Porous Bone Structure Research Articles

Multi-omics analyses reveal aberrant differentiation trajectory with WNT1 loss-of-function in type XV osteogenesis imperfecta.

Osteogenesis imperfecta (OI) is a group of severe genetic bone disorders characterized by congenital low bone mass, deformity, and frequent fractures. Type XV OI is a moderate to severe form of skeletal dysplasia caused by WNT1 variants. In this cohort study from southern China, we summarized the clinical phenotypes of patients with WNT1 variants and found that the proportion of type XV patients was around 10.3% (25 out of 243) with a diverse spectrum of phenotypes. Functional assays indicated that variants of WNT1 significantly impaired its secretion and effective activity, leading to moderate to severe clinical manifestations, porous bone structure, and enhanced osteoclastic activities. Analysis of proteomic data from human skeleton indicated that the expression of SOST (sclerostin) was dramatically reduced in type XV patients compared to patients with COL1A1 quantitative variants. Single-cell transcriptome data generated from human tibia samples of patients diagnosed with type XV OI and leg-length discrepancy, respectively, revealed aberrant differentiation trajectories of skeletal progenitors and impaired maturation of osteocytes with loss of WNT1, resulting in excessive CXCL12+ progenitors, fewer mature osteocytes, and the existence of abnormal cell populations with adipogenic characteristics. The integration of multi-omics data from human skeleton delineates how WNT1 regulates the differentiation and maturation of skeletal progenitors, which will provide a new direction for the treatment strategy of type XV OI and relative low bone mass diseases such as early onset osteoporosis.

Hollow Hydroxyapatite Microspheres Loaded with rhCXCL13 to Recruit BMSC for Osteogenesis and Synergetic Angiogenesis to Promote Bone Regeneration in Bone Defects.

Bone tissue engineering is a promising method to treat bone defects. However, the current methods of preparing composite materials that mimic the complex structure and biological activity of natural bone are challenging for recruitment of bone marrow mesenchymal stem cells (BMSCs), which affects the application of these materials in situ bone regeneration. Hollow hydroxyapatite microspheres (HHMs) possess a natural porous bone structure, good adsorption, and slow release of chemokines, but have low ability to recruit BMSCs and induce osteogenesis. In this study, The HHM/chitosan (CS) and recombinant human C-X-C motif chemokine ligand 13 (rhCXCL13)-HHM/CS biomimetic scaffolds that optimize bone regeneration and investigated their mechanism of BMSC recruitment and osteogenesis through cell and animal experiments and transcriptomic sequencing. Evaluate the physical characteristics of the HHM/CS and rhCXCL13-HHM/CS biomimetic scaffolds through Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), and the cumulative release curve of rhCXCL13. Transwell migration experiments and co-culture with BMSCs were conducted to study the recruitment ability and osteogenic differentiation of the scaffolds. Transcriptomic sequencing was performed to analyze the osteogenic differentiation mechanism. The osteogenesis and bone healing performance were evaluated using a rabbit radial defect model. SEM demonstrated that the rhCXCL13-HHM/CS scaffold comprised hydroxyapatite microspheres in a porous three-dimensional network. The rhCXCL13 showed excellent sustained release capability. The rhCXCL13-HHM/CS scaffold could recruit BMSCs and induce bone regeneration. Transcriptome sequencing and experimental results showed that the osteogenesis mechanism of rhCXCL13-HHM/CS was through the PI3K-AKT pathway. In vivo, the rhCXCL13-HHM/CS scaffold significantly promoted osteogenesis and angiogenesis at 12 weeks after surgery. The rhCXCL13-HHM/CS scaffold demonstrates excellent potential for BMSC recruitment, osteogenesis, vascularized tissue-engineered bone reconstruction, and drug delivery, providing a theoretical basis for material osteogenesis mechanism study and promising clinical applications for treating large bone defects.

Podosome-Driven Defect Development in Lamellar Bone under the Conditions of Senile Osteoporosis Observed at the Nanometer Scale.

