Intervertebral disk-like biphasic scaffold-demineralized bone matrix cylinder and poly(polycaprolactone triol malate)-for interbody spine fusion

A Novel Modality for Functional Imaging in Acute Intervertebral Disk Herniation via Tracking Leukocyte Infiltration

PURPOSE

Inflammation plays a key role in the progression of intervertebral disk (IVD) herniation and associated low back pain. However, real-time spatial diagnosis of inflammation associated with acute disk herniation has not been investigated. We sought to detect local neutrophil and macrophage infiltration near disk herniation via the formyl peptide receptor 1 (FPR1)-mediated molecular imaging in a disk puncture mouse model to elucidate pathophysiological process of disk herniation.

PROCEDURES

Disk herniation was induced in mouse with an established needle puncture procedure. Degenerative change of disk and infiltration of neutrophils and macrophages were detected with Safranin-O, hematoxylin and eosin (H&E), and immunohistochemical staining after injury. FPR1-specific imaging probes cFLFLF-PEG-Cy7 and [^99mTc]HYNIC-PEG-cFLFLF were administered systemically to sham and disk injury mice. Leukocyte infiltration was tracked by in vivo near-infrared fluorescence (NIRF) and single-photon emission tomography (SPECT) imaging. The peptide-receptor binding specificity was further investigated with FPR1^-/- mice via ex vivo NIRF scan and in vitro binding assays.

RESULTS

Safranin-O staining exhibited disorganized disk structure and loss of proteoglycan after puncture. Massive inflammatory cells were observed in the anterior region of punctured annulus in the injury group. The majority of neutrophils were detected at 1 through 3 days, while infiltration of macrophages appeared the most at 7 days after injury. NIRF and SPECT images revealed preferential accumulation of cFLFLF probes in herniation site in wild-type mice but not in FPR1^-/- mice. Binding of the cFLFLF peptide to FPR1 was also observed in RAW 267.4 cells and macrophages isolated from wild-type mice, whereas much less signal was observed in macrophages from FPR1^-/- mice. The presence of macrophage infiltration was also detected in human-herniated disk samples by immunohistochemistry.

CONCLUSION

For the first time, leukocyte infiltration around acute disk herniation site was detected directly and non-invasively in a timely fashion using FPR1-targeted molecular imaging modalities. Such functional imaging of disk herniation via infiltrated leukocytes would advance the understanding of etiology and facilitate drug delivery and treatment monitoring of disk herniation.

Regenerative Intervertebral Disc Endplate Based on Biomimetic Three-dimensional Scaffolds

STUDY DESIGN

Fabrication and characterization of a regenerative intervertebral disc (IVD) cartilaginous endplate (CEP) based on tissue culturing on biomimetic scaffolds.

OBJECTIVE

To fabricate a regenerative CEP to support nutrients and metabolites exchange between IVD and the milieu interior.

SUMMARY OF BACKGROUND DATA

CEP is the only pathway for most cells inside IVD to obtain nutrients and to eliminate metabolites. However, CEP usually fails at the same time when IVD degenerates. Therefore, reconstruction of CEP becomes an inevitable part of IVD regeneration. In this work, a novel regenerative CEP is fabricated to support nutrients and metabolites exchange of IVD.

METHODS

Three-dimensional scaffolds were fabricated by crosslinking of hyaluronic acid, chondroitin sulfate, and type II collagen. Then chondrocytes were cultured on the scaffolds. The obtained tissue was then investigated by scanning electron microscope, mechanical tests, and immunohistochemistry tests. In the end, glucose and lactic acid diffusion was carried out to test its nutrients and metabolites exchanging property.

RESULTS

Scanning electron microscopy investigations show that the 3-dimensional scaffold has microporous structure. After cell culturing, the inner structure of the obtained product becomes compact. Mechanical tests show that the obtained tissue has strong mechanical property. Immunohistochemistry tests show that the chemical compositions of the fabricated regenerative CEP are the same as its natural counterpart. Moreover, glucose and lactic acid diffuse through the regenerative CEP successfully.

CONCLUSION

The fabricated regenerative CEP shows features similar to its natural counterpart. As the most important function, nutrients and metabolites exchange is verified on it as well. This regenerative CEP may play an important role in overall fabrication of regenerative IVD in near future.

LEVEL OF EVIDENCE

N/A.

