Medical devices are becoming increasingly smaller, lighter and more portable. Miniaturization is now a feature of many new medtech products, from handheld diagnostic tools to wearable infusion pumps and compact surgical instruments. While miniaturization provides clear benefits for patients and clinicians, it also introduces mechanical constraints that can impact how reliably these devices operate over time. Here, Chris Johnson, Managing Director of bearing specialist SMB Bearings, explores how mechanical decisions that were once considered secondary can begin to determine the success of an entire product.
In emergency medical settings, small equipment can be transported directly to the patient, reducing delays when time is of the essence. The NHS’ continued investment in robotic surgery reflects this trend, with NHS England predicting that robotic systems could support up to 500,000 surgeries a year by 2035, highlighting the growing demand for compact and flexible technology.
As these systems move closer to patients and into more diverse clinical environments, the mechanical demands placed on their internal components increase. Compact rotating assemblies are now expected to provide precise movement, dosing, or sensing within very confined spaces.
British-developed systems like the Versius Surgical Robot are designed to be compact and easily moved between operating rooms, rather than being fixed to a single room. The system is currently used in more than 30,000 surgeries around the world, demonstrating how miniature mechanical designs are no longer experimental and are impacting real-world patient care.
Like many other technologies, bearings are at the heart of these systems. These support shafts, motors and gear stages in increasingly limited space. When space is limited, changes in friction, alignment, and load distribution can have a noticeable effect on output.
Where size sets limits
One of the first limitations a designer may encounter is torque transfer. As gear motor assemblies get smaller, the shaft diameter gets smaller, reducing the available contact area. This sets an upper limit on the torque that can be transmitted without increasing stress on the bearings and gears. In applications where smooth, repeatable motion is essential, such as drug delivery pumps and robotic surgical tools, even small variations in torque can impact accuracy.
Load carrying capacity presents similar challenges. Bearings with smaller internal diameters naturally support lower loads, but are often expected to operate continuously. For wearable devices that operate for hours or days at a time, underestimating the load can lead to premature wear. Engineers may try to compensate by increasing the motor’s power, but this approach can create additional stresses within the assembly.
As motor power increases, heat generation becomes more pronounced as the components shrink. Smaller systems have less mass to absorb heat and fewer paths to dissipate heat. A slight increase in friction within a bearing can cause temperatures to rise enough to affect surrounding materials, lubricants, and electronic components. This can lead to reduced service life or changes in performance characteristics over time, especially for devices that rely on stable output.
These thermal effects can also affect alignment. In compact housings, shafts and bearings operate to very tight tolerances, so small temperature changes can cause components to expand unevenly.
Misalignment measured in microns may be negligible in large assemblies, but in small systems it can result in non-uniform load distribution across the bearing raceway. This can lead to vibration, noise, and erratic motion, all of which are undesirable in precision-critical medical applications.
Materials suitable for miniature design
Material selection plays an important role in any application. However, this becomes especially important when faced with a number of new challenges. Stainless steel bearings are widely used in medtech due to their corrosion resistance and compatibility with cleaning agents. Grades such as 440C and 316 are common in devices that may be exposed to moisture.
For low precision or low load applications, acetal resin bearings are an alternative when low friction is required. These polymer bearings reduce wear and heat generation while also being resistant to corrosion and many cleaning agents. These may be suitable for compact medical devices where weight and lubrication control are important considerations. Full ceramic bearings are also suitable where electrical insulation or chemical resistance is required.
Bearing lubrication is another area where miniature design changes the rules. Conventional greases may not behave predictably in very small quantities, and excess lubricant can migrate to sensitive areas of the device. In some cases, lightly lubricated solutions or dry film solutions provide better consistency. Engineers also need to consider how lubricants react to temperature changes and repeated use, especially in equipment intended for continuous operation.
Sterilization adds an additional layer of complexity. Many medical devices must withstand repeated exposure to vapors, chemicals, or radiation. These processes can affect bearing materials, seals, and lubricants. Bearings that performed well in initial testing can deteriorate after multiple sterilization cycles if the materials are not carefully selected. For disposable devices, cost constraints can limit material choices, making correct specification even more important.
result
Overlooking these mechanical factors often has consequences late in development. A prototype may pass initial functional testing, but only if problems arise during extended trials or validation. Excessive noise, increased power consumption, or inconsistent output can require last-minute redesign, which can be costly and time-consuming in regulated environments. In some cases, these issues can delay regulatory approval or result in a post-launch recall.
For this reason, mechanical considerations should not be left until the final stages of medtech development. Bearing selection, shaft sizing, and alignment strategies benefit from early input from mechanical engineers and component experts.
Addressing these factors during the concept stage allows designers to set realistic limits on performance and ensure that small components do not exceed their practical capabilities.
