A dense poly(ethylene glycol) coating improves penetration of large polymeric nanoparticles within brain tissue

An assessment of the ability of the obstruction-scaling model to estimate solute diffusion coefficients in hydrogels

The ability to estimate the diffusion coefficient of a solute within hydrogels has important application in the design and analysis of hydrogels used in drug delivery, tissue engineering, and regenerative medicine. A number of mathematical models have been derived for this purpose; however, they often rely on fitted parameters and so have limited predictive capability. Herein we assess the ability of the obstruction-scaling model to provide reasonable estimates of solute diffusion coefficients within hydrogels, as well as the assumption that a hydrogel can be represented as an entangled polymer solution of an equivalent concentration. Fluorescein isothiocyanate dextran solutes were loaded into sodium alginate solutions as well as hydrogels of different polymer volume fractions formed from photoinitiated cross-linking of methacrylate sodium alginate. The tracer diffusion coefficients of these solutes were measured using fluorescence recovery after photobleaching (FRAP). The measured diffusion coefficients were then compared to the values predicted by the obstruction-scaling model. The model predictions were within ±15% of the measured values, suggesting that the model can provide useful estimates of solute diffusion coefficients within hydrogels and solutions. Moreover, solutes diffusing in both sodium alginate solutions and hydrogels were demonstrated to experience the same degree of solute mobility restriction given the same effective polymer concentration, supporting the assumption that a hydrogel can be represented as an entangled polymer solution of equivalent concentration.

Pretreatment of human cervicovaginal mucus with pluronic F127 enhances nanoparticle penetration without compromising mucus barrier properties to herpes simplex virus

Mucosal drug delivery nanotechnologies are limited by the mucus barrier that protects nearly all epithelial surfaces not covered with skin. Most polymeric nanoparticles, including polystyrene nanoparticles (PS), strongly adhere to mucus, thereby limiting penetration and facilitating rapid clearance from the body. Here, we demonstrate that PS rapidly penetrate human cervicovaginal mucus (CVM), if the CVM has been pretreated with sufficient concentrations of Pluronic F127. Importantly, the diffusion rate of large polyethylene glycol (PEG)-coated, nonmucoadhesive nanoparticles (PS-PEG) did not change in F127-pretreated CVM, implying that F127 did not significantly alter the native pore structure of CVM. Additionally, herpes simplex virus type 1 (HSV-1) remains adherent in F127-pretreated CVM, indicating that the presence of F127 did not reduce adhesive interactions between CVM and the virions. In contrast to treatment with a surfactant that has been approved for vaginal use as a spermicide (nonoxynol-9 or N9), there was no increase in inflammatory cytokine release in the vaginal tract of mice after daily application of 1% F127 for 1 week. Pluronic F127 pretreatment holds potential as a method to safely improve the distribution, retention, and efficacy of nanoparticle formulations without compromising CVM barrier properties to pathogens.

NCI investment in nanotechnology: achievements and challenges for the future

Nanotechnology offers an exceptional and unique opportunity for developing a new generation of tools addressing persistent challenges to progress in cancer research and clinical care. The National Cancer Institute (NCI) recognizes this potential, which is why it invests roughly $150 M per year in nanobiotechnology training, research and development. By exploiting the various capacities of nanomaterials, the range of nanoscale vectors and probes potentially available suggests much is possible for precisely investigating, manipulating, and targeting the mechanisms of cancer across the full spectrum of research and clinical care. NCI has played a key role among federal R&D agencies in recognizing early the value of nanobiotechnology in medicine and committing to its development as well as providing training support for new investigators in the field. These investments have allowed many in the research community to pursue breakthrough capabilities that have already yielded broad benefits. Presented here is an overview of how NCI has made these investments with some consideration of how it will continue to work with this research community to pursue paradigm-changing innovations that offer relief from the burdens of cancer.

In vivo treatment of Helicobacter pylori infection with liposomal linolenic acid reduces colonization and ameliorates inflammation

Helicobacter pylori infection is marked by a vast prevalence and strong association with various gastric diseases, including gastritis, peptic ulcers, and gastric cancer. Because of the rapid emergence of H. pylori strains resistant to existing antibiotics, current treatment regimens show a rapid decline of their eradication rates. Clearly, novel antibacterial strategies against H. pylori are urgently needed. Here, we investigated the in vivo therapeutic potential of liposomal linolenic acid (LipoLLA) for the treatment of H. pylori infection. The LipoLLA formulation with a size of ∼ 100 nm was prone to fusion with bacterial membrane, thereby directly releasing a high dose of linolenic acids into the bacterial membrane. LipoLLA penetrated the mucus layer of mouse stomach, and a significant portion of the administered LipoLLA was retained in the stomach lining up to 24 h after the oral administration. In vivo tests further confirmed that LipoLLA was able to kill H. pylori and reduce bacterial load in the mouse stomach. LipoLLA treatment was also shown to reduce the levels of proinflammatory cytokines including interleukin 1β, interleukin 6, and tumor necrosis factor alpha, which were otherwise elevated because of the H. pylori infection. Finally, a toxicity test demonstrated excellent biocompatibility of LipoLLA to normal mouse stomach. Collectively, results from this study indicate that LipoLLA is a promising, effective, and safe therapeutic agent for the treatment of H. pylori infection.

Super-soft hydrogel particles with tunable elasticity in a microfluidic blood capillary model

Super-soft PEG hydrogel particles with tunable elasticity are prepared via a mesoporous silica templating method. The deformability behavior of these particles, in a microfluidic blood-capillary model, can be tailored to be similar to that of human red blood cells. These results provide a new platform for the design and development of soft hydrogel particles for investigating bio-nano interactions.

Effect of surface chemistry on nanoparticle interaction with gastrointestinal mucus and distribution in the gastrointestinal tract following oral and rectal administration in the mouse

It is believed that mucoadhesive surface properties on particles delivered to the gastrointestinal (GI) tract improve oral absorption or local targeting of various difficult-to-deliver drug classes. To test the effect of nanoparticle mucoadhesion on distribution of nanoparticles in the GI tract, we orally and rectally administered nano- and microparticles that we confirmed possessed surfaces that were either strongly mucoadhesive or non-mucoadhesive. We found that mucoadhesive particles (MAP) aggregated in mucus in the center of the GI lumen, far away from the absorptive epithelium, both in healthy mice and in a mouse model of ulcerative colitis (UC). In striking contrast, water absorption by the GI tract rapidly and uniformly transported non-mucoadhesive mucus-penetrating particles (MPP) to epithelial surfaces, including reaching the surfaces between villi in the small intestine. When using high gavage fluid volumes or injection into ligated intestinal loops, common methods for assessing oral drug and nanoparticle absorption, we found that both MAP and MPP became well-distributed throughout the intestine, indicating that the barrier properties of GI mucus were compromised. In the mouse colorectum, MPP penetrated into mucus in the deeply in-folded surfaces to evenly coat the entire epithelial surface. Moreover, in a mouse model of UC, MPP were transported preferentially into the disrupted, ulcerated tissue. Our results suggest that delivering drugs in non-mucoadhesive MPP is likely to provide enhanced particle distribution, and thus drug delivery, in the GI tract, including to ulcerated tissues.

