Tensile mechanical strain up-regulates Runx2 and osteogenic factor expression in human periosteal cells: implications for distraction osteogenesis

Regulatory effects of stress release from decellularized periosteum on proliferation, migration, and osteogenic differentiation of periosteum-derived cells

Bone injury is often associated with tears in the periosteum and changes in the internal stress microenvironment of the periosteum. In this study, we investigated the biological effects of periosteal prestress release on periosteum-derived cells (PDCs) and the potential mechanisms of endogenous stem cell recruitment. Decellularized periosteum with natural extracellular matrix (ECM) components was obtained by a combination of physical, chemical, and enzymatic decellularization. The decellularized periosteum removed immunogenicity while retaining the natural network structure and composition of the ECM. The Young's modulus has no significant difference between the periosteum before and after decellularization. The extracted PDCs were further composited with the decellularized periosteum and subjected to 20% stress release. It was found that the proliferative capacity of PDCs seeded on decellularized periosteum was significantly enhanced 6 h after stress release of the periosteum. The cell culture supernatant obtained after periosteal prestress release was able to significantly promote the migration ability of PDCs within 24 h. Enzyme-linked immunosorbnent assay (ELISA) experiments showed that the expression of stroma-derived factor-1α (SDF-1α) and vascular endothelial growth factor (VEGF) in the supernatant increased significantly after 3 h and 12 h of stress release, respectively. Furthermore, periosteal stress release promoted the high expression of osteogenic markers osteocalcin (OCN), osteopontin (OPN), and collagen type I of PDCs. The change in stress environment caused by the release of periosteal prestress was sensed by integrin β1, a mechanoreceptor on the membrane of PDCs, which further stimulated the expression of YAP in the nucleus. These investigations provided a novel method to evaluate the importance of mechanical stimulation in periosteum, which is also of great significance for the design and fabrication of artificial periosteum with mechanical regulation function.

Translation of biophysical environment in bone into dynamic cell culture under flow for bone tissue engineering

Bone is a dynamic environment where osteocytes, osteoblasts, and mesenchymal stem/progenitor cells perceive mechanical cues and regulate bone metabolism accordingly. In particular, interstitial fluid flow in bone and bone marrow serves as a primary biophysical stimulus, which regulates the growth and fate of the cellular components of bone. The processes of mechano-sensory and -transduction towards bone formation have been well studied mainly in vivo as well as in two-dimensional (2D) dynamic cell culture platforms, which elucidated mechanically induced osteogenesis starting with anabolic responses, such as production of nitrogen oxide and prostaglandins followed by the activation of canonical Wnt signaling, upon mechanosensation. The knowledge has been now translated into regenerative medicine, particularly into the field of bone tissue engineering, where multipotent stem cells are combined with three-dimensional (3D) scaffolding biomaterials to produce transplantable constructs for bone regeneration. In the presence of 3D scaffolds, the importance of suitable dynamic cell culture platforms increases further not only to improve mass transfer inside the scaffolds but to provide appropriate biophysical cues to guide cell fate. In principle, the concept of dynamic cell culture platforms is rooted to bone mechanobiology. Therefore, this review primarily focuses on biophysical environment in bone and its translation into dynamic cell culture platforms commonly used for 2D and 3D cell expansion, including their advancement, challenges, and future perspectives. Additionally, it provides the literature review of recent empirical studies using 2D and 3D flow-based dynamic cell culture systems for bone tissue engineering.

The Prrx1eGFP Mouse Labels the Periosteum During Development and a Subpopulation of Osteogenic Periosteal Cells in the Adult

The identity of the cells that form the periosteum during development is controversial with current dogma suggesting these are derived from a Sox9-positive progenitor. Herein, we characterize a newly created Prrx1eGFP reporter transgenic mouse line during limb formation and postnatally. Interestingly, in the embryo Prrx1eGFP-labeled cells become restricted around the Sox9-positive cartilage anlage without themselves becoming Sox9-positive. In the adult, the Prrx1eGFP transgene live labels a subpopulation of cells within the periosteum that are enriched at specific sites, and this population is diminished in aged mice. The green fluorescent protein (GFP)-labeled subpopulation can be isolated using fluorescence-activated cell sorting (FACS) and represents approximately 8% of all isolated periosteal cells. The GFP-labeled subpopulation is significantly more osteogenic than unlabeled, GFP-negative periosteal cells. In addition, the osteogenic and chondrogenic capacity of periosteal cells in vitro can be extended with the addition of fibroblast growth factor (FGF) to the expansion media. We provide evidence to suggest that osteoblasts contributing to cortical bone formation in the embryo originate from Prrx1eGFP-positive cells within the perichondrium, which possibly piggyback on invading vascular cells and secrete new bone matrix. In summary, the Prrx1eGFP mouse is a powerful tool to visualize and isolate periosteal cells and to quantify their properties in the embryo and adult. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Induced osteogenesis using biodegradable and titanium periosteal distractors

Background

New bone formation can result from periosteal distraction. This is achieved through progressive uplifting of the periosteum by increasing the interface between it and the bone surface.

Objective

This study investigated the impact of gradual periosteal distraction using biodegradable materials and titanium distraction devices.

Materials and methods

20 rabbits were separated into 2 groups. Distraction devices were placed in all groups after reflecting the calvarial periosteum. The device was actuated following 7 days. Group 1 got titanium device and Hydroxyapatite HA with poly-l-lactide (PLLA) device was utilized in group 2. Five animals were sacrificed from each group following 4 and 6 weeks. Newly formed bone was histologically and radiographically assessed.

Results

The histological observations showed that both distraction devices successfully induced osteogenesis and effectively distracted the soft tissue following 4 and six weeks. The study showed scattered bone trabeculae, with adipose tissue and multiple dome-shaped bones. Micro-computed tomography showed newly formed bone that was far less radiopaque than the initial basal bone. The connective tissue appeared as a radiolucent area that decreased gradually toward the fixation point of the device. At 6 weeks, the percentage of new bone was significantly higher than at 4 weeks for both devices. The PLLA device showed more bone than did the titanium device at both 4 and 6 weeks, but no significant difference was observed.

Conclusions

Both distraction devices were effective in distracting the periosteum and inducing new vascularized bone. The PLLA device induced more bone than the titanium device. Thus, the distractor composition may influence the new bone.

