Biomaterials Unit 5 Quiz

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Questions and Answers

What is the primary difference between adsorption and absorption?

Adsorption involves molecules penetrating a material, while absorption involves adhesion to a surface.

Adsorption and absorption are synonyms used interchangeably in chemistry.

Adsorption is the adhesion of molecules to a solid surface, while absorption is the penetration of molecules into another material. (correct)

Absorption only occurs in biological systems, while adsorption can occur in any chemical context.

Which surface property is known to increase protein adsorption when increased?

Surface hydrophobicity (correct)

Steric concerns

Surface charge

Surface roughness

How does a significant surface charge affect protein adsorption?

It repels all proteins, regardless of their charge.

It does not have any effect on protein adsorption.

It can attract or repel charged areas of proteins, influencing their adsorption. (correct)

It promotes uniform protein distribution across the surface.

What role does surface roughness play in protein adsorption?

A high degree of roughness may trap proteins in the valleys of the surface, promoting adsorption. Signup and view all the answers

What is a common characteristic of hydrophobic materials in relation to protein adsorption?

They lead to increased protein adsorption as proteins tend to interact more with hydrophobic surfaces. Signup and view all the answers

What effect do flexible hydrophilic polymer chains have on protein adsorption?

They decrease protein adsorption by creating steric repulsion. Signup and view all the answers

Why is controlling protein adsorption to biomaterial surfaces important?

It assures biocompatibility by ensuring the body reacts favorably to the coated surface. Signup and view all the answers

What typically characterizes ceramics and metallic biomaterials compared to synthetic polymers?

They are often more hydrophilic in their unmodified state. Signup and view all the answers

What is the first step in the sputter deposition process?

Energetic ions bombard the target material. Signup and view all the answers

Which characteristic of plasma-assisted PVD is true?

Plasma is formed to create high-energy species. Signup and view all the answers

What describes the process of thermal evaporation?

The material sublimates and condenses under vacuum conditions. Signup and view all the answers

Which component is NOT part of a self-assembled monolayer (SAM)?

Polymeric base layer Signup and view all the answers

What property do self-assembled monolayer (SAM) molecules possess?

They are amphiphilic with both polar and non-polar regions. Signup and view all the answers

How do van der Waals forces contribute during the formation of a SAM?

They cause the molecules to aggregate and crystallize. Signup and view all the answers

In sputtering, what happens to the target material?

Atoms are ejected from its surface. Signup and view all the answers

What is the primary advantage of using a high vacuum environment in thermal evaporation?

It reduces oxidation and contamination. Signup and view all the answers

What is a primary concern when using biological surface modification techniques?

Maintaining the biological activity of the molecule Signup and view all the answers

What must be present on a biomaterial surface for covalent coatings to be effective?

Reactive substrate surface Signup and view all the answers

Why is water typically chosen for contact angle testing of biomedical materials?

It provides a consistent measurement of wettability Signup and view all the answers

What does the contact angle (𝜽) represent in surface characterization?

The shape and spreading of a liquid droplet on the surface Signup and view all the answers

What effect does surface modification have on wettability?

It decreases the surface tension of the liquid/solid interface Signup and view all the answers

Young's equation is used to analyze which components in contact angle analysis?

Surface tensions at three interfaces Signup and view all the answers

Which of the following is true regarding covalent biological coatings?

They may impart additional stability to the molecule. Signup and view all the answers

Which functional groups are important for forming covalent coatings on biomaterials?

Hydroxyl, carboxyl, or amine groups Signup and view all the answers

What is the maximum resolution achievable by a light microscope?

0.2 μm Signup and view all the answers

What is the role of the sample stage in a light microscope?

To hold the sample securely Signup and view all the answers

Which component of the light microscope is responsible for focusing the light beam before it passes through the sample?

Condenser lens Signup and view all the answers

How does the resolving power of a Transmission Electron Microscope (TEM) compare to that of a light microscope?

It is greater because of the use of magnetic lenses Signup and view all the answers

Which of the following can be used as the detector in a light microscope?

Either a camera or human eye Signup and view all the answers

What kind of specimens can electron microscopy be particularly useful for investigating?

Both biological and non-biological specimens Signup and view all the answers

What is the primary difference between Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM)?

TEM transmits electrons through the specimen while SEM scans the surface Signup and view all the answers

What kind of light source is primarily used in a light microscope?

White light Signup and view all the answers

What is the main reason that thin samples are required for Transmission Electron Microscopy (TEM)?

Electron beams are absorbed by thicker samples, preventing imaging. Signup and view all the answers

Which type of scattering occurs when electrons collide with sample atoms without loss of energy?

Elastic scattering Signup and view all the answers

What type of electrons are generated when an atom relaxes to a lower energy state during inelastic scattering?

Auger electrons Signup and view all the answers

Which component of a Scanning Electron Microscope (SEM) is responsible for producing accelerated electrons?

