End-Sealed High Aspect Ratio Hollow Nanotubes Encapsulating an Anticancer Drug: Torpedo-Shaped Peptidic Nanocapsules

Spontaneous assembly of a class of small molecule prodrugs directed by SN38

Small molecule self-assembling prodrugs (SAPDs) are an emerging class of amphiphilic monomers that can aggregate into supramolecular nanostructures with high drug loading identical to that of the individual prodrug. Despite great progress in creating nanodrugs via nanoprecipitation, the direct self-assembly of small molecule SAPDs in aqueous solution remains challenging, as the proper hydrophilic-hydrophobic balance and intermolecular interactions have to be rationally considered. We report a class of small molecule SAPDs by conjugating the anticancer drug SN38 as the structure-directing component with various hydrophilic auxiliaries (i.e., oligo ethylene glycol (OEG) of different lengths, amino, and carboxyl groups) via a self-immolative disulfanyl-ethyl carbonate linker. Driven by π-π interactions between SN38 units, these SAPDs spontaneously assembled into well-defined fibrous nanostructures. Variations in hydrophilic domains can robustly regulate the hydrophobicity of SAPDs, as well as the morphologies and surface features of supramolecular filaments, subsequently influencing cellular internalization behaviors. Furthermore, our study also reveals that the parent drug can be efficiently and controllably released in the presence of glutathione (GSH), exhibiting high in vitro toxicity against colorectal cancer cells. In this work, we present a delicate platform to design small molecule SAPDs that can spontaneously self-assemble into supramolecular filamentous assemblies directed by aromatic interaction of the parent drugs, providing a new strategy to optimize supramolecular drug delivery systems.

Reversible transformation of peptide assembly between densified-polysarcosine-driven kinetically and helix-orientation-driven thermodynamically stable morphologies

Stimuli-responsive transformable biomaterials development can be manipulated practically by fine-tuning the built-in molecular design of their structural segments. Here, we demonstrate a peptide assembly by the bola-type amphiphilic polypeptide, glycolic acid-polysarcosine (PSar)13-b-(L-Leu-Aib)6-b-PSar13-glycolic acid (S13L12S13), which shows morphological transformations between hydrophilic chain-driven and hydrophobic unit-driven morphologies. The hydrophobic α-helical unit (L-Leu-Aib)6 precisely controls packing in the hydrophobic layer of the assembly and induces tubule formation. The densified, hydrophilic PSar chain on the assembly surface becomes slightly more hydrophobic as the temperature increases above 70 °C, starting to disturb the helix-helix interaction-driven formation of tubules. As a result, the S13L12S13 peptide assembly undergoes a reversible vesicle-nanotube transformation following a time course at room temperature and a heat treatment above 80 °C. Using membrane fluidity analysis with DPH and TMA-DPH and evaluating the environment surrounding the PSar side chain with NMR, we clarify that the vesicle was in a kinetically stable state driven by the dehydrated PSar chain, while the nanotube was in a thermodynamically stable state.

Peptide-lipid hybrid vesicles with stimuli-responsive phase separation for controlled membrane functions

A disulfide-tethered peptide-lipid conjugate self-assembled into a homogeneously distributed peptide-lipid hybrid vesicle. Upon dithiothreitol treatment, the homogeneous peptide-lipid membrane spontaneously divided into lipid-rich and peptide-rich domains, while the vesicle retained its size and shape. Membrane phase separation enhanced temperature-dependent cargo release.

