Porous Silicon Nanoparticles Targeted to the Extracellular Matrix for Therapeutic Protein Delivery in Traumatic Brain Injury.

Traumatic brain injury (TBI) is a major cause of disability and death among children and young adults in the United States, yet there are currently no treatments that improve the long-term brain health of patients. One promising therapeutic for TBI is brain-derived neurotrophic factor (BDNF), a protein that promotes neurogenesis and neuron survival. However, outstanding challenges to the systemic delivery of BDNF are its instability in blood, poor transport into the brain, and short half-life in circulation and brain tissue. Here, BDNF is encapsulated into an engineered, biodegradable porous silicon nanoparticle (pSiNP) in order to deliver bioactive BDNF to injured brain tissue after TBI. The pSiNP carrier is modified with the targeting ligand CAQK, a peptide that binds to extracellular matrix components upregulated after TBI. The protein cargo retains bioactivity after release from the pSiNP carrier, and systemic administration of the CAQK-modified pSiNPs results in effective delivery of the protein cargo to injured brain regions in a mouse model of TBI. When administered after injury, the CAQK-targeted pSiNP delivery system for BDNF reduces lesion volumes compared to free BDNF, supporting the hypothesis that pSiNPs mediate therapeutic protein delivery after systemic administration to improve outcomes in TBI.

Relevance of Electrostatics for the Interaction of Tyrosine Hydroxylase with Porous Silicon Nanoparticles.

Tyrosine hydroxylase (TH) is the enzyme catalyzing the rate-limiting step in the synthesis of dopamine in the brain. Developing enzyme replacement therapies using TH could therefore be beneficial to patient groups with dopamine deficiency, and the use of nanocarriers that cross the blood-brain barrier seems advantageous for this purpose. Nanocarriers may also help to maintain the structure and function of TH, which is complex and unstable. Understanding how TH may interact with a nanocarrier is therefore crucial for the investigation of such therapeutic applications. This work describes the interaction of TH with porous silicon nanoparticles (pSiNPs), chosen since they have been shown to deliver other macromolecular therapeutics successfully to the brain. Size distributions obtained by dynamic light scattering show a size increase of pSiNPs upon addition of TH and the changes observed at the surface of pSiNPs by transmission electron microscopy also indicated TH binding at pH 7. As pSiNPs are negatively charged, we also investigated the binding at pH 6, which makes TH less negatively charged than at pH 7. However, as seen by thioflavin-T fluorescence, TH aggregated at this more acidic pH. TH activity was unaffected by the binding to pSiNPs most probably because the active site stays available for catalysis, in agreement with calculations of the surface electrostatic potential pointing to the most positively charged regulatory domains in the tetramer as the interacting regions. These results reveal pSiNPs as a promising delivery device of enzymatically active TH to increase local dopamine synthesis.

Stable electrically conductive, highly flame-retardant foam composites generated from reduced graphene oxide and silicone resin coatings.

To acheive flexible polyurethane (PU) foam composites with stable electrical conductivity and high flame retardancy involved first coating of graphene oxide (GO) onto PU foam surfaces and then chemically reducing the GO with hydrazine to form reduced GO (RGO). The RGO-coated PU foam is then dipped into a solution containing silicone resin (SiR) and silica nano-particles and cured. The resulting composites (PU-RGO-SiR) show superior flame retardancy, thermal stability and mechanical stability relative to the PU starting materials or PU coated with either RGO or SiR alone. The electrical conductivity of the PU-RGO-SiR composites (as high as 118 S m-1 at room temperature) could almost be retained but with small loss of 9.5% of the original value after 150 cyclic compression. When the samples were subjected to a temperature range from -50 to 400 °C, the electrical conductivity could remain constant at -50 °C, 25 °C, 100 °C, 200 °C, and even at 300 °C and 400 °C; the electrical-conductivity exhibited mild vibration but the vibration range was not beyond 5.6%. Flame retardancy tests show that the limiting oxygen index (LOI) increases from 14.7% for the pure foam to 31.5% for PU-RGO-SiR, and the PU-RGO-SiR composites exhibit a 65% reduction in the peak heat release rate (pHRR) and a 30% reduction in total smoke release (TSR). Thus, stable electrically conductive and highly flame-retardant foam composites have potential applications even in a variety of harsh conditions like high temperature, flame, organic solvents, and external compression.

