Objective . Our objective was to determine how readily disruption of the blood–brain barrier (BBB) occurred as a result of bone drilling during a craniotomy to implant microelectrodes in rat cortex. While the phenomenon of heat production during bone drilling is well known, practices to evade damage to the underlying brain tissue are inconsistently practiced and reported in the literature. Approach . We conducted a review of the intracortical microelectrode literature to summarize typical approaches to mitigate drill heating during rodent craniotomies. Post mortem skull-surface and transient brain-surface temperatures were experimentally recorded using an infrared camera and thermocouple, respectively. A number of drilling conditions were tested, including varying drill speed and continuous versus intermittent contact. In vivo BBB permeability was assayed 1 h after the craniotomy procedure using Evans blue dye. Main results . Of the reviewed papers that mentioned methods to mitigate thermal damage during craniotomy, saline irrigation was the most frequently cited (in six of seven papers). In post mortem tissues, we observed increases in skull-surface temperature ranging from +3 °C to +21 °C, dependent on drill speed. In vivo , pulsed-drilling (2 s-on/2 s-off) and slow-drilling speeds (1000 r.p.m.) were the most effective methods we studied to mitigate heating effects from drilling, while inconclusive results were obtained with saline irrigation. Significance . Neuroinflammation, initiated by damage to the BBB and perpetuated by the foreign body response, is thought to play a key role in premature failure of intracortical recording microelectrodes. This study demonstrates the extreme sensitivity of the BBB to overheating caused by bone drilling. To avoid damage to the BBB, the authors recommend that craniotomies be drilled with slow speeds and/or with intermittent drilling with complete removal of the drill from the skull during ‘off’ periods. While saline alone was ineffective at preventing overheating, its use is still recommended to remove bone dust from the surgical site and to augment other cooling methods.

The transmission of pressure waves in granular materials is complicated by the heterogeneity and nonlinearity inherent in these systems. Such waves are propagated through particle contacts primarily along the “force chains” which carry most of the load in granular materials. These fragile and ephemeral chains coupled with irregular particle packing lead to the observed heterogeneity. Nonlinearity in these systems is largely the result of the force-deformation characteristic at particle contacts. Through experiments and simulations, we study the effects of heterogeneity and nonlinearity on the properties of pressure waves through a granular bed.

Pressure waves in a granular material travel through particle contact points and are primarily transmitted by the “force chains” that carry most of the load in a granular medium. However, these force chains tend to be fragile and ephemeral and can be disrupted by very minor perturbations including the waves themselves. External vibration also disrupts the force chains and therefore also changes the wave propagation characteristics. In this paper we study the effects of vibration on wave propagation in a shaken granular bed.

Noncontact thermal measurement techniques offer rapid thermal characterization without modification or destruction of the sample being studied. A simple and versatile method has been developed, termed the “numerical mirage method,” that utilizes the transient photothermal deflection of a laser beam traversing a modulated temperature gradient. This method expands the range and simplifies the experimental procedure of traditional mirage methods. A numerical solver is used to create accurate deflection profile models and a linear curve fitting routine is developed, from which the thermal diffusivity of a material may be determined. This method allows for rapid modification of sample and heating configurations. Verification of the method is performed on bismuth and fused quartz reference samples, and good agreement with literature is obtained.