Lecture 4 Flashcards
How to choose the biopolymer for an application ?
We need to match it to the original tissue (properties)
Advantages (and disadvantages) or natural VS synthetic biomaterials
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
How do we characterize polymer chain lengths ?
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)
classification of PE and link to branching -> which is suitable for load bearing ?, properties
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
How can we find the thermal properties of a polymer ?
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.
What is the glass transition T ?
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
PP : two applications and type of polymer
Recyclable thermoplastic.
Medical packaging
Meshes for hernia repair (because doesn’t cause immune reaction)
PET : existing states, usage, disadvantage
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
PVC : main usage, why ?
For packaging mainly, because we need to add plasticizers if we want to make it soft and those are a problem for biocompatibility
What are two things you would consider for ocular applications (lenses) ?
Light transmission properties and biocompatibility
PC : main usage (why), and in medicine ?
can be a very transparent solid -> frequently used for eyeglass lenses.
Also for syringes and tubes.
PA : common in medicine ?
No
PTFE : main application in medicine and what is not possible
expanded PTFE -> artificial blood vessels (good biocompatibility).
Not for load bearing because limited resistance to wear.
PMMA : light properties, application as a biomaterial
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.
Polyurethane : main applications, advantage ?
Heart valves, artificial bladder, …
Breast implant with a LAYER of polyurethane foam -> decrease formation of fibrous capsule.
polysiloxane : states, two main types, many usages
liquid, gel, rubber, hard.
Main : PDMS and silicon resins.
Blood vessels, eye implants, lubricants, breast implants, …
PEEK : main advantage compared to others, properties and applications
Delocalized electrons -> conductive. (pacemakers)
Excellent mechanical properties and chemically inert -> cranial implants, load-bearing
Collagen : properties, which are the most relevant in tissue repair processes, main use, problem ?
Tough, tensile strength.
Type I, II, III.
Cosmetic surgery and skin substitues -> allergic reactions, diseases when from cows, alternative use of hyaluronic acid.
Chitin : main use and advantage, role in healing ?
Tough and strong and biodegradable -> surgical thread.
Chitosan makes switch between M1 and M2 macrophages -> better healing.
TCP-PLGA tooth root implant : main functions
Mechanically stable, granules support bone neogenesis, open porosity, reduction of bacterial colonization, improved aesthetic
Hydrogels : advantages, types of bonding, applications, 1 example
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
Polymers that can absorb water : chemical structure ?
Hydrophilic polymers have polar side groups (ex PHEMA, COOH).
Hydrophobic polymers have non polar side groups (PE only has H)
Why are amorphous polymers transparent ?
When large side groups -> crystallization is inhibited -> amorphous -> light is not scattered -> transparent
