Polymeric materials based on silk proteins

Silks are protein-based fibers made by arthropods for a variety of task-specific applications. In this article, we review the key features of silk proteins. This article initially focuses on the structure and function of silk proteins produced naturally by silkworms and spiders, followed by the biological and technical processing of silk proteins into a variety of morphologies (including capsules, fibers, films, foams, gels and spheres). Finally, we highlight the potential applications of silk-based materials. 

Photosensitisers - the progression from photodynamic therapy to anti-infective surfaces

Introduction: The application of light as a stimulus in pharmaceutical systems and the associated ability to provide precise spatiotemporal control over location, wavelength and intensity, allowing ease of external control independent of environmental conditionals, has led to its increased use. Of particular note is the use of light with photosensitisers.

Areas covered: Photosensitisers are widely used in photodynamic therapy to cause a cidal effect towards cells on irradiation due to the generation of reactive oxygen species. These cidal effects have also been used to treat infectious diseases. The effects and benefits of photosensitisers in the treatment of such conditions are still being developed and further realised, with the design of novel delivery strategies. This review provides an overview of the realisation of the pharmaceutically relevant uses of photosensitisers, both in the context of current research and in terms of current clinical application, and looks to the future direction of research.

Expert opinion: Substantial advances have been and are being made in the use of photosensitisers. Of particular note are their antimicrobial applications, due to absence of resistance that is so frequently associated with conventional treatments. Their potency of action and the ability to immobilise to polymeric supports is opening a wide range of possibilities with great potential for use in healthcare infection prevention strategies.

Gastroretentive Extended-Release Floating Granules Prepared Using a Novel Fluidized Hot Melt Granulation (FHMG) Technique

The objective of this work was to investigate the feasibility of using a novel granulation technique, namely, fluidized hot melt granulation (FHMG), to prepare gastroretentive extended-release floating granules. In this study we have utilized FHMG, a solvent free process in which granulation is achieved with the aid of low melting point materials, using Compritol 888 ATO and Gelucire 50/13 as meltable binders, in place of conventional liquid binders. The physicochemical properties, morphology, floating properties, and drug release of the manufactured granules were investigated. Granules prepared by this method were spherical in shape and showed good flowability. The floating granules exhibited sustained release exceeding 10 h. Granule buoyancy (floating time and strength) and drug release properties were significantly influenced by formulation variables such as excipient type and concentration, and the physical characteristics (particle size, hydrophilicity) of the excipients. Drug release rate was increased by increasing the concentration of hydroxypropyl cellulose (HPC) and Gelucire 50/13, or by decreasing the particle size of HPC. Floating strength was improved through the incorporation of sodium bicarbonate and citric acid. Furthermore, floating strength was influenced by the concentration of HPC within the formulation. Granules prepared in this way show good physical characteristics, floating ability, and drug release properties when placed in simulated gastric fluid. Moreover, the drug release and floating properties can be controlled by modification of the ratio or physical characteristics of the excipients used in the formulation.

Self-Assembled Supramolecular Gels of Reverse Poloxamers and Cyclodextrins

A series of supramolecular aggregates were prepared using a poly(propylene oxide) poly(ethylene oxide) poly(propylene oxide) (PPO-PEO-PPO) block copolymer and beta- or alpha-cyclodextrins (CD). The combination of beta-CD and the copolymer yields inclusion complexes (IC) with polypseudorotaxane structures. These are formed by complexation of the PPO blocks with beta-CD molecules producing a powder precipitate with a certain crystallinity degree that can be evaluated by X-ray diffraction (XRD). In contrast, when combining alpha-CD with the block copolymer, the observed effect is an increase in the viscosity of the mixtures, yielding fluid gels. Two cooperative effects come into play: the complexation of PEO blocks with alpha-CD and the hydrophobic interactions between PPO blocks in aqueous media. These two combined interactions lead to the formation of a macromoleculaf network. The resulting fluid gels were characterized using different techniques such as differential scanning calorimetry (DSC), viscometry, and XRD measurements.

