Material characterization
Fourier-transform infrared spectroscopy measures which infrared frequencies a sample absorbs, revealing functional groups. In biomaterials it identifies polymers, follows curing by the loss of C=C bands, and shows amide bands of adsorbed or incorporated protein.
Our ruleSimulations prepare you for the bench but don't replace hands-on practice.
FTIR
Fourier-transform infrared spectroscopy measures which infrared frequencies a sample absorbs, revealing functional groups. In biomaterials it identifies polymers, follows curing by the loss of C=C bands, and shows amide bands of adsorbed or incorporated protein.
How it differs from the standard method
- Ratio the reactive band to an unchanging internal standard (for acrylates, C=C at 1635 or 810 cm⁻¹ against C=O at about 1720).
- Dry samples or use bands clear of water's 1640 cm⁻¹ bending band.
- Take a fresh background and apply a consistent ATR pressure.
1Checking what you actually made
A biomaterial's behaviour is set by its chemistry, its structure and how both change over time, and none of these can be taken on trust from the recipe. Characterisation asks direct questions: did the crosslinking reaction go to completion, what is on the outermost few nanometres of the surface, what does the internal architecture look like, and how fast does the material lose molecular weight and mass in conditions like the body. Each method answers one of these, and each answers it only for the sample as it was prepared for the instrument.
FTIR
Infrared absorption by molecular vibrations identifies functional groups and follows reactions, such as acrylate C=C consumed on curing.
SEM
A focused electron beam scanned over a coated sample gives nanometre-scale images of fibres, pores and surfaces.
XPS
X-rays eject core electrons whose energies identify elements and their bonding in the top 5–10 nm.
Degradation testing
Molecular weight, mass, water uptake and pH over weeks in buffer at 37 °C show how the material breaks down.
2What each readout physically is
An FTIR spectrum is absorbance against wavenumber; in ATR mode the infrared wave penetrates only about a micron into the sample pressed on a crystal, so contact and water matter. Conversion is measured by ratioing a reactive band to an internal standard that does not change.
3Where the artefacts come from
- FTIR: water bands on top of the band of interest, stale backgrounds with CO₂ and vapour lines, poor ATR contact, no baseline correction.
- SEM: freeze-drying creates ice-templated pores; air-drying collapses networks; uncoated samples charge; high voltage damages soft samples; pores picked from the best-looking field.
- XPS: adventitious carbon on every air-exposed surface, silicone contamination from gloves and packaging, charging shifts, and sensitivity only to the top few nanometres.
- Degradation: wet weighing, acid build-up in unchanged buffer, non-physiological temperature, and studies too short to see the lag before mass loss.
Key terms
Practise these as flashcards →Attenuated total reflectance: FTIR sampling by an evanescent wave in a sample pressed onto a crystal.
The fraction of reactive groups (for example C=C) consumed in a reaction, measured against an unchanging internal standard band.
A few nanometres of gold, platinum or carbon deposited on an insulating sample so it does not charge in the SEM.
Replacing water with liquid CO₂ and taking it past its critical point, so the sample dries with no liquid–gas meniscus.
The hydrocarbon film that adsorbs onto any surface exposed to air, seen as C 1s at about 284.8 eV in XPS.
Degradation throughout the material: molecular weight falls everywhere, and mass is lost late and quickly.
Degradation only at the surface, so mass and size fall steadily from the start.
Acidic degradation products catalysing further ester hydrolysis, especially inside thick parts or in unchanged buffer.
When to use it
- Confirming that a crosslinking, grafting or functionalisation reaction actually happened, and how far it went.
- Measuring fibre diameter, pore size and morphology of scaffolds after fabrication.
- Verifying a surface coating or treatment chemically, beyond what a contact angle can show.
- Predicting how long an implant or scaffold will last, and what it releases as it degrades.
Compared with alternatives
Mechanical evidence of crosslinking: modulus and gel point rather than the chemical bands.
Electron microscopy in depth, including TEM for internal and nanoscale structure.
Identifies degradation products and adsorbed proteins at the molecular level.
Focuses on what a degrading device releases, such as drug or protein, over time.
The treatments whose results XPS and contact angle are used to confirm.
Sub-techniques
Choosing one here switches the whole page, including the protocol and the lab, to it.
Fourier-transform infrared spectroscopy measures which infrared frequencies a sample absorbs, revealing functional groups. In biomaterials it identifies polymers, follows curing by the loss of C=C bands, and shows amide bands of adsorbed or incorporated protein.
- Ratio the reactive band to an unchanging internal standard (for acrylates, C=C at 1635 or 810 cm⁻¹ against C=O at about 1720).
- Dry samples or use bands clear of water's 1640 cm⁻¹ bending band.
- Take a fresh background and apply a consistent ATR pressure.