Micro- and nanostructured polymer substrates for biomedical applications

Polymer implants are interesting alternatives to the contemporary load-bearing implants made from metals. Polyetheretherketone (PEEK), a well-established biomaterial for example, is not only iso-elastic to bone but also permits investigating the surrounding soft tissues using magnetic resonance imaging or computed tomography, which is particularly important for cancer patients. The commercially available PEEK bone implants, however, require costly coatings, which restricts their usage. As an alternative to coatings, plasma activation can be applied. The present paper shows the plasma-induced preparation of nanostructures on polymer films and on injection-molded micro-cantilever arrays and the associated chemical modifications of the surface. In vitro cell experiments indicate the suitability of the activation process. In addition, we show that microstructures such as micro-grooves 1 μm deep and 20 μm wide cause cell alignment. The combination of micro-injection molding, simultaneous microstructuring using inserts/bioreplica and plasma treatments permits the preparation of polymer implants with nature-analogue, anisotropic micro- and nanostructures.

Microstructural Parameters of Bone Evaluated Using HR-pQCT Correlate with the DXA-Derived Cortical Index and the Trabecular Bone Score in a Cohort of Randomly Selected Premenopausal Women.

BACKGROUND Areal bone mineral density is predictive for fracture risk. Microstructural bone parameters evaluated at the appendicular skeleton by high-resolution peripheral quantitative computed tomography (HR-pQCT) display differences between healthy patients and fracture patients. With the simple geometry of the cortex at the distal tibial diaphysis, a cortical index of the tibia combining material and mechanical properties correlated highly with bone strength ex vivo. The trabecular bone score derived from the scan of the lumbar spine by dual-energy X-ray absorptiometry (DXA) correlated ex vivo with the micro architectural parameters. It is unknown if these microstructural correlations could be made in healthy premenopausal women. METHODS Randomly selected women between 20-40 years of age were examined by DXA and HR-pQCT at the standard regions of interest and at customized sub regions to focus on cortical and trabecular parameters of strength separately. For cortical strength, at the distal tibia the volumetric cortical index was calculated directly from HR-pQCT and the areal cortical index was derived from the DXA scan using a Canny threshold-based tool. For trabecular strength, the trabecular bone score was calculated based on the DXA scan of the lumbar spine and was compared with the corresponding parameters derived from the HR-pQCT measurements at radius and tibia. RESULTS Seventy-two healthy women were included (average age 33.8 years, average BMI 23.2 kg/m(2)). The areal cortical index correlated highly with the volumetric cortical index at the distal tibia (R  =  0.798). The trabecular bone score correlated moderately with the microstructural parameters of the trabecular bone. CONCLUSION This study in randomly selected premenopausal women demonstrated that microstructural parameters of the bone evaluated by HR-pQCT correlated with the DXA derived parameters of skeletal regions containing predominantly cortical or cancellous bone. Whether these indexes are suitable for better predictions of the fracture risk deserves further investigation.

Scaling relations between trabecular bone volume fraction and microstructure at different skeletal sites

In this study, we investigated the scaling relations between trabecular bone volume fraction (BV/TV) and parameters of the trabecular microstructure at different skeletal sites. Cylindrical bone samples with a diameter of 8mm were harvested from different skeletal sites of 154 human donors in vitro: 87 from the distal radius, 59/69 from the thoracic/lumbar spine, 51 from the femoral neck, and 83 from the greater trochanter. μCT images were obtained with an isotropic spatial resolution of 26μm. BV/TV and trabecular microstructure parameters (TbN, TbTh, TbSp, scaling indices (< > and σ of α and αz), and Minkowski Functionals (Surface, Curvature, Euler)) were computed for each sample. The regression coefficient β was determined for each skeletal site as the slope of a linear fit in the double-logarithmic representations of the correlations of BV/TV versus the respective microstructure parameter. Statistically significant correlation coefficients ranging from r=0.36 to r=0.97 were observed for BV/TV versus microstructure parameters, except for Curvature and Euler. The regression coefficients β were 0.19 to 0.23 (TbN), 0.21 to 0.30 (TbTh), −0.28 to −0.24 (TbSp), 0.58 to 0.71 (Surface) and 0.12 to 0.16 (<α>), 0.07 to 0.11 (<αz>), −0.44 to −0.30 (σ(α)), and −0.39 to −0.14 (σ(αz)) at the different skeletal sites. The 95% confidence intervals of β overlapped for almost all microstructure parameters at the different skeletal sites. The scaling relations were independent of vertebral fracture status and similar for subjects aged 60–69, 70–79, and >79years. In conclusion, the bone volume fraction–microstructure scaling relations showed a rather universal character.

