Alginate Bead Based Hexagonal Close Packed 3D Implant for Bone Tissue Engineering

Abstract

Success of bone tissue engineering (BTE) relies on the osteogenic microarchitecture of the biopolymeric scaffold and appropriate spatiotemporal distribution of therapeutic molecules (growth factors and drugs) inside it. However, the existing technologies have failed to address both the issues together. Keeping this perspective in mind, we have developed a novel three-dimensional (3D) implant prototype by stacking hexagonal close packed (HCP) layers of calcium alginate beads. The HCP arrangement of the beads lead to a patterned array of interconnected tetrahedral and octahedral pores of average diameter of 142.9 and 262.9 μm, respectively, inside the implant. The swelling pattern of the implants changed from isotropic to anisotropic in the z-direction in the absence of bivalent calcium ions (Ca) in the swelling buffer. Incubation of the implant in simulated body fluid (SBF) resulted in a 2.7-fold increase in the compressive modulus. The variation in the relaxation times as derived from the Weichert viscoelasticity model predicted a gradual increase in the interactions among the alginate molecules in the matrix. We demonstrated the tunability of the spatiotemporal drug release from the implant in a tissue mimicking porous semisolid matrix as well as in conventional drug release set up by changing the spatial coordinates of the "drug loaded depot layer" inside the implant. The therapeutic potential of the implant was confirmed against Escherichia coli using metronidazole as the model drug. Detailed analysis of cell viability, cell cycle progression, and cytoskeletal reorganization using osteoblast cells (MG-63) proved the osteoconductive nature of the implant. Expression of differentiation markers such as alkaline phosphatase, runx2, and collagen type 1 in human mesenchymal stem cell in vitro confirmed the osteogenic nature of the implant. When tested in vivo, VEGF loaded implant was found capable of inducing angiogenesis in a mice model. In conclusion, the bead based implant may find its utility in non-load-bearing BTE.

Alginate and its application to tissue engineering

“…It consist of (1-4)-bonded β-d-mannuronic acid with the blocks of α-l-guluronic acid [5,6].The salt of Ca, Na and Ba alginate has the gelling capability because of the presence of divalent cations, highly viscous in the aqueous medium and hence extensively used in different biomedical fields mainly cell transplantation, tissue regeneration, drug delivery. Now the most evolutionary concept of alginate for the biological systems is to treat, supplement of any organ, tissue or any part of the human body [7,8]. Alginate is an anionic biopolymer of natural origin and more suited for biomedical applications because of its many outstanding properties such as low toxicity, biodegradability, biocompatibility, comparatively low cost of extraction and processing, mild gelation and good hydrogel forming ability due to the addition of divalent cations such as Ca 2+ .…”

Functionalization of polymers and nanomaterials for water treatment, food packaging, textile and biomedical applications: a review

“…Biodegradability is the other important feature which is needed for the safety usage of nanomaterials inside the body. This is a very important property in designing scaffolds for tissue engineering and regenerative medicine applications (Agarwal et al 2016;Maji et al 2017). Moreover, it is considered as a method for controlling the cargo release.…”

Journey into Bone Models: A Review

“…Agarwal et al built up a 3D implant by closely stacking layers of hexagonal arranged packs of calcium alginate beads together. This microstructure leads to hypoxic conditions inside the construct and a pore size that enables cell migration, resulting in osteogenic differentiation of human MSCs [ 162 ]. Using implants that are made of hexagonal alginate bead packs allows for the controlled release of various substances like the antibiotic metronidazole against Escherichia coli or vascular endothelial growth factor (VEGF) which induces angiogenesis in a mice model.…”