Evaluation of nano-porous alumina membranes for hemodialysis application

Globally, kidney failure has consistently been a major health problem. The number of patients suffering from kidney failure is radically increasing. Some studies forecast an exponential growth in the number of kidney failure patients during the coming years. This emphasizes the importance of hemodialysis (HD) membranes. Current dialysis membranes (cellulose based and synthetic polymer membranes) have irregular pore shapes and sizes, nonuniform pore distribution and limited reusable capability, which leads to low efficiency of toxin removal. New alumina membranes with uniform, controllable and well-structured nanoscale pores, channeled pores aligned perpendicular to the membrane plane, high porosity, high thermal and chemical resistance, and better mechanical properties are certainly preferable to currently used membranes. Determination of transport properties of alumina membranes will assist in the development of the alumina membranes for enhancing hemodialysis. Experiments were performed to evaluate hydraulic permeability, solute diffusive permeability, sieving coefficient, and clearance of four solutes (urea, creatinine, Vancomycin, and inulin) for alumina membrane. Based on comparison of these values against those of polyethersulfone (PES) membranes, transport performance of alumina membrane was determined. Hydraulic conductivity of the alumina membrane was approximately twice that of the PES membrane and inulin sieving coefficient for alumina membrane is approximately 21% higher than that for PES membrane. Alumina membrane has higher solute clearances and no albumin leakage, which makes it an effective replacement for current dialysis membranes.

Stage-Gate Process for the Development of Medical Devices

The medical device development process has become increasingly complex in recent years. The advent of new technology concepts, stricter regulatory requirements, and the ever increasing importance of reimbursement decisions for successful device commercialization require careful planning and strategy-setting, coordinated decisions, and consistent, rigorous business processes. The design and implementation of such processes, often captured in development models and accompanying standard operating procedures, have become a key determinant of the success of device commercialization. While various models may exist in the device industry, no comprehensive development model has been published. This paper reviews existing model representations and presents a new comprehensive development model that captures all aspects of device development and commercialization from early-concept selection to postmarket surveillance. This model was constructed based on best-practice analysis and in-depth interviews with more than 80 seasoned experts actively involved in the development, commercialization, and regulation of medical devices. The stage-gate process includes the following five phases: (1) initiation - opportunity and risk analysis, (2) formulation - concept and feasibility, (3) design and development - verification and validation, (4) final validation - product launch preparation, and (5) product launch and postlaunch assessment. The study results suggest that stage-gate processes are the predominant development model used in the medical device industry and that regulatory requirements such as the food and drug adminstration (FDA’s) Quality Systems Regulation play a substantive role in shaping activities and decisions in the process. The results also underline the significant differences between medical device innovation and drug discovery and development, and underscore current challenges associated with the successful development of the increasing number of combination products.

Policy-Induced Constraints in the Design and Commercialization of Monitoring Devices: An Assessment of Three Technologies’ Reimbursement Models

Successful commercialization of medical technologies increasingly requires developers and manufacturers to think early-on about regulatory approval and reimbursement strategies for their new devices. This can be particularly challenging in the case of monitoring devices, where demonstrating the effectiveness and finding the coding and coverage can often be a complicated and lengthy process, particularly with the given current reimbursement policy. In this paper, we use three technology case studies to examine how firms are navigating the status quo and illustrate the importance of incorporating a comprehensive understanding of current market and regulatory constraints into the development and commercialization process. The case studies suggest that viable approaches can include pairing a monitoring technology with a therapy, or relying on hospital-pay or patient-pay models that are based on demonstration of direct benefits or cost-savings to these parties. The results emphasize that successful innovation in monitoring technologies increasingly requires a very closely aligned engineering, business, and health-economic strategy. Developing a comprehensive understanding of the specific value drivers and policy-induced constraints can contribute substantially to achieving the true benefits of monitoring technologies.

Clinical application of curvilinear distraction osteogenesis for correction of mandibular deformities

PURPOSE

To report the use of a semiburied curvilinear distraction device, with a 3-dimensional (3D) computed tomography treatment planning system, for correction of mandibular deformities.