Ceria nanoparticles stabilized by organic surface coatings activate the lysosome-autophagy system and enhance autophagic clearance

Cerium oxide nanoparticles (nanoceria) are widely used in a variety of industrial applications including UV filters and catalysts. The expanding commercial scale production and use of ceria nanoparticles have inevitably increased the risk of release of nanoceria into the environment as well as the risk of human exposure. The use of nanoceria in biomedical applications is also being currently investigated because of its recently characterized antioxidative properties. In this study, we investigated the impact of ceria nanoparticles on the lysosome-autophagy system, the main catabolic pathway that is activated in mammalian cells upon internalization of exogenous material. We tested a battery of ceria nanoparticles functionalized with different types of biocompatible coatings (N-acetylglucosamine, polyethylene glycol and polyvinylpyrrolidone) expected to have minimal effect on lysosomal integrity and function. We found that ceria nanoparticles promote activation of the transcription factor EB, a master regulator of lysosomal function and autophagy, and induce upregulation of genes of the lysosome-autophagy system. We further show that the array of differently functionalized ceria nanoparticles tested in this study enhance autophagic clearance of proteolipid aggregates that accumulate as a result of inefficient function of the lysosome-autophagy system. This study provides a mechanistic understanding of the interaction of ceria nanoparticles with the lysosome-autophagy system and demonstrates that ceria nanoparticles are activators of autophagy and promote clearance of autophagic cargo. These results provide insights for the use of nanoceria in biomedical applications, including drug delivery. These findings will also inform the design of engineered nanoparticles with safe and precisely controlled impact on the environment and the design of nanotherapeutics for the treatment of diseases with defective autophagic function and accumulation of lysosomal storage material.

Neural stem cells improve intracranial nanoparticle retention and tumor-selective distribution

AIM

The purpose of this work is to determine if tumor-tropic neural stem cells (NSCs) can improve the tumor-selective distribution and retention of nanoparticles (NPs) within invasive brain tumors.

MATERIALS & METHODS

Streptavidin-conjugated, polystyrene NPs are surface-coupled to biotinylated human NSCs. These NPs are large (798 nm), yet when conjugated to tropic cells, they are too large to passively diffuse through brain tissue or cross the blood-tumor barrier. NP distribution and retention was quantified 4 days after injections located either adjacent to an intracerebral glioma, in the contralateral hemisphere, or intravenously.

RESULTS & CONCLUSION

In all three in vivo injection paradigms, NSC-coupled NPs exhibited significantly improved tumor-selective distribution and retention over free-NP suspensions. These results provide proof-of-principle that NSCs can facilitate the tumor-selective distribution of NPs, a platform useful for improving intracranial drug delivery.

Brain-penetrating nanoparticles improve paclitaxel efficacy in malignant glioma following local administration

Poor drug distribution and short drug half-life within tumors strongly limit efficacy of chemotherapies in most cancers, including primary brain tumors. Local or targeted drug delivery via controlled-release polymers is a promising strategy to treat infiltrative brain tumors, which cannot be completely removed surgically. However, drug penetration is limited with conventional local therapies since small-molecule drugs often enter the first cell they encounter and travel only short distances from the site of administration. Nanoparticles that avoid adhesive interactions with the tumor extracellular matrix may improve drug distribution and sustain drug release when applied to the tumor area. We have previously shown model polystyrene nanoparticles up to 114 nm in diameter were able to rapidly diffuse in normal brain tissue, but only if coated with an exceptionally dense layer of poly(ethylene glycol) (PEG) to reduce adhesive interactions. Here, we demonstrate that paclitaxel (PTX)-loaded, poly(lactic-co-glycolic acid) (PLGA)-co-PEG block copolymer nanoparticles with an average diameter of 70 nm were able to diffuse 100-fold faster than similarly sized PTX-loaded PLGA particles (without PEG coatings). Densely PEGylated PTX-loaded nanoparticles significantly delayed tumor growth following local administration to established brain tumors, as compared to PTX-loaded PLGA nanoparticles or unencapsulated PTX. Delayed tumor growth combined with enhanced distribution of drug-loaded PLGA-PEG nanoparticles to the tumor infiltrative front demonstrates that particle penetration within the brain tumor parenchyma improves therapeutic efficacy. The use of drug-loaded brain-penetrating nanoparticles is a promising approach to achieve sustained and more uniform drug delivery to treat aggressive gliomas and potentially other brain disorders.

Nanopropellers and their actuation in complex viscoelastic media

Tissue and biological fluids are complex viscoelastic media with a nanoporous macromolecular structure. Here, we demonstrate that helical nanopropellers can be controllably steered through such a biological gel. The screw-propellers have a filament diameter of about 70 nm and are smaller than previously reported nanopropellers as well as any swimming microorganism. We show that the nanoscrews will move through high-viscosity solutions with comparable velocities to that of larger micropropellers, even though they are so small that Brownian forces suppress their actuation in pure water. When actuated in viscoelastic hyaluronan gels, the nanopropellers appear to have a significant advantage, as they are of the same size range as the gel's mesh size. Whereas larger helices will show very low or negligible propulsion in hyaluronan solutions, the nanoscrews actually display significantly enhanced propulsion velocities that exceed the highest measured speeds in Newtonian fluids. The nanopropellers are not only promising for applications in the extracellular environment but small enough to be taken up by cells.

Overcoming the challenges in administering biopharmaceuticals: formulation and delivery strategies

The formulation and delivery of biopharmaceutical drugs, such as monoclonal antibodies and recombinant proteins, poses substantial challenges owing to their large size and susceptibility to degradation. In this Review we highlight recent advances in formulation and delivery strategies--such as the use of microsphere-based controlled-release technologies, protein modification methods that make use of polyethylene glycol and other polymers, and genetic manipulation of biopharmaceutical drugs--and discuss their advantages and limitations. We also highlight current and emerging delivery routes that provide an alternative to injection, including transdermal, oral and pulmonary delivery routes. In addition, the potential of targeted and intracellular protein delivery is discussed.

