pH-Dependent dissolving nano- and microparticles for improved peroral delivery of a highly lipophilic compound in dogs

Novel wine in an old bottle: Preventive and therapeutic potentials of andrographolide in atherosclerotic cardiovascular diseases

Atherosclerotic cardiovascular disease (ASCVD) frequently results in sudden death and poses a serious threat to public health worldwide. The drugs approved for the prevention and treatment of ASCVD are usually used in combination but are inefficient owing to their side effects and single therapeutic targets. Therefore, the use of natural products in developing drugs for the prevention and treatment of ASCVD has received great scholarly attention. Andrographolide (AG) is a diterpenoid lactone compound extracted from Andrographis paniculata. In addition to its use in conditions such as sore throat, AG can be used to prevent and treat ASCVD. It is different from drugs that are commonly used in the prevention and treatment of ASCVD and can not only treat obesity, diabetes, hyperlipidaemia and ASCVD but also inhibit the pathological process of atherosclerosis (AS) including lipid accumulation, inflammation, oxidative stress and cellular abnormalities by regulating various targets and pathways. However, the pharmacological mechanisms of AG underlying the prevention and treatment of ASCVD have not been corroborated, which may hinder its clinical development and application. Therefore, this review summarizes the physiological and pathological mechanisms underlying the development of ASCVD and the in vivo and in vitro pharmacological effects of AG on the relative risk factors of AS and ASCVD. The findings support the use of the old pharmacological compound ('old bottle') as a novel drug ('novel wine') for the prevention and treatment of ASCVD. Additionally, this review summarizes studies on the availability as well as pharmaceutical and pharmacokinetic properties of AG, aiming to provide more information regarding the clinical application and further research and development of AG.

Preparation and Evaluation of Vitamin D3 Supplementation as Transdermal Film-Forming Solution

Vitamin D3 is available in oral and injectable dosage forms. Interest in the transdermal route as an alternative to the oral and parenteral routes has grown recently. In this study, several film-forming solutions for the transdermal delivery of vitamin D3 were prepared. They contained 6000 IU/mL of vitamin D3 that formed a dry and acceptable film in less than 5 min after application. The formulations consisted of ethanol and acetone 80:20, and one or more of the following ingredients: Eudragit L100-55, PVP, PG, limonene, oleic acid, camphor, and menthol. Vitamin D3 release was studied from both the film-forming solution and pre-dried films using a Franz diffusion cell. The film-forming solution released a significant amount of vitamin D3 compared to the dry film, which is attributed mostly to the saturation driving force due to the evaporation of volatile solvents. In vitro permeation studies through artificial skin Strat M® membrane revealed that the cumulative amount of vitamin D3 permeated after 24 h under the experimental conditions was around 800 IU across 3.14 cm2. The cumulative permeation curve showed faster permeation in earlier stages. Young's modulus, viscosity, and pH of the formulations were determined. Most of the formulations were stable for 3 weeks.

A study of Kollicoat® MAE100P film's structure and properties

Generally, an organic-solvent-based film is denser and tougher than a corresponding aqueous-dispersion-based film. However, Kollicoat® MAE100P films prepared from aqueous dispersions had greater tensile strengths compared to the films cast from organic solutions. It was proposed that MAE100P polymer particles in aqueous media had a core-shell structure with a hydrophilic shell and a hydrophobic core. The hydrophilic shell was rich in ionized methacrylic acid (MAA) groups and the hydrophobic core primarily contained unionized MAA and ethyl acrylate (EA). As a result, ionized MAA formed a continuous phase which worked as a rigid frame and greatly improved the mechanical properties of aqueous-dispersion-based films. In order to prove this theory and investigate the effect of ionization level on this polymer system, the properties of pH, turbidity, zeta potential, and particle size of MAE100P dispersions were measured as a function of ionization level. The tensile strengths and thermal and mechanical properties of MAE100P films prepared from organic solution or aqueous dispersions of different ionization levels were investigated as well. FTIR was used to characterize the polymer films. Drug release in 0.1 N HCl from coated pellets was studied using the basket method. The experimental results showed that the original MAE100P polymer particles (if not specified, the ionization level is 6%) had a highly-charged surface. The properties of polymer aqueous dispersions were significantly changed by the ionization levels. Aqueous-dispersion-based MAE100P films or coats were stronger and comparable to or somewhat more effective in inhibiting drug diffusion than were organic-solvent-based coats. The tensile strength initially increased and then decreased with an increase of ionization level, while the water-uptake rate by the films continuously increased. Two endothermic peaks were observed in the DSC thermograms for cured MAE100P films. The high-T_g endothermic peak increased with an increase in ionization level, while the low-T_g peak didn't exhibit significant change except for the 18% ionization film. In the dynamic mechanical analysis, two relaxations in the storage modulus were observed in the aqueous-dispersion-based films. These data may suggest a two-phase structure in the form of a core-shell structure. The tensile-strength ratio for aqueous-dispersion-based films over organic-solvent-based films for MAE100P was close to that reported for films formed from polymer substances/particles with core-shell structures. In summary, the core-shell structure might result in a two-phase structure in the bulk MAE100P film prepared from aqueous dispersion. This special structure led to significantly-improved mechanical properties for aqueous-dispersion-based MAE100 films. The ionization levels had complicated effects on the polymer system by increasing the amount of ionic aggregates while also solubilizing the polymer and changing the mechanism of film formation.