Porous Silicon Nanoparticles Embedded in Poly(lactic-co-glycolic acid) Nanofiber Scaffolds Deliver Neurotrophic Payloads to Enhance Neuronal Growth.

Scaffolds made from biocompatible polymers provide physical cues to direct the extension of neurites and to encourage repair of damaged nerves. The inclusion of neurotrophic payloads in these scaffolds can substantially enhance regrowth and repair processes. However, many promising neurotrophic candidates are excluded from this approach due to incompatibilities with the polymer or with the polymer processing conditions. This work provides one solution to this problem by incorporating porous silicon nanoparticles (pSiNPs) that are pre-loaded with the therapeutic into a polymer scaffold during fabrication. The nanoparticle-drug-polymer hybrids are prepared in the form of oriented poly(lactic-co-glycolic acid) nanofiber scaffolds. We test three different therapeutic payloads: bpV(HOpic), a small molecule inhibitor of phosphatase and tensin homolog (PTEN); an RNA aptamer specific to tropomyosin-related kinase receptor type B (TrkB); and the protein nerve growth factor (NGF). Each therapeutic is loaded using a loading chemistry that is optimized to slow the rate of release of these water-soluble payloads. The drug-loaded pSiNP-nanofiber hybrids release approximately half of their TrkB aptamer, bpV(HOpic), or NGF payload in 2, 10, and >40 days, respectively. The nanofiber hybrids increase neurite extension relative to drug-free control nanofibers in a dorsal root ganglion explant assay.

Moldless Printing of Silicone Lenses With Embedded Nanostructured Optical Filters.

Optical lenses are among the oldest technological innovations (3000 years ago) and they have enabled a multitude of applications in healthcare and in our daily lives. The primary function of optical lenses has changed little over time; they serve mainly as a light-collection (e.g. reflected, transmitted, diffracted) element, and the wavelength and/or intensity of the collected light is usually manipulated by coupling with various external optical filter elements or coatings. This generally results in losses associated with multiple interfacial reflections, and increases the complexity of design and construction. In this work we introduce a change in this paradigm, by integrating both light-shaping and image magnification into a single lens element using a moldless procedure that takes advantage of the physical and optical properties of mesoporous silicon (PSi) photonic crystal nanostructures. Casting of a liquid poly(dimethyl) siloxane (PDMS) pre-polymer solution onto a PSi film generates a droplet with contact angle that is readily controlled by the silicon nanostructure, and adhesion of the cured polymer to the PSi photonic crystal allows preparation of lightweight (10 mg) freestanding lenses (4.7 mm focal length) with an embedded optical component (e.g. optical rugate filter, resonant cavity, distributed Bragg reflector). Our fabrication process shows excellent reliability (yield 95%) and low cost and we expect our lens to have implications in a wide range of applications. As a proof-of-concept, using a single monolithic lens/filter element we demonstrate: fluorescence imaging of isolated human cancer cells with rejection of the blue excitation light, through a lens that is self-adhered to a commercial smartphone; shaping the emission spectrum of a white light emitting diode (LED) to tune the color from red through blue; and selection of a narrow wavelength band (bandwidth 5 nm) from a fluorescent molecular probe.

Facile Surface Modification of Hydroxylated Silicon Nanostructures Using Heterocyclic Silanes.

Heterocyclic silanes containing Si-N or Si-S bonds in the ring undergo a ring opening reaction with -OH groups at the surface of porous Si nanostructures to generate -SH or -NH functional surfaces, grafted via O-Si bonds. The reaction is substantially faster (0.5-2 h at 25 °C) and more efficient than hydrolytic condensation of trialkoxysilanes on similar hydroxy-terminated surfaces, and the reaction retains the open pore structure and photoluminescence of the quantum-confined silicon nanostructures. The chemistry is sufficiently mild to allow trapping of the test protein lysozyme, which retains its enzymatic activity upon release from the modified porous nanostructure.

