BME 320: Lecture #3 Review (Structure-Property-Function Relationships & Classes of Materials)

Describe the composition of the extracellular matrix (ECM).

The ECM is a structural support network consisting of diverse proteins, sugars, and other components. Chiefly, the ECM is comprised of matrix proteins, which furnish the necessary mechanical support to cells and tissues. These proteins are categorized as either structural (e.g. collagens, elastin) or non-structural (glycoproteins; e.g. fibronectin, laminin) in accordance with their specific functionalities. Other important components include integrins, growth factors, cytokines and MMPs.

Functions of the extracellular matrix: (3)

(1) physical stabilization; (2) mechanical distinction; (3) bioactive signals

Step-wise responsibilities of a biomaterials engineer/scientist in synthesizing a new biomaterial: (8)

(1) Understand the material, learn how to modify its properties; (2) Design and test prototypes; (3) Test how biological cells respond to it (in vitro cytocompatibility); (4) Test survival and function in small animal models (mice); (5) Test performance, biocompatibility in large animal models; (6) Navigate regulatory affairs and get a product on the market; (7) Benefit patients and medical professionals

Classes of materials: (4)

(1) metals; (2) ceramics; (3) polymers; (4) composites

Classes of materials: (1) Metals

A class of materials arranged via closest packing and characterized by high thermal and electrical conductivity, malleability, and ductility deriving from the delocalized, non-directional covalent bonding pattern typical of metallic crystals

Classes of materials: (2) Ceramics

A class of nonmetallic materials comprising heterogeneous mixtures of minute silicate crystal and glassy cement phases that are strong, brittle, and resistant to heat and chemical attack

Classes of materials: (3) Polymers

A class of substances comprised of macromolecules, consisting of many repeating structural units termed monomers and formed via polymerization

Classes of materials: (4) Composites

A class of materials encompassing any multiphase material that exhibits a significant proportion of the properties of both constituent phases such that a better combination of properties is realized

Composites include multiphase . . ., . . ., and . . .

metal alloys; ceramics; polymers

To satisfy composite classification, constituent phases must derive from . . .

distinct material classes

Materials science and engineering is rooted in establishing or discovering . . .

structure-property-function relationships

structure-property-function relationship

A tenet of materials science that describes how variation in the arrangement of atoms and materials' microstructures give rise to specific mechanical, thermal, and chemical properties, which in turn inform a given material's relative suitability for particular implementations (i.e. their functions). Understanding structure-property relationships allows engineers and scientists to develop new substances or modify existing ones to suit particular functionalities.

To meet an advanced functional capability, extraordinary material properties can be achieved by . . .

processing materials using various techniques/methods to have unique microstructures

Levels of consideration in materials science and engineering: (4)

(1) composition; (2) processing; (3) structure; (4) design

Levels of consideration in materials science and engineering: (1) Composition

What the material is made of

Levels of consideration in materials science and engineering: (2) Processing

How the material is handled and worked (may impart distinct properties)

Levels of consideration in materials science and engineering: (3) Structure

How the components of a material are organized at nano-, micro-, and macroscale

Levels of consideration in materials science and engineering: (4) Design

What final shape is given to the material so that it may optimally perform its intended function

Common metals used as main component in biomaterials: (5)

(1) magnesium; (2) titanium; (3) aluminum; (4) iron; (5) gold

Common metals used as additives in biomaterials: (9)

(1) calcium; (2) zirconium; (3) chromium; (4) cobalt; (5) nickel; (6) copper; (7) silver; (8) platinum; (9) manganese

Why is magnesium a common material selection for third generation biomaterial devices fabricated from metals?

Magnesium is both bioactive and resorbable, making it unique among metals (no other metal is resorbable)

alloy

Substances containing a mixture of elements, where one element must be a metal, and having metallic properties

Types of alloys: (2)

(1) substitutional; (2) interstitial

Types of alloys: (1) Substitutional alloy

An alloy in which some of the host metal atoms are replaced by other metal atoms of a similar size (e.g. brass--1/3 of copper atoms replaced by zinc)

Types of alloys: (2) Interstitial alloy

An alloy formed when some of the interstices in the closest packed metal structure are occupied by small atoms (e.g. steel hosting carbon atoms in holes of iron structure)

stainless steel

A non-corrosive, hybrid interstitial/substitutional alloy in which carbon atoms are trapped in the interstices of the iron crystal matrix, with some iron atoms replaced with nickel and chromium atoms

Explain why stainless steel is non-corrosive.

Stainless steel is highly corrosion resistant because it is a hybrid interstitial/substitutional alloy in which chromium and nickel atoms substitute for iron atoms in the crystal lattice, while carbon atoms occupy interstitial sites. The dispersed chromium atoms preferentially oxidize at the surface to form a thin, dense, adherent layer of chromium oxide (Cr₂O₃), which passivates the material by preventing further diffusion of oxygen and moisture into the alloy. Because chromium is distributed throughout the iron matrix, this protective oxide film is self-healing if damaged. Nickel further stabilizes the alloy's microstructure and enhances corrosion resistance, while interstitial carbon primarily increases strength and hardness rather than directly contributing to passivation.

. . . are rarely used in biomaterial synthesis; rather, . . . are used

pure metals; alloys

Explain why pure metals are rarely used in biomaterial synthesis.

Pure metals are rarely used in biomaterial synthesis because their native properties are often insufficient for biomedical applications. By alloying metals and modifying their microstructure, engineers can tailor mechanical properties such as strength, ductility, toughness, and wear resistance, as well as chemical properties such as corrosion resistance and biocompatibility. These structure-property relationships allow metallic biomaterials to be designed for specific functional requirements, making alloys generally more suitable than pure metals for implants and medical devices.

Hierarchical structure in metallic materials: (3)

(1) atomic lattice -> (2) crystal/grain -> (3) pure metal