Prosthesis System Research Articles

Assessment of Postoperative Morphologic Retinal Changes by Optical Coherence Tomography in Recipients of an Electronic Retinal Prosthesis Implant

The postoperative retinal changes at the interface between an implant electrode array and the retina and whether these anatomic changes have an association with the patient visual performance are unknown. To report morphologic changes in recipients of an Argus II Retinal Prosthesis. This consecutive, noncomparative case series study included a retrospective review of the preoperative and postoperative optical coherence tomography of 33 eyes among 33 individuals who underwent Argus II Retinal Prosthesis System implantation between October 28, 2011, and June 8, 2017, at 2 different centers, by the same surgeon (S.R.). Thirteen patients received an implant at Azienda Ospedaliero Universitaria Pisana, Pisa, Italy, between October 28, 2011, and October 27, 2014, and 20 patients underwent surgery at Azienda Ospedaliera Universitaria Careggi, Florence, Italy, between December 20, 2014, and June 8, 2017. Patients were excluded if they did not reach the 6-month follow-up. All patients were evaluated before surgery, during the first postoperative day, and at 1, 3, 6, 12, and 24 months (subsequently once a year, except for patient-related adverse events), with a comprehensive ophthalmic examination, retinal fundus photography, spectral-domain optical coherence tomography, and visual function tests to evaluate the stability or improvement of their visual performance. Of the 20 patients included in the analysis, all were of white race/ethnicity, 12 (60%) were male, and the mean (SD) age was 57.4 (11.6) years. Optical coherence tomography revealed the development of a fibrosislike hyperreflective tissue limited at the interface between the array and retina in 10 eyes (50%). In 9 of 10 patients (90%), fibrosis evolved and progressed to retinal schisis. Despite the development of the fibrosis and schisis, there was no deterioration in the patient's visual performance evaluated prospectively with visual function tests (square localization and direction of motion). Optical coherence tomography may be used to observe the retinal anatomic changes in patients with an Argus II Prothesis. This analysis revealed the development of a fibrosislike hyperreflective tissue limited at the interface between array and retina that progressed to retinal schisis but with no deterioration in the patients' visual performance.

Evaluation and Comparison of the Shear Bond Strength of Porcelain Repair System for Fractured Metal-Ceramic Prosthesis Using Ni-Cr and Co-Cr Alloys: An In-Vitro Study

Evaluation and Comparison of the Shear Bond Strength of Porcelain Repair System for Fractured Metal-Ceramic Prosthesis Using Ni-Cr and Co-Cr Alloys: An In-Vitro Study

Advances in retinal prosthesis systems.

Retinal prosthesis systems have undergone significant advances in the past quarter century, resulting in the development of several different novel surgical and engineering approaches. Encouraging results have demonstrated partial visual restoration, with improvement in both coarse objective function and performance of everyday tasks. To date, four systems have received marketing approval for use in Europe or the United States, with numerous others undergoing preclinical and clinical evaluation, reflecting the established safety profile of these devices for chronic implantation. This progress represents the first notion that the field of visual restorative medicine could offer blind patients a hope of real and measurable benefit. However, there are numerous complex engineering and biophysical obstacles still to be overcome, to reconcile the gap that remains between artificial and natural vision. Current developments in the form of enhanced image processing algorithms and data transfer approaches, combined with emerging nanofabrication and conductive polymerization techniques, herald an exciting and innovative future for retinal prosthetics. This review provides an update of retinal prosthetic systems currently undergoing development and clinical trials while also addressing future challenges in the field, such as the assessment of functional outcomes in ultra-low vision and strategies for tackling existing hardware and software constraints.

An Approach for Brain-Controlled Prostheses Based on a Facial Expression Paradigm.

