Long-term continuous ammonia electrosynthesis

Ammonia is crucial as a fertilizer and in the chemical industry and is considered to be a carbon-free fuel1. Ammonia electrosynthesis from nitrogen under ambient conditions offers an attractive alternative to the Haber-Bosch process2,3, and lithium-mediated nitrogen reduction represents a promising approach to continuous-flow ammonia electrosynthesis, coupling nitrogen reduction with hydrogen oxidation4. However, tetrahydrofuran, which is commonly used as a solvent, impedes long-term ammonia production owing to polymerization and volatility problems. Here we show that a chain-ether-based electrolyte enables long-term continuous ammonia synthesis. We find that a chain-ether-based solvent exhibits non-polymerization properties and a high boiling point (162 °C) and forms a compact solid-electrolyte interphase layer on the gas diffusion electrode, facilitating ammonia release in the gas phase and ensuring electrolyte stability. We demonstrate 300 h of continuous operation in a flow electrolyser with a 25 cm2 electrode at 1 bar pressure and room temperature, and achieve a current-to-ammonia efficiency of 64 ± 1% with a gas-phase ammonia content of approximately 98%. Our results highlight the crucial role of the solvent in long-term continuous ammonia synthesis.

Biosynthesis enhancement of tropodithietic acid (TDA) antibacterial compound through biofilm formation by marine bacteria Phaeobacter inhibens on micro-structured polymer surfaces

Although aquaculture is a major player in current and future food production, the routine use of antibiotics provides ample ground for development of antibiotic resistance. An alternative route to disease control is the use of probiotic bacteria such as the marine bacteria Phaeobacter inhibens which produces tropodithietic acid (TDA) that inhibit pathogens without affecting the fish. Improving conditions for the formation of biofilm and TDA-synthesis is a promising avenue for biocontrol in aquaculture. In this study, the biosynthesis of TDA by Phaeobacter inhibens grown on micro-structured polymeric surfaces in micro-fluidic flow-cells is investigated. The formation of biofilms on three surface topographies; hexagonal micro-pit-arrays, hexagonal micro-pillar-arrays, and planar references is investigated. The biomass on these surfaces is measured by a non-invasive confocal microscopy 3D imaging technique, and the corresponding TDA production is monitored by liquid chromatography mass spectrometry (LC-MS) in samples collected from the outlets of the microfluidic channels. Although all surfaces support growth of P. inhibens, biomass appears to be decoupled from total TDA biosynthesis as the micro-pit-arrays generate the largest biomass while the micro-pillar-arrays produce significantly higher amounts of TDA. The findings highlight the potential for optimized micro-structured surfaces to maintain biofilms of probiotic bacteria for sustainable aquacultures.

Transparent and Cell-Guiding Cellulose Nanofiber 3D Printing Bioinks

For three-dimensional (3D) bioprinting to fulfill its promise and enable the automated fabrication of complex tissue-mimicking constructs, there is a need for developing bioinks that are not only printable and biocompatible but also have integrated cell-instructive properties. Toward this goal, we here present a scalable technique for generating nanofiber 3D printing inks with unique tissue-guiding capabilities. Our core methodology relies on tailoring the size and dispersibility of cellulose fibrils through a solvent-controlled partial carboxymethylation. This way, we generate partially negatively charged cellulose nanofibers with diameters of ∼250 nm and lengths spanning tens to hundreds of microns. In this range, the fibers structurally match the size and dimensions of natural collagen fibers making them sufficiently large to orient cells. Yet, they are simultaneously sufficiently thin to be optically transparent. By adjusting fiber concentration, 3D printing inks with excellent shear-thinning properties can be established. In addition, as the fibers are readily dispersible, composite inks with both carbohydrates and extracellular matrix (ECM)-derived proteins can easily be generated. We apply such composite inks for 3D printing cell-laden and cross-linkable structures, as well as tissue-guiding gel substrates. Interestingly, we find that the spatial organization of engineered tissues can be defined by the shear-induced alignment of fibers during the printing procedure. Specifically, we show how myotubes derived from human and murine skeletal myoblasts can be programmed into linear and complex nonlinear architectures on soft printed substrates with intermediate fiber contents. Our nanofibrillated cellulose inks can thus serve as a simple and scalable tool for engineering anisotropic human muscle tissues that mimic native structure and function.

