MD+DI Online is part of the Informa Markets Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them. Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.

New MDMA Head Outlines Plans for 2003

Originally Published MDDI January 2003

NEWSTRENDS

Gregg Nighswonger

The 2003 agenda of the Medical Device Manufacturers Association (MDMA) will build off of the group's accomplishments of 2002, says Mark B. Leahey, MDMA's new Executive Director. Leahey's appointment was announced on December 13. Prior to that time, Leahey was the association's Director of Federal Affairs.

"The board has stated that, in the coming year, the issue of group purchasing organizations (GPOs) still remains a top priority for the association," Leahey recently told MD&DI. The group has seen some movement among the leading GPOs, "but clearly not enough to effect change and to address the anticompetitive nature of the practices," said Leahey. "We're looking to lower healthcare costs for the system. You only need to look at the paper to see that costs are spiraling out of control." He added, "Some issues will fall by the wayside, but this is not one of them. There's strong bipartisan support up on the hill, and we look forward to continuing to work on the GPO issues as a top priority."

Regarding the Medical Device User Fee & Modernization Act (MDUFMA) of 2002, Leahey said, "We have always philosophically opposed the notion of a user fee." He adds, "We think that government regulation should be funded by the government. We obviously understood that there was a groundswell here and that the economic conditions in the country warranted discussing user fees as a last resort." Noting that MDUFMA had "quite a few holes," he said, "as we move forward in 2003, the implementation of MDUFMA will be critical to make sure that manufacturers, especially small manufacturers, are protected so that overly burdensome regulations or unintended consequences of the legislation don't happen as FDA moves forward with implementation."

Leahey also believes that congressional appropriations will be critical in 2003. "In the original [MDUFMA] legislation, manufacturers agreed to pay FDA user fees for a five-year period," he said. "If the congressional appropriations weren't there, then FDA wouldn't have to meet any performance goals. We came to the table and said this makes no sense. We wanted it similar to the Prescription Drug User Fee Act, where in the pharma world the language states that if congressional appropriations aren't there, then FDA doesn't have to meet their performance goals, but industry doesn't have to pay a user fee."

He believes device makers will face a number of other issues in the coming year. "Medicare is obviously going to be a big issue," said Leahey. "We need to make sure that new medical technologies are reimbursed at adequate levels in order to foster continued innovation and pay for the research and development." He added, "The rising cost of healthcare will be important. The pharma folks have dealt with this quite a bit, and I'm sure that the device folks are seeing this as well. But it is troubling to look at the number of folks needing medical assistance and the cost of devices. But I think if you look at the GPO issue, where you allow as many players as possible into the marketplace, then you are going to have truly the best product at the lowest price." Leahey believes there are steps that can be taken to address these issues. "We can work with the administration, work with Congress as far as adequate reimbursement levels, and also address some of the competition questions to ensure that everyone has an opportunity to contribute and that hospitals truly are getting the best product at the best price."

Leahey is a member of numerous healthcare organizations, the American Bar Association, and the Massachusetts Bar Association. He is a graduate of Georgetown University and the Georgetown Law Center. He succeeds Larry Holden, who plans to pursue other business opportunities. Paul Touhey, MDMA board chairman, says of Holden, "Larry was instrumental in asserting the position of the research-focused, entrepreneurial medical device sector in the public policy debate."

Copyright ©2003 Medical Device & Diagnostic Industry

Safe Software: A Sample Application

Originally Published MDDI January 2003

SOFTWARE SAFETY

The example application of a medical pump illustrates a safety strategy that can be incorporated in a software design. The primary hazard posed here is pump operation running uncontrolled, resulting in excess solution being delivered to the patient.

The preliminary hardware suite consists of a microcontroller (with limited input-output capability), a pump, a motor-control subsystem, and a limited user interface. As shown in the figure, Motor Manager is the gatekeeper for commanding the motor on; it separates Motor Control and Motor Safety. Motor Manager receives an on request and forwards it to both Motor Control and Motor Safety. Motor Manager does not form an opinion on whether the motor should be on; it checks if Motor Control and Motor Safety agree on whether the motor should be on.

Motor Manager is the gatekeeper, which commands the motor on by forwarding a request to Motor Control and Motor Safety.
(click to enlarge)

Motor Control regulates the voltage to the motor and monitors the motor safety circuit, which is a switch from the motor to the ground voltage. The circuit times out to an open position if it is not continually ordered to switch closed. Motor Control verifies that the on/off command passed in from Motor Manager agrees with the motor safety circuit.

Motor Safety is the counterpart to Motor Control. That is, Motor Safety controls the motor safety circuit and monitors the motor voltage signal, which is commanded by Motor Control.

If the motor is commanded off, the software should not assume that the motor has actually turned off, but should instead verify it—by listening for feedback from the motor position sensor, for example.

The motor is critical to the safe operation of the pump. The hazard analysis states that the software shall not fail when the motor is in the on position. In order for the motor to operate, all three modules must agree. A failure or corruption of any of the software or hardware elements means that the motor will not operate. In addition to the motor module set, the pump's main-state machine maintains a gross check on whether the motor should be in operation.

Copyright ©2003 Medical Device & Diagnostic Industry

Distributors' Group Extends Membership to Device Manufacturers

Originally Published MDDI January 2003

NEWSTRENDS

Lori Bryan

The Independent Medical Distributors Association (IMDA; Mission, KS) is inviting device makers to join its ranks. IMDA members—sales, marketing, and distribution firms that bring products to market—voted in September to admit manufacturers as nonvoting allied members.

