Bone Morphogenetic Protein-2 Sustained Delivery by Hydrogels with Microspheres Repairs Rabbit Mandibular Defects

Mandible defect is a difficult issue in dental surgery owing to limited therapeutic options. Recombinant human bone morphogenetic protein-2 (rhBMP2) is osteoinductive in bone regeneration. This article prepared chitosan/collagen hydrogels with rhBMP2-incorporated gelatin microsphere (GMs) for a sustained release of rhBMP2 to induce bone regeneration in rabbits. In experiments, mandibular defects of 8 mm in diameter and 3 mm in depth were surgically prepared on the right cheek of 27 rabbits. Either chitosan/collagen hydrogels alone, rhBMP2-incorporated hydrogels, or hydrogels with rhBMP2-incorporated GMs were implanted to the defect sites. The animals were euthanized at 2, 6, 12 weeks following surgery. In results, scanning electronic microscope images revealled spherical GMs. The complex delivery systems, hydrogels with rhBMP2-incorporated GMs, exhibited ideal release profiles in vitro. The complex delivery systems resulted in apparent new bone formation within 12 weeks, as evidenced by computed tomography and histological observations. All these results demonstrated that the chitosan/collagen hydrogels with rhBMP2-incorporated GMs had a better capacity to heal mandible defects than other two hydrogel scaffolds. Chitosan/collagen hydrogels with rhBMP2-incorporated GMs might be potential carriers of rhBMP2 for accelerating the repair of mandibular defects.

Study of bone-screw surface fixation in lumbar dynamic stabilization / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>We aimed to use the animal model of dynamic fixation to examine the interaction of the pedicle screw surface with surrounding bone, and determine whether pedicle screws achieve good mechanical stability in the vertebrae.</p><p><b>METHODS</b>Twenty-four goats aged 2-3 years had Cosmic ® pedicle screws implanted into both sides of the L2-L5 pedicles. Twelve goats in the bilateral dynamic fixation group had fixation rods implanted in L2-L3 and L4-L5. Twelve goats in the unilateral dynamic fixation group had fixation rods randomly fixed on one side of the lumbar spine. The side that was not implanted with fixation rods was used as a static control group.</p><p><b>RESULTS</b>In the static control group, new bone was formed around the pedicle screw and on the screw surface. In the unilateral and bilateral dynamic fixation groups, large amounts of connective tissue formed between and around the screw threads, with no new bone formation on the screw surface; the pedicle screws were loose after the fixed rods were removed. The bone mineral density and morphological parameters of the region of interest (ROI) in the unilateral and bilateral dynamic fixation group were not significantly different (P > 0.05), but were lower in the fixed groups than the static control group (P < 0.05). This showed the description bone of the ROI in the static control group was greater than in the fixation groups. Under loading conditions, the pedicle screw maximum pull force was not significantly different between the bilateral and unilateral dynamic fixation groups (P > 0.05); however the maximum pull force of the fixation groups was significantly less than the static control group (P < 0.01).</p><p><b>CONCLUSIONS</b>Fibrous connective tissue formed at the bone-screw interface under unilateral and bilateral pedicle dynamic fixation, and the pedicle screws lost mechanical stability in the vertebrae.</p>

Age-related differences in the biological parameters of vertebral cancellous bone from Chinese women / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>With aging, the human fracture risks gradually increase. This is mainly due to the corresponding changes of the biomechanical parameters of human bone presents with aging. We measured the microstructural parameters of lumbar bone from women in several age groups by micro-computed tomography and scanning electron microscopy. We observed changes in lumbar cancellous bone mineral density and in biomechanical parameters with aging to elucidate the relationship between age and risk of fracture. We provide theoretical support for human pathology, fracture risk increased with age and the individualized of each age group.</p><p><b>METHODS</b>Thirty-two fresh L3 vertebral bodies were donated from 32 women, aged 20-59 years and were divided into four age groups: 20 to 29 years (group A); 30 to 39 years (group B); 40 to 49 years (group C); and 50 to 59 years (group D). Conventional lumbar separation was performed by removing soft tissue and subsidiary structures, leaving only the vertebral body. The vertebral body was cut into halves along the median sagittal plane, maintaining the upper and lower end-plates of each half, and used for biomechanical, morphological, and density measurements.</p><p><b>RESULTS</b>Comparing group A to B, the rod-like trabecular thickness (Tb.Th) decreased; the trabecular spacing (Tb.Sp) increased; the plate-like Tb.Th decreased; bone mineral density, tissue mineral density, bone volume fraction, and bone surface fraction decreased, and the elastic modulus and the ultimate stress decreased (all changes P < 0.05). Similar significant (P < 0.05) trends were obtained when comparing group C to D. With aging, the collagen cross-linking capacity declined, the thickness of the collagen fibrils was variable (ranging from almost the same to loose, sparse, or disordered), and the finer collagen fibrils between the thick filaments were disorganized.</p><p><b>CONCLUSIONS</b>In women aged 20 to 59 years, the rod-like and plate-like Tb.Th of the vertebral body decreased, while Tb.Sp increased. Additionally, the density, elastic modulus, and ultimate stress of the cancellous bone decreased with age. These associated changes in bone microstructure, density, and biomechanics with age may lead to an increasing risk of osteoporosis and fracture.</p>

