Microneedles assisted controlled and improved transdermal delivery of high molecular drugs via in situ forming depot thermoresponsive poloxamers gels in skin microchannels.

Skin is considered as an attractive route for variety of drug molecule administration. However, it is proved to be the main physical barrier for drug flux owing to their poor permeability and low bioavailability across stratum corneum layer. In the current study, novel approach has been used to enhance transdermal delivery via microporation through combination of poloxamers gels and microneedles (MNs) arrays. The phase transition of poloxamers at various concentrations from sol-gel was evaluated using AR2000 rheometer to confirm MNs-assisted in situ forming depots. Temperature test confirmed gelation between 32 and 37 °C. Curcumin was loaded in poloxamer formulations at variable concentrations and its effect showed reduction in critical gelation temperature (CGT) owing to its hydrophobic nature. Microneedle arrays (600 µm) prepared from Gantrez S-97, PEG10000 and gelatin B using (19 × 19) laser-engineered silicone micromoulds showed high mechanical stability investigated via Texture analyzer. From in situ dissolution profile, gelatin 15% w/w based MNs displayed quicker dissolution rate in comparison to PG10000. VivoSight® OCT scanner and dye tracking confirmed that PG10000 MNs arrays pierced SC layer, infiltrate the epidermis and goes to dermis layer. From in vitro permeation, it was concluded that 20% w/w PF127® gel formulations containing (0.1% and 0.3%) curcumin displayed high curcumin permeation for comparatively longer time through microporated skin samples in comparison to non-microporated skin. The curcumin distribution in skin tissues with higher florescence intensity was noted in MNs treated skin samples by confocal microscopy. FTIR confirmed the structure formation of fabricated MNs, while TGA showed dry, brittle and rigid nature of gelatin MNs.

Rapidly dissolving bilayer microneedles enabling minimally invasive and efficient protein delivery to the posterior segment of the eye.

The discovery of proteins that neutralise vascular endothelial growth factors, such as pegaptanib, ranibizumab and aflibercept, can inhibit the process of angiogenesis, thereby restoring eyesight in individuals with retinal vascular disorders. However, due to the posterior location and chronic nature of retinal diseases, a safe and effective intraocular protein delivery system is currently lacking. Thus, dissolving bilayer microneedles (MNs) with the potential to deliver proteins to the back of the eye in an efficient and minimally invasive manner were developed in this study. A model protein, ovalbumin (OVA), was incorporated into MNs fabricated from different polymers, including hyaluronic acid (HA), polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP). Optimised PVA/PVP MNs were demonstrated to be robust enough to pierce porcine sclera with > 75% of the needle length penetrating the sclera and dissolving within 150 s. SDS-PAGE and OVA-specific ELISA revealed that the bioactivity of the model protein was maintained during the manufacture of MNs. In hen's egg-chorioallantoic membrane test, MNs fabricated from all chosen polymers were classified as non-irritants. Furthermore, ex vivo permeation studies showed that optimised MNs could permeate 86.99 ± 7.37% of OVA through the sclera, twice that of the needle-free patch (42.16 ± 3.95%), highlighting the capability of MNs to circumvent physical barriers and promote protein delivery to the posterior segment of the eye. In this work, a novel, efficient and safe intraocular protein delivery system was successfully established.

Design, optimization and characterisation of polymeric microneedle arrays prepared by a novel laser-based micromoulding technique.

PURPOSE: Design and evaluation of a novel laser-based method for micromoulding of microneedle arrays from polymeric materials under ambient conditions. The aim of this study was to optimise polymeric composition and assess the performance of microneedle devices that possess different geometries. METHODS: A range of microneedle geometries was engineered into silicone micromoulds, and their physicochemical features were subsequently characterised. RESULTS: Microneedles micromoulded from 20% w/w aqueous blends of the mucoadhesive copolymer Gantrez® AN-139 were surprisingly found to possess superior physical strength than those produced from commonly used pharma polymers. Gantrez® AN-139 microneedles, 600 µm and 900 µm in height, penetrated neonatal porcine skin with low application forces (>0.03 N per microneedle). When theophylline was loaded into 600 µm microneedles, 83% of the incorporated drug was delivered across neonatal porcine skin over 24 h. Optical coherence tomography (OCT) showed that drug-free 600 µm Gantrez® AN-139 microneedles punctured the stratum corneum barrier of human skin in vivo and extended approximately 460 µm into the skin. However, the entirety of the microneedle lengths was not inserted. CONCLUSION: In this study, we have shown that a novel laser engineering method can be used in micromoulding of polymeric microneedle arrays. We are currently carrying out an extensive OCT-informed study investigating the influence of microneedle array geometry on skin penetration depth, with a view to enhanced transdermal drug delivery from optimised laser-engineered Gantrez® AN-139 microneedles.

