Laboratory Research
Wound recurrence is a significant problem when dealing with chronic wounds. To prevent the recurrence of skin wounds, there must be adequate mechanical strength in the healed tissue. Understanding the impact of using various advanced wound dressings on skin healing is crucial.
In this study, we conducted tensile strength tests on partially and fully healed wounds in a rat model using an Instron 5544 testing machine. We developed an optimized test method for conducting tensile tests on healed full-thickness wounds in Sprague-Dawley rats with 8 mm full thickness defects. The procedure was then applied to identify variations in the mechanical characteristics of healed wounds treated with a novel wound covering that was 3D printed using an FDA- approved extrusion based printer with a bioink derived from human lipoaspirate.
Methods:
Full Thickness Animal Model
Four full thickness wounds were created on the dorsal side of each rat using an 8mm biopsy punch. Implant dimensions were approximately 1 cm squares. Samples were randomized into implantation sites across the animals and sites. Implants were harvested at 7 days and 14 days, and then fixed in neutral buffered solution (NBS).
Scaffold Generation
An FDA-approved extrusion 3D printer was used to print scaffolds with a bioink comprised of homogenized human adipose tissue. Lipoaspirate was homogenized and printed into 3 mm thick scaffolds that fit into 8mm defects created in the dorsal skin of the rats.
Tensile Testing using Instron 5544
1. ASTM D1708 dog bone die cutter is used to cut samples to the proper size and shape.
2. Length, width, and thickness measurements of the sample are taken in triplicate and averaged.
3.Tare load of 0.5 N is applied to the sample prior to test start.
4. Strain Rate of 0.40mm/min is entered into software, and load to failure is measured.
Results:
No adverse effects were noted during this study. Comparative graphs summarize the difference in material properties of the various test groups. Wound healing is observed during the study, and healing is accelerated by the addition of a placental scaffold.
Discussion:
No adverse effects were noted for any of the implant sites. Existing ASTM test methods have been modified and optimized to create a repeatable test for explanted full thickness rat wounds. This test can be used to determine differences in the mechanical properties of healed skin and provide a more in-depth view of the impacts these wound coverings have on the wound healing process.