Single particle tracking reveals spatial and dynamic organization of the E. coli biofilm matrix

Biofilms are communities of surface-adherent bacteria surrounded by secreted polymers known as the extracellular polymeric substance (EPS). Biofilms are harmful in many industries, and thus it is of great interest to understand their mechanical properties and structure to determine ways to destabilize them. By performing single particle tracking with beads of varying surface functionalization it was found that charge interactions play a key role in mediating mobility within biofilms. With a combination of single particle tracking and microrheological concepts, it was found that Escherichia coli biofilms display height dependent charge density that evolves over time. Statistical analyses of bead trajectories and confocal microscopy showed inter-connecting micron scale channels that penetrate throughout the biofilm, which may be important for nutrient transfer through the system. This methodology provides significant insight into a particular biofilm system and can be applied to many others to provide comparisons of biofilm structure. The elucidation of structure provides evidence for the permeability of biofilms to microscale objects, and the ability of a biofilm to mature and change properties over time.

Emerging insights into barriers to effective brain tumor therapeutics

There is great promise that ongoing advances in the delivery of therapeutics to the central nervous system (CNS) combined with rapidly expanding knowledge of brain tumor patho-biology will provide new, more effective therapies. Brain tumors that form from brain cells, as opposed to those that come from other parts of the body, rarely metastasize outside of the CNS. Instead, the tumor cells invade deep into the brain itself, causing disruption in brain circuits, blood vessel and blood flow changes, and tissue swelling. Patients with the most common and deadly form, glioblastoma (GBM) rarely live more than 2 years even with the most aggressive treatments and often with devastating neurological consequences. Current treatments include maximal safe surgical removal or biopsy followed by radiation and chemotherapy to address the residual tumor mass and invading tumor cells. However, delivering effective and sustained treatments to these invading cells without damaging healthy brain tissue is a major challenge and focus of the emerging fields of nanomedicine and viral and cell-based therapies. New treatment strategies, particularly those directed against the invasive component of this devastating CNS disease, are sorely needed. In this review, we (1) discuss the history and evolution of treatments for GBM, (2) define and explore three critical barriers to improving therapeutic delivery to invasive brain tumors, specifically, the neuro-vascular unit as it relates to the blood brain barrier, the extra-cellular space in regard to the brain penetration barrier, and the tumor genetic heterogeneity and instability in association with the treatment efficacy barrier, and (3) identify promising new therapeutic delivery approaches that have the potential to address these barriers and create sustained, meaningful efficacy against GBM.

Continuous polymer nanocoating on silica nanoparticles

Continuous polymer coating of nanoparticles is of interest in many industries such as pharmaceuticals, cosmetics, food, and electronics. Here we introduce a polymer coating/precipitation technique to achieve a uniform and controllable nanosize polymer coating on nanoparticles in a continuous manner. The utility of this technique is demonstrated by coating Aerosil silica nanoparticles (SNPs) of diameter 12 nm with the polymer Eudragit RL 100. Both hydrophilic and hydrophobic SNPs were successfully coated. After determining the cloud point of an acetone solution of the polymer containing a controlled amount of the nonsolvent water, the solid hollow fiber cooling crystallization (SHFCC) technique was employed to continuously coat SNPs with the polymer. A suspension of the SNPs in an acetone-water solution of the polymer containing a surfactant was pumped through the lumen of solid polypropylene hollow fibers in a SHFCC device; cold liquid was circulated on the shell side. Because of rapid cooling-induced supersaturation and heterogeneous nucleation, precipitated polymers will coat the nanoparticles. The thickness and morphology of the nanocoating and the particle size distribution of the coated SNPs were analyzed by scanning transmission electron microscopy (STEM) with electron energy loss spectroscopy (EELS), thermogravimetric analysis (TGA), and dynamic light scattering (DLS). Results indicate that uniformly polymer-coated SNPs can be obtained from the SHFCC device after suitable post-treatments. The technique is also easily scalable by increasing the number of hollow fibers in the SHFCC device.

Non-invasive delivery of stealth, brain-penetrating nanoparticles across the blood-brain barrier using MRI-guided focused ultrasound

The blood-brain barrier (BBB) presents a significant obstacle for the treatment of many central nervous system (CNS) disorders, including invasive brain tumors, Alzheimer's, Parkinson's and stroke. Therapeutics must be capable of bypassing the BBB and also penetrate the brain parenchyma to achieve a desired effect within the brain. In this study, we test the unique combination of a non-invasive approach to BBB permeabilization with a therapeutically relevant polymeric nanoparticle platform capable of rapidly penetrating within the brain microenvironment. MR-guided focused ultrasound (FUS) with intravascular microbubbles (MBs) is able to locally and reversibly disrupt the BBB with submillimeter spatial accuracy. Densely poly(ethylene-co-glycol) (PEG) coated, brain-penetrating nanoparticles (BPNs) are long-circulating and diffuse 10-fold slower in normal rat brain tissue compared to diffusion in water. Following intravenous administration of model and biodegradable BPNs in normal healthy rats, we demonstrate safe, pressure-dependent delivery of 60nm BPNs to the brain parenchyma in regions where the BBB is disrupted by FUS and MBs. Delivery of BPNs with MR-guided FUS has the potential to improve efficacy of treatments for many CNS diseases, while reducing systemic side effects by providing sustained, well-dispersed drug delivery into select regions of the brain.

Agile delivery of protein therapeutics to CNS

A variety of therapeutic proteins have shown potential to treat central nervous system (CNS) disorders. Challenge to deliver these protein molecules to the brain is well known. Proteins administered through parenteral routes are often excluded from the brain because of their poor bioavailability and the existence of the blood-brain barrier (BBB). Barriers also exist to proteins administered through non-parenteral routes that bypass the BBB. Several strategies have shown promise in delivering proteins to the brain. This review, first, describes the physiology and pathology of the BBB that underscore the rationale and needs of each strategy to be applied. Second, major classes of protein therapeutics along with some key factors that affect their delivery outcomes are presented. Third, different routes of protein administration (parenteral, central intracerebroventricular and intraparenchymal, intranasal and intrathecal) are discussed along with key barriers to CNS delivery associated with each route. Finally, current delivery strategies involving chemical modification of proteins and use of particle-based carriers are overviewed using examples from literature and our own work. Whereas most of these studies are in the early stage, some provide proof of mechanism of increased protein delivery to the brain in relevant models of CNS diseases, while in few cases proof of concept had been attained in clinical studies. This review will be useful to broad audience of students, academicians and industry professionals who consider critical issues of protein delivery to the brain and aim developing and studying effective brain delivery systems for protein therapeutics.