The degradation mechanism of human trabecular bone harvested from the central part of the femoral head of a patient with a fragility fracture of the femoral neck under conditions of senile osteoporosis was investigated by high-resolution electron microscopy. As evidenced by light microscopy, there is a disturbance of bone metabolism leading to severe and irreparable damages to the bone structure. These defects are evoked by osteoclasts and thus podosome activity. Podosomes create typical pit marks and holes of about 300–400 nm in diameter on the bone surface. Detailed analysis of the stress field caused by the podosomes in the extracellular bone matrix was performed. The calculations yielded maximum stress in the range of few megapascals resulting in formation of microcracks around the podosomes. Disintegration of hydroxyapatite and free lying collagen fibrils were observed at the edges of the plywood structure of the bone lamella. At the ultimate state, the disintegration of the mineralized collagen fibrils to a gelatinous matrix comes along with a delamination of the apatite nanoplatelets resulting in a brittle, porous bone structure. The nanoplatelets aggregate to big hydroxyapatite plates with a size of up to 10 x 20 μm2. The enhanced plate growth can be explained by the interaction of two mechanisms in the ruffled border zone: the accumulation of delaminated hydroxyapatite nanoplatelets near clusters of podosomes and the accelerated nucleation and random growth of HAP nanoplatelets due to a nonsufficient concentration of process-directing carboxylated osteocalcin cOC.

Subsidence of Additively-ManufacturedCages in Foam Substrates: Effect of Contact Topology.

Subsidence of implants into bone is a major source of morbidity. The underlying mechanics of the phenomenon are not clear, but are likely related to interactions between contact stresses and the underlying porous trabecular bone structure. To gain insight into these interactions, we studied the penetration of three-dimensional (3D)-printed indenters with systematically varying geometries into Sawbones® foam substrates and isolated the effects of contact geometry from those of overall contact size and area. When size, contact area, and indented material stiffness and strength are controlled for, we show that resistance to penetration is in fact a function of topology only. Indenters with greater line contact lengths support higher subsidence loads in compression. These results have direct implications for the design of implants to resist subsidence into bone.

The first step of patient-specific design calvarial implant: A quantitative analysis of fresh parietal bones

Accurate knowledge of the fracture of cranial bone can provide insight into the prevention of skull fracture injuries and help aid the design of energy-absorbing head protection systems and safety helmets. When cranial bone needs to be removed or is lost, subsequent reconstruction of the defect is necessary to protect the underlying brain, or correct esthetic deformities, or both. Ideal reconstruction of defected bone is possible utilizing a biocompatible implant with a bone-like design individualized for the specific patient. The purpose of this study is to investigate the anatomical and mechanical characteristics of fresh frozen human parietal bones and determine compliance of polylactic acid-based personalized three-dimensional implants in terms of mechanical properties in order to replace such defective bones. Parietal bone specimens were extracted from 19 fresh frozen cadavers. Morphological parameters of individual bone specimens were measured using Image J software. Three-point bend tests were performed to extract Young’s modulus and tensile strength of the specimens from the measured force and displacement data by modeling the bone specimens as curved linear elastic beams. Also, three-point bend tests were performed to polylactic acid-based three-dimensional replicas mimicking geometry of the bone specimens in order to determine whether the material’s Young’s modulus and tensile strength properties comply with parietal bones. Entire fresh parietal specimens were observed to be comprised of a three-layered structure: external layers consisting of compact, high-density cortical bone and the central layer consisting of low-density, irregularly porous bone structure. Mean thickness of three-layered structure was 6.25 ± 1.46 mm. Mean Young’s modulus and tensile strength of the specimens were 1.40 ± 1.34 GPa and 44.56 ± 21.94 MPa, respectively where no statistically significant differences among genders were detected (p > 0.05). Mean Young’s modulus and tensile strength of the polylactic acid-based three-dimensional implants mimicking geometry of the bone specimens were 1.8 ± 0.7 GPa and 72.8 ± 2.5 MPa, respectively. Polylactic acid-based three-dimensional implants can be considered as acceptable candidates for temporary replacement of parietal defects in terms of mechanical properties. Level of Evidence: Not ratable.

