Efficacy of treating segmental bone defects through endochondral ossification: 3D printed designs and bone metabolic activities.

Three-dimensional printing (3D printing) is a promising technique for producing scaffolds for bone tissue engineering applications. Porous scaffolds can be printed directly, and the design, shape and porosity can be controlled. 3D synthetic biodegradable polymeric scaffolds intended for in situ bone regeneration must meet stringent criteria, primarily appropriate mechanical properties, good 3D design, adequate biocompatibility and the ability to enhance bone formation. In this study, healing of critical-sized (5 â€‹mm) femur defects of rats was enhanced by implanting two different designs of 3D printed poly(l-lactide-co-ε-caprolactone) (poly(LA-co-CL)) scaffolds seeded with rat bone marrow mesenchymal stem cells (rBMSC), which had been pre-differentiated in vitro into cartilage-forming chondrocytes. Depending on the design, the scaffolds had an interconnected porous structure of 300-500 â€‹µm and porosity of 50-65%. According to a computational simulation, the internal force distribution was consistent with scaffold designs and comparable between the two designs. Moreover, the defects treated with 3D-printed scaffolds seeded with chondrocyte-like cells exhibited significantly increased bone formation up to 15 weeks compared with empty defects. In all experimental animals, bone metabolic activity was monitored by positron emission tomography 1, 3, 5, 7, 11 and 14 weeks after surgery. This demonstrated a time-dependent relationship between scaffold design and metabolic activity. This confirmed that successful regeneration was highly reproducible. The in vitro and in vivo data indicated that the experimental setups had promising outcomes and could facilitate new bone formation through endochondral ossification.

Effect of saliva contamination on the bond strength of single-step and three-step adhesive systems.

The aim of this study was to evaluate the effect of saliva contamination on bond strength to dentin with an etch-and-rinse and a self-etch adhesive system. For each of these adhesive systems, the dentin surface of 24 human molars were allocated to one of four groups representing different saliva contamination scenarios. Saliva was applied at different stages in the bonding process, and was investigated to be remedied by water rinsing and/or air drying. Uncontaminated tooth surfaces were used as controls. Bonding procedures were performed according to the manufacturer's instructions, and a polymer-based composite was placed. The bond strength was measured by a micro-tensile test. Except for the etch-and-rinse approach having contamination with saliva after etching, followed by air drying, all salivary contamination regimens resulted in a substantial number of specimens not surviving the test, and the bond strength value of these was therefore set to 0 MPa for the purposes of the statistical analysis. Water rinsing after etching and salivary contamination did significantly reduce the bond strength. Contamination after priming showed the lowest bond strength. For the self-etch approach, saliva contamination before the adhesive procedure, followed by air drying, significantly reduced the bond strength, while contamination followed by water rinsing or air drying did not statistically significantly reduce the strength.

Effect of artificial aging on high translucent dental zirconia: simulation of early failure.

Higher yttria content enhances the translucency and appearance of dental zirconia materials. Alterations in material composition also affect mechanical properties. The aim of this study was to compare the fracture load after artificial short-term aging of monolithic, full-contour zirconia crowns with different amounts of yttria-stabilization. Sixty crowns (thirty super high translucent crowns (5Y-Z) and thirty high translucent crowns (3Y-Z)) were produced to fit a model of a premolar with a shallow chamfer preparation. The crowns were cemented with self-adhesive resin cement on composite abutments. For each zirconia type, three groups of crowns (n = 10) were allocated to: (i) cyclic loading (200 N, 1 Hz, 30,000 cycles), (ii) hydrothermal aging (3 × 20 min, 134°C 3.2 bar), or (iii) no treatment (control). Surviving crowns from the aging process were quasistatically loaded until fracture. The 3Y-Z crowns had statistically significantly higher fracture values (3,449 N) than the 5Y-Z crowns (1,938 N). The aging procedures did not affect load at fracture. Fractographic analysis showed that fractures started either at the crown margin or at the occlusal intaglio area. Higher yttria content leads to a reduction in material strength and damage tolerance, and this should be reflected in recommendations for clinical use.

Strength of side-to-side and step-cut repairs in tendon transfers: biomechanical testing of porcine flexor tendons.

