Micro-CT analysis and leakage of bioceramic retrofillings after ultrasonic and Er:YAG laser cavity preparations: an in vitro study.

The purpose of the study was to determine the influence of preparation techniques on marginal adaptation and sealing of Biodentine™ and TotalFill® RRM bioceramic retrograde fillings. Fifty-two single-root teeth extracted for periodontal reasons were used. Root canals were instrumented using Reciproc Blue #25 and obturated using a single cone technique with an AH Plus® root canal sealer. Retrograde cavities were prepared with Piezomed device (Piezo), Er:YAG laser in short-pulse(SP) and quantum square pulse(QSP) modes and filled with Biodentine™ (BD) or TotalFill® RRM (TF). There were 6 groups (n=8): (1) Piezo BD, (2) Piezo TF, (3) SP BD, (4) SP TF, (5) QSP BD, and (6) QSP TF, and positive and negative controls (n=2). Micro-CT analysis was performed on two samples from each group. Percentage volumes of internal and external voids in apical 1.5 mm were determined. Rhodamine B dye leakage was done on six samples. The samples were cut longitudinally and examined under a stereomicroscope. Digital recordings were analyzed in ImageJ software. The deepest penetration of color in mm was recorded. The data were statistically analyzed using ANOVA and Duncan's test at the level of significance α=0.05. TotalFill® RRM performed significantly better than Biodentine™ in terms of sealing (p<0.05) and marginal adaptation, as evaluated by micro-CT. Sealing was significantly better in SP compared to QSP mode preparations (p<0.05). Differences between Piezomed and laser modes were not significantly different (p>0.05). Sealing was statistically significantly better with TotalFill® RRM compared to Biodentine™ and in Er:YAG SP preparations compared to Er:YAG QSP.

Evaluation of removal efficiency of capping materials used in pulp revascularization in vitro.

BACKGROUND: This study aimed to evaluate the removal efficiency of different capping materials used in pulp revascularization (PR) in a failure scenario. METHODS: The apices of freshly extracted 30 maxillary incisors were cut to mimic the immature teeth; then, root canals were shaped up to #6 Peeso reamers. The regeneration steps of the American Association of Endodontists (AAE) were followed to simulate PR treatment in vitro. The canals were dressed with the Ciprofloxacin and Metronidazole medicament mixture for 2 weeks. Then capping material groups were created: BioDentine (BD), ProRootMTA (PMTA), and RetroMTA (RMTA) (n = 10). The sealed specimens were stored for 2 weeks at 37 ºC in phosphate-buffered saline then the samples were examined by micro-computed tomography (µ-CT) analysis. Set capping materials were retrieved using a specific cement removal kit by a single blind operator. The residue materials were examined again by µCT. Kruskal-Wallis and Mann-Whitney U tests sought the significance for residue volumes. One-way ANOVA and Tukey post hoc tests with the Bonferroni corrections sought significance for the duration (p = 0.05). RESULTS: In the first examined µCT data, the mean (SD) capping material volumes of the PMTA, BD, and RMTA were 6.447 µm3 (1.086), 8.771 µm3 (0.491), and 8.114 µm3 (2.447), respectively. In the last examined µCT data, the median (IQR) residual volumes of the PMTA, BD, and RMTA were 0.051 µm3 (0.1), 0.313 µm3 (0.5), and 0.124 µm3 (0.1), respectively. A significant difference was found between BD and PMTA in the residual volumes (p < 0.05). The mean (SD) durations of the retrieving procedures of PMTA, BD, and RMTA were 19.83 min (2.34), 19.24 (3.60), and 22.04 (1.68), respectively (p = 0.063). CONCLUSIONS: Within the limitations of the presented study, it was concluded that the capping materials were largely removed from the root canals using a non-invasive approach. Nevertheless, this duration of the retrieving could be described as long.

Volumetric analysis of the periodontal microstructure under antiresorptive therapy: an experimental study in rabbits.

