Japan Advanced Institute of Science and Technology

 Research on biomaterials is an interdisciplinary field that integrates subjects such as chemistry, biology, physics, and material engineering.
In our laboratory, we intend to expand the scope of research subjects in order to develop novel biomaterials, which can contribute to the biomedical field. Hereunder, I introduce some thesis topics undertaken in our laboratory.

Use of polyampholytes as a biomaterial

Carboxyl groups were introduced into e-Poly-L-lysine

 Water constitutes 60% of the human body. Chemical reactions in living systems occur in aqueous solutions. Biopolymers such as proteins acquire unique and important characteristics in aqueous solutions.
Recent studies on polyampholytes, polymers with both positively and negatively charged groups, have focused on protein behavior, using polyampholytes as a model for proteins. In our laboratory, we are investigating the unique properties of polyampholytes and developing new biomaterials.

Cryoprotective properties of polyampholytes

 Results of our research showed that several kinds of polyampholytes have a cryoprotective effect on cells in solution. This interesting phenomenon is characteristic of polymers with high electron charge, especially polyampholytes (Figures 1 and 2. Matsumura K. et al., Biomaterials 2009). Successful cryopreservation of many cell types, including human mesenchymal stem cells and induced pluripotent stem (iPS) cells, has been achieved (Matsumura K. et al., Cell Transplantation 2010; Matsumura K. et al., Cryobiology 2011).

Cell viabilities after cryopreservation with PLL derivatives
Residual water ratios at low temperature measured by solid-state NMR

 From the cryobiological viewpoint, cells are killed because of the damage caused by the intracellular crystallization of water during freezing. Therefore, a membrane-permeable chemical such as dimethyl sulfoxide is usually added in order to cryopreserve the cells. However, the cryoprotective effect of polymers such as polyampholytes that do not penetrate the membrane cannot be explained on the basis of the current knowledge in cryobiology. In order to understand the underlying mechanisms, we examine the interaction between the polymer and the polymer, the polymer and water, and the polymer and salts at low temperatures by using solid-state nuclear magnetic resonance (NMR). By using this method, we attempt to understand the mechanisms underlying the effects of polyampholytes on the extracellular environment during freezing.

 The residual water content of several aqueous polymer solutions during freezing is shown in Figure 3. The polyampholyte (carboxylated poly-L-lysine) did not have the highest residual water content at low temperatures. This observation suggests that the residual water content during freezing might not explain its cryoprotective properties. Next, we used 23Na-NMR to examine the interaction between the polymer chains and sodium ions at low temperatures. The results showed that the sodium signal in the polyampholyte solution decreased at low temperatures; this observation suggests that the polyampholyte chains trap the sodium ions and restrain their movement at low temperatures. This phenomenon might decrease cell damage caused by an abrupt increase in osmotic pressure during freezing. In this manner, we are attempting to uncover the novel mechanisms underlying cryoprotective properties, from the viewpoint of materials science.

Application of polyampholytes as scaffold material

 The application of biomaterials has extended from artificial organ development to regenerative medicine. Many studies are being performed on the control of proliferation and differentiation of stem cells when using various three-dimensional culture scaffolds by mimicking the biological environment. For example, we are attempting to develop a novel cell culture scaffold with cryoprotective properties by using polyampholyte hydrogel.

Liquid-liquid phase separation occurs at carboxylation ratio between about 40 and 80 %

Elucidation of phase separation and its application

 Carboxylated poly-L-lysine compounds (polyampholytes) exhibit lower critical solution temperature (LCST)-type phase separation to an extent that depends on their carboxylation ratios. Phase separation responds to changes in polymer and salt concentrations and exhibits temperature responsibility. A solution of this polyamplolyte exists in a single phase at high concentrations, but separates into 2 liquid-liquid phases on dilution with water. Because this separation disappears on the addition of salt, the phase separation could be ascribed to the polyion complex of the side chains of the polyampholyte (Figure 4). We are attempting to elucidate this phenomenon and apply it to novel biomaterials such as hydrogels and nano or micro particles.

Development of biomaterials compatible with living systems

 We also perform basic and applied research on materials compatible with living systems; this research is aimed at restoring the function of living systems in tissue engineering. In particular, we are attempting to develop articular cartilage by using hydrogels with high mechanical properties (Figure 5). The research performed in our laboratory is aimed at combining chemistry and biology through the study of polymer chemistry and at developing materials that can control the function of living systems.

Artificial articular cartilage

 This laboratory was established in 2011.
We are looking forward to working with energetic and highly motivated participants.
Let’s enjoy studying the interesting world of biomaterials!