David R. Campbell, IMDA president, believes more distributors can be attracted, and its impact on industry enhanced as manufacturers are admitted. The policy change will help manufacturers get to know distributors better, and vice versa, Campbell says. "Over the years, I've felt the relationship between device manufacturers and our members hasn't been as intimate as it should be," says Campbell. He adds, "the ways in which the device business has changed, group purchasing [being one of them], make it more difficult for the smaller firms to get their products to market." Bringing these groups together, says Campbell, will create opportunities.

Manufacturer members will have the chance to connect with firms offering outsourced sales and marketing services at IMDA's conferences and annual Manufacturers Forum. "By coming to our conferences, device manufacturers will be strides ahead," Campbell says. "They can [discover] who the players are and come away with networking opportunities."

Such information exchange may be most appealing to smaller firms with fewer resources, but membership is open to any manufacturer that meets the membership criteria of IMDA's bylaws, Campbell says. While Campbell doesn't expect major players like Johnson & Johnson or U.S. Surgical to seek membership, he doesn't rule it out either. "Many but not all larger manufacturers have direct sales forces that perform the selling function, and [they] may not feel the need for services from IMDA members," he says. "However, some larger firms are recognizing the attractiveness of specialty distributors and representatives for certain product lines or certain technologies, and have developed hybrid sales organizations to address all sectors of their markets."

In addition to networking, manufacturers joining IMDA can expect other benefits, Campbell says. These include access to products liability and other types of insurance, as well as to the discount services of a legal firm specializing in medical manufacturing, distribution, and representation issues.

At press time, IMDA was planning a direct-mail campaign to manufacturers around the first of the new year. For more information on IMDA, visit the organization's Web site at www.imda.org, or call the membership chairman at 800/398-5632.

Copyright ©2003 Medical Device & Diagnostic Industry

Applying Universal Design to Medical Devices

Originally Published MDDI January 2003

DEVICE DESIGN

As more and more complex medical devices are being operated at home, manufacturers need to develop them with disabled users in mind.

Stephen B. Wilcox, PhD

The Personel Lasette from Cell Robotics (Albuquerque) is designed for easy use by people with or without disabilities.
(click to enlarge)

As the trend toward minimizing patient time in the hospital continues, one notable consequence has been the migration of medical devices from medical facilities to patients' homes. This phenomenon means that, increasingly, the patient, rather than the medical professional, is the device user. The effect of this change on the design of many medical products is substantial.

Patients and medical professionals could not be more different. Medical professionals are less likely than the general population to suffer from various disabilities and more likely to be above average in the capabilities required to operate medical devices. In contrast, users of home-healthcare devices may suffer from chronic diseases, or experience dexterity or mobility problems; visual, auditory, or other perceptual deficits; or even cognitive disabilities.

From the device designer's point of view, the trend toward home health-care changes the nature of the task. Smart, highly trained users are good at overcoming device limitations, as anyone can testify who has spent time in the operating room or any other area of a hospital. Thus, in effect, the physicians, nurses, and technicians who use medical equipment allow the medical device designer to be a bit sloppy, because the users are smart enough, strong enough, and healthy enough to forgive a multitude of sins. They readily develop work-arounds to overcome the device problems that they face.

Because patients are by comparison much less able to overcome device limitations, there is greater pressure on the designer of a home-healthcare device to reduce those limitations. The designer must assume that the user may have physical, perceptual, or cognitive disabilities. At the same time, no one, the user of a medical device included, wants to be treated as "special" in the sense of "special education." This logic is the impetus for applying so-called universal design to home-healthcare products.

Universal Design

The term universal design was originally coined by the Whirlpool Corp. The idea, also sometimes referred to as inclusive design, is to provide products that are easy for everyone to use, including those with various disabilities. The key is to make a product usable by a person with a dexterity problem or a visual or cognitive deficit, but not to telegraph the fact that the product has been designed for the disabled. Because people do not like to be stigmatized or reminded that they are disabled, they often simply refuse to use an assistive device. As Laura Gitlin puts it, "[A] reason for device abandonment is . . . that devices symbolize a change in competencies that is associated with negative social judgments."1

Universal design is a strategy with two parts:

  1. To make home-healthcare products appear as normal as possible.
  2. To accommodate those with disabilities, who will inevitably be over-represented in the population of users.

The first part is largely a matter of the designer's approach; it does not require special knowledge. Larger text for labels and lower-force control mechanisms, for example, are better for people with various disabilities but they are also easier for everyone to use. The device designer just has to think in these terms, and the incentive structure of the organization has to incorporate the consideration of universal design.

The second part is trickier, because there is a natural tendency for product designers to use themselves as their benchmark user. Thus, when the user is significantly different from the designer, there is a need for the designer to obtain additional information.

What follows, then, is a summary of some of the disabilities from which people suffer and some techniques that device developers can use to help them better understand the needs of disabled users.

Disabilities

Figure 1. Limitations involving vision, speech, and language make up more than half of all disabilities in the United States.2
(click to enlarge)

According to the U.S. Census Bureau, more than 20% of the general population suffers from some form of disability.2 The distribution of these disabilities is shown in Figure 1. Fortunately, there are effective design strategies for various conditions.

Mobility/Dexterity. An estimated 1.8 million Americans are in wheelchairs; 13.6 million have limited use of their hands. Difficulty with fine control of the fingers, which is often caused by arthritis, is one of the most common problems. Another common problem is loss of limb control as a result of spinal damage, cerebral palsy, multiple sclerosis, muscular dystrophy, or overuse injuries such as carpal tunnel syndrome.