OBJECTIVES: The objective of this study was to volumetrically assess changes in the periodontal microstructure under antiresorptive therapy. MATERIALS AND METHODS: Microtomographic scans from a total of 9 Dutch Belted rabbits having been randomly allocated to either the intravenous administration of amino-bisphosphonate (zoledronic acid) (Za) (n = 5) or a negative control group (nZa) (n = 4) were obtained at 10 months following a repeated drug administration. A quantification of the periodontal space thickness (P.Th) of both maxillary and mandibular most posterior premolars, as well as of the 2nd molars was performed. Bone micromorphometry was assessed by means of bone volume per total volume (BV/TV), the bone mineral density (BMD), trabecular thickness (Tb.Th), trabecular number (Tb.N), bone surface (BS), and the specific bone surface (BS/BV). RESULTS: Za was associated with significantly higher P.Th (P = 0.010), which was most pronounced in the upper jaw. Bone micromorphometry revealed no significant differences among the two groups, i.e., Za and nZa, for all the investigated parameters. CONCLUSIONS: Volumetric analysis revealed that antiresorptive therapy was associated with periodontal space widening, whereas major effects on the bone micro-morphology could not be observed. CLINICAL RELEVANCE: A deep understanding of specific periodontal and alveolar bone alterations in patients under antiresorptive therapy might help to prevent the onset of medication-related osteonecrosis of the jaw.

Hard tissue volumetric and soft tissue contour linear changes at implants with different surface characteristics after experimentally induced peri-implantitis: an experimental in vivo investigation.

OBJECTIVE: To evaluate the hard tissue volumetric and soft tissue contour linear changes in implants with two different implant surface characteristics after a ligature-induced peri-implantitis. MATERIAL AND METHODS: In eight beagle dogs, implants with the same size and diameter but distinct surface characteristics were placed in the healed mandibular sites. Test implants had an external monolayer of multi-phosphonate molecules (B+), while control implants were identical but without the phosphonate-rich surface. Once the implants were osseointegrated, oral hygiene was interrupted and peri-implantitis was induced by placing subgingival ligatures. After 16 weeks, the ligatures were removed and peri-implantitis progressed spontaneously. Bone to implant contact (BIC) and bone loss (BL) were assessed three-dimensionally with Micro-Ct (µCT). Dental casts were optically scanned and the obtained digitalized standard tessellation language (STL) images were used to assess the soft tissue vertical and horizontal contour linear changes. RESULTS: Reduction of the three-dimensional BIC percentage during the induction and progression phases of the experimental peri-implantitis was similar for both the experimental and control implants, without statistically significant differences between them. Soft tissue analysis revealed for both implant groups an increase in horizontal dimension after the induction of peri-implantitis, followed by a decrease after the spontaneous progression period. In the vertical dimension, a soft tissue dehiscence was observed in both groups, being more pronounced at the buccal aspect. CONCLUSIONS: The added phosphonate-rich surface did not provide a more resistant environment against experimental peri-implantitis, when assessed by the changes in bone volume and soft tissue contours. CLINICAL RELEVANCE: Ligature-induced peri-implantitis is a validated model to study the tissue changes occurring during peri-implantitis. It was hypothesized that a stronger osseointegration mediated by the chemical bond of a phosphonate-rich implant surface would develop an environment more resistant to the inflammatory changes occurring after experimental peri-implantitis. These results, however, indicate that the hard and soft tissue destructive changes occurring at both the induction and progression phases of experimental peri-implantitis were not influenced by the quality of osseointegration.

Optimization of in-line near-infrared measurement for practical real time monitoring of coating weight gain using design of experiments.

This study was conducted to develop an in-line near-infrared (NIR) spectroscopy approach that allows real time quantitative analysis of the coating weight gain on a moving tablet surface during a coating process where talc is used. A holder directly inserting a diffuse reflectance probe into a coating pan was designed, and the optimal measurement conditions were identified using the design of experiments (DoE). The surface of the probe was kept clean of coating droplets at a maximum distance between the probe and the holder of 272.5 mm, leading to the acquisition of accurate spectral data. Under this condition, partial least squares regression (PLSR) was developed using the spectra from 7197 to 6233 cm-1, which covers the specific peaks for the core tablet and the coating solution. Under the same conditions, least squares regression (LSR) was developed using the univariate predictive analysis of the single absorption spectrum of talc at 7181 cm-1. In a comparison of the accuracy of the two models, PLSR was found to be more accurate as a result of testing the significance of differences between these distributions in terms of the root mean square errors of prediction (RMSEP) using a randomization t-test. Additionally, it confirmed that the predicted weight gain using NIR spectroscopy was correlated with the coating thickness measured using micro-CT. In conclusion, this study developed an in-line NIR measurement approach for the real-time monitoring of the coating weight gain of tablets and optimized the conditions by evaluating the effect of various factors.