Stable Isotope and Trace Element Studies on Gladiators and Contemporary Romans from Ephesus (Turkey, 2nd and 3rd Ct. AD) - Implications for Differences in Diet

The gladiator cemetery discovered in Ephesus (Turkey) in 1993 dates to the 2nd and 3rd century AD. The aim of this study is to reconstruct diverse diet, social stratification, and migration of the inhabitants of Roman Ephesus and the distinct group of gladiators. Stable carbon, nitrogen, and sulphur isotope analysis were applied, and inorganic bone elements (strontium, calcium) were determined. In total, 53 individuals, including 22 gladiators, were analysed. All individuals consumed C3 plants like wheat and barley as staple food. A few individuals show indication of consumption of C4 plants. The δ13C values of one female from the gladiator cemetery and one gladiator differ from all other individuals. Their δ34S values indicate that they probably migrated from another geographical region or consumed different foods. The δ15N values are relatively low in comparison to other sites from Roman times. A probable cause for the depletion of 15N in Ephesus could be the frequent consumption of legumes. The Sr/Ca-ratios of the gladiators were significantly higher than the values of the contemporary Roman inhabitants. Since the Sr/Ca-ratio reflects the main Ca-supplier in the diet, the elevated values of the gladiators might suggest a frequent use of a plant ash beverage, as mentioned in ancient texts.

Bone dimensions in the posterior mandible: a retrospective radiographic study using cone beam computed tomography. Part 2- analysis of edentulous sites.

A precise radiographic evaluation of the local bone dimensions and morphology is important for preoperative planning of implant placement. The purpose of this retrospective study was to analyze dimensions and morphology of edentulous sites in the posterior mandible using cone beam computed tomography (CBCT) images. This retrospective radiographic study measured the bone width (BW) of the mandible at three locations on CBCT scans for premolars (PM1, PM2) and molars (M1, M2): at 1 mm and 4 mm below the most cranial point of the alveolar crest (BW1, BW2) and at the superior border of the mandibular canal (BW3). Furthermore, the height (H) of the alveolar process (distance between the measuring points BW1 and BW3), as well as the presence of lingual undercuts, were analyzed. A total of 56 CBCTs met the inclusion criteria, resulting in a sample size of 127 cross sections. There was a statistically significant increase from PM1 to M2 for the BW2 (P < .001), which was not present for BW1 and BW3 values. For the height of the alveolar process, the values exhibited a decrease from PM1 to M2 sites. Sex was a statistically significant parameter for H (P = .001) and for BW1 (P = .03). Age was not a statistically significant parameter for bone width (BW1: P = .37; BW2: P = .31; BW3: P = .51) or for the height of the alveolar process (P = .41) in the posterior mandible. Overall, 73 (57.5%) edentulous sites were evaluated to be without visible lingual undercuts; 13 (10.2%) sites exhibited lingual undercuts classified as influential for implant placement. Precise evaluation of the alveolar crest by cross-sectional imaging is of great value to analyze vertical and buccolingual bone dimensions in different locations in the posterior mandible. In addition, CBCTs are valuable to diagnosing the presence of and potential problems caused by lingual undercuts prior to implant placement.

Dacryocystography using cone beam CT in patients with lacrimal drainage system obstruction.