The aim of the study was to compare side-to-side with step-cut repairs to determine how much of the width it is possible to remove and still keep the repair strong enough to start active mobilization. Porcine flexor tendons were used to create side-to-side, one-third step-cut and half step-cut repairs. There were 15 repairs in each group. The tensile properties of the constructs were measured in a biomechanical testing machine. All repairs failed by the sutures splitting the tendon longitudinally. The maximum load and stiffness were highest in the side-to-side group. Our findings suggest that the half step-cut repair can withstand the forces exerted during active unrestricted movement of the digits in tendons of this size. The advantage of the step-cut repair is reduced bulkiness and less friction, which might compensate for the difference in strength.

Strength of Pulvertaft modifications: tensile testing of porcine flexor tendons.

The aim of the study was to present two new modifications of the Pulvertaft weave, allowing a higher number of weaves without the need for a longer overlap. The mechanical properties were measured and compared with the traditional technique. Forty-five pairs of porcine flexor tendons were randomized to a Pulvertaft repair with three weaves, a Double Pulvertaft and Locking Pulvertaft repairs. In the last two repairs one of the tendons in each repair was split in two before weaving. A difference in the maximum stiffness was observed between the three groups (p = 0.024). All repairs failed by the sutures being sheared through the tendons splitting the tendon fibres longitudinally. The two modifications were both stronger than the Pulvertaft weave and provide an alternative when a strong connection is needed and a longer overlap is impossible.

Corrosion and metal release from overlapping arterial stents under mechanical and electrochemical stress - An experimental study.

Intra-arterial stenosis due to atherosclerosis is often treated with endovascular balloon dilatation with a metal stent. Restenosis is common and is frequently treated with a new stent placed inside the existing one or the stents are placed with overlap to cover a larger area of the vessels. Observations of stent fractures, stent compression, accumulation of immunocompetent cells around stents have suggested the possibility of immunologic reactions to substances released from stents. An accelerated corrosion model was developed to study corrosion behaviour of commonly used surgical peripheral stents. Single nitinol stents (n = 6), connected stents of the same material (stent-in-stent, both nitinol, n = 7) and connected stents of dissimilar alloys (Nitinol with stainless steel stent inside, n = 7) were investigated. The stents were subjected to mechanical pulsatile radial strain (up to 8% strain at 1 Hz) and electrochemical stress (+112 mV vs. SCE). The release of nickel and titanium ions was compared. Scanning electron images were obtained. There was a higher release of nickel when combining two similar (range: 1382-8018 µg/L, p = 0.0012) and dissimilar (range: 170-2497 µg/L, p = 0.0023) stents compared to single stents (range: 0.4-216 µg/L). The concentration of titanium was low (range: 1.6-98.4 µg/L) with only a difference between the single and two similar stents (p = 0.0047). Deposits of corrosion products were clearly visible after fretting and pitting corrosion mainly on the Nitinol stents. Several mesh wires were fractured. The study demonstrated that mechanical strain combined with weak electric potential resulted in pronounced corrosion and fracture of stents, especially with overlapping stents. Single stents after pulsatile load released the lowest amount of ions. The combination of stents of the same material (Nitinol) had the highest release of metal ions.

Load transfer in the proximal femur and primary stability of a cemented and uncemented femoral stem: An experimental study on cadaver femurs.

There are principally two fixation methods in total hip arthroplasty, cemented and uncemented. Both methods have in general good long-time survival. Studies comparing cemented and uncemented femoral stems indicate that the cemented stems perform somewhat better, at least in the elderly population. The aim of this study was to compare load transfer and the initial micromotion pattern for an uncemented and a cemented stem. A total of 12 human cadavers were tested in a hip simulator during single leg and stair climbing. Strain was measured on the proximal femur before and after implantation of the prostheses, and the values were presented as percentage of physiological strain. The micromovements between the stem and bone were measured and a total point motion was calculated. The results showed small statistically significant differences between the fixation methods, the largest difference being 8.1 percentage points. The uncemented stem had somewhat higher micromotion than the cemented stem, but less than 10 µm. Both stems thus had acceptable primary stability. The main finding of this study is the strain and micromotion pattern of a cemented and an uncemented stem of similar geometry is overall equal. There were small statistical significant differences between the two fixation methods regarding strain and micromotion levels. The differences are considered too small to be clinically relevant.

