Biomimetic Formation of Hydroxyapatite Nanorods by a Single‐Crystal‐to‐Single‐Crystal Transformation

Uniform nanorods of hydroxyapatite (HAP) with an unusual orthorhombic shape have been synthesized from homogeneous solutions of Ca²⁺ and HPO₄^2– in the presence of gelatin and urea. The lengths of the nanorods are in the range of hundreds of micrometers, and the widths are about 100 nm. The HAP phase is generated by the transformation from its precursor phase of octacalcium phosphate (OCP), which has been monitored by X‐ray diffraction, NMR spectroscopy, scanning electron microscopy, and transmission electron microscopy. The rise in pH due to the decomposition of urea drives the OCP transformation to HAP. In the presence of gelatin, nanorods of OCP phase formed first and then transformed into the HAP phase, preserving the single‐crystal morphology. On the other hand, blade‐like OCP crystals form from the solution in the absence of gelatin. On increasing the pH of the solution, the large, blade‐like OCP crystals tend to crash into irregular, hexagonal HAP crystallites. A single‐crystal‐to‐single‐crystal topochemical transformation may be attributed to the evolution of HAP nanorods from the precursor OCP phase. This gives a strong indication as to the OCP to HAP transformation mechanism in the mineralization of biological apatite in tooth enamel and bone.     

Self‐Assembly of a Micelle Structure from Graft and Diblock Copolymers: An Example of Overcoming the Limitations of Polyions in Drug Delivery

A novel mixed micelle with a multifunctional core and shell is successfully prepared from a graft copolymer, poly(N‐isopropyl acrylamide‐co‐methacrylic acid)‐g‐poly(d,l ‐lactide) (P(NIPAAm‐co‐MAAc)‐g‐PLA) and two diblock copolymers, poly(ethylene glycol)‐b‐poly(d,l ‐lactide) and poly (2‐ethyl‐2‐oxazoline)‐b‐poly(d,l ‐lactide). This nanostructure completely screens the highly negative charges of the graft copolymer and exhibits multifunctionality because it has a specialized core/shell structure. An example of this micelle structure used in intracellular drug delivery demonstrates a strong relationship between drug release and the functionality of the mixed micelle. Additionally, the efficiency of the screening feature is also displayed in the cytotoxicities; mixed micelles exhibit higher drug activity and lower material cytotoxicity than micelles from P(NIPAAm‐co‐MAAc)‐g‐PLA ([NIPAAm]/[MAAc]/[PLA] = 84:5.9:2.5 mol/mol) copolymer. This study not only presents a new micelle structure generated using a graft–diblock copolymer system, but also elucidates concepts upon which the preparation of a multifunctional micelle from a graft copolymer with a single (or many) diblock copolymer(s) can be based for applications in drug delivery.     

Dextran Microgels for Time‐Controlled Delivery of siRNA

To apply siRNA as a therapeutic agent, appropriate attention should be paid to the optimization of the siRNA gene silencing effect, both in terms of magnitude and duration. Intracellular time‐controlled siRNA delivery could aid in tailoring the kinetics of siRNA gene knockdown. However, materials with easily tunable siRNA release properties have not been subjected to thorough investigation thus far. This report describes cationic biodegradable dextran microgels which can be loaded with siRNA posterior to gel formation. Even though the siRNAs are incorporated in the hydrogel network based on electrostatic interaction, still a time‐controlled release can be achieved by varying the initial network density of the microgels. To demonstrate the biological functionality of the siRNA loaded gels, we studied their cellular internalization and enhanced green fluorescent protein (EGFP) gene silencing potential in HUH7 human hepatoma cells.     

