Hierarchical Collagen–Hydroxyapatite Nanostructures Designed through Layer-by-Layer Assembly of Crystal-Decorated Fibrils

Abstract

A comprehensive understanding of the mechanism by which type I collagen (Col) interacts with hydroxyapatite nanoparticles (Hap NPs) in aqueous solutions is a pivotal step for guiding the design of biologically relevant nanocomposites with controlled hierarchical structure. In this paper we use a variety of Hap NPs differing by their shape (rod vs platelet) and their size (∼30 vs ∼130 nm) and investigate their mechanism(s) of interaction with collagen. The addition of collagen to the Hap suspensions induces different effects that strongly depend on the nanoparticle type. Interestingly, the use of small rods, typically with ∼30 nm of length (R 30 ), leads to the formation of assembled collagen fibrils decorated with Hap nanocrystals which, in turn, selfassemble progressively to form larger fibrillar Hap−Col composite. The crystals decorating collagen provide "intrinsic" negative charges to the fibrillar objects that allow their incorporation in three-dimensional structure using layer-by-layer (LbL) assembly. This offers a straightforward way to construct a collagen-based hybrid material with well-defined hierarchy under nearphysiological conditions. In situ, QCM-D monitoring revealed the buildup of soft and highly hydrated hybrid (PAH/R 30 −Col) n multilayers for which the mechanism of growth was very different from that observed for polyelectrolytes and nanoparticles without collagen (PAH/R 30 ). The LbL assembly of crystal-decorated collagen yields a hierarchical nanostructured film whose thickness and roughness can be modulated by the addition of salt and incorporate fibrillar objects of about 400 nm in width and few micrometers in length, as probed by AFM. The approach described in this work provides a relevant way to better control the (supra)molecular assembly of Col and Hap NPs with the perspective of developing hierarchical Hap−Col nanocomposites with tuned properties for various biomedical applications.

Enzyme-assisted mineralization of calcium phosphate: exploring confinement for the design of highly crystalline nano-objects

“…45 This approach, initially developed to characterize monolayer systems, has been recently used to investigate multilayered films. 46 At pH 9 (RT) and pH 7.4 (37 °C), a decrease in the ΔD/−Δf ratio with an increasing −Δf was observed, indicating that the layer progressively stiffens due to the formation of mineralized structures. The situation at pH 7.4 (RT) is however different; the ΔD/−Δf vs. −Δf plot exhibited two regimes.…”

Biomaterials for Soft Tissue Repair and Regeneration: A Focus on Italian Research in the Field

“…Inorganic materials are also, often studied in association with CL. Colaço et al [ 94 ] studied the interaction of CL with hydroxyapatite nanoparticles of different size (from 30 to 130 nm) and shape (rods and platelets) to better understand their interaction with the protein. The small rod shaped hydroxyapatite nanoparticles decorated collagen fibers gave, in turn, large self-assembling fibrillar structures, characterized by negative charges that could be exploited in layer-by-layer assembly, tuning the supramolecular structure for the requirements of different biomedical applications [ 94 ].…”

“…Colaço et al [ 94 ] studied the interaction of CL with hydroxyapatite nanoparticles of different size (from 30 to 130 nm) and shape (rods and platelets) to better understand their interaction with the protein. The small rod shaped hydroxyapatite nanoparticles decorated collagen fibers gave, in turn, large self-assembling fibrillar structures, characterized by negative charges that could be exploited in layer-by-layer assembly, tuning the supramolecular structure for the requirements of different biomedical applications [ 94 ]. The combination of CL and hydroxyapatite was studied also by Yu et al [ 95 ], which compared different microstructures, cellular or lamellar, to improve scaffold efficiency in bone regeneration [ 95 ].…”

Embedding Collagen in Multilayers for Enzyme-Assisted Mineralization: A Promising Way to Direct Crystallization in Confinement

“…The synthesis of hybrid materials, including both hard mineral and soft bio-organic phases, was, indeed, proposed as a promising option to overcome this challenge. The main advantages of hybrid materials lie in their versatility, and the possibility to tune their chemical composition, bioactivity, and mechanical properties. − In the context of biomineralization, this concept has led to the publication of numerous procedures which can be roughly divided into three categories: (i) mineralization in homogeneous phase of type I collagen, often with the addition of synthetic polymers; (ii) mineralization of adsorbed collagen layers or collagen matrices, that is, in the heterogeneous phase, , and (iii) assembly of collagen and synthesized CaP nanoparticles . These procedures have led to the elaboration of a rich and fascinating repertoire of hybrid nanostructures, which has extended their use in broad biomedical applications .…”