Calculation of stresses on 3D scaffolds fabricated using extrusion-based bioprinting using a semi-analytical approach.

The scaffold is essential to tissue engineering. In particular, the mechanical property of scaffolds has a significant impact on the success rate of regeneration. While numerous techniques exist for measuring mechanical properties, Compression test, three-point bending test, and nano-indentation test are the most common. Nevertheless, the mechanical property of porous structures cannot be accurately measured by previous testing methods. Combining superposition principles with the Flamant solution, this study developed semi-analytical solutions. Through compression testing and FEM simulation, the semi-analytical solution was fully validated. The solution can calculate not only the maximum stress of layer-by-layer construction of complex 3D scaffolds, but also the maximum load-bearing capacity if the mechanical property of the material is known.

Magnesium ions enhance infiltration of osteoblasts in scaffolds via increasing cell motility.

Magnesium (Mg) ions are the most abundant intracellular divalent cations and play a pivotal role in numerous cellular processes. Biodegradable Mg-containing materials, including scaffolds, are promising candidates for orthopedic applications. Here, we investigated the effect of Mg ions on the cellular properties of osteoblasts. Cytotoxicity tests on osteoblasts confirmed that no cytotoxic effects were found up to a supplementing Mg ion concentration of 10 mM. Mg ions at a concentration of 5 mM increased the migration and invasiveness of osteoblasts. To investigate the stimulatory effect of Mg ions on cell motility in scaffolds, we fabricated 10 wt% Mg ion-containing polycaprolactone (PCL) scaffolds, using the wire-network molding (WNM) technique. Mg ion-containing scaffolds persistently released Mg ions at a concentration of 5 mM in the media after pre-incubation. Furthermore, increased cell motility was confirmed in Mg ion-containing scaffolds by quantification of genomic DNA and protein content. Our results provide an important basis for the function of Mg ions and their effect on cell motility, and propose a novel role for Mg ions in scaffold applications.

Long-term clinical study and multiscale analysis of in vivo biodegradation mechanism of Mg alloy.

There has been a tremendous amount of research in the past decade to optimize the mechanical properties and degradation behavior of the biodegradable Mg alloy for orthopedic implant. Despite the feasibility of degrading implant, the lack of fundamental understanding about biocompatibility and underlying bone formation mechanism is currently limiting the use in clinical applications. Herein, we report the result of long-term clinical study and systematic investigation of bone formation mechanism of the biodegradable Mg-5wt%Ca-1wt%Zn alloy implant through simultaneous observation of changes in element composition and crystallinity within degrading interface at hierarchical levels. Controlled degradation of Mg-5wt%Ca-1wt%Zn alloy results in the formation of biomimicking calcification matrix at the degrading interface to initiate the bone formation process. This process facilitates early bone healing and allows the complete replacement of biodegradable Mg implant by the new bone within 1 y of implantation, as demonstrated in 53 cases of successful long-term clinical study.

Combined effect of change in humeral neck-shaft angle and retroversion on shoulder range of motion in reverse total shoulder arthroplasty - A simulation study.

BACKGROUND: We studied combined effect of change in humeral neck shaft angle and retroversion on shoulder ROM in reverse total shoulder arthroplasty using 3-dimensional simulations. METHODS: Using a 3D model construct based on the CT scans of 3 males and a 3-dimensional analysis program, a humeral component of reverse total shoulder arthroplasty was implanted in 0°, 10°, 20°, 30°,40° retroversion and 135°, 145°, and 155° neck shaft angle. Total horizontal range of motion (sum of horizontal adduction and abduction) at 30° and 60° scaption, adduction in the scapular plane and IR behind the back were measured for various combinations of neck shaft angle and retroversion. FINDINGS: Change in retroversion didn't show any effect on total horizontal range of motion. Total horizontal range of motion at both 30° and 60° scaption, showed maximum values at 135° neck shaft angle and minimum values at 155° neck shaft angle. With any combination of retroversion angles, adduction deficit was maximum at 155° neck shaft angle and no adduction deficit at 135° neck shaft angle. Every 10° decrease in neck shaft angle resulted in an average 10.4° increase in adduction. For every 10° increase in retroversion, there was loss of internal rotation behind the back up to at least one vertebral level. INTERPRETATION: 135° neck shaft angle resulted in maximum total horizontal range of motion both at 30° and 60° scaption regardless of retroversion angles. 135° neck shaft angle also reduced the chances of scapular impingement. Decrease in retroversion angle resulted in more amount of internal rotation behind the back.

Biodegradability engineering of biodegradable Mg alloys: tailoring the electrochemical properties and microstructure of constituent phases.

Crystalline Mg-based alloys with a distinct reduction in hydrogen evolution were prepared through both electrochemical and microstructural engineering of the constituent phases. The addition of Zn to Mg-Ca alloy modified the corrosion potentials of two constituent phases (Mg + Mg2Ca), which prevented the formation of a galvanic circuit and achieved a comparable corrosion rate to high purity Mg. Furthermore, effective grain refinement induced by the extrusion allowed the achievement of much lower corrosion rate than high purity Mg. Animal studies confirmed the large reduction in hydrogen evolution and revealed good tissue compatibility with increased bone deposition around the newly developed Mg alloy implants. Thus, high strength Mg-Ca-Zn alloys with medically acceptable corrosion rate were developed and showed great potential for use in a new generation of biodegradable implants.

