Deployable electrode arrays for brain interfaces: structural reconfiguration strategies for long-term stability and high-fidelity recording—a review Naser Sharafkhani, Haifeng Zhang Journal of Neural Engineering, 2025 Objective. Neural electrode arrays, as essential tools for recording and stimulating neural tissues, significantly impact therapeutic strategies for neurological disorders through deep brain stimulation, responsive neurostimulation, and brain-computer interfaces. Despite considerable advancements, the efficiency and longevity of neural electrode arrays are compromised by brain micromotion, induced by physiological activities such as cardiac pulsation and respiration. The mechanical mismatch between rigid electrode arrays and soft neural tissue generates persistent stresses at the electrode-tissue interface, triggering tissue damage, inflammatory responses, encapsulation, and ultimately electrode failure. Deployable neural electrode arrays, characterized by structural reconfiguration after implantation, have emerged to address these challenges. Deployment mechanisms, including unfolding, expanding, unrolling, or ejecting electrode arms from an initially compact configuration, reduce insertion trauma, maximize spatial coverage, and mitigate brain micromotion effects, thereby enhancing long-term stability and recording fidelity. Approach. This review provides the first comprehensive analysis of deployable intracortical and electrocorticography electrode arrays, emphasizing their design principles, deployment mechanisms, mechanical performance, advantages, and limitations. Main results. This review fills a critical gap in the existing neural electrode literature by transitioning the focus from traditional geometric and material considerations to advanced structural reconfiguration strategies. Significance. An understanding of the advantages and disadvantages of these deployment strategies provides essential insights and future directions for optimizing neural electrode technologies.
A passive variable-stiffness adaptive gripper for robotic manipulation Naser Sharafkhani, Haifeng Zhang Smart Materials and Structures, 2025 Handling both soft and rigid objects remains a significant challenge for conventional fixed-stiffness robotic grippers. Furthermore, existing adaptive grippers typically rely on active control strategies and sensor-based feedback, which increase system complexity, energy consumption, and maintenance demand. This study presents a novel, low-maintenance adaptive gripper capable of securely grasping objects with a wide range of mechanical properties, without requiring an external active control mechanism. The proposed gripper is a cylindrical, multi-layered structure composed of four curved beams separated by interlayer gaps, enabling passive transition through five discrete stiffness states. Initially soft, the structure progressively stiffens with increasing axial displacement, reaching distinct stiffness levels at specific displacement values. Ultimately, when all interlayer gaps are fully closed, the gripper reaches its maximum stiffness, equivalent to the elastic modulus of the fabrication material. The gripper returns to its original low-stiffness state once the displacement is removed, demonstrating fully reversible passive adaptation. The effective elastic modulus range spans several orders of magnitude, from hundreds of kilopascals (kPa), suitable for handling soft and light objects, to gigapascals (GPa), enabling robust gripping of rigid and heavy ones. Finite element method simulations validate the gripper’s performance, illustrating the five-state stiffness modulation as well as corresponding stress distribution and reaction forces. The gripper is fabricated using three-dimensional printing technology and experimentally tested to validate the feasibility of the design as a proof-of-concept.
A 3D printed intracortical microprobe with automatic effective stiffness control Naser Sharafkhani, John M. Long, Scott D. Adams, Abbas Z. Kouzani Bioprinting, 2024 A mechanical mismatch between a microprobe implanted in the brain and its surrounding soft tissue facilitates tissue damage and microprobe failure due to brain micromotion. Utilising soft intracortical microprobes with elastic moduli close to that of the brain may reduce tissue damage and enhance the longevity of the microprobes. Providing temporary stiffness for soft microprobes is a dominant method to prevent buckling during insertion. Nevertheless, the inability of these methods to efficiently control the stiffness results in inaccurate positioning or tissue damage. This paper presents an engineered interface between the microprobe and an inserter/neural tissue to provide an instant switch between the stiff and soft modes of the microprobe. The microprobe's equivalent elastic modulus increases to ≈4.2 GPa during insertion and positioning due to an applied compressive force by an inserter and instantly returns to ≈98 kPa after positioning. The 3D printed microprobe is experimentally tested and inserted into a lamb brain without buckling, confirming the feasibility of the design proposed in this study. The cross-sectional area of the proposed microprobe is approximately 70 % smaller than that of the existing counterpart, resulting in less tissue damage during insertion and operation.