Detecting Chronic Post-Traumatic Osteomyelitis of Mouse Tibia via an IL-13Rα2 Targeted Metallofullerene Magnetic Resonance Imaging Probe

Differential diagnosis of chronic post-traumatic osteomyelitis (CPO) from aseptic inflammation remains challenging, since both pathological processes share similar clinical symptoms. Here we utilized a novel targeted metallofullerene nanoparticle based magnetic resonance imaging (MRI) probe IL-13-TAMRA-Gd₃N@C₈₀(OH)₃₀(CH₂CH₂COOH)₂₀ to detect CPO in mouse tibia via overexpressed IL-13Rα2 receptors. The functionalized metallofullerene was characterized by X-ray photoelectron spectroscopy. Upon lipopolysaccharide (LPS) stimulation, macrophage Raw 264.7 cells showed elevated IL-13Rα2 expression via immunofluorescence staining and increased MRI probe binding via built-in TAMRA fluorescence imaging. Trauma was induced in both tibia of mice and bacteria soaked suture was inserted into the right tibia to initiate infection. During the acute phase (1.5 weeks), luminol-bioluminescence imaging revealed much higher myeloperoxidase activity in the infected tibia compared to the sham. In the chronic phase (4 weeks), X-ray radiography illustrated bone deformation in the infected tibia compared to the sham. With T₁ weighted sequences, the probe clearly exhibited hyperintensity in the infection foci at both acute and chronic phases, which was not observed in the sham tibia. Histological analysis revealed severe bone structural destruction and massive inflammatory cell infiltration in the infected tibia. Immunohistochemistry confirmed abundant expression of IL-13Rα2 in the infection site. In summary, we developed a noninvasive imaging approach to detect and differentiate CPO from aseptic inflammation using a new IL-13Rα2 targeted metallofullerene MRI probe. In addition, for the first time, IL-13Rα2 was investigated as a unique biomarker in the context of osteomyelitis. Our data established a foundation for the translational application of this MRI probe in the clinical differentiation of CPO.

A novel culture platform for fast proliferation of human annulus fibrosus cells

Tissue engineering provides a promising approach to treat degenerative disc disease, which usually requires a large quantity of seed cells. A simple and reliable in vitro culture system to expand seed cells in a timely fashion is necessary to implement the application clinically. Here, we sought to establish a cost-effective culture system for expanding human annulus fibrosus cells using extracellular matrix (ECM) proteins as culture substrates. Cells were cultured onto a plastic surface coated with various types of ECMs, including fibronectin, vitronectin, collagen type I, gelatin and cell-free matrix deposited by human nucleus pulposus cells. AF cell morphology, growth, adhesion and phenotype (anabolic and catabolic markers) were assessed by microscopy, real-time RT-PCR, western blotting, zymography, immunofluorescence staining and biochemical assays. Fibronectin, collagen and gelatin promoted cell proliferation and adhesion in a dose-dependent manner. Fibronectin elevated mRNA expression of proteoglycan and enhanced glycosaminoglycan production. Both collagen and gelatin increased protein expression of type II collagen. Consistent with increased cell adhesion, collagen and fibronectin promoted formation of focal adhesion complexes in the cell-matrix junction, suggesting enhanced binding of the actin network with both ECM substrates. On the other hand, fibronectin, collagen and gelatin decreased expression of matrix metalloproteinase-2 and matrix metalloproteinase-9 in media. Finally, a mixture of fibronectin (1.7 μg/mL) and collagen (1.3 μg/mL) was identified as the most promising in vitro culture substrate system in promoting proliferation and maintaining anabolic-catabolic balance. Our method provides a simple and cost-effective platform for tissue engineering applications in intervertebral disc research.

[Synthesis and characteristics of integrated bionic mandibular condylar scaffold]

OBJECTIVE This study aims to construct a chitosan (CS)-polycaprolactone (PCL)-hydroxyapatite (HA) composite biomimetic scaffold to replace condyle and to explore the tissue engineering applications of condylar.

METHODS

A resin mold of the mandibular condyle was prepared by using rapid prototyping techniques. A mandibular condylar integrated biomimetic scaffold model was prepared by solution casting-ice Lek. PCL and CS were mixed at a ratio of 4:1. HA at quality ratios of 40%, 50%, 60%, and 70% was added to groups a, b, c, and d, respectively. The microscopic morphology, porosity, infrared spectra, X-ray diffraction pattern, and mechanical properties of the scaffold were observed.