Tumor-Targeted Multimodal Optical Imaging with Versatile Cadmium-Free Quantum Dots.

The rapid development of fluorescence imaging technologies requires concurrent improvements in the performance of fluorescent probes. Quantum dots have been extensively used as an imaging probe in various research areas because of their inherent advantages based on unique optical and electronic properties. However, their clinical translation has been limited by the potential toxicity especially from cadmium. Here, a versatile bioimaging probe is developed by using highly luminescent cadmium-free CuInSe2/ZnS core/shell quantum dots conjugated with CGKRK (Cys-Gly-Lys-Arg-Lys) tumor-targeting peptides. This probe exhibits excellent photostability, reasonably long circulation time, minimal toxicity, and strong tumor-specific homing property. The most important feature of this probe is that it shows distinctive versatility in tumor-targeted multimodal imaging including near-infrared, time-gated, and two-photon imaging in different tumor models. In a glioblastoma mouse model, the targeted probe clearly denotes tumor boundaries and positively labels a population of diffusely infiltrating tumor cells, suggesting its utility in precise tumor detection during surgery. This work lays a foundation for potential clinical translation of the probe.

Thermally Induced Silane Dehydrocoupling on Silicon Nanostructures.

Organic trihydridosilanes can be grafted to hydrogen-terminated porous Si nanostructures with no catalyst. The reaction proceeds efficiently at 80 °C, and it shows little sensitivity to air or water impurities. The modified surfaces are stable to corrosive aqueous solutions and common organic solvents. Octadecylsilane H3 Si(CH2 )17 CH3 , and functional silanes H3 Si(CH2 )11 Br, H3 Si(CH2 )9 CH=CH2 , and H3 Si(CH2 )2 (CF2 )5 CF3 are readily grafted. When performed on a mesoporous Si wafer, the perfluoro reagent yields a superhydrophobic surface (contact angle 151°). The bromo-derivative is converted to azide, amine, or alkyne functional surfaces via standard transformations, and the utility of the method is demonstrated by loading of the antibiotic ciprofloxaxin (35 % by mass). When intrinsically photoluminescent porous Si films or nanoparticles are used, photoluminescence is retained in the grafted products, indicating that the chemistry does not introduce substantial nonradiative surface traps.

Control of the Pore Texture in Nanoporous Silicon via Chemical Dissolution.

The surface and textural properties of porous silicon (pSi) control many of its physical properties essential to its performance in key applications such as optoelectronics, energy storage, luminescence, sensing, and drug delivery. Here, we combine experimental and theoretical tools to demonstrate that the surface roughness at the nanometer scale of pSi can be tuned in a controlled fashion using partial thermal oxidation followed by removal of the resulting silicon oxide layer with hydrofluoric acid (HF) solution. Such a process is shown to smooth the pSi surface by means of nitrogen adsorption, electron microscopy, and small-angle X-ray and neutron scattering. Statistical mechanics Monte Carlo simulations, which are consistent with the experimental data, support the interpretation that the pore surface is initially rough and that the oxidation/oxide removal procedure diminishes the surface roughness while increasing the pore diameter. As a specific example considered in this work, the initial roughness ξ ∼ 3.2 nm of pSi pores having a diameter of 7.6 nm can be decreased to 1.0 nm following the simple procedure above. This study allows envisioning the design of pSi samples with optimal surface properties toward a specific process.

Development of a cobinamide-based end-of-service-life indicator for detection of hydrogen cyanide gas.