PURPOSE To assess the usefulness of cone beam CT (CBCT) for dacryocystography (DCG) using either direct syringing or passive application of contrast medium. METHODS Ten consecutive patients with epiphora who had CBCT-DCG in a sitting position were retrospectively analyzed. CBCT-DCGs were performed using 2 techniques: direct syringing with contrast medium or using the passive technique, where patients received 3 drops of contrast medium into the conjunctival sac before CBCT-DCG. Clinical and radiologic diagnoses were compared for both groups. RESULTS The 10 patients (men = 3) had a mean age of 63.2 years. Both techniques proved to be simple procedures with good delineation of the bone, soft tissue, and the contrast medium in the lacrimal system. No side effects were noted. CONCLUSIONS CBCT-DCG is a useful alternative to determine the localization of stenosis in patients with chronic epiphora.

Bone Volume Fraction and Fabric Anisotropy Are Better Determinants of Trabecular Bone Stiffness than Other Morphological Variables

As our population ages, more individuals suffer from osteoporosis. This disease leads to impaired trabecular architecture and increased fracture risk. It is essential to understand how morphological and mechanical properties of the cancellous bone are related. Morphologyelasticity relationships based on bone volume fraction (BV/TV) and fabric anisotropy explain up to 98% of the variation in elastic properties. Yet, other morphological variables such as individual trabeculae segmentation (ITS) and trabecular bone score (TBS) could improve the stiffness predictions. A total of 743 micro-computed tomography reconstructions of cubic trabecular bone samples extracted from femur, radius, vertebrae and iliac crest were analysed. Their morphology was assessed via 25 variables and their stiffness tensor (inline image) was computed from six independent load cases using micro finite element analyses. Variance inflation factors were calculated to evaluate collinearity between morphological variables and decide upon their inclusion in morphology-elasticity relationships. The statistically admissible morphological variables were included in a multi-linear regression modelling the dependent variable inline image. The contribution of each independent variable was evaluated (ANOVA). Our results show that BV/TV is the best determinant of inline image (inline image=0.889), especially in combination with fabric (inline image=0.968). Including the other independent predictors hardly affected the amount of variance explained by the model (inline image=0.975). Across all anatomical sites, BV/TV explained 87% of the variance of the bone elastic properties. Fabric further described 10% of the bone stiffness, but the improvement in variance explanation by adding other independent factors was marginal (<1%). These findings confirm that BV/TV and fabric are the best determinants of trabecular bone stiffness and show, against common belief, that other morphological variables do not bring any further contribution. These overall conclusions remain to be confirmed for specific bone diseases and post-elastic properties.

What happens to the bone flap? Long-term outcome after reimplantation of cryoconserved bone flaps in a consecutive series of 92 patients.

BACKGROUND Reimplantation of cryoconserved autologous bone flaps is a standard procedure after decompressive craniotomies. Aseptic necrosis and resorption are the most frequent complications of this procedure. At present there is no consensus regarding the definition of the relevant extent and indication for surgical revision. The objective of this retrospective analysis was to identify the incidence of bone flap resorption and the optimal duration of follow-up. METHODS Between February 2009 and March 2012, 100 cryoconserved autologous bone flaps were reimplanted at the Department of Neurosurgery, Inselspital Bern. Three patients were not available for follow-up, and five patients died before follow-up. All patients underwent follow-up at 6 weeks and a second follow-up more than 12 months postoperatively. A clinical and CT-based score was developed for judgment of relevance and decision making for surgical revision. RESULTS Mean follow-up period was 21.6 months postoperatively (range: 12 to 47 months); 48.9 % (45/92) of patients showed no signs of bone flap resorption, 20.7 % (19/92) showed minor resorption with no need for surgical revision, and 30.4 % (28/92) showed major resorption (in 4 % of these the bone flap was unstable or collapsed). CONCLUSIONS Aseptic necrosis and resorption of reimplanted autologous bone flaps occurred more frequently in our series of patients than in most reports in the literature. Most cases were identified between 6 and 12 months postoperatively. Clinical observation or CT scans of patients with autologous bone flaps are recommended for at least 12 months. Patient-specific implants may be preferable to autologous bone flaps.

