Towards a full-field strain sensor for guiding hernia repairs.

Each year, approximately 400,000 ventral hernia repairs are performed in the United States [1], [2]. Large ventral hernias (hernias that occur in the abdominal wall) are typically treated by suturing in a surgical mesh to cover and overlap the hernia defect. However, in 10-20% of patients, the hernia repair fails, resulting in recurrence of the hernia, along with other complications including infection and intestinal obstruction [3], [4]. One potential cause of hernia recurrence is the unequal distribution of stress across the mesh resulting in high stress concentrations at the tissue-mesh interface, particularly at the site of mesh fixation to the abdominal wall muscles[5], [6]. Strain across the mesh can be used as an indicator for how evenly stress is distributed across the surface of the mesh. To this end, we have built a full-field, 3D strain measurement system to enable physicians to actively identify and address areas of high strain during the surgery, thus decreasing the rate of hernia recurrence. The strain sensor uses an optical technique, called the grid method, in conjunction with the defocused particle image velocimetry (DPIV) technique to measure the 3D strain distribution across the mesh. The system can achieve a limit of detection down to 0.4% strain and across a 50 cm range z-axis displacement using a Canon EOS 7D camera with a pinhole aperture mask.