We describe an inexpensive paper-based sensor for rapid detection of low concentrations (ppm) of hydrogen cyanide gas. A piece of filter paper pre-spotted with a dilute monocyanocobinamide [CN(H2O)Cbi] solution was placed on the end of a bifurcated optical fiber and the reflectance spectrum of the CN(H2O)Cbi was monitored during exposure to 1.0-10.0 ppm hydrogen cyanide gas. Formation of dicyanocobinamide yielded a peak at 583 nm with a simultaneous decrease in reflectance from 450-500 nm. Spectral changes were monitored as a function of time at several relative humidity values: 25, 50, and 85% relative humidity. With either cellulose or glass fiber papers, spectral changes occurred within 10 s of exposure to 5.0 ppm hydrogen cyanide gas (NIOSH recommended short-term exposure limit). We conclude that this sensor could provide a real-time end-of-service-life alert to a respirator user.

Intravitreal controlled release of dexamethasone from engineered microparticles of porous silicon dioxide.

Dexamethasone is a glucocorticoid that is widely used in the ophthalmic arena. The recent FDA approved dexamethasone implant can provide a three month efficacy but with high rate of drug related cataract and high intraocular pressure (IOP). It seems that higher steroid in aqueous humor and around lens may be associated with these complications based on clinical fact that higher IOP was observed with intravitreal triamcinolone acetonide (TA) than with subtenon TA. We hypothesize that placing a sustained dexamethasone release system near back of the eye through a fine needle can maximize efficacy while mitigate higher rate of IOP rise and cataract. To develop a sustained intravitreal dexamethasone delivery system, porous silicon dioxide (pSiO2) microparticles were fabricated and functionalized with amines as well as carboxyl groups. Dexamethasone was conjugated to pSiO2 through the Steglich Esterification Reaction between hydroxyl of dexamethasone and carboxyl groups on the pSiO2. The drug loading was confirmed by Fourier transform infrared spectroscopy (FTIR) and loading efficiency was quantitated using thermogravimetric analysis (TGA). In vitro release was conducted for three months and dexamethasone was confirmed in the released samples using liquid chromatography-tandem mass spectrometry (LC/MS/MS). A pilot ocular safety and determination of vitreous drug level was performed in rabbit eyes. The drug loading study demonstrated that loading efficiency was from 5.96% to 10.77% depending on the loading reaction time, being higher with longer loading reaction time before reaching saturation around 7 days. In vitro drug release study revealed that dexamethasone release from pSiO2 particles was sustainable for over 90 days and was 80 days longer than free dexamethasone or infiltration-loaded pSiO2 particle formulation in the same setting. Pilot in vivo study demonstrated no sign of ocular adverse reaction in rabbit eyes following a single 3 mg intravitreal injection and free drug level at 2-week was 107.23 ± 10.54 ng/mL that is well above the therapeutic level but only around 20% level of dexamethasone released from OZURDEX(®) (dexamethasone intravitreal implant) in a rabbit eye model. In conclusion, dexamethasone is able to covalently load to the pSiO2 particles and provide sustained drug release for at least 3 months in vitro. Intravitreal injection of these particles were well tolerated in rabbit eyes and free drug level in vitreous at 2-week was well above the therapeutic level.

Stable "snow lantern-like" aggregates of silicon nanoparticles suitable as a drug delivery platform.

Nanomedicine is a growing field where development of novel organic and inorganic materials is essential to meet the complex requirements for drug delivery. This includes biocompatibility, suitability for surface modifications, biodegradability, and stability sufficient to carry a drug payload through various tissues for the desired timespan. Porous silicon nanoparticles (pSi NP) are shown to have several beneficial traits in drug delivery in addition to a porous structure to maximize drug loading. The conventional synthesis of pSi NP using electrochemical etching is costly, time-consuming and requires large quantities of highly toxic hydrofluoric acid (HF). As such this research attempted a novel method to address these limitations. Mesoporous silicon nanoparticles were prepared by centrifugal Chemical Vapor Deposition (cCVD) without the use of HF. This process generated aggregates consisting of multiple primary particles fused into each other, similar to snowballs fused together in a snow-lantern (snowball pyramid). Our results demonstrated that the cCVD Si particles were versatile in terms of surface chemistry, colloidal stability, degradability, minimization of acute in vitro toxicity, and modulation of drug release. Dynamic light scattering, scanning electron microscopy, and cryogenic nitrogen adsorption isotherm measurements confirmed the overall size (210 nm), morphology, and pore size (14-16 nm) of the prepared materials. Agglomeration in phosphate-buffered saline (PBS) was minimized by PEGylation by a two-step grafting procedure that employed a primary amine linker. Finally, the release rate of a model drug, hydrocortisone, was evaluated with both PEGylated and pristine particles. Conclusively, these snow-lantern cCVD Si particles do indeed appear suitable for drug delivery.

