13:00
Body - implant interfacing
Chair: Bennie ten Haken
13:00
15 mins
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Titanium Nanostructures Produced by Inductively Coupled Plasma Reactive Ion Etching and their Effects on Cells
Mahya Ganjian, Khashayar Modaresifar, Kees Hagen, Peter-Leon Hagedoorn, Linda Otten, Michelle Minneboo, Lidy Fratila-Apachitei, Amir A Zadpoor
Abstract: Upon implants insertion in the human body, both host and bacterial cells compete for adhesion and growth on the surface of the implants. Surfaces that can stimulate new tissue formation while preventing bacterial growth are therefore desirable. Topography represents one of the surface properties of implants that can be used to influence cell behavior. In this regard, methods that enable generation of controlled topographies on appropriate biomaterials are of great interest. One such method is Inductively Coupled Plasma Reactive Ion Etching (ICP RIE) which can generate high aspect ratio nanostructures (e.g., inspired by Dragonfly wings [1]) on large areas very fast, without the need for masks and wet processes as in the case of lithography-based methods. Several studies applied this method to generate nanostructures on Si wafers, known as black Si [1]–[3]. However, Si is not the material of choice for implants. Creating these topographies on Ti is clinically relevant for bone implants.
The aim of this study was twofold; firstly, the effects of the ICP RIE conditions on the morphology, wettability and mechanical properties of resultant titanium structures were investigated. Secondly, the in vitro response of preosteoblast and bacterial cells on such surfaces was assessed. Titanium foil was used as the substrate. The titanium samples were first polished and then etched using a Plasmalab System 100 (Oxford Instruments). ICP RIE conditions included Cl2/Ar flow rates, chamber pressure, temperature, and etching time.
Depending on the ICP RIE conditions used, nanoporous and high aspect ratio nanopillars were obtained. These different morphologies induced changes in wettability and mechanical properties of the structures. In addition, a differential response of preosteoblasts and bacterial cells was observed indicating the potential of these topographies for achieving bone implants with dual biofunctionalities.
[1] E. P. Ivanova et al., “Bactericidal activity of black silicon,” Nat. Commun., pp. 1–7, 2013.
[2] S. Ghosh et al., “Analysis of killing of growing cells and dormant and germinated spores of Bacillus species by black silicon nanopillars,” no. December, pp. 1–13, 2017.
[3] C. M. Bhadra et al., “Subtle Variations in Surface Properties of Black Silicon Surfaces Influence the Degree of Bactericidal Efficiency,” Nano-Micro Lett., vol. 10, no. 2, 2018.
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13:15
15 mins
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The Effect of Different Interference Fit on Micromotions and Opening in a Cementless Femoral TKA Component
Esther Sanchez Garza, Christoph Schilling, Thomas Grupp, Nico Verdonschot, Dennis Janssen
Abstract: INTRODUCTION: Cementless femoral total knee arthroplasty (TKA) implants use a press-fit or interference fit to achieve fixation. A greater interference fit, or thicker implant coating could lead to a superior fixation, but it could also introduce more damage to the bone during implantation. The primary stability is measured as the amount of relative displacement between the implant and the bone, which are known as micromotions. The purpose of the current study was to study the micromotions between two implant designs with different coating thickness.
METHODS: A previous experimental set-up was used to test 6 pairs of human cadaveric femurs implanted with e.motion femoral components (Total Knee System, B. Braun) using a standard interference fit of 350µm and a novel interference fit of 700 µm. The specimens were subjected to the peak loads of gait (1960N) and squat (1935N), based on Orthoload dataset. Digital Image Correlation (DIC) was used to measure the micromotions as the shear component of the displacement at different regions of interest (ROIs); opening and closing of the implant was considered as the normal component of displacement. Univariate General Linear Models (GLMs) were created with design, loading, and ROI as fixed factors.
RESULTS: No significant difference was found between the two interference fit (P=0.374). In contrast, loading had a significant difference (P=0.008) with micromotions being on average 10µ higher for squat. Loading also had a significant effect on gap opening (P<0.0001) with nearly 30µ higher for squat, whereas design was not a significant factor (P=0.9).
