Implantable medical devices, like pacemakers and defibrillators, require careful hermetic sealing to protect both the device and the patient.

Hermetic sealing is the encapsulation of electronic components into an airtight metal or ceramic housing using either parallel gap resistance seam welding or opposed electrode projection resistance welding. It is a key manufacturing process utilized in assembling micro-electronic packages for communication, aerospace and medical device manufacturing. 

Uses of hermetic sealing Microelectronic devices are commonly used in industrial commercial communications, transportation, military, and aerospace industries and include optical sensors, pressure sensors, communications devices, thermal and laser imaging and power amplifiers. By sealing these electronic packages, external contaminants – like moisture – are kept out preventing degradation of the electronic components inside and extending lifetime usefulness.

Implantable medical devices, like pacemakers and defibrillators, also require careful hermetic sealing to protect both the device and the patient. 

Microelectronic package types There are two primary types of packages: metallic tub and ceramic.

The preferred material for metallic tub base packages is Kovar, which has a similar Coefficient of Thermal Expansion (CTE) as glass; the use of this material prevents the metal-to-glass seals of the feedthrough connectors of the package from leaking due to material expansion from heat generated during the welding process.

Ceramic packages are made of a ceramic substrate with a brazed metal seal ring. Kovar is also used in ceramic packages; the Kovar is brazed onto the ceramic base as a seal ring to which the lid is welded. 

Parallel gap resistance seam welding Parallel gap seam welding is one way to execute a hermetic seal. A seam welder with rolling wheel electrodes is connected to a power supply, which is responsible for delivering electric current across the electrodes, through the lid and the package. The seam welder delivers multiple overlapping weld spots, thus creating a continuous weld (Figures 2 and 3).

Figure 2: Schematic of parallel gap seam welding

Opposed electrode projection resistance seam welding Another method used to execute hermetic seals is opposed electrode projection welding. This process utilizes opposing electrodes to join a header (containing the electronic device) to a cap designed with a ring or annular projection, by running current across the electrodes through both the cap and the header. The generated heat is directed through the projection in order to weld the parts together (Figure 4). A successful weld should have at least a 50-90% projection collapse; linear displacement measuring device sensors (also known as Linear Variable Differential Transformer (LVDT)) can be added to the weld head to measure this collapse. Additionally, a fillet formation is typically seen at the perimeter of the cap indicating a successful weld.

Figure 4: Projection welding schematic showing cross section of electrodes and example device. 

As with parallel gap seam welding, the part design of the metal packages in opposed electrode projection seam welding is very important. The projection can be either on the cap or the header, but there must be a constraining feature between the two so that the parts self-align. The preferred material, again, is Kovar. For best results, the projection should be located in the middle of the flange, so that as the projection collapses, the displaced material is evenly distributed across the width of the flange. 

Testing and troubleshooting Weld strength destructive testing can be performed in hermetic sealing applications to ensure that welds are secure. In destructive testing, seeing at least a 25% weld joint still intact after significant attempts to mechanically separate the lids or caps from the base is a good indicator that a strong weld was achieved. Other methods of testing hermetic reliability include helium fine leak and gross leak bubble testing, optical fine leak detection, internal gas analysis, particle impact noise detection and temperature cycling. 

Conclusion Hermetic seam sealing technology can be critical to success in a number of demanding applications such as industrial 5G commercial communications, aerospace, and military electronic devices. Ensuring an excellent seal through welding is extremely important, and only trusted weld device manufacturers who account for the demands explained above can ensure highly accurate and reliable welds. Manufacturers like Amada Weld Tech are incorporating these standards into current controlled environment welding technology, and are also developing technology for the future that will enable even greater accuracy and weld success. The future of hermetic sealing is likely to be robot-assisted seam sealing pick-and-place with smart vision systems, which have the potential to eliminate current margins of error and lead to even greater success in hermetic sealing of sensitive electronic devices.

To achieve maximum performance from a miniature linear motion application, it’s vital to make sure the motor’s specification meets the requirements.

Clémence Muron, application engineer at Portescap explains how to make the right choice of linear motion technology.

