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In order to achieve effective bone regeneration, the architectural/structural and biological environment must be considered. In this study, we investigated the influence of structure of extracellular matrix-mimicking electrospun poly ( l -lactic acid) (PLLA) fibrous scaffolds and incorporated growth factors (bone morphogenetic protein2 (BMP2) and platelet-derived growth factor (PDGF)) (GFs) on in vitro differentiation of human mesenchymal stem cells (hMSCs) cultured onto the scaffolds. Furthermore, Cargo GFs were first encapsulated into coacervate (Coa). Coa-coated nano-sized PLLA (Coa-nPLLA) exhibited relatively higher coating efficacy, than Coa-coated micro-sized PLLA (Coa-mPLLA) due to large mesh hole area of mPLLA. Consequently, a faster GF release pattern was observed in nPLLA groups. As a result of osteogenic differentiation of hMSC which cultured onto GFs loaded Coa-PLLA, the architectural cue of fiber diameters effectively modulated early osteogenic differentiation of hMSCs. Facilitated long-term differentiation of hMSCs could be achieved by synergistic effect of dual BMP2 and PDGF in nanofbrous environments.

Here we report optimization and scale-up of a biodegradable polycation, poly(ethylene argininylaspartate diglyceride) (PEAD) for the purpose of clinical translation. This polycation complexes heparin to form a coacervate. The resultant complex coacervate acts as a vehicle for controlled delivery of therapeutic proteins and through the bioactivity of heparin, greatly increases the half lives of many therapeutic proteins. In an effort to translate this drug delivery platform commercially and clinically, it is necessary to consider the scale of the synthesis, the environmental impact and the cost of the production. Therefore, we substituted the more expensive and hazardous solvents in the reactions, optimized the reaction parameters for a higher yield, scaled up the synthesis capacity up to hundreds of grams per batch and reduced the polymer cost by nearly 90%. The resultant PEAD bears more positive charges than the counterpart made using our previous method, and thus less polymer is needed to complex heparin for coacervation. The material demonstrated good cytocompatibility with human umbilical vein endothelial cells at concentrations up to 5 mg/ml, nearly 500-times more cytocompatible than the commercially resourced polyethyleneimine. Basic fibroblast growth factor was loaded in the coacervate with loading efficiency above 99%. The cargo steadily released approximately 1% over 37 days in vitro without an initial burst, indicating a highly stable coacervate for sustained release. This study paves the way for the translation of this delivery platform and may inform the scale-up of similar polymers.

Although there are numerous medical applications to recover damaged skin tissue, scarless wound healing is being extensively investigated to provide a better therapeutic outcome. The exogenous delivery of therapeutic growth factors (GFs) is one of the engineering strategies for skin regeneration. This study presents an exogenous GF delivery platform developed using coacervates (Coa), a tertiary complex of poly(ethylene argininyl aspartate diglyceride) (PEAD) polycation, heparin, and cargo GFs (i.e., transforming growth factor beta 3 (TGF-β3) and interleukin 10 (IL-10)). Coa encompasses the advantage of high biocompatibility, facile preparation, protection of cargo GFs, and sustained GF release. We therefore speculated that coacervate-mediated dual delivery of TGF-β3/IL-10 would exhibit synergistic effects for the reduction of scar formation during physiological wound healing. Our results indicate that the exogenous administration of dual GF via Coa enhances the proliferation and migration of skin-related cells. Gene expression profiles using RT-PCR revealed up-regulation of ECM formation at early stage of wound healing and down-regulation of scar-related genes at later stages. Furthermore, direct injection of the dual GF Coa into the edges of damaged skin in a rat skin wound defect model demonstrated accelerated wound closure and skin regeneration after 3 weeks. Histological evaluation and immunohistochemical staining also revealed enhanced formation of the epidermal layer along with facilitated angiogenesis following dual GF Coa delivery. Based on these results, we conclude that polycation-mediated Coa fabrication and exogenous dual GF delivery via the Coa platform effectively augments both the quantity and quality of regenerated skin tissues without scar formation. Statement of Significance This study was conducted to develop a simple administration platform for scarless skin regeneration using polycation-based coacervates with dual GFs. Both in vitro and in vivo studies were performed to confirm the therapeutic efficacy of this platform toward scarless wound healing. Our results demonstrate that the platform developed by us enhances the proliferation and migration of skin-related cells. Sequential modulation in various gene expression profiles suggests a balanced collagen-remodeling process by dual GFs. Furthermore, in vivo histological evaluation demonstrates that our technique enhances clear epidermis formation with less scab and thicker woven structure of collagen bundle, similar to that of a normal tissue. We propose that simple administration of dual GFs with Coa has the potential to be applied as a clinical approach for fundamental scarless skin regeneration.