Bone marrow-derived mesenchymal stromal cells improve vascular regeneration and reduce leukocyte-endothelium activation in critical ischemic murine skin in a dose-dependent manner

BACKGROUND AIMS Stem cells participate in vascular regeneration following critical ischemia. However, their angiogenic and remodeling properties, as well as their role in ischemia-related endothelial leukocyte activation, need to be further elucidated. Herein, we investigated the effect of bone marrow-derived mesenchymal stromal cells (BM-MSCs) in a critically ischemic murine skin flap model. METHODS Groups received either 1 × 10(5), 5 × 10(5), or 1 × 10(6) BM-MSCs or cell-free conditioned medium (CM). Controls received sodium chloride. Intravital fluorescence microscopy was performed for morphological and quantitative assessment of micro-hemodynamic parameters over 12 days. RESULTS Tortuosity and diameter of conduit-arterioles were pronounced in the MSC groups (P < 0.01), whereas vasodilation was shifted to the end arteriolar level in the CM group (P < 0.01). These effects were accompanied by angiopoietin-2 expression. Functional capillary density and red blood cell velocity were enhanced in all treatment groups (P < 0.01). Although a significant reduction of rolling and sticking leukocytes was observed in the MSC groups with a reduction of diameter in postcapillary venules (P < 0.01), animals receiving CM exhibited a leukocyte-endothelium interaction similar to controls. This correlated with leukocyte common antigen expression in tissue sections (P < 0.01) and p38 mitogen-activated protein kinase expression from tissue samples. Cytokine analysis from BM-MSC culture medium revealed a 50% reduction of pro-inflammatory cytokines (interleukin [IL]-1β, IL-6, IL-12, tumor necrosis factor-α, interferon-γ) and chemokines (keratinocyte chemoattractant, granulocyte colony-stimulating factor) under hypoxic conditions. DISCUSSION We demonstrated positive effects of BM-MSCs on vascular regeneration and modulation of endothelial leukocyte adhesion in critical ischemic skin. The improvements after MSC application were dose-dependent and superior to the use of CM alone.

Development of a specific tracer for metabolic imaging of alveolar echinococcosis: A preclinical study

Positron emission tomography (PET)-computed tomography (CT) using [18F]-fluorodeoxyglucose (FDG) (FDG-PET/CT) is a valuable method for initial staging and follow up of patients with alveolar echinococcosis (AE). However, the cells responsible for FDG uptake have not been clearly identified. The main goal of our study was to evaluate the uptake of PET tracers by the cells involved in the host-parasite reaction around AE lesions as the first step to develop a specific PET tracer that would allow direct assessment of parasite viability in AE. Candidate molecules ([18F]-fluorotyrosine (FET), [18F]-fluorothymidine (FLT), and [18F]-fluorometylcholine (FMC), were compared to FDG by in vitro studies on human leukocytes and parasite vesicles. Our results confirmed that FDG was mainly consumed by immune cells and showed that FLT was the best candidate tracer for parasite metabolism. Indeed, parasite cells exhibited high uptake of FLT. We also performed PET/CT scans in mice infected intraperitoneally with E. multilocularis metacestodes. PET images showed no FDG or FLT uptake in parasitic lesions. This preliminary study assessed the metabolic activity of human leukocytes and AE cells using radiolabeling. Future studies could develop a specific PET tracer for AE lesions to improve lesion detection and echinococcosis treatment in patients. Our results demonstrated that a new animal model is needed for preclinical PET imaging to better mimic human hepatic and/or periparasitic metabolism.

Lung Nodule Detection by Microdose CT Versus Chest Radiography (Standard and Dual-Energy Subtracted).