Neer Award 2017: wear rates of 32-mm and 40-mm glenospheres in a reverse total shoulder arthroplasty wear simulation model.

BACKGROUND: Larger glenosphere diameters have been used recently to increase prosthesis stability and impingement-free range of motion in reverse total shoulder arthroplasty. The goal of this study was to evaluate the rate of polyethylene wear for 32-mm and 40-mm glenospheres. METHODS: Glenospheres (32 mm and 40 mm, n = 6/group) and conventional polyethylene humeral liners underwent a 5-million cycle (MC) wear simulation protocol. Abduction-adduction and flexion-extension motion profiles were alternated every 250,000 cycles. At each interval, mass loss was determined and converted to volume loss and wear rate. At 0, 2.5 MC, and 5 MC, liners were imaged using micro-computed tomography to determine surface deviation. White light interferometry was performed on liners and glenospheres at 0 and 5 MC to quantify surface roughness. Wear particle morphology was characterized by environmental scanning electron microscopy. RESULTS: Total volume loss was significantly higher in 40-mm liners from 1.5 MC onward (P < .05). Overall, volumetric wear rate was significantly higher in 40-mm liners compared with 32-mm glenospheres (81.7 ± 23.9 mm3/MC vs. 68.0 ± 18.9 mm3/MC; P < .001). However, micro-computed tomography surface deviation results demonstrated increased linear penetration on 32-mm glenospheres compared with 40-mm glenospheres (0.36 ± 0.03 µm vs. 0.28 ± 0.01 µm; P = .002). Surface roughness measurements showed no difference for liners; however, increased roughness was noted for 40-mm glenospheres at 5 MC compared with 32 mm (P < .05). CONCLUSION: Larger glenospheres underwent significantly greater polyethylene volume loss and volumetric wear rates, whereas smaller glenospheres underwent greater polyethylene surface deviations. The enhanced stability provided by larger glenospheres must be weighed against the potential for increased polyethylene wear.

Applying deep learning to segmentation of murine lung tumors in pre-clinical micro-computed tomography.

Lung cancer remains a leading cause of cancer-related death, but scientists have made great strides in developing new treatments recently, partly owing to the use of genetically engineered mouse models (GEMMs). GEMM tumors represent a translational model that recapitulates human disease better than implanted models because tumors develop spontaneously in the lungs. However, detection of these tumors relies on in vivo imaging tools, specifically micro-Computed Tomography (micro-CT or µCT), and image analysis can be laborious with high inter-user variability. Here we present a deep learning model trained to perform fully automated segmentation of lung tumors without the interference of other soft tissues. Trained and tested on 100 3D µCT images (18,662 slices) that were manually segmented, the model demonstrated a high correlation to manual segmentations on the testing data (r2=0.99, DSC=0.78) and on an independent dataset (n = 12 3D scans or 2328 2D slices, r2=0.97, DSC=0.73). In a comparison against manual segmentation performed by multiple analysts, the model (r2=0.98, DSC=0.78) performed within inter-reader variability (r2=0.79, DSC=0.69) and close to intra-reader variability (r2=0.99, DSC=0.82), all while completing 5+ hours of manual segmentations in 1 minute. Finally, when applied to a real-world longitudinal study (n = 55 mice), the model successfully detected tumor progression over time and the differences in tumor burden between groups induced with different virus titers, aligning well with more traditional analysis methods. In conclusion, we have developed a deep learning model which can perform fast, accurate, and fully automated segmentation of µCT scans of murine lung tumors.

Efficacy of Shock Wave-Enhanced Emission Photoacoustic Streaming (SWEEPS) in the Removal of Different Combinations of Sealers Used with Two Obturation Techniques: A Micro-CT Study.

