NREMT-NRP techniques - NREMT National Registered Paramedic Updated: 2023

Medical Device & Diagnostic Industry Magazine
MDDI Article Index

An MD&DI April 1998 Column

COVER STORY

Four molding techniques open up a variety of new approaches to the design of medical components.

Plastics injection molding and applications development for medical devices are two areas of technology that perpetually leapfrog one another. The increased functional requirements of molded medical components drive the molding technology advances required to fulfill those needs. In turn, the increased capabilities of the injection molding process facilitate innovations in design, manufacturing, and assembly of new medical devices.

In most cases, past and present, conventional injection molding technology has been sufficient to meet the needs of the applications developed. When conventional molding has fallen short, however, novel improvements and modifications to the process have been devised to provide unique solutions to the increasingly sophisticated demands of medical design engineers. There have been many such improvements, but four in particular stand out. The first, pulsed cooling and induction coil heating, takes the conventional molding process and adds to it a greater degree of process control. For two others, gas-assisted injection molding and multi—live feed molding, auxiliary equipment is incorporated into the standard machine design. The last technique, multimaterial molding, requires modified molding machines and tooling for optimal success.

PULSED COOLING AND INDUCTION COIL HEATING

This innovative method for controlling mold temperature (Figure 1) overcomes a previously unavoidable drawback in moldcooling methodology. In the conventional molding process, coolant such as water or oil is circulated through the mold continuously while mold temperature is regulated by a controller such as a thermolator or chiller. This type of temperature control maintains a reasonably consistent water-inlet temperature to the mold.

Figure 1. Pulsed cooling and induction coil heating maintains temperature during the injection stroke by closing manifold valves and stopping water flow.When the injection stops, the valves reopen until the steel cools to the desired temperature. Illustration courtesy of Ken A. Kerouac

When plastic is injected into the mold cavity, the mold temperature rises as heat is transferred from the molten plastic to the mold itself. As the molded part cools and solidifies, heat is conveyed out of the system by transfer to the circulating cooling medium and, to a lesser extent, through the mold base to the ambient environment. Cooling continues through mold opening, part ejection, and mold closing, right up until polymer injection on the subsequent shot. This process has unfortunate implications for the polymer. The melt is now being injected into the mold at what is, from a thermal standpoint, the worst possible moment in the cycle—the point at which the mold is at its coldest temperature. Ideally, coolant should be flowing through the mold only when it is required: from the end of polymer injection to the point where the part is cool enough to be ejected.

The pulsed cooling process is designed to address this problem. A manifold fitted with solenoid-controlled water valves is placed in the supply line between the incoming water source and the mold. The manifold is linked to a controller, which is in turn linked to probes that are inserted into each half of the mold just under the parting line surface. The desired steel temperature (monitored by the probes) is set on the controller. During the injection stroke, the manifold valves are closed, permitting no water flow (and therefore no cooling) to the mold. At the end of injection, a signal is sent to the manifold to open all of the valves and pulse cold water through the system. Once the probes sense that the desired steel temperature is reached, water flow through the mold is again terminated until the next shot.

A unique feature of this system is that with larger, complex molds in which heat transfer from the part will not occur uniformly, more probes may be used in conjunction with manifolds that have a greater number of ports. This will allow for independent zones of control within the mold, so that water flow to areas that are sufficiently cooled will be closed off and diverted to warmer areas of the mold. This degree of control affords the opportunity for better part uniformity and reduced cycle time.

A coinjection molding machine forms parts using two materials (one skin and one core), taking advantage of the benefits of both (Ferromatik Milacron, Cincinnati).

With high-temperature polymers, particularly those that run with hot oil rather than water, the problem is often not losing heat too slowly but too rapidly. A high thermal gradient exists between the hot mold and the ambient air, and the resulting heat transfer may overcool the mold in spite of the benefits of the pulsed water flow. In such cases, the pulsed cooling may be supplemented by, or even replaced by, induction coils inserted into each half of the mold. These coils are also controlled by the unit that regulates the water manifold. Their function is to provide background heating to the mold around its perimeter, thus preventing excessive heat loss and maintaining a better thermal equilibrium within the mold. The drawback to induction coils is that they will only work with ferrous mold materials and therefore are not suited for prototyping efforts with molds made out of aluminum or nonferrous alloys.

Pulsed cooling can be retrofitted to existing molds relatively inexpensively. Because the polymer will fill the cavity under warmer conditions, parts with lower, more uniform molded-in stress can be achieved. This can promote better dimensional stability, including heat-distortion resistance, reduced birefringence in transparent parts, more uniform surface finish, more uniform crystallinity development, and therefore more uniform shrinkage. Studies have also Verified cycle time improvements with some applications of between 10 and 20%.

GAS-ASSISTED INJECTION MOLDING

Although the earliest patents on gas-assisted molding were issued in the mid- to late 1970s, the process has only come into its own over the last five years, after a quiet gestation period in the 1980s. Its latest explosive growth has shown it to be a truly enabling technology—things can be achieved with gas-assist that are simply not possible with any other type of molding process.