OBJECTIVE The purpose of this study was to investigate the feasibility of microdose CT using a comparable dose as for conventional chest radiographs in two planes including dual-energy subtraction for lung nodule assessment. MATERIALS AND METHODS We investigated 65 chest phantoms with 141 lung nodules, using an anthropomorphic chest phantom with artificial lung nodules. Microdose CT parameters were 80 kV and 6 mAs, with pitch of 2.2. Iterative reconstruction algorithms and an integrated circuit detector system (Stellar, Siemens Healthcare) were applied for maximum dose reduction. Maximum intensity projections (MIPs) were reconstructed. Chest radiographs were acquired in two projections with bone suppression. Four blinded radiologists interpreted the images in random order. RESULTS A soft-tissue CT kernel (I30f) delivered better sensitivities in a pilot study than a hard kernel (I70f), with respective mean (SD) sensitivities of 91.1% ± 2.2% versus 85.6% ± 5.6% (p = 0.041). Nodule size was measured accurately for all kernels. Mean clustered nodule sensitivity with chest radiography was 45.7% ± 8.1% (with bone suppression, 46.1% ± 8%; p = 0.94); for microdose CT, nodule sensitivity was 83.6% ± 9% without MIP (with additional MIP, 92.5% ± 6%; p < 10(-3)). Individual sensitivities of microdose CT for readers 1, 2, 3, and 4 were 84.3%, 90.7%, 68.6%, and 45.0%, respectively. Sensitivities with chest radiography for readers 1, 2, 3, and 4 were 42.9%, 58.6%, 36.4%, and 90.7%, respectively. In the per-phantom analysis, respective sensitivities of microdose CT versus chest radiography were 96.2% and 75% (p < 10(-6)). The effective dose for chest radiography including dual-energy subtraction was 0.242 mSv; for microdose CT, the applied dose was 0.1323 mSv. CONCLUSION Microdose CT is better than the combination of chest radiography and dual-energy subtraction for the detection of solid nodules between 5 and 12 mm at a lower dose level of 0.13 mSv. Soft-tissue kernels allow better sensitivities. These preliminary results indicate that microdose CT has the potential to replace conventional chest radiography for lung nodule detection.

Temperature Prediction Model for Bone Drilling Based on Density Distribution and In Vivo Experiments for Minimally Invasive Robotic Cochlear Implantation

Surgical robots have been proposed ex vivo to drill precise holes in the temporal bone for minimally invasive cochlear implantation. The main risk of the procedure is damage of the facial nerve due to mechanical interaction or due to temperature elevation during the drilling process. To evaluate the thermal risk of the drilling process, a simplified model is proposed which aims to enable an assessment of risk posed to the facial nerve for a given set of constant process parameters for different mastoid bone densities. The model uses the bone density distribution along the drilling trajectory in the mastoid bone to calculate a time dependent heat production function at the tip of the drill bit. Using a time dependent moving point source Green's function, the heat equation can be solved at a certain point in space so that the resulting temperatures can be calculated over time. The model was calibrated and initially verified with in vivo temperature data. The data was collected in minimally invasive robotic drilling of 12 holes in four different sheep. The sheep were anesthetized and the temperature elevations were measured with a thermocouple which was inserted in a previously drilled hole next to the planned drilling trajectory. Bone density distributions were extracted from pre-operative CT data by averaging Hounsfield values over the drill bit diameter. Post-operative [Formula: see text]CT data was used to verify the drilling accuracy of the trajectories. The comparison of measured and calculated temperatures shows a very good match for both heating and cooling phases. The average prediction error of the maximum temperature was less than 0.7 °C and the average root mean square error was approximately 0.5 °C. To analyze potential thermal damage, the model was used to calculate temperature profiles and cumulative equivalent minutes at 43 °C at a minimal distance to the facial nerve. For the selected drilling parameters, temperature elevation profiles and cumulative equivalent minutes suggest that thermal elevation of this minimally invasive cochlear implantation surgery may pose a risk to the facial nerve, especially in sclerotic or high density mastoid bones. Optimized drilling parameters need to be evaluated and the model could be used for future risk evaluation.

Pneumomediastinum and soft tissue emphysema of the neck in postmortem CT and MRI; a new vital sign in hanging?

