Structural and Mechanical Insights into the Extracellular Matrix of the Aging Human Lacrimal Gland for Tissue...

Aqueous-deficient dry eye disease (ADDE) frequently results from structural and functional impairment of the lacrimal gland. Regenerative approaches require biomaterials that replicate the extracellular matrix (ECM) composition and biomechanical properties of native lacrimal gland tissue. However, quantitative data on the ECM composition and large-strain biomechanics of the human lacrimal gland remain limited. In this study, histological and immunofluorescence-based ECM analyses were combined with large-strain mechanical testing and quantitative enzyme-linked immunosorbent assay (ELISA)-based measurements to characterize the structural and mechanical properties of native human lacrimal gland tissue obtained from elderly donors. Mechanical testing included cyclic compression-tension, stress relaxation, and cyclic torsional shear tests. The lacrimal gland ECM exhibited a heterogeneous architecture dominated by collagen III-rich networks in periacinar regions, collagen IV within basement membranes, and collagen VI surrounding acini and ducts. Mechanical testing demonstrated that lacrimal gland tissue behaves as an ultra-soft viscoelastic material characterized by compression-tension asymmetry, nonlinear stress-stretch behavior, hysteresis, and moderate stress relaxation within the investigated strain range. A hyperelastic one-term Ogden model was used for inverse identification of material parameters describing tissue stiffness and nonlinear mechanical behavior, yielding a shear modulus of 0.21 kPa and a negative nonlinearity parameter during the unconditioned loading cycle. ELISA measurements identified collagen III and VI as the predominant ECM components. These results provide the first integrated characterization of ECM composition and large-strain mechanics in aging human lacrimal gland tissue and establish quantitative reference parameters that may guide the development of biomaterials and engineered scaffolds for lacrimal gland regeneration. STATEMENT OF SIGNIFICANCE: Despite the central role of the lacrimal gland in ocular surface homeostasis, the extracellular matrix (ECM) architecture and biomechanical properties of human lacrimal gland tissue remain poorly characterized. This study provides the first integrated analysis of ECM composition and large-strain mechanical behavior in the human lacrimal gland. The results define the lacrimal gland as an ultra-soft viscoelastic tissue with an ECM predominantly composed of collagens III, IV, and elastic fiber networks. By integrating structural, biochemical, and mechanical analyses, this study establishes quantitative parameters defining the native microenvironment of lacrimal gland cells. These findings establish references for aging lacrimal gland tissue that may guide the design of ECM-mimetic biomaterials and support regenerative strategies for aqueous-deficient dry eye disease.