Mei Chin Chen

A review of the prospects for polymeric nanoparticle platforms in oral insulin delivery.

Success in the oral delivery of therapeutic insulin can significantly improve the quality of life of diabetic patients who must routinely receive injections of this drug. However, oral absorption of insulin is limited by various physiological barriers and remains a major scientific challenge. Various technological solutions have been developed to increase the oral bioavailability of insulin. Having received considerable attention, nano-sized polymeric particles are highly promising for oral insulin delivery. This review article describes the gastrointestinal barriers to oral insulin delivery, including chemical, enzymatic and absorption barriers. The potential transport mechanisms of insulin delivered by nanoparticles across the intestinal epithelium are also discussed. Finally, recent advances in using polymeric nanoparticles for oral insulin delivery and their effects on insulin transport are reviewed, along with their future.

Electrically conductive nanofibers with highly oriented structures and their potential application in skeletal muscle tissue engineering

Recent trends in scaffold design have focused on materials that can provide appropriate guidance cues for particular cell types to modulate cell behavior. In this study highly aligned and electrically conductive nanofibers that can simultaneously provide topographical and electrical cues for cells were developed. Thereafter their potential to serve as functional scaffolds for skeletal muscle tissue engineering was investigated. Well-ordered nanofibers, composed of polyaniline (PANi) and poly(ε-caprolactone) (PCL), were electrospun by introducing an external magnetic field in the collector region. Incorporation of PANi into PCL fibers significantly increased the electrical conductivity from a non-detectable level for the pure PCL fibers to 63.6±6.6mS cm(-1) for the fibers containing 3wt.% PANi (PCL/PANi-3). To investigate the synergistic effects of topographical and electrical cues using the electrospun scaffolds on skeletal myoblast differentiation, mouse C2C12 myoblasts were cultured on random PCL (R-PCL), aligned PCL (A-PCL), random PCL/PANi-3 (R-PCL/PANi) and aligned PCL/PANi-3 (A-PCL/PANi) nanofibers. Our results showed that the aligned nanofibers (A-PCL and A-PCL/PANi) could guide myoblast orientation and promote myotube formation (i.e. approximately 40% and 80% increases in myotube numbers) compared with R-PCL scaffolds. In addition, electrically conductive A-PCL/PANi nanofibers further enhanced myotube maturation (i.e. approximately 30% and 23% or 15% and 18% increases in the fusion and maturation indices) compared with non-conductive A-PCL scaffolds or R-PCL/PANi. These results demonstrated that a combined effect of both guidance cues was more effective than an individual cue, suggesting a potential use of A-PCL/PANi nanofibers for skeletal muscle regeneration.

Recent advances in chitosan-based nanoparticles for oral delivery of macromolecules

Chitosan (CS), a cationic polysaccharide, is widely regarded as a safe and efficient intestinal absorption enhancer of therapeutic macromolecules, owing to its inherent mucoadhesive feature and ability to modulate the integrity of epithelial tight junctions reversibly. By using CS-based nanoparticles, many studies have attempted to protect the loaded macromolecules against acidic denaturation and enzymatic degradation, prolong their intestinal residence time, and increase their absorption by the intestinal epithelium. Derivatives of CS such as quaternized CS, thiolated CS and carboxylated CS have also been examined to further enhance its effectiveness in oral absorption of macromolecular drugs. This review article describes the synthesis of these CS derivatives and their characteristics, as well as their potential transport mechanisms of macromolecular therapeutics across the intestinal biological membrane. Recent advances in using CS and its derivatives as carriers for oral delivery of hydrophilic macromolecules and their effects on drug transport are also reviewed.

Dissolving polymer microneedle patches for rapid and efficient transdermal delivery of insulin to diabetic rats.

This study presents a dissolving microneedle patch, composed of starch and gelatin, for the rapid and efficient transdermal delivery of insulin. The microneedles completely dissolve after insertion into the skin for 5 min, quickly releasing their encapsulated payload into the skin. A histological examination shows that the microneedles have sufficient mechanical strength to be inserted in vitro into porcine skin to a depth of approximately 200 μm and in vivo into rat skin to 200-250 μm depth. This penetration depth does not induce notable skin irritation or pain sensation. To evaluate the feasibility of using these dissolving microneedles for diabetes treatment insulin-loaded microneedles were administered to diabetic rats using a homemade applicator. Pharmacodynamic and pharmacokinetic results show a similar hypoglycemic effect in rats receiving insulin-loaded microneedles and a subcutaneous injection of insulin. The relative pharmacological availability and relative bioavailability of insulin were both approximately 92%, demonstrating that insulin retains its pharmacological activity after encapsulation and release from the microneedles. Storage stability analysis confirms that more than 90% of the insulin remained in the microneedles even after storage at 25 or 37°C for 1 month. These results confirm that the proposed starch/gelatin microneedles enable stable encapsulation of bioactive molecules and have great potential for transdermal delivery of protein drugs in a relatively painless, rapid, and convenient manner.