One of the most exciting areas of rehabilitation research is brain-controlled prostheses, which translate electroencephalography (EEG) signals into control commands that operate prostheses. However, the existing brain-control methods have an obstacle between the selection of brain computer interface (BCI) and its performance. In this paper, a novel BCI system based on a facial expression paradigm is proposed to control prostheses that uses the characteristics of theta and alpha rhythms of the prefrontal and motor cortices. A portable brain-controlled prosthesis system was constructed to validate the feasibility of the facial-expression-based BCI (FE-BCI) system. Four types of facial expressions were used in this study. An effective filtering algorithm based on noise-assisted multivariate empirical mode decomposition (NA-MEMD) and sample entropy (SampEn) was used to remove electromyography (EMG) artifacts. A wavelet transform (WT) was applied to calculate the feature set, and a back propagation neural network (BPNN) was employed as a classifier. To prove the effectiveness of the FE-BCI system for prosthesis control, 18 subjects were involved in both offline and online experiments. The grand average accuracy over 18 subjects was 81.31 ± 5.82% during the online experiment. The experimental results indicated that the proposed FE-BCI system achieved good performance and can be efficiently applied for prosthesis control.

The effects of variable mechanical parameters on peak power and energy consumption of ankle-foot prostheses at different speeds

ABSTRACTIn recent years, powered ankle-foot prostheses are developed to restore human ankle behaviour. Compared with common passive ankle prostheses, a powered ankle-foot prosthesis can provide amputees with better performance on walking gait by providing additional energy. However, the electrical peak power of powered ankle-foot prostheses at high speed is still a big challenge for the current actuation system. While most researchers focus on the energy consumption on one walking speed, we investigate the influences of several variable mechanical parameters to reduce electrical peak power during different locomotion speeds. Then we apply this concept to current ankle-foot models. It's found that the variable mechanical parameters can significantly reduce the demand of electrical peak power at different speeds. Meanwhile, the reduction of the electrical peak power does not lead to a large increment of the energy consumption. The results also show that every variable mechanical parameter has a different influence on the peak power and energy consumption of the ankle-foot prosthesis. It means the most effective and sensitive variable mechanical parameter need to be found for a specific ankle prosthesis system.

Discussion on hot topics of skeletal sternal reconstruction

Sternum is an important constituent of the thoracic cage, and a pivotal part of the anterior chest wall. When a considerable portion of the sternum needs to be resected, in order to protect the vital organs beneath, restore the anatomical structure and physiological function, reconstruction is unavoidable. Sternal reconstruction consists of two related parts: skeletal and soft tissue reconstruction. Skeletal reconstruction uses materials such as autograft or allograft of bones, metallic plates, sandwich patch, non-rigid patches, bio-synthetic patches and three-dimensional printing prosthesis. Each has its advantages and disadvantages. For example, autogenous bone transplantation is limited by the source of donor bones and surgical trauma; allograft bone transplantation demands cryopreservation and is susceptible to infection; titanium plate cannot be placed overlapped; "sandwich" patch is susceptible to local fluid accumulation and infection; non-rigid patches cannot provide enough mechanical support; the design and manufacture of three-dimensional printing prosthesis is complicated, time consuming and expensive, and cannot be adjusted due to change of extent of resection during operation. The modularized prosthesis system is a promising new technique developed on the basis of titanium plate. It is divided into standard components of different sizes that can be selected according to operational requirement and easily assembled. Until now, no perfect method or material has been found to imitate the autogenous sternum. Soft tissue reconstruction is a prerequisite to the success of large scale skeletal reconstruction of the sternum.

Development of a Parent Wireless Assistive Interface for Myoelectric Prosthetic Hands for Children.