Some design strategies include making buttons large and widely spaced, so that fine motor control is less necessary and errors less likely. Also, the use of spoken commands for device activation eliminates the need for physical manipulation of controls. Other strategies are to minimize the need for simultaneous actions (so the user will not have to perform two things at once), and the need for sustained pressure on controls (to accommodate people with poor finger or hand strength).

Cognitive. Between 6.2 and 7.7 million people in the United States suffer from mental retardation. Another 5­10% of the population suffers from learning disabilities. Other cognitive deficits include the mental confusion associated with psychosis, various language problems, and difficulty concentrating, known as attention deficit disorder.

Design strategies for accomodating such users include incorporating automatic rather than user-activated adjustments; the use of simple, unambiguous language; placement of advanced features under a separate menu; making all actions reversible; and avoiding time constraints.

Auditory. Auditory deficits affect 10% of the U.S. population. They vary from total deafness to various levels of partial deafness. The elderly tend to lose higher pitches first.

Design strategies include providing redundant visual or tactile cues for operating information, volume adjustability, and wireless coupling to hearing aids.

Visual. Close to nine million Americans suffer from visual deficits severe enough to make it difficult for them to read an ordinary newspaper. Over half a million people are legally blind. Another common problem is color blindness.

Design strategies include providing tactile landmarks on control surfaces, providing a voice mode redundant to visual information, adding tactile/auditory detents to controls for blind users, and allowing speech as an input mode.

Understanding Disabled Users' Needs

One way for the product developer to understand the needs of disabled users is to obtain technical information about the various deficits--what frequencies of sound are the most problematical, how arthritis affects the hand, etc. There is a great deal of literature on these subjects.3­7 Some other strategies are described below.

Including People with Disabilities in the Design Process. A company developing a particular device will probably have access to patients who are likely to use it. However, the problem is to identify the worst cases, so to speak, who may not be contained in a small sample of patients. Thus, it can be useful to recruit people who have particular disabilities. Some methods for doing so include the following:

  • Contacting organizations, such as the American Foundation for the Blind or the Arthritis Foundation.
  • Placing ads at retail stores that sell assistive devices.
  • Contacting the occupational or physical therapy departments of local universities.

Such people can play a number of roles. They can critique designs, participate in brainstorming sessions, or participate in usability testing.

Including Experts in the Design Process. Local universities or organizations can also be used to identify experts in particular disabilities. They can be a rich source of advice.

Creating Heuristic Design Criteria. Accommodating the needs of disabled users can be translated into various objective criteria. Experts can be helpful in developing these criteria, which then can be used as a "filter" to evaluate alternative design approaches.

Simulating Disabilities. A way to give device designers an intuitive sense of what the problems are for disabled users is to simulate disabilities by, for example,

  • Wearing blindfolds or translucent glasses.
  • Wearing ear plugs.
  • Wearing gloves.
  • Working from a wheelchair.

Such techniques can provide quick tests for alternative prototypes.

Conclusion

As more medical devices migrate into patients' homes, a universal design strategy becomes more important for making products usable. Successful universal design for these products requires a different approach than the one many medical device companies now use. However, it is a technique that has been widespread for years in the consumer products world, and one that any product development group should be able to learn easily.


REFERENCES

1. J Gitlin, "Why Older People Accept or Reject Assistive Technology," Generations, Journal of the American Society on Aging 29, no. 1 (1995): 41­46.

2. L McNeil, Americans with Disabilities: 1994-95, Data from the Survey of Income and Program Participation (Washington, DC: Bureau of the Census Current Population Reports, U.S. Department of Commerce, 1995).

3. J Pirkl, Transgenerational Design: Products for an Aging Population (New York: Von Nostrand Reinhold, 1994).

4. Dugan, Keys to Living with Hearing Loss (Hauppauge, NY: Barron's Educational Series, 1997).

5. H Kanis, "Operation of Controls on Consumer Products by Physically Impaired Users," Human Factors 35 (1993): 305­328.

6. H Petrie, "User-Centered Design and Evaluation of Adaptive and Assistive Technology for Disabled and Elderly Users," Informationstechnik and Techniche Informatik 39 (1997): 7­12.

7. G Robertson and D Hix, "User Interface Design Guidelines for Computer Accessibility for Mentally Retarded Adults," Proceedings of the Human Factors and Ergonomics Society (Santa Monica, CA: Human Factors and Ergonomics Society, 1994), 300­304.

Stephen B. Wilcox, PhD, is the founder and principal of Design Science (Philadelphia).

Copyright ©2003 Medical Device & Diagnostic Industry

QSIT's Status Quo: Successful, but Far from Perfect

Originally Published MDDI January 2003

NEWSTRENDS

Maureen Kingsley

By many accounts, the current FDA inspection techniques are fair. But are they flawless? "In terms of QSIT's effect on the industry, I think it's been positive," says Steve Lawrence, a partner with Hogan & Hartson LLP (Washington, DC) in the firm's Irvine, California, location.

Although the current QSIT is only about two years old, its recent history traces back to 1996, when Section 830 of the Code of Federal Regulations 21 was reorganized. QSIT development played a major part in that overhaul. At the time, FDA's goals for its inspections of medical device facilities were to decrease inspection time, increase focus, and ensure quality system regulation coverage. A study and validation of QSIT conducted in 1998 in three major cities showed that QSIT did, in fact, provide a well-defined, succinct, and prescriptive methodology for inspection. Lawrence believes the experience companies have had with QSIT thus far "has been very thorough and fair. They know the rules, the rules are published."

