Monomer tissue response

Adverse tissue response is usually higher for lower molecular weight polymers, and the presence of free monomer is usually cytotoxic. Many additives used in polymers give a strong, adverse tissue reaction due to a combination of their low molecular weight, higher mobility, moderate solubility in some body fluids, and their relatively reactive and toxic natures. For this reason, the use of plasticizers and/or stabilizers is ill-advised for biomedical polymers. In a similar manner, it is advantageous to remove the polymerization catalysts from the polymer before use as an implant material. 

The presence of this minor amount of residual material was probably responsible for the slight residual cellular infiltrations seen at these periods. The polymers in this study were carefully characterized regarding molecular weight, monomer content, and residual ethylene oxide levels both pre- and post-processing. Specifications were strictly enforced for this study and may account for the excellent tissue response observed. 

Aqueous formaldehyde as used for fixation contains mostly methylene glycol (-99%), its oligomers, and small amounts of formaldehyde. The proportion of the oligomers present depends inversely on the temperature. Formaldehyde solution cannot be obtained without the formation of methylene glycol. It is not the formaldehyde molecule that is primarily responsible for rapid penetration into the tissue but methylene glycol, which is the major component of formaldehyde solution. At concentrations of 2% or less, the formaldehyde in solution is present practically only as the hydrated monomer (HOCH2OH). 

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