Bone is a composite material, in which collagen fibrils form a scaffold for a highly organized arrangement of uniaxially oriented apatite crystals1,2. In the periodic 67 nm cross-striated pattern of the collagen fibril3–5, the less dense 40-nm-long gap zone has been implicated as the place where apatite crystals nucleate from an amorphous phase, and subsequently grow6–9. This process is believed to be directed by highly acidic non-collagenous proteins6,7,9–11; however, the role of the collagen matrix12–14 during bone apatite mineralization remains unknown. Here, combining nanometre-scale resolution cryogenic transmission electron microscopy and cryogenic electron tomography15 with molecular modelling, we show that collagen functions in synergy with inhibitors of hydroxyapatite nucleation to actively control mineralization. The positive net charge close to the C-terminal end of the collagen molecules promotes the infiltration of the fibrils with amorphous calcium phosphate (ACP). Furthermore, the clusters of charged amino acids, both in gap and overlap regions, form nucleation sites controlling the conversion of ACP into a parallel array of oriented apatite crystals. We developed a model describing the mechanisms through which the structure, supramolecular assembly and charge distribution of collagen can control mineralization in the presence of inhibitors of hydroxyapatite nucleation.

Internally structured self-assembled nanospheres, cubosomes, are formed from a semi-crystalline block copolymer, poly(ethylene oxide)-block-poly(octadecyl methacrylate) (PEO39-b-PODMA17), in aqueous dispersion. The poly(octadecyl methacrylate) block provides them with a temperature responsive structure and morphology. Using cryo-electron tomography, we show that at room temperature these internally bicontinuous aggregates undergo an unprecedented order-disorder transition of the microphase separated domains that is accompanied by a change in the overall aggregate morphology. This allows switching between spheres with ordered bicontinuous internal structures at temperatures below the transition temperature and more planar oblate spheroids with a disordered microphase-separated state above the transition temperature. The bicontinuous structures offer a number of possibilities for application as templates e.g. for biomimetic mineralisation or polymerization. Furthermore, the unique nature of the thermal transition observed for this system offers up considerable possibilities for their application as temperature-controlled release vessels. Amphiphilic AB and ABA block copolymers have been demonstrated to form a variety of self-assembled aggregate structures in dilute solutions where the solvent preferentially solvates one of the blocks. Temperature responsive nanospheres with bicontinuous internal structures from a semi-crystalline amphiphilic block copolymer1 The most common structures formed by these amphiphilic macromolecules are spherical micelles, cylindrical micelles and vesicles (polymersomes), with the type of aggregate depending principally upon the relative volumes of the different blocks.1 Over the past decade more complex aggregate structures have been observed and targeted for construction. The majority of these aggregates (such as disk-like and toroidal micelles) may be grouped under the description of complex micelles and can be achieved both through manipulating block copolymer structures and through physical means.2 Multicompartment micelles are typically the result of ABC block copolymers, of which one of the blocks is solvophilic and the remaining two are solvophobic but do not mix.3 Hence microphase separated micellar cores result.We recently reported the experimental observation of complex micelles with bicontinuous hydrophilic/hydrophobic internal structures from amphiphilic norbornene-based double-comb diblock copolymers, with peptide and oligo(ethylene oxide) side chain.4 Block copolymer nanoparticles with similar bicontinuous phase separation have also been observed by Wooley et al, 5 and before that were predicted by Fraaije and Sevink. 6 In the present paper we demonstrate the formation of similar complex micelles, with hydrophobic bicontinuous internal morphologies from an amphiphilic semi-crystalline AB(C) comb-like block copolymer. Using cryo-electron tomography, we show that at room temperature these internally structured nanoparticles undergo an unprecedented order-disorder transiti...

Controlled modification of horseradish peroxidase with an apolar polymer chain (see figure) by cofactor reconstitution leads to giant amphiphiles, which form vesicular aggregates in aqueous solution.

Inspired by the remarkable shapes and properties of CaCO(3) biominerals, many studies have investigated biomimetic routes aiming at synthetic equivalents with similar morphological and structural complexity. Control over the morphology of CaCO(3) crystals has been demonstrated, among other methods, by the use of additives that selectively allow the development of specific crystal faces, while inhibiting others. Both for biogenic and biomimetic CaCO(3), the crystalline state is often preceded by an amorphous precursor phase, but still limited information is available on the details of the amorphous-to-crystalline transition. By using a combination of cryoTEM techniques (bright field imaging, cryo-tomography, low dose electron diffraction and cryo-darkfield imaging), we show for the first time the details of this transition during the formation of hexagonal vaterite crystals grown in the presence of NH(4)(+) ions. The formation of hexagonal plate-like vaterite occurs via an amorphous precursor phase. This amorphous phase converts into the crystalline state through a solid state transformation in which order and morphology develop simultaneously. The mineral initially develops as polycrystalline vaterite which transforms into a single crystal directed by an NH(4)(+)-induced crystal plane that acts as a templating surface.