Source Signup and view all the answers

What role do secondary electrons play in the imaging process of SEM?

They help create images by recording surface topography. Signup and view all the answers

What is the primary purpose of the lenses in a SEM?

To focus the electron beam and reduce spot size. Signup and view all the answers

Which of the following statements accurately describes the resolution capability of SEM?

SEM can achieve a resolution of 0.2 nm. Signup and view all the answers

In which environment does SEM operate to ensure high resolution imaging?

In a vacuum Signup and view all the answers

What method is used to prepare non-conductive samples for scanning in SEM?

Physical sputtering with a metallic target Signup and view all the answers

What is the primary purpose of the secondary electron detector in SEM?

To record the locations of emitted electrons Signup and view all the answers

Which component is required for energy-dispersive X-ray analysis (EDXA) in SEM?

Specialized detector system Signup and view all the answers

How does SEM primarily differ from Transmission Electron Microscopy (TEM)?

SEM creates images by scanning the surface, while TEM images the interior Signup and view all the answers

What information can SEM provide about a sample's composition?

Chemical composition through X-ray analysis Signup and view all the answers

What is one advantage of using SEM compared to TEM?

Is generally easier to operate Signup and view all the answers

Which of the following statements about SEM is true?

It uses a focused beam of electrons to create a magnified image of the surface. Signup and view all the answers

Which of the following is a limitation of SEM?

Its ability to distinguish surface chemistry is limited. Signup and view all the answers

Study Notes

UBM008: Biomaterials - Odd Semester 2024-25

Course: B.Tech. BME 2nd year
Faculty: Debasmita Mondal
Assistant Professor, DEIE, TIET, Patiala
Email: [email protected]
Phone: 9004008796

Unit 5: Syllabus

Biomaterial Processing and Surface Properties
Processing of metals, ceramics, and polymers to enhance bulk properties
Techniques to improve biocompatibility
Chemical, biological, and physical modifications of biomaterial surfaces
Contact angle analysis
Surface characterization techniques (light and electron microscopy)

Introduction

Biomaterial processing aims to alter bulk or surface properties, for desired shapes, sterilization or improving biocompatibility
The primary targeted bulk property is mechanical strength
Stronger/harder materials require reduced dislocation motion, requiring more energy for plastic deformation
Methods to improve bulk properties of metals:
- Alloying
- Strain Hardening
- Grain size refinement
- Annealing
- Precipitation Hardening

Alloying

An alloy is a solid solution of two or more elements in a solid solution form.
Alloying introduces many substitutional point defects into the base metal.
Alloys typically exhibit higher corrosion resistance and strength compared to pure metals.
Point defects induce localized lattice strain, the strain field size depending on the size difference between alloying elements and host atoms.
Strain field interactions influence already existing dislocations and impurities.
Crystal distortion due to impurities may either increase or decrease lattice strains depending on the dislocation type (tensile or compressive) and impurity location relative to the dislocation.

Strain Hardening

Adding point and line defects (dislocations) augments metal strength.
Strain hardening, also known as cold working, occurs when a material is deformed plastically beyond its yield point.
Increasing dislocation density leads to dislocations interacting and becoming tangled or pinned, hindering further movement and thus enhancing material strength (yielding to higher force requirements for continued deformation).
Cold working enhances the material's strength but decreases ductility.

Grain Size Refinement

Reducing the size of grains improves material quality and properties (mechanical strength, response to heat etc.)
Metals are polycrystalline, meaning they are composed of grains with different orientations.
Dislocations encounter difficulty crossing grain boundaries, impacting normal slip.
For plastic deformation, dislocations need to move across grain boundaries; differences in grain orientation impede dislocation movement across these boundaries.
Finer grain sizes introduce more grain boundaries, thereby hindering dislocation movement and increasing strength.
Fewer dislocations pile up at the boundaries in fine-grained materials, leading to lower stress on the boundaries and higher yield stress, rendering the fine-grained material stronger.

Annealing

Cold working (strain hardening) enhances material strength but reduces ductility and corrosion resistance.
Annealing is a heat treatment process used to increase ductility, toughness, and reduce internal stresses in metals.
Annealing comprises:
- Heating to the required temperature
- Maintaining the material at that temperature.
- Controlled cooling (quenching)
Factors affecting annealed material properties include material composition and quenching rate.

Precipitation Hardening

Introducing volume defects (uniformly dispersed small particles of a second phase within the primary phase matrix) to a material can enhance its strength.
Precipitate hardening, also known as age hardening or particle hardening, is a heat treatment that enhances strength and hardness of materials.
Precipitates cause local lattice strains within the host crystal, acting as barriers to dislocation motion, thereby strengthening the material.
Strengthening effect decreases as particle spacing increases.
Dislocations are hindered by the closeness of closely spaced precipitate particles in the matrix.