MATERIALS AND METHODS

This was a retrospective evaluation of 13 consecutive patients, with syndromic and nonsyndromic micrognathia, who underwent correction by curvilinear distraction osteogenesis. A 3D computed tomography scan was obtained for each patient and imported into a 3D treatment planning system (Slicer/Osteoplan). Surgical guides were constructed to localize the osteotomy and to drill holes to secure the distractor's proximal and distal footplates to the mandible. Postoperatively, patients were followed by clinical examination and plain radiographs to ensure the desired vector of movement. At end distraction, when possible, a 3D computed tomography scan was obtained to document the final mandibular position.

RESULTS

Of the 13 patients, 8 were females and 5 were males, with a mean age of 11.9 years (range 15 months to 39 years). All 13 underwent bilateral mandibular curvilinear distraction. Of the 13 patients, 8 were 16 years old or younger and 5 were younger than 6 years of age. The diagnoses included Treacher Collins syndrome (n = 3), Nager syndrome (n = 3), craniofacial microsomia (n = 2), post-traumatic ankylosis (n = 1), and micrognathia (syndromic, n = 3; nonsyndromic, n = 1). The correct distractor placement, vector of movement, and final mandibular position were achieved in 10 of 13 patients. In the other 3 patients, the desired jaw position was achieved by "molding" the regenerate.

CONCLUSIONS

The use of a semiburied curvilinear distraction device, with 3D treatment planning, is a potentially powerful tool to correct complex mandibular deformities.

A tactile feedback system for robotic surgery

A tactile feedback system was developed and mounted on the da Vinci robotic surgical system. The system features silicone-based tactile balloon actuators mounted on the robotic master controls, modified commercial piezoresistive sensors mounted on the robotic end effectors, and a pneumatic control system. The system has a frequency response of up to 20 Hz, a linear input force-output pressure relationship, and provides five discrete levels of actuation over a force input range of 0 to 25 N. A demonstration of the system with four subjects grasping a phantom with an embedded pressure-sensitive film suggested that less force was applied with tactile feedback. This paper describes the design, fabrication, characterization, and demonstration of the mounted tactile feedback system and its components. Ongoing studies using the system will assess the benefit of tactile stimuli to learning and control in robotic surgery.

An integrated pneumatic tactile feedback actuator array for robotic surgery

BACKGROUND

A pneumatically controlled balloon actuator array has been developed to provide tactile feedback to the fingers during robotic surgery.

METHODS

The actuator and pneumatics were integrated onto a robotic surgical system. Potential interference of the inactive system was evaluated using a timed robotic peg transfer task. System performance was evaluated by measuring human perception of the thumb and index finger.

RESULTS

No significant difference was found between performance with and without the inactive mounted actuator blocks. Subjects were able to determine inflation location with > 95% accuracy and five discrete inflation levels with both the index finger and thumb with accuracies of 94% and 92%. Temporal tests revealed that an 80 ms temporal separation was sufficient to detect balloon stimuli with high accuracy.

CONCLUSIONS

The mounted balloon actuators successfully transmitted tactile information to the index finger and thumb, while not hindering performance of robotic surgical movements.

Tactile Feedback Induces Reduced Grasping Force in Robot-Assisted Surgery

Robot-assisted minimally invasive surgery has gained widespread use over the past decade, but the technique is currently operated in the absence of haptic feedback during tissue manipulation. We have developed a complete tactile feedback system, consisting of a piezoresistive force sensor, control system, and pneumatic balloon tactile display, and mounted directly onto a da Vinci surgical robotic system. To evaluate the effect of tactile feedback on robotic manipulation, a group of novices (n = 16) and experts ( n = 4) were asked to perform three blocks of peg transfer tasks with the tactile feedback system in place. Force generated at the end-effectors was measured in all three blocks, but tactile feedback was active only during the middle block. All subjects used higher force when the feedback system was inactive. When active, subjects immediately used substantially less force and still maintained appropriate grip during the task. After the system was again turned off, grip force increased significantly to prefeedback levels. These results demonstrate that robotic manipulations without tactile feedback are done with more force than needed to grasp objects. Therefore, the addition of tactile feedback allows the surgeon to grasp with less force, and may improve control of the robotic system and handling of tissues and other objects.

