Hydrogels porosity and bacteria penetration: Where is the pore size threshold?

The relationship between the microstructure of poly(2-hydroxyethyl methacrylate) (polyHEMA) hydrogels and the growth of microorganisms on their surface and their penetration through the network was evaluated. The hydrogels were prepared from solutions of HEMA and ethyleneglycol dimethacrylate (EGDMA) with water ranging from 0 to 60%wt. As the content in water upon synthesis increased the glass transition temperature and the degree of swelling of the hydrogels increased. Image analysis of SEM micrographs of the hydrogel surface and BET analysis of nitrogen adsorption isotherms were respectively used to characterize the size distributions of macropores and mesopores. The higher the water proportion in the monomers solution, the greater the size of meso (linear dependence) and macropores (segmental mode dependence), the area occupied by the macropores at the surface of the hydrogels, and the specific surface of the hydrogels. Hydrogels synthesized with 30% or less water showed a quite close distribution of pores with a mean size below 1 mu m and effectively hindered the penetration of Gram+ Staphylococcus aureus (0.5-1 mu m cocci) and Gram-Pseudomonas aeruginosa (0.5-0.8 mu m x 1.5-3 mu m bacilli). Logistic regression analysis points out that the probability of penetration of Staphylococcus aureus or Pseudomonas aeruginosa is above 50% when the mean pore size is greater than 3.67 mu m or 5.56 mu m, respectively. (C) 2010 Elsevier B.V. All rights reserved.