Biomaterials Microstructural Characterization

Physical and Chemical Characterization of Biomaterials

• Microstructural Characterization includes the morphology, crystallography, and chemical composition of a material.
• Crystallography includes identifying the phases of the material as well as how the atoms are packed within the phases.
• Morphology involves characterizing the shape, size, and spatial distribution of elements within the phases or on the particles.
• Optical Microscopy magnifies the imagery of a sample specimen using an objective lens and an eyepiece, allowing the user to observe it with the naked eye.
• Optical Microscopy is used in many research areas including the fields of microbiology, microelectronics, nanophysics, biotechnology, and pharmaceutical research.
• Optical Microscopy can also be useful for viewing biological samples for medical diagnoses, also known as histopathology.
• Components involved in image formation in Optical Microscopy are the collector lens, condenser, objective, eyepiece, and the refractive elements of the human eye or the camera lens.
• In optical microscopy, the resolution is limited by the wavelength of the visible light (around 400–700 nm) and by aberrations to be around 200 nm.
• The Scanning Electron Microscopy (SEM) is a versatile technique that uses an electron beam to scan the surface of a material to produce images.
• The interaction of the electron beam with the sample produces signals, including secondary electrons (SE), Auger electrons, backscattered electrons (BSE), characteristic X – Rays, cathodoluminescence.
• The emitted signals are trapped by electrical detectors, converted into digital images, and displayed on a screen as a digital image.
• The SEM can provide information about the sample’s elemental composition, structural variation, and morphology.
• SEM is highly useful in characterizing the topography (surface features), morphology (shape/size of particles), composition (elemental/compound makeup), and crystallographic information of a sample.
• Advantages of SEM include the creation of detailed 3D topographical images, rapid data collection, and the generation of data in a digital format.
• Disadvantages of SEM include the expense associated with purchasing this instrument, the required special training to operate it, the risk of artifacts occurring during sample preparation, the limitation to analyze solid samples, and the minor potential for radiation exposure.
• X-ray Diffraction and Scattering Method - Knowledge of structure and composition over small distances are important for understanding the properties of biomaterials.
• The wavelength of X-rays is on the atomic scale and can be utilized in a variety of techniques, such as X-ray diffraction (XRD) to reveal structural information about nanomaterials over a macroscopic sample volume.
• The XRD method provides a plethora of information, including phase identification, crystallite size, lattice strain, crystallographic orientation of nanostructured materials.
• In the XRD method, a monochromatic X-ray beam is incident on the crystalline material and the intensity of the elastically scattered (diffracted) beam due to the periodic arrangement of atoms in the sample is measured as a function of the diffracted angle ‘2Ɵ’.
• The Bragg’s law λ = 2dsinθ is used to calculate the interplanar spacing d between atomic planes in a material.
• XRD can measure average spacing between layers or rows of atoms, determine the orientation of a single crystal or grain, find the crystal structure of an unknown material, and measure the size, shape, and internal stress of small crystalline regions.
• Each diffraction peak is attributed to the scattering from a specific set of parallel planes of atoms.
• Miller indices (hkl) are used to identify the different planes of atoms in a sample.
• Observed diffraction peaks can be related to planes of atoms to assist in analyzing the atomic structure and microstructure of a sample.
• Fourier Transform Infrared Spectroscopy (FT-IR Spectroscopy) - IR spectroscopy is a fast, inexpensive, and widely used analytical technique for the characterization of biomaterials.
• IR spectroscopy is a form of vibrational spectroscopy based on the interaction of IR radiation with the natural vibrations of the chemical bonds among atoms that compose the material.
• In IR spectroscopy, the sample is irradiated with IR radiation. The changes in the amount of IR radiation absorbed by the sample are measured.
• A sample absorbs radiation in the IR region if there is a coincidence (resonance) between the frequencies of the IR radiation and the molecular vibration, resulting in changes in the dipole moment.
• Molecular vibrations are of two types: stretching (that changes the bond length) and bending (that changes the bond angle).
• Changes in the vibrational motion give rise to absorption bands in the vibrational spectrum.
• The position of absorption bands in the spectra are presented as wave number (v), using the reciprocal centimetre as its unit (cm-1), because it is directly proportional to energy (E) and frequency (n) of radiation.
• The IR region is subdivided into three spectral regions, i.e.the near IR (NIR – from 4000 to approximately 14,000 cm-1), mid IR (MIR –from 400 to 4000 cm-1) and far IR (FIR -from approximately 25–400 cm-1).
• The MIR is the most common and widely employed region for the characterization of materials as it depicts the primary molecular vibrations.
• The NIR and FIR are not frequently employed because only skeletal and secondary vibrations (overtones) occur in these regions producing spectra that are difficult to analyze.

Advantages of FT-IR Spectrometers

• They offer many advantages over other analytical techniques.
• They are fast, relatively inexpensive, versatile, and can be used to provide information on the chemical structure, composition, and functional groups of a variety of materials.
• They can be used to study a wide range of materials, and can be easily adapted to different sample types.
• They are non-destructive and require minimal sample preparation.

This quiz explores the physical and chemical characterization techniques of biomaterials, focusing on microstructural analysis, including crystallography and morphology. It also covers the role of optical microscopy in various research fields and its applications in medical diagnostics.