Many tissue engineering strategies seek to replace damaged or diseased tissue through controlled proliferation, differentiation, and extracellular matrix (ECM) production via stem cells seeded on a biodegradable support scaffold. However, many scaffold fabrication techniques are time consuming, expensive, and require specialized techniques not suitable for industrial scale production. In order to translate tissue engineering strategies from the laboratory to clinical practice, a high throughput, repeatable, scalable, and economical manufacturing method is needed. We hypothesized that nonwoven industry standard high throughput manufacturing techniques (spunbond, meltblowing, and carding) can meet this need. An additional challenge to the successful generation of relatively thick tissue engineering constructs is the formation of necrotic cores. As cells populate the scaffold and lay down ECM, nutrient and gas exchange becomes a limiting factor for viable cell growth in the interior of the scaffold. We further hypothesized that porous and hollow porous fibers may result in enhanced mass transport of nutrients and gases throughout the construct, limiting the formation of necrotic cores.
Many stem cell sources have been implemented for a variety of tissue engineering applications. Recently, adipose derived stem cells (hASC) have gained momentum as an abundant stem cell source for a variety of tissue engineering strategies, particularly for mesodermal lineages. Human ASC are relatively easy to harvest compared to other mesodermal stem cell sources, such as those derived from bone marrow. The goal of this research was to implement industry standard, scalable nonwoven manufacturing fabrication methods for the generation of full thickness tissue engineering scaffolds composed of fibers with enhanced mass transport properties, and validated using hASC.
The three most common industry standard nonwoven manufacturing techniques (spunbond, meltblowing, and carding) were validated as tissue engineering scaffolds using hASC. We demonstrated that solid fiber scaffolds manufactured via these techniques support viable cellular proliferation and adipogenic and osteogenic differentiation of hASC. This work was extended to fabricate scaffolds composed of porous fiber scaffolds with enhanced mass transport properties fabricated via the Spunblown process, a specialized version of meltblowing. We demonstrated the successful fabrication of Spunblown scaffolds composed of porous fibers via inclusion of a sacrificial component (AQ55S) in the primary polymer backbone, composed of poly(lactic acid) (PLA). Subsequent washing in deionized water resulted in the formation of porous fibers. We showed that porous fibers led to increased adipogenic and osteogenic differentiation of hASC, and promoted better cellular attachment throughout the scaffold thickness. Building on this work, we describe the successful fabrication of hollow porous multifilaments, and conversion to carded nonwoven scaffolds composed of hollow porous fibers using the PLA/AQ55S polymer system. Similar to porous fibers we showed that hollow porous fibers led to enhanced adipogenic and osteogenic differentiation of hASC.
Lastly, this work was extended to alternative fiber cross sections with enhanced mass transport properties. We described for the first time fabrication of novel mushroom gilled fibers, exhibiting a hollow central channel with multiple fin like extensions extending to the solid fiber surface, and subsequent conversion to gilled fiber carded scaffolds. We demonstrated that gilled fiber scaffolds led to increased proliferation of hASC and increased expression of the early osteogenic gene marker, runt related transcription factor 2 (RUNX2) when exposed to one hour of pulsatile fluid flow in the absence of soluble osteogenic induction factors. As a whole, this work demonstrates the feasibility of standard commercial nonwoven manufacturing methods as scalable, high throughput, economical fabrication techniques for clinical translation of enhanced mass transport tissue engineering scaffolds using hASC.
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