(LR-001) Characterization of Amniotic Membranes for Clinical Wound and Wrap Applications

Co-Author(s):

Alison Ingraldi, BS – Research Scientist I, Axolotl Biologix Inc; Zsuzsi Kovacs, MS – Research Scientist II, Axolotl Biologix Inc; Aaron Tabor, PhD – VP of Clinical Operations, Axolotl Biologix Inc

Introduction: Amniotic membrane (AM), the innermost placental layer has unique properties that allow for a multitude of clinical applications such as wound care and tissue wrap in surgical settings. The Dual Layer Graft† AM was analyzed for mechanical properties, porosity, antimicrobial activity and cellular biocompatibility. By understanding these characteristics, clinicians can be more effective in their application.


Methods: Mechanical Characterization, via a hybrid rheometer: hydrated (PBS) samples were tested for shear and compressive modulus (stiffness) at room and physiological temperatures. Additionally, tensile modulus, tensile strength, and suture strength were tested at room temperature for both dry and hydrated samples. Porosity: through pores were measured by capillary flow porometry. Blind/open pores and total porosity are measured by mercury intrusion and skeletal density. Antimicrobial properties are measured by modified Kirby-Bauer disk diffusion assays against Candida albicans, Escherichia coli, and Staphylococcus epidermidis and antimicrobial peptides are quantified by ELISA. Proteomics is characterized by initial tryptic digestion followed by LC/MS analysis. Cellular compatibility is assessed through culturing human dermal fibroblasts and endothelial cells on AM.

Results: Shear and compressive modulus varied between donors (shear modulus 5-25 KPa, compressive modulus 200-600 KPa). Tensile modulus demonstrated a ~5x-fold decrease in stiffness upon hydration with PBS (110 MPa dry vs. 18 MPa hydrated). Ultimate tensile strength ranged from 1.2 MPa to 2.8 MPa between donors. Ultimate Suture Strength (USS), the AM stress resistance to suture detachment calculated was 5.6 MPa. Table I summarizes the pull force of various suture sizes from the AM. For example, the force required to detach a 2-0 suture from the hydrated AM was 0.13N per single layer. Lastly, there were no measurable through pores in the AM.
Table 1: Ultimate Suture Strength (USS) determination and suture force based on suture size.

Suture Size (USP)	Suture Diameter (mm)	Suture area (mm2)	USS (MPa)	Suture Force (N)
6-0	0.07	0.005	5.6	0.03
5-0	0.10	0.008	5.6	0.04
4-0	0.15	0.012	5.6	0.07
3-0	0.20	0.016	5.6	0.09
2-0	0.30	0.024	5.6	0.13
0	0.35	0.027	5.6	0.15

Discussion: Some mechanical properties (shear modulus, compressive modulus and tensile strength) varied between donors: however, the values did not change significantly between the tested temperatures. Ultimate Suture Strength will be compared to skin substitutes and comparable products. The AM is not decellularized so an absence of through pores was an expected finding. Antimicrobial characterization will be explored using the described method and data will be included in the final poster publication.

Trademarked Items: † DualGraft, Axolotl Biologix, Inc., Flagstaff, AZ

References: