Presenting Author:

Hanah Bae, M.S.

Principal Investigator:

Jolanta Topczewska, Ph.D.

Department:

Surgery

Keywords:

Tissue expansion, skin stretch, skin growth, histological analysis, isogeometric analysis, pig skin, minipig model.

Location:

Third Floor, Feinberg Pavilion, Northwestern Memorial Hospital

B177 - Basic Science

Analysis of tissue expansion using the mini pig model

Background: Tissue expansion (TE) often has high complication rates, particularly in anatomically critical regions such as the extremities with limited donor sites. Improved understanding of the biomechanics of TE to optimize true skin growth (i.e. non-reversible deformation) vs. elastic skin stretch could serve to minimize undue tissue necrosis. The aim of the present study is to differentiate the levels of skin growth vs. skin stretch at various times after a large volume expansions, as observed by skin thickness, and to correlate biomechanical growth to histologic and gene transcriptome changes during TE. Methods: Three 6-week-old minipigs were tattooed with 4 grids, with a tissue expander implanted under 2 of these grids and the contralateral side serving as an internal control (Fig 1). Expanders were filled according to the schematic represented in Figure 2. 3D photographs were obtained before and after each expansion and the day of sacrifice, both in vivo and ex vivo. Isogeometric analysis of reconstructed 3D skin grids of pigs 1 and 2 was performed to calculate skin growth and stretch. Briefly, prestrain was calculated by amount of “snap-back” of control patches after being excised. In expanded patches, the “snap-back” after skin excision determines stretch, after controlling for prestrain. Sections of skin were stained using the Russell-Movat Pentachrome Staining method. Isolating three non-consecutive sections of control and experimental skin samples, the surface area, perimeter, and length of the epidermis and dermis were measured using ImageJ. Results: Total deformation of the 4 expanded skin patches was similar. Total deformation, however, was attributable to increasing degrees of skin growth with increased latency period after expansion (p<0.0001, Fig 3). Epidermal thickness of expander samples is greater than of corresponding control in all pigs excluding pig 1 expander 2 (Fig 4). Dermal thickness in expander samples is lesser than corresponding controls in all pigs excluding pig 1 expander 1. Pigs 2 and 3 both show significantly higher epidermal and lower dermal thickness than its corresponding control after t-test analysis. Expander 1 samples have greater epidermal thickness than expander 2 samples across all 3 pigs. Conclusion: Our results, supported by t-test analysis, suggest that acute and prolonged skin stretch induce growth as observed by skin thickness. We suspect the cause of greater thickness in expander 1 samples is due to the location of expansion on the pig. Expander 1 samples are placed over the rib of the pig, leading to higher pressure on the tissue expanders and greater skin strain. We will continue analysis with the incorporation of a higher number of tissue slides for histological evaluation. We will also perform cell proliferation analysis using immunohistochemistry. The evaluation of collagen and elastic fiber architecture and gene transcriptome analyses will follow.