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The physicochemical features of the avian eggshell membrane play an essential role in the process of calcium carbonate deposition during shell mineralization, giving rise to a porous mineralized tissue with remarkable mechanical properties and biological functions. The membrane could be useful by itself or as a bi-dimensional scaffold to build future bone-regenerative materials. This review focuses on the biological, physical, and mechanical properties of the eggshell membrane that could be useful for that purpose. Due to its low cost and wide availability as a waste byproduct of the egg processing industry, repurposing the eggshell membrane for bone bio-material manufacturing fulfills the principles of a circular economy. In addition, eggshell membrane particles have has the potential to be used as bio-ink for 3D printing of tailored implantable scaffolds. Herein, a literature review was conducted to ascertain the degree to which the properties of the eggshell membrane satisfy the requirements for the development of bone scaffolds. In principle, it is biocompatible and non-cytotoxic, and induces proliferation and differentiation of different cell types. Moreover, when implanted in animal models, it elicits a mild inflammatory response and displays characteristics of stability and biodegradability. Furthermore, the eggshell membrane possesses a mechanical viscoelastic behavior comparable to other collagen-based systems. Overall, the biological, physical, and mechanical features of the eggshell membrane, which can be further tuned and improved, make this natural polymer suitable as a basic component for developing new bone graft materials.

The eggshell is a biomineral consisting of CaCO3 in the form of calcite phase and a pervading organic matrix (1–3.5 wt.%). Transforming eggshell calcite particles into calcium phosphate (apatite) micro-nanoparticles opens the door to repurposing the eggshell waste as materials with potential biomedical applications, fulfilling the principles of the circular economy. Previous methods to obtain these particles consisted mainly of two steps, the first one involving the calcination of the eggshell. In this research, direct transformation by a one-pot hydrothermal method ranging from 100–200 °C was studied, using suspensions with a stoichiometric P/CaCO3 ratio, K2HPO4 as P reagent, and eggshells particles (Ø < 50 μm) both untreated and treated with NaClO to remove surface organic matter. In the untreated group, the complete conversion was achieved at 160 °C, and most particles displayed a hexagonal plate morphology, eventually with a central hole. In the treated group, this replacement occurred at 180 °C, yielding granular (spherulitic) apatite nanoparticles. The eggshell particles and apatite micro-nanoparticles were cytocompatible when incubated with MG-63 human osteosarcoma cells and m17.ASC murine mesenchymal stem cells and promoted the osteogenic differentiation of m17.ASC cells. The study results are useful for designing and fabricating biocompatible microstructured materials with osteoinductive properties for applications in bone tissue engineering and dentistry.

&lt;p&gt;The study of mineral decarbonation mechanisms is of great interest for its application to various geological and industrial processes. Biomineralization is a phenomenon by which living organisms are able to produce mineral phases, the most abundant of which are calcium carbonates and phosphates. Among the more abundant polymorphs of calcium carbonate are calcite and aragonite, being the most thermodynamically stable structures under biological environments (Weiner &amp; Addadi, 1997). In general, mineral phases formed by biologically controlled mineralisation processes have lower crystallinity characteristics than their geological analogues. In the current communication, the thermal degradation of biogenic calcium carbonates is comparatively studied with their respective ones of geological origin. During the transformation, chemical and microstructural alterations occur from the original polymorphs of biogenic calcite (eggshell; &lt;em&gt;Gallus gallus&lt;/em&gt;) and aragonite (mollusc shell; &lt;em&gt;Ruditapes philippinarum&lt;/em&gt;) to the final calcium oxide mineral phase. The samples were gradually heated from room temperature to 1100&amp;#176;C in order to remove the water content and organic matter components contained in the biogenic phases and to induce progressive mineral decarbonation. The kinetics of these compositional transformations were analysed by means of differential scanning calorimetry (DSC). Different analytical techniques, such as attenuated total reflectance infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM), were used for the chemical and structural characterisation of the mineral transformation of these phases. During thermal degradation, changes are observed in the molecular composition of these biogenic phases related to the distortion of the carbonate group and its association with the organic components. Furthermore, the mineral decarbonation process of calcium carbonates involves different structural transformation mechanisms that depend on the modification of unit cell parameters, thermal expansion coefficients and microstructural reorganisation (Rodriguez-Navarro et al., 2009). Accordingly, CaCO3 crystalline structures are transformed from the original calcite and aragonite phases to the cubic structure of lime, with a calcite-aragonite transformation prior to decarbonation explained by the reorientation of the CO3 group towards Ca and by changes in the packing of the Ca atoms, followed by the increase of the unit cell volume (Antao &amp; Hassan, 2010). The results show some significant differences during mineral transformation depending on their geological or biological origin. The characterization of this mineral decarbonation process has important implications in natural and industrial processes (i.e., cement production, CO2 capture).&lt;/p&gt;&lt;ul&gt;&lt;li&gt;Weiner, S.; Addadi, L. (1997) Design strategies in mineralized biological materials. Journal of Materials Chemistry, 7(5), 689-702.&lt;/li&gt; &lt;li&gt;Rodriguez-Navarro, C.; Ruiz-Agudo, E.; Luque, A.; Rodriguez-Navarro, A.B.; Ortega-Huertas, M. (2009) Thermal decomposition of calcite: mechanisms of formation and textural evolution of CaO nanocrystals. American Mineralogist 94, 578&amp;#8211;593.&lt;/li&gt; &lt;li&gt;Antao, S. M., Hassan, I. (2010) Temperature Dependence of the Structural Parameters in the Transformation of Aragonite to Calcite, as Determined from in Situ Synchrotron Powder X-Ray-Diffraction Data. Canadian Mineralogist 48, 1225&amp;#8211; 1236.&lt;/li&gt; &lt;/ul&gt;