Roland K. Chen

Multi-modality gellan gum-based tissue-mimicking phantom with targeted mechanical, electrical, and thermal properties.

This study develops a new class of gellan gum-based tissue-mimicking phantom material and a model to predict and control the elastic modulus, thermal conductivity, and electrical conductivity by adjusting the mass fractions of gellan gum, propylene glycol, and sodium chloride, respectively. One of the advantages of gellan gum is its gelling efficiency allowing highly regulable mechanical properties (elastic modulus, toughness, etc). An experiment was performed on 16 gellan gum-based tissue-mimicking phantoms and a regression model was fit to quantitatively predict three material properties (elastic modulus, thermal conductivity, and electrical conductivity) based on the phantom materials composition. Based on these material properties and the regression model developed, tissue-mimicking phantoms of porcine spinal cord and liver were formulated. These gellan gum tissue-mimicking phantoms have the mechanical, thermal, and electrical properties approximately equivalent to those of the spinal cord and the liver.

Optimal needle design for minimal insertion force and bevel length

This research presents a methodology for optimal design of the needle geometry to minimize the insertion force and bevel length based on mathematical models of cutting edge inclination and rake angles and the insertion force. In brachytherapy, the needle with lower insertion force typically is easier for guidance and has less deflection. In this study, the needle with lancet point (denoted as lancet needle) is applied to demonstrate the model-based optimization for needle design. Mathematical models to calculate the bevel length and inclination and rake angles for lancet needle are presented. A needle insertion force model is developed to predict the insertion force for lancet needle. The genetic algorithm is utilized to optimize the needle geometry for two cases. One is to minimize the needle insertion force. Using the geometry of a commercial lancet needle as the baseline, the optimized needle has 11% lower insertion force with the same bevel length. The other case is to minimize the bevel length under the same needle insertion force. The optimized design can reduce the bevel length by 46%. Both optimized needle designs were validated experimentally in ex vivo porcine liver needle insertion tests and demonstrated the methodology of the model-based optimal needle design.

The Needle With Lancet Point: Geometry for Needle Tip Grinding and Tissue Insertion Force

The grinding procedure and setup, the cutting edge inclination and rake angles of the needle with lancet point (NLP), and the NLP tissue insertion force are investigated in this paper. The NLP is the most commonly used needle tip geometry. However, there is a lack of research on the NLP grinding and cutting edge characteristics. In this study, a four-step grinding procedure and a mathematical model to calculate the inclination and rake angles along the cutting edge of the NLP are developed. Three cases of NLP are defined based on the relative position of the lancets. Prototype NLP for each case was produced and analyzed. Compared to the regular bias bevel needle, grinding two lancets in NLP can increases the inclination angle, particularly at the needle tip. Experiments with needle insertion into the porcine liver were conducted and results showed that NLP could achieve over 40% reduction of the initial peak needle insertion force compared to that of the regular bias bevel needle tip.

Electrosurgical Vessel Sealing Tissue Temperature: Experimental Measurement and Finite Element Modeling

The temporal and spatial tissue temperature profile in electrosurgical vessel sealing was experimentally measured and modeled using finite element modeling (FEM). Vessel sealing procedures are often performed near the neurovascular bundle and may cause collateral neural thermal damage. Therefore, the heat generated during electrosurgical vessel sealing is of concern among surgeons. Tissue temperature in an in vivo porcine femoral artery sealed using a bipolar electrosurgical device was studied. Three FEM techniques were incorporated to model the tissue evaporation, water loss, and fusion by manipulating the specific heat, electrical conductivity, and electrical contact resistance, respectively. These three techniques enable the FEM to accurately predict the vessel sealing tissue temperature profile. The averaged discrepancy between the experimentally measured temperature and the FEM predicted temperature at three thermistor locations is less than 7%. The maximum error is 23.9%. Effects of the three FEM techniques are also quantified.

Nano-CT Characterization of Structural Voids and Air Bubbles in Fused Deposition Modeling for Additive Manufacturing

The build quality of fused deposition modeling (FDM) parts depends on many build parameters, such as toolpath and temperature. Destructive material testing methods are widely used to examine FDM parts with different build parameters. The optimization of build parameters relies on methods of experimental design and extensive material testing. However, this approach mainly considers the bulk properties of the FDM part, without fully understanding the effect of each parameter on the build quality. This study presents a method to investigate the integrity of FDM parts using nano-focus computed tomography (NanoCT). A solid filled ULTEM sample was built and underwent NanoCT scan. The three dimensional geometry of this sample was reconstructed. Structural voids and bubbles inside the sample were also identified and quantified. The volume of this solid filled sample consists of 11.9% structural voids and bubbles. Air bubbles are further categorized into internal bubbles (bubbles inside the deposited fibers) and necking bubbles (bubbles at the bonding region of two adjacent fibers). While structural voids can be predicted according to toolpath, layer thickness, and extruder diameter, the occurrence of air bubbles are unexpected and can compromise the integrity of the built parts. NanoCT offers a non-destructive way to inspect the integrity of FDM parts. NanoCT can also be used to study three dimensional meso-structure and correlate that with build parameters. This will provide insightful information for further studying the FDM process and help to predict material strengths and to improve the part quality.© 2015 ASME