Development, optimization and in vitro evaluation of oxaliplatin loaded nanoparticles in non-small cell lung cancer

BACKGROUND

Platinum-based chemotherapy in non-small cell lung cancer (NSCLC) has been demonstrated as a promising approach by many researchers. However, due to low bioavailability and several side effects, drug targeting to lungs by intravenous administration is not a common route of administration.

OBJECTIVE

In this study, oxaliplatin loaded polycaprolactone (PCL) nanoparticles were prepared to overcome the limitations of the drug. 3³ factorial design was used to evaluate the combined effect of the selected variables on the nanoparticle characteristics and to optimize oxaliplatin loaded PCL nanoparticles.

METHODS

The factorial design was used to study the influence of three different independent variables on the response of nanoparticle particle size, polydispersity index (PDI), zeta potential, and encapsulation efficiency. The cellular uptakes of oxaliplatin loaded nanoparticles with different molecular weights of PCL were evaluated. Moreover, optimized nanoparticles were evaluated for their efficacy in non-small lung cancer using the SK-MES-1 cell line.

RESULTS

In factorial design, it is found that the homogenization speed and surfactant ratio represented the main factors influencing particle size and PDI and did not seem to depend on the PCL ratio. While the cytotoxicity of free oxaliplatin and oxaliplatin loaded nanoparticles were similar in low drug doses (2.5 and 25 μg/mL), the cytotoxicity of oxaliplatin loaded nanoparticles on SK-MES-1 cell was found higher in higher doses (p < 0.05). Moreover, oxaliplatin nanoparticles formulated with different molecular weights of PCL did not show significant differences in cellular uptake in 1 h and 2 h. However, the uptake of PCL₈₀₀₀₀ NPs was found significantly greater than free oxaliplatin at 4 h (p < 0.05).

CONCLUSION

Hence, the development of oxaliplatin loaded PCL nanoparticles can be a useful approach for effective NSCLC therapy. Development, optimization and in vitro evaluation of oxaliplatin loaded nanoparticles in non-small cell lung cancer.

An Efficient, Lung-Targeted, Drug-Delivery System To Treat Asthma Via Microparticles

BACKGROUND

Chronic diseases such as diabetes, asthma, and heart disease are the leading causes of death in developing countries. Public health plays an important role in preventing such diseases to improve individuals' quality of life. Conventional dosage schemes used in public health to cure various diseases generally lead to undesirable side effects and renders the overall treatment ineffective. For example, a required concentration of drug cannot reach the lungs using conventional methods to cure asthma. Microspheres have emerged as a confirmed drug-delivery system to cure asthma.

METHOD

In this paper, a salbutamol-loaded poly lactic acid-co-glycolic acid-polyethylene glycol (PLGA-PEG) microsphere (SPP)-based formulation was prepared using a Buchi B-90 nanospray drier. Face-centered central composite design (CCD) was applied to optimize the spray-drying process.

