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We developed a new and injectable poly‐dicalcium phosphate dihydrate (P‐DCPD) forming cement. The key structural difference between P‐DCPD and classical DCPD is that P‐DCPD is composed of interconnected P‐DCPD crystals by interlocking to the polyphosphate chains. In contrast, DCPD is composed of a package of DCPD crystals with weak mutual ionic bonding. The purpose of this continuing study was to compare the physicochemical properties between P‐DCPD and DCPD cement particles. Data collected from SEM, X‐ray diffraction, and Raman Spectroscopy approaches demonstrated that P‐DCPD has a more stable chemical structure than DCPD as evidenced by much less transformation to hydroxyapatite (HA) during setting. Nanoindentation showed a similar hardness while the elastic modulus of P‐DCPD is much lower than DCPD that might be due to the much less HA transformation of P‐DCPD. P‐DCPD has much lower zeta potential and less hydrophilicity than DCPD because of its entangled and interconnected polyphosphate chains. It is expected that superhydrophilic DCPD undergoes faster dissolution than P‐DCPD in an aqueous environment. Another interesting finding is that the pH of eluent from P‐DCPD is more neutral (6.6–7.1) than DCPD (5.5–6.5). More extensive experiments are currently underway to further evaluate the potential impacts of the different physiochemical performance observed of P‐DCPD and DCPD cement particles on the biocompatibility, degradation behavior and bone defect healing efficacy both in vivo and in vitro. [ABSTRACT FROM AUTHOR]

Exercise and physical activity are critical to maintain bone mass and strength throughout life. Both exercise and physical activity subject bone to a unique combination of stimuli in the forms of dynamic loading and a systemic increase in parathyroid hormone (PTH). Although dynamic loading is considered to be the primary osteogenic stimuli, the influence of increasing PTH levels remains unclear. We hypothesize that activation of the PTH/PTH-related peptide type 1 receptor (PPR) along the osteoblast lineage facilitates bone formation and improved mechanical properties in response to exercise. To test this hypothesis, conditional PPR-knockout mice (PPRcKO) were generated in which PPR expression was deleted along the osteoblast lineage under the osterix promoter. At 8-weeks of age, both PPRfl/fl and PPRcKO mice were subjected to treadmill running or sedentary conditions for 5-weeks. Under sedentary conditions, PPRcKO mice displayed significantly less bone mass as well as smaller structural-level strength (yield-load and ultimate load), while tissue level properties were largely unaffected. However, PPRcKO mice exposed to exercise displayed significantly less structural-level and tissue-level mechanical properties when compared to exercised PPRfl/fl mice. Overall, these data demonstrate that PPR expression along the osteoblast lineage is essential for exercise to improve the mechanical properties of cortical bone. Furthermore, the influence of PPR activation on material properties is unique to exercise and not during normal growth and development. [ABSTRACT FROM AUTHOR]