Spontaneous pneumomediastinum commonly occurs in healthy young men or parturient women in whom an increased intra-alveolar pressure (Valsalva maneuver, asthma, cough, emesis) leads to the rupture of the marginal pulmonary alveoli. The air ascends along the bronchi to the mediastinum and the subcutaneous space of the neck, causing cervico-fascial subcutaneous emphysema in 70-90% of cases. Ninety-five forensic cases, including five cases of hanging, were examined using postmortem multi-slice computed tomography (MSCT) and magnetic resonance imaging (MRI) prior to autopsy until December 2003. This paper describes the findings of pneumomediastinum and cervical emphysema in three of five cases of hanging. The mechanism of its formation is discussed based on these results and a review of the literature. In conclusion, when putrefaction gas can be excluded the findings of pneumomediastinum and cervical soft tissue emphysema serve as evidence of vitality of a hanged person. Postmortem cross-sectional imaging is considered a useful visualization tool for emphysema, with a great potential for examination and documentation.

Loss of bone strength in HLA-B27 transgenic rats is characterized by a high bone turnover and is mainly osteoclast-driven

Objective Although osteopenia is frequent in spondyloarthritis (SpA), the underlying cellular mechanisms and association with other symptoms are poorly understood. This study aimed to characterize bone loss during disease progression, determine cellular alterations, and assess the contribution of inflammatory bowel disease (IBD) to bone loss in HLA-B27 transgenic rats. Methods Bones of 2-, 6-, and 12-month-old non-transgenic, disease-free HLA-B7 and disease-associated HLA-B27 transgenic rats were examined using peripheral quantitative computed tomography, μCT, and nanoindentation. Cellular characteristics were determined by histomorphometry and ex vivo cultures. The impact of IBD was determined using [21-3 x 283-2]F1 rats, which develop arthritis and spondylitis, but not IBD. Results HLA-B27 transgenic rats continuously lost bone mass with increasing age and had impaired bone material properties, leading to a 3-fold decrease in bone strength at 12 months of age. Bone turnover was increased in HLA-B27 transgenic rats, as evidenced by a 3-fold increase in bone formation and a 6-fold increase in bone resorption parameters. Enhanced osteoclastic markers were associated with a larger number of precursors in the bone marrow and a stronger osteoclastogenic response to RANKL or TNFα. Further, IBD-free [21-3 x 283-2]F1 rats also displayed decreased total and trabecular bone density. Conclusions HLA-B27 transgenic rats lose an increasing amount of bone density and strength with progressing age, which is primarily mediated via increased bone remodeling in favor of bone resorption. Moreover, IBD and bone loss seem to be independent features of SpA in HLA-B27 transgenic rats.

Comparison of Mixed and Kinematic Uniform Boundary Conditions in Homogenized Elasticity of Femoral Trabecular Bone Using Microfinite Element Analyses

Mechanical properties of human trabecular bone play an important role in age-related bone fragility and implant stability. Micro-finite element (microFE) analysis allows computing the apparent elastic properties of trabecular bone biopsies, but the results depend on the type of applied boundary conditions (BCs). In this study, 167 femoral trabecular cubic biopsies with a side length of 5.3 mm were analyzed using microFE analysis to compare their stiffness systematically with kinematic uniform boundary conditions (KUBCs) and periodicity-compatible mixed uniform boundary conditions (PMUBCs). The obtained elastic constants were then used in the volume fraction and fabric-based orthotropic Zysset-Curnier model to identify their respective model parameters. As expected, PMUBCs lead to more compliant apparent elastic properties than KUBCs, especially in shear. The differences in stiffness decreased with bone volume fraction and mean intercept length. Unlike KUBCs, PMUBCs were sensitive to heterogeneity of the biopsies. The Zysset-Curnier model predicted apparent elastic constants successfully in both cases with adjusted coefficients of determination of 0.986 for KUBCs and 0.975 for PMUBCs. The role of these boundary conditions in finite element analyses of whole bones and bone-implant systems will need to be investigated in future work.