In this study, a one-degree-of-freedom myoelectric prosthesis system was proposed using a Parent Wireless Assistive Interface (PWAI) that allowed an external assistant (e. g., the parent of the user) to immediately adjust the parameters of the prosthetic hand controller. In the PWAI, the myoelectric potential of use of the upper limb was plotted on an external terminal in real time. Simultaneously, the assistant adjusted the parameters of the prosthetic hand control device and manually manipulated the prosthetic hand. With these functions, children that have difficulty verbally communicating could obtain properly adjusted prosthetic hands. In addition, non-experts could easily adjust and manually manipulate the prosthesis; therefore, training for the prosthetic hands could be performed at home. Two types of hand motion discrimination methods were constructed in this study of the myoelectric control system: (1) a threshold control based on the myoelectric potential amplitude information and (2) a pattern recognition of the frequency domain features. In an evaluation test of the prosthesis threshold control system, child subjects achieved discrimination rates as high as 89%, compared with 96% achieved by adult subjects. Furthermore, the high discrimination rate was maintained by sequentially updating the threshold value. In addition, a discrimination rate of 82% on average was obtained by recognizing three motions using the pattern recognition method.

Multiple Myeloma - Current Standards in Surgical Treatment.

Multiple myeloma is a haematological blood cancer in elderly patients, in which neoplastic cell populations cause osteolytic destruction in the bone skeleton. More than 50% of all patients sustain pathological fractures during the course of their disease. Of all malignant lesions of the spine, multiple myeloma is the most frequent spinal tumour and accounts for approximately 15% of all cases. 8 - 10% of the patients develop neurological deficits. In addition to systemic antineoplastic therapy, surgical treatment is often required in order to reconstruct and stabilise bone defects associated with multiple myeloma, as well as to address tumour-related complications. A comprehensive literature search was performed in PubMed using the keywords "multiple myeloma" and "surgery" or "fracture". This served to evaluate the available primary and secondary literature on the current status of the surgical therapy of multiple myeloma. Systematic reviews, meta-analyses and clinical studies and international recommendations for therapy were included - from 1975 until the spring of 2018. Stabilising surgery is essential in order to retain and restore function and mobility in bone sections affected by myeloma and for tumour-related osseous defects due to pathological fracture or instability. Absolute and relative indications for surgical treatment are distinguished and are based on the extent and localisation of bone lesions, manifest fractures, accompanying side effects and complications such as neurological deficits and bone pain that is intractable to conservative treatment. The range of options in surgical treatment of myeloma-related bone damage within the upper and lower extremities ranges from hybrid stabilisation procedures combining bone cement and various implants, to conventional and modular tumour prostheses systems. In spinal surgery, minimally invasive procedures such as kyphoplasty or vertebroplasty, as well as selective decompressive operations, dorsal spinal fusion and vertebral replacement are performed in cases of osseous defects and related fractures or instabilities. The surgical treatment and time of operation is determined by the general individual risk profile and prognosis of the patient with multiple myeloma. The surgical approach should have the objective of a final and load stable solution for the patient, which takes into account the frequent long-term course of the disease. Radiotherapy is often recommended after surgery. In therapy of multiple myeloma, surgical treatment is often required in order to reduce distress and retain the function and flexibility of myeloma affected bone sections and the mobility and quality of life of the cancer patient. The range of surgical strategies is complex and demanding.

Design and Functional Evaluation of a Dexterous Myoelectric Hand Prosthesis With Biomimetic Tactile Sensor.

This paper presents the design, tactile sensor, characterization, and control system of a new dexterous myoelectric hand prosthesis to overcome the limitations of state-of-the-art myoelectric prostheses (e.g., limited functionality, controllability, and sensory feedback). Our dexterous myoelectric hand allows independent finger movement and thumb abduction/adduction, with a motor for each finger and an additional motor for the thumb (i.e., six total motors). Each fingertip has a biomimetic tactile sensor with 13 tactile units, each of which can detect normal and tangential forces. The hand controller uses an electromyography pattern recognition controller and a tactile sensor feedback-based grasping controller to automatically and dynamically adjust the finger grasp force to prevent objects from slipping. This closed-loop controller structure will allow users to safely and effectively grasp complex objects with varying densities and shapes. In addition, the electronic hardware is integrated into the hand, and the pattern recognition controller can be implemented in the hand embedded system.

