Fiber Reinforced Soft Composites with Tunable Extensibility, Stiffness, and Strength for Synthetic Bio-tissue Applications

2020 Fiscal Year Research-status Report

• Project/Area Number: 20K20193
• Research Institution: Hokkaido University
• Principal Investigator: キング ダニエル 北海道大学, 先端生命科学研究院, 助教 (50794583)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: Biomaterials / Tunability / Composites / Toughness / Stretchability

Outline of Annual Research Achievements

We have developed a method to incorporate wrinkled fabric structures into elastomer composites with controlled wavelength. 3D printing is used to create molds with controlled shape. Fabric is compressed between these molds, and then the edges of the fabric are immersed in melted wax. When the wax solidifies, the fabric can be removed from the mold, and the fabric maintains the imposed wrinkled structure. The wrinkled fabric is then placed into a reactor, and pre-polymer solution is injected and exposed to UV light, to synthesize the elastomer. Finally a laser cutter is used to cut the sample to the desired shape. The proposed method works well to design extensible fabric-reinforced soft materials.

These samples have been mechanically characterized, and the resulting properties are unique compared to regular soft materials. The incorporation of a wrinkled structure of fabric introduced a new transition point during tensile testing. Initial stress-strain behavior appears linearly elastic, closely matching that of the matrix. A transition strain occurs, where the composite quickly becomes stiff, and the modulus in this region approaches that of the fabric. The strain at which this transition occurs is controlled by the wrinkled fabric structure. We have demonstrated that we can cause this transition to occur at strains ranging from 5-30%. This simple method allows for fabrication of J-shaped composites, similar to natural biomaterials.

Current Status of Research Progress

2: Research has progressed on the whole more than it was originally planned.

Reason

Due to the COVID19 Situation, we have had less time available for working in the laboratory. However, our proposed technique worked successfully during initial trials, and therefore we have been able to demonstrate the primary technical requirements for this proposal within the first fiscal year.

Strategy for Future Research Activity

The future plan for this research involves two additional phases. First, we aim to demonstrate complete tunability of these materials. Specifically, we will demonstrate control over 1) initial elastic modulus, 2) the maximum modulus, and 3) the transition strain. These parameters can be tuned by changing the elastomer modulus, the fabric modulus, and the aspect ratio of the incorporated wrinkle structure, respectively. When each of these parameters can successfully be tuned, we will have a method to directly match the mechanical response of biomaterials.

The second phase is to transition to using hydrogels as the matrix rather than elastomers. It is difficult to incorporate hydrogels with rigid reinforcements, because the hydrogel will swell, changing volume depending on the environment, but the rigid reinforcement does not change volume. Making use of the wrinkled structure, our composites should be capable of swelling without damage. Furthermore, we can utilize polyampholyte or particle-based double network gels, which likely will not experience issues related to swelling.

Causes of Carryover

Due to the COVID19 situation, the students who were planning to begin the project were delayed by 6 months, which meant less money was spent, and no travel occurred.

In the next fiscal year, funding will be used to continue supporting academic research through the purchase of raw materials (such as elastomer, fabric, and wax). If possible, we will present the research next year at an international conference, because we believe the research will be of widespread interest. Current methods of characterization are sufficient, and therefore no new equipment is required. Current funding will be used to purchase consumable materials for existing equipment (such as ink for 3D printing of substrates and molds). If applicable, funding may be used to support open-access publication costs.