By: Leanna Levine

 

Designing and developing molecular and immunoassay-based diagnostic products requires extensive empirical testing and repeated evaluation of functional elements. While prototyping should ideally be rapid in order to shorten the time-to-market, the traditional techniques can be slow and cumbersome. Among the more traditional approaches, injection molding offers rapid prototyping but only for the simplest designs.

Other prototyping techniques are even less accommodating to the development issues that are unique to IVDs. Stereolithography using photocurable resins produces parts that are not suitable for microfluidic applications, and machine shops typically work with acrylic for rapid prototyping and take two to three weeks to turn around a design. Other microfabrication methods that are widely used in IVD research are embossing and die-cutting. But such methods require tooling which can be very expensive, thereby limiting design iterations. Soft lithography produces devices with polydimethyl siloxane (PDMS), which limits the types of materials that can be used and the surface properties achieved. Traditional lithographic methods using silicon or glass etching to produce channels and features are also expensive and have a long lead time.

Constrained by such prototyping options, researchers have developed simpler but larger IVD devices operating at volumes and scales that require more reagents, take up more space, and are less cost-effective. But in the end, the most unfortunate unintended consequence of using such methods may be the most costly. To avoid the added costs incurred by traditional prototyping techniques, modifications to IVDs are made reluctantly, and other workaround efforts are used. While doing so lowers the short-term development costs, the end result is often a merely adequate but not superior product.

In contrast, a new microfabrication platform, polymer laminate technology manufacturing, offers prototyping of IVD devices, which can incorporate various different materials and onboard functionality such as porous membranes and onboard valves and pumps. With polymer laminate technology, IVD design and development are truly rapid because prototypes can be created in three days or less in batches of 20-30 identical devices.

What Is Polymer Laminate Technology Prototyping?

Polymer laminate technology is a microfabrication method for rapid prototyping and volume manufacturing of fluidic devices for applications in spectroscopy, environmental analysis, sample preparation, kinetic assays, microfluidic-based molecular and immunodiagnostic devices, and automated cell culture. Polymer laminate technology uses thin sheets or films of various polymeric materials to form complex structures. Channels and other functional features are precision laser cut into the layers of the polymer substrate and the bonding adhesive. The cut sheets are combined to create three-dimensional enclosed channels, multiple stacked layers of fluidic channels, and vias that are bonded or laminated together with a pressure-sensitive adhesive or thermal bond (see Figure 1).

Time-tested lamination technology, equipment, and processes are used in new ways, making the entire process inexpensive because investing in novel manufacturing tools is unnecessary. Polymer laminate technology brings the advantages of microfabrication technology to molecular and immunoassay-based diagnostic product developers, life science researchers, and cell biologists in a user-friendly, cost-effective format.

Speed and Quality in Prototyping

Rapid prototyping shortens the time-to-market by accommodating the multiple steps that need to occur in parallel during the IVD product development process. For example, IVD instrument design and disposable fluidic cartridge development should progress simultaneously so that both components can be tested in combination early on to determine whether the product design is viable or not. The earlier that problems are identified, the quicker design changes can be made. But if the development of a fluidic cartridge is delayed by the typical two to six week turnaround time of an injection molding, machine, glass fabrication, or embossing shop whenever a design is changed, instrument development also gets delayed, momentum is lost, and competing products may reach the market faster. With polymer laminate prototyping, batches of identical IVD devices can be created in a few days each time a design is modified.

High quality is also essential in prototyping. The fluidic cartridge is a vital component of the entire diagnostic analytical system and can affect assay performance. If a great deal of variability in the IVD device exists, discerning whether a problem with an assay is due to the fluidic system or the reagents is difficult. In addition to high quality, the fluidic cartridge prototype must have good batch-to-batch repeatability so that many devices with comparable fluidic performance can be tested to generate statistically significant results. While the instrument that performs the assay can be easily tested and its software and hardware can be modified as necessary, the fluidic cartridge system's biological reagents can introduce inherent variability.

Performing many tests early in the IVD product design process is necessary in order to demonstrate a fluidic component's robustness as it performs the assay. It is not unusual for IVD developers to go through 50-100 prototypes early in the design process. Once a final design is chosen, they will need thousands of prototypes to validate assay performance on the fluidic cartridge with the instrument in satellite labs in order to ensure that different labs are getting the same results. Several thousand more prototypes will also be needed for clinical trials, in which fabrication under an FDA-compliant quality system is required.