Utilization of the foot load monitor for evaluating deep plantar tissue stresses in patients with diabetes: proof-of-concept studies

The purposes of the present study were to (1) determine the internal plantar mechanical stresses in diabetic and healthy subjects during everyday activities, and (2) identify stress parameters potentially capable of distinguishing between diabetic and healthy subjects. A self-designed, portable, real-time and subject-specific foot load monitor which employs the Hertz contact theory was utilized to determine the internal dynamic plantar tissue stresses in 10 diabetic patients and 6 healthy subjects during free walking and outdoors stair climbing. Internal stress parameters and average stress-doses were evaluated, and the results obtained from the two groups were compared. Internal plantar stresses and averaged stress-doses during free walking and outdoors stairs climbing in the diabetic group were 2.5-5.5-fold higher than in the healthy group (p<0.001; stair climbing comparisons incorporated data from five diabetic patients). The interfacial pressures measured during free walking were slightly higher ( approximately 1.5-fold) in the diabetic group (p<0.05), but there was no significant difference between the two groups during stairs climbing. We conclude that during walking and stair climbing, internal plantar tissue stresses are considerably higher than foot-shoe interface pressures, and in diabetic patients, internal stresses substantially exceed the levels in healthy. The proposed method can be used for rating performances or design of footwear for protecting sub-dermal plantar tissues in patients who are at risk for developing foot ulcers. It may also be helpful in providing biofeedback to neuropathic diabetic patients.

Vision and task assistance using modular wireless in vivo surgical robots

Minimally invasive abdominal surgery (laparoscopy) results in superior patient outcomes compared to conventional open surgery. However, the difficulty of manipulating traditional laparoscopic tools from outside the body of the patient generally limits these benefits to patients undergoing relatively low complexity procedures. The use of tools that fit entirely inside the peritoneal cavity represents a novel approach to laparoscopic surgery. Our previous work demonstrated that miniature mobile and fixed-based in vivo robots using tethers for power and data transmission can successfully operate within the abdominal cavity. This paper describes the development of a modular wireless mobile platform for in vivo sensing and manipulation applications. Design details and results of ex vivo and in vivo tests of robots with biopsy grasper, staple/clamp, video, and physiological sensor payloads are presented. These types of self-contained surgical devices are significantly more transportable and lower in cost than current robotic surgical assistants. They could ultimately be carried and deployed by nonmedical personnel at the site of an injury to allow a remotely located surgeon to provide critical first response medical intervention irrespective of the location of the patient.

A phantom tissue system for the calibration of perfusion measurements

A convenient method for testing and calibrating surface perfusion sensors has been developed. A phantom tissue model is used to simulate the nondirectional blood flow of tissue perfusion. A computational fluid dynamics (CFD) model was constructed in Fluent(R) to design the phantom tissue and validate the experimental results. The phantom perfusion system was used with a perfusion sensor based on clearance of thermal energy. A heat flux gage measures the heat flux response of tissue when a thermal event (convective cooling) is applied. The blood perfusion and contact resistance are estimated by a parameter estimation code. From the experimental and analytical results, it was concluded that the probe displayed good measurement repeatability and sensitivity. The experimental perfusion measurements in the tissue were in good agreement with those of the CFD models and demonstrated the value of the phantom tissue system.

A Multielement Tactile Feedback System for Robot-Assisted Minimally Invasive Surgery

A multi-element tactile feedback (MTF) system has been developed to translate the force distribution, in magnitude and position, from 3times2 sensor arrays on surgical robotic end-effectors to the fingers via 3times2 balloon tactile displays. High detection accuracies from perceptual tests (> 96%) suggest that MTF may be an effective means to improve robotic control.