Multifunctional Core/Shell Nanoparticles Self‐Assembled from pH‐Induced Thermosensitive Polymers for Targeted Intracellular Anticancer Drug Delivery

Core/shell nanoparticles that display a pH‐sensitive thermal response, self‐assembled from the amphiphilic tercopolymer, poly(N‐isopropylacrylamide‐co‐N,N‐dimethylacrylamide‐co‐10‐undecenoic acid) (P(NIPAAm‐co‐DMAAm‐co‐UA)), have recently been reported. In this study, folic acid is conjugated to the hydrophilic segment of the polymer through the free amine group (for targeting cancer cells that overexpress folate receptors) and cholesterol is grafted to the hydrophobic segment of the polymer. This polymer also self‐assembles into core/shell nanoparticles that exhibit pH‐induced temperature sensitivity, but they possess a more stable hydrophobic core than the original polymer P(NIPAAm‐co‐DMAAm‐co‐UA) and a shell containing folate molecules. An anticancer drug, doxorubicin (DOX), is encapsulated into the nanoparticles. DOX release is also pH‐dependent. DOX molecules delivered by P(NIPAAm‐co‐DMAAm‐co‐UA) and folate‐conjugated P(NIPAAm‐co‐DMAAm‐co‐UA)‐g‐cholesterol nanoparticles enter the nucleus more rapidly than those transported by P(NIPAAm‐co‐DMAAm)‐b‐poly(lactide‐co‐glycolide) nanoparticles, which are not pH sensitive. More importantly, these nanoparticles can recognize folate‐receptor‐expressing cancer cells. Compared to the nanoparticles without folate, the DOX‐loaded nanoparticles with folate yield a greater cellular uptake because of the folate‐receptor‐mediated endocytosis process, and, thus, higher cytotoxicity results. These multifunctional polymer core/shell nanoparticles may make a promising carrier to target drugs to cancer cells and release the drug molecules to the cytoplasm inside the cells.     

Doxorubicin‐Conjugated Immuno‐Nanoparticles for Intracellular Anticancer Drug Delivery

A polymeric nanoparticle comprised of surface furan groups is used to bind, by Diels–Alder (DA) coupling chemistry, both targeting anti‐human epidermal growth factor receptor 2 (anti‐HER2) antibodies and chemotherapeutic doxorubicin (DOX) for targeted, intracellular delivery of DOX. In this new approach for delivery, where both chemotherapeutic and targeting ligand are attached, for the first time, to the surface of the delivery vehicle, the nuclear localization of DOX in HER2‐overexpressing breast cancer SKBR‐3 cells is demonstrated, as determined by confocal laser scanning microscopy. Flow cytometric analysis shows that the conjugated DOX maintains its biological function and induces similar apoptotic progression in SKBR‐3 cells as free DOX. The viable cell counts of SKBR‐3 cancer cells following incubation with different nanoparticle formulations demonstrates that the combined DOX and anti‐HER2 nanoparticle is more efficacious than the nanoparticle formulation with either DOX or anti‐HER2 alone. While free DOX shows similar cytotoxicity against both cancerous SKBR‐3 cells and healthy HMEC‐1 cells, the combined DOX‐anti‐HER2 nanoparticle is significantly more cytotoxic against SKBR‐3 cells than HMEC‐1 cells, suggesting the benefit of nanoparticle‐conjugated DOX for cell type‐specific targeting. The DOX‐conjugated immuno‐nanoparticle represents an entirely new method for localized co‐delivery of chemotherapeutics and antibodies.     

Aligned Protein-Polymer Composite Fibers Enhance Nerve Regeneration: A Potential Tissue-Engineering Platform

Sustained release of proteins from aligned polymeric fibers holds great potential in tissue-engineering applications. These protein-polymer composite fibers possess high surface-area-to-volume ratios for cell attachment, and can provide biochemical and topographic cues to enhance tissue regeneration. Aligned biodegradable polymeric fibers that encapsulate human glial cell-derived neurotrophic factor (GDNF, 0.13 wt%) were fabricated via electrospinning a copolymer of caprolactone and ethyl ethylene phosphate (PCLEEP) with GDNF. The protein was randomly dispersed throughout the polymer matrix in aggregate form, and released in a sustained manner for up to two months. The efficacy of these composite fibers was tested in a rat model for peripheral nerve-injury treatment. Rats were divided into four groups, receiving either empty PCLEEP tubes (control); tubes with plain PCLEEP electrospun fibers aligned longitudinally (EF-L) or circumferentially (EF-C); or tubes with aligned GDNF-PCLEEP fibers (EF-L-GDNF). After three months, bridging of a 15 mm critical defect gap by the regenerated nerve was observed in all the rats that received nerve conduits with electrospun fibers, as opposed to 50% in the control group. Electrophysiological recovery was seen in 20%, 33%, and 44% of the rats in the EF-C, EF-L, and EF-L-GDNF groups respectively, whilst none was observed in the controls. This study has demonstrated that, without further modification, plain electrospun fibers can help in peripheral nerve regeneration; however, the synergistic effect of an encapsulated growth factor facilitated a more significant recovery. This study also demonstrated the novel use of electrospinning to incorporate biochemical and topographical cues into a single implant for in vivo tissue-engineering applications.     

