Apr 3, 2018 | By David

A team of engineers at MIT have made use of 3D printing to develop new bandages that have significantly improved properties compared to the conventional ones.  They’re made of a special rubbery film that clings to skin, and therefore offer much improved comfort and adhesion compared to the notoriously fickle glue of bandages, that really shows its weaknesses when you’re attempting to dress a knee wound or other joint, such as elbow. Like many other ingenious 3D printing applications, the design of the dressing was inspired by traditional Japanese paper folding, and it could also be used for all kinds of wearable electronics.

 (credit: MIT News)

The MIT team’s material is incredibly adhesive over a long period of time. In tests it has proven to keep its hold even after 100 bending cycles. The key to the film’s clinginess is a pattern of slits that the researchers have cut into the film, similar to the cuts made in a paper-folding art known as kirigami, closely related to origami.

The project was started when a Chinese medical company approached the team, wondering if the rubber film material it had developed could be used to dress wounds.

“Adhesives like these bandages are very commonly used in our daily life, but when you try to attach them to places that encounter large, inhomogenous bending motion, like elbows and knees, they usually detach,” said Ruike Zhao, a researcher involved in the study. “It’s a huge problem for the company, which they asked us to solve.”

(credit:  flickr)

The films were created by 3D printing specially shaped molds, which were filled with a liquid elastomer. 3D printing technology allowed the easy placement of offset grooves at various different spacings in the molds. These molds resulted in kirigami-style films with slits. The material was then subjected to stretch tests. The team recorded the amount of stretch a kirigami film could undergo before it peeled away from a polymer surface that it had been attatched to. This gave a measurement for the material’s critical ‘energy-release rate’, which would vary at different points on the film.

Experiments with the material in different shapes allowed the team to identify three main parameters that give kirigami films their adhesive properties. One is known as shear-lag, in which shear deformation of film can reduce the strain on other parts of the film. There is also partial debonding, in which the film segments around an open slit maintain a partial bond to the underlying surface. Another key aspect of the kirigami films was inhomogenous deformation, in which a film can maintain its overall adhesion even as parts of its underlying surface may bend and stretch more than others.

Using these findings, future designers who are attempting to solve adhesion problems in a similar way can use these parameters as a blueprint to work out the best possible kirigami structure, in terms of positioning and number of cuts.

The resulting kirigami films were used by the medical company as pain-relieving pads, but they could equally function in regular wound dressings, as well as more complex products like wearable electronics. The team, which consisted of Ruike and graduate students Shaoting Lin and Hyunwoo Yuk along with Xuanhe Zhao, the Noyce Career Development Professor in MIT’s Department of Mechanical Engineering, will now be developing their work further for more advanced applications.

“The current films are purely elastomers,” Ruike says. “We want to change the film material to gels, which can directly diffuse medicine into the skin. That’s our next step.”

 

 

Posted in 3D Printing Application

 

 

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