Fortifying Angiogenesis in Ischemic Muscle with FGF9-Loaded Electrospun Poly(Ester Amide) Fibers.

Delivery of angiogenic growth factors lessens ischemia in preclinical models but has demonstrated little benefit in patients with peripheral vascular disease. Augmenting the wrapping of nascent microvessels by mural cells constitutes an alternative strategy to regenerating a functional microvasculature, particularly if integrated with a sustained delivery platform. Herein, electrospun poly(ester amide) (PEA) nanofiber mats are fabricated for delivering a mural cell-targeting factor, fibroblast growth factor 9 (FGF9). Proof-of-principle is established by placing FGF9/FGF2-loaded PEA fiber mats on the chick chorioallantoic membrane and identifying enhanced angiogenesis by 3D power Doppler micro-ultrasound imaging. To assess the delivery system in ischemic muscle, FGF9-loaded PEA fiber mats are implanted onto the surface of the tibialis anterior muscle of mice with hindlimb ischemia. The system supplies FGF9 into the tibialis anterior muscle and yields a neo-microvascular network with enhanced mural cell coverage up to 28 days after injury. The regenerating muscle that receives FGF9 display near-normal sized myofibers and reduced interstitial fibrosis. Moreover, the mice demonstrate improved locomotion. These findings of locally released FGF9 from PEA nanofibers raise prospects for a microvascular remodeling approach to improve muscle health in peripheral vascular disease.

Concurrent and Sustained Delivery of FGF2 and FGF9 from Electrospun Poly(ester amide) Fibrous Mats for Therapeutic Angiogenesis.

Therapeutic angiogenesis has emerged as a potential strategy to treat ischemic vascular diseases. However, systemic or local administration of growth factors is usually inefficient for maintaining the effective concentration at the site of interest due to their rapid clearance or degradation. In this study, we report a differential and sustained release of an angiogenic factor, fibroblast growth factor-2 (FGF2), and an arteriogenic factor, fibroblast growth factor-9 (FGF9), from α-amino acid-derived biodegradable poly(ester amide) (PEA) fibers toward targeting neovessel formation and maturation. FGF2 and FGF9 were dual loaded using a mixed blend and emulsion electrospinning technique and exhibited differential and sustained release from PEA fibers over 28 days with preserved bioactivity. In vitro angiogenesis assays showed enhanced endothelial cell (EC) tube formation and directed migration of smooth muscle cells (SMCs) to platelet-derived growth factor (PDGF)-BB and stabilized EC/SMC tube formation. FGF2/FGF9-loaded PEA fibers did not induce inflammatory responses in vitro using human monocytes or in vivo after their subcutaneous implantation into mice. Histological examination showed that FGF2/FGF9-loaded fibers induced cell niche recruitment around the site of implantation. Furthermore, controlled in vivo delivery of FGF9 to mouse tibialis anterior (TA) muscle resulted in a dose-dependent expansion of mesenchymal progenitor-like cell layers and extracellular matrix deposition. Our data suggest that the release of FGF2 and FGF9 from PEA fibers offers an efficient differential and sustained growth factor delivery strategy with relevance to therapeutic angiogenesis.

Controlled delivery of fibroblast growth factor-9 from biodegradable poly(ester amide) fibers for building functional neovasculature.

PURPOSE: For building functional vasculature, controlled delivery of fibroblast growth factor-9 (FGF9) from electrospun fibers is an appealing strategy to overcome challenges associated with its short half-life. FGF9 sustained delivery could potentially drive muscularization of angiogenic sprouts and help regenerate stable functional neovasculature in ischemic vascular disease patients. METHODS: Electrospinning parameters of FGF9-loaded poly(ester amide) (PEA) fibers have been optimized, using blend and emulsion electrospinning techniques. In vitro PEA matrix degradation, biocompatibility, FGF9 release kinetics, and bioactivity of the released FGF9 were evaluated. qPCR was employed to evaluate platelet-derived growth factor receptor-ß (PDGFRß) gene expression in NIH-3T3 fibroblasts, 10T1/2 cells, and human coronary artery smooth muscle cells cultured on PEA fibers at different FGF9 concentrations. RESULTS: Loaded PEA fibers exhibited controlled release of FGF9 over 28 days with limited burst effect while preserving FGF9 bioactivity. FGF9-loaded and unloaded electrospun fibers were found to support the proliferation of fibroblasts for five days even in serum-depleted conditions. Cells cultured on FGF9-supplemented PEA mats resulted in upregulation of PDGFRß in concentration and cell type-dependent manner. CONCLUSION: This study supports the premise of controlled delivery of FGF9 from PEA electrospun fibers for potential therapeutic angiogenesis applications.