Ocular silicon distribution and clearance following intravitreal injection of porous silicon microparticles.

Porous silicon (pSi) microparticles have been investigated for intravitreal drug delivery and demonstrated good biocompatibility. With the appropriate surface chemistry, pSi can reside in vitreous for months or longer. However, ocular distribution and clearance pathway of its degradation product, silicic acid, are not well understood. In the current study, rabbit ocular tissue was collected at different time point following fresh pSi (day 1, 5, 9, 16, and 21) or oxidized pSi (day 3, 7, 14, 21, and 35) intravitreal injection. In addition, dual-probe simultaneous microdialysis of aqueous and vitreous humor was performed following a bolus intravitreal injection of 0.25 mL silicic acid (150 µg/mL) and six consecutive microdialysates were collected every 20 min. Silicon was quantified from the samples using inductively coupled plasma-optical emission spectroscopy. The study showed that following the intravitreal injection of oxidized pSi, free silicon was consistently higher in the aqueous than in the retina (8.1 ± 6.5 vs. 3.4 ± 3.9 µg/mL, p = 0.0031). The area under the concentration-time curve (AUC) of the retina was only about 24% that of the aqueous. The mean residence time was 16 days for aqueous, 13 days for vitreous, 6 days for retina, and 18 days for plasma. Similarly, following intravitreal fresh pSi, free silicon was also found higher in aqueous than in retina (7 ± 4.7 vs. 3.4 ± 4.1 µg/mL, p = 0.014). The AUC for the retina was about 50% of the AUC for the aqueous. The microdialysis revealed the terminal half-life of free silicon in the aqueous was 30 min and 92 min in the vitreous; the AUC for aqueous accounted for 38% of the AUC for vitreous. Our studies indicate that aqueous humor is a significant pathway for silicon egress from the eye following intravitreal injection of pSi crystals.

Differential adsorption of small molecules in spatially functionalized porous silicon nanostructures.

An experimental approach to rapidly quantify the relative affinity of a small molecule analyte for two different surfaces is described. The method uses optical measurements of high surface area porous Si thin films that contain two spatially distinct surface chemistries. The chemistries are placed on the walls of the ∼10 nm diameter pores of the porous Si film by means of microdroplet patterning, where a chemical resist is drop-coated on the porous Si sample to define distinct regions across the plane of the chip. In this work, the two chemistries consist of a hydrophilic silicon oxide surface and a hydrophobic methyl-terminated silicon surface. Detection is achieved by simultaneous optical reflectance measurements of both regions, where the reflectance spectrum contains a convolution of the Fabry-Pérot interference spectrum of both the oxide and the methyl-grafted layers. The differential partitioning of a test analyte (2-acetoxybenzoic acid or diphenyl ether) from aqueous solution is determined from the Fourier transform of the optical interference spectrum. The approach is rapid and nondestructive, and it can be performed on a small sample volume as a means to quantify the partition behavior of small molecules.

Cooperative nanomaterial system to sensitize, target, and treat tumors.

