BIOM 573 - Exam 2: Metals, Ceramics, and Biological Response

Wolff’s Law

Bone responds to mechanics; bones will adapt based on stress or demands placed on them

Metals

Allergic Reactions

10-15%; higher in women than men; can cause local and systemic reactions

Metals

Stable Oxide Film

spontaneously forms upon exposure to air and biological fluids; composed primarily of TiO2; resistance to corrosion

Metals

Negatives of Stable Oxide Film

thin (5-10 nm) making it easier to be compromises, and ions and particles are released; studies show film is continuously dissolved and reconstructed in aqueous solutions

Metals

Polarization Resistance (Rp)

resistance to oxidation during the application of an external potential; directly related to corrosion rate; metal per unit area being corroded in a particular instant

Metals

Oxidation and Reduction

oxidizer: losses an electron, increases valence state

reducer: gains an electron, decreases valence state

Metals

Redox Reactions

called half-cell reactions; one of the two required reactions needed for corrosion to progress

Metals

Redox Reactions in the Body

metal cation release (by corrosion and wear) → easy to combine with biomolecule → high toxicity OR metal cation release → anion stabilizes (oxide, hydroxide, salt) → difficult to combine with biomolecules → low toxicity

Biodegradable Metals

Iron-Based (Fe)

need to be very small to be biocompatible; high strength with sufficient ductility; MR compatibility; controlled degredation within 1-2 years

Biodegradable Metals

Zinc-Based (Zn)

tailored corrosion rates (release of Zn- => can become toxic)

Biodegradable Metals

Magnesium-Based (Mg)

high corrosion rates → release of H+ → Mg(OH)2 and MgCl2 stabilize corrosion layer and may interact further with protein and cell adhesion

Biodegradable Metals

Degradation Process for Mg-Based

electrochemical reaction, adsorption/desorption reactions, mass transfer, precipitation reactions, complete reactions (creation of one large ion/molecule), acid-base reactions (pH)

Ceramics

Main Characteristics in Design

1. inert

2. bioactive

3. biodegradable

Ceramics

Bond and Micro-Structures

ionocovalent bonds (very strong and @ high temps); form 3-dimensionally creating amorphous (glass) and lattice (crystalline) structures

Ceramics

Mainly used for…

hardness, resistance to wear and degradation

Ceramics

Bioinert

isolation by fibrous capsule

Ceramics

Biodegradable

no real cellular response; typical for allowing new tissue growth

Ceramics

Bioactive

elicit a biological response that supports tissue repair; bond with tissues; typically used for bone formation and integration

Ceramics

Natural or Synthetic Hydroxyapatites (HA)

similarity to calcium phosphate apatite phase in bone

Ceramics

Key Variables to describe Synthetic HA

chemical composition (protein adsorption), phase composition (strength, biomechanics, biocompatibility), density (structure and biology), pore size, range, and interconnectivity (tissue growth on/in), physical form of graft (clinic), granule size (failure), addative

Ceramics

Calcium Phosphate within Bone

nanoscale crystals interspersed in a collagen matrix (65-70% mass), but composition can vary with age, location, diet, disease, etc.

Ceramics

Calcium Phosphate within Tooth Mineral

70-80% mass of dentin an enamel; in enamel, the matrix is formed by amelogenins and enamelins

Ceramics

HA as a Coating

for fixation of implants to host bone; Melt Plasma Spraying (MPS): HA powder is fed into high temp torch that sprays semi-molten HA onto the substrate, parameters and properties can be modified

Ceramics

Protein Adsorption on Bioceramics

upon implantation, proteins will spontaneously adsorb onto their surfaces, and then cellular attachment, proliferation and migration occurs; behavior plays a vital role during bone tissue regeneration

Protein Adsorption on Bioceramics

Properties of Proteins that affect Protein Adsorption

1. size: larger molecules have more contact;

2. charge: molecules near isoelectric point generally adsorb more readily;

3. structure stability: less stable proteins can unfold and form more contact;

4. unfolding rate: molecules that rapidly unfold can form contacts more quickly

Protein Adsorption on Bioceramics

Properties of Surfaces that Affect Protein Adsorption

1. topography: greater texture exposes more surface area for interaction;

2. composition: determines types of IMFs;

3. hydrophobicity: hydrophobic surfaces tend to bind more protein;

4. heterogeneity: non-uniformity of surface results in different interactions;

5. potential; influence the distribution of ions

Protein Adsorption on Bioceramics

How cells Interface with Biomaterials

the initial presentation of material to cells is as a layer of spontaneously adsorbed proteins, whose composition and bioactivity provide a biological interpretation of the underlying physiochemical properties

Ceramics

Bioactive Calcium Phosphates and Bioactive Glasses

positive biological effects of reaction products (leached and surface); for drug delivery; many synthesis routes (high-temp methods, controlled precipitation, sol-gel process) and many final forms (powders, granules, coatings, scaffolds)

Ceramics

Biodegradable/Resorbable Main Usages

drug delivery, scaffolds and coatings, bone fillers, paste and cements;