Injectable Shear Thinning Hydrogels

Hydrogels provide a promising new way to deliver drugs or other materials with which to regenerate damage tissue because of their flexibility and biocompatibility. Up until now, though, these could not be fully used because their solid structure tended to degrade under the harsh conditions of the human body, particularly our high body temperatures. To solve this problem, MIT researchers synthesized a special kind of shear thinning hydrogel.

Shear thinning hydrogels are notable because they can switch between a solid and liquid state depending on their surroundings. This makes them ideal as injectable gels because they're liquid when being pushed through a needle but become solid once they're inside the body. However, if the researchers left these gels as is, they would still be subject to stresses of a mechanical nature inside the body and might revert back to liquid.

To fix this, they created a self-healing, reinforcing network inside the gel that only activates when the temperature of its surroundings are body temperature. That way, their new structure would not interfere with the gel's functionality in the needle but would still be able to solve their problem of durability once inside the body.

They opted to create protein hydrogels instead of the more standard polyethylene glycol gels so that they would have better biological properties, and altered the structure so that they would have the desired characteristics. The proteins were loosely held together by links called coils to result in a rope-like structure, and then a second network was built inside that.

At higher temperatures, cross-linking results in a reinforcing network.

At low temperatures, the protein gels are hydrophilic and thus float freely within the gel. As soon as the temperature becomes high enough, though, the gel becomes hydrophobic and groups together, making polymers at the ends of the protein bind to each other. This results in cross-linking so that the gel is significantly more elastic and durable, able to withstand mechanical strength.

Painless Medical Tape

A research team at the Brigham and Women's (BWH) hospital recently created a new type of medical tape that can be removed from skin without pain. Medical tapes before this invention were very secure in terms of adhesion properties, but they damaged skin when being peeled. Current medical tapes have a lot of backing and support that allows it to stick strongly on a patient. However, when taken off, the tape used leaves some of the adhesive material on the skin. Although this does not affect all skin types, neonate skin, which is newer and more recently grown, does face more serious damage. 

Painless medical tape

The new medical tape created has three-layers which retains the strong adhesion properties of previous tape, but also adds a feature that allows the tape to be easily peeled off. There is one layer of tape that serves as the adhesive layer and another layer that serves as the backing support. A final layer exists in between these two, referred to as the anisotropic adhesive interface. The anisotropic feature means that the layer's physical properties depend on direction, opposed to an isotropic feature, which would refer to the properties of materials that are the same in all direction. For example, wood has anisotropic properties, containing lines that go in one direction. The wood contains more strength when the lines all go in one direction, causing wood to have anisotropic properties. 

Anisotropic features have advantages, being stronger in a certain direction. The scientists from BWH used laser etching and a release liner in order to make the anisotropic layer of the medical tape. This feature allows the medical tape to have a much higher shear strength as it is now dependent on direction. The release liner allows for the medical tape to be removed with little force. Solving the previous issue, if any adhesive remains of the skin, it can be gently rolled off using a finger. In other words, the medical tape would come off skin more easily. Release liners work by using silicone releasing agents, which have a low surface tension of wetting. Wetting refers to the characteristic of how a liquid deposited on another liquid or on a solid spreads out. Because silicone, a key component of release liners, has a low surface tension energy, it does not spread too much when on another layer of the medical tape and, ultimately, the skin. Thus, it can be pulled off easily without any damage to the skin. Frequently in the past, carbon-carbon backbones were utilized instead of silicone polymers, which caused a more rigid structure and, as a result, harm to skin. Silicone polymers, however, have methyl groups which interact only slightly with one another, producing little surface tension energy.  Additionally, silicone has a low adhesion in terms of sticking to the skin. When materials have diffusive adhesion, the molecules of each are soluble in the other material. They move around, and when joined, connect through diffusion. In particular, polymer chains demonstrate diffusive adhesion effectively, in which the ends of one molecule diffuses with another. 

Over 1.5 million injuries occur in the United States due to medical tape removal. Using this medical tape, this number can be reduced greatly, affecting numerous patients positively. 

http://articles.timesofindia.indiatimes.com/2012-10-30/health/34816599_1_tape-skin-release-liner 

Walking Bio-Bots

For the first time, researchers in the University of Illinois have created an autonomous robot made from plastic and living cells. With just hydrogel, heart cells, and a 3D printer, these scientists have created miniature "bio-bots" that are capable of walking by themselves, without the use of electricity.