In 2001, FDA determined that additional action was required to raise the number of inspections performed each year. Across the country, medical manufacturing coverage was badly backlogged, and resources dwindled, according to James Beaulieu, a Minneapolis-area investigator. In response, FDA implemented a new strategy to shorten inspections. The traditional baseline inspection was renamed Level 2, and the CAPA +1 inspection was created as a new, less-comprehensive (but presumably effective) process.

As of the new fiscal year beginning in October 2002, about 60% of inspections were CAPA +1, Beaulieu said during the MD&M Minneapolis conference this past autumn. This statistic suggests that the agency views the CAPA +1 inspections as successful and valuable. "I think [QSIT-type inspections] are the wave of the future," Lawrence says. As evidence, he points to the changes being made in the way manufacturers of pharmaceuticals are inspected. "There's a pilot program that tries to make the drug inspections more like the QSIT inspections," he says. "That's an indication that FDA thinks this approach is working and wants to apply it to other places."

Not all inspections are abbreviated, however, and QSIT isn't devoid of problems. There are still inspections of medical device facilities that take several weeks to complete and which involve several inspectors. "That's an area of great controversy," says Larry Pilot, partner at McKenna & Long (Washington, DC) and a former FDA employee familiar with inspections. "The inspection that is lengthy and sometimes involves multiple investigators, for which the burden on the manufacturer is great, and for which the time invested by FDA through its inspectors, is expected to produce some kind of a result." He cites a big-name example: "Look at Abbott Laboratories for a model of this. I'm sure they're not happy to be this model."

It surprises Pilot that large, well-known companies, which are expected to be more savvy than their smaller counterparts, have become "victims of the inspectional process." He attributes this to a mindset by some in the agency of, "We're going to get them."

To offset this bias, Pilot sets forth some concrete suggestions. "Properly manage your inspection. Take measures to ensure that those who manage the inspections are competent," he says. "Take advantage of the opportunity to dialogue with inspectors. That dialogue can be as short as 10 minutes, or as long as it takes to go through page after page of observations." Pilot also advises those being inspected to take advantage of the post-inspection management conference. "Companies can control their destinies," he says.

Copyright ©2003 Medical Device & Diagnostic Industry

Taking the Stress Out of Package Protection

Originally Published MDDI January 2003

PACKAGING

An examination of coupled predictive simulations of thermoforming processes and drop-impact loading in package design.

Balakrishna Haridas and Clinton A. Haynes

Thermoformed packaging is widely used today for the packaging of sterile medical devices and products. The benefits of thermoformed packaging are many. It offers easy control of shape and formability at an affordable cost, design flexibility for handling shock or impact, and an ability to maintain a sterile barrier. It also provides a diffusion pathway for EtO, gamma, and E-beam sterilization; a lightweight structure that reduces handling and shipping costs; and the delivery of brand identity for a device.

But recent medical device innovations—such as implants that incorporate onboard power systems, electronics, and delicate mechanisms for minimally invasive surgery applications—have put stringent structural requirements on packaging. These requirements usually pertain to shock and vibration protection from drop impact during handling or shipping.

The increased need for protection from such external loads is an added worry for manufacturers. To ensure that the appropriate structural-integrity criteria are met, the manufacturer must pay careful attention to the thermoformed package's structural design, material and gauge selection, and processing for optimal material distribution.

Figure 1. Factors that control the integrity of a package under drop-impact loading.
(click to enlarge)

Thermoplastic resin systems such as polyethylene terephthalate-glycol (PETG), polyvinyl chloride (PVC), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN) are among the polymers employed for thermoformed medical packaging applications. In addition to package geometry and material distribution, other important parameters to consider in the design of thermoformed packaging in medical applications include resin material properties (e.g., modulus, yield strength, and ductility), poststerilization (EtO, gamma, or E-beam), as well as thermal stability (see Figure 1).

Amorphous and semicrystalline resin systems are known to exhibit marked changes in mechanical properties as a consequence of sterilization techniques.1 Thus, while a package design and material distribution system may be adequate for sustaining structural loads such as drop impact prior to sterilization, the sterilization technique itself may compromise the package's mechanical properties and structural integrity.

For medical thermoformed packaging, drop testing has evolved as the critical test protocol for two reasons: assessing probable damage to the device, and evaluating the likelihood of a sterile-barrier breach due to package failure.

Although other loading conditions exist, such as compression due to stacking, industry has successfully shielded products from these hazards by placing the thermoformed package inside a secondary package. In turn, the secondary package is often further shielded by a corrugated shipping case. These expensive measures, however, are less effective when it comes to the rapid deceleration of the package and its contents during drop impact. In this extreme loading condition, the dynamics of the packaged instrument and the material characteristics of the thermoform can interact in a complex manner.

Currently, designing a thermoformed package is usually a reactive process. Feedback from package loading tests is available to the designer only after production-quality prototypes are available. The results of these tests and failed packages are the designer's only guide toward making design changes that satisfy both the structural requirements needed to protect the device and the need to minimize material usage (cost).

This empirical make-and-break process of structural discovery is detrimental to the product development cycle. That is especially true in situations in which the package development effort is initiated only toward the completion of the device. Make-and-break rework loops that are triggered as a consequence of failed prototype packages in drop tests can lead to costly project delays. Another major drawback of drop testing as the only technology for design assessment is that without extensive and often complex instrumentation of the package (e.g., accelerometers, strain gauges, high-speed video), it is usually very difficult to understand the fundamental physics that trigger failure modes—the key to driving design changes.