Gas-assisted molding evolved from a modification of the structural foam process known as gas counterpressure, in which a sealed mold cavity is pressurized with nitrogen before the introduction of the polymer/blowing agent blend. The pressure in the cavity prevents the foaming action of the blowing agent from taking place at the melt front, allowing a smooth skin to be formed at the surface while the cellular structure is created in the core. This process minimizes the surface swirls, splay, and imperfections that often made foamed parts difficult to finish or paint.

Gas-assist, like its parent technology, employs prepressurized nitrogen, but in this case no blowing agent is used in the polymer, and the gas is injected into the interior of the polymer shot, creating a part with a polymer skin that is either entirely hollow or solid with hollow sections, depending on the design (Figure 2). Unlike structural foam, gas-assist produces no cellular structure; the polymer and gas form separate, discrete layers.

Figure 2. Injection, hold, and release sequence for gas-assisted molding of hollow or partially hollow parts. Illustration courtesy of Cinpres, Ltd. (Tamworth, UK).

Suppliers of gas-assist equipment offer a wide choice of hardware and controls, but in all cases the basics of the process are similar. A stand-alone gas-assist unit wired to receive signals from the molding machine draws from a nitrogen source (in most cases either a bottle or a nitrogen generator) and prepares a pressurized charge of nitrogen to be delivered to the mold. As the injection stage of the cycle begins, a signal based on time, pressure, or screw position is sent to the gas unit to trigger gas injection at the appropriate time. Gas may be injected either into the polymer melt through a specially designed molding machine nozzle, which sends the gas through the sprue, runners, and gates before entering the part cavity, or directly into the mold itself through gas nozzles fitted into the mold base.

Once injected into the polymer, the gas bubble finds the path of least resistance, favoring the best combination of high temperature and low pressure. In a properly designed tool run under the proper process conditions, the nitrogen, which is much lower in viscosity than the polymer, remains isolated in the gas channels of the part without bleeding out into any thin-walled areas. The gas channels are those areas that have been thickened to achieve functional utility in the part or to promote better flow of the polymer during filling. Because of the lower viscosity of the gas, the pressure drop across the gas bubble is much lower than across a normal polymer shot. This phenomenon accounts for the ability of gas-assist to provide a higher degree of packing than is possible with the traditional process and to allow the melt to travel longer flow lengths in the mold with fewer gates.

Once the gas has aided the polymer in filling out the cavity, it is held under pressure until the material solidifies, with the gas-hold stage replacing the hold stage in a conventional cycle. The gas is then allowed to vent from the part in order to relieve the internal pressure prior to mold opening. By coring out thick sections with gas, significant cycle time savings can be achieved since there are no thick sections of plastic that require a long time to cool. During the period between the end of gas hold and part ejection, the gas unit is recharged with nitrogen for the next shot.

Gas-assist applications often fall into one of three categories:

• Short-shot molding. A process in which certain features such as ribs or thick walls are cored out with gas in an otherwise solid molded part. This process gets its name from the method of only partially filling the cavity during the polymer injection phase of the cycle and then relying on the gas injection phase to fill out the remainder of the cavity with the material the gas bubble is displacing from the core.
• Full-shot molding. A process in which the mold is completely filled during the plastic injection phase. Gas is introduced into the cavity in this case only to provide local packing and to compensate for the effects of polymer volumetric shrinkage as the part cools.
• Hollow molding. A process in which all or nearly all of the part is cored out by the gas, in effect making the part itself the gas channel. This is the method most often used to make parts with large cross sections such as rods, tubes, and handles.

With the gas-assist process, thick parts can be molded without cycle time sacrifices and associated issues such as sink marks and voids. Parts cored out with gas will be lighter, with a higher stiffness-to-weight ratio, resulting in material savings and reduced costs. Large parts can be filled more easily, creating parts with less molded-in stress and better dimensional stability. The surface appearance of gas-assist parts is much improved over that of structural foam. Many items produced by gas-assist do not require paint or any other kind of secondary finishing step.

MULTI—LIVE FEED MOLDING

The conventional injection molding process imposes severe limitations on how the polymer melt may be manipulated once it has filled the cavity. Between the end of first-stage injection and final part ejection only two external effects can act on the melt. The first is heat removal through a combination of conduction and convection. The second is the relatively static pack-and-hold pressures applied by the screw. Used to compensate for volumetric shrinkage and to prevent sinks from forming as the part solidifies, these pressures can only be applied until the gate freezes off. The multi—live feed (MLF) process (Figure 3) employs auxiliary injection molding equipment to achieve dynamic oscillation of the polymer melt within the mold cavity. This oscillation creates a shearing effect on the polymer that prolongs the time the material remains in the molten state and promotes improved orientation and weld line characteristics.

Figure 3. The multiple live feed process, showing (A) out-of-phase oscillation (fill), (B) in-phase oscillation (pack), and (C) holding phase. Illustration courtesy of Eliot M. Grossman (Cinpres-Scorim, Ltd., Tamworth, UK).

