Although silicone foams are used as ophthalmic biomaterials, they are usually hydrophobic. 20/20 has developed a method to make silicones foams that incorporate hydrophilic domains. (F refers to small domains of poly[ethylene glycol] that will be examined as bioactive delivery depots.)
Amanda Fawcett, Helen So, and Dr. Michael Brook co-authored and submitted``Silicone foams stablized by surfactants generated in situ from allyl-functionalized PEG``to Soft Matter, which was published online in January 2010. The following is the article abstract:
Silicone foams normally require the use of agents or chemical reactions that blow gases, and a surfactant for bubble stabilization. We have discovered that the presence of monoallyl-functionalized poly(ethylene glycol) (PEG) leads to large increases in the viscosity of silicone pre-elastomers such that stable foams form with bubbles mostly being generated by coalescence of dissolved gases during the normal degassing process. Although silicone elastomer cure may take up to 24 h for completion, the foams remain stable during this time when appropriate concentrations of allyl-PEG and curing catalyst are used. No traditional surfactant is required, but PEG-modified silicone surfactants are formed in situ by covalent grafting of the PEG to the silicone matrix, leading to the increase in viscosity. The presence of allyl-PEG decreases elastomer cure efficiency, but this is readily overcome, if necessary, to generate more rigid foams by the use of additional platinum catalyst, in which case foaming occurs both due to loss of dissolved gases and to hydrogen evolution. Foam stabilization with appropriate allyl-PEG compounds is a consequence of an initial viscosity increase.
Vinodh Rajendra, Yang Chen, and Dr. Michael Brook co-authored and submitted ``Structured hydrophilic domains on silicone elastomers``to Polymer Chemistry, which was published in December 2009. Included below is the article abstract:
The controlled generation of hydrophilic structures within hydrophobic polymers can be challenging. Very few examples of such structures have been described for silicones. We now report that such structures can be encoded in the air-contacting layer of a silicone elastomer by the formation of silica domains from tetraethoxysilane, optionally in the presence of poly(ethylene glycol) (PEG), using a surface active aminopropylsilicone catalyst and moisture cure. The control of the relative modulus at the upper versus lower layers and the degree and type of hydrophilic structuring requires control over the efficiency of delivery of water to the core of the pre-elastomer, which is facilitated by the surface active catalyst and may additionally be manipulated by the addition of PEG.
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