Simultaneous determination of mechanical properties and physiologic parameters in living rat brain

Shulyakov, Alexander V.; Fernando, Farrah; Cenkowski, Stefan; Bigio, Marc R. Del

doi:10.1007/s10237-008-0147-9

Cited by 13 publications

(23 citation statements)

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“…This procedure allows collective measurement of the mechanical properties of the intracranial contents. 27,30,31 …”

Section: Animal Preparationmentioning

confidence: 99%

“…After MRI, anesthetized rats were positioned on a warming blanket in the custom fabricated head holder whose stage is affixed to the open platform microhardness indentation tester (CSM Instruments SA). 27 The scalp incision was reopened, and the site of the parietal craniotomy was exposed. Twenty-one days after contusion or sham procedure, adhesions between the dura and epicranium had developed; these were separated to free the dura at the edge of the craniotomy site.…”

Section: Indentation Testingmentioning

confidence: 99%

“…The details and validations of these tests appear in prior publications. [25][26][27] A minimum recovery period of 15 minutes was allowed between tests. The measured epidural brain temperature at the end of indentation was never lower than 35.4°C.…”

Section: Indentation Testingmentioning

confidence: 99%

“…1,2 We recently developed a technique for measuring intracranial viscoelastic parameters in the living rat. 27 With the dura closed, responses to mechanical indentation are determined by the brain tissue immediately under the test device, as well as the rest of the intracranial contents. 22,27 We have shown that changes in mechanical indentation response from birth to 6 months depend on water content and on tissue protein properties.…”

mentioning

confidence: 99%

“…27 With the dura closed, responses to mechanical indentation are determined by the brain tissue immediately under the test device, as well as the rest of the intracranial contents. 22,27 We have shown that changes in mechanical indentation response from birth to 6 months depend on water content and on tissue protein properties. 26 We have also shown that acute hydrocephalus is associated with only small changes.…”

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confidence: 99%

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Intracranial biomechanics following cortical contusion in live rats

Alfasi¹,

Shulyakov

Bigio

2013

JNS

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Object. The goal of this study was to examine the mechanical properties of living rat intracranial contents and corresponding brain structural alterations following parietal cerebral cortex contusion.Methods. After being anesthetized, young adult rats were subjected to parietal craniotomy followed by cortical contusion using a calibrated weight-drop method. Magnetic resonance imaging was used to visualize the contusion. At the site of contusion, instrumented force-controlled indentation was performed 2 hours to 21 days later on the intact dural surface. The force-deformation (stress-strain) relationship was used to calculate elastic (indentation modulus) and strain changes over time, and constant hold or cyclic stress was used to evaluate viscoelastic deformation. These measurements were followed by histological studies.Results. At contusion sites, the indentation modulus was significantly decreased at 1-3 days and tended to be above control values at 21 days. Multicycle indentation showed that the brain tended to accumulate more strain (an indicator of viscosity) by 1 day after the contusion. Imaging and histological studies showed local edema and hemorrhage at 6 hours to 3 days and accumulation of reactive astrocytes, which began at 3 days and was pronounced by 21 days.Conclusions. The viscoelastic properties of living rat brain change following contusion. Initially, edema and tissue necrosis occur, and the brain becomes less elastic and less viscous. Later, along with undergoing reactive astroglial changes, the brain tends to become stiffer than normal. These quantitative data, which are related to the physical changes in the brain following trauma and which reflect subjective impressions upon palpation, will be useful for understanding emerging diagnostic tools such as magnetic resonance elastography.

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“…This procedure allows collective measurement of the mechanical properties of the intracranial contents. 27,30,31 …”

Section: Animal Preparationmentioning

confidence: 99%

Section: Indentation Testingmentioning

confidence: 99%

Section: Indentation Testingmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Intracranial biomechanics following cortical contusion in live rats

Alfasi¹,

Shulyakov

Bigio

2013

JNS

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Non-ideal effects in indentation testing of soft tissues

Finan

Fox

Morrison

2013

Biomech Model Mechanobiol

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Indentation has several advantages as a loading mode for determining constitutive behavior of soft, biological tissues. However, indentation induces a complex, spatially heterogeneous deformation field that creates analytical challenges for the calculation of constitutive parameters. As a result, investigators commonly assume small indentation depths and large sample thicknesses to simplify analysis and then restrict indentation depth and sample geometry to satisfy these assumptions. These restrictions limit experimental resolution in some fields, such as brain biomechanics. However, recent experimental evidence suggests that conventionally applied limits are in fact excessively conservative. We conducted a parametric study of indentation loading with various indenter geometries, surface interface conditions, sample compressibility, sample geometry and indentation depth to quantitatively describe the deviation from previous treatments that results from violation of the assumptions of small indentation depth and large sample thickness. We found that the classical solution was surprisingly robust to violation of the assumption of small strain but highly sensitive to violation of the assumption of large sample thickness, particularly if the indenter was cylindrical. The ramifications of these findings for design of indentation experiments are discussed and correction factors are presented to allow future investigators to account for these effects without recreating our finite element models.

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