The Mechanical Properties of Adhesive Polymer Films in Ex-vivo Study for Bowel Retraction in Laparoscopic Surgery

Objective    To develop an adhesive polymer film able to adhere strongly on serosal side of the bowel with sufficient mechanical properties to retract the bowel for laparoscopic procedures.

Method   A series of novel adhesive mono- and bi-layer polymer films were formulated in house, in which the adhesive layer was based on either Carbopol modified with N-hydroxysuccinimide (NHS) and thiobutylamidine (TBA)-chitosan (mol wt = 250k, loading of TBA = 150 µmol/g). Each polymer sample was cast in 60 mm diameter teflon moulds and air dried at 50 °C. Prior to testing of mechanical properties the individual film samples were rehydrated with phosphate buffered saline (PBS). The mechanical properties of the polymers and their adherence to bowel, were evaluated by three tests: i) tensile and shear properties ii) adhesive retraction force and work; iii) maximal stress and Young’s modulus. Ex-vivo pig bowel in 37 °C water bath and an Instron tensiometer were used for all the tests. Each polymer sample was tested 6 times and a new specimen was used for each test.

Preliminary results    The bio-adhesive polymer sustained a shear stress of 4.87kPa, which was much greater than its pure tensile stress of 1.62 kPa, using a test diameter of 28 mm (or area of 616 mm²). Polymer adhesive force during bowel retraction ranged from 3 to 5 N (using a 25mm diameter retraction probe fixed at the centre of a 60mm-diameter polymer sample). Work of adhesion at the polymer/serosa interface, defined as the area under the force-displacement curve, was from 64 to 126 mJ, which is appreciably larger than that reported using existing polymers. Young’s modulus ranged from 20 to 100 kPa, depending upon polymer sample and its rehydration. 

Conclusions    Adhesive polymers can stick to the serosal side of the bowel and its adhesive force is sufficient to lift the bowel. By exploiting the shear strength in the polymer-tissue bonding, a further reduction in device dimension is possible for MAS procedures. It is safer in low retraction stress compared to laparoscopic graspers which result in noticeably high localized pressures (210 kPa to 650 kPa) on tissue. Our ongoing R&D is to combine magnetic particles with the polymer to create a new magnetic adhesive polymer for tissue retraction and for other potential applications such as drug delivery, magnetic hyperthermia, magnetic detection or MRI contrast enhanced imaging.