Micro-Scale Bio-Inspired Structured Polymer Surfaces for Tissue Adhesion

There are many cases when it would be beneficial to provide reliable, reversible adhesion at a tissue-device interface. There are currently many adhesion mechanisms used during surgical procedures such as graspers, vacuum cups and hooks. However, these are known to cause some scale of tissue trauma. This thesis investigates the viability of using a bio-inspired, structured polymer surfaces to provide wet adhesion forces through the formation of liquid bridges on the tip of discrete pillars. The mechanism described involves a contribution from both Stefan forces and capillary forces to provide the total adhesion force.
A main factor to this work is the ability to successfully, repeatedly and reliably fabricate polymer surfaces at a micron scale with varying geometry, specifically in terms of pillar spacing. The substrate should be flexible and have the ability to tune the wettability. A number of lithography techniques have been explored for a range of polymers, finally settling on a nano-imprint lithography technique with Poly (dimethylsiloxane) (PDMS) as the polymer.
Experimental adhesion tests have been performed and it has been found, that for such an adhesion mechanism to be successful, an optimal contact angle must be reached. If the contact angle is too high, repulsive forces in convex menisci will form and the adhesion will be low as a result. If the contact angle is too low, the capillary length : pillar height ratio results in the surface acting super-hydrophobic and completely wetting the pillars, preventing the formation of liquid bridges, and again resulting in low adhesion, it is proposed that such a mechanism would occur at contact angles lower than 50°. A mathematical model has been investigated, encompassing both the Stefan and adhesion forces and the limitations of this have been discussed in relation to the complexity of this system.