Biomimetic Microgels with Controllable Deformability Improve Healing Outcomes

Abstract

Platelets mediate hemostasis by aggregating and binding to fibrin to promote clotting. Over time, platelets contract the fibrin network to induce clot retraction, which contributes to wound healing outcomes by increasing clot stability and improving blood flow to ischemic tissue. In this study, we describe the development of hollow platelet-like particles (PLPs) that mimic the native platelet function of clot retraction in a controlled manner and demonstrate that clot retraction-inducing PLPs promote healing in vivo. PLPs are created by coupling fibrin-binding antibodies to CoreShell (CS) or hollow N-isopropylacrylamide (NIPAm) microgels with varying degrees of shell crosslinking. We demonstrate that hollow microgels with loosely crosslinked shells display a high degree of deformability and mimic activated platelet morphology, while intact CS microgels and hollow microgels with increased crosslinking in the shell do not. When coupled to a fibrin-binding antibody to create PLPs, hollow particles with low degrees of shell crosslinking cause fibrin clot collapse in vitro, recapitulating the clot retraction function of platelets, while other particle types do not. Furthermore, hollow PLPs with low degrees of shell crosslinking improve some wound healing outcomes in vivo. Main TextWound repair initiates at the onset of injury with the formation of a provisional fibrin mesh to cease bleeding and promote tissue remodeling by stimulating cell migration, angiogenesis, and matrix production. Platelets play a critical role in the wound healing process through their roles in hemostasis, clot retraction, and immune modulation. In the early stages of wound repair, platelets aggregate and promote fibrin polymerization to form the primary clot and stem hemorrhage. After Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))

Platelet-like particles dynamically stiffen fibrin matrices and improve wound healing outcomes

“…15 Like native activated platelets, these particles are capable of a high degree of deformability, as indicated by atomic force microscopy (AFM) characterization of ULC deformation on a glass surface. 16 Natural platelets have been shown to generate forces within fibrin matrices, resulting in clot contraction and matrix stiffening; 3,4 however, the ability of PLPs to recapitulate this active force generation within fibrin matrices to generate bulk clot stiffening is not yet known. The effect of any potential PLP-induced clot stiffening upon fibroblast migration in vitro and corresponding healing in vivo has also not previously been investigated.…”

Development of Novel Microenvironments for Promoting Enhanced Wound Healing

“…Nandi et al detailed the process of developing these PLPs and found that the ULC base particle is capable of deforming like an activated platelet, ULCs conjugated to fibrin-targeting antibodies to form PLPs are capable of generating contractile forces and enhancing fibroblast migration in vitro, and PLPs demonstrate enhanced wound closure rates in vivo over saline controls [101]. Additional studies have corroborated these results, as well as exhibited the antimicrobial activity of these PLPs when complexed with colloidal gold [19,100]. Another similar colloidal technology produced by Muhamed et al is injectable fibrin-based nanoparticles (FBNs) which have similar porosity and composition to the native clot structure and are designed to be integrated into clot assembly.…”

“…Within these more established fields, there are numerous novel materials and methods in development that have the potential to shape the regenerative medicine field, including the use of bioactive scaffolds, hydrogels for cell delivery, and colloidal-based materials. Recent significant advancements include microporous annealed particle hydrogels for injection and in vivo crosslinking [76••], artificial microgels which recapitulate platelet function in vivo [19,100,101], and injectable pH-switchable scaffolds [102••]. The following sections will detail specific examples in these areas which have been demonstrated to be of potential benefit to wound reepithelialization and tissue remodeling.…”

“…Platelet-fibrin interactions play a critical role in determining clot properties and, in turn, the hemostatic and pro-healing properties of the wound microenvironment. Via actin/ myosin-generated contractile mechanisms, platelets pull on the fibrin strands in the clot through a process known as clot retraction, which decreases clot surface area, increases clot stability, and promotes blood flow to carry nutrients to the healing tissue [16,18,19]. Inflammation also occurs shortly after the injury, overlapping temporally with hemostasis, where immune cells such as neutrophils and macrophages are recruited to clean the wound site of bacteria and debris and secrete growth factors to stimulate the subsequent cell proliferation phase of wound repair [7,20].…”

Design and Synthesis of Core–Shell Microgels with One‐Step Clickable Crosslinked Cores and Ultralow Crosslinked Shells

“…However, in addition to those optical properties, our target particles should also display a soft, ultralow crosslinked (ULC)‐like shell that could be coupled to fibrin‐biding proteins for artificial platelet applications. [ 27,41 ] Furthermore, the two chemistries (protein and dye coupling) should be chemo‐orthogonal, thereby removing the need for protection/deprotection chemistries.…”