Biomaterials

Biomechanics

21 Adapted from Fig. 3.2, Callister & Rethwisch 8e. • Atoms touch each other along cube diagonals. --Note: All atoms are identical; the center atom is shaded differently only for ease of viewing. Body Centered Cubic Structure (BCC) ex: Cr, W, Fe (  ), Tantalum, Molybdenum 2 atoms/unit cell: 1 center + 8 corners x 1/8 Click once on image to start animation (Cour

BME423CMaterials.pdf-Adapted from Fig. 3.2, Callister &

BME406_course_outline.pdf-Faculty of Engineering, Architecture and Science

1 8. Biomechanics Application (Hip, Knee, Dental, Stents ) A vascular stent is a small metal tube, which is inserted into an artery at the site of a narrowing to act as an internal scaffolding or a support to the blood vessel. Vascular Stent 8. Biomechanics Application (Hip, Knee, Dental, Stents ) Vascular Stent 2 Expansion under displacement control until a diameter of 3 mm was reached. The stent geometry was modelled as shell elements FROM SIMPLIFIED MODELS … TO PLAQUE MODEL Healthy artery Artery with plaque 8. Biomechanics Application (Hip, Knee, Dental, Stents ) Vascular Stent Structural analysis is necessary to obtain the correct configuration for the fluid dynamics simulations: fluid domain Structural analysis Vascular Stent 8. Biomechanics Application (Hip, Knee, Dental, Stents ) 3 Boundary conditions 4 18 0 9 dynes/cm 2 0.16 s ARTERIAL REGION INSIDE STENT STRUTS HEALTHY MODEL PLAQUE MODEL Vascular Stent 8. Biomechanics Application (Hip, Knee, Dental, Stents ) PALMAZ SORIN JOSTENT CORDIS STENT MODELS, GEOMETERY RADIUS after expansion LENGTH after expansion THICKNESS CORDIS 1.5 3.53 0.1 JOSTENT 1.5 2.30 0.1 PALMAZ 1.5 2.97 0.1 SORIN 1.55 3.50 0.1 Length: 11.68 mm Internal diameter: 2.15 mm Thickness: 0.5 mm Length: 3.68 mm Internal diameter: 1.25 mm Thickness: 0.45 mm Vascular Stent 8. Biomechanics Application (Hip, Knee, Dental, Stents ) 5 CORDIS JOSTENT SORIN PALMAZ WSS < 5 dynes/cm 2 • correlated with sites of intima thickening and smooth muscle cells migration • locations where stagnation of blood occurs • prone to thrombus formation and platelet accumulation WALL SHEAR STRESSES (WSS) 0 s 0.16 s 0.32 s 0.4 s 0.44 s 85 90 95 100 % of cells 0 s 0.16 s 0.32 s 0.4 s 0.44 s Vascular Stent 8. Biomechanics Application (Hip, Knee, Dental, Stents ) WSS is the wall shear stress , measured in pressure units (N/m 2 or dynes / cm 2 , with a relation N/m 2 = 10 dynes / cm 2 ) CORDIS JOSTENT SORIN PALMAZ 0 10 20 30 40 50 0 s 0.16 s 0.32 s 0.4 s 0.44 s [dynes/cm 2 ] MAXIMUM WSS ON STENT Vascular Stent 8. Biomechanics Application (Hip, Knee, Dental, Stents ) 6 [dynes/cm 2 ] 0 10 20 30 40 50 0.16 s MAXIMUM WSS 8. Biomechanics Application (Hip, Knee, Dental, Stents ) CORDIS JOSTENT SORIN PALMAZ 0 s 0.16 s 0.32 s 0.4 s 0.44 s [dynes/cm 2 ] 0 5 10 15 20 MAXIMUM WSS ON THE ARTERIAL WALL 8. Biomechanics Application (Hip, Knee, Dental, Stents ) 7 What is an intravascular stent? • A small tubular mesh usually made of either stainless steel or Nitinol. (Shape memory alloy) • Inserted into stenotic (blocked) arteries to keep the lumen patent. Normally during angioplasty. • Used at various sites including the coronary, renal, carotid and femoral arteries. 8. Biomechanics Application (Hip, Knee, Dental, Stents ) Balloon angioplasty 8. Biomechanics Application (Hip, Knee, Dental, Stents )

