41 results found
Terzano M, Spagnoli A, Dini D, et al., 2021, Fluid-solid interaction in the rate-dependent failure of brain tissue and biomimicking gels, Journal of The Mechanical Behavior of Biomedical Materials, Vol: 119, ISSN: 1751-6161
Brain tissue is a heterogeneous material, constituted by a soft matrix filledwith cerebrospinal fluid. The interactions between, and the complexity of eachof these components are responsible for the non-linear rate-dependent behaviourthat characterizes what is one of the most complex tissue in nature. Here, weinvestigate the influence of the cutting rate on the fracture properties ofbrain, through wire cutting experiments. We also present a model for therate-dependent behaviour of fracture propagation in soft materials, whichcomprises the effects of fluid interaction through a poro-hyperelasticformulation. The method is developed in the framework of finite straincontinuum mechanics, implemented in a commercial finite element code, andapplied to the case of an edge-crack remotely loaded by a controlleddisplacement. Experimental and numerical results both show a toughening effectwith increasing rates, which is linked to the energy dissipated by thefluid-solid interactions in the process zone ahead of the crack.
Dine A, Bentley E, PoulmarcK L, et al., 2021, A dual nozzle 3D printing system for super soft composite hydrogels, HardwareX, Vol: 9, ISSN: 2468-0672
Due to their inability to sustain their own weight, 3D printing materials as soft as human tissues is challenging. Hereby we describe the development of an extrusion additive manufacturing (AM) machine able to 3D print super soft hydrogels with micro-scale precision. By designing and integrating new subsystems into a conventional extrusion-based 3D printer, we obtained hardware that encompasses a range of new capabilities. In particular, we integrated a heated dual nozzle extrusion system and a cooling platform in the new system. In addition, we altered the electronics and software of the 3D printer to ensure fully automatized procedures are delivered by the 3D printing device, and super-soft tissue mimicking parts are produced. With regards to the electronics, we added new devices to control the temperature of the extrusion system. As for the software, the firmware of the conventional 3D printer was changed and modified to allow for the flow rate control of the ink, thus eliminating overflows in sections of the printing path where the direction/speed changes sharply.
Jin L, Forte AE, Bertoldi K, 2021, Mechanical Valves for On-Board Flow Control of Inflatable Robots, Advanced Science
Inflatable robots are becoming increasingly popular, especially in applications where safe interactions are a priority. However, designing multifunctional robots that can operate with a single pressure input is challenging. A potential solution is to couple inflatables with passive valves that can harness the flow characteristics to create functionality. In this study, simple, easy to fabricate, lightweight, and inexpensive mechanical valves are presented that harness viscous flow and snapping arch principles. The mechanical valves can be fully integrated on-board, enabling the control of the incoming airflow to realize multifunctional robots that operate with a single pressure input, with no need for electronic components, cables, or wires. By means of three robotic demos and guided by a numerical model, the capabilities of the valves are demonstrated and optimal input profiles are identified to achieve prescribed functionalities. The study enriches the array of available mechanical valves for inflatable robots and enables new strategies to realize multifunctional robots with on-board flow control.
Deng B, Yu S, Forte AE, et al., 2020, Characterization, stability, and application of domain walls in flexible mechanical metamaterials., Proc Natl Acad Sci U S A, Vol: 117, Pages: 31002-31009
Domain walls, commonly occurring at the interface of different phases in solid-state materials, have recently been harnessed at the structural scale to enable additional modes of functionality. Here, we combine experimental, numerical, and theoretical tools to investigate the domain walls emerging upon uniaxial compression in a mechanical metamaterial based on the rotating-squares mechanism. We first show that these interfaces can be generated and controlled by carefully arranging a few phase-inducing defects. We establish an analytical model to capture the evolution of the domain walls as a function of the applied deformation. We then employ this model as a guideline to realize interfaces of complex shape. Finally, we show that the engineered domain walls modify the global response of the metamaterial and can be effectively exploited to tune its stiffness as well as to guide the propagation of elastic waves.
We present a two-part hands-on science outreach demonstration utilizing composite hydrogels to produce realistic models of the human brain. The blends of poly(vinyl alcohol) and Phytagel closely match the mechanical properties of real brain tissue under conditions representative of surgical operations. The composite hydrogel is simple to prepare, biocompatible, and nontoxic, and the required materials are widely available and inexpensive. The first part of the demonstration gives participants the opportunity to feel how soft and deformable our brains are. The second part allows students to perform a mock brain surgery on a simulated tumor. The demonstration tools are suitable for public engagement activities as well as for various student training groups. The activities encompass concepts in polymer chemistry, materials science, and biology.
