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.

Flux of ionic dyes across microneedle-treated skin:effect of molecular characteristics

Drug flux across microneedle (MN)-treated skin is influenced by the characteristics of the MN array, formed microconduits and physicochemical properties of the drug molecules in addition to the overall diffusional resistance of microconduits and viable tissue. Relative implication of these factors has not been fully explored. In the present study, the in vitro permeation of a series of six structurally related ionic xanthene dyes with different molecular weights (MW) and chemical substituents, across polymer MN-pretreated porcine skin was investigated in relation of their molecular characteristics. Dyes equilibrium solubility, partition coefficient in both n-octanol or porcine skin/aqueous system, and dissociation constants were determined. Results indicated that for rhodamine dyes, skin permeation of the zwitterionic form which predominates at physiological pH, was significantly reduced by an increase in MW, the skin thickness and by the presence of the chemically reactive isothiocyanate substituent. These factors were generally shown to override the aqueous solubility, an important determinant of drug diffusion in an aqueous milieu. The data obtained provided more insight into the mechanism of drug permeation across MN-treated skin, which is of importance to both the design of MN-based transdermal drug delivery systems and of relevance to skin permeation research.

Lack of in vitro-in vivo correlation for a UC781-releasing vaginal ring in macaques

This study describes the preclinical development of a matrix-type silicone elastomer vaginal ring device designed to provide controlled release of UC781, a non-nucleoside re- verse transcriptase inhibitor. Testing of both human- and macaque-sized rings in a sink condition in vitro release model demonstrated continuous UC781 release in quantities consid- ered sufficient to maintain vaginal fluid concentrations at levels 82–860-fold higher than the in vitro IC50 (2.0 to 10.4 nM) and therefore potentially protect against mucosal trans- mission of HIV. The 100-mg UC781 rings were well tolerated in pig-tailed macaques, did not induce local inflammation as determined by cytokine analysis and maintained median con- centrations in vaginal fluids of UC781 in the range of 0.27 to 5.18 mM during the course of the 28-day study. Analysis of residual UC781 content in rings after completion of both the in vitro release and macaque pharmacokinetic studies revealed that 57 and 5 mg of UC781 was released, respectively. The pharmacokinetic analysis of a 100-mg UC781 vaginal ring in pig-tailed macaques showed poor in vivo–in vitro correlation, attributed to the very poor solubility of UC781 in vaginal fluid and resulting in a dissolution-controlled drug release mecha- nism rather than the expected diffusion-controlled mechanism.

Optimisation of a two-liquid component pre-filled acrylic bone cement system: A design of experiments approach to optimise cement final properties

The initial composition of acrylic bone cement along with the mixing and delivery technique used can influence its final properties and therefore its clinical success in vivo. The polymerisation of acrylic bone cement is complex with a number of processes happening simultaneously. Acrylic bone cement mixing and delivery systems have undergone several design changes in their advancement, although the cement constituents themselves have remained unchanged since they were first used. This study was conducted to determine the factors that had the greatest effect on the final properties of acrylic bone cement using a pre-filled bone cement mixing and delivery system. A design of experiments (DoE) approach was used to determine the impact of the factors associated with this mixing and delivery method on the final properties of the cement produced. The DoE illustrated that all factors present within this study had a significant impact on the final properties of the cement. An optimum cement composition was hypothesised and tested. This optimum recipe produced cement with final mechanical and thermal properties within the clinical guidelines and stated by ISO 5833 (International Standard Organisation (ISO), International standard 5833: implants for surgery—acrylic resin cements, 2002), however the low setting times observed would not be clinically viable and could result in complications during the surgical technique. As a result further development would be required to improve the setting time of the cement in order for it to be deemed suitable for use in total joint replacement surgery.

Antimicrobial efficacy of tobramycin polymeric nanoparticles for Pseudomonas aeruginosa infections in cystic fibrosis: formulation, characterisation and functionalisation with dornase alfa (DNase).