Study of Insertion Force and Deformation for Suturing With Precurved NiTi Guidewire

This research presents an experimental study evaluating stomach suturing using a precurved nickel-titanium (NiTi) guidewire for an endoscopic minimally invasive obesity treatment. Precise path planning is critical for accurate and effective suturing. A position measurement system utilizing a hand-held magnetic sensor was used to measure the shape of a precurved guidewire and to determine the radius of curvature before and after suturing. Ex vivo stomach suturing experiments using four different guidewire tip designs varying the radius of curvature and bevel angles were conducted. The changes in radius of curvature and suturing force during suturing were measured. A model was developed to predict the guidewire radius of curvature based on the measured suturing force. Results show that a small bevel angle and a large radius of curvature reduce the suturing force and the combination of small bevel angle and small radius of curvature can maintain the shape of guidewire for accurate suturing.

Bipolar Electrosurgical Vessel-Sealing Device With Compressive Force Monitoring

Bipolar electrosurgical vessel sealing is commonly used in surgery to perform hemostasis. The electrode compressive force is demonstrably an important factor affecting the vessel seal burst pressure, an index of the seal quality. Using a piezoresistive force sensor attached to the handle of a laparoscopic surgical device, applied handle force was measured and used to predict the electrosurgical vessel compressive force and the pressure at the electrode. The sensor enables the monitoring of vessel compressive force during surgery. Four levels of compressive force were applied to seal three types of porcine vessels (carotid artery, femoral artery, and jugular vein). The burst pressure of the vessel seal was tested to evaluate the seal quality. Compressive pressure was found to be a statistically significant factor affecting burst pressure for femoral arteries and jugular veins. Vessels sealed with low compressive pressure (<300 kPa) have a higher failure rate (burst pressure<100 mm Hg) than vessels sealed with high compressive pressure. An adequate compressive force is required to generate the compressive pressure needed to form a seal with high burst pressure. A laparoscopic surgical device with compressive force monitoring capability can help ensure adequate compressive pressure, vessel burst pressure, and quality of seal.

Advanced Five-Plane Lancet Needle Design, Grinding, and Tissue Insertion

The needle with lancet point (NLP), having three planes at the tip to generate a sharp lancet point, is the most common needle tip geometry. This research presents two five-plane lancet needle designs, the five-plane lancet needle with two back bevels (FLN-B) and five-plane lancet needle with two front bevels (FLN-F), to study the effect of two additional bevel planes on the reduction of soft tissue insertion force over that of the NLP. The mathematical models for inclination and rake angles along the cutting edges, and the grinding procedure and setup parameters for FLN-B and FLN-F are developed. Prototype needles are fabricated and the needle insert test was conducted on PVC phantom tissue which mimics the soft tissue. Compared to NLP, FLN-B and FLN-F have higher inclination and rake angles and can reduce the insertion forces by 9.1% and 8.3%, respectively.Copyright

Comparison of thermal coagulation profiles for bipolar forceps with different cooling mechanisms in a porcine model of spinal surgery

Background: Coagulation accomplished using bipolar forceps is common in neurosurgery. Control of thermal spread from the forceps tips into surrounding neural tissues is a persistent concern, as neural tissues are especially vulnerable to heat injury. The purpose of our investigation was to compare the efficacy of cooling mechanisms for four different bipolar forceps and to understand thermal spread when coagulating vessels on the spinal cord. Methods: Immediately following euthanasia, the dura mater of an ex vivo porcine model was opened to expose vessels on the spinal cord for coagulation. Temperature profiles were measured at generator power of 25 W and at fixed 5-second activation times. The bipolar forceps used in this study included regular stainless steel, titanium, heat-pipe embedded, and SILVERGlide forceps. Temperature was measured by micro-thermistor at the midpoint between the bipolar tips, and 1 and 2 mm away from the midpoint along the centerline. Statistical analysis was performed to evaluate temperature differences. Results: Temperature profiles indicated that heat-pipe embedded forceps create the least amount of temperature increase and the highest normalized temperature decreasing slope after activation. The decreasing slope of SILVERGlide forceps is slightly higher than that of regular stainless steel forceps. Conclusions: Bipolar forceps incorporating either heat-pipe embedded technology or SILVERGlide coating can effectively limit excessive thermal spread, thus decreasing potential injury to adjacent tissues when compared with standard stainless steel and titanium bipolar forceps. Of the two, heat-pipe embedded technology appeared safest, having better cooling efficiency at higher temperature.

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.