Self-Assembled Peptide-Based Nanodrugs: Molecular Design, Synthesis, Functionalization, and Targeted Tumor Bioimaging and Biotherapy

Functional nanomaterials as nanodrugs based on the self-assembly of inorganics, polymers, and biomolecules have showed wide applications in biomedicine and tissue engineering. Ascribing to the unique biological, chemical, and physical properties of peptide molecules, peptide is used as an excellent precursor material for the synthesis of functional nanodrugs for highly effective cancer therapy. Herein, recent progress on the design, synthesis, functional regulation, and cancer bioimaging and biotherapy of peptide-based nanodrugs is summarized. For this aim, first molecular design and controllable synthesis of peptide nanodrugs with 0D to 3D structures are presented, and then the functional customization strategies for peptide nanodrugs are presented. Then, the applications of peptide-based nanodrugs in bioimaging, chemotherapy, photothermal therapy (PTT), and photodynamic therapy (PDT) are demonstrated and discussed in detail. Furthermore, peptide-based drugs in preclinical, clinical trials, and approved are briefly described. Finally, the challenges and potential solutions are pointed out on addressing the questions of this promising research topic. This comprehensive review can guide the motif design and functional regulation of peptide nanomaterials for facile synthesis of nanodrugs, and further promote their practical applications for diagnostics and therapy of diseases.

Morphologic design of nanostructures for enhanced antimicrobial activity

Despite significant progress in synthetic polymer chemistry and in control over tuning the structures and morphologies of nanoparticles, studies on morphologic design of nanomaterials for the purpose of optimizing antimicrobial activity have yielded mixed results. When designing antimicrobial materials, it is important to consider two distinctly different modes and mechanisms of activity-those that involve direct interactions with bacterial cells, and those that promote the entry of nanomaterials into infected host cells to gain access to intracellular pathogens. Antibacterial activity of nanoparticles may involve direct interactions with organisms and/or release of antibacterial cargo, and these activities depend on attractive interactions and contact areas between particles and bacterial or host cell surfaces, local curvature and dynamics of the particles, all of which are functions of nanoparticle shape. Bacteria may exist as spheres, rods, helices, or even in uncommon shapes (e.g., box- and star-shaped) and, furthermore, may transform into other morphologies along their lifespan. For bacteria that invade host cells, multivalent interactions are involved and are dependent upon bacterial size and shape. Therefore, mimicking bacterial shapes has been hypothesized to impact intracellular delivery of antimicrobial nanostructures. Indeed, designing complementarities between the shapes of microorganisms with nanoparticle platforms that are designed for antimicrobial delivery offers interesting new perspectives toward future nanomedicines. Some studies have reported improved antimicrobial activities with spherical shapes compared to non-spherical constructs, whereas other studies have reported higher activity for non-spherical structures (e.g., rod, discoid, cylinder, etc.). The shapes of nano- and microparticles have also been shown to impact their rates and extents of uptake by mammalian cells (macrophages, epithelial cells, and others). However, in most of these studies, nanoparticle morphology was not intentionally designed to mimic specific bacterial shape. Herein, the morphologic designs of nanoparticles that possess antimicrobial activities per se and those designed to deliver antimicrobial agent cargoes are reviewed. Furthermore, hypotheses beyond shape dependence and additional factors that help to explain apparent discrepancies among studies are highlighted.

DNA-induced fusion between lipid domains of peptide-lipid hybrid vesicles

Peptide-lipid hybrid vesicles were prepared with complementary DNA strands in their lipid domains. Hybridization of the complementary DNA strands induced the controlled fusion of the vesicles during repeated heating and cooling cycles. Vesicle fusion was indicated by a decrease in the efficiency of Förster resonance energy transfer between lipid-localized probes (from 72 to 42%) and transmission electron microscopy analysis. We suggest that this approach is a general strategy for the creation of polymersomes with membrane-fusion functionality.

End-Sealing of Peptide Nanotubes by Cationic Amphiphilic Polypeptides and Their Salt-Responsive Accordion-like Opening and Closing Behavior

One strategy to prepare phase-separated co-assembly is to use the existing assembly as a platform to architect structures. For this purpose, the edge of a sheet or tube-shaped molecular assembly, which is less hydrophilic than the bulk region can become a starting point to build assembly units to realize more complex structures. In this study, we succeeded in preparing rod-shaped nanocapsules with previously unachieved sealing efficiency (>99%) by fine-tuning the properties of cationic amphiphilic polypeptides to seal the ends of neutral charge nanotubes. In addition, we demonstrated the nanocapsule's reversible responsiveness to salt. In high salt concentrations, a decrease in electrostatic repulsion between cationic polypeptides caused tearing and shrinking of the nanocapsule's sealing dome, which resulted in an opened nanotube. On the other hand, when salt was removed, the electrostatic repulsion among the cationic peptides localizing on the edge of opened nanocapsules was recovered, and the sealing membrane swelled up like an accordion to create a distance between the peptides, resulting in the restoration of the seal.

