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The glass transition temperature of as-deposited parylene-C is first measured to be 50°C with a ramping-temperature-dependent modulus experiment. The creep behavior of parylene-C film in the primary and secondary creep region is then investigated below and above this glass transition temperature using a dynamic mechanical analysis (DMA) machine Q80...
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... Maxwell model and the Kelvin model are two of the most fundamental ones. A single Maxwell model consists of one linear spring in series with a dashpot, while a single Kelvin model is composed of one spring in parallel with a dashpot, as shown as the inserts in Figure 7. Both Maxwell element and Kelvin element are often combined either in parallel or in series to model viscoelastic behavior. ...
Context 2
... this work, it is found that 4-element Burger's model, i.e., a Kelvin element in series with a Maxwell element (hence a single retardation time constant) is adequate to describe our data. As the Burger's model shown in Figure 7, the spring of the Maxwell element represents the instantaneous strain and the dashpot simulates the steady strain rate of the creep behavior in the long time. The equilibrium equation: of the Burger's model is: ...
Citations
... However, these processes pose serious health and safety concerns (Zhang et al., 2010;Ding et al., 2015), and may also be incompatible with other electrode components, such as encapsulating polymers. For materials such as parylene-C, polyimide (PI), SU-8, and polyethylene terephthalate (PET), the glass transition temperature (T g ) lies in the $120 C-300 C range (Yokota et al., 2001;Harder et al., 2002;Lin et al., 2011;Chung and Park, 2013;Kahouli et al., 2014), which precludes high temperature annealing. Furthermore, it has been shown that hydrazine causes long-term degradation of a variety of polymeric films (Dine-Hart et al., 1971;Goel et al., 2009). ...
Nanocarbons are often employed as coatings for neural electrodes to enhance surface area. However, processing and integrating them into microfabrication flows requires complex and harmful chemical and heating conditions. This article presents a safe, scalable, cost-effective method to produce reduced graphene oxide (rGO) coatings using vitamin C (VC) as the reducing agent. We spray coat GO + VC mixtures onto target substrates, and then heat samples for 15 min at 150°C. The resulting rGO films have conductivities of ∼44 S cm-1, and are easily integrated into an ad hoc microfabrication flow. The rGO/Au microelectrodes show ∼8x lower impedance and ∼400x higher capacitance than bare Au, resulting in significantly enhanced charge storage and injection capacity. We subsequently use rGO/Au arrays to detect dopamine in vitro, and to map cortical activity intraoperatively over rat whisker barrel cortex, demonstrating that conductive VC-rGO coatings improve the performance and stability of multimodal microelectrodes for different applications.
... From Figure 3, it can be seen that our results show a sudden drop in the temperature ranging from 40°C to 50°C, which can be considered as the glass transition region of PPXC film samples. The result from quasi-static nanoindentation also shows good consistency with previous work (with TA Instruments Q800) [8], in which the T g was determined as 50°C. ...
... PPXC Film, ~3mg* DSC 44 [5] PPXC Film, 21.5 m Tensile Test 50 [8] PPXC-120,050 atoms Figure. 2(a)) was used to investigate the complex modulus (see Figure. ...
... In consequence, the master curve at 37°C can be plotted in Figure 6(a)). The PPXC's Young's modulus (with TI 950 Tribointenter) as a function of temperature, was consistent with that in the previous work (with TA Instruments Q800) ( Figure 3) [8]. In addition, the T g from Ref [8] was 50°C, while the measured curve in the present work ( Figure. ...
We present a comparative study of the viscoelasticity of parylene C (PPXC) by using Nano-DMA (Dynamical Mechanical Analysis) and Molecular Dynamics (MD) simulations. By applying sinusoidal loading on PPXC films at different temperatures and frequencies, the complex modulus and glass transition temperature (Tg) of the PPXC were obtained. The predicted Tg determined from the temperature-dependent density change in the MD model is consistent with the results in our measurements and previous works. Furthermore, with Time-Temperature Superposition Principle (TTSP), we successfully determined the master curve of PPXC, for the first time, which is critical for the parylene reliability study of bio-MEMS devices.