Three-Dimensional-Printed Poly-L-Lactic Acid Scaffolds with Different Pore Sizes Influence Periosteal Distraction Osteogenesis of a Rabbit Skull

The repair of bone defects is a big challenge in reconstructive surgery. Periosteal distraction osteogenesis (PDO), as a promising technique used for bone regeneration, forms a space between the periosteum and bone cortex to regenerate the new bone merely by distracting the periosteum. In order to investigate the influence of distractor framework on the PDO, we utilized three-dimensional (3D) printing technology to fabricate three kinds of poly-L-lactic acid (PLLA) scaffolds with different pore sizes in this study. The in vitro experiments showed that the customized PLLA scaffolds had different-sized microchannels with low toxicity, good biocompatibility, and enough mechanical strength. Then, we built up an in vivo bioreactor under the skull periosteum of New Zealand white rabbits. The distractors with different pore sizes all could satisfy the demand of periosteal distraction in the animal experiments. After 8 weeks of consolidation period, the quality and quantity of the newly formed bone were improved with the increasing pore sizes of the distractors. Moreover, the newly formed bone also displayed an increasing degree of vascularization. In conclusion, 3D printing technology could promote the innovation of PDO devices and fabricate optimized scaffolds with appropriate pore sizes, shapes, and structures. It would help us regenerate more functional tissue-engineered bone and provide new ideas for further clinical application of the PDO technique.

Prx1-Expressing Progenitor Primary Cilia Mediate Bone Formation in response to Mechanical Loading in Mice

Increases in mechanical loading can enhance the addition of new bone, altering geometry and density such that bones better withstand higher forces. Bone-forming osteoblasts have long been thought to originate from progenitors, but the exact source is yet to be identified. Previous studies indicate osteogenic precursors arise from Prx1-expressing progenitors during embryonic development and adult fracture repair. However, it is unknown whether this cell population is also a source for mechanically induced active osteoblasts. We first identified that Prx1 is expressed in skeletally mature mouse periosteum, a thin tissue covering the surface of the bone that is rich in osteoprogenitors. We then traced Prx1 progenitor lineage using a transgenic mouse model carrying both a Prx1-driven tamoxifen-inducible Cre and a ROSA-driven lacZ reporter gene. Cells that expressed Prx1 when compressive axial loading was applied were detected within the cortical bone days after stimulation, indicating osteocytes are of Prx1-expressing cell origin. In addition, we evaluated how these cells sense and respond to physical stimulation in vivo by disrupting their primary cilia, which are antenna-like sensory organelles known to enhance mechanical and chemical signaling kinetics. Although Prx1-driven primary cilium disruption did not affect osteoblast recruitment to the bone surface, the relative mineral apposition and bone formation rates were decreased by 53% and 34%, respectively. Thus, this cell population contributes to load-induced bone formation, and primary cilia are needed for a complete response. Interestingly, Prx1-expressing progenitors are easily extracted from periosteum and are perhaps an attractive alternative to marrow stem cells for bone tissue regeneration strategies.

Primary cilia are necessary for Prx1-expressing cells to contribute to postnatal skeletogenesis

Although Prx1 (also known as PRRX1)-expressing cells and their primary cilia are critical for embryonic development, they have yet to be studied in the context of postnatal skeletogenesis owing to the lethality of mouse models. A tamoxifen-inducible Prx1 model has been developed, and we determined that expression directed by this promoter is highly restricted to the cambium layers in the periosteum and perichondrium after birth. To determine the postnatal role of these cambium layer osteochondroprogenitors (CLOPs) and their primary cilia, we developed models to track the fate of CLOPs (Prx1CreER-GFP;Rosa26^tdTomato) and selectively disrupt their cilia (Prx1CreER-GFP;Ift88^fl/fl). Our tracking studies revealed that CLOPs populate cortical and trabecular bone, the growth plate and secondary ossification centers during the normal program of postnatal skeletogenesis. Furthermore, animals lacking CLOP cilia exhibit stunted limb growth due to disruptions in endochondral and intramembranous ossification. Histological examination indicates that growth is stunted due to limited differentiation, proliferation and/or abnormal hypertrophic differentiation in the growth plate. Collectively, our results suggest that CLOPs are programmed to rapidly populate distant tissues and produce bone via a primary cilium-mediated mechanism in the postnatal skeleton.

Periosteal progenitors contribute to load-induced bone formation in adult mice and require primary cilia to sense mechanical stimulation

BACKGROUND

The fully developed adult skeleton adapts to mechanical forces by generating more bone, usually at the periosteal surface. Progenitor cells in the periosteum are believed to differentiate into bone-forming osteoblasts that contribute to load-induced adult bone formation, but in vivo evidence does not yet exist. Furthermore, the mechanism by which periosteal progenitors might sense physical loading and trigger differentiation is unknown. We propose that periosteal osteochondroprogenitors (OCPs) directly sense mechanical load and differentiate into bone-forming osteoblasts via their primary cilia, mechanosensory organelles known to be involved in osteogenic differentiation.

METHODS

We generated a diphtheria toxin ablation mouse model and performed ulnar loading and dynamic histomorphometry to quantify the contribution of periosteal OCPs in adult bone formation in vivo. We also generated a primary cilium knockout model and isolated periosteal cells to study the role of the cilium in periosteal OCP mechanosensing in vitro. Experimental groups were compared using one-way analysis of variance or student's t test, and sample size was determined to achieve a minimum power of 80%.

RESULTS

Mice without periosteal OCPs had severely attenuated mechanically induced bone formation and lacked the mineralization necessary for daily skeletal maintenance. Our in vitro results demonstrate that OCPs in the periosteum uniquely sense fluid shear and exhibit changes in osteogenic markers consistent with osteoblast differentiation; however, this response is essentially lost when the primary cilium is absent.

CONCLUSIONS

Combined, our data show that periosteal progenitors are a mechanosensitive cell source that significantly contribute to adult skeletal maintenance. More importantly, an OCP population persists in the adult skeleton and these cells, as well as their cilia, are promising targets for bone regeneration strategies.

Development of a co-culture device for the study of human tenocytes in response to the combined stimulation of electric field and platelet rich plasma (PRP)

One of the objectives of rotator cuff repairs is to achieve biological healing and recovery in the tendon-bone zone. Some clinical evaluations reported the feasibility of tendon healing based on the stimulations of electric field and platelet-rich plasma (PRP). However, because of lack of appropriate tool for in vitro primary culture under complicated conditions, the efficacy and standard protocol of these healing approaches are still controversial among clinical experts. In this study, a novel co-culture device was developed for the study of tenocytes proliferation under single and combined stimulations of electric field and PRP. The device was a culture well divided into three sub-chambers separated by a barrier and embedded with a pair of parallel plate electrodes. Tenocytes and PRP gel could be respectively loaded into the sub-chambers and cultured with interlinked medium. Hence, tenocytes could concurrently receive a uniform electric field and platelet-derived growth factors by diffusion. Results revealed that the proliferation of tenocytes could be significantly enhanced by these stimulations. The device provides a precise and practical approach for the in vitro study of tendon healing, especially for PRP study. Moreover, optimization of the conditions of electric field and PRP could be determined by in vitro screening procedure before surgery to provide a personalized therapy.

