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 14 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 x 10(6) PFU/ml (plaque forming units per ml) was detected in the receiver compartment when delivered across dermatomed skin and 4.0 x 10(3) PFU/ml was detected in the receiver compartment when delivered across full thickness skin. An in vivo study resulted in 4.13 x 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 24 h, 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. (c) 2012 Elsevier B.V. All rights reserved.

Microneedle-Iontophoresis Combinations for Enhanced Transdermal Drug Delivery

It has recently been proposed that the combination of skin barrier impairment using microneedles (MNs) coupled with iontophoresis (ITP) may broaden the range of drugs suitable for transdermal delivery as well as enabling the rate of delivery to be achieved with precise electronic control. However, few reports exist on the combination of ITP with in situ drug-loaded polymeric MN delivery systems. Our in vitro permeation studies revealed that MN enhances transdermal drug delivery. The combination of dissolving MN and ITP did not further enhance the extent of delivery of the low molecular weight drug ibuprofen sodium after short application periods. However, the extent of peptide/protein delivery was significantly enhanced when ITP was used in combination with hydrogel-forming MN arrays. As such, hydrogel-forming MN arrays show promise for the electrically controlled transdermal delivery of biomacromolecules in a simple, one-step approach, though further technical developments will be necessary before patient benefit is realized.

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.

Microneedle/nanoencapsulation-mediated transdermal delivery:Mechanistic insights

A systematic study was undertaken to gain more insight into the mechanism of transdermal delivery of nanoencapsulated model dyes across microneedle (MN)-treated skin, a complex process not yet explored. Rhodamine B (Rh B) and fluorescein isothiocyanate (FITC) as model hydrophilic and hydrophobic small/medium-size molecules, respectively, were encapsulated in poly lactic-co-glycolic acid (PLGA) nanoparticles (NPs) and delivered through full thickness porcine skin pretreated with MN array. Permeation through MN-treated skin was affected by physicochemical characteristics of NPs and the encapsulated dyes. Dye flux was enhanced by smaller particle size, hydrophilicity, and negative zeta potential of NPs. Regarding encapsulated dyes, solubility at physiological pH and potential interaction with skin proteins proved to outweigh molecular weight as determinants of skin permeation. Data were verified using confocal laser scanning microscopy imaging. Findings coupled with the literature data are supportive of a mechanism involving influx of NPs, particularly of smaller size, deep into MN-created channels, generating depot dye-rich reservoirs. Molecular diffusion of the released dye across viable skin layers proceeds at a rate determined by its molecular characteristics. Data obtained provide mechanistic information of importance to the development of formulation strategies for more effective intradermal and transdermal MN-mediated delivery of nanoencapsulated therapeutic agents.

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.

Microneedle-Mediated Minimally Invasive Patient Monitoring

Background: The emerging field of microneedle-based minimally invasive patient monitoring and diagnosis is reviewed. Microneedle arrays consist of rows of micron-scale projections attached to a solid support. They have been widely investigated for transdermal drug and vaccine delivery applications since the late 1990s. However, researchers and clinicians have recently realized the great potential of microneedles for extraction of skin interstitial fluid and, less commonly, blood, for enhanced monitoring of patient health.

Methods: We reviewed the journal and patent literature, and summarized the findings and provided technical insights and critical analysis.

Results: We describe the basic concepts in detail and extensively review the work performed to date.

Conclusions: It is our view that microneedles will have an important role to play in clinical management of patients and will ultimately improve therapeutic outcomes for people worldwide.

Children's views on microneedle use as an alternative to blood sampling for patient monitoring

Objectives: To explore children's views on microneedle use for this population, particularly as an alternative approach to blood sampling, in monitoring applications, and so, examine the acceptability of this approach to children.

Methods: Focus groups were conducted with children (aged 10-14 years) in a range of schools across Northern Ireland. Convenience sampling was employed, i.e. children involved in a university-directed community-outreach project (Pharmacists in Schools) were recruited.