Traditional fabrication technologies, such as injection molding, embossing in plastic, and etching in silicon, are expensive ($10,000-$25,000 for first articles) and typically have a three to six week turnaround time. In molecular diagnostic and immunodiagnostic product development, such costs and timelines do not meet the needs of product developers that are interested in incorporating novel functions and complexities associated with newer multiplexed, multistep integrated lab cartridges.

For example, IVD manufacturers are shifting from developing single, highly complex quantitative tests that are performed in traditional clinical labs and take two to three days to deliver results, to near-patient panels that provide comparable quantitative results in mere minutes to hours. Many of the operations that were once performed by large robotic systems or by hand in clinical labs are increasingly being integrated into IVD devices that combine sample preparation with assay incubation and final measurement of the results. Such devices are so small and sophisticated that they cannot be manufactured using traditional methods.

Advantages of Polymer Laminate Prototyping

Flexibility in Materials and Structures. Traditional fabrication approaches often do not permit incorporating high feature densities, three-dimensional structures, and integrated functionalities that are associated with self-contained tests. But polymer laminate fabrication allows the design of complex functionalities, such as flexible pneumatic valves, recirculating pumps, filtration components, and simple interfaces to optical or electroactive components.

In addition, polymer laminate technology can be used with a wide choice of materials with essential performance characteristics (including cast or extruded polymethylmethacrylate (acrylic), polyethylene terphthalate, polystyrene, polypropylene, and medical-grade silicone sheets). Such flexibility in materials offers lower development costs and rapid, inexpensive modifications to the design (see Table I). Because all polymer laminate fabrication processes are done at room temperature, reagents that are stable at room temperature may also be incorporated and will not be damaged.

Choice of Materials. For polymer laminate technology, any thin film polymeric material (up to 0.010 in. some cases), including polycarbonate, cyclic olefin polymer (COP), cyclic olefin copolymer (COC), polyimide, polyetheretherketone (PEEK), polyethylene terephthalate (PET), polypropylene, or any of the fluoropolymers, can be cut using a CO2 laser. Special handling is required to reduce yellowing and melt back so that the layers laminate cleanly to the adhesive in the next layer. For materials thicker than 0.010 in., only acrylic and delrin cut cleanly.

While overall device thicknesses are less than 2 mm, thicker devices have been made by bonding subassemblies together after dicing the parts from the sheet. In some cases, the adhesives used for bonding can tolerate temperatures greater than 100ºC. All the thermoplastics, such as COC, COP, polycarbonate, PEEK, or polyimide, also have glass transition temperatures greater than 100ºC. In addition, cast acrylic, but not extruded, can tolerate temperatures of 100ºC, making it suitable for polymerase chain reaction (PCR) applications.

A common misconception is that the walls of integrated channels may not be smooth or the adhesive extends into the channel, which may cause reagents to be hung up during the course of an assay, making laminates unsuitable in such applications. However, the high quality of the bonding adhesives provides edges that are as smooth as the edges of the substrate materials that are cut, with no running or bulging of the adhesive into the channel. Cell culture, immunoassays, and PCR are all compatible with laminate devices that are fabricated using select adhesives.

In applications in which IVD devices were used with multiple wash steps, the clearance of the channels was within the expected five volumes calculated from fluid modeling. In many applications, particularly single-use, carryover or hold up volume is compensated for by providing a small overvolume. Issues with nonspecific binding are not any worse with the presence of the adhesive, and are the same as any untreated, low-surface-energy plastic. The adhesive accounts for less than 10% of the total exposed surface area that the liquid contacts. With a choice of buffer and additives (e.g., bovine serum albumin and detergents), enzyme activity can be preserved, and PCR reactions can be run.

Precise Registration of Fine Features. Accomplishing repeatability in prototyping and the performance of microfabricated IVD devices requires close attention to robust and repeatable alignment of the layers that are stacked and bonded to create the three-dimensional fluidic circuit. Such repeatability requires stacking and alignment tolerances of 50-125 µm with feature sizes in the device of 100-1000 µm. Through polymer laminate technology, such alignment is achieved using alignment fixtures that mate with features in the device.

