English
Menu

Biomaterials

Which statement about PMMA (polymethyl methacrylate) bone cement used to fix artificial joints is correct?

  1. AIt bonds chemically to the surfaces of both bone and implant and fixes the two together as an adhesive, like an epoxy resin
  2. BPMMA melted by heating to about 200℃ is injected and fixes the implant as it cools to body temperature and solidifies into a glass
  3. CWhen PMMA powder is mixed with the liquid monomer, it polymerizes at room temperature and hardens while releasing heat
Show answer and explanation

Answer: C. When PMMA powder is mixed with the liquid monomer, it polymerizes at room temperature and hardens while releasing heat

Bone cement is used by kneading PMMA powder with liquid methyl methacrylate (the monomer) during surgery. Addition polymerization by radicals generated from the initiator proceeds at room temperature, and the cement hardens in around 10 minutes. This polymerization is exothermic, and the points to watch are thermal damage to surrounding tissue from the temperature rise during hardening, residual monomer, and polymerization shrinkage. Bone cement does not bond chemically; as a filler that fills the space between the irregular bone surface and the implant and interlocks mechanically, it distributes and transfers the load to the bone. PMMA is a thermoplastic, but its melting temperature is far too high for use inside the body, so it is introduced as monomer and polymerized in the body.

Report an error

Practice this topic Back to topic

More Biomaterials questions

  1. What is the main reaction by which polylactic acid (PLA), used in absorbable sutures and bone fixation pins, degrades in the body?
  2. A bone fixation pin of crystalline poly-L-lactic acid (PLLA), made only of the L-isomer, takes several years to be fully resorbed in the body. Which is a correct way to make it degrade faster?
  3. Suppose the number-average molecular weight Mn of a biodegradable polymer falls by hydrolysis as Mn(t) = Mn₀exp(−kt). For k = 0.030 day⁻¹, which value is closest to the number of days until Mn falls to 20% of its initial value?
  4. Magnesium, studied as a biodegradable metal, corrodes in body fluids as Mg + 2H₂O → Mg(OH)₂ + H₂. When a 0.10 g magnesium screw corrodes completely, which value is closest to the volume of hydrogen released? Take the molar mass of Mg as 24.31 g/mol and the molar volume of gas at 37℃ and 1 atm as 25.4 L/mol.
  5. Which statement correctly describes the idea of biocompatibility for biomaterials?