Solving cell infiltration limitations of electrospun nanofiber meshes for tissue engineering applications

Nano-fibrous tissue engineering scaffolds capable of growth factor delivery

Tissue engineering aims at constructing biological substitutes to repair damaged tissues. Three-dimensional (3D) porous scaffolds are commonly utilized to define the 3D geometry of tissue engineering constructs and provide adequate pore space and surface to support cell attachment, migration, proliferation, differentiation and neo tissue genesis. Biomimetic 3D scaffolds provide synthetic microenvironments that mimic the natural regeneration microenvironments and promote tissue regeneration process. While nano-fibrous (NF) scaffolds are constructed to mimic the architecture of NF extracellular matrix, controlled-release growth factors are incorporated to modulate the regeneration process. The present article summarizes current advances in methods to fabricate NF polymer scaffolds and the technologies to incorporate controlled growth factor delivery systems into 3D scaffolds, followed by examples of accelerated regeneration when the scaffolds with growth factor releasing capacity are applied in animal models.

Cartilage tissue engineering using electrospun PCL nanofiber meshes and MSCs

Mesenchymal stem cells (MSCs) have been recognized for their ability to differentiate into cells of different tissues such as bone, cartilage, or adipose tissue, and therefore are of great interest for potential therapeutic strategies. Adherent, colony-forming, fibroblastic cells were isolated from human bone marrow aspirates, from patients undergoing knee arthroplasties, and the MSCs phenotype characterized by flow cytometry. Afterward, cells were seeded onto electrospun polycaprolactone nanofiber meshes and cultured in a multichamber flow perfusion bioreactor to determine their ability to produce cartilagineous extracellular matrix. Results indicate that the flow perfusion bioreactor increased the chondrogenic differentiation of hBM-MSCs, as confirmed either by morphological and RT-PCR analysis. Cartilage-related genes such as aggrecan, collagen type II, and Sox9 were expressed. ECM deposition was also detected by histological procedures. Collagen type II was present in the samples, as well as collagen type I. Despite no statistically significant values being obtained for gene expression, the other results support the choice of the bioreactor for this type of culture.

Improved cellular infiltration in electrospun fiber via engineered porosity

Small pore sizes inherent to electrospun matrices can hinder efficient cellular ingrowth. To facilitate infiltration while retaining its extracellular matrix-like character, electrospinning was combined with salt leaching to produce a scaffold having deliberate, engineered delaminations. We made elegant use of a specific randomizing component of the electrospinning process, the Taylor Cone and the falling fiber beneath it, to produce a uniform, well-spread distribution of salt particles. After 3 weeks of culture, up to 4 mm of cellular infiltration was observed, along with cellular coverage of up to 70% within the delaminations. To our knowledge, this represents the first observation of extensive cellular infiltration of electrospun matrices. Infiltration appears to be driven primarily by localized proliferation rather than coordinated cellular locomotion. Cells also moved from the salt-generated porosity into the surrounding electrospun fiber matrix. Given that the details of salt deposition (amount, size, and number density) are far from optimized, the result provides a convincing illustration of the ability of mammalian cells to interact with appropriately tailored electrospun matrices. These layered structures can be precisely fabricated by varying the deposition interval and particle size conceivably to produce in vivo-like gradients in porosity such that the resulting scaffolds better resemble the desired final structure.