Production and Potential of Bioactive Glass Nanofibers as a Next‐Generation Biomaterial

Over the past decades, bioactive glass has played a central role in the bone regeneration field, due to its excellent bioactivity, osteoconductivity, and even osteoinductivity. Herein, exploitation of bioactive glass as a one‐dimensional nanoscale fiber by employing an electrospinning process based on a sol–gel precursor is reported for the first time. Under controlled processing conditions, continuous nanofibers have been generated successfully with variable diameters. The excellent bioactivity of the nanofiber is confirmed in vitro within a simulated body fluid by the rapid induction of bonelike minerals onto the nanofiber surface. The bone‐marrow‐derived cells are observed to attach and proliferate actively on the nanofiber mesh, and differentiate into osteoblastic cells with excellent osteogenic potential. The bioactive nanofibers have been further exploited in various forms, such as bundled filament, nanofibrous membrane, 3D macroporous scaffold, and nanocomposite with biopolymer, suggesting their versatility and potential applications in bone‐tissue engineering. Based on this study, the bioactive nanofibrous matrix is regarded as a promising next‐generation biomaterial in the bone‐regeneration field.     

Uniform Rattle‐type Hollow Magnetic Mesoporous Spheres as Drug Delivery Carriers and their Sustained‐Release Property

A novel kind of rattle‐type hollow magnetic mesoporous sphere (HMMS) with Fe₃O₄ particles encapsulated in the cores of mesoporous silica microspheres has been successfully fabricated by sol–gel reactions on hematite particles followed by cavity generation with hydrothermal treatment and H₂ reduction. Such a structure has the merits of both enhanced drug‐loading capacity and a significant magnetization strength. The prepared HMMSs realize a relatively high storage capacity up to 302 mg g^?1 when ibuprofen is used as a model drug, and the IBU–HMMS system has a sustained‐release property, which follows a Fick's law.     

Novel Magnetic Hydroxyapatite Nanoparticles as Non‐Viral Vectors for the Glial Cell Line‐Derived Neurotrophic Factor Gene

Nanoparticles (NPs) of synthetic hydroxyapatite (Hap) and natural bone mineral (NBM) are rendered magnetic by treatment with iron ions using a wet‐chemical process. The magnetic NPs (mNPs), which are about 300 nm in diameter, display superparamagnetic properties in a superconducting quantum interference device, with a saturation magnetization of about 30 emu g^?1. X‐ray diffraction and transmission electron microscopy reveal that the magnetic properties of the NPs are the result of the hetero‐epitaxial growth of magnetite on the Hap and NBM crystallites. The mNPs display a high binding affinity for plasmid DNA in contrast to magnetite NPs which do not bind the plasmid well. The mHap and mNBM NPs result in substantial increases in the transfection of rat marrow‐derived mesenchymal stem cells with the gene for glial cell line‐derived neurotrophic factor (GDNF), with magnetofection compared to transfection in the absence of a magnet. The amount of GDNF recovered in the medium approaches therapeutic levels despite the small amount of plasmid delivered by the NPs.     

PEI–PEG–Chitosan‐Copolymer‐Coated Iron Oxide Nanoparticles for Safe Gene Delivery: Synthesis,Complexation, and Transfection

Gene therapy offers the potential of mediating disease through modification of specific cellular functions of target cells. However, effective transport of nucleic acids to target cells with minimal side effects remains a challenge despite the use of unique viral and non‐viral delivery approaches. Here, a non‐viral nanoparticle gene carrier that demonstrates effective gene delivery and transfection both in vitro and in vivo is presented. The nanoparticle system (NP–CP–PEI) is made of a superparamagnetic iron oxide nanoparticle (NP), which enables magnetic resonance imaging, coated with a novel copolymer (CP–PEI) comprised of short chain polyethylenimine (PEI) and poly(ethylene glycol) (PEG) grafted to the natural polysaccharide, chitosan (CP), which allows efficient loading and protection of the nucleic acids. The function of each component material in this nanoparticle system is illustrated by comparative studies of three nanoparticle systems of different surface chemistries, through material property characterization, DNA loading and transfection analyses, and toxicity assessment. Significantly, NP–CP–PEI demonstrates an innocuous toxic profile and a high level of expression of the delivered plasmid DNA in a C6 xenograft mouse model, making it a potential candidate for safe in vivo delivery of DNA for gene therapy.     

