Project > The Bandage
Most people would think it is a bad thing to have a bacteria inside a bandage. And in many ways this makes a lot of sense, since most will damage wounds more then heal them. But this one won't! One of the biggest problems in hospitals right now, are drug resistant bacteria. However, despite the hesitation of a large group of people we think we can change a lot in bandages by having a inducible secreting system. In order to achieve a safe and easy solution a lot had to be discussed. This is our idea: Bacteria inside a hydrogel.
Lactococcus lactis would be the perfect candidate as a chassis for our engineered construct mainly because the unlikeliness of infecting humans and its ability to produce lactic acid. Of course there is a lot of expertise of L. lactis in our building which enables us to get acces to a lot of information. Before we started it was already proven that L. lactis cells can survive the harsh conditions of freeze drying1. What also counted is that this bacteria is already used in production process in the dairy industry2. These caracteristics make ourproduct more approachable to the public.
Although it is a relatively save bacteria, it is still a risk to have bacteria this close to the wound. That is why we designed the bandage, a containment device to store and activate bacteria at the right time. This bandage consists of 3 layers. A top membrane that diffuses gases like oxygen and carbon dioxide, a middle layer (a hydrogel) containing freeze dried bacteria and a bottom membrane that makes sure our bacteria stay inside the bandage. This last membrane also allows diffusion of several molecules/peptides.
Although the needs for this bandage were pretty clear from the start, finding the specific materials was harder than expected. For our top membrane a polymer from the iGEM 2012 team could be used. This is called TPX or polymethylpentene. TPX is available as a thin, transparent sheet, while it still stays strong. For our middle membrane tests with polyacrylamide gels are carried out. Although acrylamide is toxic when unpolymerized, it will no longer be toxic when polymerized and properly washed. Polyacrylamide was chosen because it is a cheap and easy to handle material. For our final product we could use a different hydrogel named PMBVF/PVA. This material is harder to handle and more expansive, but it has been tested before with bacteia inside3. Our last part is the bottom membrane. A Cellulose Nitrate membrane with a pore size of 0.2µm could be used. This is small enough to keep the bacteria inside and large enough for the molecules to diffuse freely through the membrane.
More information about the bandage design and the experiments are stated below.
Design requirements:

  • It should not be toxic to humans or our bacteria inside the bandage
  • The top membrane should be permeable to gases, so the wound still has a oxygen suply
  • It should be durable and preferably inexpensive
  • It should not break too easily and it should be flexible. To a point that a person could be able to move around freely
  • It should not stick to the wound
  • The bandage could be stored for at least a month,preferably 6-12 months
  • Easy and quick to active, a simple press on the bandage should be enough. Preferably the bandage can be actived within 30 minutes

We want to add a color system which shows whether there is an infection of S. aureus or P. aeruginosa in the wound. The detection will activate as soon as the first bacteria is in sight. For the testing the detection constructs can be coupled to a GFP(or a lumniscent) signal.
Our bandage should be transparent. In this way you can look through the bandage and judge whether it should be changed or it can stay on for another day, or whether you need to see a doctor. Seeing through the bandage without having to remove it is one of the criteria for the burn wound center as well. Of course the bandage should be as thin as possible. We are aiming at a maximum thickness of one centimeter and a minimum thickness of 3 millimeter.
We have to make sure our bacteria stays inside the gel. Although it is unlikely that L. lactis infects a human, it is possible when the immune system is compromised. We can make sure the bacteria can not leave the bandage by adjusting the pore-size of this gel. Another extra safety point is the usage of a bottom membrane. This membrane will have a pore-size of 0.2um to make sure our molecules can diffuse, but the bacteria are stuck inside. Since we are aiming for hospital usage the bandage can be autoclaved or burned after use, and thrown away in the regular waste.
Comfort & User friendliness
The bandage should not stick, burns are painful wounds and we don't want to make it worse. Secondly it is important that the bandage can be activated easily. This should be within 30 minutes minimize the risk of getting infected. Also one of the requirements is the thickness the bandage, and mainly the thickness of the hydrogel. The thinner the bandage is the quicker the diffusion, and thus the quicker the treatment. Also the flexibillity of the bandage is important, the bandage should be waerable.
Prototype & Testing
So far we have done a lot of experiments with acrylamide gels. We mainly wanted to proof that bacteria can survive extreme conditions and encapsulation in a gel. We realize it wouldn't be a perfect material for an end product, but for us it is an easy and quite cheap way of testing. There will be a lot of testing, this started with what percentage of acrylamide gave the best flexibility results for us, we started with using 10-15-20-25-30 % acrylamide. Here 30% and 25% were to sturdy and thick, the 20% seems to give the best results for us. It’s the right combination between sturdy and flexible. After this we've tried freeze drying the cells itself and checking whether these survive after they are rehydrated. Until now we’re not that certain about our results. After encapsulation in the gel our cells did show a lot of GFP. Unfortunately we haven’t seen a single cell divide inside the gel which of course is the best proof of a living cell. Another thing was checking if the cells can't leave the gel, this was checked by putting cells in the gel. These parts of gel were put in a GM17 medium overnight, and if there was growth inside the media the next morning the bacteria could come out. We've tried this with ruptured gel and healthy, we clearly saw that cells could come out more easy when it was ruptured.
1. Berner, D. et al. (2006) Effect of protective agents on the viability of Lactococcus lactis subjected to freeze thawing and freeze drying. Sci. Pharm 74: 137-149
2. Todar, K. et al. Lactococcus lactis: nominated as the Wisconsin State Microbe. Online textbook of microbiology, UW Department of Bacteriology, Last visited: 17-10-2014.
3. Xiaojin, L. et al. (2012) The effect of the encapsulation of bacteria in redox phospholipid polymer hydrogels on electron transfer efficiency in living cell-based devices. Biomat. 33: 8221-8227
4. Brandwondencentra Nederland (2014) Education Brandwondencentrum Martiniziekenhuis

