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Research Papers

J. Med. Devices. 2017;12(1):011001-011001-7. doi:10.1115/1.4038221.

Right ventricular (RV) dysfunction has limited the effectiveness of mechanical circulatory support (MCS) therapy in some heart failure (HF) patients. Intravascular pumps can provide adequate circulatory support without the need for extensive operations. The development of an intravascular right ventricular assist device (RVAD), called the cavo-arterial pump (CAP), is presented. Two prototypes of the CAP were developed to demonstrate the feasibility of providing adequate pulmonary support and to demonstrate the feasibility of using axial magnetic couplings for contactless torque transmission from the motor shaft to the pump impeller. The CAP utilizing a direct drive mechanism produced a maximum pressure of 100 mm Hg and a maximum flow of 2.25 L/min when operated at 24 kRPM. When a magnetic drive mechanism was used, the overall flowrate decreased due to a loss in torque transmission. The magnetic drive CAP was able to operate up to 18.5 kRPM and produce a maximum flowrate of 1.35 L/min and a maximum pressure difference of 40 mm Hg. These results demonstrate that the CAP produces sufficient output for partial circulatory support of the pulmonary circulation, and that axial magnetic couplings can help to eliminate the sealing system needed to isolate the miniature motor and bearings from blood contact.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;12(1):011002-011002-7. doi:10.1115/1.4038222.

This paper presents the design of a mechanically driven artificial speech device to be used by laryngectomees as an affordable alternative to an electrolarynx (EL). Design objectives were based on feedback from potential end users. The device implements a mainspring powered gear train that drives a striker. The striker impacts a suspended drum-like head, producing sound. When pressed against the neck, the head transmits sound into the oral cavity, allowing the user to produce intelligible speech. The dynamics of the vibrating head and sound pressure levels (SPLs) produced at the mouth were measured to compare performance between the device and a common, commercially available EL. The results showed comparable performance and sound output.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;12(1):011003-011003-12. doi:10.1115/1.4038334.

Endovascular techniques have many advantages but rely strongly on operator skills and experience. Robotically steerable catheters have been developed but few are clinically available. We describe here the development of an active and efficient catheter based on shape memory alloys (SMA) actuators. We first established the specifications of our device considering anatomical constraints. We then present a new method for building active SMA-based catheters. The proposed method relies on the use of a core body made of three parallel metallic beams and integrates wire-shaped SMA actuators. The complete device is encapsulated into a standard 6F catheter for safety purposes. A trial-and-error campaign comparing 70 different prototypes was conducted to determine the best dimensions of the core structure and of the SMA actuators with respect to the imposed specifications. The final prototype was tested on a silicon-based arterial model and on a 23 kg pig. During these experiments, we were able to cannulate the supra-aortic trunks and the renal arteries with different angulations and without any complication. A second major contribution of this paper is the derivation of a reliable mathematical model for predicting the bending angle of our active catheters. We first use this model to state some general qualitative rules useful for an iterative dimensional optimization. We then perform a quantitative comparison between the actual and the predicted bending angles for a set of 13 different prototypes. The relative error is less than 20% for bending angles between 100 deg and 150 deg, which is the interval of interest for our applications.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;12(1):011004-011004-6. doi:10.1115/1.4038307.

This study evaluated the biomechanical efficacy of single-tunnel double-bundle anterior cruciate ligament (ACL) reconstruction technique. The graft construct is achieved using a novel fixation device that splits an ACL (SPACL) graft into two bundles, recreating the anteromedial (AM) and posterolateral (PL) bundles for ACL reconstruction. A pullout strength test of the SPACL was performed using a 7-mm bovine digital extensor tendon graft. The capability in restoration of knee kinematics after SPACL reconstruction was investigated using cadaveric human knees on a robotic testing system under an anterior tibial load of 134 N and a simulated quadriceps load of 400 N. The data indicated that the SPACL graft has a pullout strength of 823.7±172.3 N. Under the 134 N anterior tibial load, the anteroposterior joint laxity had increased constraint using the SPACL reconstruction but not significantly (p > 0.05) at all selected flexion angles. Under the 400 N quadriceps load, no significant differences were observed between the anterior tibial translation of intact knee and SPACL conditions at all selected flexion angles, but the SPACL graft induced a significant increase in external tibial rotation compared to the intact knee condition at all selected flexion angles with a maximal external rotation of −3.20 deg ±3.6 deg at 90 deg flexion. These data showed that the SPACL technique is equivalent or superior to existing ACL reconstruction techniques in restoration of knee laxity and kinematics. The new SPACL reconstruction technique could provide a valuable alternation to contemporary ACL reconstruction surgery by more closely recreating native ACL kinematics.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;12(1):011005-011005-6. doi:10.1115/1.4038335.

