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. Author manuscript; available in PMC: 2019 Aug 16.
Published in final edited form as: ACS Biomater Sci Eng. 2017 Jul 11;3(9):2033–2049. doi: 10.1021/acsbiomaterials.7b00307

Figure 5.

Figure 5.

Applications of AFM nanomechanical tests in studying cartilage aging and tissue engineering. (a) Comparison of the ultrastructure and compressive nanomechanics of native and engineered aggrecan. Top panel: compression resistance of end-attached newborn and adult (38 years old) human cartilage aggrecan monolayers measured via AFM force spectroscopy in 0.01 M NaCl solution (pH ≈5.6). Bottom panel: tapping mode AFM images of native human cartilage aggrecan and aggrecan synthesized by equine chondrocytes and bone marrow stromal cells (BMSCs) in self-assembled peptide hydrogel culture. The newborn human aggrecan shows core protein and CS-GAG side chains longer than that of the adult one. Meanwhile, engineered aggrecan by BMSCs shows longer core protein and longer CS-GAG side chains than that by age-matched chondrocytes. Adapted with permission from refs 16 and 17. Copyright 2012 Elsevier Inc. and Osteoarthritis Research Society International. (b) Impacts of growth factors on chondrocyte-engineered PCM. Top panel: schematic of AFM-nanoindentation on individual chondrons (chondrocytes-PCM composite) immobilized within silicon pyramidal wells. Bottom panel: representative indentation force versus depth loading curves (mean ± SEM, n ≥ 5 cells) on the individual composite after 21 and 28 day culture in DMEM with 10% FBS versus with insulin-like growth factor-1 (IGF-1) and osteogenic protein-1 (OP-1, also known as BMP-7). Adapted with permission from ref 119. Copyright 2016 Elsevier Ltd. (c) Impacts of predifferentiation on chondrogenetic activities of induced pluripotent stem cells (iPSCs). Top panel: Safranin-O/Fast-Green/hematoxylin stained section from pellets categorized by type II collagen (Col2)-driven green fluorescent protein (GFP): GFP+ versus GFP− iPSC cells after two passages. Bottom panel: indentation modulus Eind of the pellet bulk and cryo-sections, calculated by the Hertz model (mean ± SEM, *p < 0.05 by region, #p < 0.05 by cell type). Adapted with permission from ref 129. Copyright 2012 National Academy of Science.