Biomechanics Thor Besier Auckland Bioengineering Institute t.besier@auckland.ac.nz x86953 What is Biomechanics & Bioengineering? BIOMECHANICS: mechanics applied to biological systems Mechanics deals with the study of motion and forces and the physical properties of materials. BIOENGINEERING: biological or medical application of engineering principles or engineering equipment Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science 1 Examples of Biomechanics Applications Blood flow in arteries and veins Designing artificial tendon (tissue engineering) Designing optimal orthopaedic surgery Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science Biomechanics: Overview This set of lectures will introduce biomechanical principles and highlight some applications for reengineering the human body. The following topics will be covered 1. Animal structure and function 2. Circulation 3. Respiration 4. Musculoskeletal System (Muscles and Bones) 5. Regulation Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science 2 Resources • Course book • Lecture slides on Canvas • For those who want more: – Google – Campbell and Reece, Biology (8th ed.) – Tortora and Grabowski, Principles of Anatomy and Physiology (10th ed.) Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science Biomechanics Basic Principles of Animal Structure and Function 3 Anatomy Versus Physiology ANATOMY = Study of the BIOLOGICAL FORM of an organism, i.e. its structure and parts. PHYSIOLOGY = Study of the BIOLOGICAL FUNCTION of an organism’s structure from the cell to the whole body. We are going to find that the form or structure fits function. For example: Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science Factors Affecting Animal Structure The laws of physics that govern flow, diffusion, heat exchange, strength and motion constrain the possible structure of animals. ─ Swimming aquatic animals have streamlined bodies ─ Flying insects are limited in size due to oxygen demand ─ As body mass increases the size of the skeleton and muscles needed for support and motion become limiting factors (e.g. can T-Rex run?) ─ How can Ostriches run at sustained speeds of 60km/hr? Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science 4 Interactions with the External Environment Animal structure dictates how their bodies exchange matter and energy with environment. The rate of exchange is proportional to the surface area, while the amount of matter/ energy required is proportional to the volume of the animal’s body. In single celled organisms exchange occurs by diffusion across the cell membrane from an aqueous environment. Larger animals have complex organ systems to accomplish exchange. Internal fluids link individual cells with exchange surfaces. Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science Structural Organisation of Animals 2. Tissue Level = Cardiac Muscle 1. Cellular Level = Muscle Cell 3. Organ Level = Heart 4. Organ System Level = Circulatory System 5. Organism level: Human with multiple organ systems functioning together to regulate our internal environment. Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science 5 Tour of the Human Body Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science Tissues We are very familiar with cells, the basic functioning unit of all living things. In most multi-cellular organisms (such as humans) cells do not function alone, but instead function as a group. TISSUES: A group of many structurally similar cells that act together to perform a certain function. Animals are composed of four PRIMARY TISSUES: 1. Epithelial Tissue 2. Connective Tissue 3. Muscle Tissue 4. Nervous Tissue Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science 6 1. Epithelial Tissue Epithelial tissue covers the outside of the body and lines organs and cavities inside the body. It is made of sheets of tightly packed cells that are connected together. Epithelial cells Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science Functions of Epithelial Tissue • A barrier against injury, microbes, fluid loss • Absorption and secretion of chemical substances – Digestive, respiratory and urinary tracts – Sweat glands, mammary glands, liver,… • Sensor function – Cells lining blood vessels can sense changes in blood velocity that occur when there is increased demand for blood supply. They respond by producing chemical substances that cause blood vessels to expand. Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science 7 2. Connective Tissue Connective tissue is comprised of cells spread throughout an extracellular matrix (ECM). The ECM has a web of protein fibres embedded in a liquid, jelly-like, or solid foundation. Two kinds of protein are found in the ECM: 1. Collagen is a rigid protein that imparts strength and rigidity to the tissue. 