The research interests of our lab lie at the intersection of polymer science and biomedical engineering. Out Team is quite diverse and has expertise in Chemistry, Materials Science, Engineering, and Biology. We want to combine all those fields to develop next-generation biomedical devices based on smart polymeric materials. These materials consist of ‘shape memory polymers’ that are responsive to bodily conditions and are mechanically adaptive to comply with a tissue. Some of our custom polymers are also biodegradable. Additionally, we make sure that our novel materials are biocompatible.

Some applications we are interested in are 1) conformal and biocompatible neural devices to study the electrophysiology of the enteric nervous system, 2) responsive polymeric biomaterials for wound healing, and 3) shape memory polymer bandages to prevent of Colonic Anastomotic Leak. Details about our current Research Projects are listed below.

Development of conformal electrode arrays for surface recordings of the enteric nervous system

Irritable bowel syndrome (IBS) is the most common functional gastrointestinal (GI) disorder worldwide. It is estimated that 10–15% of the population is affected by IBS. IBS and other GI disorders, such as inflammatory bowel disease (IBD) which includes ulcerative colitis and Crohn’s disease, are diseases that are related to a dysfunction of the enteric nervous system (ENS). Understanding how the dysfunction of enteric nerves is related to GI disorders could help to improve the lives of millions of people. What if we were able to develop a gut pacemaker to actively regulate and stimulate impaired bowel activity?

Although the ENS has the largest population of neurons in the peripheral nervous system, it is not well understood and is less investigated than the central nervous system. Most of the information gathered about the function and electrophysiology of the ENS was performed ex vivo, either on pathological samples or in cell cultures. Common methods include patch clamp recordings on explanted tissue and imaging tissue in vivo, or in vitro. Current strategies for in vivo recording and stimulation of the gut are limited by lack of conformation to complex surface topography and flexibility for tissue movement. Thus, conventional stiff or cuff type electrodes cannot conform to the gut surface, do not achieve strong electrical coupling, and are susceptible to motion artifacts since they will be moving relative to the bowel.

Figure 1. Illustration of the working principle of conformal electrodes on a 3D printed model of a human gut to show the concept of softening SMP electrode arrays.

We propose that the problems caused by conventional, stiff electrodes can be solved with the use of an electrode substrate that is of a self-softening polymer. The hypothesis is that the polymer is capable of softening and changing its shape so that the device can adapt to the shape and surface topology of its surroundings. It will wrap tightly around the gut, securing the electrodes in place to enable continuous periodic recordings of motor and sensory neurons from the myenteric and submucosal plexus.

Figure 2. Dynamic mechanical analysis (DMA) of softening of polymeric substrates. The softening occurs due to plasticization.

With this proposed research, we hope to learn more about the ENS and its correlation to GI disorders.

Development of highly stretchable electrode arrays

For multiple in vivo applications, it would be beneficial if the electrode arrays would not only be flexible and conformal but also highly stretchable in order to withstand tissue and body movements without tearing. In particular, spinal cord stimulators and peripheral cuff and blanket-like devices may undergo considerable deformation during chronic applications. To fabricate fully elastic electronic devices it is not only important to have an elastic substrate, but also to have stretchable electronics. The first aspect, the substrate material, can easily be solved by the use of elastomeric polymers such as rubbery silicone. However, the materials that are commonly used for the electrodes and the traces are metals such as gold, titanium nitride or platinum and these materials are stiff and not stretchable. Often, the traces are shaped like serpentines in order to achieve some stress relief in the direction of tension, but this does not prevent the traces from breaking if too much strain is applied.

We are aiming to develop highly stretchable electrode arrays for surface recordings and stimulations (e.g. cuff electrodes and spinal cord stimulators) using elastic polymers as substrate material with conductive polymer composites (CPCs) as the electrode and trace material. The conductive characteristics of the polymer matrix can be changed through the incorporation of a filler into the polymer matrix. Different conductive filler materials, such as PEDOT, carbon nanotubes, and graphene will be investigated.

SMP Bandage to prevent Colonic Anastomotic Leak

After colonic resections that may be necessary in case of cancer or diverticulitis, the two parts of the colon need to be reattached after the procedure. This procedure is called anastomosis and can be done through manual suture or staples. In any case, there are rates between 1% and 30% of anastomotic dehiscence reported in the literature.1 Anastomotic Leak is defined as a “leak of luminal contents from a surgical join between two hollow viscera.”2 If contents from the inside of the colon leak into the abdominal area, the consequences are various clinical signs like peritonitis; feculent wound, drain discharge, abscess, or fever. “Anastomotic leakage remains today a major cause of postoperative mortality and morbidity in colorectal surgery.”3

In order to minimize the risk of anastomotic leakage, we propose to develop a bandage made of SMP, which can wrap around the colon to seal the reconnected parts from the outside and therefore prevent any fluids to get into the abdominal cavity. The SMP will be fabricated into a tube shape that has a slightly smaller radius than the colon. The tube will then be radially expanded to a radius which is 1.5 times the radius of the colon. The device will be placed at the outside of the colon, covering the part where the anastomosis took place. The polymer will recover its shape due to the plasticization induced shape memory effect and will wrap tightly around to seal the colonic part after surgery against leakage. The SMP will be designed to be biodegradable in order to dissolve over the course of 3 to 6 months so that a second surgical procedure will not be necessary. The biodegradability and time span of degradation can be tuned by the number of ester groups in the polymeric backbone and the crosslink density of the polymeric network.

Figure 3. Working principle of the SMP bandage to prevent anastomotic leak.

In addition, anti-inflammatory drugs and bioactive compounds that promote wound healing will be loaded to the polymer. This study will serve as a model to test the hypothesis that polymers loaded with bioactive compounds reveal positive effects on the healing process and can serve as a platform technology capable of concurrent drug delivery.

[1] Kingham, T. P.; Pachter, H. L., Colonic Anastomotic Leak: Risk Factors, Diagnosis, and Treatment. Journal of the American College of Surgeons 2009, 208 (2), 269-278.

[2] Peel, A. L.; Taylor, E. W., Proposed definitions for the audit of postoperative infection: a discussion paper. Surgical Infection Study Group. Annals of The Royal College of Surgeons of England 1991, 73 (6), 385-388.  

[3] Alves, A.; Panis, Y.; Trancart, D.; Regimbeau, J.-M.; Pocard, M.; Valleur, P., Factors Associated with Clinically Significant Anastomotic Leakage after Large Bowel Resection: Multivariate Analysis of 707Patients. World Journal of Surgery 2002,26 (4), 499-502