Medical Device Design Engineering

Medical device design is the first stage in the production of new tools, appliances, and instruments for use in a wide variety of medical and surgical processes. It includes not only the mechanisms and implements used to treat patients at hospitals and other medical facilities but also implantable, wearable, and portable medical devices that can perform the functions of human organs, deliver medication, and monitor patient vitals in real time. The functionality of the final product is dependant upon the design stage. At Proven Process, we have the ability to design products to be manufactured at our own facilities or create designs for clients who choose to manufacture the products themselves or at a different facility. The Proven Process team can design anything from entire medical devices to a single component of a larger device or system. Our team has years of experience in the design and manufacture of Class II and Class III complex medical devices.

Facets of Medical Device Design

Broadly speaking, the aspects of medical device design can be broken down into three categories: mechanical, electrical, and software. Some devices will not need all three aspects. Many surgical instruments - such as scalpels, clamps, and retractors - are purely mechanical. Others include both electric and mechanical components but do not need software to operate. Examples of this include blood pressure monitors and electric bone saws. Given the complex functions needed to be performed by most modern medical devices, however, most require mechanical, electrical, and software features to be designed.

The mechanical aspects of medical device design must take a number of factors into account. One is the required strength of the device, including its ability to withstand tension and torque. This will impact choices such as construction material and bond types. The material will also need to conform to the biomechanical requirements of the product, particularly in those devices that come into contact with patients. The expected lifetime of the device will also need to be considered. Single-use devices will not have the same mechanical requirements as devices meant to last for years of continuous use.

Medical device design also encompasses electrical engineering. Engineering components can take multiple forms. Some are involved in powering mechanical movements, such as the pump in a drug delivery device. Others are sensors designed to acquire physiological data about the patient (e.g., EKGs) or monitor aspects of the device itself (e.g., RPM, temperature, torque). The delivery of an electrical current can also be the primary function of the instrument, as in the case of defibrillators, electrocautery instruments, and iontophoretic drug delivery devices. Devices may also need to communicate unilaterally or bilaterally with a network or other devices, either wirelessly or via data ports. Electrical engineering must ensure the electric components of the device will not only perform as needed but do so consistently and reliably.

Software is the third component of medical device design. Today’s medical components are increasingly complex and are frequently controlled by an internal operating system. These can range from programs that handle simple device operation and data collection to complex systems incorporating algorithms in order to make critical decisions related to performance and function of the medical device. Software design will need to account for the physical characteristic of the device itself, which can limit the size and power of the processor. Proven Process uses a structured development model.

Design Stages

Medical device design typically goes through six stages. These are research and discovery, specification development, engineering, prototyping, iteration, and manufacturing process design.

Research and discovery

The research and discovery phase of medical device design focuses on determining the requirements that provide the parameters for the design. Client needs and desired device functionality provide the starting point for conceptualization. A customer needs assessment involves the direct participation of the client. Factors that need to be considered include whether the device will come into contact with patients, the operational environment of the instrument, and the lifecycle of the apparatus. Even at this initial stage, questions of manufacturing methods and materials must be taken into account in order to control costs. Risks associated with the process must also be assessed at this point and communicated to the client. Overall cost and time-to-market estimates are established. Feasibility studies are also included in this stage.

Another facet of this stage involves reviewing the FDA regulations and ISO specifications that would cover this device. Any new device used with patients in the U.S. must be approved by the FDA. Considering FDA requirements during the discovery stage avoids issues that could hamper FDA approval later. Planning for quality control necessitates knowledge of the international standards covering areas such as biocompatibility (ISO 10993), sterility (ISO 11607), and electrical safety (IEC 60601). The experienced team of engineers at Proven Process knows the applicable regulations and stays current on emerging standards covering new technology.

Specification development

Once the research and discovery phase is completed, engineers formulate specifications for the device. These specifications cover the mechanical, electrical, and software parameters of the project. They cover issues such as device functionality, material requirements and restrictions, operational tolerances, and safety features. Systems engineers create a definition for the device, including functional and structural relationships between components. Precision in the specification process is key to avoiding the need for potentially costly late-stage modifications to the project.

A knowledgeable medical device design team can anticipate the interplay between the various competing factors. For example, specifications stipulating a high tensile strength combined with biocompatibility will have implications for the choice of materials. Well-defined specifications allow design engineers to anticipate possible problems before they occur, saving both time and money.

Engineering

With the specifications in place, engineers can begin developing the actual medical device design. Mechanical engineers are responsible for formulating all physical aspects of the device. They use both traditional design tools and modern 3D-CAD software to draft the shape and physical properties of the object. Raw materials are selected to meet the specifications, and the instrument design is separated into its constituent components. Throughout this stage, the engineers remain aware of the impact their design decisions will have on the manufacturing process and the project cost.

