Surgical sites deep in the body are difficult to monitor and current diagnostic techniques alert clinicians of complications when it is already too late. Monitoring these sites is necessary for periods up to 4 weeks to ensure there are no complications and that the operation and the healing process is progressing in a satisfactory manner. Currently there are no implantable medical devices that have the ability to post-operatively monitor a surgical site. At the Hamlyn Centre we are working towards the first devices of this kind. For certain types of surgery, inadequate tissue oxygen delivery (ischemia) can serve as a prognostic marker for subsequent complications. The increase in intracellular concentration of certain ions leads to an increase in the intracellular osmotic pressure, resulting in intracellular (anoxic) oedema. The progression of the ischemic event triggers the activation of inflammatory mediators, which in turn disturb membrane permeability. The cell membrane becomes more permeable; more harmful chemicals flow into the cell and metabolic waste products accumulate. Mitochondria also break down, releasing more harmful chemicals into the cell. Ultimately, metabolic processes cease, ion pumps fail and the membrane is disrupted. Cells subsequently die (apoptosis), leading to organ failure and the release of harmful toxins into the surrounding environment. This will poison nearby neurons, cells and organs. Potentiometric (pH, K+, Na+) and impedimetric sensors have been applied to tissue ischemia monitoring; however, there has not been a single miniature flexible multi-modal sensing array that is capable of measuring the variety of sensing targets that we are interested in. Moreover, the limited examples in the literature use tethered approaches leaving the electronics far from the tissue. Additionally, these have thus far been based on commercially available discrete electronic components leading to large bulky arrangements. As a result, currently there is no implantable impedimetric system and, moreover, there in no such system combining impedance and ionic measurements. At the Hamlyn centre we are working towards the first such system using CMOS ASIC technology.
For implantable sensing, a particularly challenging case is colorectal resection via anastomosis in the gastrointestinal tract. Failure of the anastomosis can lead to colorectal anastomotic leakage (CAL), one of the most serious and challenging complications following sigmoid or rectal cancer surgery and the leading cause of death after colorectal surgery. We are investigating the use of commercial flexi/rigid printed circuit board (PCB) fabrication technologies to allow the development of mass-produced, low-cost sensors, as well as in-house fabrication of novel application specific sensors using inkjet printing techniques.
What are we using it for?
At the Hamlyn Centre we are working on the development of the next generation of implantable medical devices for post-surgical monitoring of deep surgical sites. Sites of surgical interventions deep inside the body are difficult to access to evaluate tissue viability, healing and progression. Monitoring these sites would allow physicians to determine whether there are complications that may lead to infections, prolonged post-operative hospital stays, re-operation, poor functional outcome, multiple organ failure or even mortality. Current clinical practices do not allow us to detect complications early enough leading to (as well as the effects described above) increased strains on the NHS, costing approximately one billion pounds per year. Our main goal is to introduce SMART sensing into surgical operations and patient recovery, and to introduce intelligence into passive devices such that we alleviate significant burdens from health care systems and professionals, patients and their family’s.