A hyperelastic finite-element model of human skin for interactive real-time surgical simulation.

A finite-element (FE) model of human skin is proposed for future use in an interactive real-time surgical simulation to teach surgeons procedures, such as facial reconstruction using skin-flap repair. For this procedure, skin is cut into flaps that are stretched to cover openings in the face. Thus, the model must recreate the visual, haptic, and force feedback expected by the surgeon. To develop the FE model, a series of in vitro experiments were conducted on samples of human skin, subjected to uniaxial and planar tensile straining. Reduced polynomial hyperelastic (HE) materials were found to fit many of the samples' stress-strain data well. Finally, an explicit dynamic FE mesh was developed based on the fitted HE material models. A total Lagrangian formulation with the half-step central difference method was employed to integrate the dynamic equation of motion of the mesh. The mesh was integrated into two versions of a real-time skin simulator: a single-threaded version running on a computer's main central processing unit and a multithreaded version running on the computer's graphics card. The latter was achieved by exploiting recent advances in programmable graphics technology.

In vitro skin-tissue experiment for increased realism in open surgery simulations.

In-vitro uniaxial stress tests were conducted on samples of healthy human skin, obtained as a result of plastic surgical procedures. Pairs of test strips were cut from each sample to assess the effects of local orthotropy. Each strip was then subjected to constant strain-rate tensile testing, to observe its stress/strain behaviour. Typical maximal values for Young's modulus were found to be approximately 15.3MPa and 3.48Mpa for Langer-aligned and perpendicular test strips, respectively.

Introducing a novel haptic interface for the planning and simulation of open surgery.

Existing simulation software, originally developed for the simulation and planning of inguinal hernia repair, was fused with two haptic feedback devices: the SensAble Technologies Phantom Desktop, and the ACROE/ICA Telluris system. The former allows easy integration on a PC-based platform, though in the long run, the Telluris system is preferred because of its robustness and its ability to design custom-built solutions.

Benefit of higher closed-loop bandwidths in ocular adaptive optics.

We present an ocular adaptive optics system with a wavefront sampling rate of 240 Hz and maximum recorded closed-loop bandwidth close to 25 Hz, but with typical performances around 10 Hz. The measured bandwidth depended on the specific system configuration and the particular subject tested. An analysis of the system performance as a function of achieved bandwidth showed consistently higher Strehl ratios for higher closed-loop bandwidths. This may be attributed to a combination of limitations on the available technology and the dynamics of ocular aberrations. We observed dynamic behaviour with a maximum frequency content around 30 Hz.