Investigation of osteogenic activity of primary rabbit periosteal cells stimulated by multi-axial tensile strain

Periosteum-derived cells was indicated to respond to mechanical force and have stem cell potential capable of differentiating into multiple tissue. Investigation of osteogenic activity under mechanical stimulation is important to understand the therapeutic conditions of fracture healing. In this work, a cell culture platform was developed for respectively providing isotropic and anisotropic axial strain. Primary rabbit periosteal cells were isolated and cultured in the chamber. Multi-axial tensile strain was received and osteogenic activity was investigated by mRNA expressions of CBFA1 and OPN. The highest mRNA expression was found in moderate strain (5-8%) under anisotropic axial strain. These results provided important foundation for further in vivo studies and development of tailor-made stretching rehabilitation equipment.

Periosteal elevation induces supracortical peri-implant bone formation

PURPOSE

The aim of the study was to evaluate the possibility of supracortical peri-implant bone formation after periosteal elevation.

MATERIALS AND METHODS

Periosteal elevation with an elevation height of 5 or 10 mm was performed in an animal experiment with 24 female domestic pigs. For this purpose, four implants were inserted in the frontal bone of each animal. The implants protruded from the local bone by 5 or 10 mm. In the test groups, the periosteum was attached to the protruding implants. In the control groups, the implants were covered with biocompatible degradable periosteal-shielding devices. Each 8 animals were sacrificed after 20, 40 and 60 days. De novo bone formation was evaluated radiographically and histologically.

RESULTS

Bone formation rate was higher in the test groups compared to the control groups after 20, 40 and 60 days. After 40 and 60 days, a statistically significant higher (P < 0.01) bone formation rate was found for both elevation heights. The maximum height of the generated bone was statistically significantly higher (P < 0.01) in the test groups for both elevation heights, compared to the control groups for all time points investigated.

CONCLUSION

Periosteal elevation by dental implants is a treatment option for supracortical peri-implant bone formation.

Periosteal Distraction Osteogenesis: An Effective Method for Bone Regeneration

The treatment of bone defects is challenging and controversial. As a new technology, periosteal distraction osteogenesis (PDO) uses the osteogenicity of periosteum, which creates an artificial space between the bone surface and periosteum to generate new bone by gradually expanding the periosteum with no need for corticotomy. Using the newly formed bone of PDO to treat bone defects is effective, which can not only avoid the occurrence of immune-related complications, but also solve the problem of insufficient donor. This review elucidates the availability of PDO in the aspects of mechanisms, devices, strategies, and measures. Moreover, we also focus on the future prospects of PDO and hope that PDO will be applied to the clinical treatment of bone defects in the future.

Photocrosslinkable and elastomeric hydrogels for bone regeneration

Nanocomposite biomaterials are extensively investigated for cell and tissue engineering applications due their unique physical, chemical and biological characteristics. Here, we investigated the mechanical, rheological, and degradation properties of photocrosslinkable and elastomeric nanocomposite hydrogels from nanohydroxyapatite (nHAp) and gelatin methacryloyl (GelMA). The addition of nHAp resulted in a significant increase in mechanical stiffness and physiological stability. Cells readily adhere and proliferate on the nanocomposite surfaces. Cyclic stretching of cells on the elastomeric nanocomposites revealed that nHAp elicited a stronger alignment response in the direction of strain. In vitro studies highlight enhanced bioactivity of nanocomposites as determined by alkaline phosphate (ALP) activity. Overall, the elastomeric and photocrosslinkable nanocomposite hydrogels can be used for minimally invasive therapy for bone regeneration.

Review of the cellular and biological principles of distraction osteogenesis: An in vivo bioreactor tissue engineering model

Distraction osteogenesis (DO) is a widely used technique in plastic and orthopaedic surgery. During the process, mechanical force is applied to fractured bone to enhance the regenerative processes and induce new bone formation. Although there is an abundance of literature on the clinical process of DO, there is a distinct lack of focus on the underlying biological principles governing this process. DO follows the basic premises of tissue engineering. The mechanical stress stimulates mesenchymal stem cell differentiation down an osteoblastic lineage on a matrix background. The aim of this review is to give an overview of the current knowledge of the molecular mechanism governing this process.

Ossification of subperiosteal hematoma: the potential of periosteal osteogenesis in cranioplasty

BACKGROUND

Subperiosteal hematoma is the accumulation of blood between the periosteum and the skull, which commonly occurs in the neonatal period but rarely in other ages. Subperiosteal hematoma can be self-absorbed in most cases and occasionally may cause ossification.

MATERIALS AND METHODS

This study reports a case of subperiosteal hematoma formed in a 16-year-old adolescent boy after a minor trauma. Because the hematoma did not disappear for more than a month after the trauma, the patient was treated with multiple hematoma punctures. However, the hematoma recurred and led to ossification. Finally, the patient underwent surgical treatment.

RESULTS

Finally, the ossification associated with the hematoma was treated through surgery. The head contour recovered normally.

CONCLUSIONS

The occurrence of hematoma ossification in the 16-year-old patient suggests that the periosteum has great potential for osteogenesis. This is likely caused by the joint action of some active factors in the blood and a certain tension of the hematoma on the local periosteum. This case provides the following thoughts. (1) A subperiosteal hematoma that has not been absorbed after 1 month should be treated promptly to avoid ossification. Once ossification has occurred, the hematoma should be treated surgically. (2) The potential for periosteal osteogenesis is great, which may provide a new thought for cranioplasty.