Bioorthogonal Click of Colloidal Gold Nanoparticles to Antibodies In vivo

Combining nanotechnology and bioorthogonal chemistry for theranostic strategies offers the possibility to develop next generation nanomedicines. These materials are thought to increase therapeutic outcome and improve current cancer management. Due to their size, nanomedicines target tumors passively. Thus, they can be used for drug delivery purposes. Bioorthogonal chemistry allows for a pretargeting approach. Higher target-to-background drug accumulation ratios can be achieved. Pretargeting can also be used to induce internalization processes or trigger controlled drug release. Colloidal gold nanoparticles (AuNPs) have attracted widespread interest as drug delivery vectors within the last decades. Here, we demonstrate for the first time the possibility to successfully ligate AuNPs in vivo to pretargeted monoclonal antibodies. We believe that this possibility will facilitate the development of AuNPs for clinical use and ultimately, improve state-of-the-art patient care.

Quantifying the transport of biologics across intestinal barrier models in real-time by fluorescent imaging

Unsuccessful clinical translation of orally delivered biological drugs remains a challenge in pharmaceutical development and has been linked to insufficient mechanistic understanding of intestinal drug transport. Live cell imaging could provide such mechanistic insights by directly tracking drug transport across intestinal barriers at subcellular resolution, however traditional intestinal in vitro models are not compatible with the necessary live cell imaging modalities. Here, we employed a novel microfluidic platform to develop an in vitro intestinal epithelial barrier compatible with advanced widefield- and confocal microscopy. We established a quantitative, multiplexed and high-temporal resolution imaging assay for investigating the cellular uptake and cross-barrier transport of biologics while simultaneously monitoring barrier integrity. As a proof-of-principle, we use the generic model to monitor the transport of co-administrated cell penetrating peptide (TAT) and insulin. We show that while TAT displayed a concentration dependent difference in its transport mechanism and efficiency, insulin displayed cellular internalization, but was restricted from transport across the barrier. This illustrates how such a sophisticated imaging based barrier model can facilitate mechanistic studies of drug transport across intestinal barriers and aid in vivo and clinical translation in drug development.

Covalent core-radiolabeling of polymeric micelles with 125I/211At for theranostic radiotherapy

Astatine-211 (²¹¹At) is one of the most promising α-emitters for targeted alpha therapy, especially of cancer metastases. However, the lack of a stable isotope, frequent in vivo deastatination, and limited radiochemical knowledge makes it challenging to apply. Here, we report a new strategy for radiolabeling the lipophilic core of polymeric micelles (PMs) with covalently bound ²¹¹At. The PMs were radiolabeled via either an indirect synthon-based method or directly on the amphipathic block copolymer. The radiochemistry was optimized with iodine-125 (¹²⁵I) and then adapted for ²¹¹At, enabling the use of both elements as a potential theranostic pair. PMs that were core-radiolabeled with both ¹²⁵I or ²¹¹At were prepared and characterized, based on a PEG(5k)-PLGA(10k) co-polymer. The stability of the radiolabeled PMs was evaluated in mouse serum for 21 h, showing radiochemical stability above 85%. After in vivo evaluation of the ²¹¹At- labeled PMs, 4-5 % ID/g of the ²¹¹At could still be detected in the blood, showing a promising in vivo stability of the PMs. Further, ²¹¹At-labeled PMs accumulated in the spleen (20-30 %ID/g) and the liver (2.5- 5.5 %ID/g), along with some detection of ²¹¹At in the thyroid (3.5-9 %ID/g). This led to the hypothesis that deastatination takes place in the liver, whereas good stability of the ²¹¹At core-radiolabel was observed in the blood.

Harnessing cross-resistance - Sustainable nisin production from low-value food side streams using a Lactococcus lactis mutant with higher nisin-resistance obtained after prolonged chlorhexidine exposure

Nisin has a tendency to associate with the cell wall of the producing strain, which inhibits growth and lowers the ceiling for nisin production. With the premise that resistance to the cationic chlorhexidine could reduce nisin binding, variants with higher tolerance to this compound were isolated. One of the resistant isolates, AT0606, had doubled its resistance to nisin, and produced three times more free nisin, when cultured in shake flasks. Characterization revealed that AT0606 had an overall less negatively charged and thicker cell wall, and these changes appeared to be linked to a defect high-affinity phosphate uptake system, and a mutation inactivating the oleate hydratase. Subsequently, the potential of using AT0606 for cost efficient production of nisin was explored, and it was possible to attain a high titer of 13181 IU/mL using a fermentation substrate based on molasses and a by-product from whey protein hydrolysate production.

