Bone morphogenetic protein-2-impregnated biomimetic scaffolds successfully induce bone healing in a marginal mandibular defect

Abstract

Objectives/hypothesis: To test the osteoregenerative potential and dosing of bone morphogenetic protein-2 (BMP-2)-impregnated biomimetic scaffolds in a rat model of a mandibular defect.

Study design: Prospective study using an animal model.

Methods: Varied doses of BMP-2 (0.5, 1, 0.5, 0.5 in microspheres, 5, and 15 μg) were absorbed onto a biomimetic scaffold. Scaffolds were then implanted into marginal mandibular defects in rats. Blank scaffolds and unfilled defects were used as negative controls. Two months postoperatively, bone healing was analyzed with microcomputerized tomography (microCT).

Results: MicroCT analysis demonstrated that all doses of BMP-2 induced successful healing of marginal mandibular defects in a rat mandible. Increasing doses of BMP-2 on the scaffolds produced increased tissue healing, with 15 μg demonstrating significantly more healing than all other dosing (P < .01).

Conclusions: BMP-2-impregnated biomimetic scaffolds successfully induce bone healing in a marginal mandibular defect in the rat. Percentage healing of defect, percentage of bone within healed tissue, and total bone volume are all a function of BMP-2 dosing. There appears to be an optimal dose of 5 μg beyond which there is no increase in bone volume.

Level of evidence: NA.

Figure 1

Surgical creation of a 5 × 5-mm marginal mandibular defect based on the inferior border of the mandible was made with a high-speed cutting burr with copious irrigation (A). A PLGA scaffold with varying doses of BMP-2 (B) was then placed into the defect (C) and the pterygomasseteric sling was closed over the defect and the skin over the muscle.

Figure 2

A histogram displaying the percentage of the defect healed (TV/DV) and the percentage of bone of the new tissue (BV/TV) for controls and increasing doses of BMP-2. There appeared to be an increasing trend in means with 5 μg higher than 0.5 μg (p < 0.01) and 15 μg significantly higher than all other dosing for percentage defect healed (p < 0.01 for 15 μg vs blank, 0.5 μg, 1 μg and 5 μg on Tukey’s comparisons). Similarly, there appeared to be a trend towards decreasing percentage of bone within the healed tissue seen with increasing BMP-2 doses with 15 μg demonstrating significantly less bone percentage than controls and 0.5 μg BMP-2. (** = p < 0.01 on Tukey’s comparisons)

Figure 3

A histogram displaying the absolute bone volume formed. One-way ANOVA overall p-value = 0.0002. Tukey’s pairwise comparisons demonstrates 5 μg BMP-2 created significantly more bone than 0.5 BMP-2 and the blank scaffold (p = 0.008 and p < 0.0001, respectively). (** = p < 0.01 on Tukey’s comparisons)

Figure 4

A histogram comparing 1 μg BMP-2 on a PLGA scaffold to 0.5 μg BMP-2 on a PLGA scaffold with an additional 0.5 μg BMP-2 encapsulated in microspheres. There was significantly more healing in the unencapsulated dose of BMP-2 compared to the microsphere formulation (p = 0.037). However, the percentage of bone filled within the tissue was significantly higher in the microsphere formulation (p = 0.015). (* = p < 0.05 on Tukey’s comparisons)

Figure 5

Sample histology of healed defects for BMP-2 5 μg (A) and 15 μg (B) dosing. Note the well-developed cortex in the lower dose of BMP-2 (A, white arrow) as compared to the more irregular cortex seen in the higher dose of BMP02 (B, white arrow). Also note the adipocytes (Adp) within the cortices.

Figure 6

(A) A representative 3D reconstruction of a microCT of the region of interest of the lingual side of a rat mandible regenerated with a PLGA scaffold with 5 μg of BMP-2. (B) A representative 3D reconstruction of a regenerated marginal defect using 15 μg of BMP-2 on a PLGA scaffold. Note the bone regeneration beyond the inferior border of the mandible overfilling the original defect.