Jin L, Forte AE, Deng B, et al., 2020, Kirigami-Inspired Inflatables with Programmable Shapes., Adv Mater, Vol: 32
Kirigami, the Japanese art of paper cutting, has recently enabled the design of stretchable mechanical metamaterials that can be easily realized by embedding arrays of periodic cuts into an elastic sheet. Here, kirigami principles are exploited to design inflatables that can mimic target shapes upon pressurization. The system comprises a kirigami sheet embedded into an unstructured elastomeric membrane. First, it is shown that the inflated shape can be controlled by tuning the geometric parameters of the kirigami pattern. Then, by applying a simple optimization algorithm, the best parameters that enable the kirigami inflatables to transform into a family of target shapes at a given pressure are identified. Furthermore, thanks to the tessellated nature of the kirigami, it is shown that we can selectively manipulate the parameters of the single units to allow the reproduction of features at different scales and ultimately enable a more accurate mimicking of the target.
Etard O, Kegler M, Braiman C, et al., 2019, Decoding of selective attention to continuous speech from the human auditory brainstem response, NeuroImage, Vol: 200, Pages: 1-11, ISSN: 1053-8119
Humans are highly skilled at analysing complex acoustic scenes. The segregation of different acoustic streams and the formation of corresponding neural representations is mostly attributed to the auditory cortex. Decoding of selective attention from neuroimaging has therefore focussed on cortical responses to sound. However, the auditory brainstem response to speech is modulated by selective attention as well, as recently shown through measuring the brainstem's response to running speech. Although the response of the auditory brainstem has a smaller magnitude than that of the auditory cortex, it occurs at much higher frequencies and therefore has a higher information rate. Here we develop statistical models for extracting the brainstem response from multi-channel scalp recordings and for analysing the attentional modulation according to the focus of attention. We demonstrate that the attentional modulation of the brainstem response to speech can be employed to decode the attentional focus of a listener from short measurements of 10 s or less in duration. The decoding remains accurate when obtained from three EEG channels only. We further show how out-of-the-box decoding that employs subject-independent models, as well as decoding that is independent of the specific attended speaker is capable of achieving similar accuracy. These results open up new avenues for investigating the neural mechanisms for selective attention in the brainstem and for developing efficient auditory brain-computer interfaces.
Saiz Alia M, Forte A, Reichenbach J, 2019, Individual differences in the attentional modulation of the human auditory brainstem response to speech inform on speech-in-noise deficits, Scientific Reports, Vol: 9, ISSN: 2045-2322
People with normal hearing thresholds can nonetheless have difficulty with understanding speech in noisy backgrounds. The origins of such supra-threshold hearing deficits remain largely unclear. Previously we showed that the auditory brainstem response to running speech is modulated by selective attention, evidencing a subcortical mechanism that contributes to speech-in-noise comprehension. We observed, however, significant variation in the magnitude of the brainstem’s attentional modulation between the different volunteers. Here we show that this variability relates to the ability of the subjects to understand speech in background noise. In particular, we assessed 43 young human volunteers with normal hearing thresholds for their speech-in-noise comprehension. We also recorded their auditory 30brainstem responses to running speech when selectively attending to one of two competing voices. To control for potential peripheral hearing deficits, and in particular for cochlear synaptopathy, we further assessed noise exposure, the temporal sensitivity threshold, the middle-ear muscle reflex, and the auditory-brainstem response to clicks in various levels of background noise. These tests did not show evidence for cochlear synaptopathy amongst the volunteers. Furthermore, we found that only the attentional modulation of the brainstem response to speech was significantly related to speech-in-noise comprehension. Our results therefore evidence an impact of top-down modulation of brainstem activity on the variability in speech-in-noise comprehension amongst the subjects.