Nonlinear finite-element modeling has matured to the point that all stages of the thermoformed package development process can be accurately modeled and simulated.2 The application of these methods, which range from forming simulation to assessing the interaction of the device with the thermoformed package under a wide range of loading situations, is now fairly routine. The designer's challenge of simultaneously optimizing a thermoformed package for both structural design and material usage can be completed without having to wait until production-quality packages are available for testing. This design-by-analysis process can be implemented early in the device development cycle, without the need for physical package samples. Implementing this approach guarantees that a robust package design is available by the time the device development and validation process is complete.

The Traditional Approach

Figure 2. Overview of the current process for thermoformed package development.
(click to enlarge)

In order to fully understand the opportunity that predictive structural analysis via finite-element methods offers to the package designer, it is useful to study the traditional thermoformed-package development process. Figure 2 describes the most common approach to developing a package for a medical device.

In most cases, the package design is subordinate to the development of the device. Therefore, by definition, it is not a focus until rather late in the device development process. Once the geometry of the device is established, however, the package design process begins, with the primary goal of accommodating the geometry of the product. Although structural integrity is a concern from the outset, without the benefit of predictive analysis tools the structural issues are dealt with using methods based primarily on experience and rules of thumb.

Once the initial package design is completed, a typically frantic tool-prototype-assemble-sterilize-test-redesign loop is begun. As time goes by and the launch schedule nears, the pace of this loop accelerates, generally churning out design modification after design modification, until one is identified that satisfies the minimum structural requirements—often at the expense of a heavier sheet gauge. This suboptimal thermoformed package design is then validated, submitted to FDA, and committed to production tooling. In efforts to accelerate the traditional process, it is not uncommon for manufacturers to skip the package sterilization step on the assumption that the material performance is more or less unchanged by sterilization.

The Predictive Engineering Approach

Figure 3. A modified package development process incorporating predictive engineering and eliminating costly rework loops in redesign.
(click to enlarge)

Although there is a general similarity between the traditional approach and the finite-element analysis (FEA)-based approach, the ways these development processes are executed are dramatically different (see Figure 3).

Once the first package design concept has been developed, it is prepared for virtual prototyping—rather than handing that design file to a tool builder to create a tool pass file (or to interpret the geometry from concept renderings or 2-D drawings). A combination of thermoforming process simulation and drop-impact structural analysis is used to identify the minimum sheet gauge, optimal thermoforming conditions, and package geometry (crumple zones, corner radii involved in impact, etc.) that will yield a material distribution that can reliably sustain drop-impact loads without failure.

Thermoforming Process and Drop-Impact Modeling

To illustrate the process of predictive analysis or virtual prototyping, we will examine a case study that used finite-element techniques to assess the response of an intraluminal stapler to a drop load. The drop simulations were conducted based on material-thickness distributions for the package; the material-thickness distributions were developed on the basis of a thermoforming simulation of the process. Thickness measurements and drop testing of physical samples were also completed and compared with analysis results to illustrate the level of accuracy expected from the simulations.

Thus, there are two key activities involved at this stage: the thermoforming process simulation and the drop-impact simulation.

Thermoforming Process Simulation. In this simulation, the package design concept is assessed for material distribution under manufacturing process conditions that would be employed to produce the package.

Plug-assisted thermoforming of medical device packaging involves preheating a polymer sheet (typically PETG) to just above the material's glass-transition temperature; then a plug is used in conjunction with vacuum or positive air pressure to form the sheet into the desired shape. Factors that affect the final outcome—i.e., the material distribution and end-use mechanical properties—include process variables such as the following:

  • Sheet temperature.
  • Sheet thickness.
  • Plug speed.
  • Plug temperature.
  • Cavity temperature.
  • Timing delay of vacuum or air pressure relative to plug stroke.
  • Friction between sheet and tooling.

Commercial technologies to conduct FEA simulations of thermoforming are now available to the engineer who is trained in the use of these tools. The behavior of polymeric materials at typical forming temperatures, however, poses interesting challenges. In the case of PETG for the stapler packaging application, the team involved in developing an accurate model would typically need to conduct biaxial stress-strain testing of the material at different temperatures. This would generate the required nonlinear stress-strain relationships required for input into the simulation. These relationships can be generated via specialized techniques such as bubble rheometry.

Figure 4. FEA model of the thermoforming process.

Figure 4 shows the finite-element models that were developed for the stapler packaging application. The plug-assisted forming process was simulated using the following process parameters and conditions:

  • Initial PETG sheet gauge = 0.695 mm.
  • Sheet temperature = 100°C.
  • Plug stroke/travel = 42 mm into cavity.
  • Forming pressure = 0.414 MPa (60 psi).


 

Figure 5. Evolution of sheet shape and wall thickness during forming (wall thickness contours in mm).
(click to enlarge)

Figure 5 shows the evolution of the wall thickness distribution and shape during forming that results in a final material distribution. The resulting correlations between measured data and predicted data are excellent. As the results in Figure 5 demonstrate, this modeling approach can also be used to assess the effects of initial gauge on the final outcome. Eventually, this predicted material distribution was mapped onto an FEA model using a 3-D interpolation algorithm. The FEA model was then used to conduct structural stress analysis of the package under drop-impact loading conditions.

Drop-Impact Simulation. Drop-impact simulation involves the modeling of the response of a packaged device to drop-impact loading. In this process, specific performance attributes of the package can be investigated and evaluated rapidly, without ever manufacturing and testing an actual package. These attributes may include the efficiency of the material distribution, the locations of high stresses or strains that cause failure of the package, as well as calculations of the magnitude of forces on the device as a result of the drop.