Weld lines are molding defects created when multiple polymer flow paths converge in a cavity, such as when melt fronts from different gates meet each other or when flow from a single gate is forced to split and recombine around a pin or other projection in the tool. Weld lines can create appearance problems, since their visibility on the surface may require a costly painting step, or they may be structurally objectionable, since weld lines are inherently weak areas of the parts that can act as stress concentrators and possible failure points in impact or flex situations.

The heart of the MLF process is the head, which mounts to the front of the injection barrel. Within this head, the polymer shot is divided into two independent flow paths and delivered to the mold through two nozzles rather than one, as is done conventionally. A modified sprue bushing with two sprues is required, as is a runner layout that maintains separation of the flow paths.

The head contains hydraulically actuated pistons that act on the melt and provide the oscillation and subsequent pack-and- hold phases employed by the process. Piston motion is controlled by a stand-alone unit synchronized with the injection molding machine by a signal such as first-to-second-stage transfer time or position on each shot.

The MLF process employs three modes of operation:

• The A mode uses an out-of-phase motion of the two pistons; when one piston is moving forward, driving the melt ahead of it, the other piston is retracting, creating volume for the melt to move into. This mode most often begins immediately after first-stage injection, although it can be triggered to begin during injection as well.
• In the B mode, both pistons move in the same direction simultaneously, packing out the cavity. Depending on the capability of the molding machine, the level of packing pressure the MLF unit can provide may be higher than what the machine can deliver.
• In the final C mode, both pistons move forward once and remain in the forward holding position until gate freeze-off. The B and C modes in the process take the place of the pack-and-hold stages in the conventional molding cycle.

The MLF unit controls five specific parameters:

• Temperature of the head. Thermocouples in the head regulate the operation of cartridge heaters to maintain a desired temperature.
• Sequence of operation. In most cases, the sequence of the modes will be in the order described in the previous section. However, it is possible to change the order of operating modes or to eliminate one or two of them entirely.
• Pressure. The forward and return pressure of the pistons can be controlled. The property that most often dictates pressure settings will be the viscosity of the material.
• Frequency. The number of piston oscillations per second can be set. The shear sensitivity and thermal diffusivity of the material may dictate this parameter, since it is the shearing effect of the oscillations that prolong the molten state of the polymer.
• Duration. The length of time each mode is employed within a given cycle controls orientation. If high orientation is desired (with fiber-reinforced parts, for instance), parts with thicker walls may require longer duration, since a larger percentage of the cross section is relatively unoriented polymer, compared to the highly oriented layers closer to the part surface.

The MLF process may eliminate the need to paint parts by reducing the surface weld-line severity to the point where the weld lines are virtually invisible. Whether the surface weld lines are eliminated or not, the internal ones may be altered to a degree that will make the part stronger than it would be with weld lines formed by conventional processes. In fiber-reinforced parts, orientation of the fibers is improved, achieving improved strength in the fiber direction. Filling of thin-wall parts may be facilitated if the oscillation is initiated during polymer fill, creating the shearing effect that may postpone the onset of rapid cooling and solidification that can limit the success of thin-wall molding.

MULTIMATERIAL MOLDING

Unlike the other three processes reviewed above, which superimpose auxiliary equipment and some mold modifications onto otherwise standard molding machines, multimaterial molding requires specialized molding equipment in and of itself. A number of different methods fall under the broad umbrella of multimaterial molding: coinjection, overmolding, two-shot molding, and sandwich molding. In all cases, the basic premise of multimaterial molding is to take economical advantage of two or more materials with uniquely different properties by incorporating them into one molded component.

The fundamental equipment requirement for multimaterial molding is to have as many plasticating units (machine barrels) as there are materials to incorporate into the molded part. With some machine designs, multiple barrels are mounted onto the machine base itself; with other systems, the design is more modular, allowing barrels to be added or removed as needed and aligned in different configurations (even vertically) to accommodate more or fewer materials or to adapt for floor space or ceiling height limitations.

Coinjection and Sandwich Molding. These two similar processes (coinjection is sometimes classified as a subset of sandwich molding) form parts with a skin of one material and a core of another, taking advantage of the benefits of both. The critical material requirement in this kind of molding is compatibility. If the two polymers are not compatible, they will not adhere to each other, resulting in delamination at the interface between the two polymer layers and failure of the part.

Figure 4. The coinjection process works by first injecting the skin material (A) then switching to the core material (B). A small amount of skin material can seal the gate to finish the process. Illustration courtesy of Battenfeld of America (West Warwick, RI).

In coinjection molding, two barrels are joined together by a common manifold and nozzle, through which both materials flow before entering the cavity (Figure 4). The nozzle is designed with a shutoff feature that allows only one of the materials to flow through at any given time. To set up the process, the relative percentage of skin to core material is determined, most often by trial and error, and the two barrels are each programmed with the appropriate shot size. On injection, the injection unit with the skin material (often called the A barrel or A side) injects the set amount of polymer. This is followed by the core material in the B barrel which, in a manner similar to gas-assist, penetrates the skin polymer and completes filling of the cavity without breaking through to the skin surface. Since plastics flow in injection molding is laminar, the two materials can be molded in this skin-core configuration without mixing with each other.

