Self Assembling Modifying Endgroups (SAME™) Technology  
Self assembling modifying endgroups (SAME™) technology is the second generation of surface modifying endgroups (SME™). While SME™s are generally "bio-passive," there is a desire to achieve "bio-active" surfaces using the SME™ approach. Bioactive SAME™ groups could include drug functionality such as heparin, biological groups such as peptides, or surface functionality for post device fabrication surface reactions.

The self assembling monolayer (SAM) literature has demonstrated that bioactive chemical groups can be appended to alkane chains as a method of modifying model surfaces for in vitro applications. Ideally, the chemistry used during such model studies could then be applied to actual medical devices to further improve clinical outcomes. However, SAM technologies are not easily transferred to medical device applications due to the fragility of such systems.

SAME™ technology is a breakthrough that is capable of providing polymers with "SAM-like" engineered surfaces. Relative to backbone chains, polymer end groups are more mobile, in part because they are often tethered to the backbone by a single, flexible covalent bond. Their mobility allows them to diffuse from the bulk, and assemble in the polymer surface to affect surface composition. This occurs spontaneously if the presence of the end groups in the surface reduces system interfacial energy. Simple homopathic hydrophobic end group may diffuse to an air interface, while purely hydrophilic end groups may enrich a polymer surface when exposed to aqueous body fluids. SAME™ technology utilizes either a hydrophobic or hydrophilic spacer groups, and a specific head group chemistry chosen for a particular application. The spacer groups will "self-assemble" at the surface through either hydrophobic or hydrophilic interactions, and thus present the head group as the outermost monolayer of the polymer. Additionally, the spacer groups can be optionally crosslinked to "lock" a surface structure in and thus prevent a reversal of surface chemistry as an environment is changed.

The realization of SAME™ technology was enabled by understanding the mechanism of "self-assembly" and also through the ability of characterizing polymer surfaces using sum frequency generation (SFG) surface specific spectroscopy. SAM development on gold is characterized by rapid formation of gold-thiol bonds and planar conformation of the alkane chains, followed by slower filling in of the final monolayer, attainment of the characteristic angle of the alkanes relative to the surface, and close packing of head groups. In SAME™ polymers the diffusion of end groups from the bulk 'replaces' the SAM adsorption step, but it is likely that the remaining steps in developing the equilibrium surface are similar. That is, upon arriving at the air interface from the bulk, the SME™ may initially assume a planar conformation to maximize both the coverage by hydrophobic methylene groups, and the resulting interfacial energy reduction. As more SAMEs arrive the alkane spacers begin to pack more closely in the surface and subsequently allow a tighter packing of head groups.

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