Lecture 2 Notes (BME 296)

BME 296 Lecture 2

Overview

• Introduction to biomaterials and their properties

Biological Response of Biomaterials

• Favorable Response: Example of a successful integration of biomaterial into biological systems.

• Unfavorable Response: Example of rejection or adverse reaction to a biomaterial.

Types of Biomaterials

• Metals: Used for durability and strength.

• Ceramics: Offer biocompatibility and wear resistance.

• Polymers: Can be natural or synthetic, versatile in applications.

Degradative Properties of Biomaterials

• Degradation: Can be preferred or unwanted depending on the context.

  • Example of environment: acidic conditions affecting material stability.

Surface Properties of Biomaterials

• Critical for the assimilation of biomaterials due to protein interactions.

• The surface differs from the bulk material in properties.

• Special processing methods can enhance surface characteristics to influence biological interactions.

Surface Properties - Physical

• Physical Characteristics: Topography such as roughness and patterns can affect cell behavior and biocompatibility.

• Macrophages and Foreign Body Giant Cells interact with the biomaterial's surface through these physical features.

Surface Properties - Chemical

• Chemical modifications to the outermost layers can alter hydrophobicity and surface activity.

• Experiment to determine hydrophobicity via water droplet angles on surfaces.

Application Considerations

Hydrophobic vs. Hydrophilic Polymers

• Assessing polymer choice for contact lenses.

  • Hydrophilicity may enhance moisture retention and comfort.

  • Melting temperature's relation to usage in body temperature (37°C).

Superhydrophobic Wood Surfaces

• Comparison between materials and justifications for hydrophilicity/hydrophobicity based on experimental results.

Bulk Properties of Biomaterials

• Importance of Bulk Properties: Initially determine immune response; long-term impact governed by bulk characteristics.

• Include mechanical, physical, and chemical attributes.

Characterization Techniques

• Quantitative procedures assign numerical values to properties.

• Qualitative experiments provide general observations without numerical context.

  • Example: Visual microscopy (qualitative) vs. spectroscopy (quantitative).

Structure and Bonding

Structure-Function Relationship

• Material structure determines properties and function, exemplified by water and ice's different states despite identical atomic compositions.

Atomic Bonding Types

1. Primary Bonds:

   • Ionic: Strong bonds between cations and anions, high energy and melting points.

   • Covalent: Electron sharing among non-metals, with variability in electrical conductivity.

   • Metallic: Interaction of cations with delocalized electrons, leading to ductility and electrical conductivity.

2. Secondary Bonds:

   • Hydrogen Bonds: Attractive forces involving hydrogen and electronegative elements; impact viscosity.

   • Van der Waals Forces: Weaker interactions related to dipoles, influencing biomaterial-protein interactions.

Crystallography

Crystalline vs. Amorphous Structures

• Crystalline materials exhibit ordered atomic arrangements; amorphous structures lack such order (e.g., plastics).

  • Specific examples: Snowflakes are crystalline, while rubber is amorphous.

Coordination Number

• Definition: Number of immediate neighboring atoms surrounding a central atom in a crystal.

• Unit Cell: The smallest repeating unit in a crystalline structure.

Atomic Packing Factor (APF)

• Measures volume occupied by atoms within a unit cell relative to the cell's total volume.

• APF is dimensionless and less than unity.

Calculating APF in Various Dimensions

1D & 2D APF Calculation

• Basic geometric principles applied to calculate packing efficiencies in simpler dimensions, moving towards 3D considerations.

FCC Structure

• Coordination number: 12; involves corner and face atoms within unit cells.

  • Atoms contribute fractions of their volume to overall cell volume.

BCC Structure

• Coordination number: 8; characterized by corner atoms and one atom at the center.

  • Key parameters: edge length and atomic radius, important for understanding mechanical properties.