Nanoconfined anti-oxidizing RAFT nitroxide radical polymer for reduction of low-density lipoprotein oxidation and foam cell formation

Atherosclerosis is a leading cause of death worldwide. Antioxidant therapy has been considered a promising treatment modality for atherosclerosis, since reactive oxygen species (ROS) play a major role in the pathogenesis of atherosclerosis. We developed ROS-scavenging antioxidant nanoparticles (NPs) that can serve as an effective therapy for atherosclerosis. The newly developed novel antioxidant ROS-eliminating NPs were synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization and act as a superoxide dismutase (SOD) mimetic agent. SOD is an anti-ROS enzyme which is difficult to use for passive delivery due to its low half-life and stability. Copolymers were synthesized using different feed ratios of 2,2,6,6-tetramethyl-4-piperidyl methacrylate (PMA) and glycidyl methacrylate (GMA) monomers and an anti-ROS nitroxyl radical polymer was prepared via oxidation. The copolymer was further conjugated with a 6-aminofluorescein via a oxirane ring opening reaction for intracellular delivery in RAW 264.7 cells. The synthesized copolymers were blended to create NPs (∼150 nm size) in aqueous medium and highly stable up to three weeks. The NPs were shown to be taken up by macrophages and to be cytocompatible even at high dose levels (500 μg mL-1). Finally, the nitroxide NPs has been shown to inhibit foam cell formation in macrophages by decreasing internalization of oxidized low-density lipoproteins.

Sortilin regulates blood-brain barrier integrity

Brain homeostasis depends on the existence of the blood-brain barrier (BBB). Despite decades of research, the factors and signalling pathways for modulating and maintaining BBB integrity are not fully elucidated. Here, we characterise the expression and function of the multifunctional receptor, sortilin, in the cells of the BBB, in vivo and in vitro. We show that sortilin acts as an important regulatory protein of the BBB's tightness. In rats lacking sortilin, the BBB was leaky, which correlated well with relocated distribution of the localisation of zonula occludens-1, VE-cadherin and β-catenin junctional proteins. Furthermore, the absence of sortilin in brain endothelial cells resulted in decreased phosphorylation of Akt signalling protein and increased the level of phospho-ERK1/2. As a putative result of MAPK/ERK pathway activity, the junctions between the brain endothelial cells were disintegrated and the integrity of the BBB became compromised. The identified barrier differences between wild-type and Sort1-/- brain endothelial cells can pave the way for a better understanding of sortilin's role in the healthy and diseased BBB.

Isolation methods commonly used to study the liposomal protein corona suffer from contamination issues

The liposomal protein corona has been the focus of numerous studies, but there is still no consensus regarding its extent and composition. Rather, the literature is full of conflicting reports on the matter. To elucidate whether there could be a methodological explanation for this, we here scrutinize the efficiency of three commonly used liposome isolation methods at isolating stealth liposomes from human plasma. Firstly, we show that size-exclusion chromatography (SEC) in its standard form is prone to isolating unbound protein material together with the liposomes, but also that the method may be optimized to mitigate this issue. Secondly, we demonstrate that SEC in combination with membrane ultrafiltration is no better at removing the unbound protein material than SEC alone. Thirdly, we show that centrifugation is not able to pellet the liposomes. Overall, our results suggest that previous research on the liposomal protein corona may have suffered from significant methodological problems, in particular related to contaminant proteins interfering with the analysis of the protein corona. We believe that the data presented here may help guide future research around this challenge to reach a converging understanding about the properties of the protein corona on liposomes. STATEMENT OF SIGNIFICANCE: Upon administration into the circulatory system, liposomal drug carriers encounter an environment rich in proteins. These proteins may adsorb to the liposomes to form what is known as the protein corona, potentially governing the interactions of the liposomes with tissues and cells. However, despite decades of intense research efforts, there is currently no clear understanding about the extent and composition of the liposomal protein corona, making it impossible to assess its mechanistic importance. Here we report that the methods commonly used to isolate liposomes from blood plasma or serum to study the protein corona are susceptible to protein contamination. This may be the underlying technical reason for the current confusion about the characteristics of the liposomal protein corona.

