Lecture 4

We need to match it to the original tissue (properties)

Natural : highly biocompatible because natural recognition sites in backbone (RGD sequence = Arg-Gly-Asp) Synthetic : more predictable behaviour and properties can be tailored but less biocompatible

Molecular weight, weight average molecular weight. -> PDI (ratio of the two) : characterizes the distribution of molecular mass (natural -> always 1, sythetic -> varies between 0 and 1)

UHMWPE, HDPE, LDPE, … High density has less branching -> suitable for load bearing. Low density have more branches, of different lengths. PE has small water uptake and good chemical resistance

Differential Scanning Calorimetry -> Tg, Tc (exothermic), Tm (endothermic because breaking bonds). Polymer is compared to a reference and the difference in energy supplied to both is recorded.

Amorphous or partially crystalline solids undergo a change of their local bonding state : brittle to soft during heating (and opposite) -> they can be plastically deformed above Tg

Recyclable thermoplastic. Medical packaging Meshes for hernia repair (because doesn’t cause immune reaction)

Exists as amorphous (transparent) or semi-crystalline (opaque because of light scattering on grain boundaries). Used for artificial vessels, tendons, … But is hygroscopic (absorbs water) which decreases properties -> we need to remove the water during processing

For packaging mainly, because we need to add plasticizers if we want to make it soft and those are a problem for biocompatibility

Light transmission properties and biocompatibility

can be a very transparent solid -> frequently used for eyeglass lenses. Also for syringes and tubes.

No

expanded PTFE -> artificial blood vessels (good biocompatibility). Not for load bearing because limited resistance to wear.

Highly transparent -> intraocular hard lenses. Orthopedics : bone cement made from powder and liquid MMA (monomers) -> when mixedit becomes a “dough” that gradually hardens in the body. Can be re-dissolved using a solvent and bone repositioned. Also for dentures.

Heart valves, artificial bladder, … Breast implant with a LAYER of polyurethane foam -> decrease formation of fibrous capsule.

liquid, gel, rubber, hard. Main : PDMS and silicon resins. Blood vessels, eye implants, lubricants, breast implants, …

Delocalized electrons -> conductive. (pacemakers) Excellent mechanical properties and chemically inert -> cranial implants, load-bearing

Tough, tensile strength. Type I, II, III. Cosmetic surgery and skin substitues -> allergic reactions, diseases when from cows, alternative use of hyaluronic acid.

Tough and strong and biodegradable -> surgical thread. Chitosan makes switch between M1 and M2 macrophages -> better healing.

Mechanically stable, granules support bone neogenesis, open porosity, reduction of bacterial colonization, improved aesthetic

Highly absorbent -> flexible, shape memory, structural integrity. Covalent, ionic, hydrogen, physical gels (non-covalent cross-links). Tissue regeneration, drug delivery, joint repair, cell culture coating, biosensors, glue. PHEMA

Hydrophilic polymers have polar side groups (ex PHEMA, COOH). Hydrophobic polymers have non polar side groups (PE only has H)

When large side groups -> crystallization is inhibited -> amorphous -> light is not scattered -> transparent