As in most development situations, the first design concept typically does not satisfy all the requirements, and more design iterations are needed. Using the quantitative information gained from the initial finite-element analysis as a guide, a design modification can be developed that addresses specific design deficiencies, and the analysis can be rerun. This process of physics-based design modification and reanalysis will continue and will rapidly converge at a specific design, because each iteration is based on a quantitative assessment of the previous concept.

During this virtual iteration phase, important design changes in package geometry, such as the addition of energy-absorbing features (crumple zones, corner radii), can be developed on the basis of drop simulations. This process contrasts dramatically with the traditional method, wherein a trip around the rework loop not only requires tooling modification (if the product can be reused), but also staffing and time to complete new process development and testing of physical units—a process that can consume weeks to months of schedule.

Figure 6. Structural FEA models of an assembled package.
(click to enlarge)

In order to simulate the interaction of the package with the device, it is necessary to have a structural model of the device included in the simulation. In these simulations, the device itself can be relatively crude. It only needs to represent the geometry and mass/stiffness characteristics, since the primary interest is in the packaging. Figure 6 shows a relatively crude model of a circular intraluminal stapler designed to fit into the thermoform. This approach ensures that the forces created by the device during the drop event are accurately transmitted to the thermoformed structure, and it does so without the computational baggage required to simultaneously solve the nonlinear structural equations for the structural performance of the device itself.

Figure 7. A 3-D mapping of thicknesses from thermoform model to structural drop-impact model.
(click to enlarge)

With the thermoform and device structural models complete in the case study, the appropriate velocity-boundary conditions were placed on the model. For drop-load simulations, the boundary conditions are limited to defining the desired orientation for the package as it makes contact. The thickness distribution resulting from the thermoform simulation was mapped onto the tray geometry for these impact models (see Figure 7). The entire package was rotated 10° (see Figure 6) to match the drop-test experiment (described below) and given an initial velocity of 4.429 m/sec toward the rigid plate. This is equivalent to a 1-m drop height.
 

Figure 8. Impact stresses in a package during drop.
(click to enlarge)

Figure 8 depicts the transient evolution of impact-related stresses in the package during drop. From these frames it is evident that at the point of impact, the package deforms and continues to move over a certain distance before recoiling. During this period, the instrument inside the package continues to advance and decelerate as a result of its load and internal package features. The momentum of the device is transferred to the package and results in high stresses at these locations. This is in addition to high stresses and strains developed in the package in the region of impact.

Drop Testing. An instrumented drop test of the intraluminal stapler was conducted and documented using high-speed video. Accelerometers were placed on the stapler at two locations: one very close to the impact zone, and one further away. These transducers provided data on the G-forces developed in the device during the impact event.

Results of Drop Testing and Comparison with Simulations. A sequence of frames pulled from the video illustrated the severity of the drop event on both the package and the device. This confirmed the phenomena observed in the finite element simulations. From these frames it was evident that at the point of impact, the package deformed and continued to move over a certain distance before recoiling, as predicted.

Qualitative validation of the structural model can be achieved by comparing the video with the simulation results. The test results show that the maximum G-forces in the package during this 1-m drop test are in the range of 95 G. The analysis slightly overpredicts values in the range of about 100 G. With the exception of variation related to the differences in package orientation at the time of impact, it is clear that the test and analysis are in agreement.

Conclusion

Results from the case study show that FEA for thermoforming simulation provides excellent feedback on process-related parameters and material distribution. Accuracy up to 90% (wall thickness)—i.e., errors of 10%—can be achieved using such simulations. Successful results in the context of thermoforming process modeling is highly dependent on obtaining accurate data from the thermoforming manufacturer on tooling motions and process conditions. This processing model must then be closely coupled with structural analysis to assess whether the distribution of the thermoformed material will satisfy the structural requirements. Using this coupled approach, FEA technology for drop-impact analysis is easily leveraged in the hands of the trained engineer.

Accurate drop simulation provides a breadth of quantitative data that is simply not available via testing. For example, interactions between components of a device and package, and the distribution of G-forces inside the package, are directly available from FEA modeling results. In addition, the physics of kinetic energy absorption and dissipation via the interactions between stored elastic energy and viscoelastic and plastic deformation are only revealed via simulation techniques. Again, such energy absorption features as crumple zones can be evaluated using plots to aid the process of developing a package that is reliable under drop-impact conditions.

The predictive engineering approach is unique in that it represents a deliberate physics-based process that is driven by quantitative data. Key performance attributes, vulnerabilities, failure mechanisms, and sensitivities are known and understood before the package is produced. The product and package can be optimized before tooling commitments—i.e., the process of discovery—is eliminated. The advantages of this approach are realized in risk reduction that enables a product developer to manage project schedules, costs, time-to-market, and problematic rollouts that could result in franchise damage and even potential product recalls.

Today, prototyping and predictive engineering provide the technology and tools to predict the critical attributes associated with thermoformed package performance. This process does not eliminate the key activity of physical prototyping and testing; however, physical prototyping activities can be reserved for fine-tuning and validating successful designs that were developed using predictive simulation approaches.


REFERENCES

1. "Effects of Sterilization on Plastics and Elastomers," Plastics Design Library Handbook, 1994.

2. CA Haynes and B Haridas, "Reducing Cost, Development Time with Simulation, Analysis Tools," Packaging Technology and Engineering, 1999.

Balakrishna Haridas, PhD, is the director of SES Medical Device Technologies, a division of Stress Engineering Services (Mason, OH). Clinton A. Haynes is vice president of the company.