Design of a Prototype for Vision Prosthesis

This article describes how the field of vision prostheses is currently being developed around the world to restore useful vision for people suffering from retinal degenerative diseases. The vision prosthesis system (VPS) maps visual images to electrical pulses and stimulates the surviving healthy parts in the retina of the eye, i.e. ganglion cells, using electric pulses applied through an electrode array. The retinal neurons send visual information to the brain. This article presents the design of a prototype vision prosthesis system which converts images/video into biphasic electric stimulation pulses for the excitation of electrodes simulated by an LED array. The proposed prototype laboratory model has been developed for the design of flexible high-resolution 1024-electrode VPS, using an embedded computer-based efficient control algorithm for better visual prediction. The prototype design for the VPS is verified visually through a video display on an LCD/LED array. The experimental results of VPS are enumerated for the test objects, such as, palm, human face and large font characters. The results were found to be satisfactory.

A 3.3 V, 8.89 μA and 5.5 ppm/°C CMOS bandgap voltage reference for power telemetry in retinal prosthesis systems.

A 3.3 V CMOS bandgap reference (BGR) was presented in this study that utilizes MOS transistors operating in the sub-threshold region. The complexity of the circuit and the dependency of the voltage reference on power supply variations are simultaneously decreased through the use of a new compensation circuit technique. The proposed BGR is simulated using a 0.35 $\mu \mathrm{m}$ CMOS standard process. Consequently, a 5.53 ppm/°C temperature coefficient is obtained in the -40~+125 °C temperature range, the maximum power supply rejection ratio is - 62 dB, and a 2.033 mV/V voltage line regulation is achieved for the $2.3\sim 4.3$ V supply voltage. The proposed circuit dissipates a supply current of 8.89 IJA at a 3.3 V supply voltage, and the active area is 112 $\mu \mathrm{m}\times 60 \mu \mathrm{m}$.

Argus II retinal prosthesis system: a review of patient selection criteria, surgical considerations, and post-operative outcomes.

Retinitis pigmentosa (RP) is a group of heterogeneous inherited retinal degenerative disorders characterized by progressive rod and cone dysfunction and ensuing photoreceptor loss. Many patients suffer from legal blindness by their 40s or 50s. Artificial vision is considered once patients have lost all vision to the point of bare light perception or no light perception. The Argus II retinal prosthesis system is one such artificial vision device approved for patients with RP. This review focuses on the factors important for patient selection. Careful pre-operative screening, counseling, and management of patient expectations are critical for the successful implantation and visual rehabilitation of patients with the Argus II device.

Circularly polarized implantable antenna characterization for retinal prosthesis systems

We describe a miniaturized antenna design for retinal prosthesis applications that enhances data transfer between the implant and external camera. The circularly polarized and conformal 2.4–2.48 GHz microstrip patch antenna was simulated inside the vitreous humor and is intended for biomedical applications. Modified Hilbert and serpentine geometries were used for the proposed implant antenna design. Capacitive radiator loading offered miniaturized dimensions of 5.8 × 6.5 × 2 mm³ (width × height × thickness mm³). A truncated design enhanced the intrinsic circular polarization characteristics to >3 dB axial ratio. Polydimethylsiloxane substrate and superstrate materials were used to achieve an S11 value below –15 dB across the frequency range with biocompatible characteristics. The simulated peak gains for left-hand circular polarization and right-hand circular polarization at 2.45 GHz were –50 dBi and –60 dBi, respectively. These relatively small values were due to the high conductivity of the vitreous humor (s = 1.53 S/m), which imposed significant losses. Overall, the proposed antenna had an omnidirectional radiation pattern and +8.45 dBm input to meet the specific absorption rate regulation limit.