Phages carry interbacterial weapons encoded by biosynthetic gene clusters

Bacteria produce diverse specialized metabolites that mediate ecological interactions and serve as a rich source of industrially relevant natural products. Biosynthetic pathways for these metabolites are encoded by organized groups of genes called biosynthetic gene clusters (BGCs). Understanding the natural function and distribution of BGCs provides insight into the mechanisms through which microorganisms interact and compete. Further, understanding BGCs is extremely important for biocontrol and the mining of new bioactivities. Here, we investigated phage-encoded BGCs (pBGCs), challenging the relationship between phage origin and BGC structure and function. The results demonstrated that pBGCs are rare, and they predominantly reside within temperate phages infecting commensal or pathogenic bacterial hosts. Further, the vast majority of pBGCs were found to encode for bacteriocins. Using the soil- and gut-associated bacterium Bacillus subtilis, we experimentally demonstrated how a temperate phage equips a bacterium with a fully functional BGC, providing a clear competitive fitness advantage over the ancestor. Moreover, we demonstrated a similar transfer of the same phage in prophage form. Finally, using genetic and genomic comparisons, a strong association between pBGC type and phage host range was revealed. These findings suggest that bacteriocins are encoded in temperate phages of a few commensal bacterial genera. In these cases, lysogenic conversion provides an evolutionary benefit to the infected host and, hence, to the phage itself. This study is an important step toward understanding the natural role of bacterial compounds encoded by BGCs, the mechanisms driving their horizontal transfer, and the sometimes mutualistic relationship between bacteria and temperate phages.

Soft Electronic Materials with Combinatorial Properties Generated via Mussel-Inspired Chemistry and Halloysite Nanotube Reinforcement

Soft and electrically active materials are currently being utilized for intelligent systems, including electronic skin, cybernetics, soft robotics, and wearable devices. However, fabricating materials that fulfill the complex requirements of such advanced applications remains a challenge. These attributes include electronic, adhesive, self-healing, flexible, moldable, printable, and strong mechanical properties. Inspired by the recent interest in transforming monofunctional materials into multifunctional ones through nanoreinforcement and mussel-inspired chemistry, we have designed a simple two-step methodology based on halloysite nanotube (HNT) and polydopamine (PDA) to address the grand challenges in the field. In brief, HNTs were coated with PDA and embedded within a poly(vinyl alcohol) (PVA)-based polymeric matrix in combination with ferric ions (Fe³⁺). The final composite displayed a 3-fold increase in electrical conductivity, a 20-fold increase in mechanical stiffness, and a 7-fold increase in energy dissipation in comparison to their nonfunctional counterparts, which arose from a combination of nanotube alignment and mussel-inspired chemistry. Moreover, the developed composite could elongate up to 30000% of its original length, maintain its electrical properties after 600% strain, self-heal within seconds (both electrically and mechanically), and display strain-sensitivity. Finally, it was 3D-printable and thus amenable for engineering of customized wearable electronics.

Effective Intratumoral Retention of [103 Pd]AuPd Alloy Nanoparticles Embedded in Gel-Forming Liquids Paves the Way for New Nanobrachytherapy

Local application of radioactive sources as brachytherapy is well established in oncology. This treatment is highly invasive however, due to the insertion of millimeter sized metal seeds. The authors report the development of a new concept for brachytherapy, based on gold-palladium (AuPd) alloy nanoparticles, intrinsically radiolabeled with ¹⁰³ Pd. These are formulated in a carbohydrate-ester based liquid, capable of forming biodegradable gel-like implants upon injection. This allows for less invasive administration through small-gauge needles. [¹⁰³ Pd]AuPd nanoparticles with sizes around 20 nm are prepared with radiolabeling efficiencies ranging from 79% to >99%. Coating with the hydrophobic polymer poly(N-isopropylacrylamide) leads to nanoparticle diameters below 40 nm. Dispersing the nanoparticles in ethanol with water insoluble carbohydrate esters gives "nanogels", a low viscosity liquid capable of solidifying upon injection into aqueous environments. Both nanoparticles and radioactivity are stably retained in the nanogel over 25 days (>99%) after formation in aqueous buffers. Animals bearing CT26 murine tumors are injected intratumorally with 25 MBq of the ¹⁰³ Pd-nanogel, and display tumor growth delay and significantly increase median survival times compared with control groups. Excellent retention in the tumor of both the ¹⁰³ Pd and the nanoparticle matrix itself is observed, demonstrating a potential for replacing currently used brachytherapy seeds.