Nonunion following bone fracture and segmental bone defects are challenging clinical conditions. To combat this clinical dilemma, development of new bone tissue engineering therapies using biocompatible materials to deliver bone growth factors is desirable. This aim of this study is to use a heparin/polycation coacervate sustained-release platform to compare 5 bone morphogenetic proteins (BMPs) for promoting bone defect healing in a critical sized calvarial defect model. The in vitro 3D osteogenic pellet cultures assays demonstrated that BMPs 2, 4, 6, 7 and 9 all enhanced mineralization in vitro compared to the control group. BMP2 resulted in higher mineralized volume than BMP4 and BMP6. All BMPs and the control group activated the pSMAD5 signaling pathway and expressed osterix (OSX). The binding of BMP2 with coacervate significantly increased the coacervate average particle size. BMP2, 4, 6, & 7 bound to coacervate significantly increased the Zeta potential of the coacervate while BMP9 binding showed insignificant increase. Furthermore, using a monolayer culture osteogenic assay, it was found that hMDSCs cultured in the coacervate BMP2 osteogenic medium expressed higher levels of RUNX2, OSX, ALP and COX-2 compared to the control and BMPs 4, 6, 7 & 9. Additionally, the coacervate complex can be loaded with up to 2 μg of BMP proteins for sustained release. In vivo, when BMPs were delivered using the coacervate sustained release system, BMP2 was identified to be the most potent BMP promoting bone regeneration and regenerated 10 times of new bone than BMPs 4, 6 & 9. BMP7 also stimulated robust bone regeneration when compared to BMPs 4, 6 & 9. The quality of the newly regenerated bone by all BMPs delivered by coacervate is equivalent to the host bone consisting of bone matrix and bone marrow with normal bone architecture. Although the defect was not completely healed at 6 weeks, coacervate sustain release BMPs, particularly BMP2 and BMP7, could represent a new strategy for treatment of bone defects and non-unions.

Osteoblast and osteoclast communication (i.e. osteocoupling) is an intricate process, in which the biophysical profile of bone ECM is an aggregate product of their activities. While the effect of microenvironmental cues on osteoblast and osteoclast maturation has been resolved into individual variables (e.g. stiffness or topography), a single cue can be limited with regards to reflecting the full biophysical scope of natural bone ECM. Additionally, the natural modulation of bone ECM, which involves collagenous fibril and elastin crosslinking via lysyl oxidase, has yet to be reflected in current synthetic platforms. Here, we move beyond traditional substrates and use cell-derived ECM to examine individual and coupled osteoblast and osteoclast behavior on a physiological platform. Specifically, preosteoblast-derived ECM is crosslinked with genipin, a biocompatible crosslinker, to emulate physiological lysyl oxidase-mediated ECM crosslinking. We demonstrate that different concentrations of genipin yield changes to ECM density, stiffness, and roughness while retaining biocompatibility. By approximating various bone ECM profiles, we examine how individual and coupled osteoblast and osteoclast behavior are affected. Ultimately, we demonstrate an increase in osteoblast and osteoclast differentiation on compact and loose ECM, respectively, and identify ECM crosslinking density as an underlying force in osteocoupling behavior.

Vascular endothelial growth factor (VEGF) is one of the most important signaling cues during angiogenesis. Since many delivery systems of VEGF have been reported, the presentation of VEGF using a more physiologically relevant extracellular matrix (ECM), however, has yet to be thoroughly examined. In this study, we propose that fibroblast-derived extracellular matrix (FDM) is a novel platform for angiogenic growth factor delivery and that FDM-mediated VEGF delivery can result in an advanced angiogenic response. The FDMs, activated by EDC/NHS chemistry, were loaded with varying amounts of heparin. Different doses of VEGF were subsequently immobilized onto the heparin-grafted FDM (hep-FDM); 19.6 ± 0.6, 39.2 ± 3.2, and 54.8 ± 8.9 ng of VEGF were tethered using 100, 300, and 500 ng of initial VEGF, respectively. VEGF-tethered FDM was found chemoattractive and VEGF dose-dependent in triggering human umbilical vein endothelial cells (ECs) migration in vitro. When hep-FDM-bound VEGF (H-F/V) was encapsulated into alginate capsules (A/H-F/V) and subjected to release test for 28 days, it exhibited a significantly reduced burst release at early time point compared to that of A/V. The cell proliferation results indicated a substantially extended temporal effect of A/H-F/V on EC proliferation compared to those treated with soluble VEGF. For a further study, A/H-F/V was transplanted subcutaneously into ICR mice for up to 4 weeks to assess its in vivo effect on angiogenesis; VEGF delivered by hep-FDM was more competitive in promoting blood vessel ingrowth and maturation compared to other groups. Taken together, this study successfully engineered an FDM-mediated VEGF delivery system, documented its capacity to convey VEGF in a sustained manner, and demonstrated the positive effects of angiogenic activity in vivo as well as in vitro.