Smart Soft Materials As Innovative and Advanced Materials
Smart Soft Materials As Innovative and Advanced Materials
  • Professor Kim Youn-soo (MSE)
  • 승인 2018.05.30 20:46
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▲The structure and usage of hydrogels, a typical type of soft material
▲The structure and usage of hydrogels, a typical type of soft material

There are various materials around us, having different characteristics—hard or soft, elastic or brittle, rough or smooth. We use the materials with different characteristics appropriately to make our lives rich and convenient. Hard and brittle materials, such as metals and ceramics, are called “hard materials”, while comparatively soft and waxy materials are labeled “soft materials”. We are surrounded by soft materials such as textiles, paper, silicon, rubber, and jelly.

The term, ‘soft material’ was first used by Pierre-Gilles de Gennes, the 1992 Nobel Prize winner in Physics. It is a generic term for all soft things, such as polymers, liquid crystals, colloids, surfactants, biological membranes, and biomolecules. The materials have a large internal degree of freedom, which is the ability to rotate its molecules and change its structure freely, granting them such softness. Polymers are good examples, for they can change their form with molecule movement.

We can often see daily necessities labeled as gels. Cosmetics, such as shampoo, shaving cream, toothpaste, cleansing, and mask packs and food, such as jelly are examples of gels in life. They are all soft materials. In the case of cosmetics, the fluidity of the material is appropriately controlled so it doesn’t trickle down when applied. Also, the property of absorbing and retaining large amounts of water is good for moisturizing the skin. If active components are incorporated, it is possible to release the fragrance or medical components gradually. These are great examples of how gels and its properties are being used in our daily lives.

These soft substances that contain large amounts of water are called hydrogels. They are polymer-based soft materials in which hydrophilic polymers forms three-dimensional networks. Numerous water molecules are hydrogen bonded to the network, consisting 90 percent of the whole gel. Hydrogels are environment-friendly and biocompatible, making them useful materials. Studies on application to various fields, such as cell and tissue cultivation, contact lenses and medical devices have been actively conducted throughout the world. In particular, hydrogels made of stimuli-responsive polymers can change from hydrophilic to hydrophobic while changing its volume according to the temperature, light or other factors. Since stimuli-responsive hydrogels exhibit dynamic changes in contraction and expansion according to the external environment, researches to use hydrogels as ‘actuators’ are being conducted actively. Polymer-based actuators are soft and elastic, unlike ceramic or metal, so they are anticipated to function as artificial muscles.

Soft tissues forming living organisms are those in which macromolecular substances, such as proteins and polysaccharides, are crosslinked to form a three-dimensional network structure, and water (75~78%) is taken in there. Gels are an important form of substance present in every part of the body, such as cells and tissues. Gels consisting the organism is flexible, supple and wet, being resilient to impact and immune to damage. Furthermore, it transfers energy and information, and when the environment changes, it deforms accordingly and shifts to another state, autonomously constructing functions suitable for the environment.

Thus, hydrogel actuators have excellent biocompatibility, for the body itself is highly similar to hydrogels, being mostly constituted of water. Also, since the ability to change its volume with respect to changes in external environment is very similar to behavior of muscles, it is a candidate for artificial muscles. Furthermore, stimulus-responsive hydrogel actuators are intelligent materials that are lightweight and moldable, which is a trait that traditional actuator materials lack. Research in this area is in a very early stage, with many tasks to be challenged.

Japan’s laboratories are a pyramid form composed of a professor, who is the owner of the laboratory, associated professor, lecturer, and assistant professor. Therefore, you will receive more guidance from your assistant or associated professors, rather than the professor. So, it is able to research while being guided by a relatively young teacher in close proximity. The doctoral course in Japan does not have coursework, it does not require listening to classes and earning credits, allowing relatively fast graduation. The doctoral course requires three years, basically. However, there are graduation requirements that needs to be fulfilled. In my case, the Department of Chemistry and Biotechnology of the University of Tokyo required at least two papers or one big paper, such as Nature or Science. It was not an easy requirement for an international student starting from a doctoral program to meet, like me.

I started as a professor on last year Nov. 1, and I have been here for six months now. First, POSTECH attentively supports newly appointed professors like myself to help us accommodate quickly. Personally, I was able to settle quickly thanks to the support of the kind colleague professors. POSTECH has a great environment to research, just like its title, ‘research-oriented university’. I realized that because of this excellent environment, there are a lot of exceptional professors who are doing fine research with a competitive edge. From this semester, I am teaching a graduate course called “Polymer Gels”. I was impressed by the enthusiastic attitude of the students. The class is pleansant due to their active questioning and feedback.

I hope that students can savor their moment, trying things only students can do. The twenties are a period of freedom and endless possibilities, and you can improve yourself greatly. Mistakes and failures can be overcome with youth, and because students are supposed to learn from their mistakes, there is no need to fear failures. Just like soft materials, resilient to external stress due to its large internal degree of freedom.
The key element in research is curiosity. Be even curious about everyday phenomenon and pursue it until the end. You will become an outstanding scientist representing POSTECH and Korea. I look forward to it.

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