O. Burak Ozdoganlar

An experimental investigation on thermal exposure during bone drilling

This study presents an experimental investigation of the effects of spindle speed, feed rate, and depth of drilling on the temperature distribution during drilling of the cortical section of the bovine femur. In an effort to reduce measurement uncertainties, a new approach for temperature measurements during bone drilling is presented in this study. The new approach is based on a setup for precise positioning of multiple thermocouples, automated data logging system, and a computer numerically controlled (CNC) machining system. A battery of experiments that has been performed to assess the uncertainty and repeatability of the new approach displayed adequate results. Subsequently, a parametric study was conducted to determine the effects of spindle speed, feed rate, hole depth, and thermocouple location on the measured bone temperature. This study suggests that the exposure time during bone drilling far exceeds the commonly accepted threshold for thermal injury, which may prevail at significant distances from the drilled hole. Results of this study suggest that the correlation of the thermal exposure threshold for bone injury and viability should be further explored.

A new thermal model for bone drilling with applications to orthopaedic surgery

This paper presents a new thermal model for bone drilling with applications to orthopaedic surgery. The new model combines a unique heat-balance equation for the system of the drill bit and the chip stream, an ordinary heat diffusion equation for the bone, and heat generation at the drill tip, arising from the cutting process and friction. Modeling of the drill bit-chip stream system assumes an axial temperature distribution and a lumped heat capacity effect in the transverse cross-section. The new model is solved numerically using a tailor-made finite-difference scheme for the drill bit-chip stream system, coupled with a classic finite-difference method for the bone. The theoretical investigation addresses the significance of heat transfer between the drill bit and the bone, heat convection from the drill bit to the surroundings, and the effect of the initial temperature of the drill bit on the developing thermal field. Using the new model, a parametric study on the effects of machining conditions and drill-bit geometries on the resulting temperature field in the bone and the drill bit is presented. Results of this study indicate that: (1) the maximum temperature in the bone decreases with increased chip flow; (2) the transient temperature distribution is strongly influenced by the initial temperature; (3) the continued cooling (irrigation) of the drill bit reduces the maximum temperature even when the tip is distant from the cooled portion of the drill bit; and (4) the maximum temperature increases with increasing spindle speed, increasing feed rate, decreasing drill-bit diameter, increasing point angle, and decreasing helix angle. The model is expected to be useful in determination of optimum drilling conditions and drill-bit geometries.

Experimental modal analysis for microelectromechanical systems

The structural dynamics behavior of microelectromechanical systems (MEMS), which include moving, overhung, and compliant subcomponents, plays a pivotal role in determining their performance and reliability. Traditionally, experimental modal analysis is used to characterize the dynamic behavior of structures, as well as to derive, validate, update, and correct analytical and numerical models. Due to their small size, however, conventional modal testing methods cannot be directly applied to microstructures. In this paper we provide an overview of modal testing techniques for microsystems. A particular experimental modal analysis methodology that includes base excitation via a piezoelectric shaker and measurement through a laser interferometer is then described and evaluated. A distinguishing characteristic of the methodology is its simplicity, including its simple setup and off-the-shelf components. The modal model is derived for the base excitation of microcantilever beams. The effectiveness of the methodology is illustrated through various experiments on polysilicon microcantilevers for different geometries and ambient pressures. Analysis of the damping data for different pressures has confirmed the well-documented fact that the structural damping in microsystems can be considerably less than damping arising from interaction with the ambient gases.

High-density soft-matter electronics with micron-scale line width.

A method to produce soft and stretchable microelectronics composed of a liquid-phase Gallium-Indium alloy with micron-scale circuit features is introduced. Microchannels are molded onto the surface of a poly(dimethylsiloxane) (PDMS) elastomer and filled with EGaIn using a micro-transfer deposition step that exploits the unique wetting properties of EGaIn in air. The liquid-filled channels function as stretchable circuit wires or capacitor electrodes with a 2 μm linewidth and 1 μm spacing.

Modeling and experimentation of bone drilling forces

Prediction and control of bone drilling forces are critical to the success of many orthopaedic operations. Uncontrolled and large forces can cause drill-bit breakage, drill breakthrough, excessive heat generation, and mechanical damage to the bone. This paper presents a mechanistic model for prediction of thrust forces and torques experienced during bone drilling. The model incorporates the radially varying drill-bit geometry and cutting conditions analytically, while capturing the material and friction properties empirically through a specific energy formulation. The forces from the chisel edge are modeled by considering the indentation process that occurs in the vicinity of the drill-bit axis. A procedure is outlined to calibrate the specific energies, where only a small number of calibration experiments are required for a wide range of drilling conditions and drill-bit geometry. The calibration parameters for the cortical portions of bovine tibia are identified through drilling tests. Subsequently, a series of validation tests are conducted under different feed rates and spindle speeds. The thrust forces and torques were observed to vary considerably between bones from different animals. The forces from the model were seen to match well with those from the experimentation within the inherent variations from the bone characteristics. The model can be used to select favorable drilling conditions, to assist in robotic surgeries, and to design optimal orthopaedic drill bits.

Chronic tissue response to carboxymethyl cellulose based dissolvable insertion needle for ultra-small neural probes.