Inhaled antibiotics, such as tobramycin, for the treatment of Pseudomonas aeruginosa pulmonary infections are associated with the increase in life expectancy seen in cystic fibrosis (CF) patients over recent years. However, the effectiveness of this aminoglycoside is still limited by its inability to penetrate the thick DNA-rich mucus in the lungs of these patients, leading to low antibiotic exposure to resident bacteria. In this study, we created novel polymeric nanoparticle (NP) delivery vehicles for tobramycin. Using isothermal titration calorimetry, we showed that tobramycin binds with alginate polymer and, by exploiting this interaction, optimised the production of tobramycin alginate/chitosan NPs. It was established that NP antimicrobial activity against P. aeruginosa PA01 was equivalent to unencapsulated tobramycin (minimum inhibitory concentration 0.625 mg/L). Galleria mellonella was employed as an in vivo model for P. aeruginosa infection. Survival rates of 90% were observed following injection of NPs, inferring low NP toxicity. After infection with P. aeruginosa, we showed that a lethal inoculum was effectively cleared by tobramycin NPs in a dose dependent manner. Crucially, a treatment with NPs prior to infection provided a longer window of antibiotic protection, doubling survival rates from 40% with free tobramycin to 80% with NP treatment. Tobramycin NPs were then functionalised with dornase alfa (recombinant human deoxyribonuclease I, DNase), demonstrating DNA degradation and improved NP penetration of CF sputum. Following incubation with CF sputum, tobramycin NPs both with and without DNase functionalisation, exhibited anti-pseudomonal effects. Overall, this work demonstrates the production of effective antimicrobial NPs, which may have clinical utility as mucus-penetrating tobramycin delivery vehicles, combining two widely used CF therapeutics into a single NP formulation. This nano-antibiotic represents a strategy to overcome the mucus barrier, increase local drug concentrations, avoid systemic adverse effects and improve outcomes for pulmonary infections in CF.

Microneedle characterisation: the need for universal acceptance criteria and GMP specifications when moving towards commercialisation

With interest in microneedles as a novel drug transdermal delivery system increasing rapidly since the late 1990s (Margetts and Sawyer Contin Educ Anaesthesia Crit Care Pain. 7(5):171-76, 2007), a diverse range of microneedle systems have been fabricated with varying designs and dimensions. However, there are still very few commercially available microneedle products. One major issue regarding microneedle manufacture on an industrial scale is the lack of specific quality standards for this novel dosage form in the context of Good Manufacturing Practice (GMP). A range of mechanical characterisation tests and microneedle insertion analysis techniques are used by researchers working on microneedle systems to assess the safety and performance profiles of their various designs. The lack of standardised tests and equipment used to demonstrate microneedle mechanical properties and insertion capability makes it difficult to directly compare the in use performance of candidate systems. This review highlights the mechanical tests and insertion analytical techniques used by various groups to characterise microneedles. This in turn exposes the urgent need for consistency across the range of microneedle systems in order to promote innovation and the successful commercialisation of microneedle products.

Patient safety and beyond: what should we expect from microneedle arrays in the transdermal delivery arena?

Research based upon microneedle (MN) arrays has intensified recently. While the initial focus was on biomolecules, the field has expanded to include delivery of conventional small-molecule drugs whose water solubility currently precludes transdermal administration. Much success has been achieved, with peptides, proteins, vaccines, antibodies and even particulates delivered by MN in therapeutic/prophylactic doses. Recent innovations have focused on enhanced formulation design, scalable manufacture and extension of exploitation to minimally invasive patient monitoring, ocular delivery and enhanced administration of cosmeceuticals. Only two MN-based drug/vaccine delivery products are currently marketed, partially due to limitations with older MN designs based upon silicon and metal. Even the more promising polymeric MN have raised a number of regulatory and manufacturability queries that the field must address. MN arrays have tremendous potential to yield real benefits for patients and industry and, through diligence, innovation and collaboration, this will begin to be realised over the next 3-5 years.

