Human Thumb Research Articles

Evolutionary selection and morphological integration in the hand of modern humans.

To enhance our understanding of the evolutionary dynamics of the modern human hand by analyzing the degree of integration and ability to respond to selection pressures of each phalanx and metacarpal bone. The sample comprised 96 adult individuals, both female and male, from Euro-American, Afro-American, and European populations. We collected 10 linear measurements from the 19 metacarpals and proximal, middle, and distal phalanges that constitute the five digits of the hand. Using these data, we constructed variance/covariance matrices to quantify the degree of integration and assess the hand ability to respond to selective pressures. Distal phalanges are the most evolvable and flexible elements, while being the least integrated and constrained. The thumb is similarly integrated as the second and third rays, while medial rays (fourth and fifth digits) are more integrated. However, the thumb presents different integration and response to selection patterns. No significant relationship was found between functionality and the indices of selection and integration. Finally, the correlation between hand and foot indices yielded significant results for conditional evolvability and flexibility. The findings suggest different evolutionary trajectories for the metacarpal and distal phalanx in the modern human thumb, likely reflecting varying functional and developmental pressures. The first metacarpal, characterized by high flexibility and low evolvability, appears to have reached a stable, optimal morphology, under stabilizing selection. In contrast, the distal phalanx seems to have undergone directional evolution, suggesting specialization for a specific function. Comparisons between hands and feet suggest that these structures evolve differently under directional selection but similarly under stabilizing selection.

Development of Flexure‐Based Supernumerary Robotic Finger for Hand Function Augmentation

This study introduces a flexure‐based supernumerary robotic finger (FBSF) inspired by the proportions of the human thumb, aiming to overcome existing limitations in robotic finger design. In pursuit of seamless cooperation with the user's hand, human finger proportions are replicated. Finite element analysis of all five fingers indicates that the thumb‐mimicking configuration offers the largest workspace and bending angle. The FBSF, featuring a polycarbonate paired crossed flexural hinge structure and high impact polystyrene links, closely mirrors the human thumb. Weighing 59 g (main body) and 170 g (control box), the FBSF enables user‐driven control and decoupled actuation based on user intent, utilizing the electromyographic signal of the extensor carpi ulnaris via isometric contractions. An experimental protocol, including task blocks (releasing, clenching), confirms the FBSF's responsiveness to user intentions. When utilizing FBSF, it has been verified using a motion capture camera system that it is possible to extend the existing hand workspace by approximately 29.72%. Performance tests demonstrate the FBSF's capability to grasp various objects and assist in tasks, with a maximum load‐bearing capacity of 2.6 kg experimentally verified. This study demonstrates the potential of the developed FBSF to augment hand functionality in diverse applications.

Dissolvable microarray patches of levodopa and carbidopa for Parkinson’s disease management

Carbidopa and levodopa remain the established therapeutic standard for managing Parkinson’s disease. Nevertheless, their oral administration is hindered by rapid enzymatic degradation and gastrointestinal issues, limiting their efficacy, and necessitating alternative delivery methods. This work presents a novel strategy employing dissolving microarray patches (MAPs) loaded with carbidopa and levodopa, formulated with Tween® 80 to improve their transdermal delivery. The fabricated MAPs demonstrated an acceptable mechanical strength, resisting pressures equivalent to manual human thumb application (32 N) onto the skin. Additionally, these MAPs exhibited an insertion depth of up to 650 µm into excised neonatal porcine skin. Ex vivo dermatokinetic studies could achieve delivery efficiencies of approximately 53.35 % for levodopa and 40.14 % for carbidopa over 24 h, demonstrating their significant potential in drug delivery. Biocompatibility assessments conducted on human dermal fibroblast cells corroborated acceptable cytocompatibility, confirming the suitability of these MAPs for dermal application. In conclusion, dissolving MAPs incorporating carbidopa and levodopa represent a promising alternative for improving the therapeutic management of Parkinson’s disease.

