In recent years attempts to engineer contracting cardiac patches were focused on recapitulation of the myocardium extracellular microenvironment. We report here on our work, where for the first time, a three-dimensional cardiac patch was fabricated from albumin fibers. We hypothesized that since albumin fibers' mechanical properties resemble those of cardiac tissue extracellular matrix (ECM) and their biochemical character enables their use as protein carriers, they can support the assembly of cardiac tissues capable of generating strong contraction forces. Here, we have fabricated aligned and randomly oriented electrospun albumin fibers and investigated their structure, mechanical properties, and chemical nature. Our measurements showed that the scaffolds have improved elasticity as compared to synthetic electrospun PCL fibers, and that they are capable of adsorbing serum proteins, such as laminin leading to strong cell-matrix interactions. Moreover, due to the functional groups on their backbone, the fibers can be chemically modified with essential biomolecules. When seeded with rat neonatal cardiac cells the engineered scaffolds induced the assembly of aligned cardiac tissues with high aspect ratio cardiomyocytes and massive actinin striation. Compared to synthetic fibrous scaffolds, cardiac cells cultured within aligned or randomly oriented scaffolds formed functional tissues, exhibiting significantly improved function already on Day 3, including higher beating rate (P = 0.0002 and P < 0.0001, respectively), and higher contraction amplitude (P = 0.009 and P = 0.003, respectively). Collectively, our results suggest that albumin electrospun scaffolds can play a key role in contributing to the ex vivo formation of a contracting cardiac muscle tissue.

Stabilization of the jet is necessary for the successful fabrication of continuous fibers from solutions via electrospinning. Although intensively studied over the past decade, the mechanisms underlying jet stabilization are still not precisely understood. The traditional explanation for jet stabilization emphasizes the role of the elastic response of the polymer coil in creating a sufficiently high extensional viscosity, which prevents the breakup of the filament under extension. However, comprehensive rheological studies of bovine serum albumin (BSA) solutions that can be electrospun into continuous fibers show an absence of any significant bulk elasticity in shear and extension that would account for the stabilization of the jet. In order to explain this discrepancy, it is proposed that a complex jet structure, composed of a liquid core surrounded by a viscoelastic interface, is formed during the spinning process, where the surface viscoelasticity is responsible for the jet stabilization. These rheological properties of the surface are experimentally verified using novel interfacial rheometry. It is also shown that the surface viscoelasticity is further enhanced by varying the protein conformation (unfolding), as well as its concentration in solution.2

Natural polymers share recognition sequences that promote cell adhesion, rendering them attractive candidates for scaffolding in tissue engineering applications. However, challenges remain with regard to the fabrication of robust and porous structures of such raw materials for the design of extracellular matrix (ECM) mimics of living tissues. In this study, we present a fibrous scaffold that solely consists of albumin, the most abundant protein in mammalian blood plasma. The scaffold was fabricated using the electrospinning method, and resulted in microscale fibers that demonstrated mechanical properties which were similar to those of elastin fibers, a common component of connective tissue ECM. Albumin scaffolds proved nontoxic and supported adhesion and the spreading of fibroblasts, muscle cells, and endothelial cells (ECs) in vitro. In vivo studies demonstrated ∼50% biodegradation of the albumin scaffolds within 3 weeks of implantation. In addition, it was found that the fibers were encapsulated by dense fibrosis and evoked a weak inflammatory response, similar to that triggered by poly(L-lactide)/poly(lactic-co-glycolic acid) scaffolds. Albumin tubular structures fabricated to mimic blood vessels successfully guided the formation of blood vessel-like bi-layer structures made of fibroblasts and ECs. Thus, albumin scaffolds featuring biologically relevant characteristics pose a readily applicable alternative to synthetic scaffolding materials.

Injectable hydrogels represent biomaterials attractive for many biomedical applications. Here, a hybrid material composed of dextran‐crosslinked gelatin embedded with ≈100–1 000 µm long, electrospun bovine serum albumin fibers is described. Incorporation of fibers at weight fractions of 1–6% increases the hydrogel elastic modulus by up to ≈40% and decreases the gelation time by ≈20%. The addition of short fibers does not affect the injection of the pre‐gel solution throughout medical needles at moderate shear rates. Finally, viability of seeded fibroblasts confirms the biocompatibility of the composite scaffold. This hybrid represents a class of biomaterials that structurally mimics the ECMs of common tissues and that can be delivered by a minimal‐invasive approach.

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