This study sought to evaluate the efficacy of SWEEPS in the removal of epoxy-resin-based and calcium-silicate-containing endodontic sealer combined with single-cone and carrier-based obturation techniques through a micro-CT analysis. Seventy-six single-rooted extracted human teeth with single root canal were instrumented with Reciproc instruments. Specimens were randomly divided into four groups (n = 19) according to the root canal filling material and obturation technique: (1) AH Plus sealer + Reciproc gutta-percha, (2) TotalFill BC sealer + TotalFill BC Points, (3) AH Plus sealer + Guttafusion obturator, and (4) MTA Fillapex + Guttafusion obturator. All specimens were re-treated one week later using Reciproc instruments. Following re-treatment, root canals were additionally irrigated using the Auto SWEEPS modality. The differences in the root canal filling remnants were analyzed by micro-CT scanning of each tooth after root canal obturation, after re-treatment, and after additional SWEEPS treatment. Statistical analysis was performed using an analysis of variance (p < 0.05). The additional treatment with SWEEPS significantly reduced the volume of the root canal filling materials in all experimental groups compared to the removal of root canal filling using only reciprocating instruments (p < 0.05). However, the root canal filling was not removed completely from any of the samples. SWEEPS can be used to enhance the removal of both epoxy-resin-based and calcium-silicate-containing sealers, in combination with single-cone and carrier-based obturation techniques.

Polycarboxy/Sulfo Betaine-Calcium Phosphate Hybrid Materials with a Remineralization Potential.

Biomacromolecules control mineral formation during the biomineralization process, but the effects of the organic components' functionality on the type of mineral phase is still unclear. The biomimetic precipitation of calcium phosphates in a physiological medium containing either polycarboxybetaine (PCB) or polysulfobetaine (PSB) was investigated in this study. Amorphous calcium phosphate (ACP) or a mixture of octacalcium phosphate (OCP) and dicalcium phosphate dihydrate (DCPD) in different ratios were identified depending on the sequence of initial solution mixing and on the type of the negative functional group of the polymer used. The more acidic character of the sulfo group in PSB than the carboxy one in PCB determines the dominance of the acidic solid phases, namely, an acidic amorphous phase or DCPD. In the presence of PCB, the formation of ACP with acicular particles arranged in bundles with the same orientation was observed. A preliminary study on the remineralization potential of the hybrid material with the participation of PSB and a mixture of OCP and DCPD did not show an increase in enamel density, contrary to the materials based on PCB and ACP. Moreover, the latter showed the creation of a newly formed crystal layer similar to that of the underlying enamel. This defines PCB/ACP as a promising material for enamel remineralization.

Effects of combined application of fibroblast growth factor (FGF)-2 and carbonate apatite for tissue regeneration in a beagle dog model of one-wall periodontal defect.

Introduction: There has been an increasing desire for the development of predictive periodontal regenerative therapy for severe periodontitis. In this study, we investigated the effect of the combined use of fibroblast growth factor-2 (FGF-2), a drug for periodontal regeneration approved in Japan, and carbonated apatite (CO3Ap), bioresorbable and osteoconductive scaffold, on periodontal regeneration in beagle dog model of one-wall periodontal defect (severe intraosseous defect) for 24 weeks in comparison with CO3Ap or vehicle alone. Methods: One-wall periodontal defects were created (mesiodistal width × depth: 4 × 4 mm) on the mesial portion of the mandibular first molar (M1) of beagle dogs on both side. Mixture of FGF-2 and CO3Ap, vehicle and CO3Ap, or vehicle alone were administered to the defects and designated as groups FGF-2+CO3Ap, CO3Ap, and control, respectively. To assess the periodontal regeneration, radiographic analysis over time for 24 weeks, and micro computed tomography (µCT) and histological evaluation at 6 and 24 weeks were performed. Results: For the regenerated tissue in the defect site, the mineral content of the FGF-2+CO3Ap group was higher than that of the CO3Ap group in the radiographic analysis at 6-24 weeks. In the context of new bone formation and replacement, the FGF-2+CO3Ap group exhibited significantly greater new bone volume and smaller CO3Ap volume than the CO3Ap group in the µCT analysis at 6 and 24 weeks. Furthermore, the density of the new bone in the FGF-2+CO3Ap group at 24 weeks was similar to those in the control and CO3Ap groups. Histological evaluation revealed that the length of the new periodontal ligament and cementum in the FGF-2+CO3Ap group was greater than that in the CO3Ap group at 6 weeks. We also examined the effect of the combined use of the FGF-2 and CO3Ap on the existing bone adjacent to the defect and demonstrated that the existing bone height and volume in the FGF-2+CO3Ap group remained significantly greater than those in the CO3Ap group. Conclusion: This study demonstrated that the combination of FGF-2 and CO3Ap was effective not only in enhancing new bone formation and replacing scaffold but also in maintaining the existing bone adjacent to the defect site in a beagle dog model of one-wall periodontal defect. Additionally, new periodontal tissues induced by FGF-2 and CO3Ap may follow a maturation process similar to that formed by spontaneous healing. This suggests that the combined use of FGF-2 and CO3Ap would promote periodontal regeneration in severe bony defects of periodontitis patient.

