Bone-tissue defects affect millions of people worldwide. Despite being common treatment approaches, autologous and allogeneic bone grafting have not achieved the ideal therapeutic effect. This has prompted researchers to explore novel bone-regeneration methods. In recent decades, the development of bone tissue engineering (BTE) scaffolds has been leading the forefront of this field. As researchers have provided deep insights into bone physiology and the bone-healing mechanism, various biomimicking and bioinspired BTE scaffolds have been reported. Now it is necessary to review the progress of natural bone physiology and bone healing mechanism, which will provide more valuable enlightenments for researchers in this field. This work details the physiological microenvironment of the natural bone tissue, bone-healing process, and various biomolecules involved therein. Next, according to the bone physiological microenvironment and the delivery of bioactive factors based on the bone-healing mechanism, it elaborates the biomimetic design of a scaffold, highlighting the designing of BTE scaffolds according to bone biology and providing the rationale for designing next-generation BTE scaffolds that conform to natural bone healing and regeneration.

The aim of this study was to evaluate and compare the colour stabilities of three types of orthodontic clear aligners exposed to staining agents in vitro. Sixty clear orthodontic aligners produced by three manufacturers (Invisalign, Angelalign, and Smartee) were immersed in three staining solutions (coffee, black tea, and red wine) and one control solution (distilled water). After 12-h and 7-day immersions, the aligners were washed in an ultrasonic cleaner and measured with a colourimeter. The colour changes (ΔE*) were calculated on the basis of the Commission Internationale de I’Eclairage L*a*b* colour system (CIE L*a*b*), and the results were then converted into National Bureau of Standards (NBS) units. Fourier transformation infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) were conducted to observe the molecular and morphologic alterations to the aligner surfaces, respectively. The three types of aligners exhibited slight colour changes after 12 h of staining, with the exception of the Invisalign aligners stained with coffee. The Invisalign aligners exhibited significantly higher ΔE* values (ranging from 0.30 to 27.81) than those of the Angelalign and Smartee aligners (ΔE* values ranging from 0.33 to 1.89 and 0.32 to 1.61, respectively, P<0.05). FT-IR analysis confirmed that the polymer-based structure of aligners did not exhibit significant chemical differences before and after the immersions. The SEM results revealed different surface alterations to the three types of aligner materials after the 7-day staining. The three types of aesthetic orthodontic appliances exhibited colour stability after the 12-h immersion, with the exception of the Invisalign aligners stained by coffee. The Invisalign aligners were more prone than the Angelalign and Smartee aligners to pigmentation. Aligner materials may be improved by considering aesthetic colour stability properties.

Tissue engineering provides an important approach for bone regeneration. Calcium phosphate cement (CPC) can be injected to fill complex-shaped bone defects with excellent osteoconductivity. Induced pluripotent stem cells (iPSCs) are exciting for regenerative medicine due to their potential to proliferate and differentiate into cells of all three germ layers. To date, there has been no report on iPSC seeding with CPC scaffolds. The objectives of this study were to (1) obtain iPSC-derived mesenchymal stem cells (iPSC-MSCs); (2) seed iPSC-MSCs on CPC scaffold for the first time to investigate cell attachment and proliferation; and (3) investigate osteogenic differentiation of iPSC-MSCs on CPC and mineral synthesis by the cells. iPSCs were derived from adult marrow CD34+ cells that were reprogrammed by a single episomal vector pEB-C5. iPSCs were cultured to form embryoid bodies (EBs), and MSCs were migrated out of EBs. Flow cytometry indicated that iPSC-MSCs expressed typical surface antigen profile of MSCs. Mesenchymal differentiation of iPSC-MSCs demonstrated that the iPSC-MSCs had the potential to differentiate into adipocytes, chondrocytes, and osteoblasts. iPSC-MSCs had good viability when attached on CPC scaffold. iPSC-MSCs differentiated into the osteogenic lineage and synthesized bone minerals. iPSC-MSCs on CPC in osteogenic medium yielded higher gene expressions of osteogenic markers including alkaline phosphatase (ALP), osteocalcin, collagen type I, and Runt-related transcription factor 2 than those in control medium (p<0.05). iPSC-MSCs on CPC in osteogenic medium had 10-fold increase in ALP protein than that in control medium (p<0.05). Bone mineral synthesis by iPSC-MSCs adherent to CPC scaffold was increased with time, and mineralization in osteogenic medium was three to four fold that in control medium. In conclusion, iPSCs were derived from adult marrow CD34+ cells that were reprogrammed by a single episomal vector pEB-C5, and MSCs were generated from the EBs. iPSC-MSCs showed good viability and osteogenic differentiation on CPC scaffold for the first time; hence, the novel iPSC-MSC-CPC construct is promising to promote bone regeneration in dental, craniofacial, and orthopedic repairs.