BinKhamis G, Forte AE, Reichenbach J, et al., 2019, Speech auditory brainstem responses in adult hearing aid users: Effects of aiding and background noise, and prediction of behavioral measures, Trends in Hearing, Vol: 23, Pages: 1-20, ISSN: 2331-2165
Evaluation of patients who are unable to provide behavioral responses on standard clinical measures is challenging due to the lack of standard objective (non-behavioral) clinical audiological measures that assess the outcome of an intervention (e.g. hearing aids). Brainstem responses to short consonant-vowel stimuli (speech-ABRs) have been proposed as a measure of subcortical encoding of speech, speech detection, and speech-in-noise performance in individuals with normal hearing. Here, we investigated the potential of speech-ABRs as an objective clinical outcome measure of speech detection, speech-in-noise detection and recognition, and self-reported speech understanding in adults with sensorineural hearing loss. We compared aided and unaided speech-ABRs, and speech-ABRs in quiet and in noise. Additionally, we evaluated whether speech-ABR F0 encoding (obtained from the complex cross-correlation with the 40 ms [da] fundamental waveform) predicted aided behavioral speech recognition in noise and/or aided self-reported speech understanding. Results showed: (i) aided speech-ABRs had earlier peak latencies, larger peak amplitudes, and larger F0 encoding amplitudes compared to unaided speech-ABRs; (ii) the addition of background noise resulted in later F0 encoding latencies, but did not have an effect on peak latencies and amplitudes, or on F0 encoding amplitudes; and (iii) speech-ABRs were not a significant predictor of any of the behavioral or self-report measures. These results show thatspeech-ABR F0 encoding is not a good predictor of speech-in-noise recognition or self reported speech understanding with hearing aids. However, our results suggest that speech- ABRs may have potential for clinical application as an objective measure of speech detection with hearing aids.
Carpenter G, Bozorgi S, Vladescu S, et al., 2019, A study of saliva lubrication using a compliant oral mimic, Food Hydrocolloids, Vol: 92, Pages: 10-18, ISSN: 0268-005X
Due to ethical issues and the difficulty in obtaining biological tissues, it is important to find synthetic elastomers that can be used as replacement test media for research purposes. An important example of this is friction testing to understand the mechanisms behind mouthfeel attributes during food consumption (e.g. syrupy, body and clean finish), which requires an oral mimic. In order to assess the suitability of possible materials to mimic oral surfaces, a sliding contact is produced by loading and sliding a hemispherical silica pin against either a polydimethyl siloxane (PDMS), agarose, or porcine tongue sample. Friction is measured and elastohydrodynamic film thickness is calculated based on the elastic modulus of the samples, which is measured using an indentation method. Tests were performed with both saliva and pure water as the lubricating fluid and results compared to unlubricated conditions.PDMS mimics the tongue well in terms of protein adhesion, with both samples showing significant reductions in friction when lubricated with saliva versus water, whereas agarose showed no difference between saliva and water lubricated conditions. This is attributed to PDMS's OSi(CH3)2- group which provides excellent adhesion for the saliva protein molecules, in contrast with the hydrated agarose surface. The measured modulus of the PDMS (2.2 MPa) is however significantly greater than that of tongue (3.5 kPa) and agarose (66–174 kPa). This affects both the surface (boundary) friction, at low sliding speeds, and the entrained elastohydrodynamic film thickness, at high speeds.Utilising the transparent PDMS sample, we also use fluorescence microscopy to monitor the build-up and flow of dyed-tagged saliva proteins within the contact during sliding. Results confirm the lubricous boundary film forming nature of saliva proteins by showing a strong correlation between friction and average protein intensity signals (cross correlation coefficient = 0.87). This demonstrates
Saiz-Alia M, Forte AE, Reichenbach T, 2019, Selective attention in the brainstem and speech-in-noise comprehension, Pages: 5641-5646, ISSN: 2226-7808
Understanding speech in noise is a challenging task. Moreover, the ability to understand speech in background noise varies considerably from person to person, even for people that have normal audiograms and hence no measurable hearing loss. Recently we proposed a method for measuring the brainstem's response to natural non-repetitive speech and showed that this response is modulated by selective attention to one of two competing speakers. Here we investigate to what extent this brainstem response varies from subject to subject. We find significant between-subject variation in the amplitude of the brainstem response to continuous speech, in its latency, signal-to-noise-ratio, as well as in its modulation by selective attention. This variability may result from impairments in the auditory periphery, such a cochlear synaptopathy, as well as from damages of the neural pathways in the brainstem and in the central nervous system that are responsible for sound processing, and may potentially lead to deficits with speech-in-noise comprehension.