Fibrous and filmy microplastics exert opposite effects on the mobility of nanoplastics in saturated porous media.

This study explored the influence of fibrous and filmy polyethylene terephthalate (PET) on the transportation of nanoplastics (NPs) in saturated porous media. With the strong electrostatic repulsion, the negatively charged PET fibers (-57.5 mV) improved the transport of NPs, and the mass percentage of NPs recovered from the effluent (Meff) increased from 69.3% to 86.7%. However, PET films (-49.7 mV) showed the opposite result, that is, Meff decreased from 69.3% to 57.0%. X-ray micro-computed tomography quantitatively revealed the change in effective porosity of porous media before and after adding various PET MPs. The addition of 10 mm fiber increased the porosity from 0.39 to 0.43, whereas the addition of 10 × 10 mm2 film reduced the porosity from 0.39 to 0.29. The fiber-facilitated transport of NPs is presumably due to the formation of new connected pores between fibers and sand grains, whereas the film-inhibited transport of NPs may be due to the partial truncation of transport path of NPs. Overall, the effect of coexisting MPs on the mobility of NPs strongly relies on the shape and size of MPs.

Waste Eggshells as a Natural Filler for the Poly(Vinyl Chloride) Composites.

The paper presents the characteristics of unplasticized PVC composites modified with biofiller obtained from the waste eggshells of hen eggs. The composites obtained by extrusion contained from 10 phr to 40 phr of biofiller. The filler was characterized using the SEM, TG, and sieve analysis methods. The influence of the filler on the processing properties was determined using plastographometric and MFR tests. Fundamental analysis of mechanical properties was also performed, i.e., Charpy impact strength and determination of tensile properties. The mechanical properties were supported with dynamical mechanical thermal analysis, time of thermal stability, and thermogravimetric analysis. Structure analysis was also performed using SEM and X-ray microcomputed tomography (micro-CT). The processing properties of the tested composites do not give grounds for disqualifying such material from traditional processing PVC mixtures. Notably, the biofiller significantly improves thermal stability. Ground eggshells (ES) work as scavengers for the Cl radicals released in the first stage, which delays the PVC chain's decay. Additionally, a significant increase in the value of the modulus of elasticity and softening point (VST) of the composites concerning PVC was found. Ground hen eggshells can be used as an effective filler for PVC composites.

Efficacy of Reciprocating Instruments in the Removal of Bioceramic and Epoxy Resin-Based Sealers: Micro-CT Analysis.

The objective of this study was to evaluate the efficacy of reciprocating instruments in the removal of bioceramic and epoxy resin-based sealers using micro-CT analysis. Root canals of 40 extracted human teeth were instrumented with a size R25 Reciproc instrument. Specimens were randomly divided into two groups (n = 20) according to the root canal filling material. In the first group, root canals were obturated with AH Plus sealer and Reciproc R25 gutta-percha. In the second group, a combination of bioceramic gutta-percha (TotalFill BC) and bioceramic sealer (TotalFill BC) was used. After one week, the retreatment of all specimens was performed using Reciproc instruments. To analyze the differences in the filling remnants, specimens were scanned in a micro-CT device after obturation and after the retreatment procedure. Statistical analysis was performed using the Mann-Whitney U test (p < 0.05). A combination of bioceramic sealer and bioceramic gutta-percha was more effectively removed from canals using a reciprocating instrument, with a filling remnants volume of 4.01 ± 3.13 mm3, in comparison to the combination of epoxy resin-based sealer and gutta-percha (6.96 ± 2.70 mm3) (p < 0.05). A reciprocating instrument was more effective in removing bioceramic sealers than epoxy resin-based sealers, although none of the root canal filling materials were completely removed from the root canals.

Mechanical and Microscopic Characteristics of Polyurethane-Based Pervious Pavement Composites.

