Lecture 4

Question 1

How to choose the biopolymer for an application ?

Answer 1

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

Question 2

Advantages (and disadvantages) or natural VS synthetic biomaterials

Answer 2

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

Question 3

How do we characterize polymer chain lengths ?

Answer 3

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)

Question 4

classification of PE and link to branching -> which is suitable for load bearing ?, properties

Answer 4

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

Question 5

How can we find the thermal properties of a polymer ?

Answer 5

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.

Question 6

What is the glass transition T ?

Answer 6

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

Question 7

PP : two applications and type of polymer

Answer 7

Recyclable thermoplastic.

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

Question 8

PET : existing states, usage, disadvantage

Answer 8

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

Question 9

PVC : main usage, why ?

Answer 9

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

Question 10

What are two things you would consider for ocular applications (lenses) ?

Answer 10

Light transmission properties and biocompatibility

Question 11

PC : main usage (why), and in medicine ?

Answer 11

can be a very transparent solid -> frequently used for eyeglass lenses.

Also for syringes and tubes.

Question 12

PA : common in medicine ?

Answer 12

No

Question 13

PTFE : main application in medicine and what is not possible

Answer 13

expanded PTFE -> artificial blood vessels (good biocompatibility).

Not for load bearing because limited resistance to wear.

Question 14

PMMA : light properties, application as a biomaterial

Answer 14

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.

Question 15

Polyurethane : main applications, advantage ?

Answer 15

Heart valves, artificial bladder, …

Breast implant with a LAYER of polyurethane foam -> decrease formation of fibrous capsule.

Question 16

polysiloxane : states, two main types, many usages

Answer 16

liquid, gel, rubber, hard.
Main : PDMS and silicon resins.

Blood vessels, eye implants, lubricants, breast implants, …

Question 17

PEEK : main advantage compared to others, properties and applications

Answer 17

Delocalized electrons -> conductive. (pacemakers)

Excellent mechanical properties and chemically inert -> cranial implants, load-bearing

Question 18

Collagen : properties, which are the most relevant in tissue repair processes, main use, problem ?

Answer 18

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

Question 19

Chitin : main use and advantage, role in healing ?

Answer 19

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

Question 20

TCP-PLGA tooth root implant : main functions

Answer 20

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

Question 21

Hydrogels : advantages, types of bonding, applications, 1 example

Answer 21

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

Question 22

Polymers that can absorb water : chemical structure ?

Answer 22

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

Question 23

Why are amorphous polymers transparent ?

Answer 23

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