Ligand exchange on gold nanoparticles for drug delivery and enhanced therapeutic index evaluated in acute myeloid leukemia models

Cancer chemotherapy is typically toxic. This problem could be addressed by using differences between cancer and normal cells for controlled delivery of drugs to cancer cells. One such difference is the ubiquitously elevated glutathione expression in cancer cells. We report a simple and versatile synthesis of water-soluble gold nanoparticles passivated with amine-containing molecules, which allow for controlled drug release via ligand exchange with bio-available glutathione. Taking methotrexate-passivated gold nanoparticles (Au:MTX) as an example, drug delivery and controlled release via glutathione-mediated ligand exchange was evaluated. Furthermore, the possibility of using Au:MTX to improve therapeutic index in acute myeloid leukemia (AML) models was examined in vitro and in vivo. Au:MTX exhibited cancer selectivity in vitro. Au:MTX had an elevated potency toward an AML cell line THP-1 in a dosage range of 1–5 nM, and therefore an enhanced delivery of drug, whereas normal hematopoietic stem/progenitor cell (HSPC) growth was minimally affected by Au:MTX and MTX treatments within the same range of dosage. In vivo efficacy and safety of Au:MTX was evaluated in a murine xenotransplant model of primary human AML. Au:MTX treatment, compared to control groups including MTX-only and Au nanoparticle-only treatments, produced better leukemia suppression without added toxicity, indicating an enhanced therapeutic index.

Overcoming the cystic fibrosis sputum barrier to leading adeno-associated virus gene therapy vectors

Gene therapy has not yet improved cystic fibrosis (CF) patient lung function in human trials, despite promising preclinical studies. In the human CF lung, inhaled gene vectors must penetrate the viscoelastic secretions coating the airways to reach target cells in the underlying epithelium. We investigated whether CF sputum acts as a barrier to leading adeno-associated virus (AAV) gene vectors, including AAV2, the only serotype tested in CF clinical trials, and AAV1, a leading candidate for future trials. Using multiple particle tracking, we found that sputum strongly impeded diffusion of AAV, regardless of serotype, by adhesive interactions and steric obstruction. Approximately 50% of AAV vectors diffused >1,000-fold more slowly in sputum than in water, with large patient-to-patient variation. We thus tested two strategies to improve AAV diffusion in sputum. We showed that an AAV2 mutant engineered to have reduced heparin binding diffused twice as fast as AAV2 on average, presumably because of reduced adhesion to sputum. We also discovered that the mucolytic N-acetylcysteine could markedly enhance AAV diffusion by altering the sputum microstructure. These studies underscore that sputum is a major barrier to CF gene delivery, and offer strategies for increasing AAV penetration through sputum to improve clinical outcomes.

Biodegradable polymeric nanoparticles show high efficacy and specificity at DNA delivery to human glioblastoma in vitro and in vivo

Current glioblastoma therapies are insufficient to prevent tumor recurrence and eventual death. Here, we describe a method to treat malignant glioma by nonviral DNA delivery using biodegradable poly(β-amino ester)s (PBAEs), with a focus on the brain tumor initiating cells (BTICs), the tumor cell population believed to be responsible for the formation of new tumors and resistance to many conventional therapies. We show transfection efficacy of >60% and low biomaterial-mediated cytotoxicity in primary human BTICs in vitro even when the BTICs are grown as 3-D oncospheres. Intriguingly, we find that these polymeric nanoparticles show intrinsic specificity for nonviral transfection of primary human BTICs over primary healthy human neural progenitor cells and that this specificity is not due to differences in cellular growth rate or total cellular uptake of nanoparticles. Moreover, we demonstrate that biodegradable PBAE/DNA nanoparticles can be fabricated, lyophilized, and then stored for at least 2 years without losing efficacy, increasing the translational relevance of this technology. Using lyophilized nanoparticles, we show transgene expression by tumor cells after intratumoral injection into an orthotopic murine model of human glioblastoma. PBAE/DNA nanoparticles were more effective than naked DNA at exogenous gene expression in vivo, and tumor cells were transfected more effectively than noninvaded brain parenchyma in vivo. This work shows the potential of nonviral gene delivery tools to target human brain tumors.

Manganese-containing Prussian blue nanoparticles for imaging of pediatric brain tumors

Pediatric brain tumors (PBTs) are a leading cause of death in children. For an improved prognosis in patients with PBTs, there is a critical need to develop molecularly-specific imaging agents to monitor disease progression and response to treatment. In this paper, we describe manganese-containing Prussian blue nanoparticles as agents for molecular magnetic resonance imaging (MRI) and fluorescence-based imaging of PBTs. Our core-shell nanoparticles consist of a core lattice structure that incorporates and retains paramagnetic Mn(2+) ions, and generates MRI contrast (both negative and positive). The biofunctionalized shell is comprised of fluorescent avidin, which serves the dual purpose of enabling fluorescence imaging and functioning as a platform for the attachment of biotinylated ligands that target PBTs. The surfaces of our nanoparticles are modified with biotinylated antibodies targeting neuron-glial antigen 2 or biotinylated transferrin. Both neuron-glial antigen 2 and the transferrin receptor are protein markers overexpressed in PBTs. We describe the synthesis, biofunctionalization, and characterization of these multimodal nanoparticles. Further, we demonstrate the MRI and fluorescence imaging capabilities of manganese-containing Prussian blue nanoparticles in vitro. Finally, we demonstrate the potential of these nanoparticles as PBT imaging agents by measuring their organ and brain biodistribution in an orthotopic mouse model of PBTs using ex vivo fluorescence imaging.

Strategies to deliver peptide drugs to the brain

Neurological diseases such as neurodegeneration, pain, psychiatric disorders, stroke, and brain cancers would greatly benefit from the use of highly potent and specific peptide pharmaceuticals. Peptides are especially desirable because of their low inherent toxicity. The presence of the blood brain barrier (BBB), their short duration of action, and their need for parenteral administration limits their clinical use. However, over the past decade there have been significant advances in delivering peptides to the central nervous system. Angiopep peptides developed by Angiochem (Montreal, Canada), transferrin antibodies developed by ArmaGen (Santa Monica, USA), and cell penetrating peptides have all shown promise in delivering therapeutic peptides across the BBB after intravenous administration. Noninvasive methods of delivering peptides to the brain include the use of chitosan amphiphile nanoparticles for oral delivery and nose to brain strategies. The uptake of the chitosan amphiphile nanoparticles by the gastrointestinal epithelium is important for oral peptide delivery. Finally protecting peptides from plasma degradation is integral to the success of most of these peptide delivery strategies.

