Thread/Glue That Will Degrade After a Few Weeks

Don't have much time right now: Shape Memory Polymers - Biodegradable Sutures

Thanks, but I think surgical sutures break down due to enzymic activity (reaction by the body internally). The harness will be fully external on the animal, and nothing invasive (breaking skin) can be done to them. So it has to be a reaction with the outdoor environment that does the degrading.

"Thanks, but I think surgical sutures break down due to enzymic activity"

Could suitable enzymes be applied to the thread when you attach it to the animal?

Perhaps the answer is in the application itself. Make the last job of the battery one of severing a fusible link and releasing the harness. This might even be initiated on command. I think I'll look around some and see if this is feasible economically or otherwise. Good luck!

Good Idea, a separate battery could be used to hold a small electromagnetic clasp and when the battery dies it releases.

Are these devices being recovered? Are there any worries about environmental hazards from loosing battery powered devices?

Drew K

You might look for plastics that have poor resistance to ultraviolet light. (Most people are looking for the opposite, and plastics suppliers might not highlight low-resistance types.) Searching on "biodegradable plastics" might find some ideas, though you may have tried this already.

On that, certain supermarket plastic bags (Tesco) biodegrade over time. I'm not sure of the time scale, or if it's UV dependent. They do degrade in the dark...certainly in the space of months. I've not studied/measured the time needed, I've just stored things in bags, gone back to retrieve them and had the bag disintegrate when I touch it.

Not sure where the OP is, but if he's really desperate, I could mail him some bags....

Just in case....

This was meant as a serious suggestion. The plastic bags, cut into strips would be strong enough to act as the links to hold the tags onto the animal's neck (I assume), whilst degrading and breaking the collar after a time.

I was not suggesting tying whole plastic bags round the animals!

I don't know how long the bags take to break down - more than 4 weeks, less than a year is my guess based on unobservant observations (e.g. when I pulled out a bag to use last night and it deposited plastic confetti on my floor) Tesco's website (www.tesco.com) may have some info in their environmentally aware propaganda.

The OP doesn't show his country of origin, so in case he's not in the UK, and as I know Tesco have withdrawn from the US and I don't believe they have a presence elsewhere, my offer to post/mail some is genuine.

OP: PM me if you want some!

Alternatively, I believe starch-based plastics are widely available. These are compostable, so must break down. Again, you'd need to do some research into timescales.

GA

Those bags (and others rated bio) are primarily UV degrading but also do in land fill.

As a general comment to the OP: My inclination would use UV properties - rather than soluble or enzyme materials given Baths and possibly rain, even saliva, are involved.

You might incorporate a micro electromagnet for holding the device in place, as the battery weakens so does the hold...or they have some with permanent magnet that is then neutralized with signal...

http://www.alibaba.com/product-gs/317344005/ZHI_0222_Micro_DC_AC_Electromagnet.html

Maybe check out adhesives formulated with polyvinyl alcohol.

Polyvinyl alcohol - Wikipedia, the free encyclopedia

I used this years ago as a scuttle plug to sink sonobouys deployed on the ocean.

You'll need to talk to current day suppliers, but..................

Thanks for replies so far.

Re a release mechanism on the battery - this is used on larger tags but isn't possible on mine, as the tags are already pared down to the absolute minimum weight (0.4 g) to be able to be used on the small animals. They are also already manufactured and potted in epoxy by the supplier.

The tags can't gain any more weight or be changed, so the release has to be in the harness.

What type of animals?

Would it be possible to glue the tag directly to the animal's skin or in it's hair?

There is a suture material that's made for internal stitching, that stays wet but degrades over time.

Looks like lyn already touched on it. These people say they can adjust the time of degradation.

http://polynovo.com/innovations/

Maybe here

http://www.iccm-central.org/Proceedings/ICCM17proceedings/Themes/Behaviour/SUSTAIN%20GREEN%20COMP/F23.9%20Vieira.pdf

http://en.wikipedia.org/wiki/Surgical_suture#thread

If suture material is unsuitable, then why hot directly use "superglue" onto bare skin?

One of the development reasons for "superglue" was for field dressings and is often used in hospital s now instead of suturing. If applied to the skin, it will fall off when the next layer of skin exfoliates. (Just like it does when used on people.)

Fancy that, experimenting on humans for chemicals to be used on animals!!!!

Gluing to fur/feathers/skin is an option, but they can often very easily pull the tag off, and damage themselves while doing it. Supergluing direct to the body is also considered a bit invasive/unethical (these things are overseen by the Home Office - it's pretty tightly regulated).

I'm limited to making a harness (out of 2-3 mm elastic cord), which has to have a degradable weak link, and have to be extremely light - the tag weighs 0.4 g and i can't get much above 0.5 g for the complete tag/harness set-up. Even superglued knots have to be sanded down to shave ff some weight.

The papier mache suggestion might have some legs, as a small join between two parts.

Maybe Instead of a knot, just overlap the loose ends with a spot of glue. The more overlap, maybe the longer the time to degrade.

How about making the harness/tag from Papier-mâché. It is made from flour, salt, water and paper. You make it water proof with a silicone spray or a waterproof paint. It can be made to be very strong by adding layers and when dry it is very light and strong. It will break down easily outside after a short while, the time which could be controlled by the water proofing material. The animal or his friends may even eat it off.

I'm thinking along these lines myself. I was thinking of simply using a flour paste to bond the ends of a threaded loop. The problem would be drying it quickly to set it. Maybe using ir?

Natural latex elastic rubber bands will perish with time.

In the tropics any where from a week to a month and they are finished.

At the risk of sounding like a broken record, from the link I cited earlier:

"However these properties are dependent on humidity, in other words, with higher humidity more water is absorbed. The water, which acts as a plasticiser, will then reduce its tensile strength, but increase its elongation and tear strength. PVA is fully degradable and dissolves quickly."

I'll be quiet now.

You could always eliminate the weak link altogether, or is this too expensive.

The size of a grain of rice and implanted under the skin.

http://www.corerfid.com/solutions/IndustrySolutions/IndustryAnimals.aspx