A new rectangular dielectric resonator sensor for glucose measurement: Design, modeling, and experimental validation

SummaryThis study introduces a novel sensor for glucose measurement based on a rectangular dielectric resonator (RDR) excited by a rectangular slot fed by a 50‐Ω microstrip line. The RDR operates at 6 GHz and incorporates a cubic portion section for accommodating a finger or container containing the test sample. By utilizing the distinctive resonant frequencies associated with varying dielectric permittivity of different glucose concentrations, the proposed RDR functions as a reliable sensor. The sensor's performance is evaluated through a 3D electromagnetic model of the human thumb and the application of the Cole‐Cole method for modeling the blood layer. Experimental validation is conducted using three alternatives (water, glucose, and alcohol) and a range of glucose concentrations (70 to 2000 mg/dL) in simulation. During experimental verification, an invasive glucometer is employed as a reference for blood sugar levels. Results demonstrate that the proposed RDR sensor exhibits higher sensitivity (36.86 MHz/(mg/dL)) than other sensor counterparts. The experimental outcomes confirm the resonance frequency alignment between the manufactured sensor and the simulated projections. Considering its economic viability and applicability, this sensor represents a promising alternative biosensor for monitoring blood glucose levels.

Design, Fabrication, and Characterization of a Novel Optical Six-Axis Distributed Force and Displacement Tactile Sensor for Dexterous Robotic Manipulation.

Real-time multi-axis distributed tactile sensing is a critical capability if robots are to perform stable gripping and dexterous manipulation, as it provides crucial information about the sensor-object interface. In this paper, we present an optical-based six-axis tactile sensor designed in a fingertip shape for robotic dexterous manipulation. The distributed sensor can precisely estimate the local XYZ force and displacement at ten distinct locations and provide the global XYZ force and torque measurements. Its compact size, comparable to that of a human thumb, and minimal thickness allow seamless integration onto existing robotic fingers, eliminating the need for complex modifications to the gripper. The proposed sensor design uses a simple, low-cost fabrication method. Moreover, the optical transduction approach uses light angle and intensity sensing to infer force and displacement from deformations of the individual sensing units that form the overall sensor, providing distributed six-axis sensing. The local force precision at each sensing unit in the X, Y, and Z axes is 20.89 mN, 19.19 mN, and 43.22 mN, respectively, over a local force range of approximately ±1.5 N in X and Y and 0 to -2 N in Z. The local displacement precision in the X, Y, and Z axes is 56.70 μm, 50.18 μm, and 13.83 μm, respectively, over a local displacement range of ±2 mm in the XY directions and 0 to -1.5 mm in Z (i.e., compression). Additionally, the sensor can measure global torques, Tx, Ty, and Tz, with a precision of of 1.90 N-mm, 1.54 N-mm, and 1.26 N-mm, respectively. The fabricated design is showcased by integrating it with an OnRobot RG2 gripper and illustrating real-time measurements during in simple demonstration task, which generated changing global forces and torques.

Distribution of nerve endings in human thumb interphalangeal joint.

This study aims to quantitatively analyze the distribution of encapsulated nerve endings in the human thumb interphalangeal (IP) joint capsule. There are three types of nerve endings. Type-I nerve endings (Ruffini-like ending) sense pressure changes, Type II (Pacini-like ending) nerve endings contribute to the kinesthetic sense, and Type III (Golgi-like ending) nerve ending provides proprioceptive information. We dissected five right thumbs IP joints from freshly frozen cadavers (5 men). The mean age of the cadavers at the time of death was 63.4 years (55-73). Sections were stained with the hematoxylin-eosin and antiprotein gene product 9.5 (PGP9.5) to identify encapsulated nerve endings. Transverse sections were cut and divided into volar, dorsal, and then into two equal parts, proximal and distal. The density of encapsulated nerve endings compared to volar versus dorsal and proximal versus distal regions was examined. This study showed that type 1 nerve endings were more common in the distal parts of the IP joint (p < 0.05). Also, type 3 nerve endings were observed in the thumb IP joint. There was no difference between regions in type II and type III nerve endings. The current study demonstrates that the distribution of encapsulated nerve endings in the IP joint is different from the PIP and DIP joints. Moreover, further studies are required to understand the thumb's physiology.

