Shear stress and blood coagulation: A comparative study of smokers and diabetics, with healthy individuals.

Blood coagulation is a complex physiological process governed by both biochemical and biomechanical mechanisms. While smoking, diabetes, and aging are established risk factors for thrombotic disorders, their combined interplay on shear-dependent coagulation behaviour remains poorly understood. This study investigates the effects of applied shear stress, smoking, diabetes, and age on blood coagulation using oscillatory rheometry to evaluate patient-specific haemostatic responses. Platelet-rich plasma (PRP) obtained from 30 volunteers representing healthy, smoker, and type 2 diabetic cohorts was analysed at 37 °C using an Anton Paar rheometer. Amplitude sweep experiments first established a linear viscoelastic region between 1 and 10 Pa, and subsequent rheological measurements were performed within a conservative stress range of 1-4 Pa. Time-to-gel point (TGP) was determined using the frequency-independent loss tangent criterion based on the Chambon-Winter gelation theory. Rheological findings were validated through conventional clotting time (CT) and prothrombin time (PT) measurements, while clot microstructure and platelet activation were further examined using field-emission scanning electron microscopy (FESEM) and fluorescence microscopy. A priori power analysis confirmed that the study was adequately powered to detect the observed intergroup differences. TGP decreased with increasing applied shear stress, demonstrating accelerated clot formation under higher mechanical loading. Compared with healthy controls, smokers and individuals with type 2 diabetes consistently exhibited shorter TGP, CT, and PT values, indicating enhanced coagulation potential. Older participants also demonstrated reduced TGP relative to younger healthy individuals, suggesting an age-related increase in procoagulant behaviour. FESEM revealed denser fibrin networks with reduced pore size at higher shear stresses, whereas fluorescence microscopy demonstrated increased CD62P expression, confirming progressive shear-induced platelet activation. These findings demonstrate that rheologically determined TGP is sensitive to both mechanical loading and underlying health status and, when complemented by structural and biological analyses, provides a quantitative marker for assessing patient-specific haemostatic function and thrombotic risk.