A range of complex percutaneous procedures, such as biopsy or regional anesthesia, rely heavily on accurate needle insertion. Small variations in the mechanical properties of the pierced tissue can however cause deviations from the projected needle path and can thus result in inaccurate placement of the needle. Navigation of a rigid needle towards the target tissue is traditionally based on the surgeons capacity to interpret small variations in the needle insertion force. A more accurate measurement of these small force variations enables improvement in needle targeting, can potentially aid in enhancing force feedback in robotic needle placement and can provide valuable information on tissue-tool interaction. In this study we investigated several concepts for the design of a force sensor based on a fiber-optic Fabry-Pérot interferometer to measure needle-tissue interaction forces on the tip of a 18 G needle, where special attention was given to concepts for a sensor with (1), an intrinsic low cross-sensitivity to temperature and (2), elementary design and fabrication. Three concepts, using either a quartz capillary, an Invar capillary or a thin polyimide film as the force sensitive element were prototyped and subjected to both static and dynamic testing. The force transducer based on a quartz capillary presented the lowest cross-sensitivity to temperature (12 mN/∘C) and good accuracy (maximum measurement error of 65 mN/10 N) in a measurement of static forces. However, limited strength of the sensor is expected to prevent usage of the quartz capillary in small diameter needles. The concepts for a sensor based on an Invar capillary or a thin polyimide film proved a higher cross-sensitivity to temperature (50 mN/∘C and 220 mN/∘C, respectively) and higher maximum measurement error (350 mN/10 N, 800 mN/10 N), comparable to those of FBG-based sensors reported in literature, but are likely to be more suitable for integration in very small biopsy needles.
Non-planar, three dimensional structures, not possible with conventional microfabrication processes, were achieved using post-fabrication thermal annealing of thin film Parylene-C structures facilitated by a mold (“thermoforming”). We demonstrate thermoforming of Parylene-Parylene and Parylene-metal-Parylene (PMP) structures for increased structural and mechanical functionality such as strain relief, formation of open-lumen sheath structures, and conformation-matching of curved surfaces that broaden applications for Parylene MEMS. Characterization of the material and mechanical properties as a function of thermoforming temperature is also presented. Thermoformed Parylene consistently retained bulk/surface chemical material properties following the treatment regardless of temperature, and thermoforming at higher temperatures increased structural stiffness, which is attributed to increased crystallinity of the polymer. By varying the thermoforming process parameters, the final shaped structure can be mechanically and structurally tuned for broad range of applications, most notably, structured implantable neural interfaces with integrated channels for tissue ingrowth and improved integration.
This paper presents the use of origami technique to construct a 3D spherical structure from a 2D parylene-C (PA-C) film with designed folding crease patterns. This origami technique is developed or intended for intraocular epiretinal implant application, which requires a “curved” electrode array to match the curvature of the macula. The folding method and process are described here using silicone oil as a temporary glue to hold the folded structures through meniscus force. The temporary origami is then thermally set into permanent 3D shapes at 100 °C for 30 minutes in vacuum utilizing parylene-C's viscoelastic properties. The reported origami technique enables the possibility of first making an extended device in 2D format and, after a possible minimal surgical cut and insertion, then folding it into a 3D device inside the eye for necessary geometric matching with host tissues.
As parylene-C, a thermal plastic, has been extensively used as an implant material, its viscoplastic behavior at body temperature has never been systematically studied. Presented here is the first extensive in vitro study of the viscoplastic behaviors of 20-μm-thick parylene-C film at 37°C. The viscoplastic behaviors are investigated by uniaxial tensile tests at different strain rates (Figure 2), cyclic loading/unloading test (Figure 3) abrupt strain rate changing (Figure 4), creep-recovery (Figure 5), and stress-relaxation (Figure 6). There are three major conclusions here. First, below a stress of 2.5MPa, no observable viscoplastic behavior of 20-μm-thick parylene-C is found. Secondly, parylene-C film is a strain (or stress) and strain-rate dependent viscoplastic material. Thirdly, Burger's model is adequate to describe both creep and stress relaxation behaviors. In addition, the rate of the creep recovery (modeled with a single time constant) and stress relaxation (modeled with two time constants) decreases with increasing applied stress and/or strain.