RESULTS

The scaffold that includes both upper and lower parts displayed the same features (i.e., shape, yellow-white appearance, and hard texture) as the mandibular condyle. Scanning electron microscopy showed that the composite scaffold had a 3D network spatial structure, 70%-85% porosity, and 10-200 µm pore size. Infrared spectra showed that the peak intensity reduced with decreasing HA content. X-ray diffraction showed that the diffraction peak decreased with increasing HA content. Suitable tensile and compressive and flexural strength were discovered in the presence of 50% HA.

CONCLUSION

The scaffold prepared by solution casting-ice Lek shows favorable comprehensive features and is expected to replace human condylar.

[Synthesis and characteristics of integrated bionic mandibular condylar scaffold]

OBJECTIVE This study aims to construct a chitosan (CS)-polycaprolactone (PCL)-hydroxyapatite (HA) composite biomimetic scaffold to replace condyle and to explore the tissue engineering applications of condylar.

METHODS

A resin mold of the mandibular condyle was prepared by using rapid prototyping techniques. A mandibular condylar integrated biomimetic scaffold model was prepared by solution casting-ice Lek. PCL and CS were mixed at a ratio of 4:1. HA at quality ratios of 40%, 50%, 60%, and 70% was added to groups a, b, c, and d, respectively. The microscopic morphology, porosity, infrared spectra, X-ray diffraction pattern, and mechanical properties of the scaffold were observed.

RESULTS

The scaffold that includes both upper and lower parts displayed the same features (i.e., shape, yellow-white appearance, and hard texture) as the mandibular condyle. Scanning electron microscopy showed that the composite scaffold had a 3D network spatial structure, 70%-85% porosity, and 10-200 µm pore size. Infrared spectra showed that the peak intensity reduced with decreasing HA content. X-ray diffraction showed that the diffraction peak decreased with increasing HA content. Suitable tensile and compressive and flexural strength were discovered in the presence of 50% HA.

CONCLUSION

The scaffold prepared by solution casting-ice Lek shows favorable comprehensive features and is expected to replace human condylar.

Exchange hybrid cranioplasty using particulate bone graft and demineralized bone matrix: the best of both worlds

Reconstruction of craniofacial defects in children presents several challenges that are not encountered in the adult population. Autologous bone grafts have long been the criterion standard for repairing these defects. Recently, several new materials and techniques have expanded our arsenal of reconstructive options. In this clinical report, we describe the use of both particulate bone grafting and demineralized bone matrix together to repair craniofacial defects encountered in pediatric patients.

Fast degradable citrate-based bone scaffold promotes spinal fusion

It is well known that high rates of fusion failure and pseudoarthrosis development (5~35%) are concomitant in spinal fusion surgery, which was ascribed to the shortage of suitable materials for bone regeneration. Citrate was recently recognized to play an indispensable role in enhancing osteconductivity and osteoinductivity, and promoting bone formation. To address the material challenges in spinal fusion surgery, we have synthesized mechanically robust and fast degrading citrate-based polymers by incorporating N-methyldiethanolamine (MDEA) into clickable poly(1, 8-octanediol citrates) (POC-click), referred to as POC-M-click. The obtained POC-M-click were fabricated into POC-M-click-HA matchstick scaffolds by compositing with hydroxyapatite (HA) for interbody spinal fusion in a rabbit model. Spinal fusion was analyzed by radiography, manual palpation, biomechanical testing, and histological evaluation. At 4 and 8 weeks post surgery, POC-M-click-HA scaffolds presented optimal degradation rates that facilitated faster new bone formation and higher spinal fusion rates (11.2±3.7, 80±4.5 at week 4 and 8, respectively) than the poly(L-lactic acid)-HA (PLLA-HA) control group (9.3±2.4 and 71.1±4.4) (p<0.05). The POC-M-click-HA scaffold-fused vertebrates possessed a maximum load and stiffness of 880.8±14.5 N and 843.2±22.4 N/mm, respectively, which were also much higher than those of the PLLA-HA group (maximum: 712.0±37.5 N, stiffness: 622.5±28.4 N/mm, p<0.05). Overall, the results suggest that POC-M-click-HA scaffolds could potentially serve as promising bone grafts for spinal fusion applications.

