Biology subjects

Zadpoor, A. A.

Publications and source records attributed to Zadpoor, A. A..

3 recordsLinked to original sources

bioRxiv2026

Co-contraction index improves estimates of knee joint contact forces: A musculoskeletal modelling study

Healthy individuals are hypothesized to adopt muscle coordination strategies that minimize energy expenditure. However, under pathological conditions, these patterns often change, as patients adopt alternative strategies to enhance stability. In musculoskeletal modeling, such changes in muscle coordination are often not accounted for when estimating internal quantities such as knee joint contact forces. To address this, we adapted the objective function of a muscle redundancy solver to inform muscle activations from electromyography measurements, minimizing errors in both muscle activations and co-contraction levels. The resulting estimates of knee joint contact force were compared with in vivo measurements across three activities. The co-contraction index-informed approach achieved the lowest root-mean-square-error of 0.31 body weight, averaged across all subjects and activities, improving the results of the minimum activation solver by 7% body weight. Notably, root-mean-squared-error increased with the level of co-contraction with the minimum activation approach ({beta} = 1.55, 95% confidence interval [0.79, 2.30]), whereas the co-contraction index-informed approach remained less sensitive ({beta} = 0.78, 95% confidence interval [0.14, 1.43]). These findings suggest that objective functions based on minimum muscle activation may be insufficient to accurately estimate knee joint forces in individuals with altered muscle coordination. Incorporating co-contraction information is therefore essential to capture subject-specific adaptations.

bioengineering↗

bioRxiv2023

Rational positioning of 3D printed micro-bricks to realize high-fidelity, multi-functional soft-hard interfaces

AO_SCPLOWBSTRACTC_SCPLOWLiving organisms have developed design principles, such as functional gradients (FGs), to interface hard materials with soft ones (e.g., bone and tendon). Mimicking such design principles can address the challenges faced when developing engineered constructs with soft-hard interfaces. To date, implementing these FG design principles has been primarily performed by varying the ratio of the hard phase to that of the soft phase. Such design approaches, however, lead to inaccurate mechanical properties within the transition zone. That is due to the highly nonlinear relationship between the material distribution at the microscale and the macroscale mechanical properties. Here, we 3D print micro-bricks from either a soft or a hard phase and study the nonlinear relationship between their arrangements within the transition zone and the resulting macroscale properties. We carry out experiments at the micro- and macroscales as well as finite element simulations at both scales. Based on the obtained results, we develop a co-continuous power-law model relating the arrangement of the micro-bricks to the local mechanical properties of the micro-brick composites. We then use this model to rationally design FGs at the individual micro-brick level and create two types of biomimetic soft-hard constructs, including a specimen modeling bone-ligament junctions in the knee and another modeling the nucleus pulposus-annulus fibrosus interface in intervertebral discs. We show that the implemented FGs drastically enhance the stiffness, strength, and toughness of both types of specimens as compared to non-graded designs. Furthermore, we hypothesize that our soft-hard FGs regulate the behavior of murine preosteoblasts and primary human bone marrow-derived mesenchymal stromal cells (hBMSCc). We culture those cells to confirm the effects of soft-hard interfaces on cell morphology as well as on regulating the expression of focal adhesion kinase, subcellular localization, and YAP nuclear translocation of hBMSCs. Taken together, our results pave the way for the rational design of soft-hard interfaces at the micro-brick level and (biomedical) applications of such designs.

bioengineering↗

bioRxiv2020

The local and global geometry of trabecular bone

AO_SCPLOWBSTRACTC_SCPLOWThe organization and shape of the microstructural elements of trabecular bone govern its physical properties, are implicated in bone disease, and can serve as blueprints for biomaterial design. To devise fundamental structure-property relationships, it is essential to characterize trabecular bone from the perspective of geometry, the mathematical study of shape. Here, we used the micro-computed tomography images of 70 donors at five different sites to characterize the local and global geometry of human trabecular bone, respectively quantified by surface curvatures and Minkowski functionals. We find that curvature density maps provide sensitive shape fingerprints for bone from different sites. Contrary to a common assumption, these curvature maps also show that bone morphology does not approximate a minimal surface but exhibits a much more intricate curvature landscape. At the global (or integral) perspective, our Minkowski analysis illustrates that trabecular bone exhibits other types of anisotropy/ellipticity beyond interfacial orientation, and that anisotropy varies substantially within the trabecular structure. Moreover, we show that the Minkowski functionals unify several traditional morphometric indices. Our geometric approach to trabecular morphometry provides a fundamental language of shape that could be useful for bone failure prediction, understanding geometry-driven tissue growth, and the design of complex tissue engineering scaffolds.

bioinformatics↗