A bio-inspired, chemo-responsive polymer nanocomposite for mechanically dynamic microsystems

Hess, Andreas; Dunning, J.; Harris, Jerome S.; Capadona, J. R.; Shanmuganathan, Kadhiravan; Rowan, Stuart J.; Weder, Christoph; Tyler, Dustin J.; Zorman, Christian A.

doi:10.1109/sensor.2009.5285522

Cited by 15 publications

(32 citation statements)

References 5 publications

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“…Probes for mechanical testing and buckling tests were created from a solution-cast poly (vinyl acetate)-tunicate whisker film compressed to a specified thickness (53 µm for buckling tests, 110 µm for mechanical measurements) and weakly adhered to a bare Si wafer by applying gentle pressure and heating on a hotplate set to 70°C for 3 minutes. Using a direct-write CO 2 laser at a laser power of 0.5 W, speed of 56 mm/s, and a resolution of 1000 pulses per inch (Hess et al , 2009; Hess et al , 2011), microprobes for mechanical testing were fabricated as beams 6 mm in length and 180–210 µm in width. For buckling testing, beams with a tip opening of 30° were cut using the same settings for the laser (3mm in shank length, 125 µm in width, 53 µm thick).…”

Section: Methodsmentioning

confidence: 99%

“…Initial material characterization has demonstrated that the polymer nanocomposite reduces its tensile storage modulus from ~5 GPa to 12 MPa within 15 minutes upon exposure to simulated physiological conditions in artificial cerebral spinal fluid (ACSF) at 37°C (Shanmuganathan, 2010; Capadona et al , 2009; Capadona et al , 2008). Additionally, advanced bioMEMS fabrication processes have been developed to create cortical microprobes from this novel material (Hess et al , 2009; Hess et al , 2011). …”

Section: Introductionmentioning

confidence: 99%

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In vivodeployment of mechanically adaptive nanocomposites for intracortical microelectrodes

et al. 2011

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We recently introduced a series of stimuli-responsive, mechanically-adaptive polymer nanocomposites. Here, we report the first application of these bio-inspired materials as substrates for intracortical microelectrodes. Our hypothesis is that the ideal electrode should be initially stiff to facilitate minimal trauma during insertion into the cortex, yet becomes mechanically compliant to match the stiffness of the brain tissue and minimize forces exerted on the tissue, attenuating inflammation. Microprobes created from mechanically reinforced nanocomposites demonstrated a significant advantage compared to model microprobes composed of neat polymer only. The nanocomposite microprobes exhibit a higher storage modulus (E’ = ~5 GPa) than the neat polymer microprobes (E’ = ~2 GPa) and could sustain higher loads (~17 mN), facilitating penetration through the pia mater and insertion into the cerebral cortex of a rat. In contrast, the neat polymer microprobes mechanically failed under lower loads (~7 mN) before they were capable of inserting into cortical tissue. Further, we demonstrated the material’s ability to morph while in the rat cortex to more closely match the mechanical properties of the cortical tissue. Nanocomposite microprobes that were implanted into the rat cortex for up to 8 weeks demonstrated increased cell density at the microelectrode-tissue interface and a lack of tissue necrosis or excessive gliosis. This body of work introduces our nanocomposite-based microprobes as adaptive substrates for intracortical microelectrodes and potentially other biomedical applications.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

In vivodeployment of mechanically adaptive nanocomposites for intracortical microelectrodes

et al. 2011

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“…In a preliminary study investigating these questions, we reported that laser micromachining was an adequate method of producing micro-scale PVAc-TW structures that displayed dynamic mechanical behavior comparable to bulk samples [11]. While a method to pattern the PVAc-TW itself was described, these structures did not include metal or insulator features defined using photolithographic processes.…”

Section: Introductionmentioning

confidence: 99%

Development of a stimuli-responsive polymer nanocomposite toward biologically optimized, MEMS-based neural probes

Hess

Capadona

Shanmuganathan

et al. 2011

J. Micromech. Microeng.

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This paper reports the development of micromachining processes and mechanical evaluation of a stimuli-responsive, mechanically dynamic polymer nanocomposite for biomedical microsystems. This nanocomposite consists of a cellulose nanofiber network encased in a polyvinyl acetate matrix. Micromachined tensile testing structures fabricated from the nanocomposite displayed a reversible and switchable stiffness comparable to bulk samples, with a Young's modulus of 3420 MPa when dry, reducing to ∼20 MPa when wet, and a stiff-to-flexible transition time of ∼300 s. This mechanically dynamic behavior is particularly attractive for the development of adaptive intracortical probes that are sufficiently stiff to insert into the brain without buckling, but become highly compliant upon insertion. Along these lines, a micromachined neural probe incorporating parylene insulating/moisture barrier layers and Ti/Au electrodes was fabricated from the nanocomposite using a fabrication process designed specifically for this chemical-and temperature-sensitive material. It was found that the parylene layers only slightly increased the stiffness of the probe in the wet state in spite of its much higher Young's modulus. Furthermore, the Ti/Au electrodes exhibited impedance comparable to Au electrodes on conventional substrates. Swelling of the nanocomposite was highly anisotropic favoring the thickness dimension by a factor of 8 to 12, leading to excellent adhesion between the nanocomposite and parylene layers and no discernable deformation of the probes when deployed in deionized water.

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“…This is of significant importance to the targeted application as adaptive substrates for intracortical electrodes, where an initial E 0 of >4 GPa is desirable to allow for the insertion of an electrode with typical dimensions into the cortex. 42,43 As shown above, however, the aqueous swelling of the cotton-based materials is massively reduced, which represents a significant advantage over the tunicate-based nanocomposites.…”

mentioning

confidence: 99%

Bio-inspired mechanically-adaptive nanocomposites derived from cotton cellulose whiskers

et al. 2010

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A new series of biomimetic, stimuli-responsive nanocomposites, which change their mechanical properties upon exposure to physiological conditions, was investigated. The materials were produced by introducing percolating networks of cellulose whiskers isolated from cotton into poly(vinyl acetate). Below the glass-transition temperature (T g $ 63 C), the tensile storage moduli (E 0 ) of the dry nanocomposites increased two fold, from 2 GPa for the neat polymer to 4 GPa for a nanocomposite with 16.5% v/v whiskers. The relative reinforcement was more significant above T g , where E 0 was increased nearly 40 fold, from $1.2 MPa to $45 MPa. Upon exposure to emulated physiological conditions (immersion in artificial cerebrospinal fluid at 37 C) all nanocomposites showed a pronounced decrease in E 0 , for example to 5 MPa for the 16.5% v/v whisker nanocomposites with only about 28% w/w swelling. This is a significant reduction in the amount of swelling required to decrease the E 0 , compared to earlier material versions based on cellulose whiskers with higher surface charge density; the decreased swelling may be a considerable advantage for the intended use of these materials as adaptive substrates for intracortical electrodes and other biomedical applications.

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A bio-inspired, chemo-responsive polymer nanocomposite for mechanically dynamic microsystems

Cited by 15 publications

References 5 publications

In vivodeployment of mechanically adaptive nanocomposites for intracortical microelectrodes

In vivodeployment of mechanically adaptive nanocomposites for intracortical microelectrodes

Development of a stimuli-responsive polymer nanocomposite toward biologically optimized, MEMS-based neural probes

Bio-inspired mechanically-adaptive nanocomposites derived from cotton cellulose whiskers

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