The Bio-Bot is 7 mm long and can move on its own

Each bot has one long, flexible leg that rests on a short, stout leg for support. The long leg is covered with rat cardiac cells. It pulses like a heart and as it beats, the bio-bot propels forward. The rhythmic expansions and contractions pull the little robot forward in what looks like a swimming motion.

The hydrogel part of the robot was made by a 3D printer. This makes the production of robots easier because more shapes can be made faster and easier. Because it is easy to print these plastics, several changes can be made fairly easily. The researchers can use trial and error as much as they need to improve the design of the bio-bot.

The bio-bot's unique structure allows it to manipulate into different shapes that would not be possible if it were made of metal and hard plastics. The soft plastic and cells allow the robot to be flexible, as well as function without the use of electricity. Rashid Bashir, one of the head engineers, stated “As engineers, we’ve always built things with hard materials, materials that are very predictable. Yet there are a lot of applications where nature solves a problem in such an elegant way. Can we replicate some of that if we can understand how to put things together with cells?” So far, they have been successful in creating functioning robots.

The researchers hope that these bio-biots could be used to detect chemicals in water, climb walls, or function as a sensor to react to certain elements in the water. If the bio-bots can be made using cells that respond to different stimuli, like chemical gradients, then they can definitely be used in drug screening and chemical analysis. The way the bot's motion changes would indicate the reaction of the cells to the environment and whether or not a similar reaction may occur in humans. It is the researchers' hope that if they can get the bot to move toward chemical gradients, they could design something that can look for a specific toxin and attempt to neutralize it.

A depiction of the movement of the robot

The scientists plan to continue working on this discovery. They hope to improve the bots to develop control and function. For example, they plan to create robots that can respond to light, climb steps, and utilize different numbers of legs. They believe this is the first step of many in this exciting field that utilizes nature for beneficial purposes and functions.




http://news.discovery.com/tech/walking-bio-bot-made-with-cells-gels-121115.html
http://news.illinois.edu/news/12/1115bio-bots_RashidBashir.html

Growing organs from your own cells

Andemariam Teklesenbet Beyene had a cancer-ridden windpipe, but thanks to some brilliant scientists, he left with a unique windpipe, one that was created from his own cells. This was the first time that a synthetic organ was successfully created and used to cure a person. The success marks the beginning of a time when organ transplants will no longer require a waiting list or debilitating drugs.

The process for creating an organ capable of functioning in the human body with everything else that is going on is quite complicated with trial and errors. There are many factors that must be in check for the organ to be produced properly. An amount of the patient's cells must be extracted and nurtured, than factors such as the shape, temperature, pH, and others must be monitored to ensure the organ grows correctly. Also, the organ was tested in a bioreactor, which mimics the conditions in the human body. It was only after all this that Beyene had his synthetic windpipe transplanted, and months later Christopher Lyles, had the same treatment for cancer. Due to the complexity of the process, only simple organs like windpipes are able to be constructed, while more complex organs like hearts are still impossible.


http://www.bbc.com/future/story/20120223-will-we-ever-create-organs/1

Bulletproof Spider Silk Skin

Under Project 2.6g 329m/s, researchers worked in collaboration with the Forensic Genomics Consortium Netherlands to create one of the most creative and shocking tissue engineering projects: bulletproof skin made of spider silk.

Silk has always been known to be among the strongest natural protein fibers in existence, but spider silk in particular has remarkable properties, its tensile strength larger than that of steel and its flexibility enough to be woven into a web. More intriguingly, spider silk has been proven to be biocompatible, raising the question: can spider silk replace the protein keratine, which is currently used to provide strength in human skin?

Project 2.6g 329m/s answered this question by growing a patch of human skin that consisted of a spider silk matrix in between the dermis and epidermis. As the video below attests to, this artificial skin was even able to stop a bullet.

But what exactly about spider silk makes it so flexible and strong? The answer to this question lies in its chemical structure. Similar to Kevlar, spider silk is a combination of crystalline structures in an amorphous matrix. Its main protein is called fibroin, consisting primarily of the amino acids alanine and glycine. Fibroin has two differently structured regions that contribute to the tensile and elastic properties of silk.

