PSI - Issue 52

Dita Puspitasari et al. / Procedia Structural Integrity 52 (2024) 410–417 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

412

3

the maceration method. The leaves were soaked in salt solution and dried at room temperature without being exposed to direct sunlight then ground and sieved once they dry to obtain a fine powder. The active compound from MOL is extracted by maceration method by immersing the powder in methanol. The liquid is then filtered through filter paper to discard solid residue. The filter is evaporated on a rotary evaporator until the extract is thick and then dried in a freeze-dryer. The MOL extract is stored in the freezer until use. Sericin hydrogel was fabricated by using a physical crosslinking method to avoid external chemical cross-linker agents that probably affect the toxicity of hydrogel (Deligkaris et al. (2010) and Ahmadi et al. (2015)). PVA, sericin, and MOL extract were mixed in 2 different concentrations. The solution was then poured and molded in the 24-well plate (10 mm diameter and 8 mm height per sample) and went through the freezing-thawing (F/T) process for four cycles. Each cycle consists of storing the solution in the freezer (-20  C) for 20 hours and at room temperature (25  C) for four hours. 2.2. SEM The surface and cross-section morphology structure of the hydrogels were observed under a scanning electron microscope (SEM JEOL-IT300). The specimens were freeze-dried and coated with gold sputtering before the test. This test resulted in the 2D porosity of each sample and was evaluated further by Image-J software (Schneider et al. (2012)). 2.3. Micro-CT Simulation The 3D architecture of the sample was obtained by using Bruker micro-CT Scanner SkyScan 1173 High-Energy device with high resolution scanning at 8.85 um pixels. The 2D image of each layer was constructed from the Bruker software and then reconstructed with Slicer software. At last, the data proceeded with Abaqus software to simulate compression load to the scaffold in the z- axis. The connection between thickness and Young’s Modulus was to be obtained to conclude the hyper-elastic and viscoelastic properties of the material. 2.4. Compression Test The compression test was operated on Instron 5982 by applying a 10kN load with a 5mm/min rate to the dried hydrogel until the samples were broken. The hydrogel sample is prepared into a cylindrical shape with approximately 10 mm diameter and ± 8 mm height. The test is carried out at room temperature and repeated 3 times for each sample. The formula below is used to obtain the maximum stress of each sample. = ( ) ( 2 ) 2.5. Compression Simulation The simulation used a 2D model to simplify the high porosity hydrogel sample. The size of the 2D model took the front view or cross-section of the sample. Hydrogel pore size data (minimum, maximum, and average) was used to create a 2D model and coded with Matlab. The porous 2D model was processed with CAD software to be simulated. The resulting data from the compression test was fitted for the hyperelastic material model constants. We employed Abaqus CAE as finite element software. Using a linear regression method, the Ogden model was selected for the curve fitting. The compressive load simulation was conducted on a porous 2D model with boundary conditions: no movement in all translational and rotational directions. The compressive load was simulated by providing a displacement on the negative y-axis equal to the maximum strain value on the compressive test results. The surface and cross section morphology of the hydrogels was shown in Fig. 1 and Tabel 1. A 10% indicates the concentration of total substances dissolved in aquadest. The 50S50P-05 indicates that the concentration of the sericin:PVA is 50:50 and then added 0.5% of MOL extract. Lastly, 75S25P-05 indicates the concentration of the sericin:PVA is 75:25 and 0.5% of MOL added. Both concentrations resulted in the porous structure of hydrogel which indicates the freezing-thawing process was successful. Pores are very important in scaffold architecture as they influence transport within the tissue. Both concentrations resulted in porous structures from the surface up to the inner part of the hydrogel which indicates the freezing-thawing process also succeeded. It is reported that 50-150 μ m pore size can facilitate optimal vascularization in cell migration (Garcia et al. (2022)). The porosity and pore size on the surface of the scaffold is smaller than in the cross-section area due to pressure applied during the freeze-dried process as the sample prepared before tested on SEM. 3. Results and Discussion 3.1. SEM