Supramolecular Hybrids from Cyanometallate Complexes and Diblock Copolypeptide Amphiphiles in Water

The self-assembly of discrete cyanometallates has attracted significant interest due to the potential of these materials to undergo soft metallophilic interactions as well as their optical properties. Diblock copolypeptide amphiphiles have also been investigated concerning their capacity for self-assembly into morphologies such as nanostructures. The present work combined these two concepts by examining supramolecular hybrids comprising cyanometallates with diblock copolypeptide amphiphiles in aqueous solutions. Discrete cyanometallates such as [Au(CN)2]-, [Ag(CN)2]-, and [Pt(CN)4]2- dispersed at the molecular level in water cannot interact with each other at low concentrations. However, the results of this work demonstrate that the addition of diblock copolypeptide amphiphiles such as poly-(L-lysine)-block-(L-cysteine) (Lysm-b-Cysn) to solutions of these complexes induces the supramolecular assembly of the discrete cyanometallates, resulting in photoluminescence originating from multinuclear complexes with metal-metal interactions. Electron microscopy images confirmed the formation of nanostructures of several hundred nanometers in size that grew to form advanced nanoarchitectures, including those resembling the original nanostructures. This concept of combining diblock copolypeptide amphiphiles with discrete cyanometallates allows the design of flexible and functional supramolecular hybrid systems in water.

Hollow Multicomponent Capsules for Biomedical Applications: A Comprehensive Review

Hollow capsules with multi-shelled or multicomponent structures are essential materials for various applications. Biomedical applications like disease diagnosis, therapy, and monitoring have special significance as they aim to improve health conditions. This review demonstrated a comprehensive overview of hollow, multifunctional structures incorporating meaningful use of nanotechnology and its’ unique prospects in medicine such as patient-specific treatment, multimodal imaging, multimodal therapy, simultaneous delivery of drugs and imaging probes, and actively targeted delivery. The internal hollow cavity provides safe and controlled drug release while also enabling transport of functional moieties to target sites. This review explored the performance of different organic, inorganic, and metallic multicomponent capsules that have been reported for biomedical applications, mainly diagnostic imaging and drug delivery. Material compositions, morphologies, and synthesis strategies involved in fabricating such multifunctional systems have been discussed in detail. It is expected that with time, more sophisticated and precise systems will come to light as the outcome of ongoing concentrated research efforts.

Self-assembly and disassembly mechanisms of biomimetic peptides: Molecular dynamics simulation and experimental measurement

Drug-loaded pH-responsive nanoparticles are potential drug carriers in nanotherapeutics delivery because they can remain stable in normal tissues but can disassemble and release drug molecules in tumors. In this study, the mechanisms of self-assembly and disassembly were investigated by analyzing the characteristics of three kinds of biomimetic peptides with different components and sequences. The structural parameters and energy changes during self-assembly and disassembly were calculated by molecular dynamics simulation. Transmission electron microscopy, Fourier transform infrared spectroscopy, and atomic force microscopy were used to observe morphological changes and measure the strength of hydrophobic and hydrophilic interactions between peptides. Results show that the hydrophobic and hydrophilic interactions play crucial roles in the self-assembly and disassembly processes of peptides. The structure of the peptide clusters after self-assembly became tighter as the difference between hydrophobic and hydrophilic interactions increased, whereas a decrease in this difference led to the increased disassembly of the peptides. In general, polyethylene glycol chain modification was necessary in disassembly, and peptides with straight structures had stronger disassembly ability than that with branched structures with the same components. The morphology of peptide clusters can be controlled under different pH values by changing the composition and structure of the peptides for enhanced drug retention and sustained release.