Deformation pattern and load transfer of an uncemented femoral stem with modular necks. An experimental study in human cadaver femurs.

BACKGROUND: Modular necks in hip arthroplasty allow variations in neck-shaft angles, neck version and neck lengths and have been introduced to improve accuracy when reconstructing the anatomy and hip joint biomechanics. Periprosthetic bone resorption may be a consequence of stress shielding in the proximal femur after implantation of a femoral stem. The purpose of this study was to investigate the deformation pattern and load transfer of an uncemented femoral stem coupled to different modular necks in human cadaver femurs. METHODS: A cementless femoral stem was implanted in twelve human cadaver femurs and tested in a hip simulator corresponding to single leg stance and stair climbing activity with patient-specific loading. The stems were tested with four different modular necks; long, short, retro and varus. The long neck was used as reference in statistical comparisons, as it can be considered the "standard" neck. The deformation of bone during loading was measured by strain gauge rosettes at three levels of the proximal femur on the medial, lateral and anterior side. FINDINGS: The cortical strains were overall reduced on the medial and lateral side of femur, for all implants tested, and in both loading conditions compared to the unoperated femur. Although there were statistical significant differences between the necks, the results did not show a consistent pattern considering which neck retained or lost most strain. In general the differences were small, with the highest significant difference between the necks of 3.23 percentage points. INTERPRETATION: The small differences of strain between the modular necks tested in this study are not expected to influence bone remodeling in the proximal femur.

The effect of blood protein adsorption on cellular uptake of anatase TiO2 nanoparticles.

Protein adsorption onto nanoparticles (NPs) in biological fluids has emerged as an important factor when testing biological responses to NPs, as this may influence both uptake and subsequent toxicity. The aim of the present study was to quantify the adsorption of proteins onto TiO2 NPs and to test the influence on cellular uptake. The surface composition of the particles was characterized by thermal analysis and by X-ray photoelectron spectroscopy. The adsorption of three blood proteins, ie, human serum albumin (HSA), γ-globulins (Glbs), and fibrinogen (Fib), onto three types of anatase NPs of different sizes was quantified for each protein. The concentration of the adsorbed protein was measured by ultraviolet-visible spectrophotometry using the Bradford method. The degree of cellular uptake was quantified by inductivity coupled plasma mass spectroscopy, and visualized by an ultra-high resolution imaging system. The proteins were adsorbed onto all of the anatase NPs. The quantity adsorbed increased with time and was higher for the smaller particles. Fib and Glbs showed the highest affinity to TiO2 NPs, while the lowest was seen for HSA. The adsorption of proteins affected the surface charge and the hydrodynamic diameter of the NPs in cell culture medium. The degree of particle uptake was highest in protein-free medium and in the presence HSA, followed by culture medium supplemented with Glbs, and lowest in the presence of Fib. The results indicate that the uptake of anatase NPs by fibroblasts is influenced by the identity of the adsorbed protein.

Assessment of retention force and bone apposition in two differently coated femoral stems after 6 months of loading in a goat model.

BACKGROUND: Since the introduction of uncemented hip implants, there has been a search for the best surface coating to enhance bone apposition in order to improve retention. The surface coating of the different stems varies between products. The aim was to assess the retention force and bone adaption in two differently coated stems in a weight-bearing goat model. MATERIALS AND METHODS: Hydroxyapatite (HA) and electrochemically deposited calcium phosphate (CP; Bonit) on geometrically comparable titanium-based femoral stems were implanted into 12 (CP group) and 35 (HA group) goats. The animal model included physiological loading of the implants for 6 months. The pull-out force of the stems was measured, and bone apposition was microscopically evaluated. RESULTS: After exclusion criteria were applied, the number of available goats was 4 in the CP group and 11 in the HA group. The CP-coated stems had significantly lower retention forces compared with the HA-coated ones after 6 months (CP median 47 N, HA median 1,696 N, p = 0.003). Bone sections revealed a lower degree of bone apposition in the CP-coated stems, with more connective tissue in the bone/implant interface compared with the HA group. CONCLUSION: In this study, HA had better bone apposition and needed greater pull-out force in loaded implants. The application of CP on the loaded titanium surface to enhance the apposition of bone is questioned.

