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Biomaterials & Biomechanics > Polymers & Hydrogels > Flashcards

Polymers & Hydrogels Flashcards

1
Q
  1. Name TWO parameters that can influence the properties (mechanical or chemical) of a polymer (2 marks).
A

Structure

Molecular weight

Monomer structure

Processing parameters

○ Heat treatment

○ Pressure

○ Mechanical drawing

○ Sterilisation

Addition of plasticisers/other additives

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2
Q
  1. Briefly describe the role of plasticizing agents in plastics used in the biomedical device industry (1 mark).
A

Chemicals that increase the ‘softness’ or viscosity of polymer

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3
Q
  1. Briefly describe the role of stabilizing agents in plastics used in the biomedical device industry (1 mark).
A

Chemicals that hinder/slow the degradation process

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4
Q
  1. Briefly describe why diethylhexyl phthalate is used in PVC-based blood bags (1 mark).
A

Protects red blood cells by hindering their degradation, which improves and lengthens storage life

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5
Q
  1. Briefly describe why the use of diethylhexyl phthalate in PVC-based blood bags is an issue in terms of biological safety (1 mark).
A
  • The plasticiser DEHP doesn’t bind to the structure of PVC, and leaches out over time.
  • Shown to cause liver toxicity, testicular atrophy, and carcinogenicity in animals
  • Hence work is underway towards PVC- and DEHP-free blood bags
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6
Q
  1. Briefly describe why residual bisphenol A in the production of polycarbonates is an issue in terms of biological safety (1 mark).
A
  • Bisphenol A is an xenoestrogen (i.e. Imitates the hormone estrogen)
  • As estrogen has many biological functions, not just pertaining to the reproductive system, bisphenol A has the capability to bind to estrogen receptors all over the body, and hence interfere with normal biological processes
  • Hence banned in baby bottles
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7
Q
  1. Name TWO properties that govern the choice of using polymeric materials over metallic and ceramic materials in the context of choosing materials to construct biomedical devices (2 marks).
A
  • ‘softness’ i.e. viscoelasticity and flexibility
  • Transparency
  • Chemical inertness and resistance (e.g. biofluid interactions)
  • Processability/tailorability (lightweight)
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8
Q
  1. Name FOUR medical devices where polymers are predominantly used (2 marks, half mark for each device).
A
  • Neurology - catheters (PTFE)
  • ENT - cochlear implants (silicone)
  • Dental - dentures, dental implants (PMMA)
  • Plastic surgery - breast implants (silicone)
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9
Q

For Questions 9 to 14, do not take COST/FABRICATION factors into account in determining the most ideal or least ideal material choices. Each question is worth one mark

A

-

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10
Q
  1. Which of the following materials would be MOST ideal to make wound healing patches?

(A) UHMWPE

(B) PTFE

(C) PDMS

(D) Nylon

A

• Healing patches - need to be soft (low modulus) and flexible

• C) PDMS silicone patches are commonly used as wound dressing patches: research has shown that it also triggers migration of cells into the wound region

  • Because strong, elastic, prevents microbial transmission/proliferation (structure similar to peptides in immune system that fight off infections), moisture absorption is high
  • UHMWPE probably too strong and tough; unnecessary
  • PTFE probably bad because hydrophobic?
  • PDMS (silicone) also hydrophobic, but used in some band-aids
  • But ‘soften, higher elongation to failure, easily moulded into desired shapes, chemically inert’
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11
Q
  1. Which of the following materials would be MOST ideal to make spinal cage implants?

(A) UHMWPE

(B) HDPE

(C) PMMA

(D) PEEK

A

(D) PEEK

  • Spinal cage implant: definitely load-bearing so needs strong and tough polymers. This is also an interbody implant (disk-implant-disk), which requires high bone integration to prevent stress-shielding and associated complications.
  • Both A and D are strong and tough, but PEEK offers the potential to undergo surface modification to increase bone apposition but is better suited.
  • PMMA is hard, strong and bioinert, however, it is the most brittle (out of the plastics covered)
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12
Q
  1. Which of the following materials would be MOST ideal to make articulating surfaces in knee implants?