A significant barrier to the clinical translation of systemically administered therapeutic nanoparticles is their tendency to be removed from circulation by the mononuclear phagocyte system. The addition of a targeting ligand that selectively interacts with cancer cells can improve the therapeutic efficacy of nanomaterials, although these systems have met with only limited success. Here, we present a cooperative nanosystem consisting of two discrete nanomaterials. The first component is gold nanorod (NR) "activators" that populate the porous tumor vessels and act as photothermal antennas to specify tumor heating via remote near-infrared laser irradiation. We find that local tumor heating accelerates the recruitment of the second component: a targeted nanoparticle consisting of either magnetic nanoworms (NW) or doxorubicin-loaded liposomes (LP). The targeting species employed in this work is a cyclic nine-amino acid peptide LyP-1 (Cys-Gly-Asn-Lys-Arg-Thr-Arg-Gly-Cys) that binds to the stress-related protein, p32, which we find to be upregulated on the surface of tumor-associated cells upon thermal treatment. Mice containing xenografted MDA-MB-435 tumors that are treated with the combined NR/LyP-1LP therapeutic system display significant reductions in tumor volume compared with individual nanoparticles or untargeted cooperative system.

Porous silicon embedded in a thermoresponsive hydrogel for intranasal delivery of lipophilic drugs to treat rhinosinusitis.

Intranasal delivery is the most preferred route of drug administration for treatment of a range of nasal conditions including chronic rhinosinusitis (CRS), caused by an infection and inflammation of the nasal mucosa. However, localised delivery of lipophilic drugs for persistent nasal inflammation is a challenge especially with traditional topical nasal sprays. In this study, a composite thermoresponsive hydrogel is developed and tuned to obtain desired rheological and physiochemical properties suitable for intranasal administration of lipophilic drugs. The composite is comprised of drug-loaded porous silicon (pSi) particles embedded in a poloxamer 407 (P407) hydrogel matrix. Mometasone Furoate (MF), a lipophilic corticosteroid (log P of 4.11), is used as the drug, which is loaded onto pSi particles at a loading capacity of 28 wt%. The MF-loaded pSi particles (MF@pSi) are incorporated into the P407-based thermoresponsive hydrogel (HG) matrix to form the composite hydrogel (MF@pSi-HG) with a final drug content ranging between 0.1 wt% to 0.5 wt%. Rheomechanical studies indicate that the MF@pSi component exerts a minimal impact on gelation temperature or strength of the hydrogel host. The in-vitro release of the MF payload from MF@pSi-HG shows a pronounced increase in the amount of drug released over 8 h (4.5 to 21-fold) in comparison to controls consisting of pure MF incorporated in hydrogel (MF@HG), indicating an improvement in kinetic solubility of MF upon loading into pSi. Ex-vivo toxicity studies conducted on human nasal mucosal tissue show no adverse effect from exposure to either pure HG or the MF@pSi-HG formulation, even at the highest drug content of 0.5 wt%. Experiments on human nasal mucosal tissue show the MF@pSi-HG formulation deposits a quantity of MF into the tissues within 8 h that is >19 times greater than the MF@HG control (194 ± 7 µg of MF/g of tissue vs. <10 µg of MF/g of tissue, respectively).

Two-Photon Light Trigger siRNA Transfection of Cancer Cells Using Non-Toxic Porous Silicon Nanoparticles.

The concept of using two-photon excitation in the NIR for the spatiotemporal control of biological processes holds great promise. However, its use for the delivery of nucleic acids has been very scarcely described and the reported procedures are not optimal as they often involve potentially toxic materials and irradiation conditions. This work prepares a simple system made of biocompatible porous silicon nanoparticles (pSiNP) for the safe siRNA photocontrolled delivery and gene silencing in cells upon two-photon excitation. PSiNP are linked to an azobenzene moiety, which possesses a lysine group (pSiNP@ICPES-azo@Lys) to efficiently complex siRNA. Non-linear excitation of the two-photon absorber system (pSiNP) followed by intermolecular energy transfer (FRET) to trans azobenzene moiety, result in the photoisomerization of the azobenzene from trans to cis and in the destabilization of the azobenzene-siRNA complex, thus inducing the delivery of the cargo siRNA to the cytoplasm of cells. Efficient silencing in MCF-7 expressing stable firefly luciferase with siRNAluc against luciferase is observed. Furthermore, siRNA against inhibitory apoptotic protein (IAP) leads to over 70% of MCF-7 cancer cell death. The developed technique using two-photon light allows a unique high spatiotemporally controlled and safe siRNA delivery in cells in few seconds of irradiation.