Manganese oxide and nickel oxide thin films on polyester to enable self-charging wearable supercapacitor

In this work, an extremely flexible piezoelectric driven self-charging asymmetric supercapacitor (SCAS) has been reported in which nickel oxide (NiO) thin film acts as the negative electrode, manganese oxide (MnO2) thin film as the positive electrode, and PVA-ZnO-KOH (PZK) film as a separator (as well as a piezoelectric material). The results confirmed that even after 7500 charge-discharge cycles, the asymmetrical supercapacitor (MnO2//NiO) showed 100% capacitive retention. Mechanical deformation caused by the impact of a human thumb was used to illustrate the self-charging capabilities of the SCAS, and it was observed that by repeatedly pressing and releasing, the SCAS can charge up to 380 mV within ∼35 s. Additionally, the SCAS demonstrates incredible storage capacity by holding a voltage of 310 mV for more than a minute. Moreover, the fabricated SCAS was also subjected to bending as well as twisting followed by wetting, and it retained good performance even after wetting several times with distilled water indicating high durability of the device. All of these tests show that the developed supercapacitor has a high degree of flexibility, robustness, durability and stability, as well as a substantial amount of storage and self-charging potential.

Comparative Analysis of Custom-Designed Soft Pneumatic Actuators for Human Thumb Movement in Post-Stroke Rehabilitation

One of the most potential applications of soft actuator is as wearable medical devices for post-stroke rehabilitation as a field that requires high levels of safety and adaptability. Incorporating SPAs into such devices can provide a safer and more secure solution, ensuring controlled movements that do not pose a risk to patients. However, there is a research gap regarding the design considerations for soft actuators specifically targeting the human thumb, which exhibits distinct motion patterns compared to the other fingers. This paper addresses this gap by developing and evaluating custom-designed SPAs for the movement of the human thumb, with a focus on post-stroke rehabilitation. Three SPA models (M1, M2, and M3) were proposed, and their performance in replicating the twisting motion of the thumb was assessed. The SPAs were fabricated using 3D printing, and image processing software was utilized for measurement and analysis. The results showed that the M3 model, with two sections of chambers in different axes, exhibited the best performance in generating the desired twisting angle. Integration of the M3 model with four finger-shaped SPAs enabled successful grasping and picking-like movements. This research contributes to the advancement of soft actuators in wearable medical devices, particularly in post-stroke rehabilitation, and holds promise for enhancing patient recovery and quality of life.

Bionic threshing component optimized based on MBD-DEM coupling simulation significantly improves corn kernel harvesting rate

The most widely used rigid threshing component (RTC) currently has a constant problem with high kernel damage rates. Inspired by the seldom occurrence of kernel damage in manual threshing operations, this study designed a bionic threshing component (BTC) by using the human thumb as a bionic prototype. BTC can imitate the thumb's real-time profiling capability on the shape of the corn ears, thereby reproducing the thumb's “flexible profiling impact“ method of applying force, significantly different from the “rigid impact method” of RTC. Based on EDEM and RecurDyn software, the MBD-DEM coupling simulation model of the threshing operation was constructed. Through the coupling simulation experiments, the influence law of the BTC core design parameter k (bionic joint torque elasticity coefficient) on the kernel harvesting rate η, threshing rate and damage rate was revealed. Meanwhile, the optimum value of k (2.08 KN·mm/°) was derived by modelling the k-η regression. Bench comparison and simulation accuracy verification experiments showed that BTC operated with optimal k values can increase corn kernel harvesting rates by 0.87%–1.57%, compared to RTC. (BTC was able to achieve the highest kernel harvesting and threshing rates of 98.61% and 98.97%, respectively, with breakage rates as low as 0.16%). Meanwhile, the computational results of the MBD-DEM coupling simulation model established in this study were not significantly difference from the bench experiment (P > 0.05). To sum up, this study can provide a new mechanism design idea and parameter optimization method for the development of threshing components.

The Important but Mysterious Antarctic Krill

Antarctic krill are very important animals. They are well-known as the food of ocean giants such as blue whales, but they also feed many other animals and help to slow climate change by keeping millions of tons of carbon out of the air. Antarctic krill grow no longer than a human thumb, but together they weigh more than any other wild animal species. Although Antarctic krill live only in the cold waters of the Southern Ocean, they can live anywhere from sunlit surface waters to the darkest depths, from near the coast and under sea ice to ice-free waters far from land. In this article, we explore how their huge population and ability to live in diverse conditions make Antarctic krill important for other animals, people, and the world. We also introduce some key mysteries, such as what will happen to these animals as the climate continues to change.