Piezoelectric forceps actuator: theory and experiments

This paper studies the characteristic performances of a novel piezoelectric forceps actuator (PFA) that has several potential applications for minimally invasive surgery and assembly lines of semiconductor industries. The first part of the paper treats the PFA model, which is comprised of a piezoelectric slightly curved composite beam derived using Hamilton's principle. In the latter part of the paper, the distributed transfer function method is applied to evaluate the transfer function formulation of the cantilevered PFA associated with its boundary conditions. This method will be used to resolve the radial displacements and natural frequencies of the PFA in an exact and closed-form solution, which is validated by in situ fiber optic curvature sensing measurements. The theoretical model predicted the natural frequencies of the first- and second-mode responses of the experimental quite accurately. For a cyclical low-field input, the field-induced displacement appears approximately linear, which seems comparable to the theoretical prediction and reflects primarily the converse piezoelectric effect. A cyclical high-field butterfly-shaped displacement behavior is also analogous to the behavior predicted by the model in that it demonstrates the range of validity of the linear converse piezoelectric effect without consideration of the ferroelectric domain switch effect.

Experimental investigation and computational modeling of hydrodynamics in bifurcating microchannels

Methods involving microfluidics have been used in several chemical, biological and medical applications. In particular, a network of bifurcating microchannels can be used to distribute flow in a large space. In this work, we carried out experiments to determine hydrodynamic characteristics of bifurcating microfluidic networks. We measured pressure drop across bifurcating networks of various complexities for various flow rates. We also measured planar velocity fields in these networks by using particle image velocimetry. We further analyzed hydrodynamics in these networks using mathematical and computational modeling. Our results show that the experimental frictional resistances of complex bifurcating microchannels are 25-30% greater than that predicted by Navier-Stokes equations. Experimentally measured velocity profiles indicate that flow distributes equally at a bifurcation regardless of the complexity of the network. Flow division other than bifurcation such as trifurcation or quadruplication can lead to heterogeneities. These findings were verified by the results from the numerical simulations.

Design of a Compliant Endoscopic Suturing Instrument

This paper describes the initial design and optimization of a compliant endoscopic suturing instrument. The emerging field of Natural Orifice Transluminal Endoscopic Surgery (NOTES) requires innovative instruments to meet the size limitations inherent in this type of minimally invasive surgery; using compliant mechanisms is proposed as one method of meeting this requirement. The compliant design was modeled and optimized to maximize the distal opening and provide a puncture force of at least 4.6N, while being small enough to fit within a 3.3mm working channel. The design utilizes contact for stress relief and intertwining parts for added deflection. ANSYS® was used for finite element analysis including contact and nonlinear deformations. A prototype was fabricated from the optimized geometry and experimentally tested. The best geometry is predicted to have a distal opening of 14.6mm at the tips and supply a puncturing force of 4.83N. The force supplied at the tip was measured and was found to exceed the required 4.6N. The prototype successfully passed two complete sutures and qualitative results are provided. The results of the study will lead to further refinements and improvements in future designs.

The virtual haptic back: a simulation for training in palpatory diagnosis

BACKGROUND

Models and simulations are finding increased roles in medical education. The Virtual Haptic Back (VHB) is a virtual reality simulation of the mechanical properties of the human back designed as an aid to teaching clinical palpatory diagnosis.

METHODS

Eighty-nine first year medical students of the Ohio University College of Osteopathic Medicine carried out six, 15-minute practice sessions with the VHB, plus tests before and after the sessions in order to monitor progress in identifying regions of simulated abnormal tissue compliance. Students palpated with two digits, fingers or thumbs, by placing them in gimbaled thimbles at the ends of PHANToM 3.0(R) haptic interface arms. The interface simulated the contours and compliance of the back surface by the action of electric motors. The motors limited the compression of the virtual tissues induced by the palpating fingers, by generating counterforces. Users could see the position of their fingers with respect to the back on a video monitor just behind the plane of the haptic back. The abnormal region varied randomly among 12 locations between trials. During the practice sessions student users received immediate feedback following each trial, indicating either a correct choice or the actual location of the abnormality if an incorrect choice had been made. This allowed the user to feel the actual abnormality before going on to the next trial. Changes in accuracy, speed and Weber fraction across practice sessions were analyzed using a repeated measures analysis of variance.