Non-covalent hydrogels of cyclodextrins and poloxamines for the controlled release of proteins

Different types of gels were prepared by combining poloxamines (Tetronic), i.e. poly(ethylene oxide)/poly(propylene oxide) (PEO/PPO) octablock star copolymers, and cyclodextrins (CD). Two different poloxamines with the same molecular weight (ca. 7000) but different molecular architectures were used. For each of their four diblock arms, direct Tetronic 904 presents PEO outer blocks while in reverse Tetronic 90R4 the hydrophilic PEO blocks are the inner ones. These gels were prepared by combining alpha-CD and poloxamine aqueous solutions. The physicochemical properties of these systems depend on several factors such as the structure of the block copolymers and the Tetronic/alpha-CD ratio. These gels were characterized using differential scanning calorimetry (DSC), viscometry and X-ray diffraction measurements. The 90R4 gels present a consistency that makes them suitable for sustained drug delivery. The resulting gels were easily eroded: these complexes were dismantled when placed in a large amount of water, so controlled release of entrapped large molecules such as proteins (Bovine Serum Albumin, BSA) is feasible and can be tuned by varying the copolymer/CD ratio. 

A proposed model membrane and test method for microneedle insertion studies

A commercial polymeric film (Parafilm M (R), a blend of a hydrocarbon wax and a polyolefin) was evaluated as a model membrane for microneedle (MN) insertion studies. Polymeric MN arrays were inserted into Parafilm M (R) (PF) and also into excised neonatal porcine skin. Parafilm M (R) was folded before the insertions to closely approximate thickness of the excised skin. Insertion depths were evaluated using optical coherence tomography (OCT) using either a force applied by a Texture Analyser or by a group of human volunteers. The obtained insertion depths were, in general, slightly lower, especially for higher forces, for PF than for skin. However, this difference was not a large, being less than the 10% of the needle length. Therefore, all these data indicate that this model membrane could be a good alternative to biological tissue for MN insertion studies. As an alternative method to OCT, light microscopy was used to evaluate the insertion depths of MN in the model membrane. This provided a rapid, simple method to compare different MN formulations. The use of Parafilm M (R), in conjunction with a standardised force/time profile applied by a Texture Analyser, could provide the basis for a rapid MN quality control test suitable for in-process use. It could also be used as a comparative test of insertion efficiency between candidate MN formulations. 

Gold nanoparticle surface functionalization: a necessary requirement in the development of novel nanotherapeutics

With several gold nanoparticle-based therapies currently undergoing clinical trials, these treatments may soon be in the clinic as novel anticancer agents. Gold nanoparticles are the subject of a wide ranging international research effort with preclinical studies underway for multiple applications including photoablation, diagnostic imaging, radiosensitization and multifunctional drug-delivery vehicles. These applications require an increasingly complex level of surface modification in order to achieve efficacy and limit off-target toxicity. This review will discuss the main obstacles in relation to surface functionalization and the chemical approaches commonly utilized. Finally, we review a range of recent preclinical studies that aim to advance gold nanoparticle treatments toward the clinic.

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.

Potential of hydrogel-forming and dissolving microneedles for use in paediatric populations

Development of formulations and drug delivery strategies for paediatric use is challenging, partially due to the age ranges within this population, resulting in varying requirements to achieve optimised patient outcomes. Although the oral route of drug delivery remains the preferred option, there are problematic issues, such as difficulty swallowing and palatability of medicines specific to this population. The parenteral route is not well accepted by children due to needle-related fear and pain. Accordingly, a plethora of alternative routes of drug administration have been investigated. Microneedles (MN) breach the stratum corneum (SC), the outermost layer of skin, increasing the number of drug substances amenable to transdermal delivery. This strategy involves the use of micron-sized needles to painlessly, and without drawing blood, create transient aqueous conduits in the SC. In this study, polymeric dissolving MN and hydrogel-forming MN were fabricated incorporating two model drugs commonly used in paediatric patients (caffeine and lidocaine hydrochloride). The potential efficacy of these MN for paediatric dosing was investigated via in vitro and in vivo studies. Views pertaining to MN technology were sought amongst school children in Northern Ireland, members of the UK general public and UK-based paediatricians, to determine perceived benefits, acceptance, barriers and concerns for adoption of this technology. In this study, polymeric MN were shown to substantially enhance skin permeability of the model therapeutic molecules in vitro and in vivo. In particular, hydrogel-forming MN led to a 6.1-fold increase in caffeine delivery whilst lidocaine HCl delivery was increased by 3.3-fold using dissolving MN in vitro. Application of caffeine-loaded MN led to a caffeine plasma concentration of 23.87μg/mL in rats at 24h. This research also highlighted a strong consensus regarding MN technology amongst schoolchildren, paediatricians and the general public, regarding potential use of MN in the paediatric population. Overall, 93.6% of general public respondents and 85.9% of paediatricians regarded the use of MN as a positive approach.