Key findings: A total of 86 children participated in 13 focus groups across seven schools in Northern Ireland. A widespread disapproval for blood sampling was evident, with pain, blood and traditional needle visualisation particularly unpopular aspects. In general, microneedles had greater visual acceptability and caused less fear. A patch-based design enabled minimal patient awareness of the monitoring procedure, with personalised designs, e.g. cartoon themes, favoured. Children's concerns included possible allergy and potential inaccuracies with this novel approach; however, many had confidence in the judgement of healthcare professionals if deeming this technique appropriate. They considered paediatric patient education critical for acceptance of this new approach and called for an alternative name, without any reference to 'needles'.

Conclusions: The findings presented here support the development of blood-free, minimally invasive techniques and provide an initial indication of microneedle acceptability in children, particularly for monitoring purposes. A proactive response to these unique insights should enable microneedle array design to better meet the needs of this end-user group. Further work in this area is recommended to ascertain the perspectives of a purposive sample of children with chronic conditions who require regular monitoring. © 2013 Royal Pharmaceutical Society.

Hydrogel-Forming Microneedle Arrays Can Be Effectively Inserted in Skin by Self-Application: A Pilot Study Centred on Pharmacist Intervention and a Patient Information Leaflet

Purpose: To investigate, for the first time, the influence of pharmacist intervention and the use of a patient information leaflet on self-application of hydrogel-forming microneedle arrays by human volunteers without the aid of an applicator device.
Methods: A patient information leaflet was drafted and pharmacist counselling strategy devised. Twenty human volunteers applied 11 × 11 arrays of 400 μm hydrogel-forming microneedle arrays to their own skin following the instructions provided. Skin barrier function disruption was assessed using transepidermal water loss measurements and optical coherence tomography and results compared to those obtained when more experienced researchers applied the microneedles to the volunteers or themselves.
Results: Volunteer self-application of the 400 μm microneedle design resulted in an approximately 30% increase in skin transepidermal water loss, which was not significantly different from that seen with self-application by the more experienced researchers or application to the volunteers. Use of optical coherence tomography showed that self-application of microneedles of the same density (400 μm, 600 μm and 900 μm) led to percentage penetration depths of approximately 75%, 70% and 60%, respectively, though the diameter of the micropores created remained quite constant at approximately 200 μm. Transepidermal water loss progressively increased with increasing height of the applied microneedles and this data, like that for penetration depth, was consistent, regardless of applicant.
Conclusion: We have shown that hydrogel-forming microneedle arrays can be successfully and reproducibly applied by human volunteers given appropriate instruction. If these outcomes were able to be extrapolated to the general patient population, then use of bespoke MN applicator devices may not be necessary, thus possibly enhancing patient compliance.

Dissolving Microneedle Delivery of Nanoparticle Encapsulated Antigen Elicits Efficient Cross-Priming and Th1 Immune Responses by Murine Langerhans Cells

Dendritic cells (DCs) of the skin play an important role in skin-mediated immunity capable of promoting potent immune responses. We availed of polymeric dissolving microneedle (MN) arrays laden with nano-encapsulated antigen to specifically target skin DC networks. This modality of immunization represents an economic, efficient and potent means of antigen delivery directly to skin DCs, which are inefficiently targeted by more conventional immunization routes. Following MN immunization, Langerhans cells (LCs) constituted the major skin DC subset capable of cross-priming antigen-specific CD8(+) T cells ex-vivo. While all DC subsets were equally efficient in priming CD4(+) T cells, LCs were largely responsible for orchestrating the differentiation of CD4(+) IFN-γ and IL-17 producing effectors. Importantly, depletion of LCs prior to immunization had a profound effect on CD8(+) CTL responses in vivo, and vaccinated animals displayed reduced protective anti-tumour and viral immunity. Interestingly, this cross-priming bias was lost following MN immunization with soluble antigen, suggesting that processing and cross-presentation of nano-particulate antigen is favoured by LCs. Therefore, these studies highlight the importance of LCs in skin immunization strategies and that targeting of nano-particulate immunogens through dissolvable polymeric MNs potentially provides a promising technological platform for improved vaccination strategies.Journal of Investigative Dermatology accepted article preview online, 22 September 2014. doi:10.1038/jid.2014.415.