Coinjection molding often has a third stage, in which a small amount of skin material completes the injection stage. This is known as an A-B-A injection sequence and accomplishes the task of completely encapsulating the core material, thus protecting it from any weathering, chemicals, or other exposures to which it might be susceptible.

Figure 5. Sandwich molding's multiple plasticating units serve as extruders that allow fixed amounts of material into a single injection unit. Illustration courtesy of Ferromatik Milacron (Cincinnati).

Sandwich molding also results in a skin-core structure, but the mechanics are slightly different (Figure 5). In this process, multiple plasticating units are used only as extruders to feed their percentage of the total shot to a single injection unit. The injection unit itself also accounts for one of the polymer layers. Prior to injection, then, the injection unit has built up a shot consisting of as many layers as there are materials. Again, because of the laminar nature of polymer flow in the injection molding process, these layers do not mix with each other.

Upon injection, the last material fed to the injection unit, which is at the front of the barrel, becomes the skin of the part, and all of the subsequent layers form beneath it, working toward the center, until the last material in, which was that material plasticized by the injection unit itself, becomes the very core. Because all of the injection is done through only one injection unit, there is no opportunity for an A-B-A sequence, as in coinjection; therefore, complete encapsulation of the core is not possible. The core will be exposed at the gate leading into the cavity, which is often not a problem if the gate is on an area of the part that will be hidden or if the material in the core is resistant to the detrimental effects of environmental or chemical exposure.

Coinjection and sandwich molding can provide both economical and functional advantages to a molder. Economically, material costs can be reduced by having the premium or more expensive material only on the outside of the part where it is visible, while the inside may be filled with a less expensive resin. The core of a coinjected part may also be an excellent outlet for regrind generated in production operations. Functionally, parts can combine both structure and utility. A part requiring surface features such as a soft touch, or a 100% color match to eliminate paint, may be molded with a more rigid core material, or even a filled one, to provide a good combination of a soft, pliable surface and high rigidity.

Overmolding. With sandwich or coinjection molding, it may not always be apparent that two materials are being used. Overmolding, or two-shot molding, results in parts in which it is clearly evident that more than one material is being used. In these processes, only part of a product is molded in one material, and that molded piece is manipulated so the second material can be molded around, over, under, or through it to complete the final part. This method is sometimes referred to as in-mold assembly, since the resulting part effectively acts as an assembly of two materials rather than as a layered structure.

Tool design is a critical element for successful overmolding. In some designs, the first component is molded in the first material; then sliding action in the tool creates an additional cavity space that can be filled by the second material to complete the in-mold assembly of the part. The mold cavity also has to be transported, either by mold rotation or mold shuttling, to a position of alignment with the second barrel so it can complete filling of the mold. In other cases, the first molded component has to be physically removed from its cavity and placed in another cavity for molding with the second material. The second molding stage may be another barrel on the same machine, in which the same sort of rotating or shuttling tooling may be employed, or it may be an entirely different mold on an entirely different machine, which saves tooling costs but ties up two machines instead of one.

In most cases, good compatibility of the different materials is required to promote good adhesion and to prevent delamination and part failure. In some cases, however, incompatible materials may be deliberately molded with each other for applications in which relative motion between the two subcomponents is desired. It is possible, for instance, to create a jointed part with a ball molded in one material and a socket molded in a second, incompatible material. The parts can be assembled right in the mold, and since the materials are incompatible, the ball and socket will not adhere, allowing free movement between the components.

The primary benefit of overmolding is savings on assembly costs. Downstream assembly operations may be eliminated, and time and expense are reduced if mechanical fasteners or adhesives do not have to be purchased, installed, or applied. One of the more commercially visible overmolding applications is toothbrushes that have a soft section built into the handle to achieve a better grip. This application would not be practical if it required any kind of mechanical fastener, and human oral contact may limit the kinds of adhesives that may be considered.

CONCLUSION

An article such as this can only touch upon the many innovations in molding technology that contribute to the success of medical device manufacturing. As unmet needs continue to be identified, new materials in new designs for new applications will continue to be developed. Injection molding technology will continue to keep pace with these developments and provide the manufacturing capabilities necessary to bring these products to life.

Ken A. Kerouac is a specialist with the applied fabrication technology team in the technical service and development (TS&D) department and Peter F. Grelle is a development leader in the automotive technical service and development group at Dow Plastics (Midland, MI).

Copyright ©1998 Medical Device & Diagnostic Industry

The American Society for Radiation Oncology (ASTRO) updated their guidelines on partial breast irradiation (PBI) for patients with early-stage invasive breast cancer or ductal carcinoma in situ (DCIS).

These new guidelines take into account results from multiple randomized controlled trials that have been published since ASTRO last issued recommendations for PBI in 2017. The trials included more than 10,000 women with about 10 years of follow-up, and, according to ASTRO guideline task force members, demonstrated "oncologic equivalence" between PBI and whole-breast irradiation (WBI) for the treatment of early-stage breast cancer and DCIS.