Highly compacted pH-responsive DNA nanoparticles mediate transgene silencing in experimental glioma

Complex genetic mutations are common in brain cancer, making gene therapy an attractive approach to repair or modulate altered genes and cellular pathways. Non-viral gene vectors can offer DNA delivery without the risk of immunogenicity and/or insertional mutagenesis that are common with viral vectors. We developed pH-responsive DNA nanoparticles, CH₁₂K₁₈PEG_5k, by inserting a poly-L-histidine segment between PEG and poly-L-lysine to engineer a triblock copolymer. CH₁₂K₁₈PEG_5k DNA nanoparticles trafficked through clathrin-dependent endocytosis (CME) as the primary pathway in mouse glioblastoma (GBM) cells, and protected plasmid DNA from both DNase-mediated and acidic lysosomal degradation. CH₁₂K₁₈PEG_5k DNA nanoparticles effectively silenced a tumor-specific transgene (firefly luciferase) following direct injection into mouse intracranial GBM. Toxicity and histological analysis showed no evidence of acute or delayed inflammatory responses. These results demonstrate the utility of using this DNA nanoparticle-based technology for delivering genes to tumor cells as a possible therapeutic approach for patients with brain cancer.

Carbon nanotubes in hyperthermia therapy

Thermal tumor ablation therapies are being developed with a variety of nanomaterials, including single- and multiwalled carbon nanotubes. Carbon nanotubes (CNTs) have attracted interest due to their potential for simultaneous imaging and therapy. In this review, we highlight in vivo applications of carbon nanotube-mediated thermal therapy (CNMTT) and examine the rationale for use of this treatment in recurrent tumors or those resistant to conventional cancer therapies. Additionally, we discuss strategies to localize and enhance the cancer selectivity of this treatment and briefly examine issues relating the toxicity and long term fate of CNTs.

Nanomedicine in cerebral palsy

Cerebral palsy is a chronic childhood disorder that can have diverse etiologies. Injury to the developing brain that occurs either in utero or soon after birth can result in the motor, sensory, and cognitive deficits seen in cerebral palsy. Although the etiologies for cerebral palsy are variable, neuroinflammation plays a key role in the pathophysiology of the brain injury irrespective of the etiology. Currently, there is no effective cure for cerebral palsy. Nanomedicine offers a new frontier in the development of therapies for prevention and treatment of brain injury resulting in cerebral palsy. Nanomaterials such as dendrimers provide opportunities for the targeted delivery of multiple drugs that can mitigate several pathways involved in injury and can be delivered specifically to the cells that are responsible for neuroinflammation and injury. These materials also offer the opportunity to deliver agents that would promote repair and regeneration in the brain, resulting not only in attenuation of injury, but also enabling normal growth. In this review, the current advances in nanotechnology for treatment of brain injury are discussed with specific relevance to cerebral palsy. Future directions that would facilitate clinical translation in neonates and children are also addressed.

Biodistribution of fluorescently labeled PAMAM dendrimers in neonatal rabbits: effect of neuroinflammation

Dendrimers are being explored in many preclinical studies as drug, gene, and imaging agent delivery systems. Understanding their detailed organ, tissue, cellular uptake, and retention can provide valuable insights into their effectiveness as delivery vehicles and the associated toxicity. This work explores a fluorescence-quantification based assay that enables simultaneous quantitative biodistribution and imaging of dendrimers with a single agent. We have labeled an ethylenediamine-core generation-4 hydroxyl-terminated poly(amidoamine) (PAMAM) dendrimer using the fluorescent photostable, near-IR cyanine dye (Cy5) and performed quantitative and qualitative biodistribution of the dendrimer-Cy5 conjugates (D-Cy5) in healthy neonatal rabbits and neonatal rabbits with cerebral palsy (CP). The biodistribution of D-Cy5 and free Cy5 dye was evaluated in newborn rabbits, based on the developed quantification methods using fluorescence spectroscopy, high-performance liquid chromatography (HPLC), and size exclusion chromatography (SEC) and supported by microscopic imaging. The uptake was assessed in the brain, heart, liver, lungs, kidneys, blood serum, and urine. Results obtained based on these three independent methods are in good agreement and indicate the fast renal clearance of D-Cy5 and free Cy5 with relatively higher organs accumulation of the D-Cy5 conjugate. Following systemic administration, the D-Cy5 mainly accumulated in kidneys and bladder at 24 h. The quantitative biodistribution is in good agreement with previous studies based on radiolabeling. These methods for dendrimers quantification are easier and more practical, provide excellent sensitivity (reaching 0.1 ng per gram of tissue), and allow for quantification of dendrimers in different organs over longer time periods without concerns for radioactive decay, while also enabling tissue and cellular imaging in the same animal. In kits with fetal-neuroinflammation induced CP, there was a significantly higher uptake of D-Cy5 in the brain, while biodistribution in other organs was similar to that of healthy kits.

A novel lactoferrin-modified β-cyclodextrin nanocarrier for brain-targeting drug delivery

The blood-brain barrier (BBB) restricts the transfer and delivery of most drug substances to brain. In this study, a novel nano-drug delivery system for brain-targeting was developed and investigated in vitro and in vivo. Lactoferrin (Lf) was selected as a brain-targeting ligand and conjugated to β-cyclodextrin (β-CD) via the heterobifunctional polyethyleneglycol (PEG) linker NHS-PEG-MAL, yielding Lf conjugated β-cyclodextrin (Lf-CD). UV-vis, FTIR, NMR and transmission electron microscopy (TEM) techniques clearly demonstrated the successful synthesis of Lf-CD nanoparticles with the average diameter of 92.9 ± 16.5 nm. Using near-infrared fluorescent dye IR-775 chloride (IR) as a model compound of poorly water-soluble drugs, IR-loaded Lf-CD nanoparticles (Lf-CD/IR) were successfully prepared with a high entrapment efficiency of 98.1 ± 4.8%. Biodistribution and pharmacokinetics of Lf-CD/IR were evaluated in KM mice after intravenous administration. The results of tissue distribution studies revealed that Lf-CD/IR treatment showed greatly improved BBB transport efficiency. In addition, AUC0-2h of IR in brain after Lf-CD/IR treatment was seven fold higher compared with that of IR treatment without Lf-CD nano-carriers, demonstrating that the introduction of Lf-CD drug-delivery system positively resulted in a higher AUC located in brain tissue. These results provide evidence that Lf-CD nanoparticles could be exploited as a potential brain-targeting drug delivery system for hydrophobic drugs and diagnostic reagents which normally fail to pass through the BBB.