(A) UHMWPE

(B) HDPE

(C) PMMA

(D) PEEK

A

• A) UHMWPE - Articulating surfaces need to be able to bear load and need to have high wear resistance

  • V strong and tough
  • High density-surface ratio
  • Good chemical resistance
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13
Q
  1. Which of the following materials would be LEAST ideal to make catheter tubes for blood conduits?

(A) PTFE

(B) Polyurethane

(C) PDMS

(D) PMMA

A

(D) PMMA

• Too brittle (too hard and strong); needs to be flexible

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14
Q
  1. Which of the following materials would be MOST ideal to make artificial blood vessels?

(A) PTFE

(B) PMMA

(C) Nylon

(D) Polypropylene

A

(A) PTFE

Chemically and electrically inert, very hydrophobic, soft but with decent flexibility and strength, low coefficient of friction (<0.1)

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15
Q
  1. Which of the following materials would be MOST ideal to make resorbable sutures?

(A) Nylon

(B) Polypropylene

(C) PGA

(D) Polyethylene

A

C) PGA

  • Resorbable sutures require degradable polymers within a short period of time
  • PGA (polyglycolic acid) degrades
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16
Q
  1. Name ONE biological safety risk associated with the use of PMMA bone cements for femoral shaft fixation in hip replacement implants (1 mark).
A
  • Despite being considered ‘bioinert’, there are issues with unreacted toxic MMA monomers in cement formulations that may remain in the body to cause detrimental side effects
  • Leads to ‘bone cement implantation syndrome’, with adverse tissue reactions and pain and/or loss of function
17
Q
  1. Name ONE biological safety risk associated with the use of synthetic ligaments for ACL reconstruction (1 mark).
A

• Failure rates were as high as 30-40% –> abrasion of the synthetic tendons/ligaments lead to wear particles

○ As a non-degrading polymer, this induced a foreign body reaction

• Degradation over time –> loss in strength –> early rupture

18
Q
  1. Name ONE biological safety risk associated with the use of polypropylene meshes for treating pelvic organ prolapse (1 mark).
A

• Mesh ‘cuts through’ pelvic floor with superior abdominal pressure –> through muscle and skin, leading to pain and infection

19
Q
  1. Name ONE biological safety risk associated with use of textured breast implants over non-textured breast implants for breast implant surgery (1 mark).
A
  • ALCL - anaplastic large cell lymphoma - type of white blood cell cancer
  • Rupture leading to inflammation and pain
20
Q
  1. TRUE or FALSE?

All polymers that undergo hydrolytic degradation experience 100% mass loss within 10 years under physiological conditions (1 mark).

A

FALSE

  • Most polymers don’t reach the ‘mass loss’ stage - essentially non-degradable
  • Usually no observed mass loss (unless some enzymatic/physical degradation)
21
Q
  1. TRUE or FALSE?

Polymers undergoing degradation can have decreasing average molecular weight without an accompanying mass loss over time (1 mark).

A

TRUE

• Breaking of the long molecular chains into small ones

○ If in the body, may eventually be followed by mass loss as chains eventually get small enough to be metabolised by surrounding cells

22
Q
  1. TRUE or FALSE?

Both PGA and PLA produce readily metabolizable and non-toxic by-products during their biodegradation (1 mark).

A

TRUE

  • PGA by-product - glycolic acid - metabolised by liver to CO2 + H2O or discharged through urine
  • PLA by-product - lactic acid - converted to glycogen by liver, or excreted as CO2 + H2O via lungs
23
Q
  1. TRUE or FALSE?

Both PGA and PLA undergo biodegradation predominantly through the mechanism of hydrolysis (1 mark).

A

TRUE

• Breakdown (hydrolysis) of the bonds (full of aliphatic polyesters with high hydrolytic activity)

24
Q
  1. Name TWO mechanisms of degradation for polymers (aside from hydrolysis) used in the biomedical device industry (1 mark, half mark for each mechanism).
A

Hydrolysis - bonds where electronegativity differences (polar bond) are large make them vulnerable from H2O (which is also polar).

