Curved Microneedle Array-Based sEMG Electrode for Robust Long-Term Measurements and High Selectivity

Surface electromyography is widely used in many fields to infer human intention. However, conventional electrodes are not appropriate for long-term measurements and are easily influenced by the environment, so the range of applications of sEMG is limited. In this paper, we propose a flexible band-integrated, curved microneedle array electrode for robust long-term measurements, high selectivity, and easy applicability. Signal quality, in terms of long-term usability and sensitivity to perspiration, was investigated. Its motion-discriminating performance was also evaluated. The results show that the proposed electrode is robust to perspiration and can maintain a high-quality measuring ability for over 8 h. The proposed electrode also has high selectivity for motion compared with a commercial wet electrode and dry electrode.open111615Ysciescopu

Madden, Julia; O'Mahony, Conor; Thompson, Michael; O'Riordan, Alan; Galvin, Paul

This article explores recent advances in the development of electrochemical biosensors on microneedle platforms towards on-device sensing of biomarkers present in dermal interstitial fluid. The integration of a biosensor with a microneedle platform opens the possibility for minimally invasive bio-chemical detection or continuous monitoring within the dermal interstitial fluid. An introduction to interstitial fluid is provided placing emphasis on sampling methods that have been employed to extract and/or sample tissue fluid for analysis. We look briefly at microneedle technologies used to extract dermal interstitial fluid for subsequent analysis. Successive content will focus on microneedle technologies which have been integrated with electrochemical biosensors for the quantification of various metabolites, electrolytes and other miscellaneous entities known to be present in the dermal interstitial fluid. The review concludes with some of the key challenges and opportunities faced by this next-generation wearable sensing technology

Curved Microneedle Array-Based sEMG Electrode for Robust Long-Term Measurements and High Selectivity

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Curved Microneedle Array-Based sEMG Electrode for Robust Long-Term Measurements and High Selectivity

Surface electromyography is widely used in many fields to infer human intention. However, conventional electrodes are not appropriate for long-term measurements and are easily influenced by the environment, so the range of applications of sEMG is limited. In this paper, we propose a flexible band-integrated, curved microneedle array electrode for robust long-term measurements, high selectivity, and easy applicability. Signal quality, in terms of long-term usability and sensitivity to perspiration, was investigated. Its motion-discriminating performance was also evaluated. The results show that the proposed electrode is robust to perspiration and can maintain a high-quality measuring ability for over 8 h. The proposed electrode also has high selectivity for motion compared with a commercial wet electrode and dry electrode

