Avian Egg: A Multifaceted Biomaterial for Tissue Engineering

Abstract

Most components in avian eggs, offering a natural and environmentally friendly source of raw materials, hold great potential in tissue engineering. An avian egg consists of several beneficial elements: the protective eggshell, the eggshell membrane, the egg white (albumen), and the egg yolk (vitellus). The eggshell is mostly composed of calcium carbonate and has intrinsic biological properties that stimulate bone repair. It is a suitable precursor for the synthesis of hydroxyapatite and calcium phosphate, which are particularly relevant for bone tissue engineering. The eggshell membrane is a thin protein-based layer with a fibrous structure and is constituted of several valuable biopolymers, such as collagen and hyaluronic acid, that are also found in the human extracellular matrix. As a result, the eggshell membrane has found several applications in skin tissue repair and regeneration. The egg white is a protein-rich material that is under investigation for the design of functional protein-based hydrogel scaffolds. The egg yolk, mostly composed of lipids but also diverse essential nutrients (e.g., proteins, minerals, vitamins), has potential applications in wound healing and bone tissue engineering. This review summarizes the advantages and status of each egg component in tissue engineering and regenerative medicine, but also covers their current limitations and future perspectives.

Keywords: egg white; egg yolk; eggshell; eggshell membrane; tissue engineering.

Figure 1.. Major components of a chicken egg include a calcified EG, a thin EGM, a viscous protein-rich EW, and a lipid-rich EY bulge.

The calcified ES is a rigid and semipermeable membrane that provides protection to the egg contents and embryo against physical damage and contamination by microorganisms. The EGM is a thin layer attached to the inner side of shell with a fibrous porous structure that is permeable to oxygen and gases. EW, representing about 60% of the total egg weight, is a viscous fluid covering the EY and is mainly composed of proteins, such as ovalbumin, conalbumin, ovomucoid, and lysozyme. EY, representing about 30% of the total egg weight, is the innermost component and a lipid-rich substance that also contains other vital nutrients (protein, vitamins, and minerals) that play a critical role in embryo development.

Figure 2.. The intrinsic similarity of ES to the inorganic component of bones makes it a good candidate material for bone TE.

a) Schematic depicting the preparation and characterization of ES-derived CaO₃/MgO/CMC/BMP2 (CaCO₃/MgO/CMC/BMP2) scaffolds. b) Comparison of the mechanical strength of ES-derived CaO₃/MgO/CMC (CaCO₃/MgO/CMC) and CMC scaffolds. c) High-resolution Micro-CT imaging of scaffold-mediated bone repair in critical-sized rat calvarial defects 8 weeks after implantation: NC (negative control), CMC, CaCO₃/MgO/CMC, and CaCO₃/MgO/CMC/BMP2. (a—c) Reproduced with permission. d) Scanning electron microscopy images of (I) pure GelMA hydrogel and (II) GelMA hydrogels reinforced with ES particles (GelMA-ESP). e) Comparison of the compressive modulus of GelMA and GelMA-ESP hydrogels at different ESP concentrations. Reproduced with permission.

Figure 3.. Microstructure of ESM.

Scanning electron micrograph of an ESM showing (a) side view and (b, c) top view. Reproduced with permission.

Figure 4.. Leveraging ESM for TE scaffolds.

(a) SEM images showing the microstructure of (I) ESM and PCLF-coated ESM prepared with PCLF dissolved in (II) dichloromethane or (III) acetic acid. Reproduced with permission. (b) Fluorescent imaging of human dermal fibroblasts showing their proliferation over 1 week incubation on ESM and a nanofiber-coated ESM scaffolds. Reproduced with permission. (c) Photograph showing the cross section of a bilayered ESM/TPU vascular graft. Reproduced with permission. (d) Schematic depicting in situ mineralization of HAp on the ESM. Reproduced with permission.

Figure 5.. Application of EW in TE.

(a) Structures of EW-derived proteins. Reproduced with permission. (b) Infiltration of bone marrow stromal cells into MeGC and lysozyme (MeLyz1)-containing MeGC hydrogels over 14 days. Reproduced with permission. (c) Fluorescent images of HUVECs cultured on different films showing cell spreading on the surface at various time points. Reproduced with permission. (d) SEM images depicting human dental pulp stem cells cultured on EW and ES-loaded EW hydrogels. Reproduced with permission.

Figure 6.. Exploiting EY for TE.

Transmission electron microscopy images of a) cross section and (b) longitudinal section of a chitosan/phosvitin-coated nanofiber. Reproduced with Permission.