Friction manipulation for intestinal locomotion

Macro-Scale Tread Patterns for Traction in the Intestine

GOAL

Tread patterns are widely used to increase traction on different substrates, with the tread scale, geometry and material being tailored to the application. This work explores the efficacy of using macro-scale tread patterns for a medical application involving a colon substrate - renowned for its low friction characteristics.

METHODS

Current literature was first summarized before an experimental approach was used, based on a custom test rig with ex vivo porcine colon, to assess different macro-scale tread patterns. Performance was based on increasing traction while avoiding significant trauma. Repeated testing (n = 16) was used to obtain robust results.

RESULTS

A macro-scale tread pattern can increase the traction coefficient significantly, with a static traction coefficient of 0.74 ± 0.22 and a dynamic traction coefficient of 0.35 ± 0.04 compared to a smooth (on the macro-scale) Control (0.132 ± 0.055 and 0.054 ± 0.015, respectively). Decreasing the scale and spacing between the tread features reduced apparent trauma but also reduced the traction coefficient.

CONCLUSION

Significant traction can be achieved on colon tissue using a macro-scale tread but a compromise between traction (large feature sizes) and trauma (small feature sizes) may have to be made.

SIGNIFICANCE

This work provides greater insight into the complex frictional mechanisms of the intestine and gives suggestions for developing functional tread surfaces for a wide range of clinical applications.

A magnetically actuated anchoring system for a wireless endoscopic capsule

In this study, we propose a new magnetically actuated anchoring system for wireless capsule endoscopes (WCE) by employing the principle of a switchable magnetic spring. A force model is derived to predict the magnetic force needed to support the interaction between the anchors and the intestinal lumen. The theoretical and experimental analysis conducted shows that the magnetic spring is capable of providing the force needed to activate the anchoring mechanism, which consists of four foldable legs. A prototype capsule with a size comparable with the size of a commercial WCE was designed, fabricated, and tested. The in-vitro tests with a real small intestine show that the proposed anchoring mechanism is able to raise the friction force between the anchoring legs and inner wall of the intestine by more than two times after its activation using an external magnetic field. Experimental results presented demonstrate that the proposed anchoring system, which has a low foot-print not taking up too much space on the capsule, can provide a reliable anchoring capability with the capsule inside the intestinal lumen.

Preliminary mechanical characterization of the small bowel for in vivo robotic mobility

In this work we present test methods, devices, and preliminary results for the mechanical characterization of the small bowel for intra luminal robotic mobility. Both active and passive forces that affect mobility are investigated. Four investigative devices and testing methods to characterize the active and passive forces are presented in this work: (1) a novel manometer and a force sensor array that measure force per cm of axial length generated by the migrating motor complex, (2) a biaxial test apparatus and method for characterizing the biomechanical properties of the duodenum, jejunum, and ileum, (3) a novel in vitro device and protocol designed to measure the energy required to overcome the self-adhesivity of the mucosa, and (4) a novel tribometer that measures the in vivo coefficient of friction between the mucus membrane and the robot surface. The four devices are tested on a single porcine model to validate the approach and protocols. Mean force readings per cm of axial length of intestine that occurred over a 15 min interval in vivo were 1.34 ± 0.14 and 1.18 ± 0.22 N cm(-1) in the middle and distal regions, respectively. Based on the biaxial stress/stretch tests, the tissue behaves anisotropically with the circumferential direction being more compliant than the axial direction. The mean work per unit area for mucoseparation of the small bowel is 0.08 ± 0.03 mJ cm(-2). The total energy to overcome mucoadhesion over the entire length of the porcine small bowel is approximately 0.55 J. The mean in vivo coefficient of friction (COF) of a curved 6.97 cm(2) polycarbonate sled on live mucosa traveling at 1 mm s(-1) is 0.016 ± 0.002. This is slightly lower than the COF on excised tissue, given the same input parameters. We have initiated a comprehensive program and suite of test devices and protocols for mechanically characterizing the small bowel for in vivo mobility. Results show that each of the four protocols and associated test devices has successfully gathered preliminary data to confirm the validity of our test approach.