Microneedle applications in improving skin appearance

Microneedles (MNs) are micron-sized, minimally invasive devices that breach the outermost layer of the skin, the stratum corneum (SC), creating transient, aqueous pores in the skin and facilitating the transport of therapeutic molecules into the epidermis. Following many years of extensive research in the area of MN-mediated trans- and intra-dermal drug delivery, MNs are now being exploited in the cosmeceutical industry as a means of disrupting skin cell architecture, inducing elastin and collagen expression and deposition. They are also being used as vehicles to deliver cosmeceutic molecules across the skin, in addition to their use in combinatorial treatments with topical agents or light sources. This review explores the chronology of microneedling methodologies, which has led to the emergence of MN devices, now extensively used in cosmeceutical applications. Recent developments in therapeutic molecule and peptide delivery to the skin via MN platforms are addressed and some commercially available MN devices are described. Important safety and regulatory considerations relating to MN usage are addressed, as are studies relating to public perception of MN, as these will undoubtedly influence the acceptance of MN products as they progress towards commercialisation.

Paediatricians' opinions of microneedle-mediated monitoring: a key stage in the translation of microneedle technology from laboratory into clinical practice

Microneedle (MN) arrays could offer an alternative method to traditional drug delivery and blood sampling methods. However, acceptance among key end-users is critical for new technologies to succeed. MNs have been advocated for use in children and so, paediatricians are key potential end-users. However, the opinions of paediatricians on MN use have been previously unexplored. The aim of this study was to investigate the views of UK paediatricians on the use of MN technology within neonatal and paediatric care. An online survey was developed and distributed among UK paediatricians to gain their opinions of MN technology and its use in the neonatal and paediatric care settings, particularly for MN-mediated monitoring. A total of 145 responses were obtained, with a completion response rate of 13.7 %. Respondents believed an alternative monitoring technique to blood sampling in children was required. Furthermore, 83 % of paediatricians believed there was a particular need in premature neonates. Overall, this potential end-user group approved of the MN technology and a MN-mediated monitoring approach. Minimal pain and the perceived ease of use were important elements in gaining favour. Concerns included the need for confirmation of correct application and the potential for skin irritation. The findings of this study provide an initial indication of MN acceptability among a key potential end-user group. Furthermore, the concerns identified present a challenge to those working within the MN field to provide solutions to further improve this technology. The work strengthens the rationale behind MN technology and facilitates the translation of MN technology from lab bench into the clinical setting.

Considerations in the sterile manufacture of polymeric microneedle arrays

We describe, for the first time, considerations in the sterile manufacture of polymeric microneedle arrays. Microneedles (MN) made from dissolving polymeric matrices and loaded with the model drugs ovalbumin (OVA) and ibuprofen sodium and hydrogel-forming MN composed of "super-swelling" polymers and their corresponding lyophilised wafer drug reservoirs loaded with OVA and ibuprofen sodium were prepared aseptically or sterilised using commonly employed sterilisation techniques. Moist and dry heat sterilisation, understandably, damaged all devices, leaving aseptic production and gamma sterilisation as the only viable options. No measureable bioburden was detected in any of the prepared devices, and endotoxin levels were always below the US Food & Drug Administration limits (20 endotoxin units/device). Hydrogel-forming MN were unaffected by gamma irradiation (25 kGy) in terms of their physical properties or capabilities in delivering OVA and ibuprofen sodium across excised neonatal porcine skin in vitro. However, OVA content in dissolving MN (down from approximately 101.1 % recovery to approximately 58.3 % recovery) and lyophilised wafer-type drug reservoirs (down from approximately 99.7 % recovery to approximately 60.1 % recovery) was significantly reduced by gamma irradiation, while the skin permeation profile of ibuprofen sodium from gamma-irradiated dissolving MN was markedly different from their non-irradiated counterparts. It is clear that MN poses a very low risk to human health when used appropriately, as evidenced here by low endotoxin levels and absence of microbial contamination. However, if guarantees of absolute sterility of MN products are ultimately required by regulatory authorities, it will be necessary to investigate the effect of lower gamma doses on dissolving MN loaded with active pharmaceutical ingredients and lyophilised wafers loaded with biomolecules in order to avoid the expense and inconvenience of aseptic processing.