Mechanistic, mathematical model to predict the dynamics of tissue genesis in bone defects via mechanical feedback and mediation of biochemical factors

The link between mechanics and biology in the generation and the adaptation of bone has been well studied in context of skeletal development and fracture healing. Yet, the prediction of tissue genesis within - and the spatiotemporal healing of - postnatal defects, necessitates a quantitative evaluation of mechano-biological interactions using experimental and clinical parameters. To address this current gap in knowledge, this study aims to develop a mechanistic mathematical model of tissue genesis using bone morphogenetic protein (BMP) to represent of a class of factors that may coordinate bone healing. Specifically, we developed a mechanistic, mathematical model to predict the dynamics of tissue genesis by periosteal progenitor cells within a long bone defect surrounded by periosteum and stabilized via an intramedullary nail. The emergent material properties and mechanical environment associated with nascent tissue genesis influence the strain stimulus sensed by progenitor cells within the periosteum. Using a mechanical finite element model, periosteal surface strains are predicted as a function of emergent, nascent tissue properties. Strains are then input to a mechanistic mathematical model, where mechanical regulation of BMP-2 production mediates rates of cellular proliferation, differentiation and tissue production, to predict healing outcomes. A parametric approach enables the spatial and temporal prediction of endochondral tissue regeneration, assessed as areas of cartilage and mineralized bone, as functions of radial distance from the periosteum and time. Comparing model results to histological outcomes from two previous studies of periosteum-mediated bone regeneration in a common ovine model, it was shown that mechanistic models incorporating mechanical feedback successfully predict patterns (spatial) and trends (temporal) of bone tissue regeneration. The novel model framework presented here integrates a mechanistic feedback system based on the mechanosensitivity of periosteal progenitor cells, which allows for modeling and prediction of tissue regeneration on multiple length and time scales. Through combination of computational, physical and engineering science approaches, the model platform provides a means to test new hypotheses in silico and to elucidate conditions conducive to endogenous tissue genesis. Next generation models will serve to unravel intrinsic differences in bone genesis by endochondral and intramembranous mechanisms.

Arising as a consequence of trauma, tumor resection, removal of necrotic or infected tissue, and congenital abnormalities, critical-sized defects are too large to heal spontaneously and therefore require surgical intervention. New surgical approaches harness the regenerative power of the periosteum, a tissue membrane covering most bones, which provides a niche for stem cells and plays a key role in healing after injury. The interplay of mechanical, cellular and biochemical mechanisms involved in periosteum-mediated tissue genesis and healing remains elusive, providing the impetus for the current study. Here, we develop a mechanistic, mathematical model to predict the dynamics of tissue genesis by periosteum-derived stem cells within a bone defect surrounded by periosteum or a periosteum substitute. A mechanical finite element model is coupled with a model of cellular dynamics to simulate a tested clinical scenario in which the patient's own periosteum is left around the defect after injury. Model predictions incorporating mechanical feedback match spatiotemporal patterns of bone tissue regeneration observed in a series of in vivo ovine experiments. Through combination of computational, physical and engineering science approaches, the model platform provides a means to test new hypotheses in silico. This will provide criteria conducive to endogenous tissue genesis that can be tested in follow on experiments.

Expression of osteogenic molecules in the caudate nucleus and gray matter and their potential relevance for Basal Ganglia calcification in hypoparathyroidism

BACKGROUND

Basal ganglia calcification (BGC) is an interesting example of ectopic calcification in patients with hypoparathyroidism. Its pathogenesis and reasons for predilection of calcification at basal ganglia are not clear.

OBJECTIVE

To assess the expression of osteogenesis-related molecules in the caudate nucleus and surface gray matter (an area spared from calcification) and discuss potential relevance of the results in context of BGC in idiopathic hypoparathyroidism.

METHODS

Caudate nucleus and gray matter were obtained from 14 autopsies performed in accidental deaths. The mRNA expression of bone transcription factors (RUNX2/osterix), bone morphogenetic proteins (BMPs) 2 and 4, osteonectin, osteopontin, osteocalcin, vitamin D receptor, calcium sensing-receptor, Na phosphate transporters (PiTs) 1 and 2, N-methyl-D-aspartate receptor 2B (NMDAR2B), carbonic anhydrase II (CA-II), PTH1 receptor (PTH1R), PTH2R, and PTHrP were assessed by RT-PCR. Western blot, spot densitometry, and immunohistochemistry were performed to assess protein expression of molecules showing differences in mRNA expression between caudate and gray tissues.

RESULTS

The mean mRNA expression of PiT1 (11.0 ± 10.39 vs 32.9 ± 20.98, P = .003) and PTH2R (1.6 ± 1.47 vs 13.7 ± 6.11, P = .001) were significantly lower in the caudate nucleus than the gray matter. The expression of osteonectin, osteopontin, and CA-II were significantly higher in the caudate nucleus than the gray matter (P = .01, .001, and .04, respectively). The mRNA expression of other molecules was comparable in the 2 tissues. The protein expression of both CA-II and osteonectin was 24% higher and PiT1 17% lower in caudate than the gray matter. The differences in the PTH2R and osteopontin protein expression were not appreciable.

CONCLUSIONS

The presence of several osteogenic molecules in caudate nucleus indicates that BGC would probably be the outcome of an active process. The differences in expression of these molecules in caudate over gray matter could favor BGC at this site in the unique biochemical milieu of hypoparathyroid state.

Molecular motor MYO1C, acetyltransferase KAT6B and osteogenetic transcription factor RUNX2 expression in human masseter muscle contributes to development of malocclusion

OBJECTIVE

Type I myosins are molecular motors necessary for glucose transport in the cytoplasm and initiation of transcription in the nucleus. Two of these, MYO1H and MYO1C, are paralogs which may be important in the development of malocclusion. The objective of this study was to investigate their gene expression in the masseter muscle of malocclusion subjects. Two functionally related proteins known to contribute to malocclusion were also investigated: KAT6B (a chromatin remodelling epigenetic enzyme which is activated by MYO1C) and RUNX2 (a transcription factor regulating osteogenesis which is activated by KAT6B).

DESIGN

Masseter muscle samples and malocclusion classifications were obtained from orthognathic surgery subjects. Muscle was sectioned and immunostained to determine fibre type properties. RNA was isolated from the remaining sample to determine expression levels for the four genes by TaqMan(®) RT-PCR. Fibre type properties, gene expression quantities and malocclusion classification were compared.

RESULTS

There were very significant associations (P<0.0000001) between MYO1C and KAT6B expressions. There were also significant associations (P<0.005) between RUNX2 expression and masseter muscle type II fibre properties. Very few significant associations were identified between MYO1C and masseter muscle fibre type properties.

CONCLUSIONS

The relationship between MYO1C and KAT6B suggests that the two are interacting in chromatin remodelling for gene expression. This is the nuclear myosin1 (NM1) function of MYO1C. A surprising finding is the relationship between RUNX2 and type II masseter muscle fibres, since RUNX2 expression in mature muscle was previously unknown. Further investigations are necessary to elucidate the role of RUNX2 in adult masseter muscle.

