In vitro analysis of distraction osteogenesis

An Inexpensive 3D Printed Mouse Model of Successful, Complication-free Long Bone Distraction Osteogenesis

Distraction osteogenesis (DO) is used for skeletal defects; however, up to 50% of cases exhibit complications. Previous mouse models of long bone DO have been anecdotally hampered by postoperative complications, expense, and availability. To improve clinical techniques, cost-effective, reliable animal models are needed. Our focus was to develop a new mouse tibial distractor, hypothesized to result in successful, complication-free DO.

Methods

A lightweight tibial distractor was developed using CAD and 3D printing. The device was fixed to the tibia of C57Bl/6J mice prior to osteotomy. Postoperatively, mice underwent 5 days latency, 10 days distraction (0.15 mm every 12 hours), and 28 days consolidation. Bone regeneration was examined on postoperative day 43 using micro-computed tomography (μCT) and Movat's modified pentachrome staining on histology (mineralized volume fraction and pixels, respectively). Costs were recorded. We compared cohorts of 11 mice undergoing sham, DO, or acute lengthening (distractor acutely lengthened 3.0 mm).

Results

The histological bone regenerate was significantly increased in DO (1,879,257 ± 155,415 pixels) compared to acute lengthening (32847 ± 1589 pixels) (P < 0.0001). The mineralized volume fraction (bone/total tissue volume) of the regenerate was significantly increased in DO (0.9 ± 0.1) compared to acute lengthening (0.7 ± 0.1) (P < 0.001). There was no significant difference in bone regenerate between DO and sham. The distractor was relatively low cost ($11), with no complications.

Conclusions

Histology and µCT analysis confirmed that the proposed tibial DO model resulted in successful bone formation. Our model is cost-effective and reproducible, enabling implementation in genetically dissectible transgenic mice.

Effects of hyperbaric oxygen therapy on biochemical and histological parameters of muscle groups in proximity to the distracted rat tibia

We investigated the effect of hyperbaric oxygen therapy (HBOT) on rat muscles during tibial distraction osteogenesis (DO) at normal and hyperdistraction rates. Animals in groups 1 and 2 were distracted by 0.5 mm/day and those in groups 3 and 4 by 1 mm/day. Groups 2 and 4 received HBOT during distraction. Group 5 served as control. Superoxide dismutase (SOD; U/g protein), malondialdehyde (nmol/g protein), glutathione (mmol/g protein), and protein levels (g/dl) were determined. SOD was significantly higher in group 2 (4.59 ± 0.97) than in controls (2.19 ± 0.7) (P = 0.0001), and lower in group 4 (3.74 ± 1.70) than in group 2 (P=0.011). Malondialdehyde was significantly higher in group 2 (0.72 ± 0.23) than in controls (0.38 ± 0.10) (P=0.005). Total protein levels were better preserved with HBOT in distracted muscles: group 2 (3.24 ± 0.37) vs. group 1 (1.88 ± 0.60), and group 4 (3.45 ± 0.70) vs. group 3 (2.03 ± 0.75) (both P=0.0001). Numbers of fibres were lower in group 1 (4.88 ± 0.59) than in group 2 (6.07 ± 0.86), and in group 3 (5.13 ± 0.36) than in group 4 (6.14 ± 0.74) (both P=0.001). Numbers of nuclei were higher in group 1 (11.29 ± 2.47) than in group 2 (9.03 ± 1.53) (P=0.04), and in group 3 (12.43 ± 3.32) than in group 4 (9.08 ± 1.58) (P=0.001). Fibres and nuclei with HBOT were similar to those of controls. HBOT decreased the inflammatory cell infiltrate for group 1 (19.8 ± 8.54) vs. group 2 (4.2 ± 2.53) and group 3 (36.54 ± 11.29) vs. group 4 (21.5 ± 9.23) (both P=0.001). HBOT improves the adaptation of distracted muscle by increasing fibres and antioxidants while decreasing inflammation.

Expression of MMP-1 and TIMP-1 in irradiated mandibles during distraction osteogenesis

OBJECTIVES

The study aimed to evaluate the expression of MMP-1 and TIMP-1 in irradiated mandibles during distraction osteogenesis.

STUDY DESIGN

Rabbits in the experimental group received preoperative radiation of 9 Gy for 5 fractions. After 1 month, all rabbits underwent osteotomy and distraction osteogenesis with 7 days of latency. Three rabbits in the control and experimental groups were killed at days 7, 12, 18, and 25. Specimens were subjected to immunohistochemical examination and real-time polymerase chain reaction analysis.

RESULTS

At day 7, expression of MMP-1 and TIMP-1 was significantly suppressed in the radiotherapy group in contrast to the control group. At day 12, expression of MMP-1 was significantly higher in the control group. At day 18, expression of MMP-1 and TIMP-1 was significantly higher in the control than in the radiotherapy group.

CONCLUSIONS

Radiotherapy changes the expression pattern of MMP-1 and TIMP-1.

Uniaxial mechanical strain: an in vitro correlate to distraction osteogenesis

BACKGROUND

Distraction osteogenesis is a valuable clinical tool; however the molecular mechanisms governing successful distraction remain unknown. We have used a uniaxial in vitro strain device to simulate the uniaxial mechanical environment of the interfragmentary distraction gap.

MATERIALS AND METHODS

Using the Flexcell system, normal human osteoblasts were subjected to different levels of cyclical uniaxial mechanical strain. Cellular morphology, proliferation, migration, and the expression of angiogenic (vascular endothelial growth factor [VEGF] and fibroblast growth factor-2 [FGF-2]) and osteogenic (osteonectin, osteopontin, and osteocalcin) proteins and extracellular matrix molecules (collagen IalphaII) were analyzed in response to uniaxial cyclic strain.

