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Development of an artifact-free aneurysm clip

Concept and approach for the development of an aneurysm clip entirely made from fiber-reinforced plastic materials
  • Alexander Brack EMAIL logo , Sebastian Senger , Gerrit Fischer , Henning Janssen , Joachim Oertel and Christian Brecher
Published/Copyright: September 30, 2016
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Current Directions in Biomedical Engineering
From the journal Current Directions in Biomedical Engineering Volume 2 Issue 1

Abstract

For the treatment of intracranial aneurysms with aneurysm clips, usually a follow-up inspection in MRI is required. To avoid any artifacts, which can make a proper diagnosis difficult, a new approach for the manufacturing of an aneurysm clip entirely made from fiber-reinforced plastics has been developed. In this paper the concept for the design of the clip, the development of a new manufacturing technology for the fiber-reinforced components as well as first results from the examination of the components in phantom MRI testing is shown.

Keywords: aneurysm clip; artifact-free; CFRP; fiber-reinforced plastics; intracranial aneurysm; PEEK; pultrusion

1 Introduction

Intracranial aneurysms are congenital or acquired bulges of cerebral arteries, presumably caused by local defects at the branching of basal cerebral arteries [1]. The surgical management of such aneurysms by the application of aneurysm clips is a well-established procedure in neurosurgery. With those clips the aneurysm gets clamped off in order to exclude them from bloodstream and thereby avoid life-threatening cerebral bleedings. The aim of this procedure is to totally occlude the aneurysm, while preserving flow in the involved vessels. Postoperative diagnostic is mandatory to detect possible objectionable results such as incomplete occlusions or neck remnants [2]. Materials in conventional clips, e.g. titanium, cause artifacts in Magnetic resonance imaging (MRI). Those artifacts considerably exacerbate the diagnosis of the aneurysm and the surrounding tissue. Therefore, in postoperative diagnosis often invasive examinations with catheters or examinations which go along with radiation exposure as in X-ray computed tomography (CT) have to be performed instead.

In order to allow for an artifact-free imaging and at the same time meet the mechanical requirements of the clip, innovative materials are required. Fiber-reinforced plastics (FRP) face these requirements by the combination of different fiber and matrix materials, so that highly customized components can be designed especially for the intended usage. For the precise and patient-friendly diagnosis using MRI imaging, fiber-reinforced plastics are unrivaled to other materials, as they show no spurious artefacts, show excellent mechanical properties and have good biocompatibility characteristics [3]. First attempts with hybrid solutions containing metal based springs and carbon fiber reinforced yaws did not find their way into clinical application [4].

However, the biggest challenge and obstacle up to now to actually use fiber-reinforced plastics in implants like aneurysm clips is the development and manufacturing of miniaturized, biocompatible and high strength fiber-reinforced profiles at the required level of complexity.

2 Material and methods

There are several types of aneurysm clips on the market, which have been analyzed according to the possibility to substitute the used metallic materials by fiber-reinforced plastics. The type of clip shown in Figure 1 was selected, as it shows both advantages for the manufacturing and for the application during surgery. The differential design of the clip offers the possibility to use different processes for the manufacturing of the spring and the jaws.

Figure 1: A state-of-the-art aneurysm clip made from titanium by Peter Lazic GmbH, Tuttlingen.
Figure 1:

A state-of-the-art aneurysm clip made from titanium by Peter Lazic GmbH, Tuttlingen.

Also, the exploitation of the load-optimized fiber-reinforcement can be increased by a part-wise manufacturing of the clip.

In terms of the application, this type of clip allows a better sight into the surgical field by an opening from the inside out. Also, the opening of the clips is very wide in comparison with other types of aneurysm clips [5].

Figure 2 shows the concept for the design of the clip and the used manufacturing processes for the components. A continuous fiber-reinforcement has to be used for the spring, to achieve the required spring tension. For the jaws, reinforcement with short carbon-fibers is used to enable the manufacturing of complex structures such as the brackets for the forceps or the atraumatic structuring of the jaws. In addition, different types of jaws can be easily manufactured without changing the general design.

Figure 2: Concept of manufacturing an aneurysm clip using only thermoplastic fiber-reinforced components.
Figure 2:

Concept of manufacturing an aneurysm clip using only thermoplastic fiber-reinforced components.