A self-stiffening compliant intracortical microprobe Naser Sharafkhani, John M. Long, Scott D. Adams, Abbas Z. Kouzani Biomedical Microdevices, 2024 Utilising a flexible intracortical microprobe to record/stimulate neurons minimises the incompatibility between the implanted microprobe and the brain, reducing tissue damage due to the brain micromotion. Applying bio-dissolvable coating materials temporarily makes a flexible microprobe stiff to tolerate the penetration force during insertion. However, the inability to adjust the dissolving time after the microprobe contact with the cerebrospinal fluid may lead to inaccuracy in the microprobe positioning. Furthermore, since the dissolving process is irreversible, any subsequent positioning error cannot be corrected by re-stiffening the microprobe. The purpose of this study is to propose an intracortical microprobe that incorporates two compressible structures to make the microprobe both adaptive to the brain during operation and stiff during insertion. Applying a compressive force by an inserter compresses the two compressible structures completely, resulting in increasing the equivalent elastic modulus. Thus, instant switching between stiff and soft modes can be accomplished as many times as necessary to ensure high-accuracy positioning while causing minimal tissue damage. The equivalent elastic modulus of the microprobe during operation is ≈ 23 kPa, which is ≈ 42% less than the existing counterpart, resulting in ≈ 46% less maximum strain generated on the surrounding tissue under brain longitudinal motion. The self-stiffening microprobe and surrounding neural tissue are simulated during insertion and operation to confirm the efficiency of the design. Two-photon polymerisation technology is utilised to 3D print the proposed microprobe, which is experimentally validated and inserted into a lamb’s brain without buckling.
Novel Neural Microprobe with Adjustable Stiffness Naser Sharafkhani, John M. Long, Scott D. Adams, Abbas Z. Kouzani International IEEE EMBS Conference on Neural Engineering Ner, 2023 To successfully insert a microprobe into the brain and record/stimulate the target neural tissue, it must meet two opposing requirements. Firstly, it must be stiff enough to tolerate the penetration force during insertion. Secondly, it must be compliant enough to withstand brain micromotion during operation, since a mechanical mismatch between the stiff microprobe and soft surrounding neural tissue leads to neural tissue damage and, ultimately, the failure of the microprobe within a few weeks/months of implantation. The design proposed in this study enables the creation of a neural microprobe whose elastic modulus varies from 4.2 GPa during insertion to 149 kPa during operation, as a function of the applied motion. The proposed mechanism for changing the stiffness works independently of the microprobe fabrication material and the surrounding environment's conditions. The microprobe and surrounding neural tissue are simulated to calculate the elastic modulus of the microprobe based on the finite element method and investigate the induced strain on the tissue by the brain longitudinal and lateral micromotions, simultaneously. The obtained results show that the maximum strain on the tissue surrounding the proposed microprobe is ~59 % less than that of the classic cylindrical microprobe with the same material, diameter, and length. The microprobe is fabricated based on two-photon polymerization technology.
An Intracortical Polyimide Microprobe With Piezoelectric-Based Stiffness Control Naser Sharafkhani, Julius O. Orwa, Scott D. Adams, John M. Long, Gaëlle Lissorgues, Lionel Rousseau, Abbas Z. Kouzani Journal of Applied Mechanics Transactions ASME, 2022 Insertion of a microprobe into the brain is challenging because it needs to have a minimum stiffness to be successfully implanted and a maximum softness to exhibit compliance with surrounding neural tissue during operation. A microprobe’s critical buckling force not only dictates the microprobe resistance to buckling during insertion but also reveals the corresponding compliance during operation. The methods that are currently used to insert flexible microprobes into the brain are far from perfect because they may adversely affect the microprobe intrinsic softness. In this article, a piezoelectric-based mechanism is presented, theoretically modeled, and simulated to precisely adjust the critical buckling force of a polyimide microprobe during insertion into the brain. Two parallel piezoelectric layers are extended along the length of a polyimide microprobe and connected to a voltage source. Based on analytical modeling and simulation results, placing the piezoelectric layers closer to the neutral axis of the structure leads to a microprobe with higher buckling capacity and greater compliance during insertion and operation, respectively. Depending on the applied voltage and the configurations of the microprobe and piezoelectric layers, the critical buckling force of the modified polyimide microprobe can be adjusted from less than 0.02 mN to higher than the minimum brain penetration force of 0.5 mN, compared to a fixed critical buckling force of a polyimide microprobe without the piezoelectric layer.