Conventional pervious pavement materials (PPM) that consist of cement and aggregate materials are known for poor durability due to their brittle behavior. Thus, to enhance the durability, we fabricated polymeric PPMs from durable and abundant polyurethane (PU) and undertook mechanical and microscopic characterizations. PU-based PPM samples with varying aggregate sizes were produced and examined to test their compressive strength and water permeability. Furthermore, X-ray micro-computed tomography (micro-CT) was implemented to analyze the samples' pore and tortuosity characteristics. Through the micro-CT analysis, the morphological characteristics of PPM's internal structures were identified and quantitively analyzed the correlations between the pore size distribution, connectivity, and tortuosity within the samples. Finally, the microstructures derived from micro-CT were generated as a finite element model and also numerically determined the stress distribution generated inside.

Preparation of Surface-Reinforced Superabsorbent Polymer Hydrogel Microspheres via Incorporation of In Situ Synthesized Silver Nanoparticles.

Superabsorbent polymer (SAP) particles are primarily applied for absorbing and storing liquids. Here, poly (acrylic acid) (PAA)-based SAP microspheres incorporated with silver nanoparticles (AgNPs) are prepared as an effort to maintain microsphere shape during swelling and minimize gel blocking. PAA-based SAP spheres are synthesized via inverse suspension polymerization. AgNPs are formed within SAP spheres through in situ reduction of silver nitrate (AgNO3), using polyvinylpyrrolidone as the reducing agent. The formation of AgNPs within SAP was observed via techniques such as scanning electron microscopy, ultraviolet-visible spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy and transmission electron microscopy. Energy dispersive spectroscopy analyses reveal that thin and dense layers of AgNPs are formed on the outer regions of the SAP spheres at higher concentrations of AgNO3. The water absorbency capacity decreases on increasing the amount of incorporated silver nanoparticles; however, it is comparable with that of commercially available surface-crosslinked SAP particles. Finally, micro-computerized tomography (micro-CT) study revealed that AgNP-incorporated SAP spheres maintained their shapes during swelling and exhibit higher void fractions in the packed gel bed, minimizing gel blocking and improving fluid permeability.

Comparative evaluation of retreatability of calcium silicate-based root canal sealers and epoxy resin-based root canal sealers in curved canals-An In-Vitro micro-CT analysis.

OBJECTIVE: To compare and evaluate the retreatability of calcium silicate-based root canal sealers and epoxy resin-based root canal sealers in curved canals using micro-CT scanning. MATERIALS AND METHODS: Forty-five maxillary molars with curved roots were selected after confirming with the Schneiders test. Teeth were decoronated near the cemento-enamel junction and moderate to severely curved canals were selected for the study using cone-beam computed tomography. All the samples were subjected to pre-operative micro-CT scanning. Cleaning and shaping were done using step-back preparation, obturation was done using lateral compaction technique, and homogeneous obturation was achieved. All the specimens were kept in 10 mL of phosphate buffered-saline solution at a pH of 8.4 for 48 h and transferred to a plastic container containing moistened foam with 10 mL of phosphate- buffered saline solution, and stored at 37 °C with 100% relative humidity for 4 months. Retreatment was performed for all the samples using Protaper universal retreatment files. Micro-CT scanning was performed to compare and evaluate the remaining sealer volume and resultant cracks formed in the root canal after retreatment. RESULTS: The volume of sealer remaining in the root canal and the length of a crack within the groups were analysed using kruskal-Wallis test and among the groups using post-hoc scheffe test showed that more sealer present in the Diaproseal sealer followed by MTA Fillapex and Bioroot RCS and more crack length was seen in Diaproseal sealer followed by MTA Fillapex and no visible cracks were seen in Bioroot RCS, which had statistically significant results with a P value of < 0.05. CONCLUSION: Within the limitations of the study it was concluded that in-terms of retrievability, Diaproseal sealer was the best among the tested groups followed by MTA Fillapex and Bioroot RCS.

The Role of the Loading Condition in Predictions of Bone Adaptation in a Mouse Tibial Loading Model.

The in vivo mouse tibial loading model is used to evaluate the effectiveness of mechanical loading treatment against skeletal diseases. Although studies have correlated bone adaptation with the induced mechanical stimulus, predictions of bone remodeling remained poor, and the interaction between external and physiological loading in engendering bone changes have not been determined. The aim of this study was to determine the effect of passive mechanical loading on the strain distribution in the mouse tibia and its predictions of bone adaptation. Longitudinal micro-computed tomography (micro-CT) imaging was performed over 2 weeks of cyclic loading from weeks 18 to 22 of age, to quantify the shape change, remodeling, and changes in densitometric properties. Micro-CT based finite element analysis coupled with an optimization algorithm for bone remodeling was used to predict bone adaptation under physiological loads, nominal 12N axial load and combined nominal 12N axial load superimposed to the physiological load. The results showed that despite large differences in the strain energy density magnitudes and distributions across the tibial length, the overall accuracy of the model and the spatial match were similar for all evaluated loading conditions. Predictions of densitometric properties were most similar to the experimental data for combined loading, followed closely by physiological loading conditions, despite no significant difference between these two predicted groups. However, all predicted densitometric properties were significantly different for the 12N and the combined loading conditions. The results suggest that computational modeling of bone's adaptive response to passive mechanical loading should include the contribution of daily physiological load.

