Nanochannel Delivery Systems for Controlled and Sustained Administration of Therapeutics and Cell Transplantation

Problem: Medical practitioners have long realized the need for personalized treatment that can synergize with the body’s innate response to diseases and medical conditions. Currently, the most common approaches to drug administration in medicine are 1) oral or intravenous delivery of a “bolus” (a large amount of drug delivered all at once) at regular intervals and 2) intravenous slow infusions. Bolus administration is commonly associated with adverse side effects derived from a temporary regional overdose following each administration to the patient. Infusions are required in cases of highly toxic drugs (typical of numerous chemotherapeutics), which force patients to be hospitalized for hours to days in order to monitor the severe side effects of the treatments. This conventional practice is arguably a rudimentary and impersonal approach to drug delivery, where therapeutics are often inefficiently delivered at the maximum tolerateddose (MTD). Can we instead mimic the body’s natural control over the release of molecules with accurate dosing and precise timing? The answer to personalized treatment can be found in nanotechnology and nanoscale fluid mechanics.

A conceptual design of our implantable, artificial NanoGland incorporated into a distributed biosensor network (BSN). The first inset (from left to right, top to bottom) depicts an implant prototype, containing the nanochannel membrane, the drug reservoir, sensor, telemetry, and control electronics, and a battery or RF antenna for remote powering. The second inset is an actual fabricated nanochannel membrane complete with surface deposited gold electrodes. The graph shows data (acquired at the beginning of February 2012) of the controlled release of dendritic fullerene 1 (a free radical scavenging agent) from a nanochannel membrane.

Approach: Steady-Release NanoGlands: Nanofluidic membranes reveal counterintuitive mass transport phenomena in nanochannels caused by fluid confinement. Our research in the Department of Nanomedicine has shown that by shrinking the channels by a factor close to the sizes of the diffusing molecules, it was possible to achieve a saturated, concentration-independent transport through the membranes. This shows promise for controlled transport of molecules and therapeutics. As such, we focus on the development of nanopores, nanochanneled membranes and nanoscale fluid mechanics. To advance this technology, we have used sacrificial layer techniques to reproducibly fabricate nanochannels as small as 3 nm. By exploiting nanochannels in passive systems, we were able to achieve a controlled and constant delivery of therapeutics and nanoparticles, in vitro and in vivo, for extended periods of time, while mimicking the basal and continuous release of molecules from glands to the rest of the body. This functionality cannot be attained at the macro- or microscale without the use of complex pumps and other moving components, because the diffusion of molecules is “Fickian,” which means that the release rate is dictated by the gradient of the molecular concentration.

Active-Release NanoGlands: A time-variable rate of release can be also achieved through electrokinetic phenomena that occur when an electrical potential is applied between the inlet and outlet of the channels. Electrokinetic phenomena, such as electrophoresis and electroosmosis, have been widely studied in microchannels. We have developed implantable nanochannel membranes with electrodes near the membrane inlet and outlet and demonstrated that the delivery of molecules in proportion to the applied electrical field is up to 10 times higher than for passive delivery. Additionally, by reversing the polarity of the applied electrical field, the molecule release can completely stop. As opposed to the rudimentary conventional practice where drugs are “digitally” administered, such nanochannel technologies afford “analog” time modulation, where timing, duration and frequency of administration can be precisely adjusted as needed. This approach mimics the time-variable release of molecules in the body and can enable new delivery regimens, including “chronotherapy,” the synchronization of drug delivery with optimal times during the circadian cycle of the body.

Injectable Multistage Nanovectors (MSV) for Improved Therapy and Diagnosis 

Problem: An abundance of barriers reduce the likelihood that drugs and imaging agents will reach the site of action. For drugs delivered by intravenous injection, these include enzymatic degradation, uptake by the reticulo-endothelial system and crossing the endothelial barrier, cellular membranes and cellular efflux pumps. For diseases like cancer, there is an urgent need to achieve efficient concentrations of drugs in the target tissue with minimal distribution in healthy tissue. Overcoming these biological barriers, delivering one or multiple entities and personalizing therapy have historically been addressed by trying to endow individual drug molecules with one or all of these capabilities.

Approach: Nanotechnology offers unprecedented opportunities to develop treatments that increase therapeutic efficacy, decrease undesired side effects and effectively achieve the personalization of intervention for conditions, such as cancer and cardiovascular and infectious diseases. The majority of current nanotherapeutics/nanodiagnostics in clinics and under investigation accommodate single or multiple functionalities on the same entity. However, due to a multiplicity of heterogeneous biological barriers, therapeutic and imaging agents are unable to reach their intended targets in sufficient concentrations. Thus we envisioned and introduced a multistage nanovector (MSV) in which different nanocomponents (or stages) responsible for a variety of functions are decoupled but act in a synergistic manner.

