Structural heterogeneity of pharmaceutical compacts probed by micro-indentation

Area of Science:

• Materials Science
• Pharmaceutical Sciences
• Mechanical Engineering

Background:

• Indentation testing is a standard method for measuring hardness and modulus.
• Micro-indentation's accuracy can be limited by the scale of structural inhomogeneity in compacts.
• The maximum indentation force (MIF) influences the indentation area and measurement validity.

Purpose of the Study:

• To investigate micro-indentation's capability in probing compact inhomogeneity using varying MIF.
• To assess the impact of MIF on the reliability of hardness and modulus measurements.
• To correlate micro-indentation findings with microscopy observations.

Main Methods:

• Micro-indentation testing was performed on model pharmaceutical excipient compacts (brittle and ductile).
• Maximum Indentation Force (MIF) was systematically varied.
• Indentation hardness and modulus were measured, and their standard deviations analyzed.
• Microscopy was used for comparative structural analysis.

Main Results:

• Representative hardness and modulus values were obtained at MIF > 1000 mN.
• Increasing standard deviation in hardness with decreasing MIF (below 800 mN) indicated structural inhomogeneity.
• Microcrystalline cellulose compacts showed increased hardness variation at lower MIF.
• Micro-indentation results correlated well with microscopy findings.

Conclusions:

• Micro-indentation, with adjusted MIF, can effectively probe structural inhomogeneity in pharmaceutical compacts.
• Varying MIF provides insights into material anisotropy and structural characteristics.
• This method offers a valuable approach for understanding material properties at different scales.