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CONTENTS
Volume 3, Number 1, March 2016
 

Abstract
Well-ordered porous materials are very promising in orthopedics since they allow tailoring the mechanical properties. Finite element (FE) analysis is commonly used to evaluate the mechanical behavior of well-ordered porous materials. However, FE results generally differ importantly from experimental data. In the present article, three types of manufacturing irregularities were characterized on an additive manufactured porous titanium sample having a simple cubic unit-cell: strut diameter variation, strut inclination and fractured struts. These were included in a beam FE model. Results were compared with experimental data in terms of the apparent elastic modulus (Eap) and apparent yield strength (SY,ap). The combination of manufacturing irregularities that yielded the closest results to experimental data was determined. The idealized FE model resulted in an Eap one order of magnitude larger than experimental data and a SY,ap almost twice the experimental values. The strut inclination and fractured struts showed the strongest effects on Eap and SY,ap, respectively. Combining the three manufacturing irregularities produced the closest results to experimental data. The model also performed well when applied to samples having different structural dimensions. We recommend including the three proposed manufacturing irregularities in the FE models to predict the mechanical behavior of such porous structures.

Key Words
additive manufacturing; electron beam melting; porous materials; finite element; manufacturing irregularities; mechanical properties

Address
Laboratoire de recherche en Imagerie et Orthopédie (LIO), Département de Génie de la Production Automatisée, École de Technologie Supérieure, 1100 rue Notre-Dame Ouest, H3C 1K3 Montréal, Canada

Abstract
Based on a survey done recently in Japan, 30 percent of the serious accidents occurred in oral implant surgery were concerned with the mandibular canal and 3/4 of them were related to drilling. One of the reasons lies in the lack of the education system. To overcome this problem, a new educational system focusing on drilling the mandibular trabecular bone has been developed mainly for dental college students in the form of an oral implant surgery training simulator that enables student to sense the reaction force during drilling. On the other hand, the conventional system uses polymeric model. Based on these systems, two approaches were proposed; the evaluation by experienced clinicians using the simulator, and experimental works on the polymeric model. Focusing on the combination of the drilling force sensed and drilling speed obtained through both approaches, the results were compared. It was found that the polymeric models were much softer especially near the mandibular canal. In addition, the study gave us an insight of the understanding in bone quality through tactile sensation of the drilling force and speed. Furthermore, the clinicians positively reviewed the simulator as a valid tool.

Key Words
oral implant; drilling force; drilling speed; trabecular bone; mandibular

Address
Mohammad Aimaduddin Atiq bin Kamisan, Kenichiro Yokota, Takayuki Ueno: Graduate School of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku, Yokohama, Japan

Hideaki Kinoshita: Department of Material Science, Tokyo Dental College, 2-9-18 Misaki-cho, Chiyoda, Tokyo, Japan

Shinya Homma, Yasutomo Yajima: Department of Oral and Maxillofacial Implantology, Tokyo Dental College, 2-9-18 Misaki-cho, Chiyoda, Tokyo, Japan

Shinichi Abe: Department of Anatomy, Tokyo Dental College, 2-9-18 Misaki-cho, Chiyoda, Tokyo, Japan

Naoki Takano: Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku, Yokohama, Japan

Abstract
Anterior knee pain is a major problem among adolescents and young adults especially those who participates in sports. The most common pathogenesis of anterior knee pain can arise from compression and shear forces in the patellofemoral joint. It is also caused by impingement of infrapatellar fat pad. Fat pad impingement can occur when the fat pad becomes swollen and inflamed due to a direct blow or chronic irritation. As a result, the bottom tip (or inferior pole) of the patella can pinch the fat pad. One of the many causes of swollen fat pad can be secondary to anterior cruciate ligament (ACL) injury. The aim of this study was to compare the infrapatellar fat pad volume in patients with acute ACL injury and a group of age-, gender-, and activity- matched controls with intact ligament. Axial magnetic resonance (MR) images have been performed on 32 patients with torn ACL and 40 control patients. The volume of the fat pad was measured digitally from MR image by using a 3d Reconstruction software, ellipsoidal approximation, and a MATLAB code. The results were compared between patients with torn ACL and control group. Patients with a torn ACL had a significantly larger fat pad than the controls (P=0.01). There was no significant difference between the methods used to measure the infrapatellar fat pad volume (P=0.83-0.87). Thus, lesions of the infrapatellar fat pad is often associated with ACL injury.

