How adhesives are used in prosthetics and implantable medical devices

EP42HT-2Med is one of Master Bond’s flagship medical grade epoxies that is designed specifically for use in medical applications. This two part epoxy meets both USP Class VI and ISO 10993-5 certifications. The system is capable of withstanding repeated sterilisations, including ethylene oxide (EtO), radiation, chemical sterilants, and autoclaving.

It offers bonding, sealing, and coating performance, and is castable to thicknesses of up to 2-3 inches. Highly resistant to many acids, bases, solvents, and fuels, the system features excellent electrical insulation properties, and is serviceable from -60°F to 450°F. It cures at room temperature or more rapidly at elevated temperatures, however for optimal performance and biocompatibility, the recommended cure schedule is overnight at room temperature followed by a heat cure of 150-200°F for an additional 2-4 hours. 

EP42HT-2Med is often utilised in the manufacture and assembly of surgical instruments, catheters, endoscopes, and other medical devices. Available in both amber-clear and black as a USP Class VI system, EP42HT-2Med is well suited for use in prosthetics and implantable medical devices.  

Prosthetics and fully implantable medical devices must be capable of withstanding sterilisation procedures, as well as exhibiting biocompatibility over an extended period of time. These devices must be able to maintain performance levels even when in direct contact with tissue and bodily fluids, and must not introduce toxins or cause injury, a physiological reaction, or immunological rejection. In several research and development publications, scientists and engineers have singled out EP42HT-2Med and EP42HT-2ND-2Med Black for use in their applications. Download the full case study. 

EP42HT-2ND-2Med Black is another medical grade epoxy adhesive that withstands high temperatures and repeated sterilisation. It fully complies with the testing requirements of USP Class VI and ISO 10993-5. This two component epoxy resists recurrent autoclaving and sterilisations including radiation, steam, ethylene oxide, and chemical sterilants. 

EP42HT-2ND-2Med Black is an excellent electrical insulator with a volume resistivity over 1012 ohm-cm, a thermal expansion coefficient of 35 to 40 in/in x 10-6/°C, a dielectric constant of 3.8, and a tensile strength exceeding 12,000 psi at ambient temperatures. Heat resistant up to 450°F, it also withstands chemicals such as inorganic and organic acids, alkalis, organic solvents, and aromatic hydrocarbons. 

Its optimal curing schedule is overnight at room temperature followed by 2 to 3 hours of heat curing at 100°C to 125°C. EP42HT-2ND-2Med Black has a noncritical mix ratio of 100:40 by weight or 100:50 by volume, and a paste consistency with minimal flow when applied. It offers a lengthy working life of 30 to 45 minutes for a mixed 100 gram batch at ambient temperatures, which can be increased by using shallow mixing vessels or mixing smaller batches. Like EP42HT-2Med, EP42HT-2ND-2Med Black can be used in a broad array of medical device applications including surgical instruments, diagnostic equipment, prosthetics, implantable devices, and more, where repeated sterilisation, especially autoclaving is a primary requirement. 

Following are brief descriptions of 3 applications and their use of these medical grade epoxies. 

Implantable multi-panel sensors application  

Researchers at the Swiss Federal Institute of Technology (EPFL) in Lausanne, Switzerland, the Universitá degli Studi di Genova in Italy, and the Institute for Research in Biomedicine (IRB) in Bellinzona, Switzerland, have been studying ways to develop biocompatible packaging for implantable devices to be used for remote monitoring of metabolites, such as glucose and lactate, and drugs.1,2,3,4 They designed a fully implantable sensor device consisting of a microfabricated sensing platform, custom designed integrated circuits (ICs), and a coil for power and data transmission. The device is powered through an inductive link between an external power coil and the coil embedded within the device. Metabolic readings are captured by the sensors and transmitted from the device to an external receiver. The three subcomponents were to be assembled into an integrated device and then encased in a biocompatible package prior to implantation in mice. 

Tibial implant application  

Total knee replacements generally consist of three major parts: a tibial component, which is connected to the shinbone, a femoral component, which is connected to the thighbone, and a meniscal bearing component, which is located between the other two components and allows them to slide over each other. The tibial and femoral components are usually made of metal or a metal alloy while the bearing component is made of a synthetic plastic, such as polyethylene. Early designs of prosthetic knees fixed the bearing component to the tibial component, but newer designs allow the bearing component to float to some extent, allowing increased freedom of movement within the knee. However, all knee prostheses incur some risk of dislocation or spinout, especially if the ligaments fail to provide adequate support. Ideally, a prosthetic knee should allow for some flexion and tension of the knee joint while lowering the risk of dislocation and bearing spinout. 

Transradial socket for arm prosthesis application   

For individuals who are missing part of an arm, a prosthesis may be attached to the arm remnant via a socket. Many socket designs achieve the primary goal of attaching the prosthetic arm, but present issues to the amputee that result in reluctance to wear the prosthesis. Non-permeable full-contact sockets, for instance, tend to be uncomfortably hot and humid, while open socket designs are more breathable, but are bulky and unaesthetic. Many close-fitting designs are difficult to put on and take off, while looser designs may not be sufficiently stiff to support the arm remnant. Ideally, the socket connecting the artificial arm to the arm remnant should be close-fitting, comfortable to wear, easy to put on and take off, adjustable, lightweight, and self-suspending, among other characteristics. 

To read more about the key parameters and requirements of each application above, as well as the results, please download the full case study. 

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