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Medical Device Design > Non-metallic biomaterials > Flashcards

Non-metallic biomaterials Flashcards

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USMLE® Step 1 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
Q

What do bioresorbable polymers do in the body?

A

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
Q

What are the advantages of bioresorbable polymers?

A

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
Q

How do PLA and PGA degrade?

A

From inside out (autocatalysis)
Release acidic degradation products – in an “acid burst”
PLLA-based materials slow to be resorbed (3-5 years)

27
Q

Compared PLA and PGA.

A 
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
Q

What are the efficacy and speed of action of a drug dependent on?

A

o Site of administration

o Method of administration

29
Q

What is the duration of action of a drug dependent on?

A

o Metabolic conversion

o Excretion in kidney, GI tract, skin and respiratory system

30
Q

What polymer would you use for fast functioning NSAIDs?

A

PDA

31
Q

List the forms of sustained release.

A
  • 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
Q

What is iontophoresis?

A
  • Electrically charged drug pushed through epidermis by electrostatic repulsion
33
Q

What is iontophoresis controlled by and used to administer?

A
  • 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
Q

Explain phonophoresis.

A
  • 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
Q

Define a monolithic drug delivery system.

A

Therapeutic agent dispersed in polymer matrix – release controlled by diffusion from matrix

36
Q

List four other types of drug delivery system.

A

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
Q

Liposome drug delivery

A

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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