"For patients with early-stage breast cancer, many are eligible for consideration of partial breast irradiation," Task Force Chair Janice Lyons, MD, of the University Hospitals Seidman Cancer Center in Cleveland, told MedPage Today. "This is a conversation radiation oncologists should have with their patients and they can use the guidelines as a framework on how to have that discussion and how to deliver partial breast irradiation safely."

According to Lyons, one of the key differences in the updated guidelines is that they are "more liberal" regarding the age at which PBI may be appropriate.

The 2017 guidelines recommended that women ages 50 and older be considered "suitable" for PBI outside a clinical trial, while women ages 40 to 49 were included in the "cautionary" group, and those ages 40 and under be included in the "unsuitable" group.

The updated guidelines state that, for patients with early-stage, node-negative invasive breast cancer, PBI is strongly recommended as an alternative to WBI if the patient has favorable clinical features and tumor characteristics, including grade 1 to 2 disease, estrogen receptor (ER)-positive status, age 40 or older, and small tumor size.

PBI is conditionally recommended if the patient has an indication of higher recurrence risk, including grade 3 disease, ER-negative histology, or larger tumor size. It is not recommended for patients with positive lymph nodes, positive surgical margins, or germline BRCA1/2 mutations, or those who are younger than 40, and is conditionally not recommended for patients with less favorable risk features (e.g., lymphovascular invasion or lobular histology), due to the lack of robust data on these patient subsets.

For patients with DCIS, the recommendations align with those for early-stage breast cancer. PBI is strongly recommended as an alternative to WBI for patients with favorable clinical and tumor features outlined in the guideline, conditionally recommended for those with higher-grade disease or larger tumors, and not recommended for patients with positive surgical margins, BRCA mutations, or age less than 40.

"At this point so many randomized controlled trials have been conducted that we were able to really drill down into the subgroups of patients to better define those represented sufficiently enough to strongly recommend partial breast radiation rather than whole breast radiation," said Simona F. Shaitelman, MD, of the University of Texas MD Anderson Cancer Center in Houston, who served as the task force's vice chair.

Shaitelman pointed out that the updated guidelines also dealt with issues related to the delivery of PBI.

Recommended techniques for PBI include 3-D conformal radiation therapy, intensity-modulated radiation therapy, and multi-catheter interstitial brachytherapy, based on studies showing similar long-term rates of ipsilateral breast recurrence compared with WBI.

Single-entry catheter brachytherapy is conditionally recommended, while intraoperative radiation therapy (IORT) techniques, including electron IORT and photon (kV) IORT without WBI, are not recommended unless part of a clinical trial or multi-institutional registry.

The guideline also outlines the optimal dose-fractionation regimens, target volume delineation, and treatment planning parameters for different PBI techniques.

A daily or every-other-day course of PBI is recommended over twice-daily regimens, and the guidelines also pay particular attention to clinical and cosmetic side effects of PBI.

"I think the guidelines highlight how in certain scenarios, partial breast irradiation is actually more favorable than whole-breast irradiation," said Shaitelman. "And that's an important point to highlight to patients in order to Excellerate their overall quality of life if they require radiation as part of their oncologic care."

Early Detection and Gender Disparities in COPD

Dr. MeiLan Han

In this interview, Dr. MeiLan Han, a distinguished pulmonologist and Chief of the Division of Pulmonary and Critical Care at the University of Michigan, shares her profound insights into Chronic Obstructive Pulmonary Disease (COPD).

Twenty years ago, Shoaib Akhtar became the first person recorded to bowl at 100mph (161km per hour) during the 2003 One-Day International Men's World Cup match for Pakistan against England. There was an expectation afterwards that this feat would become a regular occurrence.

As humans have continued to run faster, throw further and jump higher, it was believed that this milestone would be a stepping stone consigned to history similar to Roger Bannister breaking the four-minute mile. It was thought it might also act as a catalyst for serious worldwide improvement in fast bowling.

However, despite continuing improvement in the athletic ability of fast bowlers, the magical three-figure barrier has only been surpassed since by Brett Lee and Shaun Tait—and not for over ten years.

Has cricket fast bowling's top speed stalled? During the current 2023 One-Day International Men's World Cup being hosted in India, only a handful of bowlers have produced speeds over 90mph (145km per hour), with the fastest being around 95mph (153 km per hour).

The performance of cricket fast bowlers almost entirely depends on two factors. The first is the amount of momentum developed in the run-up and maintained before the front foot contacting the floor. The second is the technique employed to generate and transfer momentum within the body during the bowling phase between the front foot contacting the floor and the release of the ball from the bowler's hand.

Previous research has highlighted that the fastest elite male bowlers generate more momentum in their run-up, adopting a movement strategy that aims to maintain and transfer this momentum into the throw instead of generating additional momentum from their muscles.

Testing the limits

To investigate the limits of fast bowling performance, a world-leading predictive musculoskeletal computer simulation model of ten elite male fast bowlers (essentially a virtual clone of each bowler) was developed. It then optimized their technique to maximize the release speed of the ball.

Significantly, none of these bowlers were predicted by the computer model to break the 100mph barrier.

To understand why the top speed has stalled, it is important to consider how all the factors influencing human movement patterns affect the technique of fast bowlers.