Tan Z, Dini D, Rodriguez y Baena F, et al., 2018, Composite hydrogel: A high fidelity soft tissue mimic for surgery, Materials and Design, Vol: 160, Pages: 886-894, ISSN: 0264-1275
Accurate tissue phantoms are difficult to design due to the complex non-linear viscoelastic properties of real soft tissues. A composite hydrogel, resulting from a mix of poly(vinyl) alcohol and phytagel, is able to reproduce the viscoelastic responses of different soft tissues due to its compositional tunability. The aim of this work is to demonstrate the flexibility of the composite hydrogel in mimicking the interactions between surgical tools and various soft tissues, such as brain, lung and liver. Therefore compressive stiffness, insertion forces and frictional forces were used as matching criteria to determine the hydrogel compositions for each soft tissue. A full map of the behaviour of the synthetic material is provided for these three characteristics and the compositions found to best match the mechanical response of brain, lung and liver are reported. The optimised hydrogel samples are then tested and shown to mimic the behaviour of the three tissues with unprecedented fidelity. The effect of each hydrogel constituent on the compressive stiffness, needle insertion and frictional forces is also detailed in this work to explain their individual contributions and synergistic effects. This study opens important opportunities for the realisation of surgical planning and training devices and tools for in-vitro tissue testing.
Tan Z, Forte A, Rodriguez y Baena F, et al., 2018, Needle-tissue interactions during convection enhanced drug delivery in neurosurgery, International Conference on BioTribology
Forte AE, Etard OE, Reichenbach JDT, 2018, Selective Auditory Attention At The Brainstem Level, ARO 2018
Saiz Alia M, Askari A, Forte AE, et al., 2018, A model of the human auditory brainstem response to running speech, ARO 2018
Kegler M, Etard OE, Forte AE, et al., 2018, Complex Statistical Model for Detecting the Auditory Brainstem Response to Natural Speech and for Decoding Attention from High-Density EEG Recordings, ARO 2018
Etard OE, Kegler M, Braiman C, et al., 2018, Real-time decoding of selective attention from the human auditory brainstem response to continuous speech, BioRxiv
Conventional 3D bioprinting allows fabrication of 3D scaffolds for biomedical applications. In this contribution we present a cryogenic 3D printing method able to produce stable 3D structures by utilising the liquid to solid phase change of a composite hydrogel (CH) ink. This is achieved by rapidly cooling the ink solution below its freezing point using solid carbon dioxide (CO2) in an isopropanol bath. The setup was able to successfully create 3D complex geometrical structures, with an average compressive stiffness of O(1) kPa (0.49 ± 0.04 kPa stress at 30% compressive strain) and therefore mimics the mechanical properties of the softest tissues found in the human body (e.g. brain and lung). The method was further validated by showing that the 3D printed material was well matched to the cast-moulded equivalent in terms of mechanical properties and microstructure. A preliminary biological evaluation on the 3D printed material, coated with collagen type I, poly-L-lysine and gelatine, was performed by seeding human dermal fibroblasts. Cells showed good attachment and viability on the collagen-coated 3D printed CH. This greatly widens the range of applications for the cryogenically 3D printed CH structures, from soft tissue phantoms for surgical training and simulations to mechanobiology and tissue engineering.
Forte AE, Etard O, Reichenbach J, 2017, The human auditory brainstem response to running speech reveals a subcortical mechanism for selective attention, eLife, Vol: 6, ISSN: 2050-084X
Humans excel at selectively listening to a target speaker in background noise such as competing voices. While the encoding of speech in the auditory cortex is modulated by selective attention, it remains debated whether such modulation occurs already in subcortical auditory structures. Investigating the contribution of the human brainstem to attention has, in particular, been hindered by the tiny amplitude of the brainstem response. Its measurement normally requires a large number of repetitions of the same short sound stimuli, which may lead to a loss of attention and to neural adaptation. Here we develop a mathematical method to measure the auditory brainstem response to running speech, an acoustic stimulus that does not repeat and that has a high ecological validity. We employ this method to assess the brainstem's activity when a subject listens to one of two competing speakers, and show that the brainstem response is consistently modulated by attention.
