In vitro comparison of conventional surgical and rotary ultrasonic bone drilling techniques.

In orthopedic and trauma surgical operations, drilling of bone is one of the commonly used procedures performed in hospitals and is a clinical practice for fixing the fractured parts of human bones. Force, torque and temperature play a significant role during the bone drilling and decide the stability of the medical implants. Therefore, it is necessary to minimize force, torque and temperature while drilling to avoid the thermal necrosis and osteosynthesis. This study focused on studying the influence of various types of bone drilling parameters (rotational speed, feed rate, drill diameter and ultrasonic amplitude), tools (solid tool, hollow tool and conventional twist drill bit) and techniques (conventional surgical drilling, rotary ultrasonic bone drilling and rotary bone drilling) on force, torque, temperature and microcracks produced in the drilled surface of the bone. The experimental investigations were conducted on porcine bone samples to perform the comparative study. Results revealed that increasing the diameter of drill tool and feed rate results in the increase in force, torque and temperature, while low rotational speed (500 r/min) generated a low temperature, high cutting force and torque for all types of drilling processes and tools evaluated in this study. Experimental results also revealed that rotary ultrasonic bone drilling with hollow tool generated the lowest cutting force, torque, temperature (<47 °C) and microcracks in the drilled surface of the bone as compared to the other four types of drilling techniques evaluated in this study. Influence of external irrigation technique on temperature was also studied with respect to the rotary ultrasonic bone drilling with a hollow tool, which could eliminate the problem of thermal necrosis. In conclusion, this study revealed that the rotary ultrasonic bone drilling process with hollow tool produced lesser cutting force as compared to rotary bone drilling and conventional surgical drilling for hollow and solid tools. The study also revealed that rotary ultrasonic bone drilling process has the potential to minimize the cutting force, torque and temperature as compared to the conventional surgical drilling for orthopedic surgery.

In vitro degradation behaviour, cytocompatibility and hemocompatibility of topologically ordered porous iron scaffold prepared using 3D printing and pressureless microwave sintering.

Biodegradable porous iron having topologically ordered porosity and tailorable properties as per the required application has been the major requirement in the field of biodegradable biomaterials. Hence, in the present study, iron scaffolds with the topologically ordered porous structure were developed and for the first time, the effect of the variation in the topology on the in vitro degradation behaviour, cytocompatibility and hemocompatibility were investigated. Iron scaffold samples were fabricated using a novel process based on the combination of 3D printing and pressureless microwave sintering. To investigate the effect of topology, two different types of topological structures namely Truncated Octahedron (TO) (with variable strut size) and Cubic (C) were used. From the morphological characterization, it was found that fabricated iron scaffold possessed interconnected porosity varying from 50.70%-80.97% which included the random microporosities in the strut and designed macroporosity. Furthermore, it was inferred that the topology of the iron scaffold significantly affected its degradation properties and cytocompatibility. Increase in the weight loss, corrosion rate and reduction in cell viability with the reduction in porosity were obtained. The maximum corrosion rate and weight loss achieved was 1.64 mmpy and 6.4% respectively. Direct cytotoxicity test results revealed cytotoxicity, while prepared iron scaffold samples exhibited excellent hemocompatibility and anti-platelet adhesion property. A comparative study with relevant literature was performed and it was established that the developed iron scaffold exhibited favorable degradation and biological properties which could be tailored to suit appropriate bone tissue engineering applications.

Corrosion rate modelling of biodegradable porous iron scaffold considering the effect of porosity and pore morphology.

Porous iron (Fe) has shown promising capabilities to be used as biodegradable material. However, to achieve the desired rate of degradation in porous Fe, there exists a need to develop a model explaining the effect of variation in morphology of the porous structure on the corrosion rate. Hence, in the present study, an empirical model for the prediction of the corrosion rate of porous Fe scaffold samples possessing different levels of porosity and pore morphology has been developed. To develop the model, Fe scaffold samples having random porous microporous structure and designed topologically ordered porous structures were fabricated using 3D printing and pressureless microwave sintering. Potentiodynamic polarization tests were performed to assess the corrosion properties of fabricated porous Fe scaffold samples in simulated body fluid solution at 37 °C. It was found that with an increase in random microporosity and the reduction in the size of the designed macropores, an increase in corrosion rate was obtained. Mathematical relationships between governing factors affecting corrosion rate (i.e. corrosion current and exposed surface area) and porosity were deduced. The developed model was validated with the experimental results and good agreement of predicted values with the experimental values was obtained with a maximum error of 6.97%.

Corrosion behaviour of the porous iron scaffold in simulated body fluid for biodegradable implant application.