The Molecular and Cellular Events That Take Place during Craniofacial Distraction Osteogenesis

Summary:

Gradual bone lengthening using distraction osteogenesis principles is the gold standard for the treatment of hypoplastic facial bones. However, the long treatment time is a major disadvantage of the lengthening procedures. The aim of this study is to review the current literature and summarize the cellular and molecular events occurring during membranous craniofacial distraction osteogenesis. Mechanical stimulation by distraction induces biological responses of skeletal regeneration that is accomplished by a cascade of biological processes that may include differentiation of pluripotential tissue, angiogenesis, osteogenesis, mineralization, and remodeling. There are complex interactions between bone-forming osteoblasts and other cells present within the bone microenvironment, particularly vascular endothelial cells that may be pivotal members of a complex interactive communication network in bone. Studies have implicated number of cytokines that are intimately involved in the regulation of bone synthesis and turnover. The gene regulation of numerous cytokines (transforming growth factor-β, bone morphogenetic proteins, insulin-like growth factor-1, and fibroblast growth factor-2) and extracellular matrix proteins (osteonectin, osteopontin) during distraction osteogenesis has been best characterized and discussed. Understanding the biomolecular mechanisms that mediate membranous distraction osteogenesis may guide the development of targeted strategies designed to improve distraction osteogenesis and accelerate bone regeneration that may lead to shorten the treatment duration.

Epigenetic influence of KAT6B and HDAC4 in the development of skeletal malocclusion

INTRODUCTION

Genetic influences on the development of malocclusion include heritable effects on both masticatory muscles and jaw skeletal morphology. Beyond genetic variations, however, the characteristics of muscle and bone are also influenced by epigenetic mechanisms that produce differences in gene expression. We studied 2 enzymes known to change gene expressions through histone modifications, chromatin-modifying histone acetyltransferase KAT6B and deacetylase HDAC4, to determine their associations with musculoskeletal variations in jaw deformation malocclusions.

METHODS

Samples of masseter muscle were obtained from subjects undergoing orthognathic surgery from 6 malocclusion classes based on skeletal sagittal and vertical dysplasia. The muscles were characterized for fiber type properties by immunohistochemistry, and their total RNA was isolated for gene expression studies by microarray analysis and quantitative real-time polymerase chain reaction.

RESULTS

Gene expressions for fast isoforms of myosins and contractile regulatory proteins and for KAT6B and HDAC4 were severalfold greater in masseter muscles from a patient with a deepbite compared with one with an open bite, and genes related to exercise and activity did not differ substantially. In the total population, expressions of HDAC4 (P = 0.03) and KAT6B (P = 0.004) were significantly greater in subjects with sagittal Class III than in Class II malocclusion, whereas HDAC4 tended to correlate negatively with slow myosin type I and positively with fast myosin gene, especially type IIX.

CONCLUSIONS

These data support other published reports of epigenetic regulation in the determination of skeletal muscle fiber phenotypes and bone growth. Further investigations are needed to elucidate how this regulatory model might apply to musculoskeletal development and malocclusion.

Periosteal thickness and cellularity in mid-diaphyseal cross-sections from human femora and tibiae of aged donors

Due to lack of access in healthy patients, the structural properties underlying the inherent regenerative power and advanced material properties of the human periosteum are not well understood. Periosteum comprises a cellular cambium layer directly apposing the outer surface of bone and an outer fibrous layer encompassed by the surrounding soft tissues. As a first step to elucidating the structural and cellular characteristics of periosteum in human bone, the current study aims to measure cambium and fibrous layer thickness as well as cambium cellularity in human femora and tibiae of aged donors. The major and minor centroidal axes (CA) serve as automated reference points in cross-sections of cadaveric mid-diaphyseal femora and tibiae. Based on the results of this study, within a given individual, the cambium layer of the major CA of the tibia is significantly thicker and more cellular than the respective layer of the femur. These significant intraindividual differences do not translate to significant interindividual differences. Further, mid-diaphyseal periosteal measures including cambium and fibrous layer thickness and cellularity do not correlate significantly with age or body mass. Finally, qualitative observations of periosteum in amputated and contralateral or proximal long bones of the lower extremity show stark changes in layer organization, thickness, and cellularity. In a translational context, these novel data, though inherently limited by availability and accessibility of human mid-diaphyseal periosteum tissue, provide important reference values for the use of periosteum in the context of facilitated healing and regeneration of tissue.

Cyclic tensile strain enhances osteogenesis and angiogenesis in mesenchymal stem cells from osteoporotic donors

We have shown that the uniaxial cyclic tensile strain of magnitude 10% promotes and enhances osteogenesis of human mesenchymal stem cells (hMSC) and human adipose-derived stem cells (hASC) from normal, nonosteoporotic donors. In the present study, MSC from osteoporotic donors were analyzed for changes in mRNA expression in response to 10% uniaxial tensile strain to identify potential mechanisms underlying the use of this mechanical loading paradigm for prevention and treatment of osteoporosis. Human MSC isolated from three female, postmenopausal osteoporotic donors were analyzed for their responses to mechanical loading using microarray analysis of over 47,000 gene probes. Human MSC were seeded in three-dimensional collagen type I constructs to mimic the organic extracellular matrix of bone and 10% uniaxial cyclic tensile strain was applied to promote osteogenesis. Seventy-nine genes were shown to be regulated within hMSC from osteoporotic donors in response to 10% cyclic tensile strain. Upregulation of six genes were further confirmed with real-time RT-PCR: jun D proto-oncogene (JUND) and plasminogen activator, urokinase receptor (PLAUR), two genes identified as potential key molecules from network analysis; phosphoinositide-3-kinase, catalytic, delta polypeptide (PIK3CD) and wingless-type MMTV integration site family, member 5B (WNT5B), two genes with known importance in bone biology; and, PDZ and LIM domain 4 (PDLIM4) and vascular endothelial growth factor A (VEGFA), two genes that we have previously shown are significantly regulated in hASC in response to this mechanical stimulus. Function analysis indicated that 10% cyclic tensile strain induced expression of genes associated with cell movement, cell proliferation, and tissue development, including development in musculoskeletal and cardiovascular systems. Our results demonstrate that hMSC from aged, osteoporotic donors are capable of enhanced osteogenic differentiation in response to 10% cyclic tensile strain with significant increases in the expression of genes associated with enhanced cell proliferation, musculoskeletal development, and angiogenesis. Surprisingly, cyclic tensile strain of magnitude 10% not only enhanced osteogenesis in hMSC from osteoporotic donors, but also enhanced expression of angiogenic factors. Better understanding and methodologies to promote osteogenesis in hMSC from elderly, osteoporotic donors may greatly facilitate achieving long-term success in bone regeneration and functional bone tissue engineering for this ever-growing patient population.