The behavior of all our movement patterns is shaped by three types of constraint. The first is organismic: these are constraints on the individual, such as their size, strength and range of motion. The second factor shaping movement patterns is the environment the individual interacts with, including the atmosphere, temperature, equipment and surfaces. The third shaping factor is the task, which involves constraints such as the goal of the activity, the rules and the intensity.

Our previous experiences of the movement—what we have seen, what we have been told and our previous performance of the movement—also affect individual technique in fast bowling.

The innate physiology of the fast bowler, an organismic constraint, provides the only potential area for development in fast bowling. The other constraints, such as environment and task, which often lead to scientific and technological development associated with improvements in other sports, are extremely limited in fast bowling. This is due to the lack of equipment and the simplicity of the activity.

The physiological aspect often considered to be associated with improvements in fast bowling performance is an increase in muscular strength, power and endurance. However, there's a unique cricket bowling "task" constraint which requires bowlers to maintain a straight arm during the bowling phase. This significantly reduces the time available to complete the throwing movement.

Explosive activation

Elite males complete the bowling phase in approximately 100 milliseconds. This is similar to the time required to explosively activate a single muscle. This limits the ability of bowlers to develop additional momentum using their muscles in the bowling phase and neutralizes the effect of strength increases on ball speed.

This explains why maximizing momentum generated during the run-up is preferred over generating muscular momentum during the bowling phase. It also explains why fast bowling top speeds have not increased despite latest advances in fast bowlers' athletic abilities.

Interestingly, research on women fast bowlers has highlighted that bowlers who generate less momentum during the run-up and therefore have more time available to generate additional muscular momentum, adopt a movement pattern more akin to throwing. In this approach, the momentum generated in the run-up is added to via the use of large rotational torso muscles within the bowling phase.

Improvements to the performance of the large rotational torso muscles in men and women could possibly Excellerate the generation of muscular momentum. But this approach is considered a sub-optimal technique by the research that's been carried out on fast bowling.

A potential mechanism to increase the time available to develop more momentum from muscles would be to increase the range of motion that joints move through during the bowling phase.

Joint 'hypermobility'

Recent research has highlighted that, on average, elite fast bowlers with an increased range of motion in the hip and shoulder had greater ball release speeds. It was also suggested that the bowlers' techniques were probably influenced by their range of motion during their early learning years.

In addition, elbow hyperextension—where the joint travels beyond a straight position—has been shown to increase the speed of ball release by up to 5% during the bowling phase. A common misconception, however, is that taller bowlers will bowl faster due to the benefit associated with increased limb length.

Unfortunately, as limbs get longer, they get more difficult to rotate. As muscular strength does not scale equally with limb length this becomes a disadvantage. Thus, an optimal height for fast bowlers probably exists, though we don't know what it is.

Organismic factors linked with increased ball speed such as body shape, size and hypermobility are largely genetic. Since human evolution is extremely slow, advances in ball release speed are likely to follow at a similar pace.

The 100mph barrier, therefore, should be viewed more as a mountain that requires a once-every-generation bowler to scale rather than a dam in a river. The potential of this peak to grow is limited by the constraints of the task and by our innate physiology.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

When an algorithm-driven microscopy technique developed in 2021 (and able to run on a fraction of the images earlier techniques required) isn't fast enough, what do you do?

Dive DEEPer, and square it. At least, that was the solution used by Dushan Wadduwage, John Harvard Distinguished Science Fellow at the FAS Center for Advanced Imaging.

Scientists have worked for decades to image the depths of a living brain. They first tried fluorescence microscopy, a century-old technique that relies on fluorescent molecules and light. However, the wavelengths weren't long enough and they scattered before they reached an appreciable distance.

The invention of two-photon microscopy in 1990 brought longer wavelengths of light shine onto the tissue, causing fluorescent molecules to absorb not one but two photons. The longer wavelengths used to excite the molecules scattered less and could penetrate farther.

But two-photon microscopy can typically only excite one point on the tissue at a time, which makes for a long process requiring many measurements. A faster way to image would be to illuminate multiple points at once using a wider field of view but this, too, had its drawbacks.

"If you excite multiple points at the same time, then you can't resolve them," Wadduwage said. "When it comes out, all the light is scattered, and you don't know where it comes from."

To overcome this difficulty, Wadduwage's group began using a special type of microscopy, described in Science Advances in 2021. The team excited multiple points on the tissue in a wide-field mode, using different pre-encoded excitation patterns. This technique—called De-scattering with Excitation Patterning, or DEEP—works with the help of a computational algorithm.

"The idea is that we use multiple excitation codes, or multiple patterns to excite, and we detect multiple images," Wadduwage said. "We can then use the information about the excitation patterns and the detected images and computationally reconstruct a clean image."

The results are comparable in quality to images produced by point-scanning two-photon microscopy. Yet they can be produced with just hundreds of images, rather than to the hundreds of thousands typically needed for point-scanning. With the new technique, Wadduwage's group was able to look as far as 300 microns deep into live mouse brains.

Still not good enough. Wadduwage wondered: Could DEEP produce a clear image with only tens of images?