Digital Image Correlation and nanoindentation in evaluation of material parameters of cancellous bone microstructure

Purpose: Purpose of this paper is to present the possibilities of the application of the two methods: Digital Image Correlation and nanoindentation in porous bone tissues testing. Firstly, as a tool in the evaluation process of material parameters for porous microstructures, such as bone tissues or other foams and, secondly, as validation and verification tools for finite element analysis of bone or foams structures. Those methods are helpful when the high accuracy of the mechanical parameters of porous microstructures is required.Design/methodology/approach: Two methods: Digital Image Correlation (DIC) and nanoindentation are used as an efficient approach in the evaluation process of material parameters or constitutive relationship of porous structures like bone tissues. Digital image correlation enlarges the accuracy of classical mechanical tests and the nanoindentation allows to look inside the microstructure.Findings: The proposed methods were found to be effective in experimental testing and material parameters evaluation process of some special materials. Among them are porous structures, such as bone tissue. Additionally, the DIC is an excellent tool for finite element model validation and results verification.Practical implications: The presented method based on the combination of the Digital Image Correlation and nanoindentation presents new possibilities in material testing fields, material behavior and parameters evaluation. They have great advantages, among others, in the field of testing of porous bone structure or determining the mechanical parameters of bone tissue.Originality/value: The paper presents methods for testing the complicated porous bone structures: evaluating mechanical behavior of the whole structure and evaluating mechanical properties of the single element of the structure. The mechanical parameters of human cancellous bone structures are presented as the preliminary research results.

Fabrication and Characterization of Three-Dimensional Electrospun Scaffolds for Bone Tissue Engineering

There are 600,000 bone-grafting procedures performed annually as a result of significant skeletal loss and bone deficiencies. This is an increasing worldwide medical issue as the average life expectancy increases 2–3 % annually. The current standards for bone treatment are autografts and allografts; both of which have drawbacks. Therefore, there is a need for alternative bone graft substitutes such as tissue-engineered grafts. Tissue engineering has emerged as a promising option for bone treatments by using biological or synthetic scaffolds to promote tissue regeneration. The advantages of this treatment include abundant supply and customizable features. The majority of scaffold fabrication techniques used in research focuses on mimicking the porous trabecular bone structure. A major characteristic of optimal scaffold integration and viability is vascularization, which is housed within the osteon canal of the cortical bone. Namely, there is a lack of tissue-engineered scaffolds for bone regeneration that mimic both trabecular and cortical bone structures. In this study, we combined two previously fabricated structures, sintered electrospun sheets and individual osteon-like scaffolds, to create scaffolds that mimic dual structural organization of the native bone with cortical and trabecular regions. Scaffolds were successfully mineralized in 10× simulated body fluid (SBF) up to 48 h with enhanced mineral distribution throughout the scaffolds. Mineralization for 24 h significantly increased mechanical properties of the scaffolds. In vitro studies performed over 28 days with mouse-pre-osteoblastic cells, MC3T3-E1s, proved that the mineralized scaffolds promoted cellular attachment, proliferation, and early stages of osteoblastic differentiation in comparison to the non-mineralized scaffolds. The implications of this study lead to the advancement of tissue-engineered mineralized trabecular and cortical bone scaffolds. The use of tissue-engineered scaffolds to harness a patients' own bone regenerative properties following traumatic bone loss has emerged as an alternative to current bone-grafting procedures. In this manuscript, the development and characterization process of a synthetic scaffold which mimics both the porous trabecular bone structure and dense cortical bone structure is discussed. Qualitative analysis confirmed the biomimetic porous structure necessary for nutrient transport and cellular infiltration and the cortical canal structure to house vascularization. Various mineralization techniques were investigated to determine the optimal mechanical properties. The scaffold also exhibited the ability to promote osteoblastic cellular attachment and proliferation. The mineral content deposited onto the scaffold led to an increase in osteoblastic behavior of the attached cells; suggesting early stages of osteogenesis. The results of this manuscript indicate the potential of utilizing a tissue-engineering scaffold as a promising treatment for bone tissue regeneration applications.

