material to replace the bone). The polymer must be sufficiently stable chemically or thermally that it can be sterilized by chemicals or by heat.

Bioerodible materials . Polymers that are bioerodible materials that will serve a short term purpose in the body and then decompose to small molecules that can be metabolized or excreted, sometimes with the concurrent release of drug molecules. Mostly bioerodible polymers used as surgical sutures, tissue in growth materials, or controlled release of drug.

Water-soluble polymers (usually bioerodible) that form part of plasma or whole blood substitute solutions or which function as macromolecular drugs. Applications: Improvement in the behavior of pharmaceuticals. Used in synthetic blood substitutes as viscosity enhancers or as oxygen-transport macromolecules.

The design and selection of biomaterials depend on different properties – Host Response

Biocompatibility , Biofunctionality , Functional Tissue Structure and Pathobiology , Toxicology,

Appropriate Design and Manufacturability, Mechanical Properties of Biomedical polymers .

Polymers used as rocket propellants

Propellant is the chemical mixture burned to produce thrust in rockets . It consists of a fuel and an oxidizer. A fuel is a substance that burns when combined with oxygen producing gas for propulsion. An oxidizer is an agent that releases oxygen for combination with a fuel. The ratio of oxidizer to fuel is called the mixture ratio. Propellants are classified according to their state - liquid, solid, or hybrid.

The gauge for rating the efficiency of rocket propellants is specific impulse, stated in seconds. Specific impulse indicates how many pounds (or kilograms) of thrust are obtained by the consumption of one pound (or kilogram) of propellant in one second. Specific impulse is characteristic of the type of propellant, however, its exact value will vary to some extent with the operating conditions and design of the rocket engine.

Hydroxyl-terminated polybutadiene (HTPB)

It is an oligomer of butadiene terminated at each end with a hydroxyl functional group.

HTPB is a solid rocket propellant. It binds the oxidizing agent and other ingredients into a solid but it remains as elastic mass. The cured polyurethane acts as a fuel in such mixtures. For example, HTPB is used in all 3/4 stages of the Japanese M-5 rocket satellite launchers and PSLV rocket developed by ISRO for satellite launches. "HTPB/AP/Al=12/68/20", which means, proportioned by mass, HTPB plus curative 12% (binder and fuel), ammonium perchlorate 68% (oxidizer), and aluminium powder 20% (fuel).

Similar propellants, often referred to as APCP (ammonium perchlorate composite propellant) are used in larger model rockets. A typical APCP produces 2–3 times the specific impulse of the black powder propellant used in most smaller rocket motors.

HTPB is also used as a hybrid rocket fuel. With N2O (nitrous oxide, or "laughing gas") as the oxidizer, it is used to power the Space Ship .