Copyright ©2003 Medical Device & Diagnostic Industry

Pursuing Counterfeit Medical Devices

Originally Published MDDI January 2003

NEWSTRENDS

Gregg Nighswonger

Despite closer scrutiny by government and industry, the counterfeiting of electrical products in North America is believed to have grown in recent years. According to the IEC, most counterfeit products are shipped from China, Russia, Hong Kong, and Taiwan. The U.S. Customs Service believes that at least 5% of products coming to the U.S. are counterfeit. Although counterfeiting is perceived as a problem for consumer goods, some medical markets are also affected.

Both finished goods and device parts have been successfully faked. For example, intra-aortic pumps worth $7 million were recalled after malfunctioning components were found to be counterfeit. The problem has also attracted the attention of the World Health Organization (WHO). More than 2000 kits containing stethoscopes and sphygmomanometers were seized during transport from China to Greece in 1999. WHO reported that every part of the shipment had been counterfeited—packaging, instructions, all devices, and European standards marks.

Aside from compromising the safety of device users and patients, manufacturers are adversely affected by loss of sale and loss of reputation when counterfeit parts fail that have been branded with their company's trademark. Commenting on the problem of counterfeiting, Sandy Gentry of Underwriter's Laboratory says, "UL has not yet come across any medical devices bearing counterfeit marks. You can imagine the severity of the situation if, say, a defibrillator bore a bogus UL label. We're quite relieved that we have not had to deal with this type of situation with medical products."

Part of the problem, in fact, is the lack of specific data on how widespread the problem is within the medical industry. "It's quite difficult to come across just industrywide, countrywide, or globally," says Darren Pogoda of the International Anticounterfeiting Coalition. "It's obviously difficult to get facts and figures on a black market." He acknowledges that counterfeiters are definitely growing more sophisticated. "The rule of thumb among pessimists like myself is if you can make it, they can fake it," he says. "The counterfeiters have become more sophisticated as they've come to realize that counterfeiting is a good business to get into: it has very low risk of getting caught, very low risk of getting punished severely if you do get caught, and very high reward in terms of profit with low overhead."

How is the problem being dealt with by government and industry? Action is being planned and taken on several fronts. Clark Silcox of the National Electrical Manufacturers Association (NEMA) says "NEMA is in the process of working with its members on the counterfeiting issue. The program is in the development stage, but is expected to focus initially on wiring devices, dry batteries, circuit breakers, and wire."

"There are a number of fronts," says Pogoda. "Obviously, to get the government involved on the criminal side of things and actually prosecuting these guys is really the way you want to go. You want to let them know you mean business. Another way to do it is for companies themselves, the rightholders, to become more aggressive with their own investigative teams and their own inhouse people dedicated to anticounterfeiting measures." He adds, "Of course, there's also the technology answer. That is something that has become really big within the past five years." Given the limited resources of government and industry, Pogoda says, "the technology route is probably the most promising in terms of having an immediate impact."

Another aspect of efforts to combat counterfeiting is dissemination of information. CSA International, for example, published a white paper in November 2002 discussing the threat of counterfeit products and counterfeit product approval marks. The white paper provides examples of counterfeit products, use of fake product approval marks, and describes both safety and liability risks presented by the products. The publication also describes how CSA and the IACC are collaborating on anticounterfeiting measures. Copies can be downloaded from www.csa-international.org.

Copyright ©2003 Medical Device & Diagnostic Industry

Taking Blood and Tissue Measurements without the Use of Needles

Originally Published MDDI January 2003

R&D DIGEST

The sensor system being developed by Soller will measure blood and tissue chemistry without blood draws or incisions.

Many healthcare advances have resulted directly from the transfer of technologies from space and military research. A new contribution from space research may provide a method to measure a patient's blood and tissue chemistry without needlesticks.

According to researchers with the National Space Biomedical Research Institute (NSBRI; Houston), refinements to the near-infrared (NIR) spectroscopic techniques are under way. The changes are expected to enable the method to provide accurate readings that are unaffected by skin color or body fat. Says Babs Soller, PhD, researcher on the institute's Smart Medical Systems Team, "This device will allow chemical analysis and diagnosis without removing samples from the patient. It will be useful for monitoring surgery patients, assessing severity of traumatic injury, and evaluating injuries in space." Soller is also a research associate professor of surgery at the University of Massachusetts Medical School (Boston).

Intended for use on the International Space Station, the device will also be useful on Earth, Soller says. "We have three issued and three pending patents on this technology. We are currently in discussions with a few companies that are interested in commercializing the device," she adds. She explains that the initial research was funded by the Army, which has a similar requirement to NASA: how do you help minimally trained medical personnel respond to disasters and trauma? In the Army's case, says Soller, the far-forward medics do not have extensive medical training. On the space station there is a crew medical officer, but more often than not, that person is not an MD.

She says, "The device we are developing will help the medical responder choose the best treatment for a seriously injured patient." Soller adds, "This project is part of NSBRI's Smart Medical Systems Team, where the goal is to develop intelligent (computer-assisted) sensor and treatment systems. We also anticipate that the device will have application on the space station to assess astronaut fitness levels to determine if an astronaut is fit enough for certain tasks, such as work outside the station, which is very strenuous."

The device offers a number of advantages over currently available methods. Says Soller, "Conventional methods to acquire this information require taking a blood or tissue sample from the patient and sending it to the lab. Our technology is completely noninvasive. Data are acquired without a needle stick, and are immediately and continuously available."