Processing to Improve Bulk Properties

Ceramics are strengthening by enhancing slip systems, while dislocation movement in covalently bonded crystals (like many polymers) is difficult.
Polymer strength is sometimes increased by increasing percent crystallinity.
Thermal processing techniques increase crystallinity, whereas pre-drawing procedures are similar to strain hardening seen in metals.

Processing Techniques for Improving Biocompatibility

Biocompatibility implies that a material does not elicit harmful or unwanted host responses (infections, rejection).
Sterilization of biomedical implants is crucial to prevent infections.
It is often impossible to completely remove all pathogenic agents or eliminate their possible transfer to sterilized implants.
Sterility assurance levels (SAL) are used to measure and control the level of sterilization, measuring the number of surviving bacterial colonies after different sterilization times.

Steam Sterilization/Autoclaving (High Temperature)

Steam sterilization is achieved by subjecting items to high-pressure saturated steam at 121°C.
It's highly effective and relatively quick, leaving no toxic residues.
It is not suitable for materials with low melting points and/or susceptible to degradation from high temperatures.

Ethylene Oxide Sterilization

Uses a specialized apparatus to expose implants to EtO gas.
Often mixed with an inert gas, commonly at 30°C - 50°C and further purged with air.
A suitable method for a wide range of materials because of its low-temperature application.
Eto is toxic and flammable therefore appropriate safety measures are important.

Radiation Sterilization

Gamma rays or electron beams from accelerators are used for radiation sterilization.
Samples are monitored to ensure they have received the appropriate radiation dosage.
Radiation ionization of cellular components (nucleic acids) kills microorganisms.
Very rapid, effective and suitable for many materials, but requires high capital investment for sterilizing equipment and special care with some materials that might undergo degradation.

Concepts in Surface Chemistry and Biology

Biomaterial surfaces significantly influence biological responses and implant success.
Protein Adsorption and Biocompatibility
Surface of a material possesses a higher energy density compared to its bulk, making it thermodynamically unstable.
This instability drives the adsorption of atoms or molecules, including proteins, ions and water.
Controlling protein adsorption is crucial for biocompatibility.
Surface properties (hydorrophobicity, charge, roughness, steric concerns) heavily affect protein adsorption influencing favourable adsorption events.

Biocompatibility and surface Properties influencing protein adsorption

Surface hydrophobicity is a key factor in determining the tendency of a surface to adsorb proteins, with more hydrophobic surfaces having a higher level of adsorption.
Surface charge (positively or negatively charged areas) also plays a role in protein adsorption by attracting proteins with opposite charges, and repelling those with similar charges.
Surface roughness causes physical trapping of proteins in crevices, which increases likelihood of adsorption.
Adding steric considerations, like bulky hydrophilic chains (e.g poly(ethylene glycol ) (PEG)) to surfaces can reduce protein adsorption.

Physicochemical Surface Modification Techniques

Surface modifications preserve bulk material characteristics, while optimizing surface properties.
Ideal techniques:
- Thin film to minimize volume property effects
- Resistant to delamination (separation)
- Simple & robust to promote widespread use
Techniques are commonly grouped into physicochemical and biological modification approaches.

Physicochemical Surface Coatings

Techniques include:
- Plasma treatment
- Chemical Vapor Deposition (CVD)
- Physical Vapor Deposition (PVD) ( sputtering and thermal evaporation)
- Self-assembled monolayers (SAMs).
- Solution Coatings
- Langmuir-Blodgett Films

Light Microscopy

Used for largely qualitative analysis of surface topography to view thin sections under a microscope with visible light passing through these thin samples.
The sample is placed on the stage and focused by the light condenser lens which passes through the sample and is magnified by the objective and ocular lenses.
Resolution of light microscopy is around 0.2µm, with smaller features less resolved.

Electron Microscopy

Electron microscopy (EM) achieves high resolutions using electron beams instead of light.
Two main types are: Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM).
TEM requires thin samples, (20-200um), for electron beams to efficiently pass through and create an image.
SEM scans the surfaces of samples by the emitted secondary/backscattered electrons that are dependent on the surface topography.
SEM provides surface topography images, and, if XRAY analysis is performed, additional information about the sample’s chemical composition

Contact Angle Analysis

Used for determining surface hydrophobicity of a material using the contact angle (θ)
The surface free energy or surface tension can be derived by calculating the contact angle of liquids on the material surface, using Young's equation for liquid-solid interfaces
The critical surface tension can be extrapolated by plotting contact angle versus liquid surface tension.
Contact angles can range from 0° to 180°, with 180° indicating complete non-wetting and high hydrophobicity.
Instrumentation includes:
- Solid sample holder
- Liquid holder
- Contact angle measurement device (automated)
Providing information about the material surface, as a number that describes the contact angle.

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Description

Test your knowledge on biomaterial processing and surface properties in this Unit 5 quiz for B.Tech. BME. You'll cover techniques to enhance biocompatibility, processing methods for metals, ceramics, and polymers, and key characterization techniques. This quiz aims to reinforce your understanding of crucial concepts in biomaterials.