Fractographic features of glass-ceramic and zirconia-based dental restorations fractured during clinical function.

Fractures during clinical function have been reported as the major concern associated with all-ceramic dental restorations. The aim of this study was to analyze the fracture features of glass-ceramic and zirconia-based restorations fractured during clinical use. Twenty-seven crowns and onlays were supplied by dentists and dental technicians with information about type of cement and time in function, if available. Fourteen lithium disilicate glass-ceramic restorations and 13 zirconia-based restorations were retrieved and analyzed. Fractographic features were examined using optical microscopy to determine crack initiation and crack propagation of the restorations. The material comprised fractured restorations from one canine, 10 incisors, four premolars, and 11 molars. One crown was not categorized because of difficulty in orientation of the fragments. The results revealed that all core and veneer fractures initiated in the cervical margin and usually from the approximal area close to the most coronally placed curvature of the margin. Three cases of occlusal chipping were found. The margin of dental all-ceramic single-tooth restorations was the area of fracture origin. The fracture features were similar for zirconia, glass-ceramic, and alumina single-tooth restorations. Design features seem to be of great importance for fracture initiation.

Simulation of clinical fractures for three different all-ceramic crowns.

Comparison of fracture strength and fracture modes of different all-ceramic crown systems is not straightforward. Established methods for reliable testing of all-ceramic crowns are not currently available. Published in-vitro tests rarely simulate clinical failure modes and are therefore unsuited to distinguish between the materials. The in-vivo trials usually lack assessment of failure modes. Fractographic analyses show that clinical crowns usually fail from cracks initiating in the cervical margins, whereas in-vitro specimens fail from contact damage at the occlusal loading point. The aim of this study was to compare three all-ceramic systems using a clinically relevant test method that is able to simulate clinical failure modes. Ten incisor crowns of three types of all-ceramic systems were exposed to soft loading until fracture. The initiation and propagation of cracks in these crowns were compared with those of a reference group of crowns that failed during clinical use. All crowns fractured in a manner similar to fracture of the clinical reference crowns. The zirconia crowns fractured at statistically significantly higher loads than alumina and glass-ceramic crowns. Fracture initiation was in the core material, cervically in the approximal areas.

Initial stability of an uncemented femoral stem with modular necks. An experimental study in human cadaver femurs.

BACKGROUND: Uncemented implants are dependent upon initial postoperative stability to gain bone ingrowth and secondary stability. The possibility to vary femoral offset and neck angles using modular necks in total hip arthroplasty increases the flexibility in the reconstruction of the geometry of the hip joint. The purpose of this study was to investigate and evaluate initial stability of an uncemented stem coupled to four different modular necks. METHODS: A cementless femoral stem was implanted in twelve human cadaver femurs and tested in a hip simulator with patient specific load for each patient corresponding to single leg stance and stair climbing activity. The stems were tested with four different modular necks; long, short, retro and varus. The long neck was used as reference in statistical comparisons. A micromotion jig was used to measure bone-implant movements, at two predefined levels. FINDINGS: A femoral stem coupled to a varus neck had the highest value of micromotion measured for stair climbing at the distal measurement level (60µm). The micromotions measured with varus and retro necks were significantly larger than motions observed with the reference modular neck, P<0.001. INTERPRETATION: The femoral stem evaluated in this study showed acceptable micromotion values for the investigated loading conditions when coupled to modular necks with different lengths, versions and neck-shaft angles.

Role of physicochemical characteristics in the uptake of TiO2 nanoparticles by fibroblasts.