Therapeutic nanomedicine for brain cancer

Malignant brain cancer treatment is limited by a number of barriers, including the blood-brain barrier, transport within the brain interstitium, difficulties in delivering therapeutics specifically to tumor cells, the highly invasive quality of gliomas and drug resistance. As a result, the prognosis for patients with high-grade gliomas is poor and has improved little in recent years. Nanomedicine approaches have been developed in the laboratory, with some technologies being translated to the clinic, in order to address these needs. This review discusses the obstacles to effective treatment that are currently faced in the field, as well as various nanomedicine techniques that have been used or are being explored to overcome them, with a focus on liposomal and polymeric nanoparticles.

Multifunctional receptor-targeted nanocomplexes for the delivery of therapeutic nucleic acids to the brain

Convection enhanced delivery (CED) is a method of direct injection to the brain that can achieve widespread dispersal of therapeutics, including gene therapies, from a single dose. Non-viral, nanocomplexes are of interest as vectors for gene therapy in the brain, but it is essential that administration should achieve maximal dispersal to minimise the number of injections required. We hypothesised that anionic nanocomplexes administered by CED should disperse more widely in rat brains than cationics of similar size, which bind electrostatically to cell-surface anionic moieties such as proteoglycans, limiting their spread. Anionic, receptor-targeted nanocomplexes (RTN) containing a neurotensin-targeting peptide were prepared with plasmid DNA and compared with cationic RTNs for dispersal and transfection efficiency. Both RTNs were labelled with gadolinium for localisation in the brain by MRI and in brain sections by LA-ICP-MS, as well as with rhodamine fluorophore for detection by fluorescence microscopy. MRI distribution studies confirmed that the anionic RTNs dispersed more widely than cationic RTNs, particularly in the corpus callosum. Gene expression levels from anionic formulations were similar to those of cationic RTNs. Thus, anionic RTN formulations can achieve both widespread dispersal and effective gene expression in brains after administration of a single dose by CED.

Highly penetrative, drug-loaded nanocarriers improve treatment of glioblastoma

Current therapy for glioblastoma multiforme is insufficient, with nearly universal recurrence. Available drug therapies are unsuccessful because they fail to penetrate through the region of the brain containing tumor cells and they fail to kill the cells most responsible for tumor development and therapy resistance, brain cancer stem cells (BCSCs). To address these challenges, we combined two major advances in technology: (i) brain-penetrating polymeric nanoparticles that can be loaded with drugs and are optimized for intracranial convection-enhanced delivery and (ii) repurposed compounds, previously used in Food and Drug Administration-approved products, which were identified through library screening to target BCSCs. Using fluorescence imaging and positron emission tomography, we demonstrate that brain-penetrating nanoparticles can be delivered to large intracranial volumes in both rats and pigs. We identified several agents (from Food and Drug Administration-approved products) that potently inhibit proliferation and self-renewal of BCSCs. When loaded into brain-penetrating nanoparticles and administered by convection-enhanced delivery, one of these agents, dithiazanine iodide, significantly increased survival in rats bearing BCSC-derived xenografts. This unique approach to controlled delivery in the brain should have a significant impact on treatment of glioblastoma multiforme and suggests previously undescribed routes for drug and gene delivery to treat other diseases of the central nervous system.

Enhanced vaginal drug delivery through the use of hypotonic formulations that induce fluid uptake

Mucosal epithelia use osmotic gradients for fluid absorption and secretion. We hypothesized that administration of hypotonic solutions would induce fluid uptake that could be advantageous for rapidly delivering drugs through mucus to the vaginal epithelium. We found that hypotonic formulations markedly increased the rate at which small molecule drugs and mucoinert nanoparticles (mucus-penetrating particles, or MPP), but not conventional mucoadhesive nanoparticles (CP), reached the vaginal epithelial surface in vivo in mice. Additionally, hypotonic formulations greatly enhanced drug and MPP delivery to the entire epithelial surface, including deep into the vaginal folds (rugae) that drugs or MPP in isotonic formulations failed to reach efficiently. However, hypotonic formulations caused unencapsulated "free" drugs to be drawn through the epithelium, reducing vaginal retention. In contrast, hypotonic formulations caused MPP to accumulate rapidly and uniformly on vaginal surfaces, ideally positioned for localized sustained drug delivery. Using a mouse model of vaginal genital herpes (HSV-2) infection, we found that hypotonic delivery of free drug led to improved immediate protection, but diminished longer-term protection. In contrast, as we previously demonstrated, hypotonic delivery of drug via MPP led to better long-term retention and protection in the vagina. Importantly, we demonstrate that slightly hypotonic formulations provided rapid and uniform delivery of MPP to the entire vaginal surface, thus enabling formulations with minimal risk of epithelial toxicity. Hypotonic formulations for vaginal drug delivery via MPP may significantly improve prevention and treatment of reproductive tract diseases and disorders.

Scalable method to produce biodegradable nanoparticles that rapidly penetrate human mucus

Mucus typically traps and rapidly removes foreign particles from the airways, gastrointestinal tract, nasopharynx, female reproductive tract and the surface of the eye. Nanoparticles capable of rapid penetration through mucus can potentially avoid rapid clearance, and open significant opportunities for controlled drug delivery at mucosal surfaces. Here, we report an industrially scalable emulsification method to produce biodegradable mucus-penetrating particles (MPP). The emulsification of diblock copolymers of poly(lactic-co-glycolic acid) and polyethylene glycol (PLGA-PEG) using low molecular weight (MW) emulsifiers forms dense brush PEG coatings on nanoparticles that allow rapid nanoparticle penetration through fresh undiluted human mucus. In comparison, conventional high MW emulsifiers, such as polyvinyl alcohol (PVA), interrupts the PEG coating on nanoparticles, resulting in their immobilization in mucus owing to adhesive interactions with mucus mesh elements. PLGA-PEG nanoparticles with a wide range of PEG MW (1, 2, 5, and 10 kDa), prepared by the emulsification method using low MW emulsifiers, all rapidly penetrated mucus. A range of drugs, from hydrophobic small molecules to hydrophilic large biologics, can be efficiently loaded into biodegradable MPP using the method described. This readily scalable method should facilitate the production of MPP products for mucosal drug delivery, as well as potentially longer-circulating particles following intravenous administration.

