A comprehensive review on photoacoustic-based devices for biomedical applications

The photoacoustic effect is an emerging technology that has sparked significant interest in the research field since an acoustic wave can be produced simply by the incidence of light on a material or tissue. This phenomenon has been extensively investigated, not only to perform photoacoustic imaging but also to develop highly miniaturized ultrasound probes that can provide biologically meaningful information. Therefore, this review aims to outline the materials and their fabrication process that can be employed as photoacoustic targets, both biological and non-biological, and report the main components’ features to achieve a certain performance. When designing a device, it is of utmost importance to model it at an early stage for a deeper understanding and to ease the optimization process. As such, throughout this article, the different methods already implemented to model the photoacoustic effect are introduced, as well as the advantages and drawbacks inherent in each approach. However, some remaining challenges are still faced when developing such a system regarding its fabrication, modeling, and characterization, which are also discussed.This work was supported by Fundação para a Ciência e Tecnologia national funds, under the national support to R&D units grant, through the reference project UIDB/04436/2020 and UIDP/04436/2020

Simulação e desenvolvimento de uma sonda de ultrassom baseada em fotoacústica suportada por nanotecnologia para aplicações biomédicas

Dissertação de mestrado em Biomedical Engineering, Medical Electronics BranchO presente trabalho tem como intuito o desenvolvimento de uma sonda de ultrassom altamente miniaturizada, uma vez que existe uma escassez de técnicas adequadas para a monitorização em tempo real de procedimentos minimamente invasivos. A título de exemplo, um dispositivo deste tipo seria altamente vantajoso durante a ressecção de um tumor cerebral, visto que, durante este procedimento, se dá uma alteração da posição do tecido cerebral, causando diferenças notórias entre as imagens pré operatórias e a atual posição dos tecidos. O ultrassom é uma técnica de imagiologia bastante popular por auferir vantagens únicas, das quais se destacam a sua segurança por não usar radiação ionizante, a sua capacidade de fornecer imagens em tempo real, o seu baixo custo e não invasibilidade. Contudo, as sondas de ultrassom convencionais possuem grandes dimensões, o que as torna inadequadas para o uso em cirurgias minimamente invasivas. Assim, neste trabalho foram geradas ondas de ultrassom em consequência da incidência de pulsos de luz numa amostra de MWCNTs coberta com PDMS através do efeito fotoacústico, o qual permite uma elevada miniaturização. Uma conceção teórica e um modelo de simulação numa ferramenta de simulação multifísica foram incluídas para averiguar a influência dos diversos parâmetros no desempenho do sistema. Através desse modelo, obteve-se um emissor acústico direcional com 50 m de dimensão lateral, uma frequência de emissão máxima de 9 MHz e uma pressão acústica de 13.5 Pa a uma distância de 0.3 mm. De seguida, foi implementada uma configuração experimental com o intuito de verificar a ocorrência do efeito fotoacústico, sendo que nessas condições seria previsto, pelo modelo de simulação, a deteção de uma onda com 415 kPa a 0.3 mm maioritariamente à frequência de 400 kHz. Na prática, foi detetada uma onda com cerca de 250 kPa de amplitude a 2 MHz, bem como múltiplas réplicas resultantes da reflexão dessa onda nas paredes do recipiente onde se encontrava a amostra. Os benefícios supracitados tornam esta técnica bastante promissora para a melhoria dos cuidados de saúde prestados, possibilitando uma monitorização em tempo real mais precisa durante procedimentos minimamente invasivos. Como tal, estas cirurgias proporcionarão melhores resultados, aumentando as taxas de sucesso e a qualidade de vida dos pacientes.This work aims to develop a highly miniaturized ultrasound probe since there is a lack of suitable real-time monitoring techniques that can be used during minimally invasive procedures. For example, such device could be highly beneficial during brain tumor resection as a brain shift occurs entailing noticeable differences between pre-operative imaging and the actual positioning of the tissues. Ultrasound is a very popular imaging technique due to its singular advantages, such as safety because it doesn’t use ionizing radiation, ability to provide real-time imaging, disposability, low cost, and non-invasiveness. However, conventional ultrasound probes have a large size that is inadequate for minimally invasive surgeries. As such, in this work, ultrasound waves were generated through the photoacoustic effect, which allows a high degree of miniaturization of an ultrasound probe, as a result of the incidence of light pulses on a sample of MWCNTs covered by PDMS. A theoretical design and a simulation model in a multiphysics simulation tool were included to examine the influence of the different parameters on the system's performance. It was possible to obtain a directional ultrasound emitter through this model with a lateral dimension of 50 m, a maximum emission frequency of 9 MHz, and an acoustic pressure of 13.5 Pa at a distance of 0.3 mm. Afterwards, an experimental setup was developed with the purpose of verifying the occurrence of the photoacoustic effect, and under these conditions, a wave with 415 kPa at a distance of 0.3 mm and with a frequency mainly at 400 kHz was predicted by the simulation model. The photoacoustic system allowed the experimental detection of an acoustic wave with an amplitude around 250 kPa at a frequency of 2 MHz, as well as multiple replicas resulting from the reflection of this wave on the walls of the container where the sample was located. All abovementioned benefits of this technique make it very promising to improve the provided medical care, allowing more accurate real-time monitoring during minimally invasive procedures. As such, better outcomes can be achieved from these surgeries, thus improving success rates and patients’ life quality

Characterisation of microbial attack on archaeological bone

As part of an EU funded project to investigate the factors influencing bone preservation in the archaeological record, more than 250 bones from 41 archaeological sites in five countries spanning four climatic regions were studied for diagenetic alteration. Sites were selected to cover a range of environmental conditions and archaeological contexts. Microscopic and physical (mercury intrusion porosimetry) analyses of these bones revealed that the majority (68%) had suffered microbial attack. Furthermore, significant differences were found between animal and human bone in both the state of preservation and the type of microbial attack present. These differences in preservation might result from differences in early taphonomy of the bones. © 2003 Elsevier Science Ltd. All rights reserved