An ultra-thin multi-layered metamaterial for power transformer noise absorption Naser Sharafkhani Building Acoustics, 2022 A compact multi-layered structure is proposed based on the coiled-up space concept for power transformer noise absorption at 100 and 200 Hz. Current methods of constructing multi-band absorbers are impractical for power transformer noise control due to the high coupling effect deteriorating their performance. To overcome this shortcoming, the proposed structure is composed of multiple connected layers creating two separate coiled ducts with adjustable dimensions to minimise the coupling effect. In the modelling stage, the geometrical features are optimised using the genetic algorithm to maximise the absorption coefficient and minimise the thickness. The proposed dual-tone absorber has a thickness of 43.5 mm which is significantly thinner than the existing conventional absorbers. The measurement results on a 3D-printed structure demonstrate the feasibility of the design.
A Pneumatic-Based Mechanism for Inserting a Flexible Microprobe Into the Brain Naser Sharafkhani, Abbas Z. Kouzani, Scott D. Adams, John M. Long, Julius O. Orwa Journal of Applied Mechanics Transactions ASME, 2022 Insertion of flexible microprobes into the brain requires withstanding the compressive penetration force by the microprobes. To aid the insertion of the microprobes, most of the existing approaches use pushing mechanisms to provide temporary stiffness increase for the microprobes to prevent buckling during insertion into the brain. However, increasing the microprobe stiffness may result in acute neural tissue damage during insertion. Moreover, any late or premature removal of the temporary stiffness after insertion may lead to further tissue damage due to brain micromotion or inaccuracy in the microprobe positioning. In this study, a novel pneumatic-based insertion mechanism is proposed which simultaneously pulls and pushes a flexible microprobe toward the brain. As part of the brain penetration force in the proposed mechanism is supplied by the tensile force, the applied compressive force, which the microprobe must withstand during insertion, is lower compared with the existing approaches. Therefore, the microprobes with a critical buckling force less than the brain penetration force can be inserted into the brain without buckling. Since there is no need for temporary stiffness increment, neural tissue damage during the microprobe insertion will be much lower compared with the existing insertion approaches. The pneumatic-based insertion mechanism is modeled analytically to investigate the effects of the microprobe configuration and the applied air pressure on the applied tensile and compressive forces to the microprobe. Next, finite element modeling is conducted, and its analysis results not only validate the analytical results but also confirm the efficiency of the mechanism.
Acoustic impedance of a folded rectangular cross shape cavity Proceedings of 2020 International Congress on Noise Control Engineering Inter Noise 2020, 2020
Study of volumetric flow rate of a micropump using a non-classical elasticity theory International Journal of Engineering Transactions B Applications, 2018
Deployable electrode arrays for brain interfaces: structural reconfiguration strategies for long-term stability and high-fidelity recording—a review N Sharafkhani, H Zhang Journal of Neural Engineering 22 (6), 061003 , 2025 2025
A passive variable-stiffness adaptive gripper for robotic manipulation N Sharafkhani, H Zhang Smart Materials and Structures 34, 085006 , 2025 2025
A 3D printed intracortical microprobe with automatic effective stiffness control N Sharafkhani, JM Long, SD Adams, AZ Kouzani Bioprinting 38, e00333 , 2024 2024 Citations: 3