Tubular Assembly Formation Induced by Leucine Alignment along the Hydrophobic Helix of Amphiphilic Polypeptides

The introduction of α-helical structure with a specific helix-helix interaction into an amphipathic molecule enables the determination of the molecular packing in the assembly and the morphological control of peptide assemblies. We previously reported that the amphiphilic polypeptide SL12 with a polysarcosine (PSar) hydrophilic chain and hydrophobic α-helix (l-Leu-Aib)₆ involving the LxxxLxxxL sequence, which induces homo-dimerization due to the concave-convex interaction, formed a nanotube with a uniform 80 nm diameter. In this study, we investigated the importance of the LxxxLxxxL sequence for tube formation by comparing amphiphilic polypeptide SL4A4L4 with hydrophobic α-helix (l-Leu-Aib)₂-(l-Ala-Aib)₂-(l-Leu-Aib)₂ and SL12. SL4A4L4 formed spherical vesicles and micelles. The effect of the LxxxLxxxL sequence elongation on tube formation was demonstrated by studying assemblies of PSar-b-(l-Ala-Aib)-(l-Leu-Aib)₆-(l-Ala-Aib) (SA2L12A2) and PSar-b-(l-Leu-Aib)₈ (SL16). SA2L12A2 formed nanotubes with a uniform 123 nm diameter, while SL16 assembled into vesicles. These results showed that LxxxLxxxL is a necessary and sufficient sequence for the self-assembly of nanotubes. Furthermore, we fabricated a double-layer nanotube by combining two kinds of nanotubes with 80 and 120 nm diameters-SL12 and SA2L12A2. When SA2L12A2 self-assembled in SL12 nanotube dispersion, SA2L12A2 initially formed a rolled sheet, the sheet then wrapped the SL12 nanotube, and a double-layer nanotube was obtained.

Novel insights into biodegradation, interaction, internalization and impacts of high-aspect-ratio TiO2 nanomaterials: A systematic in vivo study using Drosophila melanogaster

The elongated nature of the high-aspect-ratio nanomaterials (NMs) can help us to obtain valuable information on its biodegradation, physical interaction with target-cells, and internalization. Three different length nano-titanium have been studied using Drosophila, TEM, and different biological markers. Nano-titanium, regardless of its shape, was eroded and degraded just entering the gut lumen of the larvae. Results showed that the distinguished shape of nanowires helps to understand the interactions of NMs with the intestinal barrier. The peritrophic membrane, as the first defense line of the intestinal barrier, succeeded in the reservation of NMs, though the perpendicular particles of nanowires stabbing it, making pores, and permitting their translocation into intestinal cells. On the other side, the exposure to TiO₂NPs did not decrease egg-to-adult viability, but all its different shapes, especially nanowires, mediated a wide molecular response including changes of expression in genes involved in stress, antioxidant, repair, and physical interaction responses. All these changes concerning their ability to elevate ROS levels ultimately led to potential genotoxicity. So, the high aspect ratio NMs are efficient in understanding the outstanding issues of NMs exposure, but at the same time could induce genotoxic impact rather than the low aspect ones.

Morphologic design of sugar-based polymer nanoparticles for delivery of antidiabetic peptides

Zwitterionic polymer nanoparticles of diverse morphologies (spherical, cylindrical, and platelet-like) constructed from biocompatible sugar-based polymers are designed to extend the pharmacological activities of short- and long-acting insulin peptides, thereby providing potential for therapeutic systems capable of reducing the frequency of administration and improving patient compliance. Amphiphilic block copolymers composed of zwitterionic poly(d-glucose carbonate) and semicrystalline polylactide segments were synthesized, and the respective block length ratios were tuned to allow formation of nanoscopic assemblies having different morphologies. Insulin-loaded nanoparticles had similar sizes and morphologies to the unloaded nanoparticle counterparts. Laser scanning confocal microscopy imaging of three-dimensional spheroids of vascular smooth muscle cells and fibroblasts after treatment with LIVE/DEAD® stain and FITC-insulin-loaded nanoparticles demonstrated high biocompatibility for the nanoconstructs of the various morphologies and significant intracellular uptake of insulin in both cell lines, respectively. Binding of short-acting insulin and long-acting insulin glargine to nanoparticles resulted in extended hypoglycemic activities in rat models of diabetes. Following subcutaneous injection in diabetic rats, insulin- and insulin glargine-loaded nanoparticles of diverse morphologies had demonstrated up to 2.6-fold and 1.7-fold increase in pharmacological availability, in comparison to free insulin and insulin glargine, respectively. All together, the negligible cytotoxicity, immunotoxicity, and minimal cytokine adsorption onto nanoparticles (as have been demonstrated in our previous studies) provide exciting and promising evidence of biocompatible nanoconstructs that are poised for further development toward the management of diabetes.