Microneedle arrays allow lower microbial penetration than hypodermic needles in vitro.

METHODS: In this study we determined, for the first time, the ability of microorganisms to traverse microneedle-induced holes using two different in vitro models. RESULTS: When employing Silescol membranes, the numbers of Candida albicans, Pseudomonas aeruginosa and Staphylococcus epidermidis crossing the membranes were an order of magnitude lower when the membranes were punctured by microneedles rather than a 21G hypodermic needle. Apart from the movement of C. albicans across hypodermic needle-punctured membranes, where 40.2% of the microbial load on control membranes permeated the barrier over 24 h, the numbers of permeating microorganisms was less than 5% of the original microbial load on control membranes. Experiments employing excised porcine skin and radiolabelled microorganisms showed that the numbers of microorganisms penetrating skin beyond the stratum corneum were approximately an order of magnitude greater than the numbers crossing Silescol membranes in the corresponding experiments. Approximately 10(3) cfu of each microorganism adhered to hypodermic needles during insertion. The numbers of microorganisms adhering to MN arrays were an order of magnitude higher in each case. CONCLUSION: We have shown here that microneedle puncture resulted in significantly less microbial penetration than did hypodermic needle puncture and that no microorganisms crossed the viable epidermis in microneedle-punctured skin, in contrast to needle-punctured skin. Given the antimicrobial properties of skin, it is, therefore, likely that application of microneedle arrays to skin in an appropriate manner would not cause either local or systemic infection in normal circumstances in immune-competent patients. In supporting widespread clinical use of microneedle-based delivery systems, appropriate animal studies are now needed to conclusively demonstrate this in vivo. Safety in patients will be enhanced by aseptic or sterile manufacture and by fabricating microneedles from self-disabling materials (e.g. dissolving or biodegradable polymers) to prevent inappropriate or accidental reuse.

Hydrogel-forming microneedles prepared from "super swelling" polymers combined with lyophilised wafers for transdermal drug delivery.

We describe, for the first time, hydrogel-forming microneedle arrays prepared from "super swelling" polymeric compositions. We produced a microneedle formulation with enhanced swelling capabilities from aqueous blends containing 20% w/w Gantrez S-97, 7.5% w/w PEG 10,000 and 3% w/w Na2CO3 and utilised a drug reservoir of a lyophilised wafer-like design. These microneedle-lyophilised wafer compositions were robust and effectively penetrated skin, swelling extensively, but being removed intact. In in vitro delivery experiments across excised neonatal porcine skin, approximately 44 mg of the model high dose small molecule drug ibuprofen sodium was delivered in 24 h, equating to 37% of the loading in the lyophilised reservoir. The super swelling microneedles delivered approximately 1.24 mg of the model protein ovalbumin over 24 h, equivalent to a delivery efficiency of approximately 49%. The integrated microneedle-lyophilised wafer delivery system produced a progressive increase in plasma concentrations of ibuprofen sodium in rats over 6 h, with a maximal concentration of approximately 179 µg/ml achieved in this time. The plasma concentration had fallen to 71±6.7 µg/ml by 24 h. Ovalbumin levels peaked in rat plasma after only 1 hour at 42.36±17.01 ng/ml. Ovalbumin plasma levels then remained almost constant up to 6 h, dropping somewhat at 24 h, when 23.61±4.84 ng/ml was detected. This work represents a significant advancement on conventional microneedle systems, which are presently only suitable for bolus delivery of very potent drugs and vaccines. Once fully developed, such technology may greatly expand the range of drugs that can be delivered transdermally, to the benefit of patients and industry. Accordingly, we are currently progressing towards clinical evaluations with a range of candidate molecules.

Hydrogel-forming microneedle arrays exhibit antimicrobial properties: potential for enhanced patient safety.