Impact of Rap-Phr system abundance on adaptation of Bacillus subtilis

Microbes commonly display great genetic plasticity, which has allowed them to colonize all ecological niches on Earth. Bacillus subtilis is a soil-dwelling organism that can be isolated from a wide variety of environments. An interesting characteristic of this bacterium is its ability to form biofilms that display complex heterogeneity: individual, clonal cells develop diverse phenotypes in response to different environmental conditions within the biofilm. Here, we scrutinized the impact that the number and variety of the Rap-Phr family of regulators and cell-cell communication modules of B. subtilis has on genetic adaptation and evolution. We examine how the Rap family of phosphatase regulators impacts sporulation in diverse niches using a library of single and double rap-phr mutants in competition under 4 distinct growth conditions. Using specific DNA barcodes and whole-genome sequencing, population dynamics were followed, revealing the impact of individual Rap phosphatases and arising mutations on the adaptability of B. subtilis.

Pervasive prophage recombination occurs during evolution of spore-forming Bacilli

Phages are the main source of within-species bacterial diversity and drivers of horizontal gene transfer, but we know little about the mechanisms that drive genetic diversity of these mobile genetic elements (MGEs). Recently, we showed that a sporulation selection regime promotes evolutionary changes within SPβ prophage of Bacillus subtilis, leading to direct antagonistic interactions within the population. Herein, we reveal that under a sporulation selection regime, SPβ recombines with low copy number phi3Ts phage DNA present within the B. subtilis population. Recombination results in a new prophage occupying a different integration site, as well as the spontaneous release of virulent phage hybrids. Analysis of Bacillus sp. strains suggests that SPβ and phi3T belong to a distinct cluster of unusually large phages inserted into sporulation-related genes that are equipped with a spore-related genetic arsenal. Comparison of Bacillus sp. genomes indicates that similar diversification of SPβ-like phages takes place in nature. Our work is a stepping stone toward empirical studies on phage evolution, and understanding the eco-evolutionary relationships between bacteria and their phages. By capturing the first steps of new phage evolution, we reveal striking relationship between survival strategy of bacteria and evolution of their phages.

Elucidating the anomalous membrane permeability of Ag(I), Cu(II), Zn(II) and Au(III) towards new nanoreactor strategies for synthesizing metal nanoparticles

The main structural element defining the cell is the lipid membrane, which is an integral part of regulating the fluxes of ion and nutrition molecules in and out of the cell. Surprisingly, copper ions were found to have anomalous membrane permeability. This led us to consider a broader spectrum of cations and further a new approach for using liposomes as nanoreactors for synthesis of metal and metal alloy nanoparticles. In the present study, the high membrane permeability of Cu2+ and its neighbouring transition elements in the periodic table was investigated. The permeability of Ni2+, Cu2+, Zn2+, Ag+, Au3+, Mg2+, Ca2+ and Lu3+ was assessed, and we report that Zn2+, Cu2+, Ag+ and Au3+ surprisingly are able to cross lipid bilayers. This knowledge is highly relevant for understanding trafficking of cations in biological systems, as well as for design of novel nanoparticle and nanoreactor systems. An example of its use is presented as a platform for synthesizing single highly uniform gold nanoparticles inside liposomal nanoreactors. We envision that this approach could provide a new nanoreactor methodology for forming highly structurally constrained uniform metal and metal alloy nanoparticles, as well as new methods for in vivo tracking of liposomes.

Simultaneous Cross-Linking and Cross-Polymerization of Enzyme Responsive Polyethylene Glycol Nanogels in Confined Aqueous Droplets for Reduction of Low-Density Lipoprotein Oxidation

A key initiating step in atherosclerosis is the accumulation and retention of apolipoprotein B complexing lipoproteins within the artery walls. In this work, we address this exact initiating mechanism of atherosclerosis, which results from the oxidation of low-density lipoproteins (oxLDL) using therapeutic nanogels. We present the development of biocompatible polyethylene glycol (PEG) cross-linked nanogels formed from a single simultaneous cross-linking and co-polymerization step in water without the requirement for an organic solvent, high temperature, or shear stress. The nanogel synthesis also incorporates in situ noncovalent electrostatically driven template polymerization around an innate anti-inflammatory and anti-oxidizing paraoxonase-1 (PON-1) enzyme payload-the release of which is triggered because of matrix metalloproteinase responsive elements instilled in the PEG cross-linker monomer. The results obtained demonstrate the potential of triggered release of the PON-1 enzyme and its efficacy against the production of ox-LDL, and therefore a reduction in macrophage foam cell and reactive oxygen species formation.