Advances in growth factor delivery for therapeutic angiogenesis.

Therapeutic angiogenesis is a new revascularization strategy involving the administration of growth factors to induce new vessel formation. The biology and delivery of angiogenic growth factors involved in vessel formation have been extensively studied but success in translating the angiogenic capacity of growth factors into benefits for vascular disease patients is still limited. This could be attributed to issues related to patient selection, growth factor delivery methods or lack of vessel maturation. Comprehensive understanding of the cellular and molecular cross-talk during the different stages of vascular development is needed for the design of efficient therapeutic strategies. The presentation of angiogenic factors either in series or in parallel using a strategy that mimics physiological events, such as concentration and spatio-temporal profiles, is an immediate requirement for functional blood vessel formation. This review provides an overview of the recent delivery strategies of angiogenic factors and discusses targeting neovascular maturation as a promising approach to induce stable and functional vessels for therapeutic angiogenesis.

Bioburden-responsive antimicrobial PLGA ultrafine fibers for wound healing.

Despite innovation in the design and functionalization of polymer nanofiber wound healing materials, information on their interaction with the biochemical wound environment is lacking. In an earlier study, we have reported the interaction of fusidic acid-loaded PLGA ultrafine fibers (UFs) with wound bacteria. Massive bacterial colonization and the formation of a dense biofilm throughout the mat were demonstrated. This was associated with a marked enhancement of initial drug release at concentrations allowing eradication of planktonic bacteria and considerable suppression of biofilm. The present study aimed at extending earlier findings to gain more mechanistic insights into the potential response of the fusidic acid-laden UFs under study to controlled microbial bioburden. Initial drug release enhancement was shown to involve surface erosion of the ultrafibrous mats likely mediated by microbial esterase activity determined in the study. Release data could be correlated with microbial bioburden over the inoculum size range 10³-107 CFU/ml, suggesting a bioburden-triggered drug release enhancement mechanism. Moreover, the effectiveness of fusidic acid-laden UFs in the healing of either lightly contaminated or Staphylococcus aureus heavily infected wounds in a rat model suggested in-use relevant antimicrobial release patterns. Findings indicated active participation of polymer ultrafine wound dressings in a dynamic interaction with the wound milieu, which affects their structure-function relationship. Understanding such an interaction is fundamental to the characterization and performance assessment of wound materials under biorelevant conditions and the design of polymer-based infection-responsive biomaterials.

Antimicrobial PLGA ultrafine fibers: interaction with wound bacteria.

The structure and functions of polymer nanofibers as wound dressing materials have been well investigated over the last few years. However, during the healing process, nanofibrous mats are inevitably involved in dynamic interactions with the wound environment, an aspect not explored yet. Potential active participation of ultrafine fibers as wound dressing material in a dynamic interaction with wound bacteria has been examined using three wound bacterial strains and antimicrobial fusidic acid (FA)-loaded electrospun PLGA ultrafine fibers (UFs). These were developed and characterized for morphology and in-use pharmaceutical attributes. In vitro microbiological studies showed fast bacterial colonization of UFs and formation of a dense biofilm. Interestingly, bacterial stacks on UFs resulted in a remarkable enhancement of drug release, which was associated with detrimental changes in morphology of UFs in addition to a decrease in pH of their aqueous incubation medium. In turn, UFs by allowing progressively faster release of bioactive FA eradicated planktonic bacteria and considerably suppressed biofilm. Findings point out the risk of wound reinfection and microbial resistance upon using non-medicated or inadequately medicated bioresorbable fibrous wound dressings. Equally important, data strongly draw attention to the importance of characterizing drug delivery systems and establishing material-function relationships for biomedical applications under biorelevant conditions.