Better Softness丨Comparison of physical properties between SIS material and bovine dermal material

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In this paper, the physical properties of porcine small intestinal submucosa matrix material (SIS) and commercially available acellular bovine dermal matrix (ADM) were compared and investigated, including morphology, roughness, hydrophilicity and softness. Thus, the physical properties of two different tissue-derived collagen biomaterials can be more comprehensively grasped, providing theoretical basis for the selection of clinical application of the products. The paper included in the "Material Sciences"  in July 2017. The following are excerpts.

Comparative analysis of morphology

The pore size and fiber structure of the two material samples were observed by scanning electron microscopy. The samples were dried at 40℃ for 24 h, sprayed with gold by ion sputter coater, and observed by scanning electron microscope.

The surface and cross-sectional morphologies of the two materials are shown in Fig 1. It can be seen from the figure that collagen fibers are arranged in a crisscross pattern on the surface of the two SIS materials. The fibers on the surface of the material are obvious, the fiber diameter is about 1 μm, the collagen fibers are well preserved, and the length is more than 50 μm. The communication hole penetrates into the material. The diameter of SIS fibers can be seen from the cross-section figure that both SIS materials have a layered structure with uniform distribution, but the VIDASIS layer gap is larger, which is more conducive to the entry and growth of new cells. The surface of ADM material is relatively flat and dense, with few connected pores on the surface. Many isolated lumps in the cross-section, which are the cross-section of extracellular matrix fibers, with many internal connected pores. This material should be a stack of fibers in different directions made.

In general, the two materials have connected pores, but the surface of ADM is dense and flat, with a micron-scale sheet structure with a length of more than 100 μm, which limits the ingrowth of cells. SIS has better connectivity and easier cell ingrowth.

Figure 1: SEM images of the two materials. A: SIS surface; B: ADM surface; C: SIS side; d: ADM side

Comparative analysis of roughness

The roughness of the two sets of materials was examined using a FastScan Bio atomic force microscope from Bruker Analytical Instruments, Germany. The scanning probe tip was made of Ф0.5 mm high-purity tungsten, the bias voltage between tip and sample was 80 mV, and the scanning range was 1750 nm x 1750 nm, and the images were processed by Nano-ScopeAnalysis software.

Roughness analysis by atomic force microscope, the results are shown in Table 2. The roughness of SIS material is smaller, and the roughness of ADM is significantly larger than that of SIS material. The Rq and Ra values of ADM are 224 nm and 185 nm, respectively, while the roughness of SIS material is below 100 nm. Comparing two materials,The surface of SIS is relatively flat, which is easier for cell migration and repair, thereby reducing the risk of adhesion.

Table 2. Results of roughness analysis by atomic force microscope

Hydrophilic comparative analysis

The two dried samples were placed on a cover glass, a drop of water (about 2μL) was dropped on the surface of the material, and the contact angle between the water droplet and the material was measured with a video optical contact angle meter to measure the surface energy of the material.

The water contact angle is an important measure of the wettability relationship between the reactive species and the liquid. The smaller the water contact angle, the better the hydrophilicity of the material. As shown in Figure 3: the water contact angle of the SIS product is less than 90°, indicating that the SIS material has good hydrophilicity. The water contact angle of ADM is greater than 90°, and the material is hydrophobic. The SIS material has a good hydrophilic effect, which is conducive to body fluid infiltration and vascularization, and is conducive to the growth of cells into the material, and gradually fills the material with new cells, promotes the tissue repair process, and accelerates the repair and healing of the diseased area.

Figure 3: Hydrophilic Angle test results of the two samples

The softness test of the two materials is carried out separately by the softness tester. As shown in Figure 4, under dry conditions, the softness of SIS is less than 5000 mN, and the softness of ADM material is more than 7000 mN. The results show that SIS has better softness under dry condition.

Then, the samples of the two materials were put into the physiological saline for 60 seconds to hydrate, and the softness test in the wet state was carried out. As can be seen in Figure 5: under wet conditions, the SIS sample is more compliant and fit than ADM sample, while the ADM sample is stiff and warped with poor fit. In clinical application, the softness of the product determines the compliance and adhesion between the product and the affected area, and affects the convenience of the doctor's surgical operation. Especially in the oral field, products with high softness are easier to implant in the affected area and more effective.

Figure 4: Softness test results of the two samples under dry condition

Figure 5: Comparison of softness test of two samples under wet condition

Through the above comparative analysis of morphology, roughness, hydrophilicity and softness, it can be concluded that the physical properties of SIS material are better than that of bovine dermal material (ADM), and it is more suitable for implantation in clinical surgery.

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Figure: SIS material Oral Biological Graft

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