Elucidating multiscale periosteal mechanobiology: a key to unlocking the smart properties and regenerative capacity of the periosteum?

The periosteum, a thin, fibrous tissue layer covering most bones, resides in a dynamic, mechanically loaded environment. The periosteum also provides a niche for mesenchymal stem cells. The mechanics of periosteum vary greatly between species and anatomical locations, indicating the specialized role of periosteum as bone's bounding membrane. Furthermore, periosteum exhibits stress-state-dependent mechanical and material properties, hallmarks of a smart material. This review discusses what is known about the multiscale mechanical and material properties of the periosteum as well as their potential effect on the mechanosensitive progenitor cells within the tissue. Furthermore, this review addresses open questions and barriers to understanding periosteum's multiscale structure-function relationships. Knowledge of the smart material properties of the periosteum will maximize the translation of periosteum and substitute periosteum to regenerative medicine, facilitate the development of biomimetic tissue-engineered periosteum for use in instances where the native periosteum is lacking or damaged, and provide inspiration for a new class of smart, advanced materials.

Elucidating multiscale periosteal mechanobiology: a key to unlocking the smart properties and regenerative capacity of the periosteum?

The periosteum, a thin, fibrous tissue layer covering most bones, resides in a dynamic, mechanically loaded environment. The periosteum also provides a niche for mesenchymal stem cells. The mechanics of periosteum vary greatly between species and anatomical locations, indicating the specialized role of periosteum as bone's bounding membrane. Furthermore, periosteum exhibits stress-state-dependent mechanical and material properties, hallmarks of a smart material. This review discusses what is known about the multiscale mechanical and material properties of the periosteum as well as their potential effect on the mechanosensitive progenitor cells within the tissue. Furthermore, this review addresses open questions and barriers to understanding periosteum's multiscale structure-function relationships. Knowledge of the smart material properties of the periosteum will maximize the translation of periosteum and substitute periosteum to regenerative medicine, facilitate the development of biomimetic tissue-engineered periosteum for use in instances where the native periosteum is lacking or damaged, and provide inspiration for a new class of smart, advanced materials.

Treatment outcome and long-term stability of skeletal changes following maxillary distraction in adult subjects of cleft lip and palate

AIM

To evaluate the treatment outcome and long-term stability of skeletal changes following maxillary advancement with distraction osteogenesis in adult subjects of cleft lip and palate.

MATERIALS AND METHODS

Total 12 North Indian adult patients in the age range of 17-34 years with cleft lip and palate underwent advancement of maxilla by distraction osteogenesis. Lateral cephalograms recorded prior to distraction, at the end of distraction, 6 months after distraction, and at least 24 months (mean 25.5 ± 1.94 months) after distraction osteogenesis were used for the evaluation of treatment outcome and long-term stability of the skeletal changes. Descriptive analysis, ANOVA, and post-hoc test were used, and P-value 0.05 was considered as a statistically significant level.

RESULTS

Maxillary distraction resulted in significant advancement of maxilla (P<0.001). Counterclockwise rotation of the palatal plane took place after maxillary distraction. The position of the mandible and facial heights were stable during distraction. During the first 6 months of the post-distraction period, the maxilla showed relapse of approximately 30%. However, after 6 months post distraction, the relapse was very negligible.

CONCLUSIONS

Successful advancement of maxilla was achieved by distraction osteogenesis in adult subjects with cleft lip and palate. Most of the relapse occurred during the first 6 months of post-distraction period, and after that the outcomes were stable.

Simultaneous sinus lifting and alveolar distraction of a severely atrophic posterior maxilla for oral rehabilitation with dental implants

We retrospectively reviewed a new preimplantation regenerative augmentation technique for a severely atrophic posterior maxilla using sinus lifting with simultaneous alveolar distraction, together with long-term oral rehabilitation with implants. We also analyzed the regenerated bone histomorphologically. This study included 25 maxillary sinus sites in 17 patients. The technique consisted of alveolar osteotomy combined with simultaneous sinus lifting. After sufficient sinus lifting, a track-type vertical alveolar distractor was placed. Following a latent period, patient self-distraction was started. After the required augmentation was achieved, the distractor was left in place to allow consolidation. The distractor was then removed, and osseointegrated implants (average of 3.2 implants per sinus site, 80 implants) were placed. Bone for histomorphometric analysis was sampled from six patients and compared with samples collected after sinus lifting alone as controls (n = 4). A sufficient alveolus was regenerated, and all patients achieved stable oral rehabilitation. The implant survival rate was 96.3% (77/80) after an average postloading followup of 47.5 months. Good bone regeneration was observed in a morphological study, with no significant difference in the rate of bone formation compared with control samples. This new regenerative technique could be a useful option for a severely atrophic maxilla requiring implant rehabilitation.

Análise da influência do ultrassom de baixa intensidade na região de reparo ósseo em ratos sob ausência de carga

Há evidências de que o ultrassom (US) de baixa intensidade pode acelerar a regeneração óssea. Este trabalho objetivou verificar a ação do US no defeito ósseo, criado experimentalmente em tíbias de ratos sob ausência de carga. Vinte Rattus novergicus albinus, Wistar adultos, divididos em: G1 (n=10), grupo experimental de 15 dias sem suspensão, e G2 (n=10), grupo experimental de 15 dias suspenso pela cauda, foram submetidos à osteotomia em ambas as tíbias e à aplicação do US, frequência de 1,5 MHz, ciclo de trabalho 1:4, 30 mW/cm², nas tíbias direitas por 12 sessões de 20 minutos. Após o sacrifício, as tíbias foram submetidas à análise da Densidade Mineral Óssea (DMO). Os resultados demonstraram DMO de 0,139±0,018 g/cm² para tíbia tratada; 0,131±0,009 g/cm² para tíbia controle no G1; e no G2 registrou-se 0,120±0,009 g/cm² para tíbia tratada e 0,106±0,017 g/cm² para tíbia controle. Houve diferença significante entre os grupos nos quais o G2 apresentou menor DMO, o que demonstra que a suspensão prejudica a manutenção das propriedades ósseas, e entre as tíbias tratadas e controles do G2, demonstrando que o US acelerou o processo de reparo, concluindo que a impossibilidade do estímulo mecânico causada pela não deambulação em um processo de reparo ósseo pode ser minimizada pela ação do US. No G1, a aplicação do US não teve influência significante no aumento da DMO, talvez pelo fato dos animais já terem estímulo mecânico suficiente à formação óssea.