An approach for brain-controlled prostheses based on Scene Graph Steady-State Visual Evoked Potentials

Brain control technology can restore communication between the brain and a prosthesis, and choosing a Brain-Computer Interface (BCI) paradigm to evoke electroencephalogram (EEG) signals is an essential step for developing this technology. In this paper, the Scene Graph paradigm used for controlling prostheses was proposed; this paradigm is based on Steady-State Visual Evoked Potentials (SSVEPs) regarding the Scene Graph of a subject’s intention. A mathematic model was built to predict SSVEPs evoked by the proposed paradigm and a sinusoidal stimulation method was used to present the Scene Graph stimulus to elicit SSVEPs from subjects. Then, a 2-degree of freedom (2-DOF) brain-controlled prosthesis system was constructed to validate the performance of the Scene Graph-SSVEP (SG-SSVEP)-based BCI. The classification of SG-SSVEPs was detected via the Canonical Correlation Analysis (CCA) approach.To assess the efficiency of proposed BCI system, the performances of traditional SSVEP-BCI system were compared. Experimental results from six subjects suggested that the proposed system effectively enhanced the SSVEP responses, decreased the degradation of SSVEP strength and reduced the visual fatigue in comparison with the traditional SSVEP-BCI system. The average signal to noise ratio (SNR) of SG-SSVEP was 6.31 ± 2.64 dB, versus 3.38 ± 0.78 dB of traditional-SSVEP. In addition, the proposed system achieved good performances in prosthesis control. The average accuracy was 94.58% ± 7.05%, and the corresponding high information transfer rate (IRT) was 19.55 ± 3.07 bit/min. The experimental results revealed that the SG-SSVEP based BCI system achieves the good performance and improved the stability relative to the conventional approach.

Sensorless control system for assistive robotic ankle-foot

This article presents a novel sensorless control system of assistive robotic ankle-foot prosthesis, two estimation algorithms were developed and an analogy between them has been made. The system actuator’s motor is a permanent magnet synchronous motor, unlike other powered ankle-foot, where the brushless DC motor and DC motor were used. Utilizing the permanent magnet synchronous motor will reduce the torque ripples and increase system ability to be overloaded compared to systems which utilize the brushless DC motor. Moreover, the ability of the machine to operate in all speed range makes this machine more suitable for the application. Both estimation algorithms are built using C-code and assessed in MATLAB Simulink. The estimation algorithms are used to provide motor and powered ankle-foot’s angular speed and position. Two-level control system is used to evaluate the estimation algorithms; the control system role is to mimic biological ankle-foot performance during normal ground level walking speed. Based on the result of this article the unscented Kalman filter (UKF) is applicable for the application, as a result of the observer ability to estimate the motor load and angular position. On the other hand, extended Kalman filter (EKF) accuracy is affected by the load applied to the motor. Furthermore, the angular position is evaluated by integration of the angular speed which means integration of angular speed estimation error.

Distinct frequency bands in the local field potential are differently tuned to stimulus drift rate.

Local field potential (LFP) recorded with a microelectrode reflects the activity of several neural processes, including afferent synaptic inputs, microcircuit-level computations, and spiking activity. Objectively probing their contribution requires a design that allows dissociation between these potential contributors. Earlier reports have shown that the primate lateral geniculate nucleus (LGN) has a higher temporal frequency (drift rate) cutoff than the primary visual cortex (V1), such that at higher drift rates inputs into V1 from the LGN continue to persist, whereas output ceases, permitting partial dissociation. Using chronic microelectrode arrays, we recorded spikes and LFP from V1 of passively fixating macaques while presenting sinusoidal gratings drifting over a wide range. We further optimized the gratings to produce strong gamma oscillations, since recent studies in rodent V1 have reported LGN-dependent narrow-band gamma oscillations. Consistent with earlier reports, power in higher LFP frequencies (above ~140 Hz) tracked the population firing rate and were tuned to preferred drift rates similar to those for spikes. Significantly, power in the lower (up to ~40 Hz) frequencies increased transiently in the early epoch after stimulus onset, even at high drift rates, and had preferred drift rates higher than for spikes/high gamma. Narrow-band gamma (50-80 Hz) power was not strongly correlated with power in high or low frequencies and had much lower preferred temporal frequencies. Our results demonstrate that distinct frequency bands of the V1 LFP show diverse tuning profiles, which may potentially convey different attributes of the underlying neural activity. NEW & NOTEWORTHY In recent years the local field potential (LFP) has been increasingly studied, but interpreting its rich frequency content has been difficult. We use a stimulus manipulation that generates different tuning profiles for low, gamma, and high frequencies of the LFP, suggesting contributions from potentially different sources. Our results have possible implications for design of better neural prosthesis systems and brain-machine interfacing applications.