Cell targeting strategy affects the intracellular trafficking of liposomes altering loaded doxorubicin release kinetics and efficacy in endothelial cells

Targeting nanocarrier drug delivery systems, that deliver drug payloads to the site of disease action, are frequently viewed as the future of nanocarrier based therapies but have struggled to breakthrough to the clinic in comparison to non-targeting counterparts. Using unilamellar liposomes as model nanocarriers, we show that cell targeting strategy (electrostatic, ligand and antigen) influences both the intracellular fate of the liposomes and the corresponding efficacy of the loaded drug, doxorubicin, in endothelial cells. We show that increased liposome uptake by cells does not translate to improved efficacy in this scenario but that liposome intracellular trafficking, particularly distribution between recycling endosomes and lysosomes, influences in vitro efficacy. Choosing targeting strategies that promote desired nanocarrier intracellular trafficking may be a viable strategy to enhance the in vivo efficacy of drug delivery systems.

Multifarious Biologic Loaded Liposomes that Stimulate the Mammalian Target of Rapamycin Signaling Pathway Show Retina Neuroprotection after Retina Damage

A common event in optic neuropathies is the loss of axons and death of retinal ganglion cells (RGCs) resulting in irreversible blindness. Mammalian target of rapamycin (mTOR) signaling pathway agonists have been shown to foster axon regeneration and RGC survival in animal models of optic nerve damage. However, many challenges remain in developing therapies that exploit cell growth and tissue remodeling including (i) activating/inhibiting cell pathways synergistically, (ii) avoiding tumorigenesis, and (iii) ensuring appropriate physiological tissue function. These challenges are further exacerbated by the need to overcome ocular physiological barriers and clearance mechanisms. Here we present liposomes loaded with multiple mTOR pathway stimulating biologics designed to enhance neuroprotection after retina damage. Liposomes were loaded with ciliary neurotrophic factor, insulin-like growth factor 1, a lipopeptide N-fragment osteopontin mimic, and lipopeptide phosphatase tension homologue inhibitors for either the ATP domain or the c-terminal tail. In a mouse model of N-methyl-d-aspartic acid induced RGC death, a single intravitreal administration of liposomes reduced both RGC death and loss of retina electrophysiological function. Furthermore, combining liposomes with transplantation of induced pluripotent stem cell derived RGCs led to an improved electrophysiological outcome in mice. The results presented here show that liposomes carrying multiple signaling pathway modulators can facilitate neuroprotection and transplant electrophysiological outcome.

Multicompartment Artificial Organelles Conducting Enzymatic Cascade Reactions inside Cells

Cell organelles are subcellular structures entrapping a set of enzymes to achieve a specific functionality. The incorporation of artificial organelles into cells is a novel medical paradigm which might contribute to the treatment of various cell disorders by replacing malfunctioning organelles. In particular, artificial organelles are expected to be a powerful solution in the context of enzyme replacement therapy since enzymatic malfunction is the primary cause of organelle dysfunction. Although several attempts have been made to encapsulate enzymes within a carrier vehicle, only few intracellularly active artificial organelles have been reported to date and they all consist of single-compartment carriers. However, it is noted that biological organelles consist of multicompartment architectures where enzymatic reactions are executed within distinct subcompartments. Compartmentalization allows for multiple processes to take place in close vicinity and in a parallel manner without the risk of interference or degradation. Here, we report on a subcompartmentalized and intracellularly active carrier, a crucial step for advancing artificial organelles. In particular, we develop and characterize a novel capsosome system, which consists of multiple liposomes and fluorescent gold nanoclusters embedded within a polymer carrier capsule. We subsequently demonstrate that encapsulated enzymes preserve their activity intracellularly, allowing for controlled enzymatic cascade reaction within a host cell.