Biomimetic fabrication of a three-level hierarchical calcium phosphate/collagen/hydroxyapatite scaffold for bone tissue engineering

A three-level hierarchical calcium phosphate/collagen/hydroxyapatite (CaP/Col/HAp) scaffold for bone tissue engineering was developed using biomimetic synthesis. Porous CaP ceramics were first prepared as substrate materials to mimic the porous bone structure. A second-level Col network was then composited into porous CaP ceramics by vacuum infusion. Finally, a third-level HAp layer was achieved by biomimetic mineralization. The three-level hierarchical biomimetic scaffold was characterized using scanning electron microscopy, energy-dispersive x-ray spectra, x-ray diffraction and Fourier transform infrared spectroscopy, and the mechanical properties of the scaffold were evaluated using dynamic mechanical analysis. The results show that this scaffold exhibits a similar structure and composition to natural bone tissues. Furthermore, this three-level hierarchical biomimetic scaffold showed enhanced mechanical strength compared with pure porous CaP scaffolds. The biocompatibility and osteoinductivity of the biomimetic scaffolds were evaluated using in vitro and in vivo tests. Cell culture results indicated the good biocompatibility of this biomimetic scaffold. Faster and increased bone formation was observed in these scaffolds following a six-month implantation in the dorsal muscles of rabbits, indicating that this biomimetic scaffold exhibits better osteoinductivity than common CaP scaffolds.

The Design, Rapid Manufacture, and Materials of Artificial Porous Bone Structure

By using dexelization algorithms, the Brep model of artificial bone is transformed to the three direction DEXEL model and VOXEL model. By setting the transparence attributes of VOXELs in this VOXEL model, the artificial porous bone structures are designed. In order to preserve bio-activities of materials when we manufacture the artificial porous bone structure, the low-temperature deposition manufacturingLDM is used. By using the blended materials poly-lactic-coglycolic acid (PLGA) and tricalcium phosphate (TCP), we could manufacture the artificial porous bone structures.

Computer aided modeling and pore distribution of bionic porous bone structure

Artificial bone with porous structure is crucial for tissue scaffold and clinic implants. Scaffold provides structure support for cells and guides tissues regeneration for final tissue structure. A computational aided process of porous bone modeling was developed which described the design and fabrication of tissue scaffolds by considering intricate architecture, porosity and pore size. To simulate intricate bone structure, different constructive units were presented. In modeling process, bone contour was gotten from computed tomography (CT) images and was divided into two levels. Each level was represented by relatively reconstructive process. Pore size distribution was controlled by using mesh generation. The whole hexahedral mesh was reduced by unit structure, when a 3D mesh with various hexahedral elements was provided. The simulation results show that constructive structure of porous scaffold can meet the needs of clinic implants in accurate and controlled way

Synthesis and Electrochemical Characterization of Electrically Conductive Porous Alumina Composite Modified By Nickel and Platinum Nanoparticles

Thanks to highly porous bone structure and three-dimensional nano-carbon networks in electrically conductive porous alumina (CPA) prepared by the combination of gel-casting and reductive sintering in inert atmosphere, recently a surge of increasing interest has been attracted to develop its various potential applications especially as catalyst support. In this work, CPA-based composites prepared by decoration with nickel and platinum nanoparticles indicate its potential applications especially as fuel cells. By uniformly dispersion of nickel and platinum nanoparticles with small sizes around 10 nm and 20 nm respectively on the surface of CPA, an increased electrochemical performance can be observed in 1 M NaOH solution. Raman spectroscopy, Field-emission scanning electron microscope (FE-SEM) and X-ray photoelectron spectroscopy (XPS) have been employed to detect the changes of structure and morphology during modification. Moreover, electrochemical measurements results of cyclic voltammetry prove their improved electro-catalytic activities toward oxygen reductive reaction by comparing with the classical graphite electrode, which is mainly attributed to the unique structure and surface modification of CPA.

High‐intensity focused ultrasound as a potential treatment modality for heterotopic ossification.