This is a general picture of how we see our bandage: The top layer is for air diffusion, the middle layer is the gel layer with bacteria inside whereas the water pocket is meant to activate the bandage. Our bottom layer is for extra safety and diffusion

The problem, and our vision
The problem - customer needs

  • Hospitals need to replace bandages several times a day, our bandage could inprove this to 3-4 days.
  • 3rd world countries need cheap and easy antibiotics - wound treatments,without increasing the risk at antibiotic resistance.
  • Burn wound centers are in enthousiastic about our bandage, because infections could be detected sooner.
  • A novel way is needed to fight antibiotic resistant strains4.

What would the ideal product be?

  • A product usable for hospitals and customers. Able to activate in 30 minutes and easy to neutralize.

What would it look like?

  • A completely transparent bandage, this way the consumer of nurse can decide whether the wound needs attention or not.

What would it do?

  • Cool down the wound, increase wound healing and avoid infection by P. aeruginosa and S. aureus and if infection already happened, the bandage will fight the infection.

Who is your external costumer?

  • For now we aim on hospital usage. In this way the disposal and usage of the bandage can be controlled. We would like to bring it to the public as well but then we need to meet a lot more requirements.

Fighting the bacteria works! A great halo is shown.
Planning of sub-parts
What exactly do we have to do to make a bandage?

  • Try to find several gel materials in which the bacteria are able to grow
  • Check for growth in the gel, also with several revival fluids. This could be media, normal water or demi-water.
  • Check whether our bacteria are trapped inside the bandage.

Testing of sub-parts

  • Test different kinds of gels (PAA %) for their strength and applicability
  • Test if IPM's (Infection Preventing Molecules) can diffuse through the gel
  • Test if the cells survive and revive after freeze drying
  • Test if our bacteria are stuck inside the gel


  • 20% PolyAcrylamide 1% crosslinked
  • 0.2 micrometers bottom membrane, Cellulose nitrate - Ultipore Nylon
  • TPX top membrane (from the iGEM Groningen 2012 team)

It was hard to choose our final materials. We started thinking of the molecules that should be able to stay inside the bandage and also of those that should diffuse outside. Taken in account that we have three molecules that need to diffuse outside and also several ones that need come in. For this reason we needed a bottom layer that contains our bacteria inside while the molecules should diffuse freely. So our demands for the bottom layer are:

  • Small pore size (0.2 micron)
  • Permeable to proteins
  • Hydrophilic
  • Flexible
  • Shouldn't stick to a wound

At first we thought of using Polysulfone, polyamide 66 or an acrylate copolymer. After consulting with several company's they came up with several idea's: Ultipore Nylon and EKV/PES (Pall) and a Cellulose Nitrate membrane (Sartorius) All of these could work fine although we would prefer a transparent membrane. After some research we could not find a membrane which was transparent.