We describe, for the first time, the microbial characterisation of hydrogel-forming polymeric microneedle arrays and the potential for passage of microorganisms into skin following microneedle penetration. Uniquely, we also present insights into the storage stability of these hydroscopic formulations, from physical and microbiological viewpoints, and examine clinical performance and safety in human volunteers. Experiments employing excised porcine skin and radiolabelled microorganisms showed that microorganisms can penetrate skin beyond the stratum corneum following microneedle puncture. Indeed, the numbers of microorganisms crossing the stratum corneum following microneedle puncture were greater than 105 cfu in each case. However, no microorganisms crossed the epidermal skin. When using a 21G hypodermic needle, more than 104 microorganisms penetrated into the viable tissue and 106 cfu of Candida albicans and Staphylococcus epidermidis completely crossed the epidermal skin in 24 h. The hydrogel-forming materials contained no microorganisms following de-moulding and exhibited no microbial growth during storage, while also maintaining their mechanical strength, apart from when stored at relative humidities of 86%. No microbial penetration through the swelling microneedles was detectable, while human volunteer studies confirmed that skin or systemic infection is highly unlikely when polymeric microneedles are used for transdermal drug delivery. Since no pharmacopoeial standards currently exist for microneedle-based products, the exact requirements for a proprietary product based on hydrogel-forming microneedles are at present unclear. However, we are currently working towards a comprehensive specification set for this microneedle system that may inform future developments in this regard.

Electrically-responsive anti-adherent hydrogels for photodynamic antimicrobial chemotherapy.

The loading of the photosensitisers meso-Tetra (N-methyl-4-pyridyl) porphine tetra tosylate (TMP), methylene blue (MB) and TMP with sodium dodecyl sulphate (SDS) into and release from hydrogels composed of the polyelectrolyte poly(methyl vinyl ether-co-maleic acid) crosslinked in a 2:1 ratio with PEG 10,000 were investigated as a potential rapid photodynamic antimicrobial chemotherapy (PACT) treatment for infected wounds using iontophoresis as a novel delivery method. Photosensitiser uptake was very high; (% TMP uptake; 95.53-96.72%) (% MB uptake; 90.58-93.26%) and was PMVE/MA concentration independent, whilst SDS severely limited TMP uptake (5.93-8.75%). Hydrogel hardness, compressibility and adhesiveness on the dermal surface of neonate porcine skin increased with PMVE/MA concentration and were significantly increased with SDS. The ionic conductivities of the hydrogels increased with PMVE/MA concentration. Drug release was PMVE/MA concentration independent, except for drug release under iontophoteric conditions for MB and TMP (without SDS). In just 15 min, the mean% drug concentrations released of TMP, TMP (with SDS) and MB using an electric current ranged from 22.30 to 64.72 µg ml(-1), 6.37-4.59 µg ml(-1) and 11.73-36.57 µg ml(-1) respectively. These concentrations were in excess of those required to induce complete kill of clinical strains of meticillin-resistant Staphylococcus aureus and Burkholderia cepacia. Thus these results support our contention that the iontophoteric delivery of TMP and MB using anti-adherent, electrically-responsive, PEG-crosslinked PMVE/MA hydrogels are a potential option in the rapid PACT treatment of infected wounds.

Microneedle-mediated transdermal bacteriophage delivery.

Interest in bacteriophages as therapeutic agents has recently been reawakened. Parenteral delivery is the most routinely-employed method of administration. However, injection of phages has numerous disadvantages, such as the requirement of a health professional for administration and the possibility of cross-contamination. Transdermal delivery offers one potential means of overcoming many of these problems. The present study utilized a novel poly (carbonate) (PC) hollow microneedle (MN) device for the transdermal delivery of Escherichia coli-specific T4 bacteriophages both in vitro and in vivo. MN successfully achieved bacteriophage delivery in vitro across dermatomed and full thickness skin. A concentration of 2.67 × 10(6)PFU/ml (plaque forming units per ml) was detected in the receiver compartment when delivered across dermatomed skin and 4.0 × 10(3)PFU/ml was detected in the receiver compartment when delivered across full thickness skin. An in vivo study resulted in 4.13 × 10(3)PFU/ml being detected in blood 30 min following initial MN-mediated phage administration. Clearance occurred rapidly, with phages being completely cleared from the systemic circulation within 24h, which was expected in the absence of infection. We have shown here that MN-mediated delivery allows successful systemic phage absorption. Accordingly, bacteriophage-based therapeutics may now have an alternative route for systemic delivery. Once fully-investigated, this could lead to more widespread investigation of these interesting therapeutic viruses.