Reduced Device Footprint and Cost. The ability to form enclosed three-dimensional structures (e.g., channels or chambers) without a separate bonding process reduces an IVD device's footprint and its cost. Furthermore, a reduced device footprint accommodates compact instrumentation design that is compatible with improving work flow. A panel can be run on a single small chip rather than having several separate chips for each test. The ability to stack channels and functions vertically facilitates the integration of all the required steps. Accomplishing the same functionality with traditional injection molding would require a larger footprint and limit the device to three layers, in which functionality can reside on one of two sides of the device. With polymer laminate fabrication, the channels and the vias that connect them can be stacked with up to 13 layers, permitting a compact, low dead-volume system to be developed.

Empirical Testing with Lower Development Costs. Making several variations of a design is often necessary to optimize the final IVD device's performance. Given that changing a polymer laminate channel geometry is simple to do, IVD developers have more opportunities to see how each change affects an assay. Channel dimensions can also be easily adjusted, which would not be inexpensive or as easy to achieve with an injection molding process. Thus, with polymer laminate technology, a range of modifications to the design can be evaluated in parallel, increasing experimental design during the development phase. Additional cost benefits are realized because a single fabrication run can incorporate various different modifications, avoiding the need for multiple runs to test different designs.

Customization of IVD Chips, Cartridges, or Devices. Diagnostic cartridges are developed for use in multiple IVD test situations but with a common detection system or reader since it is not cost-effective to manufacture an entirely new cartridge design and equipment for each new test. In order to use the same equipment platform and detection instrument, the cartridge has to be customized to accommodate different incubation times, use different reagents, and be composed of different materials. Polymer laminate technology makes such customization possible without a large investment in new tooling because design modification is simple and cut files only need to be adjusted when changes are required.

Troublefree Interface with Traditional Components. Laminate components can serve as functional sticky tape to mate with injection-molded components and interface with electroactive or optical detection components. The laminate component cost-effectively brings together pieces of the puzzle that might not otherwise be combined. Thus, polymer laminate technology is an important step in bringing microfabrication technologies more fully into the market.

Easy to Scale. With polymer laminate technology, further efficiencies are achieved from a linear scale-up process that facilitates the path to volume manufacturing. Because the process is linearly scalable, increasing manufacture from 1000 to 100,000 units per month is possible with a scale-up of the process used for low-volume prototyping, which meets the needs of IVD device developers that are launching a product. Without a large initial investment in manufacturing, a new IVD product can gain traction in the marketplace and begin generating revenue that will ultimately support an investment in longer-term and higher-volume manufacturing. The producer of a low to mid-volume laminate can continue to serve as the secondary supplier for an FDA-approved device.

Rapid Turnaround Time. A higher feature density of a traditional IVD device means not only more-expensive tooling but also a long turnaround time of as much as six weeks. With polymer laminate technology, development time is reduced. While turnaround times are typically 3-5 days, they may extend by a week to 10 days for process modifications and further discussions with a customer if required.

Cost. Prototyping costs can be $650-$5,000, depending on the IVD device's complexity, materials, and the testing required. A customized fluidic device that fits into a spectrometer cuvette holder or on a microscope stage can cost $850 for a set of 30 devices. A device developed based on customer requirements that has three layers can cost $1500-$2500 to produce 10-30 devices, depending on the footprint. Much of the initial costs are for setup and nonrecurring engineering costs. As volume increases, a fairly complex, five-layer device can cost around $2 each for volumes up to 15,000 units per month, with prices reducing as volume increases. Because the process is linearly scalable, it does not require cost share or a guarantee of volume for investment in capital equipment for volume manufacturing.

Conclusion

Leanna Levine, PhD, is president and chief executive officer at ALine Inc. (Redondo Beach, CA). She can be reached at llevine@alineinc.com.

While polymer laminate technology is robust, proven, and inexpensive compared with other methods, it is not a panacea. It is linearly scalable, so it does not support economies of scale when producing annually millions of IVD devices with multilayer laminates. If a device is designed properly and reaches the point that it will be produced in large volumes, a developer can work with a high-volume manufacturer to produce such quantities. Only when a product can support an investment in tooling and equipment that can generate as much as $500,000-$1 million (in which such costs can be amortized over 2-3 years when the volume of the product is produced) will the investment be worthwhile.

The sweet spot for polymer laminate technology is in applications for single-use, disposables that will be produced in volumes up to 1 million devices per year. The laminates will have complexities that make using traditional prototyping approaches expensive and time-consuming. The device takes the technology's complexities out of human hands and puts it into a small fluidic cartridge.

Part two of this article will discuss the process used for polymer laminate technology fabrication and provide case studies on its application from users in the field.