The characteristics, biodistribution and bioavailability of a chitosan-based nanoparticulate system for the oral delivery of heparin.

Heparin is a potent anticoagulant; however, it is poorly absorbed in the gastrointestinal tract. In this study, we developed a nanoparticle (NP) system shelled with chitosan (CS) for oral delivery of heparin; the NPs were prepared by a simple ionic gelation method without chemically modifying heparin. The drug loading efficiency of NPs was nearly 100% because a significantly excess amount of CS was used for the CS/heparin complex preparation. The internal structure of the prepared NPs was examined by small angle X-ray scattering (SAXS). The obtained SAXS profiles suggest that the NPs are associated with a two-phase system and consist of the CS/heparin complex microdomains surrounded by the CS matrix. The stability of NPs in response to pH had a significant effect on their release of heparin. No significant anticoagulant activity was detected after oral administration of the free form heparin solution in a rat model, while administration of NPs orally was effective in the delivery of heparin into the blood stream; the absolute bioavailability was found to be 20.5%. The biodistribution of the drug carrier, (99m)Tc-labeled CS, in rats was studied by the single-photon emission computed tomography after oral administration of the radio-labeled NPs. No significant radioactivity was found in the internal organs, indicating a minimal absorption of CS into the systemic circulation. These results suggest that the NPs developed in the study can be employed as a potential carrier for oral delivery of heparin.

Chitosan microneedle patches for sustained transdermal delivery of macromolecules

This paper introduces a chitosan microneedle patch for efficient and sustained transdermal delivery of hydrophilic macromolecules. Chitosan microneedles have sufficient mechanical strength to be inserted in vitro into porcine skin at approximately 250 μm in depth and in vivo into rat skin at approximately 200 μm in depth. Bovine serum albumin (BSA, MW=66.5 kDa) was used as a model protein to explore the potential use of chitosan microneedles as a transdermal delivery device for protein drugs. In vitro drug release showed that chitosan microneedles can provide a sustained release of BSA for at least 8 days (approximately 95% of drugs released in 8 days). When the Alexa Fluor 488-labeled BSA (Alexa 488-BSA)-loaded microneedles were applied to the rat skin in vivo, confocal microscopic images showed that BSA can gradually diffuse from the puncture sites to the dermal layer and the fluorescence of Alexa 488-BSA can be observed at the depth of 300 μm. In addition, encapsulation of BSA within the microneedle matrix did not alter the secondary structure of BSA, indicating that the gentle nature of the fabrication process allowed for encapsulation of fragile biomolecules. These results suggested that the developed chitosan microneedles may serve as a promising device for transdermal delivery of macromolecules in a sustained manner.

Fully embeddable chitosan microneedles as a sustained release depot for intradermal vaccination.

This study introduces a microneedle transdermal delivery system, composed of embeddable chitosan microneedles and a poly(L-lactide-co-D,L-lactide) (PLA) supporting array, for complete and sustained delivery of encapsulated antigens to the skin. Chitosan microneedles were mounted to the top of a strong PLA supporting array, providing mechanical strength to fully insert the microneedles into the skin. When inserted into rat skin in vivo, chitosan microneedles successfully separated from the supporting array and were left within the skin for sustained drug delivery without requiring a transdermal patch. The microneedle penetration depth was approximately 600 μm (i.e. the total length of the microneedle), which is beneficial for targeted delivery of antigens to antigen-presenting cells in the epidermis and dermis. To evaluate the utility of chitosan microneedles for intradermal vaccination, ovalbumin (OVA; MW = 44.3 kDa) was used as a model antigen. When the OVA-loaded microneedles were embedded in rat skin in vivo, histological examination showed that the microneedles gradually degraded and prolonged OVA exposure at the insertion sites for up to 14 days. Compared to traditional intramuscular immunization, rats immunized by a single microneedle dose of OVA showed a significantly higher OVA-specific antibody response which lasted for at least 6 weeks. These results suggest that embeddable chitosan microneedles are a promising depot for extended delivery of encapsulated antigens to provide sustained immune stimulation and improve immunogenicity.