Tan Z, Forte AE, Parisi C, et al., 2017, Composite hydrogel: A new tool for reproducing the mechanicalbehaviour of soft human tissues, WTC 2017
Kegler M, Etard O, Forte AE, et al., 2017, Complex statistical model for detecting the auditory brainstem response to natural speech and for decoding attention, Basic Auditory Science 2017
Forte AE, Etard O, Reichenbach J, 2017, Selective auditory attention modulates the human brainstem's response to running speech, Basic Auditory Science 2017
Forte AE, galvan S, Dini D, 2017, Models and tissue mimics for brain shift simulations, Biomechanics and Modeling in Mechanobiology, Vol: 17, Pages: 249-261, ISSN: 1617-7940
Capturing the deformation of human brain during neurosurgical operations is an extremely important task to improve the accuracy or surgical procedure and minimize permanent damage in patients. This study focuses on the development of an accurate numerical model for the prediction of brain shift during surgical procedures and employs a tissue mimic recently developed to capture the complexity of the human tissue. The phantom, made of a composite hydrogel, was designed to reproduce the dynamic mechanical behaviour of the brain tissue in a range of strain rates suitable for surgical procedures. The use of a well-controlled, accessible and MRI compatible alternative to real brain tissue allows us to rule out spurious effects due to patient geometry and tissue properties variability, CSF amount uncertainties, and head orientation. The performance of different constitutive descriptions is evaluated using a brain–skull mimic, which enables 3D deformation measurements by means of MRI scans. Our combined experimental and numerical investigation demonstrates the importance of using accurate constitutive laws when approaching the modelling of this complex organic tissue and supports the proposal of a hybrid poro-hyper-viscoelastic material formulation for the simulation of brain shift.
Forte AE, 2017, Fundamental_waveforms_extraction
GitHub, https://github.com/antn85/fundamental_waveforms_extraction, version 1
Tan Z, Bernardini A, Konstantinou I, et al., 2017, Diffusion Measurement and Modelling, European Robotics Forum 2017
Forte AE, Etard O, Reichenbach J, 2017, Complex Auditory-brainstem Response to the Fundamental Frequency of Continuous Natural Speech, ARO 2017
Forte AE, Gentleman SM, Dini D, 2016, On the characterisation of the heterogeneous mechanical response of human brain tissue, Biomechanics and Modeling in Mechanobiology, Vol: 16, Pages: 907-920, ISSN: 1617-7959
The mechanical characterization of brain tissue is a complex task scientists have tried to accomplish for over fifty years. The resultsin literatureoften differ by orders of magnitudebecause of the lack of a standard testing protocol. Different testing conditions (including humidity, temperature, strain rate),the methodologyadopted,the variety of the speciesanalysed, are all potential sources of discrepancies in the measurements.In this work we present a rigorous experimental investigation on the mechanical properties of human brain, covering both grey and white matter. The influence of testing conditions isalso shown and thoroughly discussed. The material characterisation performed is finally adopted to provide inputs toa mathematical formulation suitable fornumerical simulations of brain deformation during surgical procedures.
Leibinger A, Forte AE, Tan Z, et al., 2016, Erratum to: Soft tissue phantoms for realistic needle insertion: a comparative study, Annals of Biomedical Engineering, Vol: 44, Pages: 3750-3750, ISSN: 0090-6964
Phantoms are common substitutes for soft tissues in biomechanical research and are usually tuned to match tissue properties using standard testing protocols at small strains. However, the response due to complex tool-tissue interactions can differ depending on the phantom and no comprehensive comparative study has been published to date, which could aid researchers to select suitable materials. In this work, gelatin, a common phantom in literature, and a composite hydrogel developed at Imperial College, were matched for mechanical stiffness to porcine brain, and the interactions during needle insertions within them were analyzed. Specifically, we examined insertion forces for brain and the phantoms; we also measured displacements and strains within the phantoms via a laser-based image correlation technique in combination with fluorescent beads. It is shown that the insertion forces for gelatin and brain agree closely, but that the composite hydrogel better mimics the viscous nature of soft tissue. Both materials match different characteristics of brain, but neither of them is a perfect substitute. Thus, when selecting a phantom material, both the soft tissue properties and the complex tool-tissue interactions arising during tissue manipulation should be taken into consideration. These conclusions are presented in tabular form to aid future selection.
Synthetic phantoms are valuable tools for training, research and development in traditional and computer aided surgery, but complex organs, such as the brain, are difficult to replicate. Here, we present the development of a new composite hydrogel capable of mimicking the mechanical response of brain tissue under loading. Our results demonstrate how the combination of two different hydrogels, whose synergistic interaction results in a highly tunable blend, produces a hybrid material that closely matches the strongly dynamic and non-linear response of brain tissue. The new synthetic material is inexpensive, simple to prepare, and its constitutive components are both widely available and biocompatible. Our investigation of the properties of this engineered tissue, using both small scale testing and life-sized brain phantoms, shows that it is suitable for reproducing the brain shift phenomenon and brain tissue response to indentation and palpation.
Tan Z, Forte AE, Galvan S, et al., 2016, Composite Hydrogel: a New Tool for Reproducing the Mechanical Behaviour of Soft Human Tissues, Biotribology 2016
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.