Ex vivo characterization of particle transport in mucus secretions coating freshly excised mucosal tissues

Sustained drug delivery to mucosal surfaces has the potential to improve the effectiveness of prophylactic and therapeutic treatments for numerous diseases and conditions, including inflammatory bowel disease, sexually transmitted diseases, cystic fibrosis, glaucoma, dry eye, and various cancers. Sustained delivery systems such as nanoparticles can be useful for mucosal delivery, but recent work suggests they must penetrate the rapidly cleared mucus barrier that overlies all mucosal epithelia to achieve uniform distribution on epithelial surfaces and enhanced residence time. Thus, it is important to evaluate the mucus-penetrating ability of nanosized delivery systems in preclinical animal studies, and for administration to humans. We describe a simple ex vivo method to visualize and quantify nanoparticle transport in mucus on fresh mucosal tissues. Using this method in murine models, we observed variations in the mucus mesh at different anatomical locations, as well as cyclical variations that may have implications for mucosal delivery.

Drainage of cells and soluble antigen from the CNS to regional lymph nodes

Despite the absence of conventional lymphatics, there is efficient drainage of both cerebrospinal fluid (CSF) and interstitial fluid (ISF) from the CNS to regional lymph nodes. CSF drains from the subarachnoid space by channels that pass through the cribriform plate of the ethmoid bone to the nasal mucosa and cervical lymph nodes in animals and in humans; antigen presenting cells (APC) migrate along this pathway to lymph nodes. ISF and solutes drain from the brain parenchyma to cervical lymph nodes by a separate route along 100–150 nm wide basement membranes in the walls of cerebral capillaries and arteries. This pathway is too narrow for the migration of APC so it is unlikely that APC traffic directly from brain parenchyma to lymph nodes by this route. We present a model for the pivotal involvement of regional lymph nodes in immunological reactions of the CNS. The role of regional lymph nodes in immune reactions of the CNS in virus infections, the remote influence of the gut microbiota, multiple sclerosis and stroke are discussed. Evidence is presented for the role of cervical lymph nodes in the induction of tolerance and its influence on neuroimmunological reactions. We look to the future by examining how nanoparticle technology will enhance our understanding of CNS-lymph node connections and by reviewing the implications of lymphatic drainage of the brain for diagnosis and therapy of diseases of the CNS ranging from neuroimmunological disorders to dementias. Finally, we review the challenges and opportunities for progress in CNS-lymph node interactions and their involvement in disease processes.

Nanoparticles for brain drug delivery

The central nervous system, one of the most delicate microenvironments of the body, is protected by the blood-brain barrier (BBB) regulating its homeostasis. BBB is a highly complex structure that tightly regulates the movement of ions of a limited number of small molecules and of an even more restricted number of macromolecules from the blood to the brain, protecting it from injuries and diseases. However, the BBB also significantly precludes the delivery of drugs to the brain, thus, preventing the therapy of a number of neurological disorders. As a consequence, several strategies are currently being sought after to enhance the delivery of drugs across the BBB. Within this review, the recently born strategy of brain drug delivery based on the use of nanoparticles, multifunctional drug delivery systems with size in the order of one-billionth of meters, is described. The review also includes a brief description of the structural and physiological features of the barrier and of the most utilized nanoparticles for medical use. Finally, the potential neurotoxicity of nanoparticles is discussed, and future technological approaches are described. The strong efforts to allow the translation from preclinical to concrete clinical applications are worth the economic investments.

Transcytosis and brain uptake of transferrin-containing nanoparticles by tuning avidity to transferrin receptor

Receptor-mediated transcytosis across the blood-brain barrier (BBB) may be a useful way to transport therapeutics into the brain. Here we report that transferrin (Tf)-containing gold nanoparticles can reach the brain parenchyma from systemic administration in mice through a receptor-mediated transcytosis pathway. This transport is aided by tuning the nanoparticle avidity to Tf receptor (TfR), which is correlated with nanoparticle size and total amount of Tf decorating the nanoparticle surface. Nanoparticles of both 45 nm and 80 nm diameter reach the brain parenchyma, and their accumulation there (visualized by silver enhancement light microscopy in combination with transmission electron microscopy imaging) is observed to be dependent on Tf content (avidity); nanoparticles with large amounts of Tf remain strongly attached to brain endothelial cells, whereas those with less Tf are capable of both interacting with TfR on the luminal side of the BBB and detaching from TfR on the brain side of the BBB. The requirement of proper avidity for nanoparticles to reach the brain parenchyma is consistent with recent behavior observed with transcytosing antibodies that bind to TfR.

Recommendations for the standardisation of oxytocin nasal administration and guidelines for its reporting in human research

A series of studies have reported on the salubrious effects of oxytocin nasal spray on social cognition and behavior in humans, across physiology (e.g., eye gaze, heart rate variability), social cognition (e.g., attention, memory, and appraisal), and behavior (e.g., trust, generosity). Findings suggest the potential of oxytocin nasal spray as a treatment for various psychopathologies, including autism and schizophrenia. There are, however, increasing reports of variability of response to oxytocin nasal spray between experiments and individuals. In this review, we provide a summary of factors that influence transmucosal nasal drug delivery, deposition, and their impact on bioavailability. These include variations in anatomy and resultant airflow dynamic, vascularisation, status of blood vessels, mode of spray application, gallenic formulation (including presence of uptake enhancers, control release formulation), and amount and method of administration. These key variables are generally poorly described and controlled in scientific reports, in spite of their potential to alter the course of treatment outcome studies. Based on this review, it should be of no surprise that differences emerge across individuals and experiments when nasal drug delivery methods are employed. We present recommendations for researchers to use when developing and administering the spray, and guidelines for reporting on peptide nasal spray studies in humans. We hope that these recommendations assist in establishing a scientific standard that can improve the rigor and subsequent reliability of reported effects of oxytocin nasal spray in humans.