Multifunctional biomolecule nanostructures for cancer therapy

Biomolecule-based nanostructures are inherently multifunctional and harbour diverse biological activities, which can be explored for cancer nanomedicine. The supramolecular properties of biomolecules can be precisely programmed for the design of smart drug delivery vehicles, enabling efficient transport in vivo, targeted drug delivery and combinatorial therapy within a single design. In this Review, we discuss biomolecule-based nanostructures, including polysaccharides, nucleic acids, peptides and proteins, and highlight their enormous design space for multifunctional nanomedicines. We identify key challenges in cancer nanomedicine that can be addressed by biomolecule-based nanostructures and survey the distinct biological activities, programmability and in vivo behaviour of biomolecule-based nanostructures. Finally, we discuss challenges in the rational design, characterization and fabrication of biomolecule-based nanostructures, and identify obstacles that need to be overcome to enable clinical translation.

Solvent Effects on the Self-Assembly of an Amphiphilic Polypeptide Incorporating α-Helical Hydrophobic Blocks

The self-assembly of biological molecules is an important pathway to understanding the molecular basis of complex metabolic events. The presence of a cosolvent in an aqueous solution during the self-assembly process can promote the formation of kinetically trapped metastable intermediates. In nature, a category of cosolvents termed osmolytes can work to strengthen the hydrogen-bond network of water such that the native states of certain proteins are favored, thus modulating their function and stability. However, identifying cosolvents that act as osmolytes in biomimetic applications, such as the self-assembly of soft materials, remains challenging. The present work examined the effects of ethanol (EtOH) and acetonitrile (ACN) as cosolvents on the self-assembly of the amphiphilic polypeptide PSar₃₀-(l-Leu-Aib)₆ (S30L12), which incorporates α-helical hydrophobic blocks, in aqueous solution. The results provided a direct observation of morphological behavior of S30L12 as a function of solvent composition. Morphological transitions were investigated using transmission electron microscopy, while the packing of peptide molecules was assessed using circular dichroism analyses and evaluations of membrane fluidity. In the EtOH/H₂O mixtures, the EtOH strengthened the hydrogen-bond network of the water, thus limiting the hydrophobic hydration of S30L12 assemblies and enhancing hydrophobic interactions between assemblies. In contrast, ACN formed self-associated nanoclusters in water and at the hydrophobic cores of peptide assemblies to stabilize the edges exposed to bulk water and enhance the assembly kinetics. Fourier transform infrared (FT-IR) analysis indicated that both EtOH and ACN can modify the self-assembly of biomaterials in the same manner as osmolyte protectants or denaturants.

Sequentially-targeted biomimetic nano drug system for triple-negative breast cancer ablation and lung metastasis inhibition