RESULTS

The drug content and product yield were found to be 72%±0.8% and 86%±0.4%, respectively; drug release (91.1%) peaked for up to 12 hrs in vitro. Microspheres obtained from the spray dryer were found to be shriveled. The experiments were carried out and verified using various groups of rabbits. In our study, the particle size (8.24 µm) was observed to be an essential parameter for drug delivery. The in vivo results indicated that the targeting efficacy and drug concentration in the lung was higher with the salbutamol-loaded PLGA-PEG SPP formulation (1,410.1±10.11 µg/g, 15 mins), as compared to the conventional formulation (92±0.56 µg/g, 10 min). The final product was stable under 5°C±2°C, 25°C±2°C, and 40°C±2°C/75%±5% relative humidity. In addition, these co-polymers have a good safety profile, as determined by testing on human alveolar basal epithelium A549 cell lines.

CONCLUSION

Our results prove that microspheres are an alternative drug-delivery system for lung-targeted asthma treatments used in public health.

pH-Responsive carriers for oral drug delivery: challenges and opportunities of current platforms

Oral administration is a desirable alternative of parenteral administration due to the convenience and increased compliance to patients, especially for chronic diseases that require frequent administration. The oral drug delivery is a dynamic research field despite the numerous challenges limiting their effective delivery, such as enzyme degradation, hydrolysis and low permeability of intestinal epithelium in the gastrointestinal (GI) tract. pH-Responsive carriers offer excellent potential as oral therapeutic systems due to enhancing the stability of drug delivery in stomach and achieving controlled release in intestines. This review provides a wide perspective on current status of pH-responsive oral drug delivery systems prepared mainly with organic polymers or inorganic materials, including the strategies used to overcome GI barriers, the challenges in their development and future prospects, with focus on technology trends to improve the bioavailability of orally delivered drugs, the mechanisms of drug release from pH-responsive oral formulations, and their application for drug delivery, such as protein and peptide therapeutics, vaccination, inflammatory bowel disease (IBD) and bacterial infections.

Pharmaceutical suspension containing both immediate/sustained-release amoxicillin-loaded gelatin nanoparticles: preparation and in vitro characterization

Pharmaceutical suspension containing oral dosage forms delivering both immediate-release and sustained-release amoxicillin was developed as a new dosage form to eradicate Helicobacter pylori. Amoxicillin-loaded gelatin nanoparticles are able to bind with the mucosal membrane after delivery to the stomach and could escalate the effectiveness of a drug, providing dual release. The objective of this study was to develop amoxicillin nanoparticles using innovative new technology – the Büchi Nano Spray Dryer B-90 – and investigate such features as drug content, particle morphology, yield, in vitro release, flow properties, and stability. The nanoparticles had an average particle size of 571 nm. The drug content and percentage yield was 89.2% ± 0.5% and 93.3% ± 0.6%, respectively. Angle of repose of nanoparticle suspension was 26.3° and bulk density was 0.59 g/cm³. In vitro drug release of formulations was best fitted by first-order and Peppas models with R² of 0.9841 and 0.9837 respectively; release profile was 15.9%, while; for the original drug, amoxicillin, under the same conditions, 90% was released in the first 30 minutes. The nanoparticles used in this study enabled sustained release of amoxicillin over an extended period of time, up to 12 hours, and were stable for 12 months under accelerated storage conditions of 25°C ± 2°C and 60% ± 5% relative humidity.

pH-sensitive vesicles, polymeric micelles, and nanospheres prepared with polycarboxylates

Titratable polyanions, and more particularly polymers bearing carboxylate groups, have been used in recent years to produce a variety of pH-sensitive colloids. These polymers undergo a coil-to-globule conformational change upon a variation in pH of the surrounding environment. This conformational change can be exploited to trigger the release of a drug from a drug delivery system in a pH-dependent fashion. This review describes the current status of pH-sensitive vesicles, polymeric micelles, and nanospheres prepared with polycarboxylates and their performance as nano-scale drug delivery systems, with emphasis on our recent contribution to this field.

Factorial design analysis and optimisation of alginate-Ca-chitosan microspheres

The purpose of this study was to apply factorial design in order to determine the influence of the formulation factors and their interactions on several responses such as particle size, dissolution behaviour at pH 1.2 and pH 7.4 as well as production yield, during the development of budesonide loaded, chitosan coated Ca-alginate microparticles (MPs) intended for treatment of inflammatory diseases in the gastrointestinal tract. Produced drug-loaded MPs were spherical in shape, had smooth surfaces with low porosity and size range between 5 and 11 µm. Production yield for the formulations from the design varied from 19% to 50%. Optimisation was performed using central composite design setting the targets: particle size at 5.5 µm, maximised yield, suppressed dissolution at pH 1.2 and sustained release at pH 7.4. The optimised batches were identified with a combined desirability value of 0.967.