Mouse Positron Emission Tomography Study of the Biodistribution of Gold Nanoparticles with Different Surface Coatings Using Embedded Copper-64

By taking advantage of the ability of ⁶⁴Cu to bind nonspecifically to gold surfaces, we have developed a methodology to embed this radionuclide inside gold nanoparticles (AuNPs). ⁶⁴Cu enables the in vivo imaging of AuNPs by positron emission tomography (PET). AuNPs have a multitude of uses within health technology and are useful tools for general nanoparticle research. ⁶⁴Cu-AuNPs were prepared by incubating AuNP seeds with ⁶⁴Cu²⁺, followed by the entrapment of the radionuclide by grafting on a second layer of gold. This resulted in radiolabeling efficiencies of 53 ± 6%. The radiolabel showed excellent stability when incubated with EDTA for 2 days (95% radioactivity retention) and showed no loss of ⁶⁴Cu when incubated with 50% mouse serum for 2 days. The methodology was chelator-free, removing traditional concerns over chelator instability and altered AuNP properties due to surface modification. Radiolabeled ⁶⁴Cu-AuNP cores were prepared in biomedically relevant sizes of 20-30 nm and used to investigate the in vivo stability of three different AuNP coatings by PET imaging in a murine xenograft tumor model. We found the longest plasma half-life (T_1/2 about 9 h) and tumor accumulation (3.9%ID/g) to result from a polyethylene glycol coating, while faster elimination from the bloodstream was observed with both a Tween 20-stabilized coating and a zwitterionic coating based on a mixture of sulfonic acids and quaternary amines. In the in vivo model, the ⁶⁴Cu was observed to closely follow the AuNPs for each coating, again attributed to the excellent stability of the radiolabel.

Theranostic mesoporous silica nanoparticles biodegrade after pro-survival drug delivery and ultrasound/magnetic resonance imaging of stem cells

Increasing cell survival in stem cell therapy is an important challenge for the field of regenerative medicine. Here, we report theranostic mesoporous silica nanoparticles that can increase cell survival through both diagnostic and therapeutic approaches. First, the nanoparticle offers ultrasound and MRI signal to guide implantation into the peri-infarct zone and away from the most necrotic tissue. Second, the nanoparticle serves as a slow release reservoir of insulin-like growth factor (IGF)—a protein shown to increase cell survival. Mesenchymal stem cells labeled with these nanoparticles had detection limits near 9000 cells with no cytotoxicity at the 250 µg/mL concentration required for labeling. We also studied the degradation of the nanoparticles and showed that they clear from cells in approximately 3 weeks. The presence of IGF increased cell survival up to 40% (p<0.05) versus unlabeled cells under in vitro serum-free culture conditions.

A correlative optical microscopy and scanning electron microscopy approach to locating nanoparticles in brain tumors

The growing use of nanoparticles in biomedical applications, including cancer diagnosis and treatment, demands the capability to exactly locate them within complex biological systems. In this work a correlative optical and scanning electron microscopy technique was developed to locate and observe multi-modal gold core nanoparticle accumulation in brain tumor models. Entire brain sections from mice containing orthotopic brain tumors injected intravenously with nanoparticles were imaged using both optical microscopy to identify the brain tumor, and scanning electron microscopy to identify the individual nanoparticles. Gold-based nanoparticles were readily identified in the scanning electron microscope using backscattered electron imaging as bright spots against a darker background. This information was then correlated to determine the exact location of the nanoparticles within the brain tissue. The nanoparticles were located only in areas that contained tumor cells, and not in the surrounding healthy brain tissue. This correlative technique provides a powerful method to relate the macro- and micro-scale features visible in light microscopy with the nanoscale features resolvable in scanning electron microscopy.

A tunable silk-alginate hydrogel scaffold for stem cell culture and transplantation

One of the major challenges in regenerative medicine is the ability to recreate the stem cell niche, which is defined by its signaling molecules, the creation of cytokine gradients, and the modulation of matrix stiffness. A wide range of scaffolds has been developed in order to recapitulate the stem cell niche, among them hydrogels. This paper reports the development of a new silk-alginate based hydrogel with a focus on stem cell culture. This biocomposite allows to fine tune its elasticity during cell culture, addressing the importance of mechanotransduction during stem cell differentiation. The silk-alginate scaffold promotes adherence of mouse embryonic stem cells and cell survival upon transplantation. In addition, it has tunable stiffness as function of the silk-alginate ratio and the concentration of crosslinker--a characteristic that is very hard to accomplish in current hydrogels. The hydrogel and the presented results represents key steps on the way of creating artificial stem cell niche, opening up new paths in regenerative medicine.

