Yihao Zheng

Experimental investigation of the abrasive crown dynamics in orbital atherectomy

Orbital atherectomy is a catheter-based minimally invasive procedure to modify the plaque within atherosclerotic arteries using a diamond abrasive crown. This study was designed to investigate the crown motion and its corresponding contact force with the vessel. To this end, a transparent arterial tissue-mimicking phantom made of polyvinyl chloride was developed, a high-speed camera and image processing technique were utilized to visualize and quantitatively analyze the crown motion in the vessel phantom, and a piezoelectric dynamometer measured the forces on the phantom during the procedure. Observed under typical orbital atherectomy rotational speeds of 60,000, 90,000, and 120,000rpm in a 4.8mm caliber vessel phantom, the crown motion was a combination of high-frequency rotation at 1000, 1500, and 1660.4-1866.1Hz and low-frequency orbiting at 18, 38, and 40Hz, respectively. The measured forces were also composed of these high and low frequencies, matching well with the rotation of the eccentric crown and the associated orbital motion. The average peak force ranged from 0.1 to 0.4N at different rotational speeds.

Computational Fluid Dynamics Modeling of the Burr Orbital Motion in Rotational Atherectomy with Particle Image Velocimetry Validation

Rotational atherectomy (RA) uses a high-speed rotating burr introduced via a catheter through the artery to remove hardened atherosclerotic plaque. Current clinical RA technique lacks consensus on burr size and rotational speed. The rotating burr orbits inside the artery due to the fluid force of the blood. Different from a common RA technique of upsizing burrs for larger luminal gain, a small burr can orbit to treat a large lumen. A 3D computational fluid dynamics (CFD) model was developed to simulate the burr motion and study the fluid flow and force in RA. A particle image velocimetry experiment was conducted to measure and validate the flow field including the radial and axial velocities and a pair of counter-rotating vortices near the burr equator in CFD. The hydraulic force on the burr and the contact force between the burr and the arterial wall were estimated by CFD. The contact force can be reduced by using smaller burr and lower rotational speed. Utilizing the small burr orbital motion has the potential to be an improved RA technique.

Tissue transformation mold design and stereolithography fabrication

Purpose To obtain a vascularized autologous bone graft by in-vivo tissue transformation, a biocompatible tissue transformation mold (TTM) is needed. An ideal TTM is of high geometric accuracy and X-ray radiolucent for monitoring the bone tissue formation. The purpose of this study is to present the TTM design and fabrication process, using 3D reconstruction, stereolithography (SLA) and silicone molding. Design/methodology/approach The rat mandible, the targeted bone graft, was scanned by micro-computed tomography (CT). From the micro-CT images, the 3D mandible model was identified and used as the cavity geometry to design the TTM. The TTM was fabricated by molding the biocompatible and radiolucent silicone in the SLA molds. This TTM was implanted in a rat for in vivo tests on its biocompatibility and X-ray radiolucency. Findings SLA can fabricate the TTM with a cavity shape that accurately replicates that of the rat mandible. The bone formation inside of the silicone TTM can be observed by X-ray. The TTM is feasible for in vivo tissue transformation for vascularized bone reconstruction. Research limitations/implications Research of the dimensional and geometrical accuracy of the TTM cavity is required in the future study of this process. Practical implications The TTM fabricated in this presented approach has been used for in-vivo tissue transformation. This technique can be implemented for bone reconstruction. Originality/value The precision fabrication of the TTMs for in-vivo tissue transformation into autogenous vascularized bone grafts with complex structures was achieved by using SLA, micro-CT and silicone molding.

3D Printed composite for simulating thermal and mechanical responses of the cortical bone in orthopaedic surgery

Synthetic bones made of polyurethane (PU) foams or glass-fiber reinforced epoxy are often used in surgical training, planning, and tool analysis, but these materials cannot be 3D printed for a patient-specific design. This paper introduces a new type of bone-mimicking material made by the binder jetting technology and a post-strengthening process with epoxy, namely 3D polymer-infiltrated composite (3DPIC). 3DPIC has been previously evaluated by surgeons as a proper alternative to commercial synthetic bones, but no quantitative testing data is available. Therefore, a series of experiments are conducted in this study to verify the use of 3DPIC. The first part of experiments includes the measurement of mechanical properties using the four-point bending and the measurement of thermal properties. The second part of experiments is to test drilling haptic and thermal responses of 3DPIC as compared to the cortical bone. The results show that 3DPIC has a comparable elastic modulus but a lower strength than the cortical bone. 3DPIC can produce realistic drilling force and torque as well as representative temperature change in drilling operations, but the bone debris tends to be more ductile and continuous than that of the cortical bone. Applications and limitations of 3DPIC are discussed based on these results.