A, S. T. Investigation of formulation variables affecting the properties of lamotrigine nanosuspension using fractional factorial design

BACKGROUND AND THE PURPOSE OF THE STUDY

Lamotrigine (LMG) undergoes extensive hepatic metabolism upon oral administration and its absorption is affected in the presence of food. This study was aimed to develop nanosuspension of LMG and investigate its formulation characteristics using L(9) orthogonal array.

METHODS

Nanosuspension was prepared using emulsification-solvent diffusion method. All the formulations were subjected to in-vitro evaluation and the statistically optimized one was used for stability, scanning electron microscopic and differential scanning calorimetric studies.

RESULTS

Nanoparticles were spherical with little surface adsorbed drug. Formulation characteristics in terms of size, zeta potential, polydispersity index (PDI), entrapment efficiency (EE), drug content and in vitro drug release were consistent and within their acceptable range. All the batches provided a burst release profile during first 1 hr, followed by a controlled release extending up to 24 hrs. The values of n in Peppas model ranged between 0.2-0.4 for all the formulations indicative of Fickian release mechanism. The formulation remained reasonably stable up to 3 months. No interaction was observed among the drug and polymers.

MAJOR CONCLUSION

Results of in vitro drug release studies suggested that nanosuspension might be used as a sustained delivery vehicle for LMG. Statistical analysis revealed that size of the nanoparticles was most strongly affected by stabilizer type while EE was influenced by the drug-to-polymer ratio.

Colon-specific delivery of 5-aminosalicylic acid from chitosan-Ca-alginate microparticles

Chitosan-Ca-alginate microparticles for colon-specific delivery and controlled release of 5-aminosalicylic acid after peroral administration were prepared using spray drying method followed by ionotropic gelation/polyelectrolyte complexation. Physicochemical characterization pointed to the negatively charged particles with spherical morphology having a mean diameter less than 9 microm. Chitosan was localized dominantly in the particle wall, while for alginate, a homogeneous distribution throughout the particles was observed. (1)H NMR, FTIR, X-ray and DSC studies indicated molecularly dispersed drug within the particles with preserved stability during microencapsulation and in simulated in vivo drug release conditions. In vitro drug release studies carried out in simulated in vivo conditions in respect to pH, enzymatic and salt content confirmed the potential of the particles to release the drug in a controlled manner. The diffusional exponents according to the general exponential release equation indicated anomalous (non-Fickian) transport in 5-ASA release controlled by a polymer relaxation, erosion and degradation. Biodistribution studies of [(131)I]-5-ASA loaded chitosan-Ca-alginate microparticles, carried out within 2 days after peroral administration to Wistar male rats in which TNBS colitis was induced, confirmed the dominant localization of 5-ASA in the colon with low systemic bioavailability.

Nanosizing of a drug/carrageenan complex to increase solubility and dissolution rate

In this study, we present a novel approach of nanosizing a drug/polymeric complex to increase both solubility and dissolution rate of poorly water-soluble compounds. A hydrophilic polymer, lambda-carrageenan, was first complexed with a model poorly water-soluble compound to increase the compound's aqueous solubility. The compound/carrageenan complex was further nanosized by wet-milling to enhance the dissolution rate. By complexing with carrageenan, the compound became amorphous in the complex. Using additional carrageenan as a stabilizer for nanosizing, a nanosuspension of a compound/carrageenan complex with a median particle size of about 0.3 microm was successfully developed. The particle size of the nanosuspension did not increase significantly during the lyophilization process and was stable for at least 39 days at room temperature after lyophilization. This approach of nanosizing a drug/carrageenan complex increased the aqueous solubility of the compound from less than 1 microg/mL to 39 microg/mL. In addition to increasing aqueous solubility, a nanosized compound/carrageenan complex had a faster dissolution rate than the complex, the free compound, and the nanosuspension of the free compound.

Nanoparticles for drug delivery: the need for precision in reporting particle size parameters

Polymeric drug-loaded nanoparticles have been extensively studied in the field of drug delivery. Biodistribution depends on the physicochemical properties of particles, especially size. The global message from the literature is that small particles have an enhanced ability to reach their target. The present review highlights the difficulties in validating the data from biodistribution studies without accurate particle size determination.