As a breast cancer subtype with high mortality in women, the efficient treatment of Triple-negative breast cancer (TNBC) is still a challenge due to its unique metastatic mode and poor prognosis. In this study, we developed a biomimetic nanodelivery system (denoted as GTDC@M-R NPs) based on erythrocyte membrane (M)-camouflaged graphene oxide quantum dots (GOQDs, G) for TNBC therapy. The TAT (T) and RGD (R) peptides were used to endow targeting accumulation ability of Gamabufotalin (CS-6, C) and doxorubicin (DOX, D) in tumor tissue. In vitro assay indicated good biocompatibility, prolonged blood circulation time (3-fold longer than GT NPs), and effectively enhanced cell and nucleus targeting capability of this nanosystem. Fluorescence activated cell sorter (FACS) analysis indicated that the combination of DOX and CS-6 induced TNBC cell apoptosis more than 89 % under the ratio of 10:1. In vivo assay indicated that the accumulation of GTDC@M-R NPs in tumor sites increased about 2-fold compared to naked GTDC NPs, which was accompanied by high tumor apoptosis rates through blocking chemotherapy-activated cyclooxygenase-2 (COX-2) and enhancing DOX's anti-tumor activity of chemical drugs (85%). Moreover, comparing with the control, the average number of lung metastatic nodules in tumor-bearing mice reduced 84%, the molecular mechanism of which is related to the down expression of COX-2, matrix metalloproteinase 9 (MMP9) and vascular endothelial growth factor (VEGF). Taken together, our results proved that the developed GTDC@M-R NPs can inhibit the growth and suppress metastasis of TNBC, which broaden our insights into the application of combinational strategy for efficient TNBC therapy. STATEMENT OF SIGNIFICANCE: In this study, we developed a biomimetic nanodelivery system (denoted as GTDC@M-R NPs) based on erythrocyte membrane (M)-camouflaged graphene oxide quantum dots (GOQDs, G) for TNBC therapy. The TAT (T) and RGD (R) peptides were used to endow targeting accumulation ability of Gamabufotalin (CS-6, C) and doxorubicin (DOX, D) in tumor tissue. These GTDC@M-R NPs indicated synergistic chemotherapy against TNBC cells through the precise cell and nuclear targeting, immune escape, and improved DOX sensitivity. A effective inhibition of tumor growth and metastasis was achieved by inhibiting Bcl-2/BAX, COX-2 and VEGF related signal pathways. Our finding suggests that the developed GTDC@M-R NPs present great treating effects in the preclinical models of TNBC, which broaden our insights into the application of combinational strategy for efficient TNBC therapy.

Synthesis and Characterization of Dendrimer-Based Polysarcosine Star Polymers: Well-Defined, Versatile Platforms Designed for Drug-Delivery Applications

This paper describes the synthesis of star polymers designed for future drug-delivery applications. A generation-5 lysine dendrimer was used as a macroinitiator for the ring-opening polymerization of the sarcosine N-carboxyanhydride monomer to produce 32-arm star polymers with narrow molar mass distributions and desirable hydrodynamic size control. Fluorescent dye-labeled polymers were dosed in mice to measure plasma pharmacokinetics. Long circulation times were observed, representing ideal properties for biophysical targeting of tumors. In vivo efficacy of one of these star polymers conjugated to the therapeutic molecule SN-38 was evaluated in mice bearing SW620 xenografted tumors to demonstrate high antitumor activity and low body weight loss compared to the SN-38 prodrug irinotecan and this shows the potential of these delivery systems. As a further build, we demonstrated that these star polymers can be easily chain-end-functionalized with useful chemical moieties, giving opportunities for future receptor-targeting strategies. Finally, we describe the synthetic advantages of these star polymers that make them attractive from a pharmaceutical manufacturing perspective and report characterization of the polymers with a variety of techniques.

Multimodal theranostics augmented by transmembrane polymer-sealed nano-enzymatic porous MoS2 nanoflowers

