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Biomaterial-enabled de novo formation of non-fibrotic tissue in situ would provide an important tool to physicians. One example application, glottic insufficiency, is a debilitating laryngeal disorder wherein vocal folds do not fully close, resulting in difficulty speaking and swallowing. Preferred management of glottic insufficiency includes bulking of vocal folds via injectable fillers, however, the current options have associated drawbacks including inflammation, accelerated resorption, and foreign body response. We developed a novel iteration of microporous annealed particle (MAP) scaffold designed to provide persistent augmentation. Following a 14-month study of vocal fold augmentation using a rabbit vocal paralysis model, most MAP scaffolds were replaced with tissue de novo that matched the mixture of fibrotic and non-fibrotic collagens of the contralateral vocal tissue. Further, persistent tissue augmentation in MAP-treated rabbits was observed via MRI and via superior vocal function at 14 months relative to the clinical standard., (© 2023. The Author(s).)

Background: Ideal acellular dermal matrices (ADM) for breast reconstruction exhibit native extracellular matrix (ECM) structure to allow rapid biointegration and appropriate mechanical properties for desired clinical outcomes. In a novel in vivo model of irradiated breast reconstruction, we describe the cellular and vascular ingrowth of Artia, a porcine product chemically prepared to mimic the biomechanics of human ADM, with retained natural ECM structure to encourage cellular ingrowth., Methods: Utilizing the murine dorsal skinfold model, Artia was implanted into 16 C57bl/6 mice. Eight of the mice received a single dose 35 Gy radiation to the skin, followed by 12 weeks to produce radiation fibrosis and 8 mice served as nonradiated controls. Real-time photoacoustic microscopy of vascular integration and oxygen saturation within the ADM were made over 14 days. At 21 days, vascular ingrowth (CD31), fibroblast scar tissue formation (alpha smooth-muscle actin α-SMA, vimentin), and macrophage function (M2/M1 ratio) were evaluated. Scanning electron microscopy images of Artia were produced to help interpret the potential orientation of cellular and vascular ingrowth., Results: Repeated photoacoustic microscopy imaging demonstrated vascular ingrowth increasing over 14 days, with a commensurate increase in oxygen saturation within both radiated and nonradiated ADM-albeit at an insignificantly lower rate in the radiated group. By day 21, robust CD31 staining was seen that was insignificantly greater in the nonradiated group. Of the fibroblast markers, vimentin expression was significantly greater in the radiated group (P < 0.05). Macrophage lineage phenotype was consistent with remodeling physiology in both radiated and nonradiated groups. Scanning electron microscopy demonstrated transversely organized collagen fibrils with natural porous ECM structure to allow cellular ingrowth., Conclusions: Artia demonstrates appropriate biointegration, with increased oxygen saturation by 14 days, consistent with the performance of other collagen substrates in this model. Radiation fibrosis resulted in higher vimentin expression yet did not impact macrophage phenotype while only modestly decreasing Artia biointegration suggesting that ADM may have a role in reconstructive efforts in a radiated setting. Taken together with its enhanced biomechanics, this porcine ADM product is well poised to be clinically applicable to breast reconstruction.

Background: The purpose of this study is to assess the feasibility of a novel microporous annealed particle (MAP) scaffolding hydrogel to enable both articular cartilage and subchondral bone biointegration and chondrocyte regeneration in a rat knee osteochondral defect model., Methods: An injectable, microporous scaffold was engineered and modified to match the mechanical properties of articular cartilage. Two experimental groups were utilized-negative saline control and MAP gel treatment group. Saline and MAP gel were injected into osteochondral defects created in the knees of Sprague-Dawley rats. Photo-annealing of the MAP gel was performed. Qualitative histologic and immunohistochemical analysis was performed of the treated defects at 2, 4, and 8 weeks postsurgery., Results: The injectable MAP gel successfully annealed and was sustained within the osteochondral defect at each timepoint. Treatment with MAP gel resulted in maintained size of the osteochondral defect with evidence of tissue ingrowth and increased glycosaminoglycan production, whereas the control defects presented with evidence of disorganized scar tissue. Additionally, there was no significant inflammatory response to the MAP gel noted on histology., Conclusions: We have demonstrated the successful delivery of an injectable, flowable MAP gel scaffold into a rat knee osteochondral defect with subsequent annealing and stable integration into the healing wound. The flowable nature of this scaffold allows for minimally invasive application, for example, via an arthroscopic approach for management of wrist arthritis. The MAP gel was noted to fill the osteochondral defect and maintain the defect dimensions and provide a continuous and smooth surface for cartilage regeneration, suggesting its ability to provide a stable scaffold for tissue ingrowth. Future chemical, mechanical, and biological gel modifications may improve objective evidence of cartilage regeneration.