A pilot study on a new anchoring mechanism for surgical applications based on mucoadhesives

In order to minimize the invasiveness of laparoscopic surgery, different techniques are emerging from research to clinical practice. Whether the incision is performed on the outside - as in Single Port Laparoscopy (SPL) - or on the inside - as in Natural Orifice Transluminal Endoscopic Surgery (NOTES) - of the patient's body, inserting and operating all the instruments from a single access site seems to be the next challenge in surgery. Magnetic guidance has been recently proposed for controlling surgical tools deployed from a single access. However, the exponential drop of magnetic field with distance makes this solution suitable only for the upper side of the abdominal cavity in nonobese patients. In the present paper we introduce a polymeric anchoring mechanism to lock surgical assistive tools inside the gastric cavity, based on the use of mucoadhesive films. Mucoadhesive properties of four formulations, with different chemical components and concentration, are evaluated by using both in vitro and ex vivo test benches on porcine stomach samples. Hydration of mucoadhesive films by contact with the aqueous mucous layer is analyzed by means of in vitro swelling tests, whereas optimal preloading conditions and adhesion performances, in terms of detachment force, supported weight and size are investigated ex vivo. Mucoadhesion is observed with all the four formulations. For a contact area of 113 mm(2), the maximum normal and shear detachment forces withstood by the adhesive film are 2,6 N and 1 N respectively. These values grow up to 12,14 N and 4,5 N when the contact area increases to 706 mm(2). Lifetime of the bonding on the inner side of the stomach wall was around two hours. Mucoadhesive anchoring represents a fully biocompatible and safe approach to deploy multiple assistive surgical tools on mucosal tissues by minimizing the number of access ports. This technique has been quantitatively assessed ex vivo for anchoring on the inner wall of the gastric cavity or in gastroscopic surgery. By properly varying the chemical formulation, this approach can be extended to other cavities of the human body.

Stick, unstick, restick sticky films in the colon

The main challenge in designing diagnostic devices able to move along the colon is their locomotion method. Manipulating friction with the colonic surface is a key requirement for their safe and atraumatic propagation. One possible solution is to generate friction by means of adhesive forces. For this reason, a diagnostic device can be covered with mucoadhesive films that are able to stick on the colonic surface by generating high static friction. For a smooth transition from static to dynamic regime, the mucoadhesive films should unstick just before the initialisation of motion. Experiments have shown that promoting cohesive fracture of the films by controllable air introduction does not lead to friction reduction sufficient for smooth unsticking. Introducing water at the film-colon interface, however, reduces the static friction significantly, and makes the device to unstick and slide smoothly without leaving film fragments on the colonic surface behind. If unsticking is initiated by means of air or water introduction, a new film is required each time the device is required to restick. As an alternative, the possibility of coating the device with environmentally-sensitive mucoadhesive polymers that can respond reversibly to external stimuli and alter their properties is discussed.

Mucoadhesives in the gastrointestinal tract: revisiting the literature for novel applications

This article investigates applying mucoadhesives to manipulate friction and to achieve locomotion of an alternative colonoscopic device through the large intestine. Considering that such an application of mucoadhesives is new, the authors recognised the need to revisit the different aspects of mucoadhesion in the gastrointestinal tract on the basis of the literature and to re-evaluate them according to the requirements for intestinal locomotion. First, the material properties, which are critical for the locomotion mechanism and specific categories of mucoadhesives characterised by those critical properties were identified. The next step was to examine the structural characteristics of those categories to specify which of the already synthesised mucoadhesives are promising candidates for friction manipulation. Then, the response of those mucoadhesives to a number of environmental stimuli was examined. At the end, two in vitro experiments were carried out to study the potential of mucoadhesives for intestinal locomotion. A comparative analysis of the role of mucoadhesives in drug delivery and in intestinal locomotion leads to the conclusion that the two applications can be approached to one extent with common principles, but crucial differences are present as well.