A planar microwave sensor for noninvasive detection of glucose concentration using regression analysis

AbstractThis paper presents a planar microwave sensor for the noninvasive detection of glucose concentration in diabetic patients. The designed sensor operates from the 3.8 to 6.2 GHz frequency band, which covers the 5.8 GHz Industrial Scientific and Medical (ISM) band. The designed sensor shows a percentage bandwidth of 23.8% with a reflection coefficient (S11) of −50 dB at the resonance frequency of 5.7 GHz. The detection was carried out by varying the relative permittivity of the blood in accordance with the glucose concentration based on the Cole–Cole model. The measured result is calculated in terms of varying resonance frequency with variation in the reflection coefficient |S11| of the designed sensor. The observed frequency shift and corresponding sensitivity of the sensor are found at 1.7 GHz and 0.089 MHz/mg dL−1, respectively. An experimental validation has also been performed, and the frequency shift is analyzed by interacting the human thumb with the sensor. The simulated and experimental results of the designed sensor suggest that it can be useful for detecting glucose concentration noninvasively for diabetic patients.

An SFEM Abaqus UEL for Nonlinear Analysis of Solids

In this paper, three different smoothed finite element method (SFEM), viz., node-based smoothed finite element method (NS-FEM), face-based smoothed finite element method (FS-FEM) and [Formula: see text]-finite element method ([Formula: see text]-FEM) are adopted for 3D solids undergoing large deformation. The common feature of all these techniques is the introduction of smoothed strain which is written as a weighted average of the compatible strain field over smoothing domains. The choice of smoothing domain is what differentiates them. The spatial discretization can be based on the simplest and automatically genera-table four-node tetrahedral elements and aforementioned techniques have shown to yield accurate results even on a coarser discretization. To take the advantages of the SFEM, it is beneficial to the FEM community to have it implemented in the widely used Abaqus[Formula: see text] software. Such an implementation is challenging because the neighboring SFEM elements are interconnected in the smoothed strain matrices in the elemental level. In this work, the above-mentioned SFEM models are implemented in the commercial software Abaqus using the softwares’ user element (UEL) feature. The challenges during the definition and the assembly of the smoothing domains are effectively addressed in this work. The developed UEL and the associated files can be downloaded from https://github.com/nsundar/3DSFEM. The implementation is validated against benchmark examples and the robustness is demonstrated with complicated real-life problems, viz., tire patch contact with road and simulation of human thumb.

Measuring fascicle lengths of extrinsic and intrinsic thumb muscles using extended field-of-view ultrasound

Complex motion of the human thumb is enabled by the balanced architectural design of the extrinsic and intrinsic thumb muscles. Given that recent imaging advances have not yet been applied to enhance our understanding of the in vivo properties of thumb muscles, the objective of this study was to test the reliability and validity of measuring thumb muscle fascicle lengths using extended field of view ultrasound (EFOV-US). Three muscles (FPL: flexor pollicis longus, APB: abductor pollicis brevis, and ECU: extensor carpi ulnaris) were imaged in eight healthy adults (4 female; age, 21.6 ± 1.3 years; height, 175.9 ± 8.3 cm)[mean ± SD]. Measured fascicle lengths were compared to cadaveric data (all muscles) and ultrasound data (ECU only). Additionally, to evaluate how fascicle lengths scale with anthropometric measurements, height, forearm length, hand length, and hand width were recorded. The EFOV-US method obtained precise fascicle length measurements [mean ± SD] for the FPL (6.2 ± 0.5 cm), APB (5.1 ± 0.3 cm), and ECU (4.0 ± 0.4 cm). However, our EFOV-US measurements were consistently different (p < 0.05) than prior cadaveric data, highlighting the need to better understand differences between in vivo and ex vivo fascicle length measurements. Fascicle length was significantly related to only hand length (r2 = 0.56, p = 0.03) for APB, highlighting that anthropometric scaling may not accurately estimate thumb muscle length. As the first study to apply EFOV-US to measure thumb muscle fascicle lengths, this study expands the utility of this imaging technology within the upper limb.