Transdermal Delivery Systems Based on Natural Polymeric Biomaterials

The human skin provides a unique delivery pathway for therapeutic and other active agents. Although several approaches have been proposed and implemented, including the use of syn-thetic and natural polymers, there is a persistent pursuit of alternative biomaterials for enhanc-ing the development of transdermal delivery systems. Therefore, in this study, natural poly-mers, namely the chitin-glucan complex (CGC), FucoPol, and polyhydroxyalkanoates (PHA), have been prospected for use as biomaterials for the fabrication of hydrogels and micronee-dles (MN) arrays, two innovative approaches for efficient and controlled drug delivery through the skin. CGC was solubilized using NaOH/urea solvent systems through a freeze/thaw procedure, overcoming its previous insolubility challenge. This approach resulted in a significant solubili-zation rate of 63–68%, yielding a chitosan-glucan complex (ChGC). Based on this process, hy-drogels were fabricated using different alkali solvent systems, NaOH and KOH solutions, via a freeze-thaw procedure. The hydrogels exhibited varying microstructures, viscoelastic proper-ties, and textures depending on the type of solvent used and their ionic strength. Furthermore, the hydrogels were biocompatible. Subsequently, optimization of the process parameters al-lowed the reduction of the time needed to prepare the CGC hydrogels, and the optimized structures demonstrated a spontaneous swelling ratio and good water retention capacity. When loaded with caffeine, hydrogels' mechanical and rheological properties were significantly affected, and the caffeine release rate depended on the pH and ionic strength of the surround-ing solution. Additionally, it was shown that increasing the CGC concentration led to the for-mation of hydrogels with a denser and tighter microstructure and increased their mechanical and rheological parameters. The hydrogels were loaded with different types of active pharma-ceutical ingredients (APIs), exhibiting permeation fluxes through artificial membranes corre-lated to the APIs' physicochemical characteristics. FucoPol was used as a structuring agent to fabricate hydrogel membranes (HMs) using Fe3+ as a crosslinker. It was demonstrated that, after a threshold of 1.5 g/L, Fe3+ concentration had a limited effect on HMs strength, while varying the concentration of FucoPol significantly in-fluenced their properties. Three FucoPol concentrations (1.0, 1.75, and 2.5wt%) combined with Fe3+ (1.5 g/L) resulted in HMs with varying microstructures, swelling ratios, and hardness values. These HMs were non-cytotoxic and exhibited anti-inflammatory properties. Additionally, the FucoPol HMs were loaded with caffeine or diclofenac sodium using different methods to assess drug loading capacity. The results showed that the loading method had an impact on the me-chanical and rheological properties of the HMs and led to distinct drug release profiles. PHAs with different compositions, including homopolymer poly(3-hydroxybutyrate) (PHB), copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) with varying HV content (14, 43, and 87wt%), and terpolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hy-droxyhexanoate) (PHBVHx), were used to fabricate MNs through a micromolding process. While these biopolymers were successfully utilized for MN fabrication, their distinct physico-chemical properties led to MNs with differing characteristics. PHB, PHBV (43% HV), and PHBVHx produced sharp MNs with similar failure forces (~5.5 N), suggesting the ability to pierce the human skin. PHBVHx MNs displayed greater deformation resistance and insertion studies in Parafilm multilayer systems revealed their ability to penetrate up to 396 μm without breaking. Furthermore, diclofenac sodium was coated onto PHBVHx MNs and the resulting coated MNs exhibited comparable failure forces, decreased mechanical stiffness, and a rapid drug release profile. Overall, this work demonstrated that the natural polymers CGC, FucoPol, and PHAs can be used as structuring agents for the development of novel biomaterials, namely, hydrogels and MNs, with very promising properties, thus contributing to the sustainable fabrication of im-proved transdermal delivery systems.A pele humana proporciona uma via de administração única para agentes terapêuticos e outros compostos ativos. Embora várias abordagens tenham sido propostas e implementadas, incluindo o uso de polímeros sintéticos e naturais, persiste a procura por biomateriais alterna-tivos para melhorar o desenvolvimento de sistemas de administração transdérmica. Assim, nesta tese foram utilizados biomateriais naturais, nomeadamente o complexo quitina-glucano (CQG), FucoPol e polihidroxialcanoatos (PHAs), na fabricação de hidrogéis e matrizes de mi-croagulhas (MN), duas abordagens inovadoras para entrega eficiente e controlada de fármacos através da pele. CQG foi solubilizado utilizando sistemas de solventes NaOH/ureia através de um procedi-mento de congelamento/descongelamento, superando seu desafio de insolubilidade. Esta abordagem resultou em uma taxa de solubilização significativa de 63–68%, produzindo um complexo quitosano-glucano (ChGC). Com base nesse processo, foram fabricados hidrogéis utilizando diferentes sistemas de solventes alcalinos, nomeadamente soluções de NaOH e KOH, por meio de um procedimento de congelamento/descongelamento. Esses hidrogéis apresentaram microestruturas, propriedades viscoelásticas e texturas variáveis, dependendo do tipo de solvente utilizado e da sua força iónica. Além disso, os hidrogéis demonstraram ser biocompatíveis. Posteriormente, a otimização dos parâmetros do processo permitiu a redução do tempo necessário para preparar os hidrogéis, e as estruturas otimizadas demonstraram absorção de água espontânea, bem como uma boa capacidade de retenção de água. Quando carregados com cafeína, as propriedades mecânicas e reológicas dos hidrogéis foram signifi-cativamente afetadas, e a taxa de liberação de cafeína dependeu do pH e da força iónica da solução de libertação. Além disso, foi demonstrado que o aumento da concentração de CQG levou à formação de hidrogéis com uma microestrutura mais densa e compacta, e ao aumento dos parâmetros mecânicos e reológicos. Os hidrogéis de CQG foram capazes de ser carregados com diferentes tipos de ingredientes farmacêuticos ativos (APIs), exibindo fluxos de permeação através de membranas artificiais correlacionados com as características físico-químicas dos APIs. FucoPol foi utilizado como agente estruturante no fabrico de membranas de hidrogel (HMs) usando Fe3+ como reticulante. Foi demonstrado que, acima de um valor de 1,5 g/L, a concen-tração de Fe3+ tem um efeito limitado na resistência das membranas, enquanto a variação da concentração de FucoPol influenciou significativamente suas propriedades. Três concentrações de FucoPol (1,0, 1,75 e 2,5%) combinadas com Fe3+ (1,5 g/L) resultaram em membranas com diferentes microestruturas, capacidade de absorção de água e propriedades mecânicas. As membranas demonstraram ser biocompatíveis, exibindo propriedades anti-inflamatórias. Além disso, as membranas de FucoPol foram carregadas com cafeína ou diclofenac de sódio através de diferentes métodos para avaliar a sua capacidade de incorporação de fármacos. Os resul-tados demostraram que o método de incorporação utilizado teve impacto nas propriedades mecânicas e reológicas das membranas, levando a perfis distintos de libertação. PHAs com diferentes composições, incluindo PHB, PHBV com diferentes conteúdos em 3HV (14, 43 e 87%), e PHBVHx, foram usados para fabricar MNs através de um processo de micro-moldagem por fusão. Embora estes biopolímeros tenham sido bem-sucedidos no fabrico das MNs, as suas distintas propriedades físico-químicas resultaram em MNs com características diferentes. PHB, PHBV contendo 43% em 3HV, e PHBVHx produziram MNs pontiagudas com forças de falha semelhantes (~5,5 N), sugerindo capacidade de perfurar a pele humana. As MNs de PHBVHx exibiram maior resistência à deformação e estudos de inserção em sistemas multicamadas de Parafilm revelaram a sua capacidade de penetrar até 396 μm sem quebrar. Além disso, diclofenac de sódio foi utilizado para revestir MNs de PHBVHx, sendo que as MNs revestidas apresentaram forças de falha comparáveis às MNs não revestidas, rigidez mecânica diminuída e um perfil de libertação rápida do fármaco. No geral, esta tese demonstrou que os polímeros naturais CGC, FucoPol e PHAs podem ser usados como agentes de estruturação para o desenvolvimento de novos biomateriais, nome-adamente, hidrogéis e MNs, com propriedades muito promissoras, contribuindo, assim, para a fabricação sustentável de melhores sistemas de administração transdérmica