Correction: Protein patterns template arrays of magnetic nanoparticles.

[This corrects the article DOI: 10.1039/C6RA07662A.].

Morphological transformations in the magnetite biomineralizing protein Mms6 in iron solutions: a small-angle X-ray scattering study.

Magnetotactic bacteria that produce magnetic nanocrystals of uniform size and well-defined morphologies have inspired the use of biomineralization protein Mms6 to promote formation of uniform magnetic nanocrystals in vitro. Small angle X-ray scattering (SAXS) studies in physiological solutions reveal that Mms6 forms compact globular three-dimensional (3D) micelles (approximately 10 nm in diameter) that are, to a large extent, independent of concentration. In the presence of iron ions in the solutions, the general micellar morphology is preserved, however, with associations among micelles that are induced by iron ions. Compared with Mms6, the m2Mms6 mutant (with the sequence of hydroxyl/carboxyl containing residues in the C-terminal domain shuffled) exhibits subtle morphological changes in the presence of iron ions in solutions. The analysis of the SAXS data is consistent with a hierarchical core-corona micellar structure similar to that found in amphiphilic polymers. The addition of ferric and ferrous iron ions to the protein solution induces morphological changes in the micellar structure by transforming the 3D micelles into objects of reduced dimensionality of 2, with fractal-like characteristics (including Gaussian-chain-like) or, alternatively, platelet-like structures.

Nucleation of iron oxide nanoparticles mediated by Mms6 protein in situ.

Biomineralization proteins are widely used as templating agents in biomimetic synthesis of a variety of organic-inorganic nanostructures. However, the role of the protein in controlling the nucleation and growth of biomimetic particles is not well understood, because the mechanism of the bioinspired reaction is often deduced from ex situ analysis of the resultant nanoscale mineral phase. Here we report the direct visualization of biomimetic iron oxide nanoparticle nucleation mediated by an acidic bacterial recombinant protein, Mms6, during an in situ reaction induced by the controlled addition of sodium hydroxide to solution-phase Mms6 protein micelles incubated with ferric chloride. Using in situ liquid cell scanning transmission electron microscopy we observe the liquid iron prenucleation phase and nascent amorphous nanoparticles forming preferentially on the surface of protein micelles. Our results provide insight into the early steps of protein-mediated biomimetic nucleation of iron oxide and point to the importance of an extended protein surface during nanoparticle formation.

The role of glucose transporters in the distribution of p-aminophenyl-α-d-mannopyranoside modified liposomes within mice brain.

The effective treatment of central nervous system diseases is a major challenge due to the presence of the blood-brain barrier (BBB). P-aminophenyl-α-d-mannopyranoside (MAN), a kind of mannose analog, was conjugated onto the surface of liposomes (MAN-LIP) to enhance the brain delivery. In this study, we investigated the brain distribution of MAN-LIP based on our previous studies and tried to explore the relationship between the distribution of MAN-LIP and glucose transporters (GLUTs) on the cells. In vivo optical imaging was used to assess the distribution of liposomes in mice brain. The mice administered with MAN-LIP had significantly higher brain fluorescence intensity and MAN-LIP relatively concentrated in the cerebellum and cerebral cortex. Fluorescent microscope and Western blot were used to evaluate the results of lentiviral vector-mediated hSLC2A1 and hSLC2A3 gene transfection into C6, PC12 and vessels of endothelial cell line, bEND.3. The results from live cell station and flow cytometry showed that the cellular uptake of MAN-LIP was significantly improved by GLUT1 and GLUT3 overexpression cells. The transport experiments also demonstrated that the transendothelial ability of MAN-LIP was much stronger when crossing LV-GLUT1/bEND.3 cell monolayers or LV-GLUT3/ bEND.3 cell monolayers, of which GLUT1 and GLUT3 were overexpressed. The combined data indicated that the transcytosis by GLUT1 and GLUT3 was a pathway of MAN-LIP into brain, and the special brain distribution of MAN-LIP was closely related to the non-homogeneous distribution of GLUT1 and GLUT3 in the brain.

Emerging nanostructured materials for musculoskeletal tissue engineering.

The musculoskeletal tissues are highly ordered nanostructured materials, and they have self-healing capability. However, when the tissue damage is beyond the capability, therapeutic approaches to repair or regenerate the tissues are needed. Nanomaterials have attracted much research attention to create novel tissue engineering scaffolds, because of their small size, large surface area, enhanced mechanical properties, tunable molecular and chemical structures, and various surface functionalities. With the development of nanotechnology, nanostructured materials with properties that more closely fulfill the requirement in the course of recovery of native tissues were designed, synthesized, characterized and utilized systematically. Here, we introduce the microenvironment of the extracellular matrix in musculoskeletal tissues. We further summarize the nanostructured materials currently used in musculoskeletal tissue engineering including natural polymers, synthetic polymers and inorganic materials. Specifically, the fabrication and applications of different nanomaterials in bone, cartilage, and muscle tissue engineering are discussed in detail. The most recent research achievements in each category are presented and discussed. Overall, nanostructured materials can be synthesized with controlled composition, size, geometry, and morphology. In order to enhance biocompatibility, immune compatibility and cell adhesion, the surface of these materials can be modified for different applications in musculoskeletal tissue scaffolds. Although more tasks and challenges need to be addressed and resolved in order to translate them into commercialized products, nanostructured materials represent very promising candidates in the development of musculoskeletal tissue engineering in the future.

