Prefabrication technique by preserving a muscular pedicle from masseter muscle as an in vivo bioreactor for reconstruction of mandibular critical‐sized bone defects in canine models

Abstract

In vivo bioreactors serve as regenerative niches that improve vascularization and regeneration of bone grafts. This study has evaluated the masseter muscle as a natural bioreactor for βTCP or PCL/βTCP scaffolds, in terms of bone regeneration. The effect of pedicle preservation, along with sole, or MSC‐ or rhBMP2‐combined application of scaffolds, has also been studied. Twenty‐four mongrel dogs were randomly placed in six groups, including βTCP, βTCP/rhBMP2, βTCP/MSCs, PCL/βTCP, PCL/βTCP/rhBMP2, and PCL/βTCP/MSCs. During the first surgery, the scaffolds were implanted into the masseter muscle for being prefabricated. After 2 months, each group was divided into two subgroups prior to mandibular bone defect reconstruction; one with a preserved vascularized pedicle and one without. After 12 weeks, animals were euthanized, and new bone formation was evaluated using histological analysis. Histological analysis showed that all β‐TCP scaffold groups had resulted in significantly greater rates of new bone formation, either with a pedicle surgical approach or non‐pedicle surgical approach, comparing to their parallel groups of βTCP/PCL scaffolds (p ≤ .05). Pedicled β‐TCP scaffold groups that were treated with either rhBMP2 (48.443% ± 0.250%) or MSCs (46.577% ± 0.601%) demonstrated the highest rates of new bone formation (p ≤ .05). Therefore, masseter muscle can be used as a local in vivo bioreactor with potential clinical advantages in reconstruction of human mandibular defects. In addition, scaffold composition, pedicle preservation, and treatment with MSCs or rhBMP2, influence new bone formation and scaffold degradation rates in the prefabrication technique.

Regeneration of Critical‐Sized Mandibular Defects Using 3D‐Printed Composite Scaffolds: A Quantitative Evaluation of New Bone Formation in In Vivo Studies

“…A similar improvement was obtained by Nokhbatolfoghahaei et al and Park et al, who seeded MSCs and TMSCs on PCL/ β ‐TCP scaffolds, showing quantitatively the improvement in bone regeneration (15.430% ± 0.547% and 5.813% ± 1.345%), compared to scaffolds alone or scaffolds combined only with growth factors. [ 39,40 ] Finally, Temple et al and Roskies et al have proven the efficacy of the seeding of ACSCs aggregates on both PCL (Figure 8C) and PEKK (Figure 8D) scaffolds, showing a higher cell infiltration in the seeded scaffolds after 7 days of in vivo implantation. [ 48,49 ]…”

“…[ 42 ] Nokhbatolfoghahaei et al have also tested β ‐TCP scaffolds in several conditions in a canine animal model, and always reported higher histomorphometry values of NB in the presence of rh‐BMP‐2 (NB = 48.443 ± 0.250%). [ 39 ] On the other hand, despite reporting a modest trend of bone formation for PCL/ β ‐TCP scaffolds soaked into a BMP‐2/collagen solution (BV/TV ≈ 13%), results of Lee et al lacked statistical significance when compared to the control group (PCL/ β ‐TCP alone). [ 36 ] Similar outcomes were reported in another PCL/ β ‐TCP scaffold study, where intra‐scaffold injections of a rhBMP‐2 and bdECM bioink improved bone‐to‐implant contact ratio (BIC) (BIC = 51.29 ± 14.64%), but NB was again not significantly ameliorated.…”

“…[35,38] Depending on the structure (e.g., 0-90°pattern, kagome, or 0-45°or 0-30°pattern) and the presence of ceramic elements, PCL scaffolds displayed compressive strength values between 10 and 30 MPa and E flex between 70 and 170 MPa. [36,39,40,76] These values are at least one order of magnitude lower than cancellous bone and two orders of magnitude lower than cortical bone. In mandibular bone reconstruction applications, mechanical strength and load-bearing capacity are crucial factors, as the mandible experiences high loads during its lifespan.…”

“…Significantly greater rate of NB (NB = 48.443 ± 0.250%) was obtained in vivo but, despite all, capillary formation within the constructs could not be proven by histological analysis (Figure 7C). [39] Finally, Konopnicki et al hypothesized that vessels penetration in 𝛽-TCP/PCL scaffolds seeded with porcine bone marrow progenitor cells (pBMPCs) was improved by early implanting the constructs in a critical-size mandibular defect (i.e., before the 14th days of in vitro culture). [34] The problem of scaffold vascularization in the context of mandibular BTE remains the narrowest bottleneck that is currently limiting translation of academic research into clinic.…”

3D-Printing for Critical Sized Bone Defects: Current Concepts and Future Directions

“…To address these obstacles, a novel approach involves the in vivo implantation of a scaffold into an ectopic site such as skin or muscle, termed an in vivo bioreactor (IVB), with subsequent transfer of the newly vascularized scaffold into the bony site of interest [ 58 , 59 , 60 , 61 , 62 ]. To date, many preclinical studies have demonstrated robust bone healing responses using the IVB method [ 63 , 64 , 65 , 66 ]. The majority of IVB use in humans involves grafting periosteum along with its vascular supply to the site of interest [ 67 , 68 , 69 , 70 ], but actual prefabrication techniques involving ectopic maturation of a scaffold with subsequent transfer to the site of interest are rare in clinical studies.…”