The presented work aims to evaluate the effect of porosity on the corrosion behaviour of porous iron scaffold for biodegradable implant application. Two different types of iron scaffold samples were prepared using a newly developed process based on the amalgamation of 3D printing and pressureless microwave sintering. Random porous iron scaffold (RPIS) sample having only random microporous structure and topologically ordered porous iron scaffold (TOPIS) sample having designed interconnected macroporous structure were investigated. Dense iron sample was also prepared for comparison purpose. Microstructural and morphological characterization of the prepared iron scaffold samples were performed using scanning electron microscopy and micro-computed tomography. Three different types of pore characteristics namely large sized interconnected micropores, small sized isolated micropores and designed interconnected macropores were obtained and analyzed. The corrosion properties were assessed in simulated body fluid solution at 37 °C using polarization curves and EIS measurements. Corrosion mechanisms were established using suitable circuit models. Impedance results showed that the corrosion of porous iron scaffold samples was mainly governed by the diffusion process. Electrochemical results indicated that an increase in random microporosity and reduction in designed macroporosity resulted in an increased corrosion rate of iron scaffold.

Development of an orthosis for simultaneous three-dimensional correction of clubfoot deformity.

BACKGROUND: Clubfoot is a three-dimensional deformity of the foot in which the foot is twisted in three mutually perpendicular planes from the normal shape of the foot. Of the various treatment methods that are available to manage clubfoot, non-operative approaches are preferred. The conventional non-operative method of treatment is to apply a series of casts to the infant's clubfoot to gradually manipulate its position. However, prolonged use of casts can result in skin rash, skin dehydration and ulcers on the soft skin of an infant. Treatment using orthosis represents an alternative non-operative and convenient technique because an orthosis can be put on and taken off at any time. METHODS: In the present study, an orthosis was developed according to the rotation of three mutually perpendicular planes and was subsequently tested on five patients over the duration of one week. FINDINGS: In all five cases, the desired incremental correction to the clubfoot was achieved through the one week intervention with the orthosis. No form of rash, dehydration, ulcers, and so on were observed on the skin of any baby involved in the study during or following application of the orthosis. INTERPRETATION: By using the developed orthosis, partial correction of the clubfoot deformity was achieved over a short period of time. However the widespread use of this device for extended durations and with a larger number of patients will generate further evidence of the extent to which this orthosis can reliably treat clubfoot.

Modeling of un-deformed chip thickness in RUM process and study of size effects in µ-RUM.

Un-deformed chip thickness is a critical parameter in machining processes. Measuring un-deformed chip thickness experimentally is a complicated process, especially in micro machining and may not even be measured accurately. The un-deformed chip thickness has an influence on material removal rate, cutting forces, specific energy and surface finish etc. In ceramic machining, it is also an indication of material removal mode such as ductile or brittle fracture. In the present study, an effort is made to model undeformed chip thickness, cutting forces and specific cutting energy in rotary ultrasonic machining (RUM) applied to the side milling operation. RUM may be considered as super-imposition of ultrasonic vibrations on the grinding process. The kinematics of ultrasonic motion has been applied to the grinding for the development of the RUM process models. To validate the models, machining experiments have been performed on borosilicate glass in RUM and grinding modes. Percentage of ductile mode of fracture for the machined surfaces has been evaluated using SEM images. Surface roughness values have also been compared for the same material removal rate conditions to ascertain fracture mode. Developed models have been verified and found that ductile mode of fracture as well as surface finish were higher in RUM as compared to grinding process for same material removal rate. RUM process for six aerospace grade materials has also been tried using micro and macro tools and size effects studied.

Rotary ultrasonic drilling on bone: A novel technique to put an end to thermal injury to bone.

Bone drilling is common in orthopedic procedures and the heat produced during conventional experimental drilling often exceeds critical temperature of 47 °C and induces thermal osteonecrosis. The osteonecrosis may be the reason for impaired healing, early loosening and implant failure. This study was undertaken to control the temperature rise by interrupted cutting and reduced friction effects at the interface of drill tool and the bone surface. In this work, rotary ultrasonic drilling technique with diamond abrasive particles coated on the hollow drill tool without any internal or external cooling assistance was used. Experiments were performed at room temperature on the mid-diaphysis sections of fresh pig bones, which were harvested immediately after sacrifice of the animal. Both rotary ultrasonic drilling on bone and conventional surgical drilling on bone were performed in a five set of experiments on each process using identical constant process parameters. The maximum temperature of each trial was recorded by K-type thermocouple device. Ethylenediaminetetraacetic acid decalcification was done for microscopic examination of bone. In this comparative procedure, rotary ultrasonic drilling on bone produced much lower temperature, that is, 40.2 °C ± 0.4 °C and 40.3 °C ± 0.2 °C as compared to that of conventional surgical drilling on bone, that is, 74.9 °C ± 0.8 °C and 74.9 °C ± 0.6 °C with respect to thermocouples fixed at first and second position, respectively. The conventional surgical drilling on bone specimens revealed gross tissue burn, microscopic evidence of thermal osteonecrosis and tissue injury in the form of cracks due to the generated force during drilling. But our novel technique showed no such features. Rotary ultrasonic drilling on bone technique is robust and superior to other methods for drilling as it induces no thermal osteonecrosis and does not damage the bone by generating undue forces during drilling.