Development of potent oral nanoparticulate formulation of coenzyme Q10 for treatment of hypertension: can the simple nutritional supplements be used as first line therapeutic agents for prophylaxis/therapy?

Coenzyme Q10 (CoQ10) is an antioxidant with well-established pharmacological activities against several chronic diseases; however, it is marketed only as a nutritional supplement without any claims of its therapeutic activity and one of the reasons for this could be the poor oral bioavailability rendering difficulties in administering this molecule to achieve therapeutic concentrations. Therefore, the present investigation was aimed at improving the oral bioavailability of CoQ10 by delivering it as nanoparticulate formulation. Biodegradable nanoparticulate formulations based on poly(lactide-co-gylcolide) (PLGA) were prepared by emulsion technique using quaternary ammonium salt didodecyldimethylammonium bromide (DMAB) as a stabilizer. The effect of initial CoQ10 loading on entrapment efficiency and the particle size was studied using 5-75% initial load resulting in good entrapment efficiency (61-83%) without any appreciable increase in the particle size for 5-30% loading (107-110 nm). However, 50% and 75% led to increase in particle size with no appreciable changes in entrapment efficiency. The intestinal uptake of CoQ10 as a suspension in carboxymethylcellulose (CMC), a commercial formulation and the developed nanoparticulate formulation was studied in male Sprague-Dawley (SD) rats and found to be 45%, 75% and 79%, respectively, suggesting that solubility and permeability related problems of CoQ10 were overcome by nanoparticulate formulation. Furthermore, the developed nanoparticulate formulation was evaluated for its therapeutic potential in renal hypertensive animals (Goldblatt 2K1C model), demonstrating improved efficacy at a 60% lowered dose as compared to CoQ10 suspension and superior efficacy than the commercial formulation at an equal dose. Together, these results indicate the potential of nanotechnology in improving the therapeutic value of molecules like CoQ10, facilitating its usage as first line therapeutic agent thus revolutionizing its role in current medical therapy.

Encapsulation of lipophilic drugs within enteric microparticles by a novel coacervation method

Enteric microparticles were prepared by a novel microencapsulation method in order to improve the oral bioavailability of lipophilic drugs. This method involved the addition of an aqueous polymer solution to an organic enteric polymer solution containing lipophilic drugs. In contrast to classical coacervation microencapsulation methods, the drugs were initially also dissolved and not dispersed in the organic polymer solution. The hydrophilic polymer (hydroxypropyl methylcellulose (HPMC), hydroxypropyl cellulose (HPC) and Poloxamer 407) was dissolved in the aqueous phase and acted as a stabilizer for the coacervate droplets, preventing their coalescence and leading to the formation of enteric microparticles. The size of the enteric microparticles decreased with higher concentrations of the hydrophilic polymers, a higher pH of the aqueous polymer solution, a higher content of carboxyl groups of the enteric polymer and with better polymer solvents. Amide-containing lipophilic drugs, such as carbamazepine, lidocaine and cyclosporine A, were successfully encapsulated in the enteric microparticles in a non-crystalline state and were physically stable for 5 months. The high solubility of carbamazepine in the enteric polymer (>30%, w/w), a high partition coefficient between polymer-rich/-poor regions and strong drug/polymer interactions contributed to the high drug encapsulation efficiency (90%, w/w). In contrast, carboxyl-containing drugs (indomethacin, ibuprofen) and hydroxyl-containing drug (17beta-estradiol hemihydrate) crystallized inside or outside the polymeric matrix due to their low solubility in the enteric polymer.

Nanosuspension formulations for low-soluble drugs: pharmacokinetic evaluation using spironolactone as model compound

Various particle sizes of spironolactone as a model low solubility drug were formulated to yield micro-and nanosuspensions of the type solid lipid nanoparticles and DissoCubes. Seven oral and one i.v. formulations were tested in an in vivo pharmacokinetic study in rats with the aim of characterizing the bioavailability of spironolactone on the basis of its metabolites canrenone and 7-alpha-thiomethylspirolactone. In addition, a dose escalation study was carried out using nonmicronized spironolactone suspension as well as a nanosuspension type DissoCubes. On the basis of AUC as well as Cmax ratios, three groups of formulations were distinguished. The biggest improvement was seen with a solid lipid nanoparticle formulation yielding a 5.7-fold increase in AUC for canrenone and a similar improvement based on the Cmax metric, followed by a group of three formulations containing nanosized, micronized, and coarse drug material and surfactant. The DissoCubes nanosuspension yielded highly significant improvements in bioavailability averaging 3.3-fold in AUC and 3.0-fold in terms of Cmax for canrenone. The third class encompasses all other formulations, which showed very little to no improvement in bioavailability. The results show that the particle size minimization was not the major determining factor in the bioavailability improvement. Rather, the type of surfactant used as stabilizer in the formulations was of greater importance. Improvement in drug solubility in the intestine as well as in dissolution rate of spironolactone are the most likely mechanisms responsible for the observed effect, although additional mechanisms such as permeability enhancement may also be involved.