Hydrogen-bonded polyalanine regions.

The first are the polyalanine regions, which give silk its strength. These are exactly what they sound like: repeating blocks of multiple alanine molecules linked together. Due to hydrogen bonding, these different blocks have strong interactions with each other and connect together in a highly ordered crystalline structure. Cross-linking individual proteins in this manner is what results in such high strength.

In the glycine-rich spiral regions, a sequence of five amino acids is repeated over and over similar to the polyalanine regions, but the twist is that the molecule takes a 180 degree turn at the end of each sequence. This results in, as the name suggests, a spiral which is so densely twisted that some types of spider silk can even stretch up to 4 times its original length.

Crystalline regions juxtaposed with amorphous regions.

Further contributing to the elasticity, the glycine-rich spiral regions comprise the amorphous areas of the silk. Somewhat less ordered polyalanine regions connect the amorphous areas to the more ordered polyalanine regions, resulting in an overall structure that is both immensely strong and surprisingly flexible.

Artificial Blood Vessels Created with Aid of Lightning

Scientists at the Texas A&M University have been looking into a way of building artificial blood vessels, and by this, artificial organs by using lightning bolts. It may be questioned how lightning could possibly help create an object, but, in fact, the high electric discharge from lightning can actually make a series of miniature tunnels or holes in materials. For example, if a block of plastic is electrically charged by gaining or losing electrons, lightning is able to permeate areas all around the plastic block. 

A tap of a nail is being used to produce a Lichtenberg figure.

 In particular, the tunnels created when lightning streaks are applied to plastic blocks are very similar to the features of the capillary system of the body. In the human body, these "tunnels" are actually arteries and vessels. When tunnels are created in this artificial manner, they are quite accurate in the sense that they are the same size as capillaries and are connected internally. Lightning is used in this process because it allows tunnels to be made throughout the block instead of simply at several places on the surface of a block. If made into artificial blood vessels, blood will be able to flow throughout the entire organ. 

In particular, a bolt of lightning allows a similar effect on a plastic block to the result if electrons were trapped inside the plastic block. When electrons travel, they create an electric current, which is what is present in the block. The current does exit the block, causing the plastic to be damaged because of the heat produced by the current. This is what ultimately creates the various tunnels. Scientists replicate this by using a Wimshurst machine or a Van de Graaf generator to create static electricity. This electricity is discharged, causing the plastic to have a pattern of charges. Called a Lichtenberg figure, the ending plastic block with tunnels was originally created in a different process in the eighteenth century. Back in this time, scientist Georg Lichtenberg utilized powdered sulfur and minium to test the process. Powdered sulfur was found to be negatively charged from the friction between it and the container it was set in. Because opposites attract, the negatively charged powdered sulfur attracted to the positive spots on the plastic block surface. The minium, a red powder, was positively charged due to friction as well, and was attracted to the negative spots. This combination allowed hidden features to be revealed in the figures and allowed a better visual to see.

In the past, prolithography, a method used to create computer chips, has been utilized to make these 3D artificial vessels. The technique of using lightning streaks is, in this way, quite efficient as the entire process only spans a couple of seconds. Using this method, artificial vessels are not only less of an expense to make but are also faster. 

However, there is also a potential disadvantage to this process.When each block of plastic is created, the tunnels present inside each are constructed in the same manner, but produce different tunnels. On the other hand, when using prolithography, all the tunnels end up exactly the same. This might be inefficient if certain systems need to be reproduced for various organs. Other scientists argue that artificial organs do not need to be exactly the same. Rather, the organs only need to have several processes in common, such as those to gather nutrients and eliminate waste from the body.

Overall, this is a revolutionary discovery in the world of tissue engineering. Because of this research, scientists will soon be able to approach using implant cells, which can be combined to create vessels, and eventually, organs. The cells would continue growing, and the plastic used would someday degrade, which does not cause harm to the body. However, the process still does involve many risks, and so, it will be implemented in animals after many years. Humans will be tested if the animal test runs successfully. 


http://news.discovery.com/tech/lightning-artificial-blood-vessels.html 
http://www.popsci.com/diy/article/2008-02/trap-lightning-block 
http://205.243.100.155/frames/lichtenbergs.html