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

Pro-vasculogenic Fibers by PDA-Mediated Surface Functionalization Using Cell-Free Fat Extract (CEFFE)

Formation of adequate vascular network within engineered three-dimensional (3D) tissue substitutes postimplantation remains a major challenge for the success of biomaterials-based tissue regeneration. To better mimic the in vivo angiogenic and vasculogenic processes, nowadays increasing attention is given to the strategy of functionalizing biomaterial scaffolds with multiple bioactive agents. Aimed at engineering electrospun biomimicking fibers with pro-vasculogenic capability, this study was proposed to functionalize electrospun fibers of polycaprolactone/gelatin (PCL/GT) by cell-free fat extract (CEFFE or FE), a newly emerging natural "cocktail" of cytokines and growth factors extracted from human adipose tissue. This was achieved by having the electrospun PCL/GT fiber surface coated with polydopamine (PDA) followed by PDA-mediated immobilization of FE to generate the pro-vasculogenic fibers of FE-PDA@PCL/GT. It was found that the PDA-coated fibrous mat of PCL/GT exhibited a high FE-loading efficiency (∼90%) and enabled the FE to be released in a highly sustained manner. The engineered FE-PDA@PCL/GT fibers possess improved cytocompatibility, as evidenced by the enhanced cellular proliferation, migration, and RNA and protein expressions (e.g., CD31, vWF, VE-cadherin) in the human umbilical vein endothelial cells (huvECs) used. Most importantly, the FE-PDA@PCL/GT fibrous scaffolds were found to enormously stimulate tube formation in vitro, microvascular development in the in ovo chick chorioallantoic membrane (CAM) assay, and vascularization of 3D construct in a rat subcutaneous embedding model. This study highlights the potential of currently engineered pro-vasculogenic fibers as a versatile platform for engineering vascularized biomaterial constructs for functional tissue regeneration.

A Comparative Analysis of the Wound Healing-Related Heterogeneity of Adipose-Derived Stem Cells Donors

Adipose-derived Stem cells (ASCs) are on the verge of being available for large clinical trials in wound healing. However, for developing advanced therapy medicinal products (ATMPs), potency assays mimicking the mode of action are required to control the product consistency of the cells. Thus, greater effort should go into the design of product assays. Therefore, we analyzed three ASC-based ATMPs from three different donors with respect to their surface markers, tri-lineage differentiation, proliferation, colony-forming unit capacity, and effect on fibroblast proliferation and migration, endothelial proliferation, migration, and angiogenesis. Furthermore, the transcriptome of all three cell products was analyzed through RNA-sequencing. Even though all products met the criteria by the International Society for Cell and Gene Therapy and the International Federation for Adipose Therapeutics and Science, we found one product to be consistently superior to others when exploring their potency in the wound healing specific assays. Our results indicate that certain regulatory genes associated with extracellular matrix and angiogenesis could be used as markers of a superior ASC donor from which to use ASCs to treat chronic wounds. Having a panel of assays capable of predicting the potency of the product would ensure the patient receives the most potent product for a specific indication, which is paramount for successful patient treatment and acceptance from the healthcare system.

Expression and function of FGF9 in the hypertrophied ligamentum flavum of lumbar spinal stenosis patients

BACKGROUND CONTEXT

Ligamentum flavum (LF) hypertrophy plays a dominant role in lumbar spinal stenosis (LSS). A previous study found that fibroblast growth factor 9 (FGF9) was upregulated with mechanical stress in rabbit LF. However, the expression and function of FGF9 are not well understood in human LF.

PURPOSE

To evaluate FGF9 expression and function in human LF with and without hypertrophy.

STUDY DESIGN

This study employed a basic research study design utilizing human LF tissue for histological analyses.

PATIENT SAMPLES

Hypertrophied LF tissue sample from patients with LSS, and nonhypertrophied (control) LFs from patients with lumbar disc herniation or other diseases were obtained during surgery.

METHODS

LF specimens were histologically analyzed for FGF9 and vascular endothelial growth factor A (VEGF-A) by immunohistochemistry. The number of total and FGF9 immuno-positive cells and blood vessels were counted and compared between LF with and without hypertrophy. For functional analysis, the effect of FGF9 on cell proliferation and migration was examined using a primary cell culture of human LF.

RESULTS

Histological studies revealed that the total cell number was significantly higher in the LF of patients with LSS than in the LF of control patients. Immunohistochemistry showed that the percentage of FGF9-positive cells was significantly higher in the LF of patients with LSS than in the controls, and it positively correlated with patients' age, regardless of disease. Double immune-positive cells for FGF9 and VEGF-A were often observed in vascular endothelial cells and fibroblasts in the fibrotic area of hypertrophied LF, and the number of double positive vessels was significantly higher in LF of LSS patients than in the LF of controls. Primary cell culture of human LF revealed that FGF9 promoted the proliferation and migration of LF cells.

