Converting 2D Nanofiber Membranes to 3D Hierarchical Assemblies with Structural and Compositional Gradients Regulates Cell Behavior

Abstract

from uniaxial alignment at tendons, to moderate alignment at fibrocartilage sites, to random organization at bones. [3] Likewise, in articular cartilage, collagen fibers in the superficial zone are parallel to the articular surface, randomly oriented in the middle zone, and perpendicular to the articular surface in the deep zone. [4] The other type of gradient in biological systems is related to a varying degree to the variations in local concentrations/contents of biominerals, inorganic ions, and biomolecules, and water. Compositional gradients play a critical role in developmental biology, tissue homeostasis, and tissue repair by enabling cells to infer their spatial location and determine their fate accordingly. [5-7] Morphogens acting as graded positional cues control cell fate specification in many developing tissues. [8,9] Tranforming growth factor-beta 1 is secreted from the bone matrix and activated during bone tissue breakdown carried out by osteoclasts, resulting in a gradient that directs migration of bone mesenchymal stem cells (BMSCs) to bone remodeling sites, thereby balancing bone resorption and formation. [10] Transforming the ideas of these naturally occurring gradients into synthetic scaffolds renders tremendous potential to ameliorate their functions for regulating cell responses including distribution, morphology, adhesion (attachment), survival (proliferation), migration, metabolism, and differentiation. [9,11,12] Attempts have been made to fabricate scaffolds with structural (e.g., pore size, fiber organization) and compositional (e.g., minerals, adhesion ligands, growth factors) gradients using 3D printing, microfluidics, contact printing, ultravioletassisted capillary molding, porogen, thermally induced phase separation, deposition, diffusion, etching, buoyancy, and centrifugal force. [2,11-25] However, these methods yield scaffolds that often lack biomimetic nanofibrous architecture, aligned topographic cues, 3D configuration, or high cell seeding efficiency. To maximize the physiological relevance and cell seeding efficiency and direct cell behavior, there is a great need to develop biomimetic 3D scaffolds with incorporation of structural and compositional gradients. We reported, for the first time, the conversion of 2D electrospun poly(ε-caprolactone) (PCL) nanofiber membranes into biomimetic, stem-cell regulating, 3D hierarchical assemblies with structural and compositional gradients. We chose PCL as raw material as it is biodegradable New methods are described for converting 2D electrospun nanofiber membranes to 3D hierarchical assemblies with structural and compositional gradients. Pore-size gradients are generated by tuning the expansion of 2D membranes in different layers with incorporation of various amounts of a surfactant during the gas-foaming process. The gradient in fiber organizations is formed by expanding 2D nanofiber membranes composed of multiple regions collected by varying rotating speeds of mandrel. A compositional gradient on 3D assemblies consisting of radially alig...

Biomaterials with structural hierarchy and controlled 3D nanotopography guide endogenous bone regeneration

“…RAS and VAS were fabricated by transformation of 2D electrospun nanofiber membranes through the solids of revolution-inspired gas-foaming expansion following our established protocols ( 19 , 20 ). Briefly, we cut the 2D mat consisting of uniaxially aligned nanofibers into a rectangular shape in liquid nitrogen.…”

“…Thus, we established two different in vitro migration models to examine the efficacy of RAS and VAS in guiding and promoting cell migration (fig. S4) ( 20 ). Bone marrow stem cells (BMSCs) were chosen for this study as they are the major and important cell source for bone regeneration ( 21 ).…”

“…However, current technologies are mainly limited to generation of the patterned grooves or aligned nanofiber membranes in a 2D form, which may not be able to match the geometric shape of tissue defects. To this end, we developed a solid of revolution inspired gas-foaming technique to convert traditional electrospun nanofiber mats into 3D objects with hierarchy structure and controlled alignment (e.g., RAS and VAS) ( 19 , 20 ). The RAS and VAS can promote not only BMSC migration along the direction of fiber alignment from the surrounding to the center and from the bottom to the top but also the expression of bone regeneration related genes in vitro.…”

Large‐scale synthesis of compressible and re‐expandable three‐dimensional nanofiber matrices

“…[22] Most recently, 3D nanofiber assemblies with structural and compositional gradients were also generated through the transformation of 2D electro-spun membranes based on the gas-foaming expansion technique. [23] However, the above-mentioned studies involved the use of the traditional laboratory single-nozzle electrospinning setup and gas-foaming expansion to generate 3D nanofiber matrices, resulting in slow production and a low yield. Traditional electrospinning setups includes a syringe, a needle, a syringe pump, a high voltage generator, and a grounded collector.…”

“…[ 22 ] Most recently, 3D nanofiber assemblies with structural and compositional gradients were also generated through the transformation of 2D electrospun membranes based on the gas‐foaming expansion technique. [ 23 ]…”