Stage 1 mesoporous silicon particles (S1MP) were rationally designed and fabricated using semiconductor fabrication techniques, photolithography and electrochemical etching in a non-spherical geometry to enable superior blood margination and to increase cell surface adhesion. The main task of S1MP is to efficiently transport the payload nanoparticles, termed Stage 2 nanoparticles (S2NP), which are loaded into the porous structure. Depending on the S1MP surface modifications and porosity, a variety of S2NPs (such as liposomes, micelles, metal particles and carbon structures) or nanoparticle “cocktails” can be loaded and efficiently delivered to the disease site, enabling simultaneous functions.

The versatility of the MSV platform allows for a multiplicity of applications. For example, loading of contrast agents for magnetic resonance imaging to hemispherical and discoidal S1MP enabled a significant increase in contrast efficiency (up to 50 times compared to clinically available agents.) Furthermore, administration of a single dose of MSV loaded with nanoliposomes containing siRNA, enabled sustained gene silencing for at least 21 days and, as a result, reduced tumor burden in orthotopic ovarian cancer models. We have also shown that intracellular trafficking and cell-to-cell communication can be controlled by surface modifications of S1MP and S2NP. The therapeutic and imaging potential of MSV is being investigated in primary and disseminated tumors as well as in cardiovascular and infectious diseases. 

Schematic summary of possible MSV mechanisms of action

Central compartment: hemispherical or disc-shaped nanoporous silicon S1MPs are engineered to exhibit an enhanced ability to marginate within blood vessels and adhere to disease-associated endothelium. Once positioned at the disease site, the S1MP can (top right) release the drug/siRNA-loaded S2NP to achieve the desired therapeutic effect, prior to the complete biodegradation of the carrier particle; release an imaging agent (top left) or external energy-activated S2NP (e.g., gold nanoparticles, nanoshells, bottom right). Another possible mechanism of action is cell-based delivery of the MSVs into the disease loci followed by triggered release of the S1MP/S2NP from the cells

Bio-inspired Cell-Like Vectors for Intravenous Therapeutic Delivery

Problem: Biophysical barriers protect the body by regulating the trafficking, exchange and clearance of foreign materials. Drugs and delivery platforms are often constrained by the mononuclear phagocyte system, vessel wall and other barriers, collectively referred to as vascular barriers (VB). We have previously developed delivery platforms capable of sequentially overcoming biological barriers. The multistage delivery system was designed for optimal navigation in the blood flow, to protect cargo/payload from the direct exposure to biological barriers and to increase the delivery of theranostic agents to the endothelial target site. While multistage vectors exhibited improved biodistribution upon modifying their shape and size, avoidance of opsonizing agents and non-specific clearance continue to remain substantial hurdles for drug delivery platforms. In answer to this challenge, we developed injectable carriers that are able to penetrate and evade VB while having minimal or no impact on tissue homeostasis. 

Approach: The cell-like vector (CLV) consists of a synthetic core (the “nano” component) that is amenable to payload retention and delivery. This core is decorated with a natural multifunctional coating of cellular membranes (the “bio” component) obtained from various infiltrating cell types. We aspire to use the CLV to bridge the gaps existing between traditional chemotherapy, biological and nanoparticle-based approaches. These naturally derived membranes allow synthetic cores to negotiate VB and transfer cytotoxic payloads through the tumor-associated VB. The advantages of CLV include the following:

• Coatings to endow injectable particles with cell-like functions 
• Improved stability and modulation of the release of loaded payload
• Delay of phagocytic uptake by leveraging self-recognition mechanisms
• Binding inflamed endothelium and facilitating transport across the endothelial layer while eluding the lysosomal pathway
• Delayed liver clearance and increased tumor accumulation 
• Retention of a therapeutic cargo and increased accumulation at target sites

Schematic of the proposed CLV: assembly and function. A) Primary leukocytes will be collected. B) Cellular membranes will be purified, and the presence of the molecular machinery necessary for immune self tolerance, for the transport across the endothelium, and for the targeting and adhesion to tumor-associated vasculature will be confirmed through molecular and biochemical methods. C) The final CLV contains all the naive membrane proteins. D) The CLV can bypass immune surveillance, E) localize at the tumor site and F) transport the payload to the tumor.

We have engineered a delivery system that is recognized by the body as “self” rather than “foreign” and simultaneously possesses the molecular machinery necessary to interact and overcome VB. Additionally, by implementing various cell sources as our coating, we are able to accomplish various benefits, tailored to meet the individual’s immediate need. This unique feature also extends to the nano- or microparticle core that enables further tunability. This approach, akin to a Trojan horse strategy, consists of a therapeutic agent loaded into a microparticle and camouflaged with white blood cell membranes. This acts as a harmless, seemingly “endogenous cell,” although it is, rightfully, a synthetic hybrid bio-nano CLV.



Images of the individual components of the CLV. The membrane of T-cells (A) or macrophages (B) can be harvested and used to coat a core of either PLGA (C) or multistage vectors (D), which can in turn be loaded with a therapeutic payload consisting of micelles (E) or nanoporous silica nanospheres (F).