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Non-metallic biomaterials Flashcards

1
Q

What are polymers?

A
  • Polymers are made up of large numbers of similar repeat units linked to each other by covalent bonding
  • Repeat units – monomers – most likely liquid form and then go through polymerisation to become a polymer – usually monomers are toxic (have to ensure no monomer residue)
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2
Q

Describe the two groups of polymers

A

Thermoplastics - polymers with linear molecules (substances that soften upon heating and can be remoulded and recycled)
Thermosets - substances that do not soften under heat and pressure and must be re-machined or incinerated to remove from the environment

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3
Q

Why do we use polymers for medical devices?

A 
Biocompatible
Easy to produce 
Often cheaper
Designed to mimic
Designed to prevent requirement for revision surgery
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4
Q

Name some inert polymers.

A

PMMA
Acrylic
Silicone

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5
Q

Name some thermoplastic polymers for biomaterials.

A

PMMA, Polyolefin, Teflon, Polyvinyl chloride, polycarbonate, polyester, nylon

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6
Q

Name some thermosetting polymers for biomaterials.

A

Butyl rubber, chlorosulfonated polyethylene, epichlorohydrin rubber, polyurethane, natural rubber & silicon rubber

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6
Q

Name some thermosetting polymers for biomaterials.

A

Butyl rubber, chlorosulfonated polyethylene, epichlorohydrin rubber, polyurethane, natural rubber & silicon rubber

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7
Q

What is PTFE commonly used for?

A

For a heart valve, it serves as a sewing ring / receptor for sutures
Shunts to carry cerebral spinal fluid from hydrocephalic patient
Middle ear drain tubes, sutures – heart valves

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8
Q

What are acrylic polymers used for?

A

e.g., PMMA

o Used for contact lenses, bone cement, dentures, maxillofacial prostheses

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9
Q

What are polyurethanes used for?

A

Vascular tubes, artificial heart assist devices

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10
Q

What are polyamides used for?

A

Applications in intracardiac catheters, components in dialysis device, sutures

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11
Q

What is silicone used for and what is the most widely used type?

A

o The most widely used is polydimethylsiloxane
o Used for:
Catheters, lines
Silicone prostheses: finger, toe, mammary, maxillofacial surgery

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12
Q

List the natural bioresorbable polymers.

A 
o	Fibrin – blood clotting 
o	Collagen
o	Chitosan
o	Gelatin
o	Hyaluronan
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13
Q

List the synthetic bioresorbable polymers.

A 
o	PLA, PGA, PLGA,PCL (Polyorthoesters)
o	Poly(dioxanone)
o	Poly(anhydrides)
o	Poly(hydroxybuterates)
o	Polyphosphazenes
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14
Q

List the properties of PCL.

A
  • Biodegradable polymer
  • Semi-crystalline
  • Modulus = 0.5 GPa, Strength = 16 MPa
  • Low melting point (60 °C)
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15
Q

List the properties for PLA.

A
  • Biodegradable polymer
  • Two forms:
    Semi-crystalline P-L-LA
    Amorphous P-DL-LA
  • Modulus = 1.8 GPa, Strength = 50 MP
16
Q

What is PGA?

A

Polyglycolic acid - relatively very fast resorbing polymer

17
Q

What is PLGA?

A

Polylactic-co-glycolic acid - one of the most widely investigated biodegradable polymers for drug delivery

18
Q

What are the two types of polymerisation?

A

Chain-reaction (or addition) and step-reaction (or condensation) polymerisation

19
Q

Explain the chain reaction.

A

It is a three-step process (initiation, propagation and termination) involving two chemical entities (monomer and catalyst)

20
Q

Explain what is meant by linear, branched and cross-linked polymers.

A

o Linear polymers are made up of one long continuous chain
o Branched polymers have a chain structure that consists of one main chain with smaller molecular chains branching from it.
o Cross-linking in polymers occurs when primary valence bonds are formed between separate polymer chain molecules.

21
Q

What two distinct physical structures can segments of polymers exist in?