Histomorphometric analysis of new bone obtained by osteogenic periosteal distraction in ovariectomized rabbits

OBJECTIVE

The aim of this study was to evaluate the effects of estrogen deficiency on newly formed bone obtained by osteogenic periosteal distraction histomorphometrically.

STUDY DESIGN

Thirty-six female rabbits were divided into 2 groups. The experimental group underwent a bilateral ovariectomy and a sham operation was applied to the control group to equalize the stress of ovariectomy surgery. Four weeks postoperatively, a gradual distraction of the mandibular corpus was performed.

RESULTS

In the experimental group, callus formation was delayed and the new bone was less mineralized; conversely, when histomorphometric measurements were compared statistically, there were no significant differences between the ovariectomized and sham-operated subgroups in the mean extent of newly formed bone tissue.

CONCLUSIONS

Although osteoporosis caused by the lack of estrogen has negative effects on osteogenic periosteal distraction (OPD), these negative effects do not appear to present a contraindication to OPD.

Microarray analysis of human adipose-derived stem cells in three-dimensional collagen culture: osteogenesis inhibits bone morphogenic protein and Wnt signaling pathways, and cyclic tensile strain causes upregulation of proinflammatory cytokine regulators and angiogenic factors

Human adipose-derived stem cells (hASC) have shown great potential for bone tissue engineering. However, the molecular mechanisms underlying this potential are not yet known, in particular the separate and combined effects of three-dimensional (3D) culture and mechanical loading on hASC osteogenesis. Mechanical stimuli play a pivotal role in bone formation, remodeling, and fracture repair. To further understand hASC osteogenic differentiation and response to mechanical stimuli, gene expression profiles of proliferating or osteogenically induced hASC in 3D collagen I culture in the presence and absence of 10% uniaxial cyclic tensile strain were examined using microarray analysis. About 847 genes and 95 canonical pathways were affected during osteogenesis of hASC in 3D culture. Pathway analysis indicated the potential roles of Wnt/β-catenin signaling, bone morphogenic protein (BMP) signaling, platelet-derived growth factor (PDGF) signaling, and insulin-like growth factor 1 (IGF-1) signaling in hASC during osteogenic differentiation. Application of 10% uniaxial cyclic tensile strain suggested synergistic effects of strain with osteogenic differentiation media on hASC osteogenesis as indicated by significantly increased calcium accretion of hASC. There was no significant further alteration in the four major pathways (Wnt/β-catenin, BMP, PDGF, and IGF-1). However, 184 transcripts were affected by 10% cyclic tensile strain. Function and network analysis of these transcripts suggested that 10% cyclic tensile strain may play a role during hASC osteogenic differentiation by upregulating two crucial factors in bone regeneration: (1) proinflammatory cytokine regulators interleukin 1 receptor antagonist and suppressor of cytokine signaling 3; (2) known angiogenic inductors fibroblast growth factor 2, matrix metalloproteinase 2, and vascular endothelial growth factor A. This is the first study to investigate the effects of both 3D culture and mechanical load on hASC osteogenic differentiation. A complete microarray analysis investigating both the separate effect of soluble osteogenic inductive factors and the combined effects of chemical and mechanical stimulation was performed on hASC undergoing osteogenic differentiation. We have identified specific genes and pathways associated with mechanical response and osteogenic potential of hASC, thus providing significant information toward improved understanding of our use of hASC for functional bone tissue engineering applications.

Anisotropic mechanical properties of ovine femoral periosteum and the effects of cryopreservation

The mechanical properties of periosteum are not well characterized. An understanding of these properties is critical to predict the environment of pluripotent and osteochondroprogenitor cells that reside within the periosteum and that have been shown recently to exhibit a remarkably rapid capacity to generate bone de novo. Furthermore, the effects of cryopreservation on periosteal mechanical properties are currently unknown. We hypothesized that the periosteum is pre-stressed in situ and that the periosteum exhibits anisotropic material properties, e.g. the elastic modulus of the periosteum depends significantly on the direction of loading. We measured the change in area, axial length, and circumferential length of anterior, posterior, medial, and lateral fresh periosteal samples removed from underlying bone (t=0-16 h) as well as the average strain in axially and circumferentially oriented anterior periosteal samples subjected to tensile strain (0.004 mm/s) until failure. The elastic modulus was calculated from the resulting stress-strain curves. Tensile testing was repeated with axially aligned samples that had been slowly cryopreserved for comparison to fresh samples. Periosteal samples from all aspects shrank 44-54%, 33-47%, and 9-19% in area, axial length, and circumferential length, respectively. At any given time, the periosteum shrank significantly more in the axial direction than the circumferential direction. Tensile testing showed that the periosteum is highly anisotropic. When loaded axially, a compliant toe region of the stress-strain curve (1.93±0.14 MPa) is followed by a stiffer region until failure (25.67±6.87 MPa). When loaded circumferentially, no toe region is observable and the periosteum remained compliant until failure (4.41±1.21 MPa). Cryopreservation had no significant effect on the elastic modulus of the periosteum. As the periosteum serves as the bounding envelope of the femur, anisotropy in periosteal properties may play a key role in modulating bone growth, healing and adaptation, in health, disease, and trauma.

Net change in periosteal strain during stance shift loading after surgery correlates to rapid de novo bone generation in critically sized defects

In an ovine femur model, proliferative woven bone fills critically sized defects enveloped by periosteum within 2 weeks of treatment with the one-stage bone-transport surgery. We hypothesize that mechanical loading modulates this process. Using high-definition optical strain measurements we determined prevailing periosteal strains for normal and surgically treated ovine femora subjected ex vivo to compressive loads simulating in vivo stance shifting (n = 3 per group, normal vs. treated). We determined spatial distribution of calcein green, a label for bone apposition in first the 2 weeks after surgery, in 15°, 30°, and 45° sectors of histological cross sections through the middle of the defect zone (n = 6 bones, three to four sections per bone). Finally, we correlated early bone formation to either the maximal periosteal strain or the net change in maximal periosteal strain. We found that treatment with the one-stage bone-transport surgery profoundly changes the mechanical environment of cells within the periosteum during stance shift loading. The pattern of early bone formation is repeatable within and between animals and relates significantly to the actual strain magnitude prevailing in the periosteum during stance shift loading. Interestingly, early bone apposition after the surgery correlates well to the maximal net change in strain (above circa 2000-3000 με, in tension or compression) rather than strain magnitude per se, providing further evidence that changes in cell shape may drive mechanoadaptation by progenitor cells. These important insights regarding mechanobiological factors that enhance rapid bone generation in critically sized defects can be translated to the tissue and organ scale, providing a basis for the development of best practices for clinical implementation and the definition of movement protocols to enhance the regenerative effect.