A self-stiffening compliant intracortical microprobe N Sharafkhani, JM Long, SD Adams, AZ Kouzani Biomedical Microdevices 26 (1), 17 , 2024 2024 Citations: 6
A binary stiffness compliant neural microprobe N Sharafkhani, JM Long, SD Adams, AZ Kouzani Sensors and Actuators A: Physical 363, 114759 , 2023 2023 Citations: 16
Novel Neural Microprobe with Adjustable Stiffness N Sharafkhani, JM Long, SD Adams, AZ Kouzani 2023 11th International IEEE/EMBS Conference on Neural Engineering (NER), 1-4 , 2023 2023 Citations: 5
An intracortical polyimide microprobe with piezoelectric-based stiffness control N Sharafkhani, JO Orwa, SD Adams, JM Long, G Lissorgues, L Rousseau, ... Journal of Applied Mechanics 89 (9), 091008 , 2022 2022 Citations: 19
A pneumatic-based mechanism for inserting a flexible microprobe into the brain N Sharafkhani, AZ Kouzani, SD Adams, JM Long, JO Orwa Journal of Applied Mechanics 89 (3), 031010 , 2022 2022 Citations: 15
An ultra-thin multi-layered metamaterial for power transformer noise absorption N Sharafkhani Building Acoustics 29 (1), 53-62 , 2022 2022 Citations: 13
A Helmholtz resonator-based acoustic metamaterial for power transformer noise control N Sharafkhani Acoustics Australia 50 (1), 71-77 , 2022 2022 Citations: 27
Neural tissue-microelectrode interaction: Brain micromotion, electrical impedance, and flexible microelectrode insertion N Sharafkhani, AZ Kouzani, SD Adams, JM Long, G Lissorgues, ... Journal of Neuroscience Methods 365, 109388 , 2022 2022 Citations: 85
Acoustic impedance of a folded rectangular cross shape cavity N Sharafkhani, X Qiu, D Wei INTER-NOISE and NOISE-CON Congress and Conference Proceedings 261 (6), 267-272 , 2020 2020
Out-of-plane vibration of an electrostatically actuated microbeam immersed in flowing fluid M Rezaee, N Sharafkhani Nonlinear Dynamics 102 (1), 1-17 , 2020 2020 Citations: 22
Nonlinear dynamic analysis of an electrostatically actuated cylindrical micro-beam subjected to cross fluid flow M Rezaee, N Sharafkhani International Journal of Applied Mechanics 11 (06), 1950061 , 2019 2019 Citations: 20
Dynamic behavior of a micro-beam subjected to voltage and fluid flow as a micro vortex generator M Rezaee, N Sharafkhani, MT Shervani Tabar Amirkabir Journal of Mechanical Engineering 52 (8), 2231-2242 , 2018 2018 Citations: 14
Study of volumetric flow rate of a micropump using a non-classical elasticity theory A Pasandi, S Afrang, S Dowlati, N Sharafkhani, G Rezazadeh International Journal of Engineering-Transactions C: Aspects 31 (6), 986-996 , 2018 2018 Citations: 4
Electrostatically frequency tunable micro-beam-based piezoelectric fluid flow energy harvester M Rezaee, N Sharafkhani Smart Materials and Structures 26 (7), 075008 , 2017 2017 Citations: 22
Stability analysis of FGM microgripper subjected to nonlinear electrostatic and temperature variation loadings R Jahanghiry, R Yahyazadeh, N Sharafkhani, VA Maleki Science and Engineering of Composite Materials 23 (2), 199-207 , 2016 2016 Citations: 37
Study of structural noise owing to nonlinear behavior of capacitive microphones H Madinei, G Rezazadeh, N Sharafkhani Microelectronics Journal 44 (12), 1193-1200 , 2013 2013 Citations: 16
Electrostatically actuated FGM micro-tweezer under the thermal moment M Rezaee, N Sharafkhani, A Chitsaz Microsystem technologies 19 (11), 1829-1837 , 2013 2013 Citations: 22
MOST CITED SCHOLAR PUBLICATIONS
Neural tissue-microelectrode interaction: Brain micromotion, electrical impedance, and flexible microelectrode insertion N Sharafkhani, AZ Kouzani, SD Adams, JM Long, G Lissorgues, ... Journal of Neuroscience Methods 365, 109388 , 2022 2022 Citations: 85