Key Words
patellofemoral; ACL injury; infrapatellar fat pad; Knee

Address
B. Cheruvu, T. Goswami: Department of Biomedical Engineering, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH 45435, USA

J. Tsatalis: Department of Radiology, Wright State University, Boonshoft School of Medicine, 3640 Colonel Glenn
Highway, Dayton, OH 45435, USA

R. Laughlin: Department of Orthopedic Surgery, Sports Medicine, and Rehabilitation, Wright State University, Boonshoft
School of Medicine, 3640 Colonel Glenn Highway, Dayton, OH 4543, USA

Abstract
To maintain activity in a coenzyme/enzyme mixture system, such as β-nicotinamide adenine dinucleotide (NADH)/dehydrogenase, the water-soluble 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers as an additive were synthesized and investigated for their stabilizing function. The inhibitor for the NADH/dehydrogenase reaction was spontaneously formed when the NADH was stored in the dehydrogenase solution. Therefore, we hypothesized that if the additive polymer could interact with an inhibitor without any adverse effect on the dehydrogenase, the activity in the NADH/dehydrogenase mixture could be maintained. We selected lactose dehydrogenase (LDH) as the enzyme, and the NADH was dissolved and incubated at 37°C in the LDH solution containing the polymers. The phospholipid polymers used in this study were poly(MPC) (PMPC), poly(MPC-co-3-trimethylammonium-2-hydroxypropyl methacrylate chloride) (PMQ) and poly[MPC-co-potassium 3-methacryloyloxypropyl sulfonate (MSO3)] (PMMSO3). The poly(MSO3) was used as a reference. For the PMQ and PMSO3 aqueous solutions, the activity of the NADH/LDH mixture system decreased with incubation time as the same level or lower than that in the Tris buffered solution in the absence of the polymers. However, for the poly(MPC-co-MSO3) (PMMSO3) aqueous solution, the activity of the NADH/LDH mixed system was six times higher than that in the buffered solution even after a 3-days incubation. The LDH activity was 1.5-1.8 times higher in the presence of the PMMSO3 compared with that in the PMSO3 solution. The mixture of two polymers, poly(MPC) and poly(MSO3), did not produce any stabilization. Thus, both the MPC and MSO3 units in the polymer chain had important and cooperative effects for stabilizing the NADH/LDH mixture.

Key Words
2-methacryloyloxyethyl phosphorylcholine (MPC) polymer; charged polymers; polymeric additive; NADH/LDH mixture system; stabilization

Address
Kyoko Fukazawa and Kazuhiko Ishihara: Department of Materials Engineering, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku,Tokyo 113-8656, Japan

Kazuhiko Ishihara: Department of Bioengineering, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan

Abstract
Results from multiple high profile experiments on the parameters influencing the impacts that cause skull fractures to the frontal, temporal, and parietal bones were gathered and analyzed. The location of the impact as a binary function of frontal or lateral strike, the velocity, the striking area of the impactor, and the force needed to cause skull fracture in each experiment were subjected to statistical analysis using the JMP statistical software pack. A novel neural network model predicting skull fracture threshold was developed with a high statistical correlation (R2=0.978) and presented in this text. Despite variation within individual studies, the equation herein proposes a 3 kN greater resistance to fracture for the frontal bone when compared to the temporoparietal bones. Additionally, impacts with low velocities (<4.1 m/s) were more prone to cause fracture in the lateral regions of the skull when compared to similar velocity frontal impacts. Conversely, higher velocity impacts (>4.1 m/s) showed a greater frontal sensitivity.

Key Words
biomedical engineering; bone biomechanics; mechanics coupled with human activity; modeling and simulation; medical mechanics

Address
Department of Biomedical, Industrial, and Human Factors Engineering, Wright State University, 257 Russ Engineering Center, Fairborn, OH 45435, US

Abstract
A surface resisting protein adsorption and cell adhesion is highly desirable for many biomedical applications such as diagnostic devices, biosensors and blood-contacting devices. In this study, a surface conjugated with sulfobetaine molecules was fabricated via the click reaction for the anti-fouling purpose. An alkyne-containing substrate (Alkyne-PPX) was generated by chemical vapor deposition of 4-ethynyl- [2,2]paracyclophane. Azide-ended mono-sulfobetaine molecules were synthesized and then conjugated on Alkyne-PPX via the click reaction. The protein adsorption from 10% serum was reduced by 57%, while the attachment of L929 cells was reduced by 83% onto the sulfobetaine-PPX surface compared to the protein adsorption and cell adhesion on Alkyne-PPX. In conclusion, we demonstrate that conjugation of monosulfobetaine molecules via the click chemistry is an effective way for reduction of non-specific protein adsorption and cell attachment.

Key Words
anti-fouling; sulfobetaine; cell adhesion; protein adsorption; click chemistry

Address
Hsiu-Wen Chien, Ming-Chun Keng, Hsien-Yeh Chen, Wei-Bor Tsai: Department of Chemical Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei 106, Taiwan

Sheng-Tung Huang: Graduate Institute of Biochemical and Biomedical Engineering, National Taipei University of Science and Technology, No. 1, Sec. 3, Chung-Hsiao E. Rd., Taipei, 106, Taiwan


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