Following this concept, a small, unidirectional fiber-reinforced rod is manufactured, which is subsequently formed to a helical torsion spring. The forming step requires a thermoplastic polymer, as only this class of polymers allows the subsequent melting and re-shaping. The jaws are manufactured in an injection molding process using short carbon-fiber reinforced plastic. The assembly of the clip is done by plastic welding.

The material for both the spring and the jaws was chosen to be carbon-fiber reinforced PEEK, because of its very high mechanical forces, especially in terms of bending stiffness and strength and the possibility of a subsequent forming. It also shows no artifact in MRI and the biocompatibility for implants is proven [6].

3 Approach

The approach for the manufacturing of the spring is the use of the micro-pultrusion technology. Pultrusion is a process for the continuous and automated production of unidirectional fiber-reinforced profiles. It has been miniaturized at Fraunhofer IPT for manufacturing diameters down to 200 μm and has been successfully applied for the manufacturing of medical devices, such as fiber-reinforced puncture needles, catheters and guide wires [7].

Pultrusion allows the highest possible mechanical properties in terms of bending stiffness and strength by a consistent alignment of the fibers in axial direction only and a very high fiber-volume content of up to 80%. As the load case in a helical torsion spring induces mainly bending forces on the profile, pultrusion is an applicable manufacturing process for the wire. However, only thermoset polymers are currently suitable for miniaturized pultrusion processes, which have the major drawback for the use in the clip, as they cannot be melted and re-shaped after curing. Also, only a few thermoset polymers suitable for FRP are certified for biocompatibility standards [8].

The biggest challenge of processing thermoplastic polymers such as PEEK in the micro-pultrusion process is the high melt viscosity of the matrix material, which makes a proper impregnation of the fibers difficult and requires high processing temperatures and pressures. The chosen approach is the processing of pre-impregnated materials, so called prepregs or tapes, instead of separated fiber and matrix materials. Using this principle, the impregnation and consolidation step is done already by the tape manufacturer and does not have to be realized within the used equipment. One drawback of using tapes for pultrusion is the very high costs for the materials compared to the prices of the raw materials [9]. As only small amounts of material are processed for the production of the spring element, this disadvantage can be neglected.

Figure 3 shows the machine setup, which was developed and built up during the project. Tapes with a rectangular cross-section are slitted to the correct dimension and pulled through a heated forming die, where they perform a continuous forming process to realize the desired geometry.

Figure 3: Pultrusion unit for the manufacturing of the FRP rod.
Figure 3:

Pultrusion unit for the manufacturing of the FRP rod.

After the manufacturing of a FRP rod, a thermoforming step is required. For this, a small test rig was built up to investigate the feasibility of the process.

4 Results

Using FEM-simulations it could be shown that the bending stiffness to achieve the required clipping force can be achieved by using a micro-profile made from carbon-fiber reinforced plastic with a diameter of around 1.1 mm. At the same time, the opening of the jaws can be realized by the use of a helical torsion spring with a multiple number of turns.

In first trials, small rods with a diameter of 1.1 mm were manufactured, using tape material of PA12 and PEEK, continuously reinforced with 55 vol.-% carbon fibers. The analysis of the manufactured profiles showed a homogenous fiber distribution and high fiber volume content. The mechanical properties were in the same range as the used tape material. Figure 4 shows microscopic images of the cross-section of the pultruded profiles.

Figure 4: Pultruded micro-profiles made from PEEK/CF (left) and PA12/CF (right).
Figure 4:

Pultruded micro-profiles made from PEEK/CF (left) and PA12/CF (right).

In further trials the forming of the profiles was investigated. For a first analysis of the feasibility, a heated pin was used, where the pre-heated profiles were bent around manually. The result of this manual winding of a PA12/CF rod can be seen in Figure 5. A winding diameter of 3 mm using a rod with a diameter of 1.1 mm could be achieved with a satisfying quality of the profile.

Figure 5: Helical torsion spring made from unidirectional reinforced PA12/CF.
Figure 5:

Helical torsion spring made from unidirectional reinforced PA12/CF.

Spring samples made from PA12/CF were tested in water solution via three Tesla MRI (Skyra, Siemens, Germany). MRI was performed including the following sequences: T2 in the axial plane [repetition time (TR) of 7.300, echo time (TE) of 88, slice thickness of 2 mm] and coronar plane (TR of 8.600, TE of 91, slice thickness of 1.5 mm), T1 in the coronar plane (TR of 600, TE of 12, slice thickness of 0.7 mm).

