Characterisation of Plasma Blood Clots in Different Physical States Using Positron Annihilation Lifetime Spectroscopy

<ns3:p>Objective. To quantitatively assess how different preparation methods alter the nanoscale free-volume architecture of human plasma blood clots using positron annihilation lifetime spectroscopy (PALS), and to establish the relevance of PALS for fibrin network characterization in biomedical research. Materials. Human plasma blood clots prepared in four distinct physical states: fresh, glutaraldehyde-fixed, desiccator-dried, and critical-point-dried (CPD).Methods. High-resolution fast-coincidence PALS measurements were conducted at 37 C. Ortho- positronium (o-Ps) lifetimes and intensities were extracted using PALS Avalanche and validated through independent fitting in Origin. Comparative analysis across preparation states was performed to evaluate nanoscale free-volume changes associated with dehydration, fixation, and CPD processing. Results. Distinct o-Ps lifetime (τ₃) and intensity (I₃) patterns were observed across clot states: fresh (1.95 0.01 ns; 11 0.07%), fixed (2.11 0.02 ns; 16 0.16%), desiccator-dried (2.15 0.04 ns; 6 0.11%), and CPD (1.95 0.01 ns; 9 0.07%). Dehydration resulted in reduced o-Ps intensity and structural compaction, whereas chemical fixation and CPD differentially preserved nanoscale voids. These findings show that preparation methods significantly modulate the fibrin network’s free-volume distribution. Conclusions. Sample preparation exerts a critical influence on the nanoscale architecture of fibrin clots, and PALS provides a sensitive quantitative probe of these changes. This work demonstrates, for the first time, a systematic PALS-based comparison of blood clots in multiple physical states, highlighting its potential for advancing biomaterials characterization, improving thrombus research, and guiding standardized protocols for nanoscale analysis in biological tissues.</ns3:p>