"Transport distraction osteogenesis for reconstruction of mandibular defects": our experience

INTRODUCTION

Mandibular defects usually involve a combination of osseous and soft tissue deficiency and are among the most challenging problems in maxillofacial surgery, many options are available for mandibular reconstruction. One of the options discussed in literature recently being distraction osteogenesis.

AIM AND OBJECTIVE

The aims and objectives of the study were to evaluate clinically the technique of distraction osteogenesis to reconstruct mandibular defects, using indigenous transport distractors, and to evaluate the efficacy of Indigenous transport distraction osteogenesis device.

MATERIALS AND METHODS

A prospective, experimental study was designed to examine the use of transport distraction osteogenesis in the treatment of defects of the mandible. Four patients with defects of the mandible were subjected to distraction osteogenesis with indigenously manufactured distraction device. The regenerate was assessed clinically and radiographically.

RESULTS

The results showed that the regenerate was clinically as hard as the adjacent unaffected mandible and radiologic evidence of bone regeneration was observed. The major advantage being regeneration of hard tissue and soft tissue components without the morbidity of donor site, so that functional rehabilitation of the patient is possible.

CONCLUSION

Thus from our study it is shown that transport distraction osteogenesis using indigenous distractors is a reliable yet affordable option for reconstruction of mandibular defects.

Multiscale mechanobiology of de novo bone generation, remodeling and adaptation of autograft in a common ovine femur model

The link between mechanics and biology in the generation and the adaptation of bone has been studied for more than a century in the context of skeletal development and fracture healing. However, the interplay between mechanics and biology in de novo generation of bone in postnatal defects as well as healing of morcellized bone graft or massive cortical bone autografts is less well understood. To address this, here we integrate insights from our previously published studies describing the mechanobiology on both de novo bone generation and graft healing in a common ovine femoral defect model. Studying these effects in a common experimental model provides a unique opportunity to elucidate factors conducive to harnessing the regenerative power of the periosteum, and ultimately, to provide mechanistic insights into the multiscale mechanobiology of bone generation, remodeling and adaptation. Taken together, the studies indicate that, as long as adequate, directional transport of cells and molecules can be insured (e.g. with periosteum in situ or a delivery device), biological factors intrinsic to the periosteum suffice to bridge critical sized bone defects, even in the absence of a patent blood supply. Furthermore, mechanical stimuli are crucial for the success of periosteal bone generation and bone graft healing. Interestingly, areas of highest periosteal strain around defects correlate with greatest amounts albeit not greatest mineralization of newly generated bone. This may indicate a role for convection enhanced transport of cells and molecules in modulation of tissue generation by pluripotent cells that ingress into the defect center, away from the periosteum and toward the surface of the intramedullary nail that fills the medullary cavity. These insights bring us much closer to understanding the mechanobiological environment and stimuli that stimulate the proliferation and differentiation of periosteum-derived progenitor cells and ultimately drive the generation of new bone tissue. Furthermore, these insights provide a foundation to create virtual predictive computational models of bone mechanophysiology, to develop cell seeding protocols for scale up and manufacture of engineered tissues, to optimize surgical procedures, and to develop post-surgical therapies with the ultimate goal of achieving the best possible healing outcomes for treatment and/or reconstruction of postnatal bone defects.

NELL1 promotes high-quality bone regeneration in rat femoral distraction osteogenesis model

NELL1 (NEL-like molecule-1; NEL [a protein strongly expressed in neural tissue encoding epidermal growth factor like domain]) is a cranisynostosis-associated molecule directly regulated by Runx2, the master molecule in controlling osteoblastic differentiation. NELL1 has exhibited potent osteoinductive activity for bone regeneration in several animal models. However, its capacity for promoting repair of long-bone defects remains unknown. In this study, we investigated the osteogenic effects of NELL1 on femoral distraction osteogenesis using adenoviral gene delivery and multiple approaches of in vivo analysis. Thirty Sprague-Dawley (SD) rats were randomly assigned to 3 groups for treatment (n=10 each): adenovirus-green fluorescent protein (Ad-GFP)-NELL1 or Ad-GFP at 1×10⁹ plaque-forming units/ml diluted in saline, or saline alone. The femoral distraction was at a speed of 0.25 mm every 12h for 14 days, and a single injection of Ad-GFP-NELL1 or Ad-GFP was given at the mid-distraction period. The effective NELL1 delivery in vivo after Ad-GFP-NELL1 injection was evaluated by optical imaging. The bone regeneration was assessed quantitatively at days 21, 28, 42, and 56 by live 3-D micro-computed tomography (micro-CT), and animals were sacrificed at day 56 for biomechanical testing and histological analysis. Exogenous NELL1 was expressed in the distracted gap for at least 14 days after Ad-GFP-NELL1 transfection. The bone union rate in the distracted gap was significantly higher with Ad-GFP-NELL1 than with Ad-GFP (9/9 vs. 4/9 rats) or saline alone (5/9 rats) at day 56. The serial 3-D micro-CT images and quantitation obtained with the development and application of radiolucent external fixators showed less callus but more mature cortical bones formed with Ad-GFP-NELL1 than with Ad-GFP transfection and saline administration during distraction osteogenesis. The biomechanical properties of femur samples with Ad-GFP-NELL1 transfection were better than samples with Ad-GFP transfection or saline treatment, and were similar with unoperated femurs. Histology revealed cartilaginous tissues in the middle of distraction gaps with Ad-GFP transfection and saline treatment but only bony bridges with Ad-GFP-NELL1 transfection at the final time point (day 56). Coincidently, the expression of Runx2, BMP2, and BMP7 did not differ among groups at day 56, whereas the expression of osteocalcin and osteopontin was slightly higher with Ad-GFP-NELL1 transfection. Thus, sustained Ad-NELL1 protein delivery into a local area of a rat femoral distraction osteogenesis model remarkably improved regeneration of good-quality bones and accelerated bone union at a high rate. Acquiring serial micro-CT data during rat femoral distraction osteogenesis and regional adenovirus delivery of NELL1 may facilitate future in vivo studies.