Design and physicochemical characterisation of novel dissolving polymeric microneedle arrays for transdermal delivery of high dose, low molecular weight drugs

We describe formulation and evaluation of novel dissolving polymeric microneedle (MN) arrays for the facilitated delivery of low molecular weight, high dose drugs. Ibuprofen sodium was used as the model here and was successfully formulated at approximately 50% w/w in the dry state using the copolymer poly(methylvinylether/maleic acid). These MNs were robust and effectively penetrated skin in vitro, dissolving rapidly to deliver the incorporated drug. The delivery of 1.5mg ibuprofen sodium, the theoretical mass of ibuprofen sodium contained within the dry MN alone, was vastly exceeded, indicating extensive delivery of the drug loaded into the baseplates. Indeed in in vitro transdermal delivery studies, approximately 33mg (90%) of the drug initially loaded into the arrays was delivered over 24h. Iontophoresis produced no meaningful increase in delivery. Biocompatibility studies and in vivo rat skin tolerance experiments raised no concerns. The blood plasma ibuprofen sodium concentrations achieved in rats (263μgml(-1) at the 24h time point) were approximately 20 times greater than the human therapeutic plasma level. By simplistic extrapolation of average weights from rats to humans, a MN patch design of no greater than 10cm(2) could cautiously be estimated to deliver therapeutically-relevant concentrations of ibuprofen sodium in humans. This work, therefore, represents a significant progression in exploitation of MN for successful transdermal delivery of a much wider range of drugs.

RALA-mediated delivery of FKBPL nucleic acid therapeutics

Aims: RALA is a novel 30 mer bioinspired amphipathic peptide that is showing promise for gene delivery. Here, we used RALA to deliver the FK506-binding protein like – FKBPL gene (pFKBPL) – a novel member of the immunophilin protein family. FKBPL is a secreted protein, with overexpression shown to inhibit angiogenesis, tumor growth and stemness, through a variety of intra- and extracellular signaling mechanisms. We also elucidated proangiogenic activity and stemness after utilizing RALA to deliver siRNA (siFKBPL). Materials & methods: The RALA/pFKBPL and RALA/siFKBPL nanoparticles were characterized in terms of size, charge, stability and toxicity. Overexpression and knockdown of FKBPL was assessed in vitro and in vivo. Results: RALA delivered both pFKBPL and siFKBPL with less cytotoxicity than commercially available counterparts. In vivo, RALA/pFKBPL delivery retarded tumor growth, and prolonged survival with an associated decrease in angiogenesis, while RALA/siFKBPL had no effect on tumor growth rate or survival, but resulted in an increase in angiogenesis and stemness. Conclusion: RALA is an effective delivery system for both FKBPL DNA and RNAi and highlights an alternative therapeutic approach to harnessing FKBPL's antiangiogenic and antistemness activity.

Probing The effects of Experimental Conditions on the Character of Drug-Polymer Phase Diagrams Constructed Using Flory-Huggins Theory

Purpose: Amorphous drug-polymer solid dispersions have been found to result in improved drug dissolution rates when compared to their crystalline counterparts. However, when the drug exists in the amorphous form it will possess a higher Gibb’s free energy than its associated crystalline state and can recrystallize. Drug-polymer phase diagrams constructed through the application of the Flory Huggins (F-H) theory contain a wealth of information regarding thermodynamic and kinetic stability of the amorphous drug-polymer system. This study was aimed to evaluate the effects of various experimental conditions on the solubility and miscibility detections of drug-polymer binary system. Methods: Felodipine (FD)-Polyvinylpyrrolidone (PVP) K15 (PVPK15) and FD-Polyvinylpyrrolidone/vinyl acetate (PVP/VA64) were the selected systems for this research. Physical mixtures with different drug loadings were mixed and ball milled. These samples were then processed using Differential Scanning Calorimetry (DSC) and measurements of melting point (Tend) and glass transition (Tg) were detected using heating rates of 0.5, 1.0 and 5.0°C/min. Results: The melting point depression data was then used to calculate the F-H interaction parameter (χ) and extrapolated to lower temperatures to complete the liquid–solid transition curves. The theoretical binodal and spinodal curves were also constructed which were used to identify regions within the phase diagram. The effects of polymer selection, DSC heating rate, time above parent polymer Tg and polymer molecular weight were investigated by identifying amorphous drug miscibility limits at pharmaceutically relevant temperatures. Conclusion: The potential implications of these findings when applied to a non-ambient processing method such as Hot Melt Extrusion (HME) are also discussed.

