Deformation in Metals

High ductility

Covalent bond

Hyaluronic acid

Structure/composition

Ionic bond

Van der Waals forces

Low melting point

Atomic Force Microscopy (AFM)

θC > 90° is hydrophobic

Transmission Electron Microscopy (TEM)

Scanning Electron Microscopy (SEM)

Each crystal is a separate grain within the material

Deformation

Surface sensitivity

Implanted devices that exhibit similar mechanical properties to the natural neural environment

Biomimicry closely matches the natural subject, while bioinspiration leverages materials from nature to enhance an engineered system

Permanent synthetic structures causing inflammation and damage over time

Physical, chemical, and electrical alterations

Proteins

Protein conformation

They are not dynamic and living

Near-Field Scanning Optical Microscopy (NSOM)

~ 100 mm

Lateral force mode

Atomic Force Microscopy (AFM)

~ 4 mm

Thermal scanning

Near-Field Scanning Optical Microscopy (NSOM)

Non-contact mode

Atomic Force Microscopy (AFM)

Scanning a very small light source very close to the sample and detecting the light energy forms the image.

NSOM can provide resolution below that of the conventional light microscope.

~ 100 mm

~ 4 mm

~ 20-40 nm

Contact mode

Non-contact mode

Frictional forces

The distribution of thermal conductivity

Biomimicry aims to match the natural subject as closely as possible, while bioinspiration leverages materials, methods, or other cues from nature and applies them toward analogous functions to enhance an engineered system.

Proteins are the first molecules to react to device implantation in the neural context.

Permanent synthetic structures are more likely to cause inflammation and damage over time in the neural context because they are not dynamic and living like the natural neural environment.

The conformation of proteins determines the downstream effects of device implantation in the neural context.

The structure-function relationship of a material determines its function according to the text.

The three types of alterations in implanted devices in the neural context are mechanical, chemical, and electrical alterations.

Permanent synthetic structures are NOT a common biomimetic approach in the neural context.

Some advantages of living systems in dynamically responding to a changing environment include bulk stiffness and flexibility, managing the protein corona, ionic conductors, cell-seeded scaffolding, surface topography, bioactive surfaces, flexible conductors, tissue ingrowth/remodeling, size and form factor, antioxidants and free-radical scavengers, electrically responsive materials, and biodegradable systems.

Some important material properties for medical applications include acoustical properties, atomic properties, chemical properties, electrical properties, environmental properties, magnetic properties, manufacturing properties, mechanical properties, optical properties, radiological properties, and thermal properties.

Some advantages of natural materials in biomaterials include biofunctionality, biodegradability, and less inflammation.

Some advantages of synthetic materials in biomaterials include property tuning and processing.

Some disadvantages of natural materials in biomaterials include mechanical properties, stability, processing, and immunogenicity.

Some disadvantages of synthetic materials in biomaterials include loss of cell function, inflammation, and potential for the loss of cell function.

Some characteristics of ceramics include being nonmetallic and inorganic solids, having ionic bonding, high melting points, great hardness and strength, considerable durability, low electrical and thermal conductivity, and chemical inertness.

The more grain boundaries there are, the more dislocations and plastic deformation are hindered, resulting in increased strength.

Young's equation describes the thermodynamic equilibrium between three phases (gas/air, liquid, and solid) at the interface. It relates the contact angle (θC) to the interfacial energy and provides information about the wettability of the surface. A contact angle less than 90° indicates hydrophilicity, while a contact angle greater than 90° indicates hydrophobicity.

The depth of analysis for FTIR-ATR depends on the refractive index of the ATR scanning element and is typically greater than 0.5 mm. FTIR-ATR provides more information than ESCA but is less surface sensitive.

XPS, also known as ESCA, involves the impingement of X-rays on a sample surface, resulting in the release of core electrons as photoelectrons. The kinetic energy and binding energy of these photoelectrons can be measured and mapped to the parent element/atom, making XPS useful for elemental analysis of polymer surfaces and coatings.