Inhibition of Nogo expression to promote repair after spinal cord injury / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>One of the reasons for poor neuroregeneration after central nervous system injury is the presence of inhibitory factors such as Nogo. Here, we tested the inhibition of Nogo by RNA interference both in vitro and in vivo, using recombinant adenovirus-mediated transfection of short hairpin RNAs, to explore a new method of treatment for spinal cord injury.</p><p><b>METHODS</b>We designed and cloned two Nogo-specific short hairpin RNAs and an unrelated short hairpin RNA, packaged the clones into adenovirus, and amplified the recombinant virus in 293 cells. We then tested the inhibition of Nogo expression both in vitro in adenovirus-transfected oligodendrocytes and in vivo in spinal cord tissue from adenovirus-transfected spinal cord injury model rats. We tested Nogo expression at the mRNA level by reverse-transcription PCR and at the protein level by Western blotting and immunohistochemistry.</p><p><b>RESULTS</b>In vitro, the two specific Nogo short hairpin RNAs decreased Nogo mRNA expression by 51% and 49%, respectively, compared with Nogo expression in cells transfected with the unrelated control small hairpin RNA (P < 0.005). Similarly, Nogo protein expression decreased by 50% and 48%, respectively (P < 0.005). In vivo, in spinal cord injury model rats, the two specific Nogo short hairpin RNAs decreased Nogo mRNA expression by 45% and 40%, respectively, compared with Nogo expression in spinal cord injury model rats transfected with the unrelated control short hairpin RNA (P < 0.005). The Nogo protein level was similarly decreased.</p><p><b>CONCLUSIONS</b>We were successful in specifically downregulating Nogo at the mRNA and protein levels by adenovirus-mediated delivery of short hairpin RNAs, both in vitro and in vivo. This confirms the effectiveness of RNA interference for the inhibition of Nogo gene expression and the efficiency of using adenovirus for delivery. Thus gene therapy may be an effective treatment for spinal cord injury.</p>

In vivo study of extracellular matrix coating enhancing fixation of the pedicle screw-bone's interface / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Based on in vivo research on the effect of the coating of the extracellular matrix composition of pedicle screws on the conduction and induction of bone formation in young sheep, the aim of this study was to investigate the application of coated pedicle screws in sheep with scoliosis whose spines are under constant development.</p><p><b>METHODS</b>Four groups of pedicle screws were randomly implanted into bilateral L2-L5 pedicles of 2.5- to 3-month-old sheep. A static experiment was performed on one side and a loading test was performed on the other side by implanting connecting rods at the L2-L3 and L4-L5 segments. The changes in the force on the coated screws and the combination of the surface of the coated screws with the surrounding bone in the growth process of young sheep's spines with aging were observed. After 3 months, the lumbar vertebrae with the screws were removed and examined by micro-CT, histological, and biomechanical analyses.</p><p><b>RESULTS</b>Under nonloading conditions, there is bone formation around the surfaces of coated screws. The bone forming on the surface of collagen/chondroitin sulfate/hydroxyapatite coating of pedicle screws is the most, the one of the collagen/chondroitin sulfate coating and hydroxyapatite coating is followed, and no significant difference between the two groups. In terms of the trabecular bone morphology parameters of the region of interest around the surface of the pedicle screws, such as bone mineral content, bone mineral density, tissue mineral content, tissue bone mineral density, bone volume fraction, and connection density, those associated with collagen/chondroitin sulfate/hydroxyapatite coatings are largest and those unassociated with coatings are smallest. Under nonloading conditions, the pullout strength of the collagen/chondroitin sulfate/hydroxyapatite-coated screws was largest, and that of the uncoated screws was minimal (P < 0.01). Under loading conditions, the maximum pullout strength of each group of pedicle screws was less than that of the pedicle screws in the nonloading state (P < 0.01) with no significant difference between the groups (P > 0.05).</p><p><b>CONCLUSIONS</b>Under nonloading conditions, the coatings of both organic and inorganic components of the extracellular matrix of titanium pedicle screws can conduct or induce bone formation around the surface of the screws. The ability of collagen/chondroitin sulfate/hydroxyapatite coatings to induce bone formation is stronger; under loading conditions, a large amount of connective tissue formed around the surfaces of the screws in each group. No significant differences were found between the groups.</p>

Feasibility of vertebral internal fixation using deer and sheep as animal models / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Studies on new vertebral internal fixations of animals are very important prior to clinical application. This study aimed to determine the feasibility of vertebral internal fixation on morphologic and biomechanical properties using deer and sheep as animal models and comparing to human data.</p><p><b>METHODS</b>Thirty sets of fresh Sika deer lumbar, 30 sets of fresh sheep lumbar, and 20 sets of fresh lumbar from male cadavers were used. We examined the morphology of the centra and pedicles of the three groups, and determined the cancellous bone density and biomechanical properties in all groups.</p><p><b>RESULTS</b>There were marked differences in all parameters measured between the different species. The sizes of the upper, middle, and lower transverse diameter were largest in the human, followed by the deer, then the sheep. The index of centrum transverse diameters and sagittal diameters were less than 0.8 (a triangle), and the deer was more similar to the human. The heights of the right vertebral pedicles and the anterior disc heights (IDH) were largest in the human, followed by the deer, then the sheep. The apparent density, elastic modulus, and ultimate load were largest in the sheep, followed by the deer, then the human. The range of motion (ROM) of functional lumbar units (FLUs) with a combined flexion-extension moment was largest in the human, followed by the deer then the sheep.</p><p><b>CONCLUSIONS</b>The deer lumbar is more similar to that of human in anatomical form and biomechanics than the sheep lumbar. As such, deer is more appropriate as an animal model for use in vertebral internal fixation studies.</p>