The mechanical engineering aspect of medical device design includes decisions about the manufacturing process. The appropriate means of forming components must be selected. The choice of injection molding, extrusion, or other processes will be dictated by factors in the specifications and the choice of material. The proper methods of joining parts will also need to be selected from options such as the use of a bonding agent or a process like ultrasonic welding, tungsten inert gas welding, or resistance welding. The assignment of manufacturing steps to separate cells is part of this stage.

Electrical engineering is the second component of medical device design. After determining the electronic requirements of the project, schematic capture is used to plan the layout of the circuitry. The power supply is determined, addressing questions like alternating or direct current, battery or external power, and voltage and amperage. These issues will be constrained by the size of the device, its portability, and its function. CAD tools are used to design the physical configuration of the electrical system, whether it is a few wires or a complex printed circuit board. Any connectors will also need to be discussed with the mechanical engineers to determine whether standard connectors can be used or proprietary connectors need to be created. More complex devices may require the design of application-specific integrated circuits (ASICs) to control various aspects of device operation. Digital and analog simulation in the design stage ensure that device specifications are being met.

Many modern devices also require the development of dedicated software to operate the system. Software engineers determine the appropriate operating system (whether commercial, open source, or custom). That, along with the needs of the project, determine the programming language to be used. Proven Process software engineers work with Windows, Linux, QNX, and other real-time operating systems, and they program in most major languages, including C, C++, C#, Visual Basic, and assembly languages. In addition to large systems, the Proven Process team designs firmware for embedded microprocessors and digital communication systems within the device. Software design decisions are made in consultation with the electrical engineers.

Medical grade software development must be compliant with the IEC 62304 Medical Device Lifecycle Model. The FDA also has software-specific guidelines for the design of instruments to be used with patients. Cybersecurity needs to be addressed, as digital attacks on medical devices are becoming more common. Software validation is carried out via testing protocols that ensure the programs perform according to specification. Software planning also needs to include methods for updating and patching software over the lifecycle of the instrument.

Prototyping

Once the engineering phase of the medical device design process has been completed, the next step involves the creation of a prototype. A prototype is a full-scale, working version of the design that is produced in limited quantities. It is generally produced through one-off manufacturing processes rather than through cell manufacturing. 3D printing capability makes it possible to produce prototypes more quickly and cost-effectively.

The prototype allows for the verification and validation of the device. Verification is the process of determining whether the specifications of the device have been met by the design process. Each aspect of the design - mechanical, electrical, and software - is tested. Validation, on the other hand, looks at the overall function of the instrument to ensure that its functions meet the needs of the client while conforming to all applicable international standards and FDA regulations. Documentation for each step is produced for the client and to be used in the FDA approval process.

Validation and verification require comprehensive testing. Risk assessment is done in compliance with ISO 14971. Fault tree modeling, failure modes and effects criticality analysis, and other models allow engineers to track any errors to their source components. Electrical safety is validated per IEC 60601, while biocompatibility verification is done to the specifications in ISO 10993. Environmental testing ensures that the device functions under all likely use conditions. Finally, sterility validation is carried out in accordance with ISO 11607 and packaging transit requirements are verified per ASTM and ISTA standards.

Iteration

Any problems or difficulties identified through prototype testing require parts of the design process to be revisited. The design is returned to the mechanical, electrical, and software design teams to be refined. Once the design issues have been addressed, another round of prototyping and testing begins. This process is repeated until the medical device meets all specifications and passes validation and verification. This iterative modification of the design allows problems to be corrected before full-scale production begins.

Manufacturing Process Design

When the design and testing of the device are completed and the client has approved the final iteration, the last stage of medical device design requires the development of the manufacturing process. Proven Process uses a cell manufacturing model with specialized production stations. Each cell performs one function, such as the production or refinement of an individual component or the fitting and bonding of multiple components. This method of production allows for small changes to be made to the process in a cost-efficient way without having to take the entire production line out of service. Many of the decisions that are implemented in this stage will have been developed in the engineering phase, but the final form of the manufacturing process will need to be set at this time. Once this is completed, the move to the production stage can be made.

Conclusion

Medical device design is a complex, multi-stage process. The research and discovery phase allows the needs of the client to be determined and the applicable regulations to be reviewed. Based on the results of that process, the specifications of the design can be created through collaboration between the mechanical, electrical, and software teams. Prototyping develops working models that can be tested to provide validation and verification, with design problems being addressed through an iterative approach. Once the final design is approved, the manufacturing process can be designed and full-scale production can commence.