Electrically enhanced solute permeation across poly(ethylene glycol)-crosslinked poly(methyl vinyl ether-co-maleic acid) hydrogels: effect of hydrogel crosslink density and ionic conductivity.

Swelling kinetics, ionic conductivity and electrically assisted solute permeation (theophylline, methylene blue and fluorescein sodium) of poly(ethylene glycol) (PEG) crosslinked poly(methyl vinyl ether-co-maleic acid) (PMVE/MA) hydrogels are presented. The effects of PMVE/MA concentration and PEG molecular weight (MW) on swelling behaviour and network parameters were investigated in phosphate buffered saline (pH 7.4). The percentage swelling of hydrogels increased, and the crosslink density decreased, with a decrease in PMVE/MA content and with an increase in PEG MW. The ionic conductivity of the formulation was found to increase with an increase in PEG MW. The application of an electrical current led to a significant enhancement in the rate and extent of solute permeation across the swollen hydrogels. Furthermore, it was found that the extent of solute permeation enhancement following current application was dependent upon the crosslink density and ionic conductivity of the formulation. In general, a decrease in crosslink density and an increase in ionic conductivity led to a greater enhancement in solute permeation following current application. The electro-responsive nature of these hydrogels suggests that have a potential application in electrically controlled drug delivery systems.

Microneedle arrays as medical devices for enhanced transdermal drug delivery.

In order to exploit the transdermal route for systemic delivery of a wide range of drug molecules, including peptide/protein molecules and genetic material, a means of disrupting the excellent barrier properties of the uppermost layer of the skin, the stratum corneum, must be sought. The use of microneedle (MN) arrays has been proposed as a method to temporarily disrupt the barrier function of the skin and thus enable enhanced transdermal drug delivery. MN arrays consist of a plurality of micron-sized needles, generally ranging from 25 to 2000 µm in height, of a variety of different shapes and composition (e.g., silicon, metal, sugars and biodegradable polymers). The application of such MN arrays to the skin results in the creation of aqueous channels that are orders of magnitude larger than molecular dimensions and, therefore, should readily permit the transport of macromolecules. This article will focus on recent and future developments for MN technology, focusing on the materials used for MN fabrication, the forces required for MN insertion and potential safety aspects that may be involved with the use of MN devices.

Optical coherence tomography is a valuable tool in the study of the effects of microneedle geometry on skin penetration characteristics and in-skin dissolution.

In this study, we used optical coherence tomography (OCT) to extensively investigate, for the first time, the effect that microneedle (MN) geometry (MN height, and MN interspacing) and force of application have upon penetration characteristics of soluble poly(methylvinylether-co-maleic anhydride, PMVE/MA) MN arrays into neonatal porcine skin in vitro. The results from OCT investigations were then used to design optimal and suboptimal MN-based drug delivery systems and evaluate their drug delivery profiles cross full thickness and dermatomed neonatal porcine skin in vitro. It was found that increasing the force used for MN application resulted in a significant increase in the depth of penetration achieved within neonatal porcine skin. For example, MN of 600µm height penetrated to a depth of 330µm when inserted at a force of 4.4N/array, while the penetration increased significantly to a depth of 520µm, when the force of application was increased to 16.4N/array. At an application force of 11.0N/array it was found that, in each case, increasing MN height from 350 to 600µm to 900µm led to a significant increase in the depth of MN penetration achieved. Moreover, alteration of MN interspacing had no effect upon depth of penetration achieved, at a constant MN height and force of application. With respect to MN dissolution, an approximate 34% reduction in MN height occurred in the first 15min, with only 17% of the MN height remaining after a 3-hour period. Across both skin models, there was a significantly greater cumulative amount of theophylline delivered after 24h from an MN array of 900µm height (292.23±16.77µg), in comparison to an MN array of 350µm height (242.62±14.81µg) (p<0.001). Employing full thickness skin significantly reduced drug permeation in both cases. Importantly, this study has highlighted the effect that MN geometry and application force have upon the depth of penetration into skin. While it has been shown that MN height has an important role in the extent of drug delivered across neonatal porcine skin from a soluble MN array, further studies to evaluate the full significance of MN geometry on MN mediated drug delivery are now underway. The successful use of OCT in this study could prove to be a key development for polymeric MN research, accelerating their commercial exploitation.