Noncovalent Polymer‐Gatekeeper in Mesoporous Silica Nanoparticles as a Targeted Drug Delivery Platform

Selective targeting of tumor cells and release of drug molecules inside the tumor microenvironment can reduce the adverse side effects of traditional chemotherapeutics because of the lower dosages required. This can be achieved by using stimuli‐responsive targeted drug delivery systems. In the present work, a robust and simple one‐pot route is developed to synthesize polymer‐gatekeeper mesoporous silica nanoparticles by noncovalent capping of the pores of drug‐loaded nanocontainers with disulfide cross‐linkable polymers. The method offers very high loading efficiency because chemical modification of the mesoporous nanoparticles is not required; thus, the large empty pore volume of pristine mesoporous silica nanoparticles is entirely available to encapsulate drug molecules. Furthermore, the polymer shell can be easily decorated with a targeting ligand for selective delivery to specific cancer cells by subsequent addition of the thiol‐containing ligand molecule. The drug molecules loaded in the nanocontainers can be released by the degradation of the polymer shell in the intracellular reducing microenvironment, which consequentially induces cell death.     

Self‐Assembling Peptide as a Potential Carrier for Hydrophobic Anticancer Drug Ellipticine: Complexation,Release and In Vitro Delivery

The self‐assembling peptide EAK16‐II is capable of stabilizing hydrophobic compounds to form microcrystal suspensions in aqueous solution. Here, the ability of this peptide to stabilize the hydrophobic anticancer agent ellipticine is investigated. The formation of peptide‐ellipticine suspensions is monitored with time until equilibrium is reached. The equilibration time is found to be dependent on the peptide concentration. When the peptide concentration is close to its critical aggregation concentration, the equilibration time is minimal at 5 h. With different combinations of EAK16‐II and ellipticine concentrations, two molecular states (protonated or cyrstalline) of ellipticine could be stabilized. These different states of ellipticine significantly affect the release kinetics of ellipticine from the peptide‐ellipticine complex into the egg phosphatidylcholine vesicles, which are used to mimic cell membranes. The transfer rate of protonated ellipticine from the complex to the vesicles is much faster than that of crystalline ellipticine. This observation may also be related to the size of the resulting complexes as revealed from the scanning electron micrographs. In addition, the complexes with protonated ellipticine are found to have a better anticancer activity against two cancer cell lines, A549 and MCF‐7. This work forms the basis for studies of the peptide‐ellipticine suspensions in vitro and in vivo leading to future development of self‐assembling peptide‐based delivery of hydrophobic anticancer drugs.     

Synthesis of Magnetic,Up‐Conversion Luminescent,and Mesoporous Core–Shell‐Structured Nanocomposites as Drug Carriers

The synthesis (by a facile two‐step sol–gel process), characterization, and application in controlled drug release is reported for monodisperse core–shell‐structured Fe₃O₄@nSiO₂@mSiO₂@NaYF₄: Yb³⁺, Er³⁺/Tm³⁺ nanocomposites with mesoporous, up‐conversion luminescent, and magnetic properties. The nanocomposites show typical ordered mesoporous characteristics and a monodisperse spherical morphology with narrow size distribution (around 80 nm). In addition, they exhibit high magnetization (38.0 emu g^?1, thus it is possible for drug targeting under a foreign magnetic field) and unique up‐conversion emission (green for Yb³⁺/Er³⁺ and blue for Yb³⁺/Tm³⁺) under 980 nm laser excitation even after loading with drug molecules. Drug release tests suggest that the multifunctional nanocomposites have a controlled drug release property. Interestingly, the up‐conversion emission intensity of the multifunctional carrier increases with the released amount of model drug, thus allowing the release process to be monitored and tracked by the change of photoluminescence intensity. This composite can act as a multifunctional drug carrier system, which can realize the targeting and monitoring of drugs simultaneously.     