In a latest paper published in Light: Science and Applications, he turned to machine learning to make the imaging technique even faster. He and his co-authors used AI to train a neural network-driven algorithm on multiple sets of images, eventually teaching it to reconstruct a perfectly resolved image with only 32 scattered images (rather than the 256 reported in their first paper). They named the new method DEEP-squared: Deep learning powered de-scattering with excitation patterning.

The team took images produced by typical two-photon point-scanning microscopy, providing what Wadduwage called the "ground-truth." The DEEP microscope then used physics to make a computational model of the image formation process and put it to work simulating scattered input images. These trained their DEEP-squared AI model. Once AI produced reconstructed images that resembled Wadduwage's ground-truth reference, the researchers used it to capture new images of blood vessels in a mouse brain.

"It is like a step-by-step process," Wadduwage said. "In the first paper we worked on the optics side and reached a good working state, and in the second paper we worked on the algorithm side and tried to push the boundary all the way and understand the limits. We now have a better understanding that this is probably the best we can do with the current data we acquire."

Still, Wadduwage has more ideas for boosting the capabilities of DEEP-squared, including improving instrument design to acquire data faster. He said DEEP-squared exemplifies cross-disciplinary cooperation, as will any future innovations on the technology.

"Biologists who did the animal experiments, physicists who built the optics, and computer scientists who developed the algorithms all came together to build one solution," he said.

This story is published courtesy of the Harvard Gazette, Harvard University's official newspaper. For additional university news, visit Harvard.edu.

Medical Device & Diagnostic Industry Magazine
MDDI Article Index

An MD&DI  January 1998 Column

THERMAL MANAGEMENT

Choosing the right thermal control element helps ensure accurate functioning of complex electronic, imaging, and processing systems.

Equipment engineers seeking to develop faster and more accurate medical and laboratory products are beginning to recognize the importance of proper thermal management. The speed or accuracy of sensitive electronic devices such as microprocessors and lasers can be affected by thermal conditions, and cooling generally has a positive effect on equipment reliability. Chemical reaction rates are proportional to temperature, and the working time or shelf life of a biological demo or laboratory reagent can be increased by keeping the substance at an optimal temperature. Instruments such as DNA cyclers, tunable laser diodes, and thermal-stress analyzers all require a capacity for cycling an object or demo through a range of temperatures with speed and precision.

Heat sinks can be used with or without fans and offer considerable installation flexibility, but they cannot cool components below ambient temperature. Photo courtesy of Melcor Corp. (Trenton, NJ)

There are many different tools and methods for transferring heat. Which method is best depends on the temperatures and tolerances of the application. Simpler devices might function well enough with passive cooling elements such as heat sinks, while devices that operate in more demanding environments might require an active cooling method such as a compressor-based or thermoelectric system. A fan, for example, can be used to remove the heat generated inside an electronics cabinet. If the cabinet is sealed, a heat sink or heat pipe is needed. If the cabinet's temperature must be controlled, a heat pump or air conditioner is indicated. The best design will be determined by system needs and limitations. System needs would address the amount of heat to be added or removed to achieve the required temperature. Limitations might involve space, cost, allowable vibration, and available power. Once these factors are defined, the thermal engineering choices become apparent. The following is an overview of the thermal management technologies readily available to the engineer, listed from the simplest to the most sophisticated.

FANS AND BLOWERS

Fans operate by passing air over a hot component, absorbing the component's heat. Overall cooling effectiveness is determined by the air's flow rate and temperature together with the component's size and output. Typically, fans and fan trays are used in cabinets for bulk cooling of electronics. Fans and blowers are relatively inexpensive and provide a high measure of flexibility in installation. On the other hand, the constant exchange of air raises the potential for contamination from dust and moisture. Moreover, fans and blowers can prove ineffective for high-power devices and cannot cool an object at or below ambient temperature.

HEAT SINKS

Generally, heat sinks are made from aluminum because of the metal's relatively high thermal conductivity and low cost. They are either extruded, stamped, bonded, cast, or machined to achieve a shape that will maximize surface area, facilitating the absorption of heat by the surrounding cooler air. Most have a fin or pin design. When used with fans (forced convection), heat sinks can dissipate large amounts of heat while keeping the targeted components at 10°—15°C above ambient temperature. Heat sinks without fans (free convection) result in a higher component temperature because of the decreased impingement of air. Like fans, heat sinks are inexpensive and offer installation flexibility but cannot cool components at or below ambient temperature. Also, heat sinks do not permit temperature control.

Thermoelectric coolers made from semiconductor pairs between ceramic plates (Melcor Corp., Trenton, NJ).

LIQUID COLD PLATES

Liquid cold plates are typically made from copper, aluminum, or aluminum-clad copper tubing. Heat is absorbed by a liquid pumped through the plate, which is attached directly to the object being cooled. In an open-loop system, the liquid (usually tap water) runs through the plate and out through a drain. In a closed-loop system, a pump recirculates the liquid through a heat exchanger or radiator. Liquid cold plates are characterized by a small size (at point of attachment), and they offer effective heat dissipation. The devices are limited by the fact that they cannot cool below ambient (liquid) temperature and permit no temperature control. The potential for leakage is also a concern, and the availability of liquid sources can sometimes pose a problem.

