title: Effects of storage in simulated skin secretions on mechanical behavior and color of polydimethylsiloxanes elastomers.
abstract: BACKGROUND
  Among the deteriorations that occur in maxillofacial prosthesis due to exposure in various environmental factors, sebaceous oils (sebum) and perspiration are also responsible for several alterations.
  
  
  OBJECTIVE
  Mechanical properties and color changes of 3 different medical-grade polydimethylsiloxanes were investigated in this study (Elastomer 42, Techsil 25, and M511), after immersion for 6 months in simulated sebum and perspiration at 37 °C. The purpose of this study was to determine the effects of storage in their physical properties. The null hypothesis investigated was that immersion time did not affect the measured properties.
  
  
  METHODS
  Polydimethylsiloxane specimens were immersed in simulated perspiration and in sebum. Compression tests were conducted on a Zwick testing machine. Shore A hardness measurements were carried out in a CV digital Shore A durometer. Weight changes were measured, and color changes were determined in the CIELAB system, using a MiniScan XE spectrophotometer. Simple mathematical models were developed to correlate the measured properties with the immersion time. The data were analyzed by analysis of variance and Tukey multiple range test at a level of α = 0.05.
  
  
  RESULTS
  Specimens immersed in simulated skin secretions became harder because of facilitation of the propagation of cross-linking reaction that probably occurred during aging of the polydimethylsiloxane samples, except for Elastomer 42, which seems to become more soft and ductile after immersed in sebum. Some weight increase was observed for the specimens immersed into the aqueous solutions, whereas for those immersed in sebum, weight loss was recorded, probably because of extraction of some compounds. The color change was higher for the specimens immersed in sebum than that corresponding to simulated perspiration. According to statistical analysis, all measured properties changed significantly after immersion in simulated perspiration and in sebum. Moreover, mathematical models reveal major alterations as well, which were introduced through their constants. Thus, the hypothesis investigated was rejected.
  
  
  CONCLUSIONS
  Significant changes were observed in all the examined elastomers. The elastomers were aged for a period, which simulates 1.5 years of clinical service. Within the limitation of this study, concerning the mechanical behavior and mostly the color changes, sebum and perspiration greatly affect the examined elastomers.
authors.affiliation: Department of Process Analysis and Plant Design, School of Chemical Engineering, National Technical University of Athens, Athens, Greece. peleni@central.ntua.gr
authors.forename: Panagiota N
authors.initials: PN
authors.lastname: Eleni
authors.forename: Magdalini K
authors.initials: MK
authors.lastname: Krokida
authors.forename: Gregory L
authors.initials: GL
authors.lastname: Polyzois
mesh_terms: D000042:Absorption; D000704:Analysis of Variance; D055598:Chemical Phenomena; D003116:Color; D004129:Dimethylpolysiloxanes / Q000737:chemistry*; D004548:Elasticity; D020724:Elastomers / Q000737:chemistry*; D006245:Hardness Tests; D006863:Hydrogen-Ion Concentration; D007101:Immersion; D008422:Materials Testing; D008447:Maxillofacial Prosthesis; D012629:Sebum / Q000737:chemistry*; D013542:Sweat / Q000737:chemistry*; D013997:Time Factors
chemical_list: D004129:Dimethylpolysiloxanes; D020724:Elastomers; C013830:baysilon