By Leslie Langnau, Managing Editor
Medical science continues to push boundaries in health care. With the aid of the innovative engineer, physicians, surgeons, and medical researchers move ever closer to the goal of providing superior health care.
Over the last few years, engineers have contributed their skills to a number of interesting and unique developments and devices. Here’s a look at a few of the recent innovations.
In congestive heart failure, the heart muscle strains to pump blood throughout the circulatory system. To reduce this strain, Orqis Medical Corp., Lake Forest, Calif., recently developed the Cancion® System, a device that helps supplement the heart’s job of pumping blood to the body. One of the factors engineers had to consider in this device’s design was to ensure that it would not damage fragile blood cells or bring about clotting as it augments blood flow through the patient’s descending aorta. Thus, the choice of the material used to fabricate some of the components was crucial. That’s why the engineers chose to use Makrolon® 2558 polycarbonate resin from Bayer MaterialScience LLC (BMS) for many of the components.
The Cancion System, which is undergoing evaluation in the Momentum clinical trial, continuously augments aortic flow through an innovative centrifugal pump and proprietary catheters to create a supplemental circuit that takes pressure off the heart. The company calls this a “rest to recovery” treatment for acutely decompensated congestive heart failure patients who do not respond adequately to standard medical therapy. By alleviating the heart from some of its work, Orqis hopes to show that the heart can grow stronger, allowing patients to feel better, and limit hospital visits or stays.
In use, the catheters are inserted into the patient’s femoral arteries, drawing blood out through the left artery and into the pump, which propels it back into the body through a longer catheter. The longer catheter enters the right artery and extends up through the descending artery where it terminates with a U-turn near the aorta, discharging blood back into the normal flow. The polycarbonate material is used in the critical catheter connectors because of its biocompatibility, robustness and clarity. These same attributes led Levitronix® LLC of Waltham, Mass., to choose the polycarbonate for its CentriMag® Blood Pump, a key component of the Orqis system.
Makrolon 2558 is an easy-flow polycarbonate resin with excellent impact strength and ductility, electrical properties and dimensional stability. Certain color formations meet the requirements of the FDA-modified ISO 10993, Part 1 “Biological Evaluation of Medical Devices” tests. Biocompatibility and durability are critical to the applications.
“Most catheters are intended for short-duration, single-use injections, ” said Robert Pecor, senior R&D engineer for Orqis. “Unlike the Cancion System, very few are for long-term use with blood continuously flowing through them. We have to be very careful to minimize the potential for thrombosis or damage to the blood cells. ” Therefore, the engineers designed the polycarbonate connectors to create smooth joints between the urethane catheters and PVC tubing used in the system.
Bayer’s engineering team helped refine the injection molding process for the connectors to assure proper flow and establish better processing parameters. The connectors are molded by Advanced Technology of Corona, Calif.
The CentriMag centrifugal pump uses magnetic levitation to create the fluid dynamics necessary for circulatory support. The pump is assembled from four Makrolon polycarbonate parts and a magnet. The magnet is encased in two white polycarbonate components, creating the pump’s impeller. The impeller floats inside a clear polycarbonate housing, made of two parts bonded together to form a chamber with a top inlet orifice and a side discharge outlet. This pump is placed inside a motor receptacle with no moving parts. The motor uses electromagnetic forces to levitate and rotate the impeller within the pump chamber.
When the CentriMag is used as a left ventricular assist system, blood from the failing heart is directed from the left ventricle or atrium to the inlet orifice of the pump. Blood exits through the discharge outlet to the systemic circulation. When used as a right ventricular support system, blood from the failing right heart is directed from the right ventricle or atrium to the pump’s inlet orifice (cannula). Blood exits the pump through the discharge outlet (cannula) ultimately to the pulmonary circulation.