The relation between the physico-chemical properties of nanoparticles (NPs) and the degree of cellular uptake is incompletely elucidated. In this study, we investigated the influence on the cellular uptake of a wide range of fully characterized TiO2 NPs. L929 fibroblasts were exposed for 24 h to clinically relevant concentrations of nano-TiO2 and the degree of their association was assessed by ultrahigh resolution imaging microscopy (URI), scanning (SEM) and transmission (TEM) electron microscopy, as well as inductivity coupled plasma-mass spectroscopy (ICP-MS). The role of actin polymerization, a central feature of active internalization, was also studied and the results indicated that the internalization of TiO2 NPs involves a combination of actin-dependent uptake of large agglomerates as well as non actin-dependent uptake of small agglomerates. SEM and TEM revealed that the agglomerates of all NPs types were attached to the cellular membrane as well as internalized and confined inside cytoplasmic vesicles. URI and ICP-MS demonstrated that the particle association with cells was dose-dependent. The highest association was observed for spherical particles having mixed anatase-rutile crystallographic phase and the lowest for spindle-shaped rutile particles. ICP-MS revealed that the association was size-dependent in the order 5>10>40 nm for anatase spherical nanoparticles.

Different osteosyntheses for Colles' fracture: a mechanical study in 42 cadaver bones.

BACKGROUND AND PURPOSE: In recent years several different plate designs for internal fixation of fractures of the distal radius have been developed. However, few biomechanical studies have been performed to compare these new implants. The purpose of this study was to compare the mechanical properties of 5 different commercially available plates (3 volar and 2 dorsal) with standard K-wire fixation using a distal radial cadaver model. MATERIAL AND METHODS: 42 human radial bones from 26 cadavers were included. The bone mineral density (BMD) was measured by DEXA in all bones, and the radial bones were assigned to 6 equiv alent groups based on bone density and total amount of mineral. A distal radial osteotomy was done and a dorsal 30-degree wedge of bone was removed. 1 K-wire fixation group and 5 plate groups were tested for rigidity, yield load, and maximum load. RESULTS: When data from dorsally and volarly applied plates were pooled, we did not find any statistically significant differences between them regarding stiffness, yield load, and maximum load. The K-wire group showed significantly lower yield load than 3 of the plate groups. There were no statistically significant differences in yield load between the 5 plate groups. The K-wire group showed lower rigidity than the plate groups. The K-wire group and 1 plate group failed at a statistically significant lower maximum load than the 4 other plate groups. INTERPRETATION: The volar plates had the same mechanical stability as the dorsally applied plates, and they are therefore a good alternative to dorsally applied plates. K-wire osteosynthesis was inferior to plate osteosyntheses regarding all mechanical properties.

Qualitative and quantitative fracture analyses of high-strength ceramics.

The aims of this study were to assess the applicability and repeatability of qualitative and quantitative analyses of the fracture patterns of four different high-strength ceramics. Ten bar-shaped specimens of four high-strength ceramics with different material composition and fabrication methods had been fractured by three-point bending in water (n = 40). Commonly used fractographic patterns for brittle materials, such as mirror and mist, were used to characterize and quantify the fractured surfaces of these specimens. The analyses were performed twice, on separate occasions, by the same operator. Assessment of the association between fractographic patterns and fracture stress was carried out, and repeatability assessments of the measurements were performed. The fracture initiator site and the common fractographic markers surrounding this site were found in all specimens. Statistically significant correlations were found between certain fracture patterns and stress at fracture. The repeatability of the measurements of the different fractographic patterns varied among the materials. Fracture analyses seem applicable as a tool to determine the fracture initiation site and to estimate the force vectors involved in the fracture of dental high-strength ceramics.

Agglomeration and sedimentation of TiO2 nanoparticles in cell culture medium.

The physicochemical characterization of nanoparticles in suspension is a prerequisite for the adequate assessment of their potential biological effect. Little is known to date about the colloidal stability of TiO2 nanoparticles in cell culture medium. This study investigates the effect of particle concentration, ionic strength, pH, and the presence of fetal bovine serum (FBS) and human serum albumin (HSA) on the colloidal stability of TiO2 nanoparticles in RPMI cell culture medium, by sedimentation measurements, dynamic light scattering, and electrokinetic measurements (zeta-potential). TEM revealed that the particles were polydisperse, with diameters ranging from approximately 15 to approximately 350 nm. The agglomeration rate and sedimentation rate increased with particles' concentration. The size of the agglomerates at 100 mg/L TiO2 was significantly reduced, from 1620+/-160 to 348+/-13 and 378+/-15 nm, upon the addition of 10% (v/v) FBS and 1% (w/w) HSA, respectively. The isoelectric point of TiO2 in water was 2.9 and the measured zeta-potential in RPMI was -16+/-2 mV at pH 7.4. A slight increase in the zeta-potential of TiO2 in RPMI was observed upon the addition of FBS and HSA. The addition of FBS and HSA prevented high agglomeration, leading to a stable dispersion of TiO2 nanoparticles for at least 24 h, possibly due to steric stabilization of the particles.