Heterotopic ossification (HO) is the growth of bone in abnormal locations such as soft tissue. HO is a frequent secondary complication of common trauma, e.g., amputation or spinal cord injury. HO causes pain, motion restriction, and poor prosthetic fitting. Current HO treatments include non‐steroidal anti‐inflammatory drugs, radiation, surgery, and shock‐waves, but HO often returns. In this work, feasibility of HO treatment using high‐intensity focused ultrasound (HIFU) is studied. HIFU may induce destruction of HO nodules by a combination of thermal ablation and mechanical erosion through bubble activity. In preliminary experiments bone sections from rodent proximal tibiae embedded in polyacrylamide gel were used as tissue phantoms; subsequent experiments were performed on HO induced in a mouse calf muscle. A 2‐MHz focused transducer was used to generate pulses of shock waves with peak positive pressure of 67 MPa, duration of 10–100 ms, and 1%–10% duty cycle. High‐resolution microCT imaging of the samples was performed prior to and following HIFU exposure. Both mechanical damage of the porous bone structure and thermal denaturation of the bone were observed. The data obtained suggest that HIFU may be an option for non‐invasive treatment of HO. [Work supported by NSBRI_SMSTO1601 and NIH_DK007742].

Ultrasonic characterization of trabecular bone: Two scatterers’ population model

The paper describes the computer simulations allowing investigating the properties of the ultrasound pulse-echo signal, as it is received on the transducer surface after scattering in trabecular bone. A novel computer simulation model provides better understanding of ultrasonic scattering in porous bone structure and it can be also used to yield an ideal environment in which, the effects of various parameters (scatterer mechanical and geometrical properties, scatterer’ concentration), the shape of incident wave and experimental conditions influencing the scattering of ultrasonic waves in trabecular bone structure can be examined individually. The results proved that the computer simulation has a particular relevance in studying scattering in cancellous bone which may be approximated as a collection of two populations of scatterers, cylindrical and spherical that imitate thick and thin trabeculae respectively.

The mechanical properties of cranial bone: The effect of loading rate and cranial sampling position

Linear and depressed skull fractures are frequent mechanisms of head injury and are often associated with traumatic brain injury. Accurate knowledge of the fracture of cranial bone can provide insight into the prevention of skull fracture injuries and help aid the design of energy absorbing head protection systems and safety helmets. Cranial bone is a complex material comprising of a three-layered structure: external layers consist of compact, high-density cortical bone and the central layer consists of a low-density, irregularly porous bone structure. In this study, cranial bone specimens were extracted from 8 fresh-frozen cadavers ( F=4, M=4; 81±11 years old). 63 specimens were obtained from the parietal and frontal cranial bones. Prior to testing, all specimens were scanned using a μCT scanner at a resolution of 56.9 μm. The specimens were tested in a three-point bend set-up at different dynamic speeds (0.5, 1 and 2.5 m/s). The associated mechanical properties that were calculated for each specimen include the 2nd moment of inertia, the sectional elastic modulus, the maximum force at failure, the energy absorbed until failure and the maximum bending stress. Additionally, the morphological parameters of each specimen and their correlation with the resulting mechanical parameters were examined. It was found that testing speed, strain rate, cranial sampling position and intercranial variation all have a significant effect on some or all of the computed mechanical parameters. A modest correlation was also found between percent bone volume and both the elastic modulus and the maximum bending stress.

Bone Microarchitecture Parameter for Early Diagnosis of Osteopenia in Thalassemia.