Target of physiological gait: Realization of speed adaptive control for a prosthetic knee during swing flexion.

Prosthetic knee is the most important component of lower limb prosthesis. Speed adaptive for prosthetic knee during swing flexion is the key method to realize physiological gait. This study aims to discuss the target of physiological gait, propose a speed adaptive control method during swing flexion and research the damping adjustment law of intelligent hydraulic prosthetic knee. According to the physiological gait trials of healthy people, the control target during swing flexion is defined. A new prosthetic knee with fuzzy logical control during swing flexion is designed to realize the damping adjustment automatically. The function simulation and evaluation system of intelligent knee prosthesis is provided. Speed adaptive control test of the intelligent prosthetic knee in different velocities are researched. The maximum swing flexion of the knee angle is set between sixty degree and seventy degree as the target of physiological gait. Preliminary experimental results demonstrate that the prosthetic knee with fuzzy logical control is able to realize physiological gait under different speeds. The faster the walking, the bigger the valve closure percentage of the hydraulic prosthetic knee. The proposed fuzzy logical control strategy and intelligent hydraulic prosthetic knee are effective for the amputee to achieve physiological gait.

Numerical comparison of two different tibial nails: expert tibial nail and innovative nail

The extended usage of unreamed tibial nailing resulted in reports of an increased rate of complications, especially for the distal portion of the tibia. Unreamed nailing favors biology at the expense of the achievable mechanical stability, it is therefore of interest to define the limits of the clinical indications for this method. Extra-articular fractures of the distal tibial metaphysis, meta-diaphyseal junction, and adjacent diaphysis are distinct in their management from impaction derived “pilon” type fractures and mid-diaphyseal fractures. With this purpose a complete model of the human tibia was realized, simulating a mid-diaphyseal fracture, classified as A2 type 1, according to the AO classification. Two different FE models of nail were developed in order to carry on a mechanical comparison between an innovative design of nail for fractures occurring on long bones and a traditional intra-medullary nail expert tibial nail (DePuy Synthes $$^{\textregistered }$$ ). The innovative nail’s functioning is based essentially on sliding of conical surfaces, located in a spindle and in holding pins. Spindle and holding pins are connected together by a sleeve. The sliding transforms the rotational and translational motion of the spindle to a radial expansion of the holding pins, protruding inside the intramedullary canal. Results obtained by a non-linear finite element analysis of the models were performed with Abaqus version 5.4 (Hibbitt, Karlsson and Sorensen, Inc., Pawtucket, RI, USA) using the geometric non-linearity and automatic time stepping options. In particular, analyses confirmed a satisfactory behavior of the nail in terms of stress and strain shielding, comparable to the other traditional system of prosthesis. In conclusion, this kind of nail appears to offer a good solution for elderly patients, which could not endure complications due to a complex surgery, as distal or medial screws are not necessary.

Advanced Functional Materials Solutions to Engineering the Neural Interface

Advanced Functional Materials Solutions to Engineering the Neural Interface

Retinal prosthesis system: a revolutionary advancement for the severely visually impaired

Despite all the advancements in modern ophthalmology, disease can affect vision, resulting in blindness. Worldwide, there are 200 000 people who have retinitis pigmentosa, 2 million with age-related macular degeneration (AMD) and 6 million have other forms of sight loss.