Patricia S. Wolfe

Electrospinning of collagen/biopolymers for regenerative medicine and cardiovascular tissue engineering.

The process of electrospinning has seen a resurgence of interest in the last few decades which has led to a rapid increase in the amount of research devoted to its use in tissue engineering applications. Of this research, the area of cardiovascular tissue engineering makes up a large percentage, with substantial resources going towards the creation of bioresorbable vascular grafts composed of electrospun nanofibers of collagen and other biopolymers. These bioresorbable grafts have compositions that allow for the in situ remodeling of the structure, with the eventual replacement of the graft with completely autologous tissue. This review will highlight some of the work done in the field of electrospinning for cardiovascular applications, with an emphasis on the use of biopolymers such as collagens, elastin, gelatin, fibrinogen, and silk fibroin, as well as biopolymers used in combination with resorbable synthetic polymers.

The use of air-flow impedance to control fiber deposition patterns during electrospinning

Electrospun non-woven structures have the potential to form bioresorbable vascular grafts that promote tissue regeneration in situ as they degrade and are replaced by autologous tissue. Current bioresorbable grafts lack appropriate regeneration potential since they do not have optimal architecture, and their fabrication must be altered by the manipulation of process parameters, especially enhancing porosity. We describe here an air-impedance process where the solid mandrel is replaced with a porous mandrel that has pressurized air exiting the pores to impede fiber deposition. The mandrel design, in terms of air-flow rate, pore size, and pore distribution, allows for control over fiber deposition and scaffold porosity, giving greater cell penetration without a detrimental loss of mechanical properties or structural integrity.

A Preliminary Study on the Potential of Manuka Honey and Platelet-Rich Plasma in Wound Healing

Aim. The purpose of this study was to determine the in vitro response of cells critical to the wound healing process in culture media supplemented with a lyophilized preparation rich in growth factors (PRGF) and Manuka honey. Materials and Methods. This study utilized cell culture media supplemented with PRGF, as well as whole Manuka honey and the medical-grade Medihoney (MH), a Manuka honey product. The response of human fibroblasts (hDF), macrophages, and endothelial cells (hPMEC) was evaluated, with respect to cell proliferation, chemotaxis, collagen matrix production, and angiogenic potential, when subjected to culture with media containing PRGF, MH, Manuka honey, and a combination of PRGF and MH. Results. All three cell types demonstrated increases in cellular activity in the presence of PRGF, with further increases in activity seen in the presence of PRGF+MH. hDFs proved to be the most positively responsive cells, as they experienced enhanced proliferation, collagen matrix production, and migration into an in vitro wound healing model with the PRGF+MH-supplemented media. Conclusion. This preliminary in vitro study is the first to evaluate the combination of PRGF and Manuka honey, two products with the potential to increase regeneration individually, as a combined product to enhance dermal regeneration.

Natural and Synthetic Scaffolds

Tissue engineering is an interdisciplinary field aimed at the application of the principles and methods of engineering and life sciences toward the fundamental understanding of structure–function relationships in normal and pathological mammalian tissues and the development of biological substitutes to restore, maintain, or improve tissue functions [8, 38, 56, 57, 78, 111]. Typically, this involves collaborative efforts between materials scientists, cell and molecular biologists, immunologists, surgeons, and engineers to create replacement tissues that will be accepted by the body and promote native extracellular matrix (ECM) production. This requires the use of materials that do not activate catabolic pathways in the body, ultimately leading to fibrous encapsulation or destruction of the material [25, 78, 104, 111].

The Creation of Electrospun Nanofibers from Platelet Rich Plasma

Activated platelet rich plasma (a PRP) contains supra physiologic amounts of autologous growth factors and cytokines known to enhance wound healing and tissue regeneration. Here we report the first results of electro spinning nanofibers from a PRP to create fibrous scaffolds that could be used for various tissue engineering applications. Human platelet rich plasma (PRP) was created, activated by a freeze-thaw-freeze process, and lyophilized to form a powdered preparation rich in growth factors (PRGF). It was dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol (HFP) at different concentrations to form fibers with average diameters of 0.3 ? 3.6 ?m. A sustained release of protein from the PRGF scaffolds was demonstrated up to 35 days, and cell interactions with the PRGF scaffolds confirmed cell infiltration after just 3 days. As electro spinning is a simple process, and PRGF contains naturally occurring growth factors in physiologic ratios, creating nanofibrous structures from PRGF has the potential to be beneficial for a variety of tissue engineering applications.