Requirements for linear motion, miniature applications range from filling syringes through to medical devices, or robotic applications used in the operating theatre. The first consideration for a design engineer is the method used to transfer the rotary motion of a miniature motor into linear motion. The most common way of achieving this is by mounting a screw and nut system on the motor shaft. It operates on rolling contact between the nut and a screw, which can provide low friction, good efficiency, and high load capability. The disadvantage however is the cost and the time to design such a solution, especially for applications which don’t require high load handling.

A more cost-effective means of achieving linear motion can be reached with a standard linear motorized solution by choosing a motor with an integrated lead screw. A digital linear actuator (or DLA) utilizes a can stack stepper motor combined with a screw. Inherent with stepper technology, the motor controls its own positioning and is both an accurate and cost-effective solution, doing away with the requirement for an additional feedback system. Resolution can be managed in full, half, or micro steps. With a special optimized ball bearing assembly, the axial play can even be eliminated, improving positioning accuracy as well as repeatability of motion. In addition, with stepper technology, the motor has a detent torque. As a result, it can hold its position when the power is removed. The nut can be over-molded in the rotor assembly with special material, minimizing, friction and consequently increasing efficiency and lifetime.

For a high-optimized linear solution, a customized package can deliver the maximal performance and characteristics most suited to the application if the motorized solution is well designed. Taking the screw section, this could include considerations over dimensions, pitch, material, ball, or lead screw.

Regarding the miniature motor, the can stack stepper motor can be replaced with various choices dependent on requirement. As an example, a low inertia disc magnet stepper motor ensures the highest acceleration with the benefit of the stepper technology, providing ease of control, positioning capability and detent torque. Alternatively, a brushless DC motor maximizes power density. For applications which demand energy efficiency, such as battery powered devices, a coreless brush DC motor can be advantageous. Control devices can also be added, such as an encoder for high resolution positioning feedback or a gearbox for optimized torque performance.

Motor and lead screw example

Designing the optimal motor assembly means understanding the application’s power demand as well as the motor’s power generation. The desired output force and linear speed vary depending on the application’s requirements. Power is generated by the motor’s torque and rotational speed and it can be calculated by using the expected output power and by taking into account motor efficiency and the lead screw parameter, including the efficiency and pitch.

Now let’s take an example with the development of a laboratory medical device for low volume liquid transfer, a single motor package limited to a maximum diameter of 20mm controls a multi-pipette channel. The filling stage must take less than 2.5 seconds and the pipettes then travel 50mm in 4 seconds where they are emptied in 30 sub-steps. The application requires a high-resolution system and a good repeatability to consistently provide the same amount of liquid for each sub-step.

For this kind of application, a standard digital linear motor with a lead screw will usually fulfil requirements with no special development necessary, beneficial to keep costs down. A can stack stepper motor enables pipette filling control as a result of the multi-step resolution over liquid delivery into sub-volumes, and thanks to an optimized ball bearing assembly, the axial play is removed, ensuring high repeatability.

In an alternative application, a recent example of a battery-powered medical device handled by a doctor during an operation demands efficient power usage. It also has to be lightweight and compact, requiring a solution with a maximum diameter of just 13mm and for this application, coreless brush DC motors ensure high efficiency. For size optimization, the mini motor should also be paired with a gearbox. For the geared motor selection, the engineer will take in account the duty cycle and in this case the medical device will be used over several minutes in continuous duty. To determine the required input power (torque and speed) generated by the motor, some calculations are necessary. First the conversion of the linear motion (force and linear speed) requested by the application into rotative motion (torque and rotational speed). This depends on the lead screw parameters (pitch and efficiency). To know the necessary power at the motor level, you will need to consider the ratio and efficiency of the gearbox. To ensure that the motor is powerful enough in continuous use, the required motor torque should be lower than the rated torque specified by the manufacturer. When the motor and gearbox demands have been ascertained, the power requirement and efficiency of the solution can be calculated.

Supporting linear motion application design, Portescap can support engineers with standard and customized solutions. Defining the technical requirements for the application, it’s vital that the miniature motor is correctly specified and sized to ensure optimum integration and consequently, the application’s maximum performance.

Design, modeling, and demonstration of a new dual-mode back-assist exosuit with extension mechanism.

