Biomechanics Characterization of Autonomic and Somatic Nerves by High Dynamic Closed-Loop MEMS force sensing.

The biomechanics of peripheral nerves are determined by the blood-nerve barrier (BNB), together with the epineural barrier, extracellular matrix, and axonal composition, which maintain structural and functional stability. These elements are often ignored in the fabrication of penetrating devices, and the implant process is traumatic due to the mechanical distress, compromising the function of neuroprosthesis for sensory-motor restoration in amputees. Miniaturization of penetrating interfaces offers the unique opportunity of decoding individual nerve fibers associated to specific functions, however, a main issue for their implant is the lack of high-precision standardization of insertion forces. Current automatized electromechanical force sensors are available; however, their sensitivity and range amplitude are limited (i.e. mN), and have been tested only in-vitro. We previously developed a high-precision bi-directional micro-electromechanical force sensor, with a closed-loop mechanism (MEMS-CLFS), that while measuring with high-precision (-211.7µN to 211.5µN with a resolution of 4.74nN), can be used in alive animal. Our technology has an on-chip electrothermal displacement sensor with a shuttle beam displacement amplification mechanism, for large range and high-frequency resolution (dynamic range of 92.9 dB), which eliminates the adverse effect of flexural nonlinearity measurements, observed with other systems, and reduces the mechanical impact on delicate biological tissue. In this work, we use the MEMS-CLFS for in-vivo bidirectional measurement of biomechanics in somatic and autonomic nerves. Furthermore we define the mechanical implications of irrigation and collagen VI in the BNB, which is different for both autonomic and somatic nerves (~ 8.5-8.6 fold density of collagen VI and vasculature CD31+ in the VN vs ScN). This study allowed us to create a mathematical approach to predict insertion forces. Our data highlights the necessity of nerve-customization forces to prevent injury when implanting interfaces, and describes a high precision MEMS technology and mathematical model for their measurements.

Rosette-scan video-rate atomic force microscopy: Trajectory patterning and control design.

We present an analysis and a systematic design methodology for a novel nonraster scan method based on a rosette pattern and demonstrate its application in video-rate atomic force microscopy. This pattern is traced when the lateral axes of a parallel kinematic scanner are commanded to follow a combination of two sinusoids with identical amplitudes and different frequencies. We design an internal-model-based controller to enhance the tracking performance of this pattern and implement the scheme on a microelectromechanical system scanner. The results reveal high-precision tracking of the rosette pattern in order to acquire time-lapsed atomic force microscope images at the rate of 10 frames/s.

Note: A silicon-on-insulator microelectromechanical systems probe scanner for on-chip atomic force microscopy.

A new microelectromechanical systems-based 2-degree-of-freedom (DoF) scanner with an integrated cantilever for on-chip atomic force microscopy (AFM) is presented. The silicon cantilever features a layer of piezoelectric material to facilitate its use for tapping mode AFM and enable simultaneous deflection sensing. Electrostatic actuators and electrothermal sensors are used to accurately position the cantilever within the x-y plane. Experimental testing shows that the cantilever is able to be scanned over a 10 µm × 10 µm window and that the cantilever achieves a peak-to-peak deflection greater than 400 nm when excited at its resonance frequency of approximately 62 kHz.

High-stroke silicon-on-insulator MEMS nanopositioner: control design for non-raster scan atomic force microscopy.

A 2-degree of freedom microelectromechanical systems nanopositioner designed for on-chip atomic force microscopy (AFM) is presented. The device is fabricated using a silicon-on-insulator-based process and is designed as a parallel kinematic mechanism. It contains a central scan table and two sets of electrostatic comb actuators along each orthogonal axis, which provides displacement ranges greater than ±10 µm. The first in-plane resonance modes are located at 1274 Hz and 1286 Hz for the X and Y axes, respectively. To measure lateral displacements of the stage, electrothermal position sensors are incorporated in the design. To facilitate high-speed scans, the highly resonant dynamics of the system are controlled using damping loops in conjunction with internal model controllers that enable accurate tracking of fast sinusoidal set-points. To cancel the effect of sensor drift on controlled displacements, washout controllers are used in the damping loops. The feedback controlled nanopositioner is successfully used to perform several AFM scans in contact mode via a Lissajous scan method with a large scan area of 20 µm × 20 µm. The maximum scan rate demonstrated is 1 kHz.

Experimental wound healing using microamperage electrical stimulation in rabbits.

We investigated the effects of microamperage electrical stimulation (MES) on the healing of skin incision in rabbits. Thirty male adult rabbits were randomly divided into sham-treated and experimental groups. Each group was divided into three subgroups, based on the duration of experiment (4, 7, and 15 days). A full-thickness incision was made on the skin of each rabbit. The experimental group received an MES of 200 microamperes current intensity for 2 h/day. Morphometrical and biomechanical evaluations were carried out. The mean number of fibroblasts at day 7 and the mean of tensile strength at day 15 were found to be significantly higher for the experimental group than for those in the sham-treated group (p < 0.01 and p < 0.05, respectively). Daily application of MES significantly accelerated the wound-healing process of full-thickness incision in the rabbits' skin.