Bioinspired synthesis of self-assembled calcium phosphate nanocomposites using block copolymer-peptide conjugates
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P. Thiyagarajan Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439
Mufit Akinc, Klaus Schmidt-Rohr, and Surya Mallapragadab) Ames Laboratory, Ames, Iowa 50011 (Received 29 April 2008; accepted 18 August 2008)
Thermoreversibly gelling block copolymers conjugated to hydroxyapatite-nucleating peptides were used to template the growth of inorganic calcium phosphate in aqueous solutions. Nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), transmission electron microscopy, x-ray diffraction, and small-angle scattering were used to characterize these samples and confirm that the peptides promoted the growth of hydroxyapatite as the inorganic phase. Three different polymer templates were used with varying charges on the polymer chains (nonionic, anionic, and zwitterionic), to investigate the role of charge on mineralization. All of the polymer-inorganic solutions exhibited thermoreversible gelation above room temperature. Nanocomposite formation was confirmed by solid-state NMR, and several methods identified the inorganic component as hydroxyapatite. Small angle x-ray scattering and electron microscopy showed thin, elongated crystallites. Thermogravimetric analysis showed an inorganic content of 30–45 wt% (based on the mass of the dried gel at ∼200 °C) in the various samples. Our work offers routes for bioinspired bottom-up approaches for the development of novel, self-assembling, injectable nanocomposite biomaterials for potential orthopedic applications. I. INTRODUCTION
Tremendous literature has appeared in recent years to explore ways to mimic biomineralization1–4 and to understand the mechanism(s) involved in it with proteins, enzymatic biocatalysts, and other biopolymers.5–9 Numerous studies have appeared on the in vitro synthesis and characterization of biominerals including calcium phosphate, calcium carbonate, and silica.10–15 All of these studies have focused on templating at the nanoscale or at the macroscale, but mostly only on the surface. Controlling the structure at the molecular level as well as impressing hierarchical order over multiple-length scales as seen commonly in nature is a formidable challenge that has not been achieved yet, but significant progress is being made in these directions. Polymer templating has the advantage of molecular-level control and a promise to extend to the macroscale by hierarchical ordering. Our recent work has shown that synthetic block copolymers that undergo self-assembly at multiplea)
These authors contributed equally to this work. Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0388 b)
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http://journals.cambridge.org
J. Mater. Res., Vol. 23, No. 12, Dec 2008 Downloaded: 18 Mar 2015
length scales can serve as effective templates for precipitation of calcium phosphates on nanoscale micelles, which can self-assemble further into macroscale gels and solids.16 This is one of the first approaches for bottom-up design of macroscale composites with hierarchical order down to the n
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