This paper reports the design, development, and initial evaluation of a robotic laparoscopic clipping tool for single manipulator wound closure and anastomosis (tubular reconnection). The tool deploys biodegradable clips and clasps with the goal of (i) integrating grasping and suturing into a single device for single hand or manipulator use, (ii) applying the equivalent of interrupted sutures without the need of managing suture thread, and (iii) allowing for full six degrees-of-freedom (DOFs) laparoscopic control when mounted on a robot arm. The specifications, workflow, and detailed design of the robotic laparoscopic tool and injection molded bio-absorbable T shaped clip and locking clasp are reported. The clipping tool integrates forceps to grab and stabilize tissue and a clip and clasp applier to approximate and fixate the tissue. A curved needle is advanced on a circular needle path and picks up and drags clips through tissue. The clip is then tightened through the tissue and a clasp is clamped around the clip, before the clip is released from the needle. Results of several bench test runs of the tool show: (a) repeatable circular needle drive, (b) successful pick-up and deployment of clips, (c) successful shear of the clip to release the clip from the needle, and (d) closure of clasp on clip with an average of 2.0 N holding force. These data indicate that the robotic laparoscopic clipping tool could be used for laparoscopic wound closure and anastomosis.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2017;12(1):011006-011006-7. doi:10.1115/1.4038308.

The multiphotodiode array (MPA) is a novel transmission photoplethysmography (PPG) sensor to measure pulse wave velocity (PWV) in the finger. To validate the MPA, a setup was built to generate a red laser dot traveling over the MPA with known and constant scanning velocities. These scanning velocities were chosen to include speeds at least twice as high as those found in the normal range of PWV in healthy populations and were set at 12.9, 25.8, 36, or 46.7 m/s. The aim of this study was to verify the functionality of the MPA: performing local noninvasive PWV measurements. To illustrate the applicability of the MPA in clinical practice, an in vivo pilot study was conducted using the flow-mediated dilation (FMD) technique. The in vitro accuracy of the MPA was ±0.2%, 0.3%, 0.5%, and 0.6% at the applied scanning velocities. The MPA can measure PWVs with a maximum deviation of 3.0%. The in vivo pilot study showed a PWV before the FMD of 1.1±0.2 m/s. These results suggest that this novel MPA can reliably and accurately measure PWV within clinically relevant ranges and even well beyond.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Med. Devices. 2017;12(1):014501-014501-5. doi:10.1115/1.4038562.

Accurate force simulation is essential to haptic simulators for surgical training. Factors such as tissue inhomogeneity pose unique challenges for simulating needle forces. To aid in the development of haptic needle insertion simulators, a handheld force sensing syringe was created to measure the motion and forces of needle insertions. Five needle insertions were performed into the neck of a cadaver using the force sensing syringe. Based on these measurements a piecewise exponential needle force characterization, was implemented into a haptic central venous catheterization (CVC) simulator. The haptic simulator was evaluated through a survey of expert surgeons, fellows, and residents. The maximum needle insertion forces measured ranged from 2.02 N to 1.20 N. With this information, four characterizations were created representing average, muscular, obese, and thin patients. The median survey results showed that users statistically agreed that “the robotic system made me sensitive to how patient anatomy impacts the force required to advance needles in the human body.” The force sensing syringe captured force and position information. The information gained from this syringe was able to be implemented into a haptic simulator for CVC insertions, showing its utility. Survey results showed that experts, fellows, and residents had an overall positive outlook on the haptic simulator's ability to teach haptic skills.

Topics: Haptics , Robotics , needles
Commentary by Dr. Valentin Fuster

Design Innovation Paper

J. Med. Devices. 2017;12(1):015001-015001-5. doi:10.1115/1.4038439.

Unloader knee braces are prescribed for patients with unicompartmental osteoarthritis of the knee. These braces aim to reduce pain in patients by applying a coronal moment to the knee to unload the symptomatic knee compartment. However, existing unloading mechanisms use straps that go directly behind the knee joint, to apply the needed moment. This can impinge on the popliteal artery and peroneal nerves thereby causing discomfort to the patient. Hence, these braces cannot be worn for prolonged periods of time. This research focused on developing a new knee brace to improve comfort while unloading the osteoarthritic knee. A new knee brace was developed that uses a four-point bending approach to unload the knee. In this brace, unloading can be adjusted, and the unloading mechanism is away from the joint. The new brace was tested on a cadaver specimen to quantify its capability to unload the knee compartment. The brace was also worn by a patient with osteoarthritis who subjectively compared it to his existing unloader brace. During cadaver testing, the new brace design could reduce the force exerted on the medial condyle by 25%. Radiographic images of the patient's knee confirmed that the brace unloaded the medial condyle successfully. The patient reported that the new brace reduced pain, was significantly comfortable to wear and could be used for a longer duration in comparison to his existing brace.

Commentary by Dr. Valentin Fuster

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