The evaluation of the MRI images showed only minor artifacts caused by small air bubbles at the sample surface (Figure 6). No difference in image quality between the different number of windings was seen in the MRI. Overall a clear delineation of the profile to the surrounding water was possible.

Figure 6: T2 images of PA12/CF springs with different winding numbers.
Figure 6:

T2 images of PA12/CF springs with different winding numbers.

5 Discussion

For the development of an artifact-free aneurysm clip entirely made from fiber-reinforced plastics, a concept has been developed, which allows the manufacturing of the components using different and especially designed production processes. The concept takes all the different requirements for the clip into account, such as mechanical forces, small size, wide opening of the jaws, biocompatibility and visibility in MRI.

A new process for the continuous manufacturing of miniaturized rods made from thermoplastic FRP using pre-impregnated tape material could be established. The required system technology has been developed, built up and put into operation. Sample rods using carbon-fiber reinforced PA12 and PEEK show the possibilities of the process. Based on the results of the manufacturing process, all kinds of thermoplastic polymers, that are available as tape material, can be processed with the developed technology. Also, the diameter of the profiles can be further reduced.

The feasibility of a thermoforming of the profile in the required dimensions could be shown. The forming of PA12 profiles has shown decent results, whereas the forming of PEEK profiles requires some deeper investigations of the process. The assembly of the clip using plastic welding was not investigated yet.

The MRI investigation revealed the required absence of artefacts as expected. In vivo investigations for more detailed analyses including breathing artefacts and contrast agent enhanced imaging are currently in progress.

Acknowledgement

The results described in this paper were made during the research project “MR-Clip”. The authors like to thank all participants of the project, namely Peter Lazic GmbH, Werner Grathwohl Werkzeugbau and M.TEC GmbH. We would like to thank Prof. Reith and the Institute of Neuroradiology for the support in the MRI-analysis.

Author’s Statement

Research funding: The authors would like to thank the German Federal Ministry for Education and Research (BMBF) for funding the research project “Vollständig artefaktfreier Aneurysmaclip aus Faserverbundkunststoff (MR-Clip)” within the funding initiative “KMU-innovativ: Medizintechnik” (contract number 13GW00622E). Conflict of interest: Authors state no conflict of interest. Material and methods: Informed consent: Informed consent is not applicable. Ethical approval: The conducted research is not related to either human or animal use.

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Published Online: 2016-9-30
Published in Print: 2016-9-1

©2016 Alexander Brack et al., licensee De Gruyter.

