Hong Kong Polytechnic Yi Jielun Macromol Mater Eng: Application of 3D Printing Negative Poisson’s Ratio Structure in the Treatment of Hypertrophic Scar

In different fields of research, how to fit the design to the human body is an urgent challenge. Different designs such as wearable sensors or functional clothing need to fit snugly against the skin to be effective. For decades, pressure clothing has been an important treatment method for the initial control of hypertrophic scar treatment, but relying on pressure clothing alone does not provide stable pressure on the scar, thus affecting the treatment effect.exist
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Above, the therapist uses polyethylene foam to fill in the hollows of the body to achieve an ideal pressure level. Although polyethylene foam is a relatively soft material, to cope with a large degree of skin stretching and deformation on the joints, polyethylene foam does not fit on the skin, which affects the transmission of pressure.

The negative Poisson’s ratio structure will form a sympathetic curved surface instead of a saddle-shaped curved surface with a traditional structure when it is bent out of plane (Fig. 1).To improve pressure therapy for hypertrophic scar treatment, this paper proposes fused deposition modeling3D printingThe negative Poisson’s ratio structure replaces the traditional polyethylene foam filling to stabilize the pressure level of the pressure suit on the scar during joint flexion and extension (Figure 2).

Recently, Dr. Yi Jielun from Hong Kong Polytechnic University published a research article entitled “3D Printing Auxetic Architectures for Hypertrophic Scar Therapy” in Macromolecular Materials and Engineering. This paper analyzes the physical properties including shape plasticity and structural changes of two traditional negative Poisson’s ratio structures (re-entrant and double-arrowhead) in the out-of-plane direction when a spherical force is applied in the out-of-plane direction. In-depth analysis and discussion. The designed finite element model showed acceptable agreement with the experimental data. The data show that the interior angle of negative Poisson’s ratio structures plays an important role in shape plasticity.

At the same time, in order to understand the change of the pressure transmission of the 3D printing negative Poisson’s ratio structural filling designed in this paper, a wear test was carried out to compare the difference between the traditional polyethylene foam filling and the new design. The results revealed that their design helps maintain a stable pressure level between wrist flexion and extension, thereby promoting scar maturation and recovery.

Key points of this article

In this paper, the shape plasticity and structural change of negative Poisson’s ratio structures in the out-of-plane direction are systematically analyzed for the first time. Multiple repeating negative Poisson’s ratio structures are stressed out-of-plane, while loads and displacements are recorded to determine the shape plasticity of the different structures. The data reveal that double arrowheads may have better shape plasticity than concave structures and are more suitable for fillers treated with pressure.
In addition, in the finite element analysis, the change of the structure with negative Poisson’s ratio under pressure was also analyzed, and the characteristics based on the change of the interior angle were divided into four stages. The shape plasticity of the structure is particularly important.

Afterwards, a volunteer was invited to conduct a wear test to compare the difference in pressure transmission between traditional polyethylene foam padding and the new design. First, the pressure glove is worn on the wrist, the different padding is placed between the back of the wrist and the pressure glove, and the pressure sensor is placed between the skin and the padding. During the experiment, the wrist will be flexed and extended continuously and the pressure changes in different postures will be measured at the same time.
The shape plasticity and structural changes in the out-of-plane direction of the structures with negative Poisson’s ratio quantified herein not only contribute to the development of treatments for hypertrophic scars, but also to any type of
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Devices, such as human monitoring sensors.

Finite Element Analysis of Influence of Inner Angle of Concave Structure on Out-of-Plane Bending

Through finite element analysis, they showed the effect of changing the interior angle of the concave structure on the bending in the out-of-plane direction, the minimum and maximum curvatures were estimated by Heron’s formula and their total curvature was calculated. As the inner angle increases, the total curvature decreases gradually and turns from a sympathetic surface to a saddle-shaped curved surface structure.

Shape plasticity of concave and double-arrow structures in out-of-plane directions

Through experimental analysis, they demonstrated the shape plasticity of the concave and double-arrow structures with different interior angle angles, and among the two different structures, the samples with smaller interior angle angles also exhibited better shape plasticity. Since the volumes of the 60oRE and 30oDAH samples are similar, when directly comparing the force-displacement curve of the polyethylene foam with the conventional one, the force-displacement of the double-arrow structure sample at 10 μm is about 60% and 40% lower than that of the concave structure and the polyethylene foam, respectively; at 25 The micrometer displacement is about 27% lower.