In-situ tool wear monitoring and its effects on the performance of porcine cortical bone drilling: a comparative in-vitro investigation.

BACKGROUND: Drilling is one of the most widely used process in orthopaedic surgical operation and the same drill bit is used a number of times in hospitals. Using the same drill bit a several times may be the cause of osteosynthesis and osteonecrosis. METHODS: In the present work, the effect of repeated orthopaedic surgical twist drill bit on the tool wear, force, torque, temperature and chip morphology during porcine cortical bone drilling is studied. Results were compared with rotary ultrasonic drilling (RUD) on the same bone using a hollow drill tool coated with diamond grains. A sequence of 200 experiments (100 with each process, RUD and CD) were performed with constant process parameters. RESULTS: Wear area on the drill bit is significantly increased as the drill bit is used repeatedly in CD, whereas no attritious wear was found on the diamond coated grains in RUD. CONCLUSIONS: Comparative results showed that cutting force, torque and temperature increased as a function of tool wear in CD as the same drill bit was used a number of times. No significant variation in the cutting force and torque was observed in RUD as the number of drilled holes increased.

Rotary ultrasonic bone drilling: Improved pullout strength and reduced damage.

Bone drilling is one of the most common operations used to repair fractured parts of bones. During a bone drilling process, microcracks are generated on the inner surface of the drilled holes that can detrimentally affect osteosynthesis and healing. This study focuses on the investigation of microcracks and pullout strength of cortical-bone screws in drilled holes. It compares conventional surgical bone drilling (CSBD) with rotary ultrasonic bone drilling (RUBD), a novel approach employing ultrasonic vibration with a diamond-coated hollow tool. Both techniques were used to drill holes in porcine bones in an in-vitro study. Scanning electron microscopy was used to observe microcracks and surface morphology. The results obtained showed a significant decrease in the number and dimensions of microcracks generated on the inner surface of drilled holes with the RUBD process in comparison to CSBD. It was also observed that a higher rotational speed and a lower feed rate resulted in lower damage, i.e. fewer microcracks. Biomechanical axial pullout strength of a cortical bone screw inserted into a hole drilled with RUBD was found to be much higher (55-385%) than that for CSBD.

Experimental investigation and statistical modeling of temperature rise in rotary ultrasonic bone drilling.

Thermal necrosis is one of the major problems associated with the bone drilling process in orthopedic/trauma surgical operations. To overcome this problem a new bone drilling method has been introduced recently. Studies have been carried out with rotary ultrasonic drilling (RUD) on pig bones using diamond coated abrasive hollow tools. In the present work, influence of process parameters (rotational speed, feed rate, drill diameter and vibrational amplitude) on change in the temperature was studied using design of experiment technique i.e., response surface methodology (RSM) and data analysis was carried out using analysis of variance (ANOVA). Temperature was recorded and measured by using embedded thermocouple technique at a distance of 0.5mm, 1.0mm, 1.5mm and 2.0mm from the drill site. Statistical model was developed to predict the maximum temperature at the drill tool and bone interface. It was observed that temperature increased with increase in the rotational speed, feed rate and drill diameter and decreased with increase in the vibrational amplitude.

Optimization of machining and vibration parameters for residual stresses minimization in ultrasonic assisted turning of 4340 hardened steel.

The residual stresses generated in the machined work piece have detrimental effect on fatigue life, corrosion resistance and tribological properties. However, the effect of cutting and vibration parameters on residual stresses in Ultrasonic Assisted Turning (UAT) has not been dealt with. The present paper highlights the effect of feed rate, depth of cut, cutting velocity and percentage intensity of ultrasonic power on residual stress generation. XRD analysis has been carried out to measure the residual stress while turning 4340 hardened steel using UAT. The experiments were performed based on response surface methodology to develop statistical model for residual stress. The outcome of ANOVA revealed that percentage intensity and feed rate significantly affect the residual stress generation. The significant interactions between process parameters have also been presented tin order to understand the thermo-mechanical mechanism responsible for residual stress generation.

Design and development of a device to measure the deformities of clubfoot.

Clubfoot describes a range of foot abnormalities usually present at birth, in which the foot of a baby is twisted out of shape or position. In order to develop an effective treatment plan for clubfoot and/or assess the extent to which existing interventions are successful, medical practitioners need to be able to accurately measure the nature and extent of the deformity. This is typically performed using a goniometer. However, this device is only able to measure one dimension at a time. As such, a complete assessment of the condition of a foot can be extremely burdensome and time-consuming. This article describes a new device that can quickly and efficiently take several measurements on feet of various sizes and shapes. The use of this device was verified by measuring the deformities of real clubfeet. A silicone rubber clubfoot model was also used in this study to clearly illustrate the effectiveness with which the proposed device can measure the various deformities of clubfoot. It is envisaged that the use of this device will significantly reduce the time and effort orthopedists require to measure clubfoot deformities and develop and assess treatment plans.