A novel scalable manufacturing process for the production of hydrogel-forming microneedle arrays

A novel manufacturing process for fabricating microneedle arrays (MN) has been designed and evaluated. The prototype is able to successfully produce 14 × 14 MN arrays and is easily capable of scale-up, enabling the transition from laboratory to industry and subsequent commercialisation. The method requires the custom design of metal MN master templates to produce silicone MN moulds using an injection moulding process. The MN arrays produced using this novel method was compared with centrifugation, the traditional method of producing aqueous hydrogel-forming MN arrays. The results proved that there was negligible difference between either methods, with each producing MN arrays with comparable quality. Both types of MN arrays can be successfully inserted in a skin simulant. In both cases the insertion depth was approximately 60% of the needle length and the height reduction after insertion was in both cases approximately 3%.

The potential of electron beam irradiation for simultaneous surface modification and bioresorption control of PLLA for medical device applications

Bioresorbable polymers have been widely investigated as materials exhibiting significant potential for successful application in the medical fields of bone fixation devices and drug delivery. Further to the ability to control degradation, surface engineering of polymers has been highlighted as a key method central to their development. Previous work has demonstrated the ability of electron beam (e-beam) technology to control the degradation profiles and bioresorption of a number of commercially relevant bioresorbable polymers (poly-l-lactic acid (PLLA), L-lactide/ DL-lactide co-polymer (PLDL) and poly(lactic-co-glycolic acid) (PLGA). This work investigates the further potential of e-beam technology to impart added biofunctionality through the manipulation of polymer (PLLA) surface properties. A Dynamatron Continuous DC e-beam unit (Synergy Health, UK), with beam energies of 0.5, 0.75, and 1.5 MeV, was used for the irradiation of PLLA samples with delivered surface doses of 150 or 500 kGy at each energy level. The chosen conditions reflect the need to achieve a specific surface modification for the control of surface degradation as demonstrated in previous work. Surface characterization was then performed using contact angle analysis, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and atomic force microscopy.
Results demonstrated a significant increase in surface wettability post e-beam treatment. In correlation with this, XPS data showed the introduction of oxygen-containing functional groups to the surface of PLLA. Raman spectroscopy indicated chain scission in the near surface region of PLLA. E-beam irradiation did not seem to affect the surface roughness of PLLA as a direct consequence of the treatment. In conclusion electron beam surface modification has been found to modify both the surface-to-bulk bioresorption profile and the surface hydrophilicity. Both could provide benefits in relation to the performance of implantable medical devices.

Ultrashort self-assembling peptidomimetic nanomaterials target resistant pathogenic infections

The impending and increasing threat of antimicrobial resistance has led to a greater focus into developing alternative therapies as substitutes for traditional antibiotics for the treatment of multi-drug resistant infections.1 Our group has developed a library of short, cost-effective, diphenylalanine-based peptides (X1-FF-X2) which selective eradicate (viability reduced >90% in 24 hours) the most resistant biofilm forms of a range of Gram-positive and negative pathogens including: methicillin resistant and sensitive Staphyloccoccus aureus and Staphyloccoccus epidermidis; Pseudomonas aeruginosa, Proteus mirabilis and Escherichia coli. They demonstrate a reduced cell cytotoxic profile (NCTC929 murine fibroblast) and limited haemolysis.2 Our molecules have the ability respond to subtle changes in pH, associated with bacterial infection, self-assembling to form β-sheet secondary structures and supramolecular hydrogels at low concentrations (~0.5%w/v). Conjugation of variety of aromatic-based drugs at the X1 position, including non-steroidal anti-inflammatories (NSAIDs), confer further pharmacological properties to the peptide motif enhancing their therapeutic potential. In vivo studies using waxworms (Galleria mellonella) provide promising preliminary results demonstrating the low toxicity and high antimicrobial activity of these low molecular weight gelators in animal models. This work shows biofunctional peptide-based nanomaterials hold great promise for future translation to patients as antimicrobial drug delivery and biomaterial platforms.3 [1] G. Laverty, S.P. Gorman and B.F. Gilmore. Int.J.Mol.Sci. 2011, 12, 6566-6596. [2] G. Laverty, A.P. McCloskey, B.F. Gilmore, D.S. Jones, J Zhou, B Xu. Biomacromolecules. 2014, 15, 9, 3429-3439. [3] A.P. McCloskey, B.F. Gilmore and G.Laverty. Pathogens. 2014, 3, 791-821.