  • In the context of polymers, when carbon binds to larger molecules such as Cl, N, S, O, etc, the carbon atom is more positively charged in the bond. As a result, when water molecules come in contact (H2O aka H+-OH-), the hydroxyl group (OH-) is bonded to the carbon and therefore breaks the polymer into two separate molecules.

Oxidation - by hydrogen peroxides

  • Oxidation degradation of polymer is usually a result of hydrogen abstraction, where the hydrogen atoms in the C-H bonds are knocked off by oxidising agents, forming free radicals (H+). sometimes the C=C double bonds are also attacked and becomes C-C.

Enzymatic - of mostly natural polymers

Physical - due to wear and abrasion

25
Q
  1. Briefly describe hydrolytic degradation. You may use diagrams to help you answer the question (2 marks)
A
  • ‘broken’ (-lysis’) by water (hydro’)
  • ‘vulnerable’ bonds in the chain react with water & break up

○ Often occurs in carbon bonds where there’s a large element (i.e. O, S, N, P) adjacent to carbon

○ ‘drags away’ the electron from carbon

○ Carbon now net positively charged, and water attacks this carbon - breaks the bond to form 2 smaller molecules

26
Q
  1. Which of the following polymeric materials would be most susceptible to hydrolytic activity (1 mark)?

(A) Polyethylene

(B) PEEK

(C) Polyurethane

(D) PDMS

A

(C) Polyurethane

Polymers that contain weak carbon bonds (C- O, S, N and P) will be easily attacked by hydrolysis due to uneven charge distribution.

27
Q
  1. Which of the following polymeric materials would be most susceptible to oxidative attack (1 mark)?

(A) Polyethylene

(B) PEEK

(C) Polyurethane

(D) PDMS

A

(A) Polyethylene

From table: PE, PP > PU, nylon, PEEK, PMMA, PDMS

28
Q
  1. Name ONE biological safety issue related to biodegradation of polymers used in the biomedical device industry (1 mark).
A

It results in loss or change in the polymer structure:

  • Mass loss, translating to loss of strength, which will affect the functions of a device (e.g. early rupture of synthetic ligaments)
  • Wear particles released into the body cause a foreign body response
  • PGA and PLA when they degrade form acidic byproducts. In an environment like the blood where pH is 7.4, this may have adverse effects on cellular function. An acidic environment in the body is often associated with inflammation.
29
Q
  1. Choose ONE method of medical device sterilization, and briefly describe the issues of using the chosen sterilization method in the context of sterilizing polymeric biomedical devices. (2 marks)
A

The conditions needed to kill bacteria are often the conditions that break down organic structures & bonds

  • Heat, >160 degrees C is unsuitable for polymers with melting temperatures close to this value = most polymers
    • Melts/softens polymers = unwanted/uncontrolled deformation
  • Chemical sterilisation (e.g. Ethylene oxide)
    • Can react w polymer; alkylating agent adds alkyl groups = mechanism of toxicity
  • Radiation (e.g. UV/gamma) = breaking of polymer chains
30
Q
  1. Name ONE current application of polymeric hydrogels in the biomedical industry (1 mark).
A

Hydrogels = polymeric ‘mesh’ with v high water adsorption content

  • Very similar in microstructure to native ECM
  • Controllable mechanical properties (e.g. Crosslinking density, MW)

Applications:

  • Wound dressings (predominantly carboxymethycellulose-based) - absorbs exudates
  • Contact lenses - PHEMA (polhydroxyethyl methacrylate)
  • Optical transparency, oxygen permeability, stability, mechanical integrity
31
Q
  1. Name ONE potential application of conductive polymers in the biomedical industry (1 mark).
A

Biosensing & stimulating devices –> neuromodulation field potentials

(weaknesses: poor mechanical & biological properties)

Biomaterials & Biomechanics (4 decks)

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