Dispersion of ceramic granules within human fractionated adipose tissue to enhance endochondral bone formation

Engineering of materials consisting of hypertrophic cartilage, as physiological template for de novo bone formation through endochondral ossification (ECO), holds promise as a new class of biological bone substitutes. Here, we assessed the efficiency and reproducibility of bone formation induced by the combination of ceramic granules with fractionated human adipose tissue ("nanofat"), followed by in vitro priming to hypertrophic cartilage. Human nanofat was mixed with different volumetric ratios of ceramic granules (0.2-1 mm) and cultured to sequentially induce proliferation (3 weeks), chondrogenesis (4 weeks), and hypertrophy (2 weeks). The resulting engineered constructs were implanted ectopically in nude mouse. The presence of ceramic granules regulated tissue formation, both in vitro and in vivo. In particular, their dispersion in nanofat at a ratio of 1:16 led to significantly increased cell number and glycosaminoglycan accumulation in vitro, as well as amount and inter-donor reproducibility of bone formation in vivo. Our findings outline a strategy for efficient utilization of nanofat for bone regeneration in an autologous setting, which should now be tested at an orthotopic site. STATEMENT OF SIGNIFICANCE: In this study, we assessed the efficiency and reproducibility of bone formation by a combination of ceramic granules and fractionated human adipose tissue, also known as nanofat, in vitro primed into hypertrophic cartilage. The resulting engineered cartilaginous constructs, when implanted ectopically in nude mouse, resulted in bone and bone marrow formation, more reproducibly and strongly that nanofat alone. This project evaluates the impact of ceramic granules on the functionality and chondrogenic differentiation of mesenchymal progenitors inside their native adipose tissue niche and outlines a novel strategy for an efficient application of nanofat for bone regeneration in an autologous setting.

Effect of water glass coating of tricalcium phosphate granules on in vivo bone formation

BACKGROUND

Recently, some authors introduced a water glass (WG, sodium-silicate glass; Na₂O·SiO₂·nH₂O) coating over tricalcium phosphate (TCP) bioceramic to modulate its resorption rate and enhance the bone cell behaviors. In this study, four different types of granular samples were prepared to evaluate the ability of new bone formation in vivo using micro-computed tomography and histology.

METHODS

Four types sample groups: group A (pure HA as a negative resorption control); group B (pure TCP as a positive resorption control); group C (WG-coated TCP as an early resorption model); and group D (same as group C but heat-treated at 500°C as a delayed resorption model). Cylindrical tube-type carriers with holes were fabricated with HA by extrusion and sintering. Each carrier was filled densely with each granular sample. Four types of tubes were implanted into the medial femoral condyle and medial tibial condyle of New Zealand White rabbits.

RESULTS

The HA group (A) showed the lowest amount of new bone formation. All the TCP sample groups (B, C, and D) showed more new bone formation. On the other hand, among the TCP groups, group C (early resorption model) showed slightly more bone formation. The amount of residual bioceramics was most abundant in the HA group (A). All the TCP sample groups showed less residual bioceramics than group A. Among the TCP groups, group C showed slightly more residual bioceramics. Group B showed the lowest amount of residual bioceramics.

CONCLUSIONS

The WG-coated TCP sample (group C) is the best bone substitute candidate because of its proper biodegradation rate and the Si ions release because the WG-coated layer reduces the material resorption and enhances the new bone formation. That is, the WG-coated TCP is believed to be the best material for the application of an artificial bone substitute material.