Developing an all-in-one multimodal theranostic platform that can synergistically integrate sensitive photoacoustic (PA) imaging, enhanced photothermal therapy (PTT) and photodynamic therapy (PDT) as well as the nano-enzyme activated chemodynamic therapy (CDT) presents a great challenge for the current nanomedicine design. Herein, a simple hydrothermal method was used to prepare porous molybdenum disulfide (MoS₂) nanoflowers. These nanoflowers were assembled by three dimensional (3D)-stacked MoS₂ nanosheets with plentiful pores and large surfaces, which thus exhibited enhanced photothermal conversion via light trapping and peroxidase (POD)-like activity via active defects exposure. Consequently, this 3D-MoS₂ nanostructure could be well-sealed by polyethylene glycol-polyethylenimine polymer modified with nucleolar translocation signal sequence of the LIM Kinase 2 protein (LNP) via strong electrostatic interaction, which not only benefited to stably deliver anticancer drug doxorubicin (DOX) into the tumor cells for pH/NIR-responsive chemotherapy, but also provided strong photoacoustic, photothermal performances and stimulated generation of reactive oxygen species (ROS) for imaging-guided PTT/PDT/CDT combined therapy. This work promised a simple all-in-one multimodal theranostic platform to augment the potential antitumoral therapeutic outcomes.

Neutron Activated 153Sm Sealed in Carbon Nanocapsules for in Vivo Imaging and Tumor Radiotherapy

Radiation therapy along with chemotherapy and surgery remain the main cancer treatments. Radiotherapy can be applied to patients externally (external beam radiotherapy) or internally (brachytherapy and radioisotope therapy). Previously, nanoencapsulation of radioactive crystals within carbon nanotubes, followed by end-closing, resulted in the formation of nanocapsules that allowed ultrasensitive imaging in healthy mice. Herein we report on the preparation of nanocapsules initially sealing "cold" isotopically enriched samarium (152Sm), which can then be activated on demand to their "hot" radioactive form (153Sm) by neutron irradiation. The use of "cold" isotopes avoids the need for radioactive facilities during the preparation of the nanocapsules, reduces radiation exposure to personnel, prevents the generation of nuclear waste, and evades the time constraints imposed by the decay of radionuclides. A very high specific radioactivity is achieved by neutron irradiation (up to 11.37 GBq/mg), making the "hot" nanocapsules useful not only for in vivo imaging but also therapeutically effective against lung cancer metastases after intravenous injection. The high in vivo stability of the radioactive payload, selective toxicity to cancerous tissues, and the elegant preparation method offer a paradigm for application of nanomaterials in radiotherapy.

Tubular Network Formation by Mixing Amphiphilic Polypeptides with Differing Hydrophilic Blocks

Artificial tubular networks are promising structures for biomaterial applications because of their large surface areas. A tubular network was formed by co-assembling two different amphiphilic polypeptides, poly(ethylene glycol)-b-(l-Leu-Aib)₆ (PL12) and polysarcosine-b-(l-Leu-Aib)₆ (SL12). They both have the same hydrophobic 12-mer helical block (l-Leu-Aib)₆ but different hydrophilic chains, poly(ethylene glycol) and polysarcosine. In water, both polypeptides self-assembled into a tubular structure having a uniform 80 nm diameter that was formed by packing among the hydrophobic L12 blocks. The SL12 nanotubes were short (200 nm), straight, and robust. PL12 formed long (>1 μm), bendable, and fusogenic nanotubes. The amphiphiles were then co-assembled with various mixing ratios to form tubular networks. Higher concentrations of PL12 made the nanotubes more bendable and fusogenic between open tube ends, which produced branching junctions under heat treatment.

The controlled synthesis of complex hollow nanostructures and prospective applications†

Functionality in nanoengineered materials has been usually explored on structural and chemical compositional aspects of matter that exist in such solid materials. It is well known that the absence of solid matter is also relevant and the existence of voids confined in the nanostructure of certain particles is no exception. Indeed, over the past decades, there has been great interest in exploring hollow nanostructured materials that besides the properties recognized in the dense particles also provide empty spaces, in the sense of condensed matter absence, as an additional functionality to be explored. As such, the chemical synthesis of hollow nanostructures has been driven not only for tailoring the size and shape of particles with well-defined chemical composition, but also to achieve control on the type of hollowness that characterize such materials. This review describes the state of the art on late developments concerning the chemical synthesis of hollow nanostructures, providing a number of examples of materials obtained by distinct strategies. It will be apparent by reading this progress report that the absence of solid matter determines the functionality of hollow nanomaterials for several technological applications.