High-Performance of a Thick-Walled Polyamide Composite Produced by Microcellular Injection Molding.

Lightweight moldings obtained by microcellular injection molding (MIM) are of great significance for saving materials and reducing energy consumption. For thick-walled parts, the standard injection molding process brings some defects, including a sink mark, warpage, and high shrinkage. Polyamide 66 (PA66)/glass fiber (GF) thick-walled moldings were prepared by MuCell® technology. The influences of moldings thickness (6 and 8.4 mm) and applied nitrogen pressure (16 and 20 MPa) on the morphology and mechanical properties were studied. Finally, the microcellular structure with a small cell diameter of about 30 µm was confirmed. Despite a significant time reduction of the holding phase (to 0.3 s), high-performance PA66 GF30 foamed moldings without sink marks and warpage were obtained. The excellent strength properties and favorable impact resistance while reducing the weight of thick-walled moldings were achieved. The main reason for the good results of polyamide composite was the orientation of the fibers in the flow direction and the large number of small nitrogen cells in the core and transition zone. The structure gradient was analysed and confirmed with scanning electron microscopy (SEM) images, X-ray micro computed tomography (micro CT) and finite element method (FEM) simulation.

3D printed scaffolds with random microarchitecture for bone tissue engineering applications: Manufacturing and characterization.

Additive manufacturing for tissue engineering applications offers the possibility to design scaffolds characterized by a fine and detailed microarchitecture. Several fabrication technologies are currently available which allow to prepare tailored structures with a large selection of materials for restoring and healing tissues. However, 3D printed scaffolds are generally collected by assembling repetitive geometrical units or reproducing specific patterns in the layering direction, leading to a highly ordered architecture that does not mimic the morphology of the natural extracellular matrix (ECM), one of the main goals to be reached for an effective therapeutic approach. It is usually stated in the tissue engineering field that a scaffold has to be considered a temporary ECM, resembling all the peculiar features as close as possible and, in this regard, an ordered microstructure cannot be usually observed within biological tissues and organs. With the aim to overcame this limitation and offer a potential approach for bone tissue applications, the present study proposes a design methodology to fabricate 3D printed scaffolds characterized by a random microarchitecture which can be repeatedly reproduced thanks to the intrinsic controllable process of additive manufacturing. In this framework, four different models in polylactic acid were fabricated by means of fused deposition modelling, including a three-dimensional random distribution of spherical pores of 400, 500, and 600 µm for the first three cases, and a randomly varied distribution in the range 400-600 µm for the fourth case. A detailed assessment by means of microcomputed tomography and mechanical evaluation was then carried out in order to fully analyse the resulting scaffolds, providing both morphological and quantitative data.

The Microcellular Structure of Injection Molded Thick-Walled Parts as Observed by In-Line Monitoring.

The aim of the study was to detect the influence of nitrogen pressure on the rheological properties and structure of PA66 GF30 thick-walled parts, produced by means of microcellular injection molding (MIM), using the MuCell® technology. The process was monitored in-line with pressure and temperature sensors assembled in the original injection mold. The measured data was subsequently used to evaluate rheological properties inside an 8.4 mm depth mold cavity. The analysis of the microcellular structure was related to the monitored in-line pressure and temperature changes during the injection process cycle. A four-times reduction of the maximum filling pressure in the mold cavity for MIM was found. At the same time, the holding pressure was taken over by expanding cells. The gradient effect of the cells distribution and the fiber arrangement in the flow direction were observed. A slight influence of nitrogen pressure on the cells size was found. Cells with a diameter lower than 20 µm dominate in the analyzed cases. An effect of reduction of the average cells size in the function of distance to the gate was observed. The creation of structure gradient and changes of cells dimensions were evaluated by SEM images and confirmed with the micro CT analysis.