Imaging articular cartilage tissue using atomic force microscopy (AFM).

Area of Science:

• Biomaterials Science
• Tissue Engineering
• Biophysics

Background:

• Cartilage is a vital avascular tissue, primarily water, with a complex extracellular matrix (ECM) rich in aggrecans and collagen II.
• The ordered ECM structure is crucial for shock absorption and protecting bone ends.
• Understanding cartilage's micro- and nanostructure is key to elucidating its mechanical function.

Purpose of the Study:

• To detail a protocol using Atomic Force Microscopy (AFM) to investigate cartilage structure-function relationships.
• To differentiate the mechanical contributions of collagen and proteoglycans within the cartilage ECM.
• To provide insights into cartilage biomechanics at the nanoscale.

Main Methods:

• Utilizing Atomic Force Microscopy (AFM) for imaging and mechanical testing at both micrometer and nanometer scales.
• Employing bare AFM tips for nanoscale analysis to resolve molecular components.
• Analyzing AFM force maps to distinguish collagen fibers and proteoglycan gel morphology.

Main Results:

• Micrometer-scale AFM reveals bulk ECM and chondrocytes with unimodal stiffness distribution.
• Nanometer-scale AFM with bare tips shows a bimodal stiffness distribution, reflecting collagen and proteoglycan contributions.
• AFM imaging and force mapping differentiate collagen and proteoglycan structures.

Conclusions:

• AFM provides a powerful tool for dissecting the distinct mechanical properties of cartilage ECM components.
• Nanoscale mechanical mapping reveals the heterogeneous nature of cartilage stiffness.
• This protocol facilitates a deeper understanding of cartilage biomechanics and potential therapeutic strategies.