Increasing the pore sizes of bone-mimetic electrospun scaffolds comprised of polycaprolactone, collagen I and hydroxyapatite to enhance cell infiltration

Abstract

Bone-mimetic electrospun scaffolds consisting of polycaprolactone (PCL), collagen I and nanoparticulate hydroxyapatite (HA) have previously been shown to support the adhesion, integrin-related signaling and proliferation of mesenchymal stem cells (MSCs), suggesting these matrices serve as promising degradable substrates for osteoregeneration. However, the small pore sizes in electrospun scaffolds hinder cell infiltration in vitro and tissue-ingrowth into the scaffold in vivo, limiting their clinical potential. In this study, three separate techniques were evaluated for their capability to increase the pore size of the PCL/col I/nanoHA scaffolds: limited protease digestion, decreasing the fiber packing density during electro-spinning, and inclusion of sacrificial fibers of the water-soluble polymer PEO. The PEO sacrificial fiber approach was found to be the most effective in increasing scaffold pore size. Furthermore, the use of sacrificial fibers promoted increased MSC infiltration into the scaffolds, as well as greater infiltration of endogenous cells within bone upon placement of scaffolds within calvarial organ cultures. These collective findings support the use of sacrificial PEO fibers as a means to increase the porosity of complex, bone-mimicking electrospun scaffolds, thereby enhancing tissue regenerative processes that depend upon cell infiltration, such as vascularization and replacement of the scaffold with native bone tissue.

The effect of electrospun polycaprolactone scaffold morphology on human kidney epithelial cells

“…It is an excellent biomaterial due to its mechanical properties and biocompatibility. Tissue engineering applications include: bone (Bye et al 2013;Phipps et al 2012), cartilage (Steele et al 2014), ligament (Petrigliano et al 2014), cornea (Baradaran-Rafii et al 2016) and vascular (Wise et al 2011) to name a few. Polymer-based scaffolds, such as PCL, have been highlighted as a potential avenue for tissue engineered kidneys (Moon et al 2016), but there is little investigation down this stream.…”

“…This variation in morphology has been shown to affect the way cells behave and integrate with the scaffold, larger fibres allow for greater cell integration, nanofibres represent the natural ECM and aligned fibres have shown to guide neural, vascular and cornea cell growth (Yan et al 2012;Balguid et al 2009;Wang et al 2012). Other methods have been proposed to increase the porosity of scaffolds to allow for greater cell integration; dual-spinning using a water soluble sacrificial material allows for a scaffold with greater porosity (Lowery et al 2010;Phipps et al 2012) and techniques such as cell electrospinning enable cell to be directly integrated within the scaffold (Jayasinghe 2013;Townsend-Nicholson & Jayasinghe 2006). Techniques such as cryogenic electrospinning have also been proposed, this utilises the deposition of ice crystals on a cooled surface as a template for electrospun fibres, giving greater porosity (Leong et al 2013;Bulysheva et al 2013).…”

Electrospun fibers/branched-clusters as building units for tissue engineering

“…Additionally, the use of these fibers/branched-clusters creates constructs with much more even cell distribution than that seen in whole electrospun templates, even with the use of sacrificial fibers, enzymatic digestion, or air-impedance electrospinning to improve template porosity [12,25,28]. However, the use of fibers/branched-clusters as template elements is not without limitations.…”

“…In a 2012 study, Phipps et al used a plastic petri dish on top of a grounded aluminum plate with twenty needles inserted through the petri dish contacting the aluminum plate underneath as the collecting plate for the electrospun fibers. While this method was effective in reducing template packing density, it only worked with templates electrospun from 100% polycaprolactone (PCL), severely limiting its applicability [28]. A more versatile method was developed by McClure et al that same year, in which a cylindrical metal mandrel with air flowing outward through evenly-spaced pores was used as the grounded fiber collector.…”

Preparation of fiber-microsphere scaffolds for loading bioactive substances in gradient amounts

“…Electrospinning has attracted much attention in recent years because of its potential applications in tissue engineering. Electrospun membranes have nanofibrous structures with large surface-to-volume ratios and interconnecting pores, and can be tailored to mimic the structure and composition of a natural extracellular matrix [1,2]. Several modified electrospinning techniques such as blending electrospinning [3,4], emulsion electrospinning [5,6], coaxial electrospinning [7,8], and emulsion-coaxial electrospinning [9] have been developed for delivering bioactive molecules via electrospun fibers.…”