The pump can generate blood flow rates as high as 9.9 liters per minute, with a lower limit of flow of 400 milliliters per minute required by neonatal cases. Use of magnetic levitation eliminates shafts, seals, bearings and heat-generating friction, minimizing the risk of hemolysis and thrombus deposition. The efficient design of the pump accommodates the low flow rates required by the Cancion System without blood stasis occurring.
The pumps are injection molded and robotically assembled in a clean-room environment, and the chambers are bonded with a UV-curable adhesive. “We put this material through many tests to demonstrate that it didn’t cause thrombosis and could be used for the intended duration, ” said Kurt Dasse, Ph. D, CEO, Levitronix.
Safe pump support through magnetic levitation
The Levitronix CentriMag Ventricular Assist System is comprised of a single-use centrifugal blood pump, a primary motor, a primary drive console, a back up motor, a back up drive console, and cannulae. It is unique in that it operates without mechanical bearings or seals. The motor levitates the rotor magnetically, achieving rotation without friction, regions of stasis, or component wear during operation. The lack of thermal damage from frictional losses and the elimination of regions of stasis reduces the risk of thrombus formation within the pump. In addition, eliminating bearings and component wear reduces hemolysis.
The device is based on “bearingless motor” technology, which uses the principal of magnetic support of the rotor. The design combines drive, magnetic bearing, and pump rotor functions into one unit without valves, seals, mechanical bearings, or moving parts aside from the magnetically levitated rotor.
The bearing forces are generated in the motor itself, not by separate mechanical or magnetic bearings positioned on the sides of the motor block. Thus, the active motor generates not only the torque, but also the radial magnetic bearing force, which is needed to suspend the rotor.
When the rotor is deflected or tilted, the magnetic field lines are lengthened, resulting in a natural restoring force. This passive stabilization of three degrees of freedom is also possible in classical magnetic bearings, but, in this case, may be destabilized by magnetic tractive forces associated with the addition of the motor to the system. The bearingless slice motor controls these tractive forces through a combination of motor and bearings, requiring only a single active radial magnetic bearing.
To achieve a compact device and create room for the pump outlet port, Levitronix engineers developed the “temple motor” concept. The layout uses “L” shaped iron cores as opposed to traditional radial cores. This layout is necessary so that the coil windings do not obstruct the outflow port. An additional advantage of the temple motor over all other “mag-bearing” pump concepts is that this pump construction is modular and independent of the motor unit, reducing manufacturing costs as well as enabling easy disposal.
This approach achieves a simple and compact centrifugal pump. The rotor slice can be directly integrated into the impeller, whereas the pump itself consists of few parts: the impeller/rotor, and an outer two-piece shell. Due to passive stabilization in three degrees of freedom, only one motor phase and two control phases (three power amplifiers) are the minimum needed for operation. An additional motor phase allows the use of a vector-controlled drive. Furthermore, only two position sensors are required, leading to a more straightforward electronic design and motor assembly, and allowing for fault tolerant construction without increasing the size of the motor and controls.
Under normal operating conditions, the electromotive force produced by the motor windings drives the levitated rotor. Rotation of the rotor with integral vanes creates a vortex that accelerates the blood using axial and centrifugal force. The energy imparted by the rotor increases the velocity of blood along the direction of the axis of rotation through the pump outlet. The system is capable of operating over a range of speeds up to 5,500 rpm generating flows up to 10 liters per minute under normal physiologic pressures and conditions. All system components, with the exception of the single-use pump, are intended for use on multiple patients – one patient at a time.
“It speaks to Makrolon’s strengths for medical uses that it was chosen by two discerning customers for use in this pioneering therapeutic tool, ” said Kevin Dunay, BMS LLC NAFTA Market Segment Leader for Medical.
Increasing degrees of freedom
Another version of the Makrolon polycarbonate material is used in micro forceps and scissors. Alcon Grieshaber AG, a leading medical technology manufacturer based in Schaffhausen, Switzerland, has developed surgical instruments to help combat vision-impairing retinal disease, most commonly caused through macular degeneration. The Grieshaber Revolution™ DSP micro forceps and scissors have an advantage over similar commercial instruments: they can be freely rotated while in use. This novel capability is made possible in part by a plastic basket of thin-walled ribs that forms part of the instrument body.
