Regenerative tissue filler for breast conserving surgery and other soft tissue restoration and reconstruction needs

Abstract

Complete removal of cancerous tissue and preservation of breast cosmesis with a single breast conserving surgery (BCS) is essential for surgeons. New and better options would allow them to more consistently achieve this goal and expand the number of women that receive this preferred therapy, while minimizing the need for re-excision and revision procedures or more aggressive surgical approaches (i.e., mastectomy). We have developed and evaluated a regenerative tissue filler that is applied as a liquid to defects during BCS prior to transitioning to a fibrillar collagen scaffold with soft tissue consistency. Using a porcine simulated BCS model, the collagen filler was shown to induce a regenerative healing response, characterized by rapid cellularization, vascularization, and progressive breast tissue neogenesis, including adipose tissue and mammary glands and ducts. Unlike conventional biomaterials, no foreign body response or inflammatory-mediated "active" biodegradation was observed. The collagen filler also did not compromise simulated surgical re-excision, radiography, or ultrasonography procedures, features that are important for clinical translation. When post-BCS radiation was applied, the collagen filler and its associated tissue response were largely similar to non-irradiated conditions; however, as expected, healing was modestly slower. This in situ scaffold-forming collagen is easy to apply, conforms to patient-specific defects, and regenerates complex soft tissues in the absence of inflammation. It has significant translational potential as the first regenerative tissue filler for BCS as well as other soft tissue restoration and reconstruction needs.

Figure 1

Purified liquid collagen forms viscoelastic fibrillar scaffold with soft tissue-like properties. (a) Kit consisting of syringe containing sterile type I oligomeric collagen solution, a syringe of propriety neutralization (self-assembly) buffer, a luer-lock adapter, and applicator tip. (b) Images showing mixing of two reagents followed by injection into a plastic mold maintained at body temperature (37 °C), where the liquid transitions into a stable, shape-retaining fibrillar collagen scaffold. (c) SDS–PAGE (4–20% and 6% gels) documenting purity and characteristic banding pattern of type I oligomeric collagen. Images represent full length gels and show all relevant lanes. Lane 1: molecular weight standard. Lane 2: type I oligomeric collagen. Uncropped images of the full gel length are shown in Supplementary Figure S1. (d) Table summarizing collagen polymerization kinetics and performance specifications (mean ± SD; N = 4, n = 6–8) of prototype collagen scaffold.

Figure 2

Overview of simulated lumpectomy procedure. (a) Table summarizing surgically excised mammary tissue volume, which represented roughly one-fourth total breast tissue volume. Data (mean ± SD) compiled from both longitudinal and radiation studies (1 week: collagen filler: n = 12, no fill = 6; 4 weeks: collagen filler: n = 18, no fill: n = 9; 16 weeks: collagen filler: n = 18, no fill: n = 9). Surgical void (b) before and (c) after filling with collagen. (d) Application of scaffold-forming collagen. (e) Excised mammary tissue. Surgical sites (f) immediately following surgery showing bandaging and (g) 16 weeks following simulated lumpectomy with irradiation.

Figure 3

Collagen filler persists and induces site-appropriate tissue regeneration. (a) Graph showing breast uniformity/consistency scores (mean ± SD; collagen: n = 12; no fill: n = 6) assigned by breast surgeon for collagen and no fill (negative control) treated voids at various time points following simulated lumpectomy. All no surgery breasts scored 0. (b) Cross-sections of surgical voids following treatment with collagen or no fill compared to normal breast tissue. Arrows represent surgical clips placed to mark boundaries of surgical void.

Figure 4

Collagen filler supports breast tissue neogenesis without evoking an inflammatory response. (a) Cross-sections (H&E) of collagen filled voids at 1 week, 4 weeks, and 16 weeks following simulated lumpectomy. Low magnification images show treated voids and their interface with the surrounding host tissue (large arrows indicate surgical clip sites). High magnification images feature the central region of the collagen filler and the filler/host tissue interface. Cellular infiltration, vascularization, and site-appropriate tissue generation of the scaffold occur over time. By 16 weeks, the collagen is completely cellularized and vascularized (small arrows indicated blood vessels) with evidence of regenerated mammary gland (RG) and adipose tissue (RF). O_nc: oligomer scaffold with no cell infiltration, O_c: oligomer scaffold with cellular infiltrate. (b) Cross-sections (H&E) of untreated (no fill) surgical voids at 1 week, 4 weeks, and 16 weeks following simulated lumpectomy. Low magnification images show voids and the surrounding host tissue. High magnification images feature the central region of the voids and the void/host tissue interface. Hematomas (H) were commonplace at 1 week, followed by progressive defect contraction and scar tissue formation (S).

Figure 5

Collagen filler does not interfere with radiography or ultrasonography. Representative (a) ultrasound images and (b) radiographs of surgical voids treated with collagen or no fill compared to normal breast tissue at 1-week, 4-week, and 16-week time points. Radiopaque marker clips evident within radiographs indicate boundaries of surgical void and show evidence of contraction for no fill voids.

Figure 6

Radiation has little to no effect on collagen filler and associated tissue response. (a) Graph showing breast uniformity/consistency scores (mean ± SD; collagen: n = 6; no fill: n = 3) assigned by breast surgeon for collagen treated and no fill (negative control) voids at various time points following simulated lumpectomy and radiation. All no surgery breasts scored 0. (b) Cross-sections of surgical voids following treatment with collagen or no fill and radiation compared to no surgery normal breast tissue. Arrows represent surgical clips placed to mark boundaries of surgical void. (c) Cross-sections (H&E) of collagen filled voids at 4 weeks and 16 weeks following simulated lumpectomy with irradiation. Low magnification images show treated voids and their interface with the surrounding host tissue. High magnification images feature the central region of the collagen filler and the filler/host tissue interface. Cellular infiltration, vascularization, and site-appropriate tissue generation of the collagen implant occur over time, albeit at a slower rate than sites from non-irradiated animals. By 16 weeks, the collagen is completely cellularized and vascularized (small arrows indicated blood vessels) with evidence of regenerated adipose tissue (RF). O_nc: oligomer scaffold with no cell infiltration, O_c: oligomer scaffold with cellular infiltrate. (d) Cross-sections (H&E) of untreated (no fill) surgical voids at 4 weeks and 16 weeks following simulated lumpectomy with radiation. Low magnification images show voids and the surrounding host tissue, with scar tissue (S) and a suture-related granuloma (G) evident at 4 weeks (large arrow indicates surgical clip site). High magnification images feature the central region of the scar tissue and the scar/host tissue interface.

Figure 7

Collagen filler does not compromise interpretation of diagnostic images of breast tissue even after irradiation. Representative (a) ultrasound images and (b) radiographs of surgical voids treated with collagen or no fill and irradiation compared to normal breasts at 4-week and 16-week time points. Radiopaque marker clips evident within radiographs indicate boundaries of surgical void and show evidence of contraction for no fill voids.

Figure 8

Timelines and processes of healing responses observed in porcine simulated lumpectomy model. Schematics comparing and contrasting the phases and processes associated with the (a) normal reparative response observed with no fill and the (b) proposed regenerative response observed with the collagen filler.