Geometric Basics and Calculation Methods for the Design of a Technical Saddle Joint based on Owl Neck Vertebrae

A saddle joint enables the movement of two components relative to each other primarily about two axes of rotation and, to a limited extent, in translational direction. This type of joint is primarily found in nature, for example in the human thumb, in the ossicles and the cervical spine of owls. Motivated by the high degree of the owls’ head mobility, the authors aim to make this high motion potential technically accessible by defining relevant design parameters and developing calculation methods for dimensioning the saddle joint components. First, an abstracted contact geometry model based on the owls’ saddle joints is defined. A method for calculating the kinematics of the joint as a function of the previously introduced design parameters of the contact is derived mathematically. Regarding the implementation in a design process, this model is used to calculate the restoring forces required to stabilize the joint parts as well as the actuator torque needed for a specific rotational movement around those axes. Furthermore, the rotational stiffness of a specific joint geometry is calculated as an important design criterion. In summary, the defined contact geometry, the kinematics, and the computable forces serve as basis for designing technical saddle joints in the future.

Novel Bionic Soft Robotic Hand With Dexterous Deformation and Reliable Grasping

Bionic soft robotic hand has been developed rapidly, as it can achieve considerable flexibility and mimic human hand to perform actions such as grasping. This study develops a novel bionic soft robotic hand, which consists of a palm and five fingers that can operate independently. Unlike other soft hands, the fingers of the developed soft robotic hand are capable of stretching and bending. The thumb can mimic the joint activities of human thumb. An air chamber is placed on the back of robotic hand to mimic the elongation of muscles on the back of human hand. As such, the curvature of the palm can be changed. A particle jamming method is used in the hand palm to achieve passive variable stiffness during grasping, which improves the grasping stability of the bionic hand and the ability of wrapping target objects. Grasping experiments are conducted to evaluate and validate the grasping performance of the developed soft robotic hand. The experimental results show that the developed soft hand can effectively grasp sheet, columnar, and irregular objects when the driving pressure of finger and hand back are 50 kPa and 40 kPa, respectively. The maximum grasping mass is comparable to the mass of the soft robotic hand.

Human thumb consists of three phalanges and lacks metacarpal? A morphometric study on the long bones of the hand.

For many years, it was thought that the thumb consists of just two phalanges that differentiate it from the other four medial triphalangeal fingers. But there are some old reports that few former scientists believed the thumb has three phalanges and it lacked a metacarpal, and the thumb metacarpal is a phalanx. So this anthropometric study was carried out by investigating the morphology of the long bones of the hand and correlations between the thumb metacarpal and other miniature long bones of the hand. We studied anterior-posterior X-ray images of the right hands of 80 individuals from 18 to 65years old. The exploration targets were the length of all metacarpals (MC), proximal phalanges (PP), middle phalanges (MP), and distal phalanges (DP). Friedman Repeated Measures Analysis of Variance and Dunn's post hoc test were carried out to compare the means of all variables. The correlation between all quantitative factors was done by Spearman Rank Correlation (Spearman's Rho) coefficient. Our results showed that the length of the phalanges and the total length of the fingers are independent of the related metacarpal length (P < 0.001). Also, the thumb metacarpal length in comparison to all bones of the hand was significantly different from all long bones of the hand except the proximal phalanx of the middle finger (P = 1). Based on the morphology of the long bones of the hand and the high similarity between the thumb metacarpal and phalanges especially the proximal phalanx of the middle finger, it can be suggested that the current thumb metacarpal is a proximal phalanx of the thumb.

LSTM Network Classification of Dexterous Individual Finger Movements

Electrical activity is generated in the forearm muscles during muscular contractions that control dexterous movements of a human finger and thumb. Using this electrical activity as an input to train a neural network for the purposes of classifying finger movements is not straightforward. Low cost wearable sensors i.e., a Myo Gesture control armband (www.bynorth.com), generally have a lower sampling rate when compared with medical grade EMG detection systems e.g., 200 Hz vs 2000 Hz. Using sensors such as the Myo coupled with the lower amplitude generated by individual finger movements makes it difficult to achieve high classification accuracy. Low sampling rate makes it challenging to distinguish between large quantities of subtle finger movements when using a single network. This research uses two networks which enables for the reduction in the number of movements in each network that are being classified; in turn improving the classification. This is achieved by developing and training LSTM networks that focus on the extension and flexion signals of the fingers and a separate network that is trained using thumb movement signal data. By following this method, this research have increased classification of the individual finger movements to between 90 and 100%.