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

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https://doi.org/10.1515/cdbme-2016-0120
Keywords for this article
aneurysm clip; artifact-free; CFRP; fiber-reinforced plastics; intracranial aneurysm; PEEK; pultrusion
Creative Commons
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  85. Smart control for functional electrical stimulation with optimal pulse intensity
  86. Tactile display on the remaining hand for unilateral hand amputees
  87. Effects of sustained electrical stimulation on spasticity assessed by the pendulum test
  88. An improved tracking framework for ultrasound probe localization in image-guided radiosurgery
  89. Improvement of a subviral particle tracker by the use of a LAP-Kalman-algorithm
  90. Learning discriminative classification models for grading anal intraepithelial neoplasia
  91. Regularization of EIT reconstruction based on multi-scales wavelet transforms
  92. Assessing MRI susceptibility artefact through an indicator of image distortion
  93. EyeGuidance – a computer controlled system to guide eye movements
  94. A framework for feedback-based segmentation of 3D image stacks
  95. Doppler optical coherence tomography as a promising tool for detecting fluid in the human middle ear
  96. 3D Local in vivo Environment (LivE) imaging for single cell protein analysis of bone tissue
  97. Inside-Out access strategy using new trans-vascular catheter approach
  98. US/MRI fusion with new optical tracking and marker approach for interventional procedures inside the MRI suite
  99. Impact of different registration methods in MEG source analysis
  100. 3D segmentation of thyroid ultrasound images using active contours
  101. Designing a compact MRI motion phantom
  102. Cerebral cortex classification by conditional random fields applied to intraoperative thermal imaging
  103. Classification of indirect immunofluorescence images using thresholded local binary count features
  104. Analysis of muscle fatigue conditions using time-frequency images and GLCM features
  105. Numerical evaluation of image parameters of ETR-1
  106. Fabrication of a compliant phantom of the human aortic arch for use in Particle Image Velocimetry (PIV) experimentation
  107. Effect of the number of electrodes on the reconstructed lung shape in electrical impedance tomography
  108. Hardware dependencies of GPU-accelerated beamformer performances for microwave breast cancer detection
  109. Computer assisted assessment of progressing osteoradionecrosis of the jaw for clinical diagnosis and treatment
  110. Evaluation of reconstruction parameters of electrical impedance tomography on aorta detection during saline bolus injection
  111. Evaluation of open-source software for the lung segmentation
  112. Automatic determination of lung features of CF patients in CT scans
  113. Image analysis of self-organized multicellular patterns
  114. Effect of key parameters on synthesis of superparamagnetic nanoparticles (SPIONs)
  115. Radiopacity assessment of neurovascular implants
  116. Development of a desiccant based dielectric for monitoring humidity conditions in miniaturized hermetic implantable packages
  117. Development of an artifact-free aneurysm clip
  118. Enhancing the regeneration of bone defects by alkalizing the peri-implant zone – an in vitro approach
  119. Rapid prototyping of replica knee implants for in vitro testing
  120. Protecting ultra- and hyperhydrophilic implant surfaces in dry state from loss of wettability
  121. Advanced wettability analysis of implant surfaces
  122. Patient-specific hip prostheses designed by surgeons
  123. Plasma treatment on novel carbon fiber reinforced PEEK cages to enhance bioactivity
  124. Wear of a total intervertebral disc prosthesis
  125. Digital health and digital biomarkers – enabling value chains on health data
  126. Usability in the lifecycle of medical software development
  127. Influence of different test gases in a non-destructive 100% quality control system for medical devices
  128. Device development guided by user satisfaction survey on auricular vagus nerve stimulation
  129. Empirical assessment of the time course of innovation in biomedical engineering: first results of a comparative approach
  130. Effect of left atrial hypertrophy on P-wave morphology in a computational model
  131. Simulation of intracardiac electrograms around acute ablation lesions
  132. Parametrization of activation based cardiac electrophysiology models using bidomain model simulations
  133. Assessment of nasal resistance using computational fluid dynamics
  134. Resistance in a non-linear autoregressive model of pulmonary mechanics
  135. Inspiratory and expiratory elastance in a non-linear autoregressive model of pulmonary mechanics
  136. Determination of regional lung function in cystic fibrosis using electrical impedance tomography
  137. Development of parietal bone surrogates for parietal graft lift training
  138. Numerical simulation of mechanically stimulated bone remodelling
  139. Conversion of engineering stresses to Cauchy stresses in tensile and compression tests of thermoplastic polymers
  140. Numerical examinations of simplified spondylodesis models concerning energy absorption in magnetic resonance imaging
  141. Principle study on the signal connection at transabdominal fetal pulse oximetry
  142. Influence of Siluron® insertion on model drug distribution in the simulated vitreous body
  143. Evaluating different approaches to identify a three parameter gas exchange model
  144. Effects of fibrosis on the extracellular potential based on 3D reconstructions from histological sections of heart tissue
  145. From imaging to hemodynamics – how reconstruction kernels influence the blood flow predictions in intracranial aneurysms
  146. Flow optimised design of a novel point-of-care diagnostic device for the detection of disease specific biomarkers
  147. Improved FPGA controlled artificial vascular system for plethysmographic measurements
  148. Minimally spaced electrode positions for multi-functional chest sensors: ECG and respiratory signal estimation
  149. Automated detection of alveolar arches for nasoalveolar molding in cleft lip and palate treatment
  150. Control scheme selection in human-machine- interfaces by analysis of activity signals
  151. Event-based sampling for reducing communication load in realtime human motion analysis by wireless inertial sensor networks
  152. Automatic pairing of inertial sensors to lower limb segments – a plug-and-play approach
  153. Contactless respiratory monitoring system for magnetic resonance imaging applications using a laser range sensor
  154. Interactive monitoring system for visual respiratory biofeedback
  155. Development of a low-cost senor based aid for visually impaired people
  156. Patient assistive system for the shoulder joint
  157. A passive beating heart setup for interventional cardiology training
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