RESULTS

Osteoblasts exposed to strain assumed a fusiform spindle-shaped morphology aligning parallel to the axis of uniaxial strain and osteoblasts exposed to strain or conditioned media had a 3-fold increase in proliferation. Osteoblast migration was maximal (5-fold) in response to 9% strain. Angiogenic cytokine, VEGF, and FGF-2, increased 32-fold and 2.6-fold (P < 0.05), respectively. Osteoblasts expressed greater amounts of osteonectin, osteopontin, and osteocalcin (2.1-fold, 1.8-fold, 1.5-fold respectively, P < 0.01) at lower levels of strain (3%). Bone morphogenic protein-2 production increased maximally at 9% strain (1.6-fold, P < 0.01). Collagen I expression increased 13-, 66-, and 153-fold in response to 3, 6, and 9% strain, respectively.

CONCLUSIONS

Uniaxial cyclic strain using the Flexcell device under appropriate strain parameters provides a novel in vitro model that induces osteoblast cellular and molecular expression patterns that simulate patterns observed in the in vivo distraction gap.

Favorable Morphologic Change of Preosteoblasts in a Three-Dimensional Matrix with In Vitro Microdistraction

BACKGROUND

Distraction osteogenesis has been used to correct hypoplastic and asymmetric bony deformities in the growing patient, yet its underlying cellular mechanisms are poorly understood. Using a new in vitro model, the microdistractor, morphologic properties of preosteoblasts under mechanical strain were studied.

METHODS

Mouse calvarial MC3T3 cells were suspended in a polymerized three-dimensional collagen gel and stressed for 14 days as one of three groups (n = 30): (1) distraction (0.5 mm/day); (2) oscillation (1 mm/day for 2 days alternated with 1 mm/day for 2 days); and (3) control (no force). A computer modeling system, KS-300, was used to record cell shape (aspect ratio) and orientation (deviance from axis of stress).

RESULTS

In part I of the study, morphologic cellular changes were found to be even throughout different regions of the gel (central versus peripheral, versus different vertical layers), suggesting the force was evenly applied to all cells in the gel. In addition, when linear distraction forces were applied, morphologic change occurred over time, suggesting a morphologic response to the applied stress. In part II of the study, with different forces applied, morphologic changes occurred over time such that linear distraction forces caused cells to elongate and align in a parallel direction to the force, whereas oscillation caused cells to switch from parallel (with distraction) to perpendicular (with compression) orientation relative to the force applied.

CONCLUSION

The authors' data suggest that the microdistractor device is an effective in vitro model for studying the cellular response to distraction stresses. It may be used in future studies to optimize clinical methods of distraction.

The role of angiogenesis in a murine tibial model of distraction osteogenesis

Distraction osteogenesis (DO) is one of the most dramatic in vivo applications of mechanical stimulation as a means of inducing bone regeneration. A simple and reproducible murine model of tibia distraction osteogenesis was developed using a monolateral fixator. Bone formation was assessed histologically over a 35-day time course. The steady state expression of a broad family of angiogenesis-associated genes was assessed by microarray hybridization analyses over the same time course, while the immediate gene response that was induced during each cycle of distraction was assessed at 30 min and 8 h after the first and last rounds of activation of the fixator. Distraction osteogenesis promoted new bone formation primarily through an intramembranous process with maximal osteogenesis during the active distraction period. Histological analysis also showed that dense cortical bone continued to be formed, during the consolidation phase, for 2 weeks after distraction ended. The analysis of steady state mRNA expression levels over the time course of DO showed that VEGF-A and neuropilin, an alternate receptor for VEGF-A, both angiopoietin (Ang) 1 and 2 factors, and the Ang receptor Tie2 were the critical angiogenic factors during DO. A key transcriptional regulator of many of the angiogenic factors, hypoxia-induced factor1alpha (Hif-1a), the FGF binding protein pleiotropin/OSF1, and multiple MMP(s), were also induced during the active distraction period. Examination of the expression of angiogenic factors that were induced after each cycle of activation, demonstrated that Hif-1a, Nrp1, and VEGF-A were all cyclically induced after each increment of distraction. These results suggest that these factors are early mediators that are produced by distraction and contribute toward the processes that promote bone formation. These experiments represent the first step in defining the molecular mechanisms that regulate skeletal regeneration and the functional relationship between angiogenesis and osteogenesis during distraction osteogenesis.

Short-term load bearing capacity of osteochondral autografts implanted by the mosaicplasty technique: an in vitro porcine model

Articular surface congruency and graft stability are considered essential factors in the success of osteochondral grafting; however, quantitative measures of short-term load bearing capacity of grafts implanted by the mosaicplasty technique have not been reported. The purpose of this study was to develop a live tissue in vitro model to examine short-term fixation strength of mosaicplasty autografts immediately after and 1 week following graft implantation. Cylindrical osteochondral autografts were implanted in vitro by the mosaicplasty technique on five pairs of porcine femoral condyles within one and a half hours of animal sacrifice. Immediately following the surgical procedure, graft push-in and pull-out strength tests as well as indentation tests to determine modulus of the surrounding cancellous bone were performed on half of the specimens from the distal femurs of each animal. The remaining specimens, matched for location in the contralateral leg, were incubated in culture medium for 7 days prior to performing the same set of mechanical tests. Averaged push-in and pull-out graft fixation strength decreased 44% from 135.7 to 75.5N over the 7-day period, while no change in modulus was detected in the surrounding cancellous bone. These in vitro results demonstrate a substantial deterioration of short-term fixation strength of mosaicplasty grafts from the immediate post-operative state. Such a reduction in short-term graft load bearing capacity may pose a threat to the surgically established articular surface congruency and blood vessels formed during the early stages of the healing response.