CONCLUSION

The present study demonstrated that FGF9 expression is highly upregulated in hypertrophied human LF. FGF9 potentially plays a pivotal role in the process of hypertrophy of LF, which is associated with mechanical stress, through cell proliferation and migration.

CLINICAL SIGNIFICANCE

The results from this study partially reveal the molecular mechanisms of LF hypertrophy and suggest that FGF9 may be involved in the process of LF degeneration in elderly patients.

Multidrug-loaded electrospun micro/nanofibrous membranes: Fabrication strategies, release behaviors and applications in regenerative medicine

Electrospun micro/nanofibrous membranes (EFMs) have been widely investigated as local drug delivery systems. Multiple drugs can be simultaneously incorporated into one EFM to create synergistic effects, reduce side effects, and play their respective roles in the complex physiological processes of tissue regeneration and postoperative adhesion prevention. Due to the versatile electrospinning techniques, sustained and programmed release behaviors of multiple drugs could be achieved by modulating the structure of the EFMs and the location of the drugs. In this review, various multidrug incorporation approaches based on electrospinning are overviewed. In particular, the advantages and limitations of each drug incorporation technique, the methods to control drug release and the effect of one drug release on another are discussed. Then the applications of multidrug-loaded EFMs in regenerative medicine, including wound healing, bone regeneration, vascular tissue engineering, nerve regeneration, periodontal regeneration and adhesion prevention are comprehensively reviewed. Finally, the future perspectives and challenges in the research of multidrug-loaded EFMs are discussed.

Electrospun Nanofibers for Improved Angiogenesis: Promises for Tissue Engineering Applications

Angiogenesis (or the development of new blood vessels) is a key event in tissue engineering and regenerative medicine; thus, a number of biomaterials have been developed and combined with stem cells and/or bioactive molecules to produce three-dimensional (3D) pro-angiogenic constructs. Among the various biomaterials, electrospun nanofibrous scaffolds offer great opportunities for pro-angiogenic approaches in tissue repair and regeneration. Nanofibers made of natural and synthetic polymers are often used to incorporate bioactive components (e.g., bioactive glasses (BGs)) and load biomolecules (e.g., vascular endothelial growth factor (VEGF)) that exert pro-angiogenic activity. Furthermore, seeding of specific types of stem cells (e.g., endothelial progenitor cells) onto nanofibrous scaffolds is considered as a valuable alternative for inducing angiogenesis. The effectiveness of these strategies has been extensively examined both in vitro and in vivo and the outcomes have shown promise in the reconstruction of hard and soft tissues (mainly bone and skin, respectively). However, the translational of electrospun scaffolds with pro-angiogenic molecules or cells is only at its beginning, requiring more research to prove their usefulness in the repair and regeneration of other highly-vascularized vital tissues and organs. This review will cover the latest progress in designing and developing pro-angiogenic electrospun nanofibers and evaluate their usefulness in a tissue engineering and regenerative medicine setting.

Systematic Interrogation of Angiogenesis in the Ischemic Mouse Hind Limb: Vulnerabilities and Quality Assurance

Supplemental Digital Content is available in the text.

Objective:

There has been little success in translating preclinical studies of mouse hind limb ischemia into benefit for patients with peripheral artery disease. Using systematic strategies, we sought to define the injury and angiogenesis landscapes in mice subjected to hind limb ischemia and ascertain whether published studies to date have used an analysis strategy concordant with these data.

Approach and Results:

Maps of ischemic injury were generated from 22 different hind limb muscles and 33 muscle territories in 12-week-old C57BL/6 mice, based on loss or centralization of myofiber nuclei. Angiogenesis was similarly mapped based on CD (cluster of differentiation) 31–positive capillary content. Only 10 of 33 muscle territories displayed consistent muscle injury, with the distal anterior hind limb muscles most reliably injured. Angiogenesis was patchy and exclusively associated with zones of regenerated muscle (central nuclei). Angiogenesis was not observed in normal appearing muscle, necrotic muscle, or injury border zones. Systematic review of mouse hind limb angiogenesis studies identified 5147 unique publications, of which 509 met eligibility criteria for analysis. Only 7% of these analyzed manuscripts evaluated angiogenesis in distal anterior hind limb muscles and only 15% consistently examined for angiogenesis in zones of muscle regeneration.

Conclusions:

In 12-week C57BL/6 mice, angiogenesis postfemoral artery excision proceeds exclusively in zones of muscle regeneration. Only a minority of studies to date have analyzed angiogenesis in regions of demonstrably regenerating muscle or in high-likelihood territories. Quality assurance standards, informed by the atlas and mapping data herein, could augment data reliability and potentially help translate mouse hind limb ischemia studies to patient care.