Maximal strengths of dielectric elastomer fingers for a passive grip

Dielectric elastomer minimum energy structures (DEMESs) are useful as low-force robotic grippers; they can sweep a large angle but carry not much load. It was a design dilemma to reinforce the benders without compromising the stroke angle. As a stronger variant of DEMES, a dielectric elastomer (DE) finger can unbend the ‘phalanges’ of a load beam upon activation of the ‘intrinsic muscles’ of the dielectric elastomer actuator (DEA). The DE finger used a uniform tendon hood that raises the tension center of a single-layered DEA and thus enhances the moment generation and load capacity. In this work, we further optimize the structural design of a slender DE finger by mimicking the human thumb profile. This thumb-inspired DE finger has a tapered load beam for hood shaping of multi-layered DEAs with a blunter fingertip. This thumb-up profile greatly enhances the passive lift strength (against a tip weight) by 54% as compared to the earlier rectangular design, at the cost of a 13% reduction in the active stroke. Further, it exploited the axial stiffness to achieve an order-greater pull strength as compared to the lift strength. Finally, the optimized DEMES grippers carried a payload well exceeding the lift strength; they managed to pick an apple of nearly ten times the gripper weight. In addition, a foot of three DE toes hung upside-down to a branch of a horizontal tube while supporting a payload of close to ten times the foot’s weight.

Attractive forces slow contact formation between deformable bodies underwater

Thermodynamics tells us to expect underwater contact between two hydrophobic surfaces to result in stronger adhesion compared to two hydrophilic surfaces. However, the presence of water changes not only energetics but also the dynamic process of reaching a final state, which couples solid deformation and liquid evacuation. These dynamics can create challenges for achieving strong underwater adhesion/friction, which affects diverse fields including soft robotics, biolocomotion, and tire traction. Closer investigation, requiring sufficiently precise resolution of film evacuation while simultaneously controlling surface wettability, has been lacking. We perform high-resolution in situ frustrated total internal reflection imaging to track underwater contact evolution between soft-elastic hemispheres of varying stiffness and smooth-hard surfaces of varying wettability. Surprisingly, we find the exponential rate of water evacuation from hydrophobic-hydrophobic (adhesive) contact is three orders of magnitude lower than that from hydrophobic-hydrophilic (nonadhesive) contact. The trend of decreasing rate with decreasing wettability of glass sharply changes about a point where thermodynamic adhesion crosses zero, suggesting a transition in mode of evacuation, which is illuminated by three-dimensional spatiotemporal height maps. Adhesive contact is characterized by the early localization of sealed puddles, whereas nonadhesive contact remains smooth, with film-wise evacuation from one central puddle. Measurements with a human thumb and alternatively hydrophobic/hydrophilic glass surface demonstrate practical consequences of the same dynamics: adhesive interactions cause instability in valleys and lead to a state of more trapped water and less intimate solid-solid contact. These findings offer interpretation of patterned texture seen in underwater biolocomotive adaptations as well as insight toward technological implementation.

Area Design of Keyboard Layout for Comfortable Texting Ability with the Thumb Jacobian Matrix

ABSTRACT The objective of this paper is to develop a theory for designing the keyboard area of smartphones, and endowing the users with comfortable texting ability via one thumb. In light of the fact that most users tend to hold the smartphone in one hand and manipulate with one thumb in daily life, this paper extracts the thumb kinematic chain from the thumb anatomy of the human hand, and defines the manipulation comfort ellipsoid of the thumb. Then some indexes such as the morphology and volume of the comfort ellipsoid, and the condition number of the thumb Jacobian are presented to evaluate the manipulation comfort of the thumb. Finally, the design problem of the smartphone’s keyboard area is transformed into an optimization problem that determines the most comfortable manipulation space for the human thumb. The proposed quantitative study method of the thumb manipulation comfort is verified by 12 subjects who hold a smartphone with one hand and manipulate the screen with one thumb, and the most comfortable keyboard layout of smartphone is determined for the 12 subjects. The proposed method for the manipulation comfort of the human thumb bridges the gap between the layout planning of soft keyboard of smartphones and the comfort of single thumb manipulation.