Permeabilization of the blood-brain barrier via mucosal engrafting: implications for drug delivery to the brain

Utilization of neuropharmaceuticals for central nervous system(CNS) disease is highly limited due to the blood-brain barrier(BBB) which restricts molecules larger than 500Da from reaching the CNS. The development of a reliable method to bypass the BBB would represent an enormous advance in neuropharmacology enabling the use of many potential disease modifying therapies. Previous attempts such as transcranial catheter implantation have proven to be temporary and associated with multiple complications. Here we describe a novel method of creating a semipermeable window in the BBB using purely autologous tissues to allow for high molecular weight(HMW) drug delivery to the CNS. This approach is inspired by recent advances in human endoscopic transnasal skull base surgical techniques and involves engrafting semipermeable nasal mucosa within a surgical defect in the BBB. The mucosal graft thereby creates a permanent transmucosal conduit for drugs to access the CNS. The main objective of this study was to develop a murine model of this technique and use it to evaluate transmucosal permeability for the purpose of direct drug delivery to the brain. Using this model we demonstrate that mucosal grafts allow for the transport of molecules up to 500 kDa directly to the brain in both a time and molecular weight dependent fashion. Markers up to 40 kDa were found within the striatum suggesting a potential role for this technique in the treatment of Parkinson’s disease. This proof of principle study demonstrates that mucosal engrafting represents the first permanent and stable method of bypassing the BBB thereby providing a pathway for HMW therapeutics directly into the CNS.

Nanoparticle diffusion in, and microrheology of, the bovine vitreous ex vivo

Intravitreal injection of biodegradable nanoparticles (NP) holds promise for gene therapy and drug delivery to the back of the eye. In some cases, including gene therapy, NP need to diffuse rapidly from the site of injection in order to reach targeted cell types in the back of the eye, whereas in other cases it may be preferred for the particles to remain at the injection site and slowly release drugs that may then diffuse to the site of action. We studied the movements of polystyrene (PS) NP of various sizes and surface chemistries in fresh bovine vitreous. PS NP as large as 510nm rapidly penetrated the vitreous gel when coated with polyethylene glycol (PEG), whereas the movements of NP 1190nm in diameter or larger were highly restricted regardless of surface chemistry owing to steric obstruction. PS NP coated with primary amine groups (NH2) possessed positively charged surfaces at the pH of bovine vitreous (pH=7.2), and were immobilized within the vitreous gel. In comparison, PS NP coated with COOH (possessing negatively charged surfaces) in the size range of 100-200nm and at particle concentrations below 0.0025% (w/v) readily diffused through the vitreous meshwork; at higher concentrations (~0.1% w/v), these nanoparticles aggregated within vitreous. Based on the mobility of different sized PEGylated PS NP (PS-PEG), we estimated the average mesh size of fresh bovine vitreous to be ~550±50nm. The bovine vitreous behaved as an impermeable elastic barrier to objects sized 1190nm and larger, but as a highly permeable viscoelastic liquid to non-adhesive objects smaller than 510nm in diameter. Guided by these studies, we next sought to examine the transport of drug- and DNA-loaded nanoparticles in bovine vitreous. Biodegradable NP with a diameter of 227nm, composed of a poly(lactic-co-glycolic acid) (PLGA)-based core coated with poly(vinyl alcohol) rapidly penetrated vitreous. Rod-shaped, highly-compacted CK30PEG10k/DNA with PEG coating (neutral surface charge; hydrodynamic diameter ~60nm) also diffused rapidly within vitreous. These findings will help guide the development of nanoparticle-based therapeutics for the treatment of vision-threatening ocular diseases.

Nanoparticle diffusion in respiratory mucus from humans without lung disease

A major role of respiratory mucus is to trap inhaled particles, including pathogens and environmental particulates, to limit body exposure. Despite the tremendous health implications, how particle size and surface chemistry affect mobility in respiratory mucus from humans without lung disease is not known. We prepared polymeric nanoparticles densely coated with low molecular weight polyethylene glycol (PEG) to minimize muco-adhesion, and compared their transport to that of uncoated particles in human respiratory mucus, which we collected from the endotracheal tubes of surgical patients with no respiratory comorbidities. We found that 100 and 200 nm diameter PEG-coated particles rapidly penetrated respiratory mucus, at rates exceeding their uncoated counterparts by approximately 15- and 35-fold, respectively. In contrast, PEG-coated particles ≥500 nm in diameter were sterically immobilized by the mucus mesh. Thus, even though respiratory mucus is a viscoelastic solid at the macroscopic level (as measured using a bulk rheometer), nanoparticles that are sufficiently small and muco-inert can penetrate the mucus as if it were primarily a viscous liquid. These findings help elucidate the barrier properties of respiratory mucus and provide design criteria for therapeutic nanoparticles capable of penetrating mucus to approach the underlying airway epithelium.

Nanoparticle diffusion in, and microrheology of, the bovine vitreous ex vivo

Intravitreal injection of biodegradable nanoparticles (NP) holds promise for gene therapy and drug delivery to the back of the eye. In some cases, including gene therapy, NP need to diffuse rapidly from the site of injection in order to reach targeted cell types in the back of the eye, whereas in other cases it may be preferred for the particles to remain at the injection site and slowly release drugs that may then diffuse to the site of action. We studied the movements of polystyrene (PS) NP of various sizes and surface chemistries in fresh bovine vitreous. PS NP as large as 510nm rapidly penetrated the vitreous gel when coated with polyethylene glycol (PEG), whereas the movements of NP 1190nm in diameter or larger were highly restricted regardless of surface chemistry owing to steric obstruction. PS NP coated with primary amine groups (NH2) possessed positively charged surfaces at the pH of bovine vitreous (pH=7.2), and were immobilized within the vitreous gel. In comparison, PS NP coated with COOH (possessing negatively charged surfaces) in the size range of 100-200nm and at particle concentrations below 0.0025% (w/v) readily diffused through the vitreous meshwork; at higher concentrations (~0.1% w/v), these nanoparticles aggregated within vitreous. Based on the mobility of different sized PEGylated PS NP (PS-PEG), we estimated the average mesh size of fresh bovine vitreous to be ~550±50nm. The bovine vitreous behaved as an impermeable elastic barrier to objects sized 1190nm and larger, but as a highly permeable viscoelastic liquid to non-adhesive objects smaller than 510nm in diameter. Guided by these studies, we next sought to examine the transport of drug- and DNA-loaded nanoparticles in bovine vitreous. Biodegradable NP with a diameter of 227nm, composed of a poly(lactic-co-glycolic acid) (PLGA)-based core coated with poly(vinyl alcohol) rapidly penetrated vitreous. Rod-shaped, highly-compacted CK30PEG10k/DNA with PEG coating (neutral surface charge; hydrodynamic diameter ~60nm) also diffused rapidly within vitreous. These findings will help guide the development of nanoparticle-based therapeutics for the treatment of vision-threatening ocular diseases.