Multifunctional nanoparticles for targeted delivery of immune activating and cancer therapeutic agents.

Nanoparticles (NPs) have been extensively investigated for applications in both experimental and clinical settings to improve delivery efficiency of therapeutic and diagnostic agents. Most recently, novel multifunctional nanoparticles have attracted much attention because of their ability to carry diverse functionalities to achieve effective synergistic therapeutic treatments. Multifunctional NPs have been designed to co-deliver multiple components, target the delivery of drugs by surface functionalization, and realize therapy and diagnosis simultaneously. In this review, various materials of diverse chemistries for fabricating multifunctional NPs with distinctive architectures are discussed and compared. Recent progress involving multifunctional NPs for immune activation, anticancer drug delivery, and synergistic theranostics is the focus of this review. Overall, this comprehensive review demonstrates that multifunctional NPs have distinctive properties that make them highly suitable for targeted therapeutic delivery in these areas.

Integrated self-assembly of the Mms6 magnetosome protein to form an iron-responsive structure.

A common feature of biomineralization proteins is their self-assembly to produce a surface consistent in size with the inorganic crystals that they produce. Mms6, a small protein of 60 amino acids from Magnetospirillum magneticum strain AMB-1 that promotes the in vitro growth of superparamagnetic magnetite nanocrystals, assembles in aqueous solution to form spherical micelles that could be visualized by TEM and AFM. The results reported here are consistent with the view that the N and C-terminal domains interact with each other within one polypeptide chain and across protein units in the assembly. From studies to determine the amino acid residues important for self-assembly, we identified the unique GL repeat in the N-terminal domain with additional contributions from amino acids in other positions, throughout the molecule. Analysis by CD spectroscopy identified a structural change in the iron-binding C-terminal domain in the presence of Fe3+. A change in the intrinsic fluorescence of tryptophan in the N-terminal domain showed that this structural change is transmitted through the protein. Thus, self-assembly of Mms6 involves an interlaced structure of intra- and inter-molecular interactions that results in a coordinated structural change in the protein assembly with iron binding.

Self-assembly and biphasic iron-binding characteristics of Mms6, a bacterial protein that promotes the formation of superparamagnetic magnetite nanoparticles of uniform size and shape.

Highly ordered mineralized structures created by living organisms are often hierarchical in structure with fundamental structural elements at nanometer scales. Proteins have been found responsible for forming many of these structures, but the mechanisms by which these biomineralization proteins function are generally poorly understood. To better understand its role in biomineralization, the magnetotactic bacterial protein, Mms6, which promotes the formation in vitro of superparamagnetic magnetite nanoparticles of uniform size and shape, was studied for its structure and function. Mms6 is shown to have two phases of iron binding: one high affinity and stoichiometric and the other low affinity, high capacity, and cooperative with respect to iron. The protein is amphipathic with a hydrophobic N-terminal domain and hydrophilic C-terminal domain. It self-assembles to form a micelle, with most particles consisting of 20-40 monomers, with the hydrophilic C-termini exposed on the outside. Studies of proteins with mutated C-terminal domains show that the C-terminal domain contributes to the stability of this multisubunit particle and binds iron by a mechanism that is sensitive to the arrangement of carboxyl/hydroxyl groups in this domain.

Synthesis of a novel photopolymerized nanocomposite hydrogel for treatment of acute mechanical damage to cartilage.

Intra-articular fractures initiate a cascade of pathobiological and pathomechanical events that culminate in post-traumatic osteoarthritis (PTOA). Hallmark features of PTOA include destruction of the cartilage matrix in combination with loss of chondrocytes and acute mechanical damage (AMD). Currently, treatment of intra-articular fractures essentially focuses completely on restoration of the macroanatomy of the joint. However, current treatment ignores AMD sustained by cartilage at the time of injury. We are exploring aggressive biomaterial-based interventions designed to treat the primary pathological components of AMD. This study describes the development of a novel injectable co-polymer solution that forms a gel at physiological temperatures that can be photocrosslinked, and can form a nanocomposite gel in situ through mineralization. The injectable co-polymer solution will allow the material to fill cracks in the cartilage after trauma. The mechanical properties of the nanocomposite are similar to those of native cartilage, as measured by compressive and shear testing. It thereby has the potential to mechanically stabilize and restore local structural integrity to acutely injured cartilage. Additionally, in situ mineralization ensures good adhesion between the biomaterial and cartilage at the interface, as measured through tensile and shear testing. Thus we have successfully developed a new injectable co-polymer which forms a nanocomposite in situ with mechanical properties similar to those of native cartilage, and which can bond well to native cartilage. This material has the potential to stabilize injured cartilage and prevent PTOA.