Nanoparticles that communicate in vivo to amplify tumour targeting.

Nanomedicines have enormous potential to improve the precision of cancer therapy, yet our ability to efficiently home these materials to regions of disease in vivo remains very limited. Inspired by the ability of communication to improve targeting in biological systems, such as inflammatory-cell recruitment to sites of disease, we construct systems where synthetic biological and nanotechnological components communicate to amplify disease targeting in vivo. These systems are composed of 'signalling' modules (nanoparticles or engineered proteins) that target tumours and then locally activate the coagulation cascade to broadcast tumour location to clot-targeted 'receiving' nanoparticles in circulation that carry a diagnostic or therapeutic cargo, thereby amplifying their delivery. We show that communicating nanoparticle systems can be composed of multiple types of signalling and receiving modules, can transmit information through multiple molecular pathways in coagulation, can operate autonomously and can target over 40 times higher doses of chemotherapeutics to tumours than non-communicating controls.

Nanoparticle-induced vascular blockade in human prostate cancer.

The tumor-homing pentapeptide CREKA (Cys-Arg-Glu-Lys-Ala) specifically homes to tumors by binding to fibrin and fibrin-associated clotted plasma proteins in tumor vessels. Previous results show that CREKA-coated superparamagnetic iron oxide particles can cause additional clotting in tumor vessels, which creates more binding sites for the peptide. We have used this self-amplifying homing system to develop theranostic nanoparticles that simultaneously serve as an imaging agent and inhibit tumor growth by obstructing tumor circulation through blood clotting. The CREKA nanoparticles were combined with nanoparticles coated with another tumor-homing peptide, CRKDKC, and nanoparticles with an elongated shape (nanoworms) were used for improved binding efficacy. The efficacy of the CREKA peptide was then increased by replacing some residues with nonproteinogenic counterparts, which increased the stability of the peptide in the circulation. Treatment of mice bearing orthotopic human prostate cancer tumors with the targeted nanoworms caused extensive clotting in tumor vessels, whereas no clotting was observed in the vessels of normal tissues. Optical and magnetic resonance imaging confirmed tumor-specific targeting of the nanoworms, and ultrasound imaging showed reduced blood flow in tumor vessels. Treatment of mice with prostate cancer with multiple doses of the nanoworms induced tumor necrosis and a highly significant reduction in tumor growth.

Different effect of hydrogelation on antifouling and circulation properties of dextran-iron oxide nanoparticles.

Premature recognition and clearance of nanoparticulate imaging and therapeutic agents by macrophages in the tissues can dramatically reduce both the nanoparticle half-life and delivery to the diseased tissue. Grafting nanoparticles with hydrogels prevents nanoparticulate recognition by liver and spleen macrophages and greatly prolongs circulation times in vivo. Understanding the mechanisms by which hydrogels achieve this "stealth" effect has implications for the design of long-circulating nanoparticles. Thus, the role of plasma protein absorption in the hydrogel effect is not yet understood. Short-circulating dextran-coated iron oxide nanoparticles could be converted into stealth hydrogel nanoparticles by cross-linking with 1-chloro-2,3-epoxypropane. We show that hydrogelation did not affect the size, shape and zeta potential, but completely prevented the recognition and clearance by liver macrophages in vivo. Hydrogelation decreased the number of hydroxyl groups on the nanoparticle surface and reduced the binding of the anti-dextran antibody. At the same time, hydrogelation did not reduce the absorption of cationic proteins on the nanoparticle surface. Specifically, there was no effect on the binding of kininogen, histidine-rich glycoprotein, and protamine sulfate to the anionic nanoparticle surface. In addition, hydrogelation did not prevent activation of plasma kallikrein on the metal oxide surface. These data suggest that (a) a stealth hydrogel coating does not mask charge interactions with iron oxide surface and (b) the total blockade of plasma protein absorption is not required for maintaining iron oxide nanoparticles' long-circulating stealth properties. These data illustrate a novel, clinically promising property of long-circulating stealth nanoparticles.