Why Selecting the Right Motor, Drives Product Development

Power tools play an important factor in medical procedures. However, the right drive or motor must be selected to ensure optimum efficiency. Maxon's Peter van Beek breaks down motor selection and how power tools are enhancing some medical procedures. 

Let’s discuss the role of power tools used in medical procedures. A very broad question I know, but can we discuss some of the applications these devices are used with?

Peter:  Power tools use in medical applications include:  Large and small bone manipulation tools; shaving and bone augmentation prior to a knee, hip, and shoulder replacement; cartilage repair or removal; spine drills, reamers, and saws; cranial bone cutting and tissue removal tools; biopsy tools; and staplers to close procedures.  Surgical power tools are used in conjunction with a surgical robot or simply handheld.

Do the drive assemblies for surgical power tools require any sort of maintenance?  

In the vast majority of applications, the motors & gearing systems do not require maintenance.  They are engineered and further validated to withstand the environmental and cleaning protocols.  

If a tool is contaminated with biohazard’s during use, how are the tools and enclosed drive assemblies cleaned between uses?

Peter: In some designs, the core tool is protected with a shrouding system.  Upon surgery completion, the shroud is removed and discarded.  Next, the removal of gross biohazards from the tool is typically done in stages:  The initial step would be a cleaning chemistry wipe down of the tool.  Next, the tool would be placed in an ultra-sound or dishwasher with its associated cleaning chemistry; finally, the tool is placed into an autoclave for final sterilization with the combination of elevated pressure, steam, and high temperature.    

How large of an issue is corrosion and damage to sensitive electrical components (which reside in the motors) when exposed to autoclave sterilization,  various cleaning agents, and saline?  Does Maxon have a special family of motors designed for such applications? 

Peter: I would like to discuss the different approaches utilized to achieve sterilization of a power tool between uses: Autoclave is essentially cleaning with high-pressure steam; water alone is not corrosive or damaging to electronic components.  However, in most cases autoclave is not used alone but in combination with other cleaning methods described but most often, prior to use of autoclave cleaning agents, enzymes and saline are responsible for corrosion and damage to electrical components within a motor, sensor and gearing.  Maxon has two families of motors: one intended for autoclave only and a second family for both autoclave and ability to be withstand exposure to saline, cleaning chemistry, and enzymes. Maxon designs gearing with corrosion-resistant materials and additionally sealing systems to stop the ingress of fluids.  Sensors are also designed to be able to withstand these harsh environments.   

Is it possible for Maxon to confirm lifetime expectations in a particular application?   Is it best practice to confirm the lifetime of a drive assembly in the application or by alternative methods?   How does Maxon’s validation lifetime to a specification?

Peter: Maxon has the capability to confirm lifetime in an application for defined torques & speeds, oscillations, directional changes etc.  However, it is always best practice for the end user of the drive assembly to perform life testing under real-world conditions.  Nothing mimics the environmental considerations (humidity, temp range), radial, and axial loading as seen in use.  When a drive assembly is in a housing and, they are always encapsulated in something, cleaning processes etc.

Is there a trend in surgical power tools to one-time-use or does the multi-use historical philosophy still prevail?  How many times can a motor assembly be realistically reused?  

Peter: There is a real trend to use motors one time and dispose of them after each surgery. In that situation, the motor has to be very inexpensive. Maxon currently has motors, which can be. Sterilization becomes the main issue when you're talking about reuse because you have to clean it in between each use.  Maxon currently has the maximum 2,000 cycles of sterilization that it can withstand for certain variants of our motors and somewhere as low as 1,000. But I would say typically most customers are wanting like 500 to 1000 autoclave cycles before they throw it away. And in a time when everything is disposable and landfills are filling, from my personal perspective, I like to see that we're reusing things as many times as possible. But with that being said, the industry seems to be really pushing surgical power tools for one-time use and then disposing of it.

Let's talk a bit about the design of surgical power tools. In some cases, surgeons hold and use these tools for extended periods. Can you describe how ergonomics dictate the electric drive assembly design, and what attributes are most requested in these sort in these sorts of designs?

Peter: Users are looking for high reliability, validated quality, high power density, smaller physical size, lighter, quieter, longer life, and capable of standing harsh environments such as saline cleaning, chemistry, autoclave, and sterilization.

Cannulation is essential to certain power tools which allow saline to flow through the motor for lubrication and flushing. Can you speak about this particular-motor construction?

Peter: Cannulation in essence is having a hollow shaft running through your motor and you have to be able to isolate the flow of like saline for example through the motor. You have to seal up the rest of the motors so that the saline basically can't enter the motor and cause damage - because saline is corrosive, and it will. Also, it's electrically conductive and it will short out the motor, so Maxon is working on designs currently and what we're calling the medical motor, which would be capable of being exposed to saline even if the saline would somehow on the front end or the back end of the motor. It's basically an over molded design, stater, which encapsulates the printed circuit board inside there so that the saline, or any cosmetic chemistry or cleaning chemistry, cannot get to the motor and cause it to fail.

What are some of the largest challenges facing motor or drive assembly suppliers used in surgical power tools?

Peter: Creating for one would be creating the quality structure for any kind of surgical power tool within our own organization. The days of just building motors is past us and now you have to go through a very regimented step of risk analysis. Drawing creation specification, drawing with the customer, and creating this whole change control and validation structure for any drive assembly. So that's very challenging. It takes a long time, and most customers aren't always in a hurry, and I don't want to wait for the development and the quality side of things. They just want to move ahead with their design. And that is probably one of the largest challenges I see also you know every customer is asking for a lot of customization which results in a lot of custom parts, different parts that are not catalog parts that have to be validated and actually to find a supplier for those parts and to just create structures for those parts is a daunting task.

Is there anything you’d like to add?

Peter: Companies are very good at designing and bringing a design forward. An afterthought is often the quality and the validation requirements associated with the project. In a perfect world, designing quality need to run in parallel to reach the finish line at the same time. Don’t forget about quality or it will delay your launch to market. [At Maxon] we have the know-how and expertise to guide our customers seamlessly through the quality and design process, saving them time and money.