Stability analysis of FGM microgripper subjected to nonlinear electrostatic and temperature variation loadings R Jahanghiry, R Yahyazadeh, N Sharafkhani, VA Maleki Science and Engineering of Composite Materials 23 (2), 199-207 , 2016 2016 Citations: 37
A Helmholtz resonator-based acoustic metamaterial for power transformer noise control N Sharafkhani Acoustics Australia 50 (1), 71-77 , 2022 2022 Citations: 27
Study of mechanical behavior of circular FGM micro-plates under nonlinear electrostatic and mechanical shock loadings N Sharafkhani, G Rezazadeh, R Shabani Acta Mechanica 223 (3), 579-591 , 2012 2012 Citations: 24
Static and dynamic response of carbon nanotube-based nano-tweezers R Shabani, N Sharafkhani, VM Gharebagh INTERNATIONAL JOURNAL OF ENGINEERING 24 (4), 377-386 , 2011 2011 Citations: 23
Out-of-plane vibration of an electrostatically actuated microbeam immersed in flowing fluid M Rezaee, N Sharafkhani Nonlinear Dynamics 102 (1), 1-17 , 2020 2020 Citations: 22
Electrostatically frequency tunable micro-beam-based piezoelectric fluid flow energy harvester M Rezaee, N Sharafkhani Smart Materials and Structures 26 (7), 075008 , 2017 2017 Citations: 22
Electrostatically actuated FGM micro-tweezer under the thermal moment M Rezaee, N Sharafkhani, A Chitsaz Microsystem technologies 19 (11), 1829-1837 , 2013 2013 Citations: 22
Dynamic analysis of an electrostatically actuated circular micro-plate interacting with compressible fluid R Shabani, N Sharafkhani, S Tariverdilo, G Rezazadeh Acta Mechanica 224 (9), 2025-2035 , 2013 2013 Citations: 22
Nonlinear dynamic analysis of an electrostatically actuated cylindrical micro-beam subjected to cross fluid flow M Rezaee, N Sharafkhani International Journal of Applied Mechanics 11 (06), 1950061 , 2019 2019 Citations: 20
An intracortical polyimide microprobe with piezoelectric-based stiffness control N Sharafkhani, JO Orwa, SD Adams, JM Long, G Lissorgues, L Rousseau, ... Journal of Applied Mechanics 89 (9), 091008 , 2022 2022 Citations: 19
Stability analysis and transient response of electrostatically actuated microbeam interacting with bounded compressible fluids N Sharafkhani, R Shabani, S Tariverdilo, G Rezazadeh Journal of Applied Mechanics 80 (1), 011024 , 2013 2013 Citations: 17
A binary stiffness compliant neural microprobe N Sharafkhani, JM Long, SD Adams, AZ Kouzani Sensors and Actuators A: Physical 363, 114759 , 2023 2023 Citations: 16
Study of structural noise owing to nonlinear behavior of capacitive microphones H Madinei, G Rezazadeh, N Sharafkhani Microelectronics Journal 44 (12), 1193-1200 , 2013 2013 Citations: 16
A pneumatic-based mechanism for inserting a flexible microprobe into the brain N Sharafkhani, AZ Kouzani, SD Adams, JM Long, JO Orwa Journal of Applied Mechanics 89 (3), 031010 , 2022 2022 Citations: 15
Dynamic behavior of a micro-beam subjected to voltage and fluid flow as a micro vortex generator M Rezaee, N Sharafkhani, MT Shervani Tabar Amirkabir Journal of Mechanical Engineering 52 (8), 2231-2242 , 2018 2018 Citations: 14
An ultra-thin multi-layered metamaterial for power transformer noise absorption N Sharafkhani Building Acoustics 29 (1), 53-62 , 2022 2022 Citations: 13
A self-stiffening compliant intracortical microprobe N Sharafkhani, JM Long, SD Adams, AZ Kouzani Biomedical Microdevices 26 (1), 17 , 2024 2024 Citations: 6
Novel Neural Microprobe with Adjustable Stiffness N Sharafkhani, JM Long, SD Adams, AZ Kouzani 2023 11th International IEEE/EMBS Conference on Neural Engineering (NER), 1-4 , 2023 2023 Citations: 5
Study of volumetric flow rate of a micropump using a non-classical elasticity theory A Pasandi, S Afrang, S Dowlati, N Sharafkhani, G Rezazadeh International Journal of Engineering-Transactions C: Aspects 31 (6), 986-996 , 2018 2018 Citations: 4