A novel two-step sintering for nano-hydroxyapatite scaffolds for bone tissue engineering

In this study, nano-hydroxyapatite scaffolds with high mechanical strength and an interconnected porous structure were prepared using NTSS for the first time. The first step was performed using a laser characterized by the rapid heating to skip the surface diffusion and to obtain the driving force for grain boundary diffusion. Additionally, the interconnected porous structure was achieved by SLS. The second step consisted of isothermal heating in a furnace at a lower temperature (T₂) than that of the laser beam to further increase the density and to suppress grain growth by exploiting the difference in kinetics between grain-boundary diffusion and grain-boundary migration. The results indicated that the mechanical properties first increased and then decreased as T₂ was increased from 1050 to 1250°C. The optimal fracture toughness, compressive strength and stiffness were 1.69 MPam^1/2, 18.68 MPa and 245.79 MPa, respectively. At the optimal point, the T₂ was 1100°C, the grain size was 60 nm and the relative density was 97.6%. The decrease in mechanical properties was due to the growth of grains and the decomposition of HAP. The cytocompatibility test results indicated that cells adhered and spread well on the scaffolds. A bone-like apatite layer formed, indicating good bioactivity.

Therapeutic foam scaffolds incorporating biopolymer-shelled mesoporous nanospheres with growth factors

A novel therapeutic scaffolding system of engineered nanocarriers within a foam matrix for the long-term and sequential delivery of growth factors is reported. Mesoporous silica nanospheres were first functionalized to have an enlarged mesopore size (12.2nm) and aminated surface, which was then shelled by a biopolymer, poly(lactic acid) (PLA) or poly(ethylene glycol) (PEG), via electrospraying. The hybrid nanocarrier was subsequently combined with collagen to produce foam scaffolds. Bovine serum albumin (BSA), used as a model protein, was effectively loaded within the enlarged nanospheres. The biopolymer shell substantially prolonged the release period of BSA (2-3weeks from shelled nanospheres vs. within 1week from bare nanospheres), and the release rate was highly dependent on the shell composition (PEG>PLA). Collagen foam scaffolding of the shelled nanocarrier further slowed down the protein release, while enabling the incorporation of a rapidly releasing protein, which is effective for sequential protein delivery. Acidic fibroblast growth factor (aFGF), loaded onto the shelled-nanocarrier scaffolds, was released over a month at a highly sustainable rate, profiling a release pattern similar to that of BSA. The biological activity of the aFGF was evidenced by the significant proliferation of osteoblastic precursor cells in the aFGF-releasing scaffolds. Furthermore, the aFGF-delivering scaffolds implanted in rat subcutaneous tissue for 2weeks showed a substantially enhanced invasion of fibroblasts with a homogeneous population. Taken together, it is concluded that the biopolymer encapsulation of mesoporous nanospheres effectively prolongs the release of growth factors over weeks to a month, providing a nanocarrier platform for a long-term growth factor delivery. Moreover, the foam scaffolding of the nanocarrier system is a potential therapeutic three-dimensional matrix for cell culture and tissue engineering.

Annulus fibrosus cell characteristics are a potential source of intervertebral disc pathogenesis

In the end stage of intervertebral disc degeneration, cartilage, bone, endothelial cells, and neurons appear in association with the worsening condition. The origin of the abnormal cells is not clear. This study investigated the properties of progenitor cells in the annulus fibrosus (AF) using one in vitro and two in vivo models. Cultivation of rabbit AF cells with chondrogenic media significantly increased expressions of collagen and aggrecan. Upon exposure to osteogenic conditions, the cultures showed increased mineralization and expression of osteopontin, runx2, and bmp2 genes. Two models were used in the in vivo subcutaneous implantation experiments: 1) rabbit AF tissue in a demineralized bone matrix (DBM) cylinder (DBM/AF), and, 2) rat intact and needle punctured lumbar discs. Bone formation in the AF tissue was detected and hypertrophic chondrocytes and osteoblasts were present 1 month after implantation of the DBM/AF to nude mice. In addition to collagen I and II, immunostaining shows collagen X and osteocalcin expression in DBM/AF specimens 4 months after implantation. Similar changes were detected in the injured discs. Almost the entire needle punctured disc had ossified at 6 months. The results suggest that AF cells have characteristics of progenitor cells and, under appropriate stimuli, are capable of differentiating into chondrocytes and osteoblasts in vitro as well as in vivo. Importantly, these cells may be a target for biological treatment of disc degeneration.