Novel pH-sensitive supramolecular assemblies for oral delivery of poorly water soluble drugs: preparation and characterization

The objective of the present study was to synthesize novel pH-sensitive block copolymers forming supramolecular assemblies and to explore their potential as poorly water-soluble drug carriers for oral delivery. Diblock copolymers of polyethylene glycol and t-butyl methacrylate (tBMA), ethyl acrylate (EA) or n-butyl acrylate (nBA) were synthesized by atom transfer radical polymerization (ATRP). The pH-sensitive polymers obtained by hydrolysis of t-butyl groups were characterized for aggregation behaviour. Poorly water-soluble model drugs, i.e., indomethacin (IND), fenofibrate (FNB) and progesterone (PRG), were incorporated in supramolecular assemblies by dialysis or oil-in-water (O/W) emulsion methods. Process parameters for emulsion method were studied to maximize drug loading. Progesterone release was evaluated in vitro as a function of pH. Polymers with controlled molecular weights and low polydispersities were obtained by ATRP. All polymers exhibited pH-dependent aggregation behaviour and their critical aggregation concentration (CAC) decreased with increase in the hydrophobic block length. Drug loadings of <6% and 6-14% w/w were achieved by the dialysis and emulsion methods, respectively. Polymer composition, drug concentration and solubilization of polymer in water or dichloromethane (DCM) affected the loading. Progesterone release from supramolecular assemblies increased when the pH of the release medium was raised from 1.2 to 7.2. The results suggest that these supramolecular assemblies with high drug loadings and pH-dependent release kinetics can potentially enhance the oral bioavailability of poorly water-soluble drugs.

Enhanced Intestinal Absorption of Drugs by Activation of Peptide Transporter PEPT1 Using Proton‐Releasing Polymer

Utilization of carrier-mediated transport systems in the gastrointestinal tract to increase the bioavailability of drugs is of great interest. In the present study, an increased supply of the driving force for peptide transporter PEPT1 by utilizing a proton-releasing polymer, Eudragit L100-55, was employed to increase the intestinal transport activity. Intestinal absorption of zwitterionic cefadroxil and dianionic cefixime was studied in rats by using in situ ileal closed loops and by in vivo oral administration of the drugs concomitantly with Eudragit L100-55. The results showed that Eudragit L100-55 decreased the pH in the intestinal loops, and increased the disappearance of both cefadroxil and cefixime from the loops. In rats, the plasma concentration after oral administration was increased significantly by coadministration of Eudragit L100-55, whereas a proton-nonreleasing analogous polymer, Eudragit RSPO, did not have any effect. Furthermore, the increased absorption of cefixime caused by Eudragit L100-55 was blocked by simultaneous administration of cefadroxil, a PEPT1 substrate/inhibitor, in a concentration-dependent manner. These results demonstrate that improvement of intestinal absorption of peptide-mimetics via a peptide transporter is possible by optimizing the transporter activity through coadministration of a proton-releasing polymer that supplies the driving force for the transporter.

Small-scale systems for in vivo drug delivery

Recent developments in the application of micro- and nanosystems for drug administration include a diverse range of new materials and methods. New approaches include the on-demand activation of molecular interactions, novel diffusion-controlled delivery devices, nanostructured 'smart' surfaces and materials, and prospects for coupling drug delivery to sensors and implants. Micro- and nanotechnologies are enabling the design of novel methods such as radio-frequency addressing of individual molecules or the suppression of immune response to a release device. Current challenges include the need to balance the small scale of the devices with the quantities of drugs that are clinically necessary, the requirement for more stable sensor platforms, and the development of methods to evaluate these new materials and devices for safety and efficacy.