Performance of bone cements: are current preclinical specifications adequate?

BACKGROUND: Current specifications (standards) for preclinical testing of bone cements (ISO 5833: 2002, ASTM F451-99a) require simple mechanical testing after ageing for 24 h under dry conditions at 23 degrees C. Some bone cements have fulfilled the requirements in the specifications, and yet had inferior clinical results. Clinically, bone cements are subjected to complex loading patterns in a moist or wet environment at 37 degrees C. Thus, both the validity and the robustness of current standard testing protocols can be questioned. METHODS: We examined the influence of temperature and storage medium on the properties of bone cement. We also compared the results of storage and testing under standard conditions of 23 degrees C in dry air, with the results obtained at 37 degrees C in water or plasma. RESULTS: The dry specimens showed an increase in strength and elastic modulus with time, while the values of the wet ones decreased. There was no difference between specimens stored in water or in plasma. Ultimate compressive strength of dry specimens after 24 h was 1.16 times higher than that of the ones stored wet, increasing to 1.34 times after 1 month, and 1.46 times after 6 months (p<0.001 for all comparisons). INTERPRETATION: Testing under dry conditions-as required in current standards-always gave higher values for mechanical properties than did storage and testing under more physiological conditions. The sensitivity of test values to different environments implies that testing conditions for bone cements should be scrutinized in order to develop more relevant testing protocols that reflect the in vivo environment more closely.

Induction of cell death by TiO2 nanoparticles: studies on a human monoblastoid cell line.

The cellular responses to degradation products from titanium (Ti) implants are important indicators for the biocompatibility of these widely used implantable medical devices. The potential toxicity of nanoparticulate matter released from implants has been scarcely studied. The aim of this study was to investigate the potential of TiO2 nanoparticles to induce modifications characteristic for death by apoptosis and/or necrosis in U937 human monoblastoid cells. Suspensions of TiO2 nanoparticles with a diameter <100nm were prepared in RPMI cell culture medium at concentrations that covered a range (0.005-4mg/ml) corresponding to concentrations found in blood, plasma, or in tissues surrounding Ti implants. The cells were exposed to the nanoparticulate suspensions for 24 and 48h and the responses were evaluated by flow cytometry and transmission electron microscopy. TiO2 nanoparticles induced both apoptotic and necrotic modifications in U937 cells.

Are inflatable nails an alternative to interlocked nails in tibial fractures?

Recently developed inflatable nails avoid reaming and interlocking screws in tibial fractures and reflect a new principle for stabilization of long bone fractures. We asked if the bending stiffness, rotational rigidity, or play (looseness of rotation) differed between an inflatable versus large-diameter reamed interlocked nails, and whether the maximal torque to failure of the two bone-implant constructs differed. In a cadaveric model, we compared the biomechanical properties with those of an interlocked nail in eight pairs of fractured tibial bones. Bending stiffness, rotational rigidity, play (looseness in rotation), and torsional strength within 20 degrees rotation were investigated using a biaxial servohydraulic testing system. For all biomechanical variables, we found a large interindividual variance between the pairs attributable to bone quality (osteoporosis) for both fixation methods. The inflatable nail had a higher bending stiffness, with a mean difference of 58 N/mm, and a lower torsional strength, with a mean difference of 13.5 Nm, compared with the locked nail. During torsional testing we noted slippage between the inflatable nail and bone. We observed no differences in play or rotational rigidity. Given the lower torsional strength we recommend caution with weightbearing until there are signs of fracture consolidation.