A nanoscale drug-entrapment strategy for hydrogel-based systems for the delivery of poorly soluble drugs.

The hydrophilic nature of hydrogel matrices makes them disadvantageous to entrap poorly soluble therapeutic agents and greatly restricts their applications as drug-delivery systems. In this study, we demonstrated that sustained delivery of lipophilic drugs in hydrogel-based devices can be readily achieved by enhancing retention of drugs within micelles. This nanoscale drug-entrapment strategy was applied to develop a polymeric drug-eluting stent. Sirolimus, a lipophilic anti-proliferative/immunosuppressive drug, was entrapped into the hydrophobic core of Pluronic L121 micelles and then blended in a chitosan-based strip and crosslinked by an epoxy compound to fabricate test stents. It was found that the use of such a nanoscale drug-entrapment strategy was able to significantly increase the loading efficiency of lipophilic drugs, prevent the drug from aggregation and beneficially reduce its initial burst release; thus, the duration of drug release was extended considerably. When implanting the stent in rabbit infrarenal abdominal aortas, in-stent restenosis was markedly reduced and less inflammatory reaction was observed, while unfavorable effects such as delayed endothelial healing caused by the overdose of sirolimus could be significantly evaded.

The characteristics and in vivo suppression of neointimal formation with sirolimus-eluting polymeric stents.

Drug-eluting stents have emerged as a predominant percutaneous strategy in patients with coronary artery disease. However, hypersensitivity reactions caused by their nonerodable polymer coatings and bare-metal stents may result in serious clinical sequelae. In this report, a new biodegradable sirolimus-eluting stent, made from chitosan-based strips fixed by an epoxy compound, coated with a hydrophobic heparin was developed. Due to the covalent crosslinks formed in the stent matrix, the fabricated stent had a shape-memory property to memorize its permanent shape. The shape-memory ability and mechanical strength of the stent could be enhanced by increasing its degree of crosslinking. The cytocompatibility of the stent was demonstrated in vitro. The heparin coating on the stent effectively reduced platelet adhesion; additionally, it acted as a diffusion barrier and led to a nearly linear sustained-release profile of sirolimus. Cell-cycle analysis demonstrated that the released sirolimus could inhibit smooth muscle cell proliferation by inducing cell-cycle arrest in G(1) phase. When compared to the unloaded stent, neointimal formation was significantly suppressed after implantation of the sirolimus-eluting stent in rabbit infrarenal abdominal aortas. These findings suggested that the developed sirolimus-eluting polymeric stent can be a potential alternative for treatment of atherosclerosis.

Near-Infrared Light-Activatable Microneedle System for Treating Superficial Tumors by Combination of Chemotherapy and Photothermal Therapy

Because of the aggressive and recurrent nature of cancers, repeated and multimodal treatments are often necessary. Traditional cancer therapies have a risk of serious toxicity and side effects. Hence, it is crucial to develop an alternative treatment modality that is minimally invasive, effectively treats cancers with low toxicity, and can be repeated as required. We developed a light-activatable microneedle (MN) system that can repeatedly and simultaneously provide photothermal therapy and chemotherapy to superficial tumors and exert synergistic anticancer effects. This system consists of embeddable polycaprolactone MNs containing a photosensitive nanomaterial (lanthanum hexaboride) and an anticancer drug (doxorubicin; DOX), and a dissolvable poly(vinyl alcohol)/polyvinylpyrrolidone supporting array patch. Because of this supporting array, the MNs can be completely inserted into the skin and embedded within the target tissue for locoregional cancer treatment. When exposed to near-infrared light, the embedded MN array uniformly heats the target tissue to induce a large thermal ablation area and then melts at 50 °C to release DOX in a broad area, thus destroying tumors. This light-activated heating and releasing behavior can be precisely controlled and switched on and off on demand for several cycles. We demonstrated that the MN-mediated synergistic therapy completely eradicated 4T1 tumors within 1 week after a single application of the MN and three cycles of laser treatment. No tumor recurrence and no significant body weight loss of mice were observed. Thus, the developed light-activatable MN with a unique embeddable feature offers an effective, user-friendly, and low-toxicity option for patients requiring long-term and multiple cancer treatments.