Clinical Use of the Self-Assembling Peptide RADA16: A Review of Current and Future Trends in Biomedicine

Abstract

RADA16 is a synthetic peptide that exists as a viscous solution in an acidic formulation. In an acidic aqueous environment, the peptides spontaneously self-assemble into β-sheet nanofibers. Upon exposure and buffering of RADA16 solution to the physiological pH of biological fluids such as blood, interstitial fluid and lymph, the nanofibers begin physically crosslinking within seconds into a stable interwoven transparent hydrogel 3-D matrix. The RADA16 nanofiber hydrogel structure closely resembles the 3-dimensional architecture of native extracellular matrices. These properties make RADA16 formulations ideal topical hemostatic agents for controlling bleeding during surgery and to prevent post-operative rebleeding. A commercial RADA16 formulation is currently used for hemostasis in cardiovascular, gastrointestinal, and otorhinolaryngological surgical procedures, and studies are underway to investigate its use in wound healing and adhesion reduction. Straightforward application of viscous RADA16 into areas that are not easily accessible circumvents technical challenges in difficult-to-reach bleeding sites. The transparent hydrogel allows clear visualization of the surgical field and facilitates suture line assessment and revision. The shear-thinning and thixotropic properties of RADA16 allow its easy application through a narrow nozzle such as an endoscopic catheter. RADA16 hydrogels can fill tissue voids and do not swell so can be safely used in close proximity to pressure-sensitive tissues and in enclosed non-expandable regions. By definition, the synthetic peptide avoids potential microbiological contamination and immune responses that may occur with animal-, plant-, or mineral-derived topical hemostats. In vitro experiments, animal studies, and recent clinical experiences suggest that RADA16 nanofibrous hydrogels can act as surrogate extracellular matrices that support cellular behavior and interactions essential for wound healing and for tissue regenerative applications. In the future, the unique nature of RADA16 may also allow us to use it as a depot for precisely regulated drug and biopharmaceutical delivery.

Keywords: RADA16; endoscopy; hemostasis; nanofiber; self-assembling peptide hydrogel; surgery; tissue regeneration; wound healing.

FIGURE 1

Chemical structure of RADA16 peptide. RADA16 peptide chemical structure showing the 16 amino acids organized as sequentially repeated 4-amino acid sequences containing R (positively charged arginine), A (hydrophobic alanine), and D (negatively charged aspartic acid) residues.

FIGURE 2

Macro, micro, and nanostructures of RADA16 in an aqueous solution. Spontaneous and reversible self-assembly of RADA16 molecules occurs in acidic solutions to generate nanofibers. RADA16 molecules with β-sheet conformation interact through face-to-face hydrophobic interactions and edge-to-edge hydrogen bonding to form layered and extended nanofibers, ∼6 nm in width. These ECM-like nanofibers form a viscous and transparent aqueous solution at a relatively low concentration range (e.g., 0.1∼2.5% weight/volume).

FIGURE 3

Illustration of RADA16 structure and properties as it is applied to and gels on a wound site. Acidic aqueous solutions of RADA16 are viscous and exhibit shear-thinning and thixotropic disassembly/reassembly, which allows their easy administration to wound sites through catheters and syringes with viscosity returning immediately after administration. Upon contact with the physiological pH of body fluids including blood and interstitial fluid, the surface net charges of RADA16 nanofibers become zero resulting in the physical crosslinking by hydrophobic interactions between neighboring RADA16 nanofibers, so that RADA16 solution forms in situ hydrogels on the wound site and act as a physical barrier to bleeding.

FIGURE 4

Hemostatic use of RADA16 self-assembling peptide hydrogel to control bleeding from wound surfaces of the liver. In a porcine model, punch biopsy of the liver surface (A) results in frank bleeding (B). After site irrigation and drying (C), residual bleeding (D) is stopped by the easy single-syringe application of RADA16 solution (E), which rapidly forms a transparent hemostatic in situ hydrogel barrier upon contact with physiological fluids (F). This approach can be used to stop topical bleeding at surgical and wound sites in skin, organs, vessels, and other tissues.

FIGURE 5

Hemostatic mechanism of action of RADA16 self-assembling peptide hydrogel on bleeding wound surfaces. Upon contact with physiological fluids present at the surgical site, the RADA16 solution rapidly forms a transparent hemostatic in situ hydrogel barrier on the oozing suture lines of vascular anastomoses (A) and the topical/surgical oozing sites such as ulcer and resected tissue after surgery (B). In a porcine model using the femoral artery, a longitudinal suture line was conventionally irrigated and sponge-dried, and RADA16 was syringe-applied to the suture line on the vessel’s outer surface. The white arrow shows the direction of syringe movement during application. RADA16 solution can stop residual bleeding at blood vessel suture lines and anastomoses sites during cardiothoracic and vascular surgeries (A). In a general topical/surgical bleeding site, in situ hemostatic hydrogel formation is initiated at the interface between the bleeding site and the applied RADA16 layer. This is represented diagrammatically (B). The transparent nature of the hydrogel allows easy visualization of the surgical field and underlying sutures and bleeding sites, thus enabling the surgeon to evaluate the surgical site for satisfactory hemostasis and the possible need to perform revisions.

FIGURE 6

Current and future clinical uses of the self-assembling peptide RADA16. Hemostatic RADA16 formulations are currently in use for stopping intraoperative bleeding and preventing delayed/rebleeding in cardiovascular, gastrointestinal, and otorhinolaryngological surgical procedures. Experimentation is underway to determine if RADA16 can act as a surrogate extracellular matrix to improve wound healing and tissue regeneration in diverse tissues and organs, and possibly act as a precisely regulated drug delivery depot.