A scanning transmission electron microscopy approach to analyzing large volumes of tissue to detect nanoparticles

The use of nanoparticles for the diagnosis and treatment of cancer requires the complete characterization of their toxicity, including accurately locating them within biological tissues. Owing to their size, traditional light microscopy techniques are unable to resolve them. Transmission electron microscopy provides the necessary spatial resolution to image individual nanoparticles in tissue, but is severely limited by the very small analysis volume, usually on the order of tens of cubic microns. In this work, we developed a scanning transmission electron microscopy (STEM) approach to analyze large volumes of tissue for the presence of polyethylene glycol-coated Raman-active-silica-gold-nanoparticles (PEG-R-Si-Au-NPs). This approach utilizes the simultaneous bright and dark field imaging capabilities of STEM along with careful control of the image contrast settings to readily identify PEG-R-Si-Au-NPs in mouse liver tissue without the need for additional time-consuming analytical characterization. We utilized this technique to analyze 243,000 mm³ of mouse liver tissue for the presence of PEG-R-Si-Au-NPs. Nanoparticles injected into the mice intravenously via the tail vein accumulated in the liver, whereas those injected intrarectally did not, indicating that they remain in the colon and do not pass through the colon wall into the systemic circulation.

Iron administration before stem cell harvest enables MR imaging tracking after transplantation

PURPOSE

To determine whether intravenous ferumoxytol can be used to effectively label mesenchymal stem cells (MSCs) in vivo and can be used for tracking of stem cell transplants.

MATERIALS AND METHODS

This study was approved by the institutional animal care and use committee. Sprague-Dawley rats (6-8 weeks old) were injected with ferumoxytol 48 hours prior to extraction of MSCs from bone marrow. Ferumoxytol uptake by these MSCs was evaluated with fluorescence, confocal, and electron microscopy and compared with results of traditional ex vivo-labeling procedures. The in vivo-labeled cells were subsequently transplanted in osteochondral defects of 14 knees of seven athymic rats and were evaluated with magnetic resonance (MR) imaging up to 4 weeks after transplantation. T2 relaxation times of in vivo-labeled MSC transplants and unlabeled control transplants were compared by using t tests. MR data were correlated with histopathologic results.

RESULTS

In vivo-labeled MSCs demonstrated significantly higher ferumoxytol uptake compared with ex vivo-labeled cells. With electron microscopy, iron oxide nanoparticles were localized in secondary lysosomes. In vivo-labeled cells demonstrated significant T2 shortening effects in vitro and in vivo when they were compared with unlabeled control cells (T2 in vivo, 15.4 vs 24.4 msec; P < .05) and could be tracked in osteochondral defects for 4 weeks. Histologic examination confirmed the presence of iron in labeled transplants and defect remodeling.

CONCLUSION

Intravenous ferumoxytol can be used to effectively label MSCs in vivo and can be used for tracking of stem cell transplants with MR imaging. This method eliminates risks of contamination and biologic alteration of MSCs associated with ex vivo-labeling procedures.

Advanced Characterization Techniques for Nanoparticles for Cancer Research: Applications of SEM and NanoSIMS for Locating Au Nanoparticles in Cells

The ability of nano secondary ion mass spectrometry (NanoSIMS) to locate and analyze Raman active gold core nanoparticles (R-AuNPs) in a biological system is compared with the standard analysis using the scanning electron microscope (SEM). The same cell with R-AuNPs on and inside the macrophage was analyzed with both techniques to directly compare them. SEM analysis showed a large number of nanoparticles within the cell. Subsequent NanoSIMS analysis showed fewer R-AuNPs with lower spatial resolution. SEM was determined to be superior to NanoSIMS for the analysis of inorganic nanoparticles in complex biological systems.

Photoacoustic imaging of mesenchymal stem cells in living mice via silica-coated gold nanorods

Improved imaging modalities are critically needed for optimizing stem cell therapy. Techniques with real-time content to guide and quantitate cell implantation are especially important in applications such as musculoskeletal regenerative medicine. Here, we report the use of silica-coated gold nanorods as a contrast agent for photoacoustic imaging and quantitation of mesenchymal stem cells in rodent muscle tissue. The silica coating increased the uptake of gold into the cell more than 5-fold, yet no toxicity or proliferation changes were observed in cells loaded with this contrast agent. Pluripotency of the cells was retained, and secretome analysis indicated that only IL-6 was disregulated more than 2-fold from a pool of 26 cytokines. The low background of the technique allowed imaging of down to 100,000 cells in vivo. The spatial resolution is 340 μm, and the temporal resolution is 0.2 s, which is at least an order of magnitude below existing cell imaging approaches. This approach has significant advantages over traditional cell imaging techniques like positron emission tomography and magnetic resonance imaging including real time monitoring of stem cell therapy.