The best design will be determined by system needs, such as the amount of heat to be removed, and limitations, such as space, cost, power, and permissible vibration.

HEAT PIPES

A heat pipe is a sealed vessel that transfers heat by the evaporation and condensation of an internal working fluid. Ammonia, water, acetone, or methanol are typically used, although special fluids are used for cryogenic and high-temperature applications. As heat is absorbed at the evaporator, the working fluid is vaporized, creating a pressure gradient within the heat pipe. The vapor is forced to flow to the cooler end of the pipe, where it condenses, giving up its latent heat to the ambient environment. The condensed working fluid returns to the evaporator via gravity or capillary action within the wick structure. Because heat pipes exploit the latent heat effects of the working fluid, they can be designed to keep a component near ambient conditions. Though they are most effective when the condensed fluid is working with gravity, heat pipes can work in any orientation. Using forced air at the condenser allows for larger amounts of heat dissipation. Heat pumps are typically small and highly reliable, but they can't cool objects below ambient temperature and do not permit temperature control.

COMPRESSOR-BASED COOLING

Compressor-based cooling systems, found in commercial refrigerators and air conditioners, contain three fundamental parts: an evaporator, a compressor, and a condenser. In the evaporator, pressurized refrigerant is allowed to expand, boil, and evaporate, absorbing heat as it changes from a liquid to a gas. The compressor acts as the refrigerant pump and recompresses the gas to a liquid. The condenser expels the heat absorbed (along with the heat produced during compression) into the ambient environment. Compressor-based refrigeration is effective for large heat loads (300 W or more) and can cool components far below ambient temperature. The technique also allows users to control temperature. These refrigerators must be used in their designed orientation, which limits installation flexibility. Maintenance and reliability are also compromised by moving parts. Compressor-based systems also tend to be bulky and noisy.

THERMOELECTRIC COOLERS

Thermoelectric coolers (TECs) are solid-state heat pumps made from semiconductor materials. They have no moving parts but comprise a series of p-type and n-type semiconductor pairs or junctions sandwiched between ceramic plates. Heat is absorbed by electrons at the cold junction as they pass from a low energy level in a p-type element to a higher energy level in an n-type element. At the hot junction, energy is expelled to a heat sink as the electrons move from the high-energy n-type element to a low-energy p-type element. A dc power supply provides the energy to move the electrons through the system. A typical TEC will contain up to 127 junctions and can pump as much as 120 W of heat. The amount of heat pumped is proportional to the amount of current flowing through the TEC; therefore, tight temperature control (<0.01°C) is possible. By reversing the current, TECs can function as heaters, which can be useful in controlling an object in changing ambient environments or in cycling at different temperatures. Sizes range from 2 to 62 mm, and multiple TECs can be used for greater cooling. Because of the relatively large amount of heat being pumped over a small area, TECs require a heat sink to dissipate the heat into the ambient environment. The modular units can be used in any orientation and are compatible with heat sinks, cold plates, and heat pipes. On the down side, TECs require a dc power source and are more expensive than passive components.

THERMAL COMPOUNDS

When mounting a cooling device to a component or assembling a cooling system, designers must select a thermal bonding material that will allow heat to flow out of the device with minimal resistance. Designers should take into account mechanical stresses at the interfaces caused by differing material coefficients of thermal expansion. The idea is to eliminate any air pockets between the two surfaces.

The most common interface material is thermal grease, typically made from zinc oxide in a silicon or petroleum base. There are also pastes available with thermal conductors such as aluminum oxide and aluminum nitride. Pads and foils are less messy to apply and can be cut to match the component footprint. Some pads are available with adhesive surfaces to allow permanent attachment. Aluminum oxide and aluminum nitride are used in thermal pads, as are sheets made from graphite, indium, and aluminum.

Thermal epoxies create rigid, permanent bonds. They are typically supplied as two-part systems comprising a hardener and a resin filled with silver, aluminum, aluminum oxide, or aluminum nitride. Because they are permanent, epoxies should be used only in areas that will not require future disassembly. Rigid bonds can also be achieved using solder. Eutectic and noneutectic formulations are available for use in a wide temperature range. Soldered surfaces offer a good rigid thermal joint and can be disassembled by simply reflowing the solder. As with all rigid joints, the effects of differing thermal expansions should be considered.

CONCLUSION

High-performance electronics, sensitive imaging equipment, and sample-processing systems all require proper thermal control to ensure accuracy and functionality. Design engineers need to identify temperature-sensitive components in order to create an integrated system with parts that are both compatible and economical. They should do this early in the design process; the sooner thermal limitations are identified, the more flexibility the engineer has in choosing from the available options. In the final analysis, retrofitting thermal products is usually not as effective and economical as generating a solid thermal design from day one.

Robert Smythe is vice president of sales and marketing at Melcor Corp. (Trenton, NJ).

Copyright ©1998 Medical Device & Diagnostic Industry