Medical device powered from smartphone - isolation

[Jonssa]

Hello everyone,

Our customer asked us to design non-invasive medical device which is going to be powered via USB-C cable directly from smartphone with data exchange. It is going to be used in home healthcare envionment and we assume that patient is going to be simultaneously (lay) operator. I have some experience with internally powered MD but I am not sure how to classify device with such requirements.

Device is not internally powered (it has no battery) and cannot be powered with main supply (typical smartphone has one USB connector).

I am wondering if MOOPs are neccessary in this case (I assume that yes) and if yes, if just 1 MOOP is sufficient (it seems reasoneable considering that mobiles shall adhere to IEC 60950) or we shall be separated with 2 MOOPs from smartphone's 5V d.c. (forseeable misuse that user connects device to charger)?

 

[Peter Selvey]

What kind of patient contact is involved? For example conductive sensors, electrodes or just plastic covered interface?

 

[Jonssa]

You can imagine it as alcometer connected to mobile - handheld device with mouthpiece. It has 2 applied parts - part where patient helds smartphone and mouthpiece.

At this moment it is just non-conductive material, there are no electrodes or conductive sensors.

 

[Tidge]

I just want to put this out there: I bought a special cable specifically so that my smartphone can be controlling external storage via USB-on-the-go and also have power on the USB bus from an external power supply (from an OOTS charger) at the same time. Smart phone batteries have a very uneven performance with USBOTG in my experience... even a simple micro-SD USBOTG reader drains my phones more than I'd like.... which is why I went looking for a cable to do just this.

 

[FelipeSchneider]

If the device can be used when it is connected to the mains, then you will have much bigger problems. I would say that merely adding a warning in the device's IFU is not sufficient to control this risk; you should either add something to the software or the hardware to prevent such misuse.

That being said, we are designing a device that can be powered by a cellphone USB. We are aiming for 1 MOOP because there is no contact with the patient. However, in your case, I would recommend using 2 MOPP as it is necessary.

 

[Jonssa]

Thank You @Tidge and @FelipeSchneider, I see Your point. True, it is possible to use this device when concurrently smartphone is charging via USB cable with adapter as @Tidge said and warning in IFU is not enough.

Funny thing is that our device falls under IVDR not MDR and IVDR rather implies IEC 61010-1 than IEC 60601-1 but as for IEC 60601-1 it defines medical device: "If the equipment has an applied part or transfers energy to or from the patient or detects such energy transfer to or from the patient and which is compensation or alleviation of disease, injury, or disability it is a medical device and 60601-1 applies". It is obvious that this device has applied part and, as for me, IEC 60601-1 shall apply. Could somebody confirm that I am thinking right?

I am mostly concerned about clearances and creepages distances. The only conductive part, which may be somehow accessible to user, is USB socket (sensors used for medical examination are hidden and user can't access them). When device is not powered, there is no problem. But how to ensure 2x MOPPs when USB is connected? It is quite easy to isolate device secondary circuit (i.e. with isolated DCDC converter) but still it isolates only the device, not USB cable. USB cable remains unisolated as it is directly connected to smarphone/mains using adapter as @Tidge mentioned.

For patient I imagine that mains (i.e. wall plug) is isolated with 1 MOPP (wall plug shall comply with IEC60950/62368) and in case of failure, the device shall incorporate second 1 MOPP (4 mm creepage, 2.5 mm clearance for 400V) but it seems to be overkill for USB to ensure 1 MOPP for USB socket when connected... For me the device introduces no more risk for operator than using (charging or not) smartphone.

Please, maybe there is someone who can help me understand it.

 

[Peter Selvey]

I'm out of the loop recently, but I expect both MDR and IVDR can use both standards and other standards depending on the case. For example, disinfection machines, special radiology printers can fall under the MDR but use 61010 and 62368-1 respectively, not 601-1. Similarly, a device that samples blood (contacting the patient) but analyzes is on the bench (desk) might be IVDR but uses 601-1. Someone with current experience can comment?