RESULTS

Students improved in accuracy and speed of diagnosis with practice. The smallest difference in simulated tissue compliance users were able to detect improved from 28% (SD = 9.5%) to 14% (SD = 4.4%) during the practice sessions while average detection time decreased from 39 (SD = 19.8) to 17 (SD = 11.7) seconds. When asked in anonymous evaluation questionnaires if they judged the VHB practice to be helpful to them in the clinical palpation and manual medicine laboratory, 41% said yes, 51% said maybe, and 8% said no.

CONCLUSION

The VHB has potential value as a teaching aid for students in the initial phases of learning palpatory diagnosis.

A biodegradable stent based on poly(L-lactide) and poly(4-hydroxybutyrate) for peripheral vascular application: preliminary experience in the pig

PURPOSE

To assess the technical feasibility and biocompatibility of a novel stent based on poly(L-lactide) (PLLA) and poly(4-hydroxybutyrate) (P4HB) for peripheral vascular applications.

METHODS

A polytetrafluoroethylene aortobi-iliac graft was implanted in 5 pigs through a midline abdominal incision. After transverse graft limb incision, 5 PLLA/P4HB stents and 5 metal stents (316L stainless steel) were randomly deployed at both iliac anastomotic sites with 6-mm balloon catheters. Angiography was performed to determine patency prior to sacrifice at 6 weeks. Stented segments were surgically explanted and processed for quantitative histomorphometry. Vascular injury and inflammation scores were assigned to the stented iliac segments.

RESULTS

No animals were lost during follow-up. All PLLA/P4HB stents were deployed within 2 minutes by balloon inflation to 8 bars without rupture of the stent struts or anastomotic suture. All stents were patent on postprocedural angiography. Histological analysis showed no signs of excessive recoiling or collapse. PLLA/P4HB stents demonstrated decreased residual lumen area and increased neointimal area after 6 weeks (12.27+/-0.62 and 8.40+/-1.03 mm(2), respectively) compared to 316L stents (13.54+/-0.84 and 6.90+/-1.11 mm(2), respectively) as the result of differences in stent areas (PLLA/P4HB: 4.31+/-0.15 mm(2); 316L: 2.73+/-0.29 mm(2)). Vascular injury scores showed only mild vascular trauma for all stents (PLLA/P4HB: 0.41+/-0.59; 316L: 0.32+/-0.47). Inflammatory reaction was slightly higher around PLLA/P4HB stent struts (1.39+/-0.52) compared to 316L (1.09+/-0.50).

CONCLUSION

Rapid balloon expansion of PLLA/P4HB stents is feasible without risk of strut rupture. PLLA/P4HB stents provide adequate mechanical stability after iliac anastomotic stenting in pigs. Smaller residual luminal areas in the PLLA/P4HB stents might have been caused by tissue ingrowth into the larger strut interspaces due to higher strut thickness (stent area) in this group. This limitation needs to be addressed in future work on the stent design.

A biodegradable slotted tube stent based on poly(L-lactide) and poly(4-hydroxybutyrate) for rapid balloon-expansion

Safe vascular stent application requires rapid expansion of the stent to minimize the risk of procedural ischemia. While high expansion speeds can be achieved with metallic stents, they are not necessarily feasible with biodegradable polymeric stents due to the viscoelastic material behavior. This study reports on a novel biodegradable polymer blend material based on poly(L-lactide) (PLLA) and poly(4-hydroxybutyrate) (P4HB), and describes the mechanical properties and in vitro degradation behavior of a balloon-expandable slotted tube stent concept. The stent prototypes with nominal dimensions of 6.0 x 25 mm were manufactured by laser machining of solution cast PLLA/P4HB tubes (I.D. = 2.8 mm, d = 300 microm). The stents were expanded within 1 min by balloon inflation to 8 bar, after 5 min preconditioning in 37 degrees C water. Recoil and collapse pressure were 4.2% and 1.1 bar, respectively. During in vitro degradation collapse pressure initially increased to a maximum at 4 w and then decreased thereafter. After 48 w, molecular weight was decreased by 82%. In summary, the PLLA/P4HB slotted tube stents allowed for rapid balloon-expansion and exhibited adequate mechanical scaffolding properties suitable for a broad range of vascular and non-vascular applications.