Background: There is currently a need for a clinically relevant small-animal model for irradiated, implant-based breast reconstruction. Present models are inadequate in terms of suboptimal location of expander placement and mode of radiation delivery, correlating poorly with the human clinical scenario. The authors hypothesized that by delivering fractionated radiation and placing an expander under the scalp of the animal, they would achieve soft-tissue changes histologically analogous to those seen in human irradiated, implant-based breast reconstruction., Methods: This study consisted of 11 immunocompetent, hairless rats divided into three groups as follows: untreated control (n = 3), tissue-expanded scalps (n = 4), and fractionated irradiation plus tissue expansion of the scalp (n = 4). At the completion of the experiment for each group, skin tissue samples were analyzed histologically for vascularity, epidermal and dermal thickness, and collagen fiber alignment or scar formation., Results: Expanded rat epidermis was significantly thicker and dermis was more vascular than nonexpanded skin. The authors observed a greater degree of collagen fiber alignment in the expanded group compared with nonexpanded skin. The combination of irradiation and expansion resulted in significant dermal thinning, vascular depletion, and increased scar formation compared with expanded skin alone., Conclusions: The authors describe a novel small-animal model for irradiated, implant-based breast reconstruction where histologic analysis shows structural changes in the skin consistent with known effects of radiation therapy and expansion in human skin. This model represents a significant improvement from previous ones and, as such, holds the potential to be used to test new therapeutic agents to improve clinical outcomes.

Objective: The use of autologous fat as a soft tissue filler has increased over the past decade in both reconstructive and aesthetic surgeries. Enhancement of autologous fat grafts with the addition of the stromal vascular fraction (SVF) has been reported to improve long-term volume retention. Stromal vascular fraction is most commonly isolated using enzymatic digestion, but it is unknown what effect the digestion process has on the adipocytes and SVF cells that comprise the graft. Some clinicians have reported use of enzymatically digested fat grafts to alter the physical properties of the tissue in specialized applications. We have previously reported that increasing collagenase digestion duration adversely affects the viability of adipocytes and SVF cells. Here, we aimed to determine if collagenase digestion of adipocytes before grafting is detrimental to long-term graft retention and if SVF supplementation can abrogate these potential deleterious effects., Methods and Results: We used a published xenograft model in which human lipoaspirate was implanted into the scalp of immunocompromised mice to study the effects of collagenase digestion on in vivo graft survival after 12 weeks. We used 4 experimental groups: grafts composed of collagenase-digested and nondigested adipocytes (50-minute digestion) and grafts with and without SVF supplementation. We used microcomputed tomography to serially and noninvasively quantify graft volume, in conjunction with hematoxylin-eosin staining of histological cross-sections of implanted and excised grafts to assess overall tissue viability. We found that adipocytes that were collagenase-digested before implantation had significantly lower retention rates at 12 weeks and poorer tissue health, which was assessed by quantifying the number of intact adipocytes, the number of cystic formations, and by scoring the degree of inflammation and fibrosis. Further, we found that SVF supplementation of the digested grafts improved graft survival, but not to the level observed in undigested grafts., Conclusions: We conclude that collagenase digestion adversely affects the long-term volume retention of fat grafts, but that graft retention is improved by SVF supplementation. These experimental results can serve as an initial framework to further elucidate the reported efficacy and safety of using collagenase-digested fat grafts and SVF in the clinical setting.

Background: Biointegration, a concept involving a dynamic interplay among three processes-inflammation, cellular infiltration, and angiogenesis-is key to understanding the interaction between acellular dermal matrices and the host. The current standard for evaluating acellular dermal matrix biointegration involves histologic analysis at fixed time points; however, the authors' approach uses advanced imaging techniques to serially assess biointegration in real time., Methods: The authors have adapted two advanced imaging techniques-two-photon microscopy and photoacoustic microscopy-to investigate biointegration in a murine deepithelialized dorsal skin-fold window chamber model, specifically engineered to recapitulate the host microenvironment of acellular dermal matrix-assisted breast reconstruction. Four mice per group were assessed. Two-photon imaging of dual-transgenic mice allows for detection of fluorescently labeled perivascular cells, and macrophage lineage cells. Photoacoustic microscopy noninvasively assesses oxygen and hemoglobin concentration in living tissues, generating high-resolution, three-dimensional mapping of the nascent acellular dermal matrix-associated microvasculature and metabolic consumption of oxygen. These outcomes were corroborated by confirmatory histologic analysis at the terminal time point., Results: The acellular dermal matrix/host interface is characterized by robust inflammation (0 to 3 days), increased oxygen consumption and neoangiogenesis in the matrix border zone (10 to 14 days), and vascular and inflammatory cell penetration into the center of the matrix (>21 days)., Conclusion: The data broaden the core knowledge of acellular dermal matrix biology, and serve as a potential template for elucidating the key differences among various commercially available and developmental products to guide the reconstructive surgeon to better select a reconstructive adjunct that meets their specific needs.