Combining Allograft Adipose and Fascia Matrix As an Off-the-Shelf Scaffold for Adipose Tissue Engineering Stimulates Angiogenic Responses and Activates a Proregenerative Macrophage Profile in a Rodent Model

Objective: Bioscaffolds for treating soft tissue defects have limitations. As a bioscaffold, allograft adipose matrix (AAM) is a promising approach to treat soft tissue defects. Previously, we revealed that combining superficial adipose fascia matrix with AAM, components of the hypodermis layer of adipose tissue, improved volume retention, adipogenesis, and angiogenesis in rats 8 weeks after it was implanted compared with AAM alone. Here, we modified the fascia matrix and AAM preparation, examined the tissue over 18 weeks, and conducted a deeper molecular investigation. We hypothesized that the combined matrices created a better scaffold by triggering angiogenesis and proregenerative signals. Methods: Human AAM and fascia matrix were implanted (4 [1 mL] implants/animal) into the dorsum of male Fischer rats (6-8 weeks old; similar to 140 g) randomly as follows: AAM, fascia, 75/25 (AAM/fascia), 50/50, and 50/50 + hyaluronic acid (HA; to improve extrudability) (n = 4/group/time point). After 72 hours, as well as 1, 3, 6, 9, 12, and 18 weeks, graft retention was assessed by a gas pycnometer. Adipogenesis (HE), angiogenesis (CD31), and macrophage infiltration (CD80 and CD163) were evaluated histologically at all time points. The adipose area and M1/M2 macrophage ratio were determined using ImageJ. RNA sequencing (RNA-seq) and bioinformatics were conducted to evaluate pathway enrichments. Results: By 18 weeks, the adipose area was 2365% greater for 50/50 HA (281.6 +/- 21.6) than AAM(11.4 +/- 0.9) (P < 0.001). The M1/M2 macrophage ratio was significantly lower for 50/50 HA (0.8 +/- 0.1) than AAM (0.9 +/- 0.1) at 6 weeks (16%; P < 0.05). This inversely correlated with adipose area (r = -0.6; P > 0.05). The RNA-seq data revealed that upregulated adipogenesis, angiogenesis, and macrophage-induced tissue regeneration genes were temporally different between the groups. Conclusions: Combining the fascia matrix with AAM creates a bioscaffold with an improved retention volume that supportsM2 macrophage-mediated angiogenesis and adipogenesis. This bioscaffold is worthy of further investigation.