In recent decades, survival in thalassemia patients has been prolonged; as a result, complications such as osteoporosis not previously observed will need earlier attention and better diagnostic tools. The diagnosis of osteoporosis is typically made by endocrine assessment and bone mineral density (BMD) measurements like dual energy x-ray absorptiometry (DXA). However, DXA may be insufficient to assess fracture risk in patients with thalassemia. We compared the microarchitecture and volumetric density of bone using high-resolution peripheral quantitative computed tomography (HR-pQCT) with planar BMD (DXA). In 18 transfused patients (age: 13 – 43 y) with beta-thalassemia, BMD of the lumbar spine (LS) and total hip was measured by DXA resulting in 7/18 patients with calculated Z-scores < −2.0. In addition, we assessed the volumetric BMD and the bone microarchitecture of the non-dominant distal radius and tibia by HR-pQCT (XtremeCT®). BMD values by DXA, correlated with cortical thickness (Spearman rank correlation RS = 0.78, p=0.0001), cortical density (RS = 0.67, p=0.003), while LS Z-scores correlated best with total volumetric density (RS = 0.60, p=0.009) measured by HR-pQCT at the distal radius. Thus, a porous inner bone structure may appear masked by DXA measurements due to a massive corticalis. From the many different HR-pQCT parameters measured, those with the highest variability (COV) might be of greatest promise to predict defective bone architecture in thalassemia. These parameters were compared with reference data from Boutroy et al (J Clin Endocrinol Metab 2005; 90:6508–15) of normal and osteopenic women. Despite relative uniformity in DXA Z-scores, TbSp and TbSp SD parameters of the radius covered a broad range (COV, F-test) of high values in thalassemia compared to osteopenic women (Table I).The SD of the trabecular separation (TbSp SD) of radius and tibia, characterizing the porosity of the spongiosa, may become the most interesting parameter in thalassemia as it was significantly correlated with hip Z-score (RS = −0.49, p=0.044), osteocalcin (RS = −0.70, p=0.001), FSH (RS = −0.65, p=0.005) and with liver iron concentration (tibia: RS = 0.55, p=0.017), respectively. Patients with hypogonadism (n = 9/18) were significantly different (U-test) from normals with respect to TbSp (p=0.024) and TbSp SD (p=0.019), but not DXA Z-scores. Patients with fractures (n=5) had lower trabecular TbSp SD (p=0.02) at the tibia. For patients with hypogonadism, the measurement of bone microarchitecture by HR-pQCT of low radiation burden (3 μSv) may help to identify risk early and avoid or minimize future morbidity, especially, in the presence of still normal results from DXA measurements.Table IComparison of Z-scores and radial trabecular density (Dtrab), separation (TbSp), inhomogeneity (TbSp SD) with reference parameters from Boutroy et al (2005) of normal and osteopenic women (Fcritical > 3.0 for p < 0.001).Thalassemia (n = 18)Normal (n = 108)Osteopenic (n = 113)ParameterMean ± SDCOVMean ± SDF-testMean ± SDF-testLS-Zscore (DXA)−1.7 ± 1.380 %0NA−1.4 ± 0.64.9Hip-Zscore (DXA)−1.3 ± 1.078 %0NA−1.6 ± 0.53.9Dtrab [mg/cm3]138 ± 7151 %160 ± 334.6123 ± 363.9TbSp [μm]959 ± 1265132 %517 ± 88207656 ± 18746TbSp SD [μm]600 ± 890148 %212 ± 58236342 ± 20120

Volume flow rate distribution in flow (non-Newtonian) through porous bone structure

Volume flow rate distribution in flow (non-Newtonian) through porous bone structure

The Genetics of Low-Density Lipoprotein Receptor-Related Protein 5 in Bone: A Story of Extremes

A few years ago, human genetic studies provided compelling evidence that the low-density lipoprotein receptor-related protein 5 (LRP5) is involved in the regulation of bone homeostasis because pathogenic LRP5 mutations were found in monogenic conditions with abnormal bone density. On the one hand, the osteoporosis pseudoglioma syndrome results from loss of function of LRP5, whereas on the other hand, gain-of-function mutations in LRP5 cause conditions with an increased bone density. On the molecular level, these types of mutations result in disturbed (respectively, decreased and increased) canonical Wnt signaling, an important metabolic pathway in osteoblasts during embryonic and postnatal osteogenesis. This signaling cascade is activated by binding of Wnt ligand to the Frizzled/LRP5 receptor complex. In addition to the involvement of LRP5 in conditions with extreme bone phenotypes, the genetic profile of this gene has also been shown to contribute to the determination of bone density in the general population. Quite a number of studies already demonstrated that common polymorphic variants in LRP5 are associated with bone mineral density and consequently osteoporosis, a multifactorial trait with low bone mass and porous bone structure. These genetic studies together with results obtained from in vitro and in vivo studies emphasize the importance of LRP5 and canonical Wnt signaling in the regulation of bone homeostasis. Therefore, unraveling the exact mechanisms of this signaling cascade has become an important area in bone research. This review focuses on the genetics of LRP5 and summarizes the findings on monogenic bone conditions as well as the current knowledge of its involvement in the pathogenesis of osteoporosis.