An Apparatus and Protocol to Measure Shoulder Girdle Strength

Muscles actuating the shoulder girdle are important for stabilizing the scapula and coordinating phased kinematics of the shoulder complex. If these muscles become weak or imbalanced, joint instability and injury may result. Reliable measurement of shoulder strength is thus important for prevention, diagnosis, and rehabilitation of shoulder problems. To date, studies quantifying the strength of the shoulder girdle are limited. The purpose of this work was to design and evaluate a custom apparatus and corresponding protocol for measuring maximal, voluntary, isometric strength of the shoulder girdle during various forms of shrugging exercise. A custom apparatus was constructed as a rigid frame with a vertical post supporting a seat, seat back, and horizontal beam. The beam extends laterally on either side beyond and around the shoulders of a seated subject. A pair of arm extension members pivots on the beam about an axis aligned with the shoulder flexion-extension axis. These members can be locked in place at any angle. Between them is mounted a force-sensing grip assembly, which can be adjusted proximally or distally to accommodate varying shoulder girdle positions. Subjects grasp the grip assembly handles with extended elbows and push or pull as forcefully as possible. Nine female and ten male subjects participated in a protocol using the apparatus to measure maximum isometric force generated at three positions each for elevation, depression, protraction, and retraction of the shoulder girdle (3positions×4modes=12tests). A video motion capture system was used to measure shoulder girdle angles. The reliability of the approach was evaluated based on the repeatability of measured shoulder elevation angle, protraction angle, and total force over three days of testing. The apparatus performed well during the tests, providing a stable, rigid, yet adjustable platform for measuring shoulder girdle strength. Repeatability of force measurements was interpreted as very good to excellent, with intraclass correlation coefficient (ICC) (2,1) values ranging from 0.83 to 0.95 for all tests except one (ICC=0.79). Repeatability of angle measurements was interpreted as good to excellent. For tests measuring elevation and depression strength, the ICC of elevation angle ranged from 0.85 to 0.89. For tests measuring protraction and retraction strength, the ICC of protraction angle ranged from 0.68 to 0.88. This type of apparatus could be an effective clinical tool for measuring strength in the shoulder girdle muscles. Use of the video motion capture system is optional.

Recent in vivo surgical robot and mechanism developments

The surgical landscape is quickly changing because of the major driving force of robotics. Well-established technology that provides robotic assistance from outside the patient may soon give way to alternative approaches that place the robotic mechanisms inside the patient, whether through traditional laparoscopic ports or through other, natural orifices. While some of this technology is still being developed, other concepts are being evaluated through clinical trials. This article examines the state of the art in surgical robots and mechanisms by providing an overview of the ex vivo robotic systems that are commercially available to in vivo mechanisms, and robotic assistants that are being tested in animal models.

Design of an Endoscopic Biopsy Needle With Flexural Members

As a minimally invasive means of extracting a tissue sample from a patient, current endoscopic biopsy needles generally do not preserve tissue histology and often require multiple attempts to obtain a tissue sample. This paper presents an endoscopic biopsy needle with internal flexures that enables tissue to enter the hollow needle and then be severed from the surrounding tissue when the needle is withdrawn. Using force-deflection and sample weight data from 10× scaled prototypes, variations of a flexural design captured 1.1grams of a tissue phantom on average, as compared to wedge-type designs that averaged 0.7-0.8grams. Sample mass exhibited an increase in mass as the feature angle decreased. Peak entrance forces (P2) for the flexure design were lower than for both wedge and extended wedge designs, and resistance forces (S2) were higher upon needle extraction. A low-angle (15 and 30deg) feature also produced a lower entrance friction (S1) and higher exit resistance (S2) compared with 45 and 60deg features. These results suggest that a biopsy needle with 15deg flexures could increase sample length and mass as well as sampling success rates for core biopsy procedures. Future tests of the flexural biopsy needle design will use this information to determine dimensions for laser cut features of 1× scale needles.