ARTICLE IN PRESS JID: JJBE [m5G;May 12, 2015;21:12] Medical Engineering and Physics 000 (2015) 1–8 Contents lists available at ScienceDirect Medical Engineering and Physics journal homepage: www.elsevier.com/locate/medengphy Evaluation of delamination in drilling of bone Rupesh Kumar Pandey, Sudhansu Sekhar Panda ∗ Indian Institute of Technology Patna/Mechanical Engineering Department, Patna 800013, India article info Article history: Received 20 September 2014 Revised 4 April 2015 Accepted 20 April 2015 Available online xxx Keywords: Delamination Bone drilling Orthogonal array Regression ANOVA Taguchi method abstract In this paper, delamination of bone associated with drilling is investigated using design of experiments. Experiments have been planned based on L 25 design of the orthogonal arrays with different conditions of drill bit, spindle speed and feed rate. Regression analysis is used to develop a mathematical model of delamination as a function of bone drilling process parameters. Analysis of variance (ANOVA) is carried out to find the significance of the developed model along with the percentage contribution of each factor on delamination. Optimum setting of bone drilling parameters for minimum delamination is determined using Taguchi optimization methodology. Finally, the results obtained are validated by conducting confirmation experiments. © 2015 Published by Elsevier Ltd on behalf of IPEM. 1. Introduction Implant site preparation through drilling of bone for the insertion of screws and wires to mount the implant or to fixate the fractured bones is frequently done during orthopedic fracture treatment [1–5]. Minimally invasive bone drilling has a great demand in orthopedic surgical process as it helps in better fixation and quick healing of bones post operatively [1–5]. Bone is a non-homogeneous and anisotropic material, composed of an outer hard layer termed as cortical bone and an inner spongy layer known as cancellous bone [6]. At microscopic level bone is seen to have a composite structure [7–9] as like fiber rein- forced composite. The majority of the bone is made up of bone matrix comprising principally of inorganic hydroxyapatite and organic colla- gen. The bone is manufactured by the hardening of this matrix entrap- ping the cells [7–9]. Most of the composite structure reported damage associated with machining known as delamination. During drilling of fiber reinforced composite, damage occurs both at the entrance as well as at the exit of the drilled hole, in the form of peel-up and push- out delaminations, respectively [10]. It not only reduces the structural integrity of the material, but also results in poor assembly tolerance and has the potential for long-term performance deterioration [11]. The mechanical damage occurred around the drilled hole (delami- nation) is a major concern during bone drilling as greater the damage greater will be the postoperative healing time. Also, it can hamper the engagement of screws with the bone adjacent to the drilled hole ∗ Correspondence author. Tel.:+91 612 2552037; fax: +91 612 2277383. E-mail addresses: rupeshiitp@gmail.com (R.K. Pandey), sspanda@iitp.ac.in (S.S. Panda). leading to the loosening of fixation resulting in its misalignment [11–12]. Previously, several researchers have carried out investiga- tions so as to examine the effect of various process parameters on the invasion induced to the bone during drilling and its consequences on healing [1–10]. To the authors’ knowledge, however, few investiga- tions have been undertaken to evaluate the damage induced to the bone surrounding the drill site. Literature related to damage associ- ated with drilling composite and method of calculating delamination factor has been reported by several investigators [10–14]. As bone resembles like a fibrous composite, hence a better understanding of the delamination process during drilling and its minimization may lead to improved post-operative outcomes for patients. The aim of the present investigation is to study the effect of drilling process parameters such as drill point angle, helix angle, feed rate and spindle speed on the percentage delamination in drilling of bone. Mathematical model relating the percentage increase in delamination with the above studied parameters was obtained using regression analysis. The significance of the model developed and the percentage contribution of each factor was determined using ANOVA. Taguchi’s signal to noise ratio was employed along with response table and response graph for determining the best setting of bone drilling pa- rameters for minimum mechanical damage around the drilled hole. 2. Experimentation In this investigation, feed rate (mm/min), spindle speed (rpm) and five different types of drill bits (different drill point angle and helix angle combinations) are considered for carrying out the bone drilling experiments. The experiments are conducted on bovine femoral dia- physis (middle part) as it is the closest animal bone having properties http://dx.doi.org/10.1016/j.medengphy.2015.04.008 1350-4533/© 2015 Published by Elsevier Ltd on behalf of IPEM. Please cite this article as: R.K. Pandey, S.S. Panda, Evaluation of delamination in drilling of bone, Medical Engineering and Physics (2015), http://dx.doi.org/10.1016/j.medengphy.2015.04.008