DISCUSSION: In the current study, the primary stability of the same implant with two different interference fit was evaluated. The results demonstrate that increasing the coating thickness does not automatically influence the primary stability of a femoral TKA component. The exact relation between interference fit and primary implant stability still remains subject to debate and requires further evaluation, possibly utilizing a computational technique approach.
SIGNIFICANCE: It is necessary to ensure a good primary stability between the bone and the implant for a better long-term fixation and reduce the risk of implant loosening.
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13:30
15 mins
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Surface Physical Nanocues with Bactericidal Activity
Khashayar Modaresifar, Mahya Ganjian, Manon Ligeon, Dwisetya Widyaratih, Cornelis Hagen, Peter-Leon Hagedoorn, Linda Otten, Lidy Fratila-Apachitei, Amir Zadpoor
Abstract: Implant-associated infection is one of the major causes of orthopaedic implants failure. To date, numerous chemical and physical methods have been proposed to combat the bacterial infection, including the use of nanopatterns which mechanically rupture and kill the bacteria [1]. Although there are several methods to produce such nanopatterns (e.g. reactive ion etching, chemical etching, and nanoimprint lithography), the control of relevant pattern characteristics such as the interspace and controlled disorder is still limited. This hinders the advances with regard to rational design and optimization of such structures for maximizing their antibacterial activity. The aim of this study was to investigate the potential of electron beam induced deposition (EBID) technique for developing bactericidal nanopatterns. EBID conditions were optimized to fabricate ordered and controlled disordered nanopillars with different diameters and heights. Gram-negative bacteria, E. coli, and Gram-positive bacteria, S. aureus, were cultured on such nanopatterned surfaces at 37 °C for 18 h. The bacteria were then fixed and their morphology was investigated by scanning electron microscopy (SEM) to observe any damage or death in cells. The results showed that ordered nanopillars with a height of 186 ± 8 nm, base diameter of 75 ± 5 nm, and interspacing of 172 ± 4 nm exhibit a high bactericidal efficiency against both type of bacteria. The direct penetration of nanopatterns into the bacterial cell wall and its mechanical rupture was also observed in the SEM images. Additionally, it was shown that controlled disorder may affect the bactericidal efficiency of the nanopatterns. The results of this study are promising for designing biomaterials capable of killing the bacteria without using antibiotics or antibacterial releasing systems which could help circumvent the growing crisis of antibacterial resistance.
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13:45
15 mins
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Energy Efficient Sampling and Conversion of Bio-Signals Using Time-Mode Circuits
Omer Can Akgun, Wouter Serdijn
Abstract: With the continuous developments in science and engineering, specifically in the fields of electronics and manufacturing, implantable electronic devices have become a reality during the last decades. Implantable electronic devices have hard design constraints: 1) As small size as possible to reduce tissue damage, 2) Minimum heat generation to protect the surrounding tissue, and 3) Minimum energy dissipation as these devices are mostly operated using a small battery or wireless power transfer.
The advancement and scaling of CMOS technologies has always been based on improving the performance of digital systems. With each new technology node, the threshold voltages of the available MOS transistors and the supply voltage of the process node is scaled as well. Scaling of the supply voltage reduces the headroom that is available to the transistors for operating in the region. Even though reducing the supply voltage reduces the energy dissipation, without transistors operating in the saturation region, it is very hard to realize signal processing and amplification functions in the analogue domain.
To address the mentioned hard constraints of implantable electronic device design, we propose time-mode circuits for energy efficient sampling and conversion of bio-signals in advanced process technologies. The types of circuits we are proposing benefit both from voltage scaling and smaller size of advanced process nodes while being able to process digital signals with analogue accuracy, i.e., time-mode circuits represent an analogue signal by the time difference between two binary switching events. For example, when compared to standard digital CMOS circuit operation, to transfer N bits of data in parallel, the number of switchings required may change from 0 to N in standard CMOS, while it always takes time-mode circuits two switching if the rising and falling edges of a pulse is used for signal representation.