BME | 406 | Biomechanics | lecture notes | 1 8. Biomechanics Application 

6 7. Bone-Implant Systems & Fracture Fixation Devices Fracture Fixation Devices Screw Fixation (e.g., fracture of distal tibia with lag screws through the fragments.) Fracture Fixation Devices Plates, Intramedullary Rods and Nails (e.g., a fracture of the humeral shaft fixed by the locked intramedullary rod. Locking is achieved by the transverse screws through holes in the ends of the rod.) 7. Bone-Implant Systems & Fracture Fixation Devices Plates, Intramedullary Nails (e.g., a femoral neck fracture with a sliding hip nail.) 7 7. Bone-Implant Systems & Fracture Fixation Devices Fracture Fixation Devices Screw Fixation (e.g., external fixator for a fracture of the distal radius.) Loading Types • Bending • Axial Loading – Tension – Compression • Torsion Bending Compression Torsion 7. Bone-Implant Systems & Fracture Fixation Devices 8 Fracture Mechanics 7. Bone-Implant Systems & Fracture Fixation Devices Fracture Mechanics • Bending load: – Compression strength greater than tensile strength – Fails in tension 7. Bone-Implant Systems & Fracture Fixation Devices 9 Fracture Mechanics • Torsion – The diagonal in the direction of the applied force is in tension – cracks perpendicular to this tension diagonal – Spiral fracture 45º to the long axis 7. Bone-Implant Systems & Fracture Fixation Devices Fracture Mechanics • Combined bending & axial load – Oblique fracture – Butterfly fragment 7. Bone-Implant Systems & Fracture Fixation Devices 10 Fracture Mechanics • Fracture Callus – Moment of inertia proportional to r 4 – Increase in radius by callus greatly increases moment of inertia and stiffness 1.6 x stronger 7. Bone-Implant Systems & Fracture Fixation Devices IM Nails Moment of Inertia • Stiffness proportional to the 4 th power. 7. Bone-Implant Systems & Fracture Fixation Devices 11 IM Nail Diameter 7. Bone-Implant Systems & Fracture Fixation Devices Interlocking Screws • Controls torsion and axial loads • Advantages – Axial and rotational stability – Angular stability • Disadvantages – Time and radiation exposure – Stress riser in nail 7. Bone-Implant Systems & Fracture Fixation Devices 12 Internal Fixation 7. Bone-Implant Systems & Fracture Fixation Devices Biomechanics of Internal Fixation 7. Bone-Implant Systems & Fracture Fixation Devices • Screw Anatomy – Inner diameter – Outer diameter – Pitch 13 Screw Fixation • To increase strength of the screw & resist fatigue failure: – Increase the inner root diameter • To increase pull out strength of screw in bone: – Increase outer diameter – Decrease inner diameter – Increase thread density – Increase thickness of cortex – Use cortex with more density. 7. Bone-Implant Systems & Fracture Fixation Devices Plate Fixation • Plates: – Bending stiffness proportional to the thickness (h) of the plate to the 3 rd power. I= bh 3 /12 Base (b) Height (h) 7. Bone-Implant Systems & Fracture Fixation Devices

BME | 406 | Biomechanics | lecture notes | 6 7. Bone-Implant Systems & Fr

Biomechanics (BME406) Instructor: Prof. A. Varvani Office: EPH 306C E-mail: avarvani@ryerson.ca Classes: Thurs. (8:00-10:00) Fri. (9:00-10:00) Labs: sec.2 Mon. (10:00-12:00) Sec.3 Tues (10:00-12:00) Sec.4 Tues (16:00-18:00) Sec. 1 Thurs (16:00-18:00) Office hours: Thurs. (10:00-11:00) Fri. (10:00-11:00) Midterm test: Thursday March 9 , 2017 ( Format: Multiple-choices and problems) Course Evaluation: Assignment: 10% Laboratory: 20% Midterm test: 25% Final exam: 45% (Prerequisites: BLG600 and BME323 ) Course Textbooks: 1. On-line course lectures through D2L, and 2. Orthopaedic Biomechanics : Mechanics and Design in Musculoskeletal Systems (D.L. Bartel, D.T. Davy,T.M. Keaveny, Prentice Hall). Course Objective: Biomechanics course intends to provide background and principles of biomechanics. Topics include ligament, tendon, bone, muscle; joints, gait analysis; exercise physiology. The course is structured to discuss the physics; statics, dynamics and mechanics of tissues under physiological activities in one hand and the examination of organ/anatomical response of live tissues with related biomedical devices. Topics to Study: • Introduction to Biomechanics and Musculoskeletal System • Statics and Dynamics in Musculoskeletal System • Mechanics of Bone • Mechanics of Cartilage, Ligaments, Tendons, and Skeletal Muscles • Mechanics of Human Heart • Biomechanics of Joints: Spine, Knee and Hip • Orthopaedic Implants and Fracture Fixation Devices. • Applications: Dental, Artificial Heart, Stents, Hip Replacement Weeks 2-6 (Jan. 14-Feb.13) • Introduction to Biomechanics Laboratory • Hardness test on bovine femur and rib samples • Three-point bending tests on rib samples • Torsion test on bovine femur samples • Fatigue test on bovine femur samples Week 7 (Feb. 18-24): Study week- no laboratory! Weeks 8-14 (Feb.25-April 10) • Electrocardiogram (ECG or EKG) • Electromyography (EMG) • Gait analysis (I) • Gait analysis (II) BME406 Laboratory Experiments A few notes on the lab experiments: -Groups are formed from the class list and are kept unchanged for the entire semester. -Lab reports are submitted to TAs in the lab every week. -Make sure to review the experimental procedure before attending labs. Laboratory Report: MBE406 students consist of groups A,B,C, D (section I) and E, F, G, H (section II) are required to submit their lab reports for every lab experiments they perform. For example members of group A (consists of 5 students) require to perform each laboratory test, and write its lab report and present it together to the TA every week. A Laboratory Report has to include : (i) cover page (consists of the full names and IDs of group members, titles of lab reports, group, section,…), (ii) List of content, (iii) Introduction, (iv) Testing procedure, (v) Results, (vi) Discussion of results. This section should also address the “questions”, for each lab experiment, (vii) Summary, and (viii) References.

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