Clay Minerals as Bioink Ingredients for 3D Printing and 3D Bioprinting: Application in Tissue Engineering and Regenerative Medicine

Abstract

The adaptation and progress of 3D printing technology toward 3D bioprinting (specifically adapted to biomedical purposes) has opened the door to a world of new opportunities and possibilities in tissue engineering and regenerative medicine. In this regard, 3D bioprinting allows for the production of tailor-made constructs and organs as well as the production of custom implants and medical devices. As it is a growing field of study, currently, the attention is heeded on the optimization and improvement of the mechanical and biological properties of the so-called bioinks/biomaterial inks. One of the strategies proposed is the use of inorganic ingredients (clays, hydroxyapatite, graphene, carbon nanotubes and other silicate nanoparticles). Clays have proven to be useful as rheological and mechanical reinforcement in a wide range of fields, from the building industry to pharmacy. Moreover, they are naturally occurring materials with recognized biocompatibility and bioactivity, revealing them as optimal candidates for this cutting-edge technology. This review deals with the use of clays (both natural and synthetic) for tissue engineering and regenerative medicine through 3D printing and bioprinting. Despite the limited number of studies, it is possible to conclude that clays play a fundamental role in the formulation and optimization of bioinks and biomaterial inks since they are able to improve their rheology and mechanical properties, thus improving printability and construct resistance. Additionally, they have also proven to be exceptionally functional ingredients (enhancing cellular proliferation, adhesion, differentiation and alignment), controlling biodegradation and carrying/releasing actives with tissue regeneration therapeutic activities.

Development of New Collagen/Clay Composite Biomaterials

“…Thus, Coll sample presented the minimum pore size with Dmed = 132 µm while the samples with mineral clays exhibited slightly higher values starting from Dmed = 147 µm for unmodified clay sample (Coll-ClNa) to Dmed ~160 to 170 µm for organomodified mineral clays containing samples [ 33 ]. These findings are in good agreement with other studies that observed greater pore sizes when clay particles are added to the biopolymer matrix [ 41 , 42 , 43 ].…”

Inorganic Nanomaterials in Tissue Engineering

“…These are generally formed by metal cations such as Al 3+ , Fe 3+ , Mg 2+ , and Fe 2+ . The apical oxygen atom of the tetrahedral sheet (T) connects the tetrahedral and octahedral (O) sheets [10][11][12][13].…”

“…The apical oxygen atom of the tetrahedral sheet (T) connects the tetrahedral and octahedral (O) sheets. [10][11][12][13].…”

“…Due to this space, the clay minerals are able to adsorb water, leading to an increase in the volume occupied by the clay-water suspension and, consequently, to a swelling in aqueous environments, behaving as hydrogels. Under certain conditions, the layers can also completely delaminate, leading to clay mineral exfoliation [12,13].…”

“…The apices of the tetrahedral sheet point in different directions, forcing spatial modifications of the discontinuous octahedral sheet, which create channels into the structure. Charges are balanced along the channels by protons, water, and exchangeable cations [13]. The clay minerals most frequently used are natural products derived from mining, which means that they are not subjected to treatments.…”