The three most common scanning probe techniques are Atomic Force Microscopy (AFM), Scanning Tunneling Microscopy (STM), and Scanning Probe Microscopy (SPM). AFM measures the interaction force between a tip and surface, STM measures a weak electrical current flowing between a tip and sample, and SPM is very good for surface profiling/ultrastructure/surface interaction analysis.

In SEM, the sample surface is bombarded with electrons, resulting in the excitation and emission of secondary and backscattered electrons from atoms in a small area extending into the sample surface. The emitted electrons are detected as an 'area map' (micrograph) of the characteristic bombarded region.

Light microscopy, including brightfield, darkfield, phase contrast, and fluorescence microscopy, is good for analyzing samples at micron level resolution. It is also useful for cell-material analysis since most cells are in the micron range.

Mechanical properties = Orthopedic Implants Chemical properties = All materials Magnetic properties = MRI compatible materials Thermal properties = Ablation, RF Heat Dissipation

Ionic bond = Electrostatic forces between oppositely charged ions Covalent bond = Sharing of valence electrons between two atoms Metallic bond = Sharing of valence electrons between groups of atoms in 3-D Hydrogen bonding = Secondary bonding, weak intermolecular interaction

Ceramics = High melting points, great hardness and strength, low electrical and thermal conductivity Metals = Conductivity, often used in medical devices Natural materials = Biofunctionality, biodegradable, less inflammation Synthetic materials = Property 'tuning', processing, can cause inflammation and loss of cell function

Natural materials = Proteins: collagen, fibrin, elastin Synthetic materials = Polymers: polyurethanes, PTFE, PE, polysiloxanes Ceramics = HA, bioactive glasses Metals = Ti/Ti-alloys, Co-Cr alloys, stainless steel

Ionic bonds = Ceramics Covalent bonds = Polymers, organics Metallic bonds = Metals Hydrogen bonds = Intermolecular interactions

Electrical properties = Neuromodulation, Stimulation Manufacturing properties = All materials, Processing Radiological properties = Intraoperative Imaging Optical properties = Contact Lenses

Natural materials = Biofunctionality, biodegradable, less inflammation Synthetic materials = Property 'tuning', processing Ceramics = High melting points, great hardness and strength, low electrical and thermal conductivity Metals = Conductivity, often used in medical devices

Biomimicry = Approach to match the natural subject as closely as possible Biocompatibility = Ability of a material to perform with an appropriate host response in a specific application Bioinspiration = Approach that leverages materials, methods, or other cues from nature to enhance an engineered system Inflammation = A protective response involving immune cells, blood vessels, and molecular mediators

Physical = Brain features are small and mechanically pliant Chemical = Proteins are the first molecules to react to device implantation Electrical = Neural tissues are excitable by ionic currents

StructureFunction = Materials aspect of bioMATERIALS Material Selection / Design = Process of choosing materials based on their properties for specific applications Tissue Engr. = Engineering of tissues for medical purposes Drug Delivery = Method of delivering drugs to a patient in a manner that increases the concentration of the drug in some parts of the body relative to others

Biomimetic = Derived from living forms, mimics the structure or function of a biological entity Bio-Inspired Biomaterials = Materials inspired by biological processes and structures Neural Context = Referring to the nervous system Scale NanoMacro = Refers to the scale from nano (very small) to macro (very large)

Protein-Material Interactions = Interactions between proteins and materials that influence the performance of a material Cell-Material Interactions = Interactions between cells and materials that influence the performance of a material Blood Compatibility = The ability of a material to perform with an appropriate host response in blood-related applications Orthopedic Applications = Use of materials in the treatment of musculoskeletal disorders

Biomimicry = An approach that attempts to emulate nature's strategies and principles to solve human problems Bioinspiration = An approach that uses ideas from nature to improve engineering systems Neural Context = Referring to the nervous system Biomaterials = Materials used in contact with the human body for medical purposes

Bio aspect of BIOmaterials = The biological component of materials used in medicine Materials aspects of bioMATERIALS = The physical properties and behaviors of materials used in medicine Neural = Relating to the nervous system Orthopedic = Relating to the branch of medicine dealing with the correction of deformities of bones or muscles