Karl E. Zelik, assistant professor of mechanical engineering, and recent Ph.D. graduate Erik P. Lamers revealed a new exosuit designed to bring back relief to workers who have been under high strain throughout the pandemic, including last-mile delivery drivers and essential workers. The suit can redirect forces on the body and extend capabilities and applications of existing occupational exoskeletons, which are generally ill-suited for workers like delivery drivers climbing in and out of vehicles. Zelik and his team previously introduced a low-profile, lightweight exosuit produced by his spinoff company HeroWear.

Why it matters Low back pain is a leading cause of disability, resulting in over 264 million missed workdays and more than $100 billion in costs in the U.S. annually. Back pain from overexertion injuries is especially common in industries requiring repetitive bending and lifting. Exosuits have potential to improve safety and provide back relief to millions of workers in essential industries such as logistics, construction, manufacturing, military, and healthcare. 

What's next Zelik aims to commercialize this new spin on assistive exosuits in the next few years. “There are still so many essential workers who cannot yet use existing exoskeletons or exosuits to help them due to their unique job constraints,” Zelik says. “This new design has the potential to bring physical relief to people in jobs that are currently unserved and who deserve the support.”

This work was partially funded by the National Institutes of Health grant R01EB028105.

Researchers at USC Viterbi School of Engineering have developed a low-cost, dynamically controlled surface for 3D printers that reduces waste, saves time.

3D printing has the potential to revolutionize product design and manufacturing in a vast range of fields – from custom components for consumer products, to 3D printed dental products and bone and medical implants that could save lives. However, the process also creates a large amount of expensive and unsustainable waste and takes a long time, making it difficult for 3D printing to be implemented on a wide scale.

Each time a 3D printer produces custom objects, especially unusually shaped products, it also needs to print supports ­ printed stands that balance the object as the printer creates layer by layer, helping maintain its shape integrity. However, these supports must be manually removed after printing, which requires finishing by hand and can result in shape inaccuracies or surface roughness. The materials the supports are made from often cannot be re-used, and so they're discarded, contributing to the growing problem of 3D printed waste material.

For the first time, researchers in USC Viterbi's Daniel J. Epstein Department of Industrial and Systems Engineering have created a low-cost reusable support method to reduce the need for 3D printers to print these wasteful supports, vastly improving cost-effectiveness and sustainability for 3D printing.

The work, led by Yong Chen, professor of industrial and systems engineering and PhD student Yang Xu, has been published in Additive Manufacturing.

Traditional 3-D printing using the Fused Deposition Modeling (FDM) technique, prints layer-by-layer, directly onto a static metal surface. The new prototype instead uses a programmable, dynamically controlled surface made of moveable metal pins to replace the printed supports. The pins rise as the printer progressively builds the product. Chen says that testing of the new prototype has shown it saves around 35% in materials used to print objects.

"I work with biomedical doctors who 3D print using biomaterials to build tissue or organs," Chen says. "A lot of the material they use are very expensive ­ we're talking small bottles that cost between $500 to $1,000 each."

"For standard FDM printers, the materials cost is something like $50 per kilogram, but for bioprinting, it's more like $50 per gram. So, if we can save 30% on material that would have gone into printing these supports, that is a huge cost saving for 3D printing for biomedical purposes," Chen says.

In addition to the environmental and cost impacts of material wastage, traditional 3D printing processes using supports is also time-consuming, Chen notes.

"When you're 3D printing complex shapes, half of the time you are building the parts that you need, the other half of the time you're building the supports. So, with this system, we're not building the supports. Therefore, in terms of printing time, we have a savings of about 40%."

Chen says that similar prototypes developed in the past relied on individual motors to raise each of the mechanical supports, resulting in highly energy-intensive products that were also much more expensive to purchase, and thus not cost-effective for 3D printers.

"So if you had 100 moving pins and the cost of every motor is around $10, the whole thing is $1,000, in addition to 25 control boards to control 100 different motors. The whole thing would cost well over $10,000."

The research team's new prototype works by running each of its individual supports from a single motor that moves a platform. The platform raises groups of metal pins at the same time, making it a cost-effective solution. Based on the product design, the program's software would tell the user where they need to add a series of metal tubes into the base of the platform. The position of these tubes would then determine which pins would raise to defined heights to best support the 3-D printed product, while also creating the least amount of wastage from printed supports. At the end of the process, the pins can be easily removed without damaging the product.