Amino Acid Pairing for De Novo Design of Self‐Assembling Peptides and Their Drug Delivery Potential

Molecular self‐assembly has emerged as the “bottom‐up” engineering route to fabricate functional supramolecules for diverse applications. The design of molecular building units becomes critical in determining the structure, properties, and function of the resulting assemblies. Here, a de novo design principle of amino acid pairing (AAP) to generate new classes of self‐assembling peptides (SAPs) is presented. In this study, the AAP focuses on hydrogen bonding, and ionic and hydrophobic interactions among amino acid pairs. With solely hydrogen bond pairs, SAPs can be constructed with only two amino acids. With all three AAP strategies (hydrogen bonds, ionic and hydrophobic pairs), a short novel SAP is constructed. This peptide can self‐assemble into β‐sheet‐rich nanofibers with a relatively low “critical aggregation concentration (CAC)” of ～10 μM . It also shows the ability to stabilize and deliver the hydrophobic anticancer agent ellipticine in aqueous solution. The peptide‐drug complexes/co‐assemblies exhibit anticancer activity against human lung carcinoma cells A549 and breast cancer cells MCF‐7, and have good dilution stability. The presented AAP design provides a new strategy to fabricate functional supramolecules with potential applications in nanomedicine.     

Selenium‐Containing Polymer@Metal‐Organic Frameworks Nanocomposites as an Efficient Multiresponsive Drug Delivery System

The development of efficient multiresponsive drug delivery systems (DDSs) to control drug release has been widely explored. Herein, a facile strategy is reported that enables the micelles of the selenium‐containing polymer with the drug to be encapsulated in metal‐organic frameworks (MOFs), which serves as multiresponsive drug release by employing the selenium‐containing polymers with redox‐triggered property and the MOFs with pH‐triggered property in DDS. In this case, the micelles of selenium‐containing polymers, as core easily disassembles in the presence of redox agents, can then release the drug in MOFs matrixes. The ZIF‐8 (one type of MOFs) crystal frameworks serving as shell can collapse only under low pH conditions, and the drug can be further released. In the presence of external redox agents as well as the pH stimuli, the prepared nanocomposite (P@ZIF‐8) drug system exhibits the capability of multiresponsive release of the doxorubicin (DOX) and possesses good selectivity in releasing the DOX under low pH conditions instead of normal pH conditions. In addition, the merits of P@ZIF‐8 such as good biocompatibility, multiresponsive release properties, and especially the selective release properties under different pH conditions make the materials highly promising candidates for the realization of controlled drug delivery in tumor tissue systems.     

Porous Polymersomes with Encapsulated Gd‐Labeled Dendrimers as Highly Efficient MRI Contrast Agents

The use of nanovesicles with encapsulated Gd as magnetic resonance (MR) contrast agents has largely been ignored due to the detrimental effects of the slow water exchange rate through the vesicle bilayer on the relaxivity of encapsulated Gd. Here, the facile synthesis of a composite MR contrast platform is described; it consists of dendrimer conjugates encapsulated in porous polymersomes. These nanoparticles exhibit improved permeability to water flux and a large capacity to store chelated Gd within the aqueous lumen, resulting in enhanced longitudinal relaxivity. The porous polymersomes, ～130 nm in diameter, are produced through the aqueous assembly of the polymers, polyethylene oxide‐b‐polybutadiene (PBdEO), and polyethylene oxide‐b‐polycaprolactone (PEOCL). Subsequent hydrolysis of the caprolactone (CL) block resulted in a highly permeable outer membrane. To prevent the leakage of small Gd‐chelate through the pores, Gd was conjugated to polyamidoamine (PAMAM) dendrimers via diethylenetriaminepentaacetic acid dianhydride (DTPA dianhydride) prior to encapsulation. As a result of the slower rotational correlation time of Gd‐labeled dendrimers, the porous outer membrane of the nanovesicle, and the high Gd payload, these functional nanoparticles are found to exhibit a relaxivity (R1) of 292 109 mM ^?1 s^?1 per particle. The polymersomes are also found to exhibit unique pharmacokinetics with a circulation half‐life of >3.5 h and predominantly renal clearance.