RESUMO
Copolyesters based on glycolic acid (G) combined with adipic acid (A) and ethylene glycol (E) were synthesized in different percentage of molar ratios (A: 100-50% and G: 100%) and their hydrolytic degradation was studied and correlated with their structures. According to the DSC, the production of polyesters leads to the formation of copolyesters and not to mixtures of homopolyesters. The crystallites in the copolyesters mainly consist of continuous sequences of ethylene adipate structural units. The hydrolytic degradation of the polyesters was followed by their weight loss during hydrolysis and by the FTIR spectra of the initial polyesters compared with that of the degraded polyesters at equilibrium. The region between 1142 and 800 cm(-1) can be utilized to evaluate the extent of degradation of polyesters after their hydrolysis. The absorption bands at 1142, 1077 and 850 cm(-1) due to the amorphous region decrease after hydrolysis, whereas those at 972, 901 and 806 cm(-1) due to the crystalline region increase. The experimental data of the hydrolytic degradation were fitted with exponential rise to maximum type functions using two-parameter model, which describes very well mainly the initial part of the degradation, and four-parameter model (containing two exponential terms), which is appropriate for fitting the hydrolytic degradation on the entire time period (including the equilibrium). Furthermore, the kinetics of the hydrolytic degradation of the polyesters for the initial time period based on both models results to similar values of the rate constant, k. The synthesized copolyesters of glycolic acid combined with adipic acid and ethylene glycol are soluble in many common organic solvents opposite to PGA, leading to modified biodegradable polyesters and therefore they can be easily processed.
Assuntos
Adipatos/farmacocinética , Glicolatos/farmacocinética , Poliésteres/farmacocinética , Implantes Absorvíveis , Adipatos/química , Materiais Biocompatíveis/química , Biodegradação Ambiental , Biotransformação , Portadores de Fármacos/síntese química , Portadores de Fármacos/química , Portadores de Fármacos/farmacocinética , Glicolatos/química , Hidrólise , Teste de Materiais/métodos , Modelos Estatísticos , Estrutura Molecular , Poliésteres/síntese química , Poliésteres/química , Espectroscopia de Infravermelho com Transformada de Fourier , Relação Estrutura-Atividade , Propriedades de Superfície , TemperaturaRESUMO
BACKGROUND: The aim of the present study was to compare the prevalence of asthma among schoolchildren in 1978, 1991, and 1998 in Patras, Greece. METHODS: The study populations of the three comparable cross sectional surveys comprised third and fourth grade public school children in Patras, Greece. Sample sizes in 1978, 1991, and 1998 were 3735, 2952 and 3397 children and response rates were 80.4%, 81.9%, and 90.6%, respectively. Prevalence of current, non-current, and lifetime asthma or recurrent wheezing was determined by parental questionnaire. Personal communication with the parents of asthmatic children in 1991 and 1998 provided data on lost schooldays. RESULTS: Prevalence rates of current asthma or wheezing in 1978, 1991, and 1998 were 1.5%, 4.6%, and 6.0%, respectively (1978-91: p=0.01, 1991-98: p=0.02, 1978-98: p=0.03). Lifetime prevalences of asthma or wheezing in 1991 and 1998 were 8.0% and 9.6%, respectively (p=0.03). Current diagnosed asthma increased proportionally to diagnosed wheezing during 1991-98. The number of schooldays lost in the previous 2 years because of asthma did not change (p>0.1) between 1991 (0.31 per child) and 1998 (0.34 per child). CONCLUSIONS: Our results support a true increase in the prevalence of current and lifetime asthma in the last 20 years among pre-adolescent children in Patras, Greece.