Chen explains the system could also be easily adapted for large scale manufacturing, such as in the automotive, aerospace and yacht industries.

"People are already building FDM printers for large size car and ship bodies, as well as for consumer products such as furniture. As you can imagine, their building times are really long – we're talking about a whole day," Chen says. "So, if you can save half of that, your manufacturing time could be reduced to half a day. Using our approach could bring a lot of benefits for this type of 3D printing."

Chen says the team had also recently applied for a patent for the new technology. The research was co-authored by Ziqi Wang, previously a visiting student at USC, from the School of Computer and Communication Sciences, EPFL Switzerland, and Siyu Gong from USC Viterbi.

Researchers found that in comparison to the BMS, their stent performed better in both decreasing stenosis and promoting endothelial coverage.

Researchers from North Carolina State University have developed an exosome-coated stent with a smart-release trigger that could both prevent reopened blood vessels from narrowing and deliver regenerative stem cell-derived therapy to blood-starved, or ischemic, tissue.

Angioplasty – a procedure that opens blocked arteries – often involves placing a metal stent to reinforce arterial walls and prevent them from collapsing once the blockage is removed. However, the stent’s placement usually causes some injury to the blood vessel wall, which stimulates smooth muscle cells to proliferate and migrate to the site in an attempt to repair the injury. The result is restenosis: a re-narrowing of the blood vessel previously opened by angioplasty.

“The inflammatory response that stents cause can decrease their benefit,” says Ke Cheng, corresponding author of the research. “Ideally, if we could stop smooth muscle cells from over-reacting and proliferating, but recruit endothelial cells to cover the stent, it would mitigate the inflammatory response and prevent restenosis.” Cheng is the Randall B. Terry Jr. Distinguished Professor in Regenerative Medicine at NC State and a professor in the NC State/UNC-Chapel Hill Joint Department of Biomedical Engineering.

There are drug-eluting stents currently in use coated with drugs that discourage cell proliferation, but these anti-proliferative drugs also delay stent coverage by endothelial cells – which are the cells healthcare providers want to coat the stent.

To solve this problem, Cheng and his team developed a stent coating composed of exosomes derived from mesenchymal stem cells. Exosomes are tiny nano-sized sacs secreted by most cell types. The idea behind the coating was two-fold: first, since the exosomes are composed of materials not much different from cell membranes, they camouflage the stent to trick smooth muscle cells and the body’s immune system. Second, the exosomes promote coverage of the stent by endothelial cells and, in the case of injury, travel downstream to the site to promote tissue repair.

To prevent premature depletion of the therapy, the stent releases exosomes when it encounters reactive oxygen species (ROS) – which are more prevalent during an inflammatory response.

“Think of it as a smart release function for the exosomes,” Cheng says. “Ischemic reperfusion injuries, which occur when blood flow is diminished and then reestablished, create a lot of ROS. Let’s say the heart is damaged by ischemia. The enhanced ROS will trigger the release of the exosomes on the stent, and regenerative therapy will travel through the blood vessel to the site of the injury.”

The research team performed in vitro testing to ensure biocompatibility and test the release mechanism. They found that in the presence of ROS, the exosomes released up to 60% of their secretions within 48 hours post-injury.

In a rat model of ischemic injury, the researchers compared their exosome-eluting stent (EES) to both a bare metal stent (BMS) and a drug-eluting stent (DES). They found that in comparison to the BMS, their stent performed better in both decreasing stenosis and promoting endothelial coverage. While the DES performed similarly to the EES in preventing restenosis, the EES was less injurious to the vessel wall and had better endothelial coverage overall. In addition, the exosomes released from EES promoted muscle regeneration in rats with hind limb ischemia. The researchers plan to test the stent in a large animal model with an eye toward eventual clinical trials.

“This bioactive stent promotes vascular healing and ischemic repair, and a patient wouldn’t need additional procedures for regenerative therapy after the stent is in place,” Cheng says. “The stent is the perfect carrier for exosomes, and the exosomes make the stent safer and more potent in tissue repair.”

The research appears in Nature Biomedical Engineering and was supported by the National Institutes of Health and the American Heart Association. NC State postdoctoral research scholars Shiqi Hu and Zhenhua Li are co-first authors.