A

Crystalline or Amorphous
Crystalline is ordered geometry – amorphous is random. Most polymers are a combination of tangled and disordered regions surrounding the crystalline areas

22
Q

Which polymers undergo surface erosion and what is the process?

A

Poly(ortho)esters and polyanhydrides
o Sample is eroded from the surface
o Mass loss is faster than the ingress of water into the bulk

23
Q

Which polymers undergo bulk degradation and what is the process?

A

PLA, PGA, PLGA, PCL
o Degradation takes place throughout the whole of the sample
o Ingress of water is faster than the rate of degradation

24
What do bioresorbable polymers do in the body?
Materials and/or devices used in repair procedures that: o Breakdown over time to materials that can be eliminated from the body via natural pathways o Ideally leave no evidence of the repair injury
25
What are the advantages of bioresorbable polymers?
o Eliminated from the body and replaced by host tissue o No need for second surgical procedure to remove implant o Avoid complications of metal implants – stress shielding, corrosion, release of metal ions o Allow transfer of loads to healing bone o Revision surgery not complicated by presence of implant o Compatible with MRI imaging o Can be used to deliver bioactive agents etc.
26
How do PLA and PGA degrade?
From inside out (autocatalysis) Release acidic degradation products – in an “acid burst” PLLA-based materials slow to be resorbed (3-5 years)
27
Compared PLA and PGA.
``` PGA degrades more quickly PGA has higher acidity/toxicity of products but PGA response seen within 8-16 weeks PLA degrades in 1.5 – 3/5 years ```
28
What are the efficacy and speed of action of a drug dependent on?
o Site of administration | o Method of administration
29
What is the duration of action of a drug dependent on?
o Metabolic conversion | o Excretion in kidney, GI tract, skin and respiratory system
30
What polymer would you use for fast functioning NSAIDs?
PDA
31
List the forms of sustained release.
- Zero-order - Continuous administration of constant dose - Positioned - Absorption of drug at predetermined position in GI tract - Quick-Slow - Fast, concentrated dose, followed by controlled release - Slow-Quick - Concentrated dose with a fast bolus after a time delay - Accelerated - Starts slow and gets faster - Time Delay - Drug released after a predetermined delay - Binary - Two different drugs from one formulation - Multiple Pulse (clinical trial)
32
What is iontophoresis?
- Electrically charged drug pushed through epidermis by electrostatic repulsion
33
What is iontophoresis controlled by and used to administer?
- Delivery rate controlled by current density, pulsed voltage, drug concentration, ionic strength - Used to deliver o Lidocaine (topical anaesthetic) o Pilocarpine (diagnosis of cystic fibrosis) o Dexamethasone (anti-inflammatory into joints)
34
Explain phonophoresis.
- Combines ultrasound therapy and topical drug therapy - Ultrasonic vibrations enhance transport of drug through dermal layer - Typically used to administer hydrocortisone in conjunction with physiotherapy o Drug is mixed with ultrasound gel
35
Define a monolithic drug delivery system.
Therapeutic agent dispersed in polymer matrix – release controlled by diffusion from matrix
36
List four other types of drug delivery system.
Membrane Controlled - Membrane limits rate of release Osmotically Controlled - Water is osmotically driven into compartment containing osmotic agent. Increase in volume pushes moveable partition, forcing agent out through delivery orifice Chemically Controlled - Polymer Backbone (B-B-B-B), covalently bonded (A) to drug. Drug is released as bond A is hydrolysed. Polymer is broken down and excreted (hydrolysis of bond B). Reactivity A>B Swelling Controlled
37
Liposome drug delivery
o Water soluble drug contained within phospholipid bilayer. Administered as an emulsion into the bloodstream o 0.02 to 10μm o Site-specific, targeted drug delivery o Easily taken up by reticulo-endothelial macrophages (common in liver, spleen, bone marrow). - Stealth Liposomes o Liposome coated with polymer – avoids detection by immune system

Medical Device Design (7 decks)

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