PMMA is extremely durable. Used as an excellent biocompatible material in healthcare.
PMMA chains can be mainly degraded by radiolysis, or high temperature depolymerization.
the side ester groups can be hydrolyzed : see for example:
Compositional microstructure of polymer prepared by partial hydrolysis of isotactic poly(methyl methacrylate)
Danica Doskočilová*, František Mikeš, Jan Pecka andJaroslav Kříž
Die Makromolekulare Chemie
Volume 193, Issue 10, pages 2529–2538, October 1992
regards
PMMA as such is not degradable by human body but it is biocompatible. thats why PMMA is the main component and widely used for dentures..
Degradability of PMMA in human body - strongly depends on environment (pH, salinity of liquid). In relation with this subject I can give a very tragic example: 20-25 years ago PMMA was used to replace the eye crystalline lenses "crystal ball". Then during the 1st year the patients who underwent such an replacement operation - were the happiest people in the world - because before the operation they hardly recognized the images , and just After the operation their vision became 100% !!! But it worked only ca. 3 years - then after degradation - they returned back - to seeing nothing. I do not know of how aggressive is the liquid media surrounding these PMMA crystals, neither its pH or composition --- BUT anyway it is a true story. Thus under action of some environments in human body - PMMA rather slow, but undergoes destruction. LEONID
for continuing te discussion, if PMMA is hydrolyzed, methanol is released and it is a hazardous substance for humans !
Emmanuel, I guess no one is going to make an artificial body of PMMA
Dear all,
there are two possible ways that the PMMA undergoes physico-chemical changes or degradation. If the main C-C backbone is the subject than I am sure that is practically impossible under physiological conditions. However, it the leteral ester group is concerned than it is alteration is more convinient and possible under physiological conditions, and this infact this the more suitable explanation of Dr. Leonid V. Vladimirov, where due to the hydrolysis of the ester group the lenses lost their performance. Regards
Please take into account that the first critical step could be the sterilization: gamma- and electron-sterilization cleave partly C-C and C-O bonds generating radicals (= big problem for UHMWPE as implant material in hip endoprosthesis!), EO could damage the ester bonds. Radicalic species of the injured PMMA matrix can react with ROS (radical chain reactions), the ester groups can be attacked by enzymes. Therefore, the sterilization method should be carefully tested. The degradation rate in the body depends on the local conditions and differs from patient to patient.. Degradation can take months or years. Unfortunately, prognosis is impossible.
PMMA normally is inert under in vivo conditions, but in seldom cases contact allergies exist with PMMA and dental materials which are based on bis-GMA (reaction product of methacrylic acid which bisphenol-A-diglycidylether) or urethane acrylates (reactions product of diisocyanates whith HEMA, hydroxyethyl methacrylate). The conventional hypothesis is, that traces of unreacted monomers (MMA, HEMA, metharylic acid) causes the allergy but I am not sure if this is true. Perhaps there is a radical degradation process in the body which can form back the monomers under scission of the C-C-bonds? The question arises, if contact allergy agains polymethacrylates is a real allergy but a special kind of metabolism which enables very few persons to split carbon-carbon bonds by radical reactions?
the radiodegradation of PMMA was described by Charlesby in the 50's.
the bond between quaternary carbon and ester group is cleaved and the radical rearrange into a vinyl + a chain scission og the skeletton.
The proability of the reaction (also named the yield) is 2 which means that almot two chain sicssion occur when 100 eV are absorbed, or, with current units, 2.10^(-7) mol kg-1 of chain scission per absorved Gray.
regards
Just a simple note: PMMA is not degradable in the body unless it was treated before its use physically or chemically. The main uses of PMMA for healthcare are at the dentist clinic for teeth fillings/false teeth and at the optician's clinic as hard contact lenses. These contact lenses were problematic so researchers moved into using HEMA "2-hydroxyethylmethacrylate" homopolymer which was better but was not a very good one. Comfortable soft contact lenses were,eventually, made from copolymers of HEMA with other monomers including MMA, silicone...etc. taking into account two main criteria: water & air smooth passage and optical transperancy.
what is the final reply on degradation path from polymer experts and biologists?
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