Mechanical and Histological Characteristics of Phasix™ ST Mesh in a Porcine Model of Hernia Repair

Figures & data

Figure 1. Scanning electron micrograph (SEM) of Phasix™ ST Mesh (40× magnification; scale bar = 200 µm). Phasix™ ST Mesh is comprised of fully resorbable poly-4-hydroxybutyrate (P4HB) fibers co-knitted with polyglycolic acid (PGA) and coated with a resorbable hydrogel layer on the visceral side of the mesh. The hydrogel layer is comprised of sodium hyaluronate (HA), carboxymethylcellulose (CMC), and polyethylene glycol (PEG).

Figure 2. Simulated hernia defects surgically created in the midline of Yucatan pigs: (A) 4 cm defect group, unclosed; (B) 8 cm defect group, unclosed; (C) 8 cm buttress group prior to closure; and (D) 8 cm buttress group after closure.

Figure 3. 4 cm unclosed repair immediately after defect closure and fixation of mesh using SorbaFix™ Absorbable Fixation System fasteners in a double crown technique.

Table 1. Morphometric evaluation of defect area, length, and width demonstrating successful creation of consistent surgical defects.

Mean ± Std Dev	4cm defect		8cm defect		8cm buttress
	48 weeks	72 weeks	48 weeks	72 weeks	48 weeks	72 weeks
Defect Area (cm^2)	11.1 ± 2.1	10.2 ± 1.7	35.3 ± 5.2	27.5 ± 8.2	35.2 ± 7.4	29.4 ± 1.9
Length (cm)	4.9 ± 0.8	4.7 ± 0.3	9.0 ± 0.6	8.2 ± 0.7	8.6 ± 1.0	8.5 ± 0.7
Width (cm)	3.1 ± 0.3	3.0 ± 0.4	5.4 ± 0.4	4.3 ± 1.0	5.6 ± 0.7	4.9 ± 0.5

Figure 4. Phasix™ ST Mesh at 48 weeks (top row) and 72 weeks (bottom row) postimplantation. Inset photos depict Phasix™ ST Mesh after collagenase digestion of adherent native tissue. Phasix™ ST Mesh remained intact at 48 weeks, but only low molecular weight fragments remained at 72 weeks.

Figure 5. Ball burst strengths of Phasix™ ST Mesh-repaired sites (mean ± standard error of the mean). Dashed line represents Deeken-Matthews recommended 72 N strength threshold [13] (*p < 0.05 relative to T₀).

Figure 6. Molecular weight (mean ± standard deviation) of explanted Phasix™ ST Mesh compared to non-implanted (T₀) samples (*p < 0.05 relative to T₀).

Figure 7. Hematoxylin & Eosin (H&E), Masson’s Trichrome (MT), and Picrosirius Red (PSR) stained slides of Phasix™ ST Mesh-repaired sites at 48 and 72 weeks postimplantation, taken from the center of the defect (scale bar = 500 µm). For a given defect size and time point depicted in a single row, all three images were taken from the same tissue block derived from a single animal. Local tissue response was histologically comparable between groups, regardless of defect type/length and time point. H&E slides show minimal mesh-associated inflammation, consisting of macrophages, lymphocytes, and giant cells, with few eosinophils. MT slides demonstrate mature and well organized fibrotic (collagen) and fibrovascular tissue around and within all segments of the Phasix™ ST Mesh interstices, including the segment of the mesh overlying the defect. PSR slides depict predominantly mature, type I collagen (red-orange) with minimal immature, type III collagen (green).

Figure 8. Hematoxylin & Eosin (H&E) stained slides obtained to the left, center, and right of the 8 cm unclosed defect site (72 weeks postimplantation). The left, center, and right locations denoted in the top panel indicate the approximate location of the slides displayed in the bottom panel; A = Mesh/Peritoneal Surface, B = Preperitoneal Fat and Abd Muscle = Abdominal Muscle. Comparable mature collagen/fibrovascular tissue was observed around and within the Phasix™ ST Mesh interstices, including the segment of mesh overlying the defect.

Table 2. Median scores for key histomorphological parameters: Inflammation, fibrosis, neovascularization, and collagen morphology shown for all three defect types and both time points.

Median score	4cm defect						8cm defect						8cm buttress
	48 weeks			72 weeks			48 weeks			72 weeks			48 weeks			72 weeks
	L	C	R	L	C	R	L	C	R	L	C	R	L	C	R	L	C	R
Inflammation	1.0	1.0	1.0	1.0	1.0	1.0	1.0	1.0	1.0	1.0	1.0	1.0	1.0	1.0	1.0	1.0	1.0	1.0
Fibrosis	1.0	1.0	1.0	2.0	2.0	2.0	1.0	1.0	1.0	2.0	1.0	1.5	1.0	1.0	1.0	2.0	2.0	2.0
Neovascularization	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0
Collagen Morphology	3.0	3.0	3.0	3.0	3.0	3.0	3.0	3.0	3.0	3.0	3.0	3.0	3.0	3.0	3.0	3.0	3.0	3.0

L: evaluated to the left of the defect, C: evaluated in the central area overlying the defect, and R: evaluated to the right of the defect.

Table 3. Comparison of measured ball burst and molecular weight data with predicted mesh and host tissue contributions.

Time (Weeks)	Defect type	Measured ball burst strength (N)	Mw (kDa)	Predicted mesh contribution to burst strength N (%)	Predicted host tissue contribution to burst strength N (%)
0	Unimplanted mesh only	204.6	336	220 (100)	0 (0)
48	4 cm unclosed defect	142.4	47	12 (8.4)	130.4 (91.6)
48	8 cm unclosed defect	142.3	45	10 (7.0)	132.3 (93.0)
48	8 cm buttress	168.8	47	12 (7.1)	156.8 (92.9)
72	4 cm unclosed defect	110.0	20	0 (0)	110.0 (100)
72	8 cm unclosed defect	138.6	20	0 (0)	138.6 (100)
72	8 cm buttress	160.6	20	0 (0)	160.6 (100)

Deeken CR, Abdo MS, Frisella MM, Matthews BD. Physicomechanical evaluation of absorbable and nonabsorbable barrier composite meshes for laparoscopic ventral hernia repair. Surg Endosc. 2011;25(5):1541–1552. doi:https://doi.org/10.1007/s00464-010-1432-0.

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