BMP2-loaded hollow hydroxyapatite microspheres exhibit enhanced osteoinduction and osteogenicity in large bone defects

Figures & data

Figure 1 Scanning electron microscopy images of hollow hydroxyapatite microspheres.

Notes: (A) External surface under low magnification. (B) Fractured section under high magnification.

Figure 2 Cumulative release of recombinant human bone morphogenetic protein 2 (rhBMP2) from hollow hydroxyapatite microspheres into phosphate-buffered saline.

Note: The insert graph shows an initial burst release within 48 hours.

Figure 3 Serum alkaline phosphatase level.

Notes: Group A: BMP2-loaded hollow HA microspheres; Group B: hollow HA microspheres without BMP2; Group C: soluble BMP2 without a carrier. Different symbols (^&, ^#, and *) represent different serum alkaline phosphatase activities at each time point (P<0.05). N=4/group/time point.

Abbreviations: HA, hydroxyapatite; BMP2, bone morphogenetic protein 2; S-ALP, serum alkaline phosphatase.

Figure 4 X-ray images of segmental radius at 4, 8, 12, and 16 weeks with different implants.

Notes: (A) BMP2-loaded hollow HA microspheres; (B) hollow HA microspheres without BMP2; (C) soluble BMP2 without a carrier. Arrows: defective and repairing sites.

Abbreviations: HA, hydroxyapatite; BMP2, bone morphogenetic protein 2.

Table 1 Lane–Sandhu radiographical bone formation score (mean ± standard deviation)

Group	4 weeks	8 weeks	12 weeks	16 weeks
A	4.00±0.9661a,b	6.25±1.1382a,b	9.88±1.1230a,b	11.75±0.500a,b
B	2.94±0.7719a	5.17±1.0300a	8.63±0.9160a	10.00±0.8165a
C	0.94±0.7719	2.50±0.5222	3.00±0.7559	3.50±0.5774

Notes:

a A or B versus C, P<0.05;

b A versus B, P<0.05; n=4/group/time point.

Figure 5 Three-dimensional tomographic images of the segmental radius at 4 and 16 weeks.

Notes: (A) BMP2-loaded hollow HA microspheres; (B) hollow HA microspheres without BMP2; (C) soluble BMP2 without a carrier.

Abbreviations: HA, hydroxyapatite; BMP2, bone morphogenetic protein 2.

Table 2 Percentage of new bone formation (mean ± standard deviation)

Group	4 weeks	8 weeks	12 weeks	16 weeks
A	30.4±10.1a,b	49.2±11.2a,b	79.2±10.3a,b	102.2±4.3a,b
B	21.7±8.3a	40.1±10.2a	63.9±9.2a	85.2±9.2a
C	8.2±5.3	20.3±5.3	23.3±6.2	29.3±4.3

Notes:

a A or B versus C, P<0.05;

b A versus B, P<0.05; n=4/group/time point.

Figure 6 Histological evaluation of three groups at 4, 8, 12, and 16 weeks.

Notes: (A) BMP2-loaded hollow HA microspheres; (B) hollow HA microspheres without BMP2; (C) soluble BMP2 without a carrier. Scale bars: 400 μm, 10× magnification; 100 μm, 40× magnification.

Abbreviations: BC, blood cells; BMP2, bone morphogenetic protein 2; CC, chondrocytes; FT, fibrous tissue; HA, hydroxyapatite; IC, inflammatory cells; Mat, material; NB, new bone; NLB, new lamellar bone; OB, osteoblasts; OC, osteocytes; OT, osteon; V, vessel.

Figure 7 Counts from ROI at the fractured side.

Notes: (A) Blood pool phase; (B) static phase. Group A: BMP2-loaded hollow HA microspheres; Group B hollow HA microspheres without BMP2; Group C soluble BMP2 without a carrier. Different symbols (^&, ^# and *) represent different ROI counts at each time point (P<0.05). N=4/group/time point.

Abbreviations: BMP2, bone morphogenetic protein 2; HA, hydroxyapatite; ROI, region of interest.

Figure 8 Biomechanical test of defective radius.

Notes: (A) mechanical testing facility; (B) the maximum flexural strength of defective radius. Group A: BMP2-loaded hollow HA microspheres; Group B, hollow HA microspheres without BMP2. Different symbols (^& and ^#) represent different biomechanical strengths at each time point (P<0.05). N=4/group/time point.

Abbreviations: BMP2, bone morphogenetic protein 2; HA, hydroxyapatite.