As for using the USB C, in this case it becomes an ME SYSTEM with a generic power supply. There's a few options how to play it and to some extent it depends more on who the ultimate decision maker is. For example, if it is a self declaration and no test labs get involved you could use a bit of common sense in the interpretations, but if you want to get NRTL mark or a CB certificate, it's best to get them involved early and see what they will accept. As far as actual risk goes, it's not a serious situation. The reason why 601-1 has special requirements is due to the assumption of low impedance contact (electrodes, catheters etc.); long term use; patient may be immobile, patient may have low impedance to earthed from other medical equipment. None of these really apply here, at best you could be thinking saliva somehow connecting to the phone's circuitry but who hasn't picked up their smartphone with a sweaty or wet hand at some stage? So normal safety standards should be OK, and a common sense interpretation of 601-1 if applied

 

[FelipeSchneider]

@Jonssa, if you want to play very safe you may buy some Medical Standard AC/DC wall power supplies on Mouser and Digikey.
Another great topic where @Peter Selvey gave a really good explanation about USB cables and MOOPs/MOPPs is this topic.

 

[Benjamin Weber]

Thank You @Tidge and @FelipeSchneider, I see Your point. True, it is possible to use this device when concurrently smartphone is charging via USB cable with adapter as @Tidge said and warning in IFU is not enough.

Funny thing is that our device falls under IVDR not MDR and IVDR rather implies IEC 61010-1 than IEC 60601-1 but as for IEC 60601-1 it defines medical device: "If the equipment has an applied part or transfers energy to or from the patient or detects such energy transfer to or from the patient and which is compensation or alleviation of disease, injury, or disability it is a medical device and 60601-1 applies". It is obvious that this device has applied part and, as for me, IEC 60601-1 shall apply. Could somebody confirm that I am thinking right?

I am mostly concerned about clearances and creepages distances. The only conductive part, which may be somehow accessible to user, is USB socket (sensors used for medical examination are hidden and user can't access them). When device is not powered, there is no problem. But how to ensure 2x MOPPs when USB is connected? It is quite easy to isolate device secondary circuit (i.e. with isolated DCDC converter) but still it isolates only the device, not USB cable. USB cable remains unisolated as it is directly connected to smarphone/mains using adapter as @Tidge mentioned.

For patient I imagine that mains (i.e. wall plug) is isolated with 1 MOPP (wall plug shall comply with IEC60950/62368) and in case of failure, the device shall incorporate second 1 MOPP (4 mm creepage, 2.5 mm clearance for 400V) but it seems to be overkill for USB to ensure 1 MOPP for USB socket when connected... For me the device introduces no more risk for operator than using (charging or not) smartphone.

Please, maybe there is someone who can help me understand it.

Hi Jonssa,
first: IVD-devices are also medical devices. The difference between ME-devices and IVD-devices ist, that IVD-devices are usually not in contact with the patient in order to fulfil their intended use. While an IVD (not IVD-device) may be in contact with the patient. Two examples here:

#1:
The IVD is a antigen test, fully passive like a COVID test. Maybe this test collects the sample directly from the patient's mouth (lollypp style). If this test was given into an analyzing device that automatically scans the test and control lines on the antigen test, this is the IVD device. Which regulations and standard apply for the device? In oppinion this would be IVDR and IEC 61010-1 with -2-101. There is medical indication, yet the device that not have an aplied part or transfers energy from/to a patient.

#2:
You have an alcohol tester (smart example ;-) ) which is used directly on the person with a mouthpiece. Which regulation / standard applies? This depends on the intended use. Let us assume, there is medical intended use, e.g. for alcolhol withdrawal for therapy control oaf alcoholics. In this case the MDR applies with IEC 60601-1 for medical electrical (ME) devices, because it has an applied part.

Hope this helps

 

[Loekje]

If you conclude that you must follow the 601-1:

As the USB-C may be stuck in every unsafe power adapter or computer I would suggest you make your device safe as if it was connected directly to MAINS.
That means that nothing would blow or melt when connected to say 250V AC, and all your applied and accessible parts have isolation and creepage/clearance of 2 MOPPs for MAINS (that includes the cable from phone to device).
For a plastic mouth piece and cable it sounds doable.