Tensile Tests of a Regenerative Medical Product - Cultured Epidermis

Various research institutes and businesses have been developing regenerative medical products*1 in the recent years in order to facilitate the spread of regenerative medicine. Since quality control is crucial for regenerative medical products, various material[1][2] has been issued by the Pharmaceuticals and Medical Devices Agency (PMDA) which conducts reviews. Although the issued material calls for dynamic evaluations in addition to biological evaluations, they do not include a description of specific evaluation methods. Dynamic evaluation was conducted upon transplanting iPS cell-derived retinal pigment epithelial cell sheets, but the evaluation method was no more than qualitative, consisting of only checks for damage at the time of graft preparation.[3]

However, quantitative evaluations will likely be necessary for cell sheets[5] which require mechanical strength such as cultured skin sheets[4] and myocardial cell sheets. Furthermore, unlike the current regenerative medical products using autologous cells, it is possible that regenerative medical products using allogeneic cells[6], which are expected to become mainstream in the future, will be required to observe specification tests based on quantitative quality standards.

In this research, tensile tests were performed using cultured epidermis, which is a regenerative medical product, and milk membrane imitating cultured epidermis (collected from the surface of hot milk) as an example of a quantitative evaluation of a material's mechanical properties.

*1Regenerative medical products are items created by processing human or animal cells for reconstructing, repairing, or forming body structures and functions or for treating or preventing diseases.” D.Hiramaru, Y Kamei.

Measurement System

Tables 1 and 2 respectively, show the make-up of the system and the specimen data. Figure 1 illustrates a cultured epidermis specimen. The experiments were implemented using milk membrane imitating cultured epidermis (dummy specimen) and two varieties of research-purpose cultured epidermis (A and B)*2 with varying levels of firmness, developed through the same process used for autologous cultured epidermis JACE®.

The construction of the specimens comprised a small number of layers of epidermal cells, while the cultured epidermis specimens’ thickness was below 100 μm. Specimens were supple and were prevented from drying out by being soaked in preservative solution. As such, it was necessary to mount and measure the specimens at a rapid pace during the tensile tests to avoid them drying out.

Figure 2 shows an image of the test. Cylinder shaped sponges were employed for the fixture, as specimens can be wrapped around these to be fixed in place for the test without the risk of damage. The test conditions can be seen in Table 3. The test was fixed at a low speed, within the speed range at which specimens are known to keep their moisture.

*2 Provided by Japan Tissue Engineering Co., Ltd.

Table 1. System Composition

. .
Testing system EZ-LX
Load cell 10 N
Test fixture Tensile test fixture for cultured epidermis

Table 2. Specimen Information

. .
Dimensions 50 mm × 100 mm
Thickness of less than 100 μm
Types Milk membrane
Cultured epidermis A
Cultured epidermis B

Table 3. Test Conditions

. .
Test speed 20 mm/min
Test environment Room temperature

Cultured Epidermis

Figure 1. Cultured Epidermis

Picture of the Test (Milk Membrane)

Figure 2. Picture of the Test (Milk Membrane)

Test Results

The load-displacement curves can be seen in Figure 3, while Table 4 shows the greatest load applied to each material and the slope of the linear section of the curves. The maximum load applied to a material demonstrates the material’s strength, thus, a higher figure indicates a more sturdy material.

Load - Displacement Curves

Figure 3. Load - Displacement Curves

Table 4. Test Results (Average)

Specimen Maximum load
[mN]
Slope of the linear portion
[mN/mm]
Milk membrane 95 10.2
Cultured epidermis A 579 13.1
Cultured epidermis B 237 12.6

The slope of the linear section of the curve shows compliance, and therefore, the suppleness of each material. In relation to the greatest load applied, a distinct variance between cultured epidermis A and B could be observed. However, while some deviation was seen on the slopes of the linear portion of the curves on the graph, there was no clear difference identified between the cultured epidermis specimens.

Conclusion

Within this study, tensile tests were carried out using cultured epidermis, a regenerative medical product, and milk membrane, to demonstrate a quantitative evaluation of a material's mechanical properties. The tests were fruitful and confirmed the difference between two varieties of cultured epidermis specimens through the use of a recently developed tension test fixture for cultured epidermis.

This evaluation method allows for assessments of the mechanical properties of regenerative medical products and is appropriate for the development and appraisal of regenerative medical products.

References and Further Reading

[1] PMDA (2016), "Technical Guidance for the Quality of Regenerative Medical Products (Human Cell-Processed Products) and Implementation of Non-Clinical and Clinical Tests", Notification issued by the Ministry of Health, Labor and Welfare of Japan

[2] PMDA (2012), "Quality and Safety Assurance of Cell-Processed Medical and Pharmaceutical Products", PFSB Notification No. 0907002 through 0907006

[3] PMDA (2013), "Evaluation Index for Autologous iPS Cell-Derived Retinal Pigment Epithelial Cells", PFSB/ELD/OMDE Notification No. 0529001

[4] V. Trottier (2008), "IFATS Collection: Using Human Adipose Derived Stem/Stromal Cells for the Production of New Skin Substitutes", pp. 2713-2723, Vol. 26, Issue 10, October, STEM CELLS

[5] Satsuki Fukushima (2014), "Developing myocardial regeneration therapy using induced pluripotent stem cells of allogeneic origin", pp. 199-205, Vol. 21, No. 2, Organ Biology

[6] N. Nakatsuji (2008), "HLA-haplotype banking and iPS cells", Vol. 26, No. 7, July, Nature Biotechnology

This information has been sourced, reviewed and adapted from materials provided by Shimadzu Scientific Instruments.

For more information on this source, please visit Shimadzu Scientific Instruments.

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