Implantable neural electrodes must drastically improve chronic recording stability before they can be translated into long-term human clinical prosthetics. Previous studies suggest that sub-cellular sized and mechanically compliant probes may result in improved tissue integration and recording longevity. However, currently these design features are restricted by the opposing mechanical requirements needed for minimally damaging insertions. We designed a non-cytotoxic, carboxymethylcellulose (CMC) based dissolvable delivery vehicle (shuttle) to provide the mechanical support for insertion of ultra-small, ultra-compliant microfabricated neural probes. Stiff CMC-based shuttles rapidly soften immediately after being placed ∼1 mm above an open craniotomy as they absorb vapors from the brain. To address this, we developed a sophisticated targeting, high speed insertion (∼80 mm/s), and release system to implant these shuttles. After implantation, the goal is for the shuttle to dissolve away leaving only the electrodes behind. Here we show the histology of chronically implanted shuttles of large (300 μm × 125 μm) and small (100 μm × 125 μm) size at discrete time points over 12 weeks. Early time points show the CMC shuttle expanded after insertion as it absorbed moisture from the brain and slowly dissolved. At later time points neuronal cell bodies populate regions within the original shuttle tract. The large CMC shuttles show that the CMC expansion can cause extended secondary damage. On the other hand, the smaller CMC shuttles show limited secondary damage, wound closure by 4 weeks, absence of activated microglia at 12 weeks, as well as evidence suggesting neural regeneration at the implant site. This shuttle, therefore, shows great promise facilitating the implantation of nontraditional ultra-small, and ultra-compliant probes.

Evaluation of a spindle-based force sensor for monitoring and fault diagnosis of machining operations

This paper presents an evaluation of a spindle-based force sensor, the force ring, which is a strong candidate for in-process monitoring and fault diagnosis of machining operations. The evaluation criteria include the effect of integration of the force ring on the dynamics of the spindle, the drift behavior due to temperature change inside the spindle, the cross-talk between the channels, and the existence and compensation of the spindle-internal forces. The application of the force ring to process model-based monitoring and fault diagnosis has been demonstrated by the determination of force calibration coefficients using the force ring and their comparison with results obtained with a platform dynamometer. It has been concluded that the force ring provides dynamometer quality force measurements.

Dissolvable Microneedle Arrays for Intradermal Delivery of Biologics: Fabrication and Application

ABSTRACTPurposeDesign and evaluate a new micro-machining based approach for fabricating dissolvable microneedle arrays (MNAs) with diverse geometries and from different materials for dry delivery to skin microenvironments. The aims are to describe the new fabrication method, to evaluate geometric and material capability as well as reproducibility of the method, and to demonstrate the effectiveness of fabricated MNAs in delivering bioactive molecules.MethodsPrecise master molds were created using micromilling. Micromolding was used to create elastomer production molds from master molds. The dissolvable MNAs were then fabricated using the spin-casting method. Fabricated MNAs with different geometries were evaluated for reproducibility. MNAs from different materials were fabricated to show material capability. MNAs with embedded bioactive components were tested for functionality on human and mice skin.ResultsMNAs with different geometries and from carboxymethyl cellulose, polyvinyl pyrrolidone and maltodextrin were created reproducibly using our method. MNAs successfully pierce the skin, precisely deliver their bioactive cargo to skin and induce specific immunity in mice.ConclusionsWe demonstrated that the new fabrication approach enables creating dissolvable MNAs with diverse geometries and from different materials reproducibly. We also demonstrated the application of MNAs for precise and specific delivery of biomolecules to skin microenvironments in vitro and in vivo.

A Rotating-Tip-Based Mechanical Nano-Manufacturing Process: Nanomilling

We present a rotating-tip-based mechanical nanomanufacturing technique, referred to here as nanomilling. An atomic force microscopy (AFM) probe tip that is rotated at high speeds by out-of-phase motions of the axes of a three-axis piezoelectric actuator is used as the nanotool. By circumventing the high-compliance AFM beam and directly attaching the tip onto the piezoelectric actuator, a high-stiffness arrangement is realized. The feeding motions and depth prescription are provided by a nano-positioning stage. It is shown that nanomilling is capable of removing the material in the form of long curled chips, indicating shearing as the dominant material removal mechanism. Feature-size and shape control capabilities of the method are demonstrated.

Effects of Crystallographic Anistropy on Orthogonal Micromachining of Single-Crystal Aluminum

Anisotropy of workpiece crystals has a significant effect in micromachining since the uncut chip thickness values used in micromachining are commensurate with characteristic dimensions of crystals in crystalline materials. This paper presents an experimental investigation on orthogonal micromachining of single-crystal aluminum at different crystallographic orientations for varying uncut chip thicknesses and cutting speeds using a diamond tool. Micromachining forces, specific energies, effective coefficient of friction, shear angles, shear stresses, and chip morphology were examined for six crystallographic orientations at uncut chip thicknesses ranging from 5 μm to 20 μm and cutting speeds ranging from 5 mm/s to 15 mm/s. Three distinct types of forces were observed, including steady (Type-I), bistable (Type-II), and fluctuating (Type-III) force signatures. The forces were seen to vary by as much as threefold with crystallographic orientation. Although the effect of cutting speed was small, the uncut chip thickness was seen to have a significant orientation-dependent effect on average forces. Chip morphology, analyzed under scanning electron microscopy, showed shear-front lamella, the periodicity of which was seen to vary with crystallographic orientations and uncut chip thicknesses.