Based on these observations, we designed a bio-signal sampling and conversion system that consists of an analogue-to-time converter (ATC) followed by an asynchronous time-to-digital converter (A-TDC). The ATC converts the sampled bio-signal to a time-pulse with a high analogue-to-time conversion gain, and the A-TDC resolves this generated pulse to a digital value, completing the sampling and conversion process. We will present the design process and simulation results of such an implementation that operates with a supply voltage of 0.6V in a standard 0.18um process.
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14:00
15 mins
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A Soft Exosuit for Assistance of the Elbow Joint: Design and Control
Lorenzo Masia, Michele Xiloyannis
Abstract: The use of fabric-based frames and tendon driven actuation to deliver forces and torques to the human body provides a new design which actively assist motion and which is characterized by lighter, more comfortable and cosmetically less invasive architectures than traditional rigid exoskeletons. This approach has shown to be successful in reducing the metabolic cost and muscular effort of human movements and in assisting impaired subject in daily activities. Yet still very little is known about how to design and optimise the transmission of forces at the interface between the suit and the human body, with significant implications for comfort, efficiency and safety of the device. Our research aims to outline the design and characterisation of a soft, textile-based exosuit for assistance of flexion/extension of the elbow joint and of the hand, with emphasis on a data-driven design for optimising the efficiency of the transmission and the distribution of forces at the interface between the wearer and the exosuit. Quantifying and understanding how design choices such as the materials used for transmitting power and the structure of the functional components of the suit affect these parameters can help us to improve the ergonomics, safety and effectiveness of such devices. Results obtained by comparing different transmissions constructions show that the ones with a linear-strand construction offer the highest efficiency and stiffness, lowest backlash and lowest viscous friction. Combining semi-rigid components with fabric at the anchor points of the suit allows for a more homogeneous distribution of force at the human-suit interface, avoiding peaks of pressure that can disrupt subcutaneous blood flow and cause tissue damage. We also would like to propose a novel hierarchical control architecture which use embedded sensors and a simple model of the arm's biomechanics to increase the transparency of the device, provide robustness and fidelity of haptic rendering.
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14:15
15 mins
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Polymer-Encapsulated Single-Chip Implants for Bioelectronic Medicine
Kambiz Nanbakhsh, Wouter Serdijn, Vasiliki Giagka
Abstract: The main goal of bioelectronic medicine is to, one day, replace conventional chemical drugs with miniaturized implants. This way, tiny electrical pulses will be locally delivered to a small group of neurons in order to influence and modify biological functions. Developing such implants, however, has brought many new challenges both in the technological and biological domains. One technical challenge, is packaging such tiny deceives in a way that protects the sensitive electronics inside from the harsh body environment [2], while, at the same time ensures certain flexibility that allows the implant to conform to the surrounding soft tissue.
Conventionally, medical implants have relied on a titanium (Ti) or ceramic box to protect the inside electronics. Driven by the increased functionality offered by CMOS technologies and the need for further miniaturization, in recent years tremendous efforts have been made in designing miniaturized implants by integrating the majority of components on a single chip [3]. Such a single-chip approach, however, would require novel packaging solutions since the box would consume greater volume compared to the chip and greatly limit the flexibility of the implant. Polymer encapsulation could be an alternative packaging solution which meets the physical constraints needed for bioelectronic medicine [1-2].
One main drawback of polymeric encapsulation, however, is the eventual penetration of water through the polymer. For this purpose, extensive efforts have been carried out on finding thin multi-layer coatings that could delay water and ion penetration and thereby, increase device lifetime [3]. Despite the increased protection offered by these layers, it has been shown that device lifetime can still be reduced when exposed to high electric fields. For example, the authors of [4] have found that continuous DC biasing of the device reduced the lifetime by a factor of 13 compared to a state where the devices were idle.
In this research, we intend to work towards a single-chip implant by investigating the effect of different electric fields on device lifetimes in soak conditions. For this aim, test structures have been fabricated in standard CMOS technologies and currently being tested in saline. More detailed and up-to-date results will be shared during the conference.
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