The fundamental NIR spectroscopy concept is a familiar one since it is the basis of the pulse oximeters used to measure oxygen saturation. "Light in the near-infrared region has slightly longer wavelengths than red light," Soller explains. "It is important for medicine because those wavelengths, for the most part, actually pass through skin and to some extent bone, allowing you to get chemical information about tissues and blood."

Current efforts to refine the technology for a broader range of measurements require gathering data from more patients. Study participants include cancer, cardiac surgery, and trauma patients. To make the device accurate regardless of skin color or body-fat content, Soller's group is gathering data from 100 subjects representing five ethnic groups. Soller says, "Our technical work is focusing on refining our calculation algorithms to provide accurate and precise measurements for all subjects, regardless of skin color, body mass, and measurement location." Soller explains that the researchers are currently measuring hematocrit, tissue pH, and tissue oxygenation using the new device and standard techniques. "These data will give us the information needed to derive equations to calibrate the new NIR instrument," she adds.

The final step will be to develop clinical guidelines for the measurements, so that physicians know the significance of the readings. The researcher explains, "Tissue pH and oxygenation are new medical parameters, so we have to determine specific values that, based on the readings, allow us to identify when a person is in shock or in need of treatment. We also see this device as a means to assess the adequacy of the treatment employed."

Soller believes that the device will be particularly useful for treating patients with shock caused by excessive bleeding or heart attack, patients with internal bleeding, and pediatric patients, where it can be difficult to take multiple blood samples. The technology also has potential use in exercise and endurance training by measuring tissue pH to determine how hard a person's muscles are working.

Soller says, "We have a functional prototype now, which we are using on patients to refine our algorithms." A commercial version of the device is expected to be available within five years.

Copyright ©2003 Medical Device & Diagnostic Industry

Noninvasive SCD Test Focus of Multicenter Study

Originally Published MDDI January 2003

NEWSTRENDS

Studies of a noninvasive test to precisely assess a person's risk of sudden cardiac death (SCD) will begin early this year. The trials will involve up to 50 hospitals worldwide and will include 1800 patients in all. The study will focus on use of Microvolt T-Wave Alternans (MTWA), developed by Cambridge Heart Inc. (Cambridge, MA) to stratify SCD risk. Results of the study should be available in 2005.

The test is intended to assess post-myocardial infarction patients for risk of a second infarct. About 10% of such patients die of subsequent rhythm abnormalities within two years. Use of implantable cardioverter defibrillators (ICDs) has been shown to improve survival by 30%. But ICDs are expensive and not all will benefit. MTWA detects extremely subtle electronic fluctuations in a person's heartbeat that cannot be seen on electrocardiograms. Such fluctuations are believed to be a strong predictor of SCD. Precisely stratifying this population with a simple test could pinpoint patients likely to benefit from an ICD. This would help reduce mortality rates in that group, and make ICD treatment more cost effective.

Copyright ©2003 Medical Device & Diagnostic Industry

"Ice Slurry" Used to Treat Cardiac Arrest

Originally Published MDDI January 2003

R&D DIGEST

Time is an essential factor in treating patients experiencing a cardiac arrest. Within 10 to 12 minutes of an arrest, lack of blood flow causes brain cells to begin dying rapidly. But research suggests that the timely application of cold to reduce the patient's body temperature may be a key to reducing morbidity and mortality resulting from cardiac arrest. A number of techniques and devices are currently being studied (see R&D Digest in the September 2001 MD&DI, p. 50).

A new approach developed by researchers at the U.S. Department of Energy's Argonne National Laboratory (Argonne, IL) and the University of Chicago's Emergency Resuscitation Research Center entails injecting patients with a high-fluidity ice particle mixture—essentially an ice slurry—to cool the blood and preserve cells. The researchers explain that during the procedure, the slurry would be injected into the lungs to cool the surrounding blood. Chest compression would be performed by medical personnel to circulate the cooled blood, allowing it to reach the brain and preserve cells there.

The researchers include Roger Poeppel, director of the Argonne Energy Technology Division, and Ken Kasza, a senior mechanical engineer who leads the research at Argonne. In 1999, they began working with Lance Becker and Terry Vanden Hoek from the University of Chicago Hospitals to develop the Emergency Resuscitation Research Center where health problems such as cardiac arrest could be studied.

When cells are cooled, their metabolism and chemical processes slow significantly. The researchers note, for example, that a skater who falls into an icy pond can be resuscitated even after being submerged for a long period of time. Because external cooling works slowly, however, the researchers proposed that the ice slurry be injected directly into the body to induce internal cooling at a more rapid rate. They suggested that the method could quickly and effectively cool critical organs using just a small amount of coolant. The slurry melts slowly in the body, and is removed later with a suction device on the end of an endotracheal tube.

Data from the university team's initial studies have shown that the method cools the brain cells by 2° to 5°C, and can maintain the reduced temperature for about an hour. This would give medical personnel and doctors more time to attempt restoration of normal blood flow and brain activity. The group believes that this extra time could reduce the incidence of brain damage to little or none.

Kasza and Becker explain that the ice slurry procedure will still be secondary to defibrillation. Treatment would begin immediately with defibrillation. If a proper response were not obtained, however, the cooling procedure would then be used. The researchers believe the method could also be used to treat stroke, but say a number of issues will require additional research. Studies are needed to determine optimal cooling levels and identify correct timing and protocols. Toxicity levels also must be assessed, and it must be determined how much of the brain is conserved by the method.

Copyright ©2003 Medical Device & Diagnostic Industry