NSOM = Scans a small light source very close to the sample AFM = Uses a cantilever and tip for imaging AFM (contact mode) = Has a strong (repulsive) force of interaction AFM (non-contact mode) = Has a weak (attractive) force of interaction

Contact mode = Strong (repulsive) Non-contact mode = Weak (attractive) Lateral force mode = Frictional forces exert a torque on the scanning cantilever Magnetic force mode = Images the magnetic field of the surface

Cantilever length = ~ 100 mm Tip diameter at cantilever interface = ~ 4 mm Tip diameter at apex = ~ 20-40 nm

Contact mode = Strong (repulsive) Non-contact mode = Weak (attractive) Lateral force mode = Frictional forces exert a torque Thermal scanning mode = Images the distribution of thermal conductivity

NSOM = Can provide resolution below that of the conventional light microscope AFM = Can image the distribution of thermal conductivity when operating in thermal scanning mode

Cantilever = ~ 100 mm long Tip at cantilever interface = ~ 4 mm dia Tip at apex = ~ 20-40 nm dia

Contact mode = Strong (repulsive) Non-contact mode = Weak (attractive) Lateral force mode = Frictional forces exert a torque on the scanning cantilever

AFM (contact mode) = Maintains constant force or distance NSOM = Scans a small light source very close to the sample AFM = Uses a cantilever and tip for imaging AFM (non-contact mode) = Uses a vibrating probe

Contact mode = Strong (repulsive) force of interaction Non-contact mode = Weak (attractive) force of interaction Lateral force mode = Frictional forces exert a torque on the scanning cantilever Magnetic force mode = Images the magnetic field of the surface

Scanning Electron Microscopy (SEM) = Sample surface is bombarded with electrons, creating an 'area map' of the bombarded region Light Microscopy = Good for analyzing samples at micron level resolution Scanning Probe Microscopy (SPM) = Very good for surface profiling/ultrastructure/surface interaction analysis X-ray Photoelectron Spectroscopy (XPS) = Useful for elemental analysis of polymer surfaces and coatings

Slip = Allows plastic deformation without breaking an entire plane of atoms at once, common in metals Young's Equation = Describes the thermodynamic (energy) equilibrium between three phases at the interface Polycrystalline materials = Materials with many crystals, each crystal is a separate grain within the material Contact Angle = The angle at which a fluid interface meets a solid surface

Atomic Force Microscopy (AFM) = Measures the interaction force between the tip and surface Scanning Tunneling Microscopy (STM) = Measures a weak electrical current flowing between tip and sample Surface profiling = A process that involves scanning the surface of a material to obtain its profile Ultrastructure = The detailed structure of a biological specimen, such as a cell, tissue, or organ, that is visible only with an electron microscope

Hydrophilic = Describes a surface that has a contact angle less than 90 degrees Hydrophobic = Describes a surface that has a contact angle greater than 90 degrees Interfacial energy = Can be measured using the contact angle Wettability = A property of a surface that can be inferred from the contact angle

Light Microscopy = Good for cell-material analysis since most cells are in the micron range Scanning Electron Microscopy (SEM) = Useful for examining the surface of a material Scanning Probe Microscopy (SPM) = Excellent for surface profiling and surface interaction analysis X-ray Photoelectron Spectroscopy (XPS) = Very useful for elemental analysis of polymer surfaces and coatings

Dislocation = Can transit across grain boundaries, but very difficult Slip = Allows plastic deformation without breaking an entire plane of atoms at once Grain boundaries = The interface where crystals of different orientations meet within a polycrystalline material Ductility = A measure of a material's ability to undergo significant plastic deformation before rupture

Depth of analysis = Depends on refractive index of ATR scanning element in FTIR-ATR Surface Energy = Can be determined using Young's Equation X-ray Photoelectron Spectroscopy (XPS) = Also called Electron Spectroscopy for Chemical Analysis (ESCA) Trade-offs = Considerations such as depth, spatial resolution and cost in surface characterization techniques