Microneedles: A New Frontier in Nanomedicine Delivery

This review aims to concisely chart the development of two individual research fields, namely nanomedicines, with specific emphasis on nanoparticles (NP) and microparticles (MP), and microneedle (MN) technologies, which have, in the recent past, been exploited in combinatorial approaches for the efficient delivery of a variety of medicinal agents across the skin. This is an emerging and exciting area of pharmaceutical sciences research within the remit of transdermal drug delivery and as such will undoubtedly continue to grow with the emergence of new formulation and fabrication methodologies for particles and MN. Firstly, the fundamental aspects of skin architecture and structure are outlined, with particular reference to their influence on NP and MP penetration. Following on from this, a variety of different particles are described, as are the diverse range of MN modalities currently under development. The review concludes by highlighting some of the novel delivery systems which have been described in the literature exploiting these two approaches and directs the reader towards emerging uses for nanomedicines in combination with MN.

Microneedle-mediated delivery of donepezil: Potential for improved treatment options in Alzheimer's disease

Transdermal drug delivery is an attractive route of drug administration, however there are relatively few marketed transdermal products. To increase delivery across the skin, strategies to enhance skin permeability are widely investigated, with microneedles demonstrating particular promise. Hydrogel-forming microneedles are inserted into the skin, and following dissolution of a drug loaded reservoir and movement of the drug through the created channels, the microneedle array is removed intact, and can then be readily and safely discarded. This study presents the formulation and evaluation of an integrated microneedle patch containing the Alzheimer's drug, donepezil hydrochloride. The integrated patch consisted of hydrogel-forming microneedles in combination with a donepezil hydrochloride containing film. Formulation and characterisation of plasticised films, prepared from poly(vinylpyrrolidone) or poly (methyl vinyl ether co-maleic anhydride/acid) (Gantrez(®)) polymers, is presented. Furthermore, in vitro permeation of donepezil hydrochloride across neonatal porcine skin from the patches was investigated, with 854.71 μg ± 122.71 μg donepezil hydrochloride delivered after 24 h, using the optimum patch formulation. Following administration of the patch to an animal model, plasma concentrations of 51.8 ± 17.6 ng/mL were obtained, demonstrating the success of this delivery platform for donepezil hydrochloride.

Novel methods of drug administration for the treatment and care of older patients

The number of older people globally is increasing, contributing to a growing burden of morbidity and mortality. With this shift in population demographic, comes a new challenge in terms of appropriate healthcare for the over 65 years age group. As medication is the principal therapeutic intervention, it is essential that it be fully optimised, to meet the needs of this heterogeneous population. The most common routes of drug administration are oral and injectable, which may display some limitations for older people, in cases of dysphagia or frailty for example. This review considers alternative methods of drug delivery to the norm, specifically discussing the nasal, pulmonary and transdermal routes, as well as novel orally disintegrating tablets. The changing physiology as ageing occurs must be considered in the development of novel drug delivery devices. This review considers the various aspects of ageing that will influence future drug formulation design and development.

Transcending epithelial and intracellular biological barriers; a prototype DNA delivery device

Microneedle technology provides the opportunity for the delivery of DNA therapeutics by a non-invasive, patient acceptable route. To deliver DNA successfully requires consideration of both extra and intracellular biological barriers. In this study we present a novel two tier platform; i) a peptide delivery system, termed RALA, that is able to wrap the DNA into nanoparticles, protect the DNA from degradation, enter cells, disrupt endosomes and deliver the DNA to the nucleus of cells ii) a microneedle (MN) patch that will house the nanoparticles within the polymer matrix, breach the skin's stratum corneum barrier and dissolve upon contact with skin interstitial fluid thus releasing the nanoparticles into the skin. Our data demonstrates that the RALA is essential for preventing DNA degradation within the poly(vinylpyrrolidone) (PVP) polymer matrix. In fact the RALA/DNA nanoparticles (NPs) retained functionality when in the MN arrays after 28days and over a range of temperatures. Furthermore the physical strength and structure of the MNs was not compromised when loaded with the NPs. Finally we demonstrated the effectiveness of our MN-NP platform in vitro and in vivo, with systemic gene expression in highly vascularised regions. Taken together this 'smart-system' technology could be applied to a wide range of genetic therapies.