Embryonic Mesenchymal Multipotent Cell Differentiation on Electrospun Biodegradable Poly(ester amide) Scaffolds for Model Vascular Tissue Fabrication

Vascular differentiation of stem cells and matrix component production on electrospun tubular scaffolds is desirable to engineer blood vessels. The mouse embryonic multipotent mesenchymal progenitor cell line (10T1/2) provides an excellent tool for tissue engineering since it shares similar differentiation characteristics with mesenchymal stem cells. Although 10T1/2 cells have been widely studied in the context of skeletal tissue engineering, their differentiation to smooth muscle lineage is less known. In this study, we fabricated tubular electrospun poly(ester amide) (PEA) fibers from L-phenylalanine-derived biodegradable biomaterials and investigated cell-scaffold interactions as well as their differentiation into vascular smooth muscle cell and subsequent elastin expression. PEA scaffolds fabricated under different collector speeds did not have an impact on the fiber directionality/orientation. 10T1/2 cytocompatibility and proliferation studies showed that PEA fibres were not cytotoxic and were able to support proliferation for 14 days. Furthermore, cells were observed infiltrating the fibrous scaffolds despite the small pore sizes (~ 5 µm). Vascular differentiation studies of 10T1/2 cells using qPCR, Western blot, and immunostaining showed a TGFβ1-induced upregulation of vascular smooth muscle cell (VSMC)-specific markers smooth muscle alpha-actin (SM-α-actin) and smooth muscle myosin heavy chain (SM-MHC). Differentiated 10T1/2 cells produced both elastin and fibrillin-1 suggesting the potential of fibrous PEA scaffolds to fabricate model vascular tissues.

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.

Emerging Strategies for Stem Cell Lineage Commitment in Tissue Engineering and Regenerative Medicine

Stem cells have transformed the fields of tissue engineering and regenerative medicine, and their potential to further advance these fields cannot be overstated. The stem cell niche is a dynamic microenvironment that determines cell fate during development and tissue repair following an injury. Classically, stem cells were studied in isolation of their microenvironment; however, contemporary research has produced a myriad of evidence that shows the importance of multiple aspects of the stem cell niche in regulating their processes. In the context of tissue engineering and regenerative medicine studies, the niche is an artificial environment provided by culture conditions. In vitro culture conditions may involve coculturing with other cell types, developing specific biomaterials, and applying relevant forces to promote the desired lineage commitment. Considerable advance has been made over the past few years toward directed stem cell differentiation; however, the unspecific differentiation of stem cells yielding a mixed population of cells has been a challenge. In this review, we provide a systematic review of the emerging strategies used for lineage commitment within the context of tissue engineering and regenerative medicine. These strategies include scaffold pore-size and pore-shape gradients, stress relaxation, sonic and electromagnetic effects, and magnetic forces. Finally, we provide insights and perspectives into future directions focusing on signaling pathways activated during lineage commitment using external stimuli.

High heparin content surface-modified polyurethane discs promote rapid and stable angiogenesis in full thickness skin defects through VEGF immobilization

Three-dimensional scaffolds have the capacity to serve as an architectural framework to guide and promote tissue regeneration. Parameters such as the type of material, growth factors, and pore dimensions are therefore critical in the scaffold's success. In this study, heparin has been covalently bound to the surface of macroporous polyurethane (PU) discs via two different loading methods to determine if the amount of heparin content had an influence on the therapeutic affinity loading and release of (VEGF₁₆₅ ) in full thickness skin defects. PU discs (5.4 mm diameter, 300 µm thickness, and interconnected pore size of 150 µm) were produced with either a low (2.5 mg/g) or high (6.6 mg/g) heparin content (LC and HC respectively), and were implanted into the modified dorsal skin chamber (MDSC) of C57BL/6 J mice with and without VEGF. Both low- and high-content discs with immobilized VEGF₁₆₅ (LCV and HCV, respectively) presented accelerated neovascularization and tissue repair in comparison to heparin discs alone. However, the highest angiogenetic peak was on day 7 with subsequent stabilization for HCV, whereas other groups displayed a delayed peak on day 14. We therefore attribute the superior performance of HCV due to its ability to hold more VEGF_165, based on its increased heparin surface coverage, as also demonstrated in VEGF elution dynamics. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2543-2550, 2017.

The effects of nanotopography and coculture systems to promote angiogenesis for wound repair

Insufficient angiogenesis in severe wounds delays wound repair because of a lack of blood supply to the wound site. Therefore, pro-angiogenic therapeutics may enhance wound repair. Many studies have investigated various physical and biochemical cues to improve angiogenesis, such as biocompatible materials, surface modifications, angiogenic factors and coculture systems using various cell types. However, the present capability to mimic the micro- and nanostructure of the natural microenvironment, particularly its porous, fibrous features, is limited. Nanotopography may represent a promising tool to overcome these limitations. Here, we discuss various approaches to the use of nanotopography to enhance angiogenesis and consider the combination of coculture systems with nanotopography to mimic the native environment for promotion of angiogenesis in wound healing and repair.