Evaluation of thrombogenic potential of electrospun bioresorbable vascular graft materials: acute monocyte tissue factor expression.

The purpose of this study was to quantify the acute expression of tissue factor (TF) by monocytes on interaction with electrospun bioresorbable constructs. A minimal expression of TF will demonstrate the potential for scaffolds to be used as a vascular graft without enhanced risk of failure from acute thrombotic occlusion. Polydioxanone (PDO) (60, 80, 120, and 160 mg/mL) and polycaprolactone (PCL) (80, 10, and 160 mg/mL) dissolved in 1,1,1,3,3,3 hexafluoro-2-propanol (HFP) were electrospun to form fibrous scaffolds. Circular discs (10 mm diameter) of each scaffold were disinfected and seeded with human monocytes (50,000 cells/well). The discs were statically cultured under standard conditions (37 degrees C and 5% CO2), and removed after 24 h for TF analysis with an In-Cell Western assay. Fiber diameter was calculated through ImageTool analysis of scanning electron micrographs. Acute monocyte interaction with scaffolds of PCL (120 mg/mL) resulted in the lowest amount of TF expressed (4 ng/disc), whereas scaffolds of 160 mg/mL PDO elicited the highest amount of TF expressed (51 ng/disc). TF levels expressed on all scaffolds were comparable with the amount expressed on e-PTFE (20 ng/disc). Preliminary data for TF expression on scaffolds of silk (70 mg/mL and 150 mg/mL) and silk:PCL (100 mg/mL, v/v) blends (50:50 and 70:30) resulted in values of TF expression ranging from 0 to 24 ng. Results from this study reveal electrospun grafts composed of PDO and PCL provide no greater risk of failure from an acute thrombotic occlusion due to TF expression when compared with that of the standard e-PTFE graft.

Bioengineered vascular grafts: improving vascular tissue engineering through scaffold design

Arteriosclerosis has accounted for three quarters of the deaths related to cardiovascular disease (CVD). Arteriosclerosis is a vascular disease that is characterized by a thickening of the arterial wall and subsequent decrease in the arterial lumen, eventually causing loss of circulation distal to the site of disease. Small diameter arteries (

Quantified In Vitro Release of Interleukin-8 from Electrospun Bioresorbable Vascular Graft Materials

Interleukin-8 (IL-8) is a chemokine from the CXC family that has been shown to have angiogenic properties through the activation of macrophages. Angiogenesis is a critical factor in tissue regeneration, specifically of implanted electrospun bioresorbable vascular grafts. The purpose of this study was to analyze the release of IL-8 from electrospun scaffolds of different materials to demonstrate these scaffolds can be used as a chemotactive agent for macrophages to promote increased tissue regeneration in vascular grafts. Polycaprolactone (PCL), poly(glycolic acid) (PGA), fibrinogen (FBG), and silk solutions were electrospun from 1,1,1,3,3,3 hexafluoro-2-propanol (HFP) with and without the addition of 3000 ng/ml human IL-8. High and low concentrations of polymer were used to form scaffolds of micro- to nano-sized fiber diameters, respectively. From these scaffolds, 6 mm discs were punched, placed in a 96 well plate, and incubated under standard conditions with the addition of complete media (200μl). Media was retained at days 1, 3, 5, and 7 for ELISA analysis of IL-8 release. Preliminary results of IL-8 release from electrospun constructs reveal a steady decrease of chemokine throughout the seven day time period from all scaffolds, with the exception of PGA. Silk scaffolds release the highest amount of IL-8 (0.07-0.21 ng/ml), whereas scaffolds of PCL exhibit the lowest amount of chemokine release (0.01-0.06 ng/ml). Although PGA scaffolds display a steady release of chemokine for days 1, 3, and 5 (0.03 ng/day), at day 7 there is an increase (0.06 ng/day and 0.04 ng/day for low and high concentrations, respectively) due to bulk degradation of the scaffold. Control scaffolds (those without IL-8) display undetectable amounts of IL-8. While these scaffolds seem to demonstrate the ability to enhance cell migration and promote increased tissue regeneration, future work, including analyzing the chemotactic property of scaffolds on macrophages and fibroblasts, will be necessary to verify these results.