When working the thin-walled ribs, the engineers called on Bayer MaterialScience to provide a material with strength, stiffness and toughness. The Makrolon 2458 polycarbonate, which is approved for medical applications, fulfilled all these requirements. “Its dimensional stability makes it possible for this delicate injection-molded component to be easily removed from the mold and for the forceps or scissors to work reliably, ” explains Markus Krieter, Medical Market Manager in the Polycarbonates Business Unit of BMS AG.
Eight of the single-use operating instrument’s individual components are made of polycarbonate in an injection molding process from Gebr. Renggli AG in Schaffhausen. The parts are made using a laminar flow process, then cleaned and finished in a clean room. The actual instruments themselves are assembled in a clean room at Alcon Grieshaber.
Miniature universal joints transmits power
When the engineers at Belden Inc. were working with Tuebingen Scientific Medical GmbH, a spin-off company of the University of Tübingen, Germany, on a new surgical tool for minimally invasive surgery, the tool needed a joint that could transmit power from the handle to the connecting shaft.
The resulting surgical system fills the gap between conventional surgical instruments and surgical robotics. Conventional instrumentation does not meet the requirements of advanced endoscopic surgeons, and robotic systems are too complex and costly for daily routine use. Tuebingen’s manual manipulator system, called Radius Surgical System, represents a new class of surgical devices offering full freedom to operate with optimal ergonomics, but without the complexity of electromechanical robotic devices. The surgical system improves endoscopic suturing and other surgical manoeuvres in different clinical specialties.
The Radius Surgical System consists of two hand-guided surgical manipulators. Depending on the task, graspers, scissors, needle holders and other devices can be attached to the tip. Changeover only takes a few seconds
The universal joint transmits the power from the handle, which acts as a natural extension that emulates the movement of the hand, to the connecting shaft. The stainless steel joint has an outside diameter of 8 mm to accommodate the space limitations of the surgical tool. A deflectable and rotatable tip provides all degrees of handling freedom.
During development, the customer requested a special hub configuration to ensure a secure connection and precise operation. Belden altered some of its manufacturing processes to modify the standard universal joint concept and delivered prototypes for testing. The final design now incorporates the universal joint and a component of the internal extension as a single piece. Originally, it was configured as two separate pieces.
These miniature universal joints suit other applications in which space is restricted, including miniature machinery and model making.
Precise liquid dispensing for small volumes
As pharmaceutical laboratories change into factories, researchers face the challenge of increasing the number of research drugs they can sample without compromising sample integrity. The typical autosampler, which is an automated fluidic handling system that prepares and presents clean samples to analytical instruments, handles each step separately. The engineers at Parker Hannifin developed a device that turns the sampling procedure into a parallel process, thereby increasing throughput.
The Smart Syringes are miniature fluidic dispensing syringes with integrated control, memory, and motion for precise liquid dispensing in the sub-micro-liter volume range. Their internal intelligence directs workflow. Measuring only 8 mm in diameter and weighing 26 grams, the syringes do not need electrical or fluidic tethers. An on-board microprocessor and memory in each syringe signals when to execute, store, and record sample workflows, making workflow management automated and sample-centric. Thus, the syringes can be picked up and dropped off by a robotic system. A benefit of this development is that it enables parallel operations to occur simultaneously on the same work deck, increasing sample throughput.
The Smart Syringe can be configured as a single or multiple syringe system capable of independently aspirating and dispensing liquid in a variety of applications. A proprietary position control algorithm precisely meters fluid. Typical applications include general liquid handling, medical diagnostic instrumentation, high pressure liquid dispensing (autosamplers), and microfluidics (lab-on-a-chip.)
Companies mentioned in this article:
Bayer MaterialScience LLC