Measurment of Strain Generated Potential Near Bone and Implant Interface for Assessment of Osseointegration

In this study, a minimally invasive assessment using bone strain generated potential (SGP) was developed to examine the amount of osseointegration (OI) at bone-implant interface. SGP is generated by interstitial fluid flow in porous bone structure. Four experimental white New Zealand rabbits underwent pure titanium implant insertion surgery to tibia after amputation. After surgery, two animals were kept in small cages with minimal movement (Group 1). In contrast, the other rabbits were kept in a large cage that was large enough for jumping and walking (Group 2). At the end of the 5 weeks, all experimental animals were euthanized and the amputated tibia-implants were harvested. Then, a quasi-static force was applied to a bone site near the bone-implant interface for each tibia-implant specimen. Also, SGPs were measured near the interface using needle or probe electrodes. After the measurements, digital radiographs were taken to check the amount of OI for the interfaces. Full OI was observed for animals in Group 1. However, incomplete OI was found for animals in Group 2. Also, significant difference was found for mean SGP values between Group 1 and 2. The results could imply that SGP could be used as a minimally invasive assessment method to check the OI at the bone-implant interface.

Influence of oscillatory mixing on the injectability of three acrylic and two calcium-phosphate bone cements for vertebroplasty.

Injecting acrylic and, increasingly, calcium-phosphate cements into the porous bone structure is an emerging procedure, referred to as vertebroplasty, for the augmentation of osteoporotic vertebrae. Despite the benefits of vertebroplasty, it has limitations. The limitations of interest in this study are the injectability of bone cements and their mixing variability (i.e., low reproducibility of resulting viscosity). The objective of this study is to investigate the effect of oscillatory versus manual mixing on cement viscosity and mixing variability. Five cements are tested: (a) Vertebroplastic, (b) DP-Pour, (c) Antibiotic Simplex, (d) chronOS Inject, and (e) Biopex. Compared to manual mixing, oscillatory mixing significantly decreased the mean viscosity and the mixing variability, which was inferred from the coefficient of variation. For example, under oscillatory mixing, the viscosity and the variability for Vertebroplastic decreased to one-third of the corresponding values for manual mixing. Similar results were obtained for the other cements. The decrease in viscosity is attributed to the pseudo-plastic behavior of bone cements. The decrease in the variability of cement viscosity was attributed to greater dispersive mixing of the cement components under oscillatory mixing. The decrease in viscosity eases the injection by reducing the pressure required. The decrease in the variability of cement viscosity increases reproducibility of the cement injection. Oscillatory mixing appears to have the potential to contribute to improving vertebroplasty.

Experimental and theoretical investigation of directional permeability of human vertebral cancellous bone for cement infiltration

The use of acrylic polymers in infiltrating the porous bone structure is an emerging procedure for the augmentation of osteoporotic vertebrae. Although this procedure is employed frequently, it is performed based on empirical knowledge, and therefore, does not take into consideration the porosity-dependent permeability of human vertebral cancellous bone. The purpose of this study was to: (a) experimentally and theoretically investigate interdependence of the vertebral cancellous bone permeability and porosity, and (b) examine if the bone permeability of spinal cancellous bone can be predicted using bone mineral density measurements. If these relations can be established, they can be useful in optimizing the injection conditions for predicable cement infiltration. To determine the porosity-dependent and directional permeability, 34 bone cores—20 samples in the superior–inferior (SI) direction and 14 in the anterior–posterior (AP) direction—were cut from 20 lumbar vertebrae and infiltrated with silicone oil with a viscosity matching that of PMMA. The permeability of the cores was determined based on Darcy's law. The mean permeability of SI and AP cores was 4.45±1.72×10 −8 and 3.44±1.26×10 −8 m 2, respectively. An interesting finding of this study was that the permeability of the AP cores was approximately 78% of that of SI cores, though the porosity of the SI and AP cores taken from the same vertebra was approximately equal. In addition, we provided a theoretical model for the porosity-dependent permeability that accurately described non-linear dependency of the bone permeability and porosity in both directions. Although the relation of the bone permeability and porosity was established, bone mineral density was a weak predictor of the bone permeability. The experimental and theoretical results of this study can be used to understand polymer flow in cement infiltration procedures.