2. Elastin is a flexible protein that imparts elasticity and resilience to the tissue. In addition to these, the extracellular matrix also contains protein-carbohydrate complexes. Photomicrograph of collagen and elastin Unravelling collagen by Julian Voss-Andrade, San Francisco Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science Collagen and Elastin: Mechanical Properties Collagen and elastin stretch when a tensile force is applied. If we plot the force required to produce a given strain (= change in length over original length = x - x 0 ): Label the curves for collagen and elastin. F (x – x0)/x0 x0 x0 Collagen is rigid or stiff – stretches less at any given force (dashed line). Elastin more flexible – stretches more for the same applied force (solid line). x F When the strain is small the force-deformation relation is linear, i.e. F = k(x – x0)/x0, where k is a constant. At higher strains the force required increases more rapidly so that k is no longer a constant, but increases with the strain. This kind of behaviour is called STRAIN HARDENING. Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science 8 Types of Connective Tissue Variation in extracellular matrix means that there are various types of connective tissue. The six major types of connective tissue are: 1. Loose connective tissue (holds organs in place) 2. Adipose tissue (stores fat) 3. Blood (transports substances) 4. Fibrous connective tissue (tendons, ligaments) 5. Cartilage (outer ear, joints) 6. Bone (rubbery fibres plus calcium) The mechanical properties of connective tissue depend on the relative proportion of the different components of the extracellular matrix and their structural organisation. Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science Connective Tissue continued Loose network of fibres, randomly scattered. Fills space, provides packing Rigid matrix of calciumcontaining minerals. Bears weight, provides structural integrity. Stores fat Transports substances Rubbery matrix. Distributes load, lubrication Dense network of fibres parallel to each other. Connects bones to muscles (tendons), and other bones (ligaments) Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science 9 Mechanical Regulation of Connective Tissue Adapted from Carter & Beaupré, Skeletal Function & Form Not examinable! Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science 3. Muscle Tissue Muscle tissue is the most abundant tissue in most animals and is specialised for contraction. Each long, thin muscle cell has proteins arranged so that a signal from a nerve cell can stimulate contraction. Muscle cells are bundled together to form muscle fibres and a number of these fibres makes muscle tissue. There are three types of muscle tissue: 1. Skeletal Muscle – attached via tendons to bones so that contractions cause movements of the skeleton. This muscle tissue is said to be striated (striped). 2. Cardiac Muscle – striated muscle found only in the heart. Adjacent cells have special areas of contact so that a contraction signal is propagated to all the muscle cells, resulting in a coordinated heart beat. Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science 10 Muscle Tissue continued 3. Smooth Muscle – muscle without striations found in the digestive tract, blood vessels, bronchioles, urinary and reproductive systems. Contraction is involuntary. Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science Checkpoint 1 Label the tissues as: smooth, skeletal or cardiac muscle. Skeletal Smooth Cardiac Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science 11 4. Nervous Tissue Nervous tissue senses stimuli and enables communication between different parts of the body using electrical signals called nerve impulses. This tissue has two types of cells: 1. Neurons that generate and transmit nerve impulses 2. Glial cells that protect, insulate and nourish neurons Neurons: Long extensions for transmitting electrical signals Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science Organs An organ can be defined as a structure that is made up of at least two, and often all four primary tissue types. The tissue types work together to serve the specific function of that organ. Examples of organs are: • Skin (largest) • Heart • Brain • Liver • Small intestine etc….. Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science 12 Organ Systems Not examinable! The organs of most animals are organised into organ systems that perform essential body functions. Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science Checkpoint One Epithelial tissues are characterised as such because they_______________. A) sense stimuli B) transmit impulses C) cause body movements D) form a framework that supports the body E) cover both external and internal body surfaces Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science 13 Checkpoint Two Which of the following statements about organs is FALSE? A) An organ consists of many cells. B) An organ represents a higher level of structure than the tissues composing it. C) An organ carries out the functions of the single tissue type that it is composed of. D) Organs play a role in homeostasis (maintaining the normal environment within the body). E) An organ consists of several tissues Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science Checkpoint Three Contractions of the intestine to push ingested food along are called peristalsis. Which muscle type(s) is involved in peristalsis? A) cardiac muscle only B) smooth muscle only C) skeletal muscle only D) cardiac and smooth muscle E) skeletal and smooth muscle Thor Besier, Auckland Bioengineering Institute & Department of Engineering Science 14
