PHEMA gradient

Fig. 43 Dry thickness of poly(2-hydroxyethyl methacrylate) (PHEMA) as a function of the position on the substrate (lower panel). The fluorescence microscopy images show the corresponding structure of fibrinogen at three positions along the PHEMA gradient (upper panel). (Reproduced with permission from [164])...

PHEMA films with depth-wise gradient crosslinking allowed formation of wrinkling pattern in a poor solvent, such as water (3 = 47.8), as wrinkling instability occurs in low compressive strains (see the discussion above). Large cracks and delimitations were observed for DMSO ( s = 26.7), whereas creasing instabilities were observed in methanol (5 = 29.6) and ethanol (3 = 26.5). When solvent composition of ethanol-water mixture was dynamically tuned in situ, reversible transition of wrinkle to crease instabilities or vice versa was observed. 

Mei et al. prepared the gradient PHEMA brush on a silicon wafer by SI-ATRP and investigated protein/cell adhesions on the brush surface [51]. First, they immobilized the fixed initiator on a silicon wafer with gradient density a SAM of octyltrichlorosilane (OTS), which did not have an initiating site for ATRP, was deposited on a silicon wafer by evaporation. Then the OTS-gradient substrate was placed upright in the reaction vessel, and... 

Protein and cell adhesions on gradient PHEMA brushes, (a) Illustration of preparation of the gradient initiator surface, (b) Gradient PHEMA brush. (Redrawn from Mei, Y., et al., /. Biomed. Mater. Res., 79A(4), 974,2006.)... 

In a series of papers Kimmich et al. 34-36) prepared interpenetrating networks of PHEMA and poly(ethylene glycol) (PEG) by UV curing of microphase-separated mixtures of the monomer with PEG. The PEG content was 20 wt. %. The authors were able to visualize the isolated channels of PEG using electron microscopy and estimate the diameter of the PEG channels using field-gradient diffusometry, and obtained an estimate of the pore radius in PHEMA of 8-10 nm. 

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