Rapid in vitro corrosion induced by crack-like pathway in biodegradable Mg-10% Ca alloy.

The in vitro corrosion mechanism of the biodegradable cast Mg-10% Ca binary alloy in Hanks' solution was evaluated through transmission electron microscopy observations. The corrosion behavior depends strongly on the microstructural peculiarity of Mg2Ca phase surrounding the island-like primary Mg phase and the fast corrosion induced by the interdiffusion of O and Ca via the Mg2Ca phase of lamellar structure. At the corrosion front, we found that a nanosized crack-like pathway was formed along the interface between the Mg2Ca phase and the primary Mg phase. Through the crack-like pathway, O and Ca are atomically exchanged each other and then the corroded Mg2Ca phase was transformed to Mg oxides. The in vitro corrosion by the exchange of Ca and O at the nanosized pathway led to the rapid bulk corrosion in the Mg-Ca alloys.

The modification of microstructure to improve the biodegradation and mechanical properties of a biodegradable Mg alloy.

The effect of microstructural modification on the degradation behavior and mechanical properties of Mg-5wt%Ca alloy was investigated to tailor the load bearing orthopedic biodegradable implant material. The eutectic Mg/Mg2Ca phase precipitated in the as-cast Mg-5wt%Ca alloy generated a well-connected network of Mg2Ca, which caused drastic corrosion due to a micro galvanic cell formed by its low corrosion potential. Breaking the network structure using an extrusion process remarkably retarded the degradation rate of the extruded Mg-5wt%Ca alloy, which demonstrates that the biocompatibility and mechanical properties of Mg alloys can be enhanced through modification of their microstructure. The results from the in vitro and in vivo study suggest that the tailored microstructure by extrusion impede the deterioration in strength that arises due to the dynamic degradation behavior in body solution.

Early clinical results of reverse total shoulder arthroplasty in the Korean population.

BACKGROUND: We evaluated the short-term clinical outcomes and compared the component's sizes of reverse total shoulder arthroplasty (RTSA) in Korean Population. MATERIALS AND METHODS: We performed an RTSA on 42 patients between December 2007 to February 2010. The mean age at surgery was 72.5 ± 5.6 (10 men, 32 women) and average follow-up period was 24 months. Twenty-two cuff tears arthropathy, 15 irreparable massive rotator cuff tears with pseudoparalysis, 5 proximal humeral fractures, and 2 infection cases were included. We evaluated clinical outcomes and also the intra- and postoperative complications to determine if any of the complications were unique to the use of a RTSA in a Korean population. In the anatomic study, 92 uninjured shoulders of 92 patients were used for measuring the inferior glenoid size, and we compared the component's sizes of RTSA with those of the normal population. RESULTS: The ASES (American Shoulder and Elbow), UCLA, and KS (Knee Society) scores significantly improved from preoperative 35 (0-63), 12 (5-27), and 39 (3-81) to postoperative 68 (37-95), 24 (16-35), and 68 (34-88), respectively (P < .05). Postoperative complications were seen in 20% and scapular notching 35%. Three patients required further surgery for shoulder dislocation, periprosthetic fracture, and stem loosening. In the anatomic study, mean radius of the inferior glenoid was 17.1 ± 2.1 mm in male and 15.4 ± 1.6 mm in female. CONCLUSION: The short-term clinical results of an RTSA in Korean population are excellent despite high complication rate. However, the size of the glenoid is sometimes smaller than the baseplate (29 mm diameter) in female patients. More adequate size of the glenoid component should be considered.

Biocompatibility and strength retention of biodegradable Mg-Ca-Zn alloy bone implants.

The biocompatibility and strength retention of a Mg-Ca-Zn alloy were studied to evaluate its efficacy for osteosynthesis applications. Mg-Ca-Zn alloy and self-reinforced poly l-lactide (SR-PLLA) bone screws were implanted into New Zealand rabbits for radiography analysis, micro computed tomography analysis, histomorphometry, hematology, serum biochemistry, histopathology, and inductively coupled plasma mass spectrometry analysis. Bending and torsion tests were performed on intact specimens to find the initial mechanical strength of these Mg-Ca-Zn alloy bone screws. Strength retention of the Mg-Ca-Zn alloy implants were calculated from in vivo degradation rates and initial mechanical strength. Based on the animal study, Mg-Ca-Zn alloy bone screw showed absence of subcutaneous gas pockets, characteristic surface erosion properties, faster degradation rate than SR-PLLA bone screw, normal reference range of hematology and serum biochemistry, better histopathological response than SR-PLLA bone screw, and stable concentrations of each constituent element in soft tissues surrounding the implants. The initial strength and strength retention of Mg-Ca-Zn alloy were compared with those of various biomaterials. The initial strength of Mg-Ca-Zn alloy was higher than those of biostable and biodegradable polymers. The strength retention of Mg-Ca-Zn alloy bone screws was similar to those of biodegradable polymer. Therefore, this Mg-Ca-Zn alloy represents an excellent biodegradable biomaterial candidate for osteosynthesis applications.

In vivo corrosion mechanism by elemental interdiffusion of biodegradable Mg-Ca alloy.

We elucidated the in vivo corrosion mechanism of the biodegradable alloy Mg-10 wt % Ca in rat femoral condyle through transmission electron microscope observations assisted by focused ion beam technique. The alloy consists of a primary Mg phase and a three-dimensional lamellar network of Mg and Mg(2)Ca. We found that the Mg(2)Ca is rapidly corroded by interdiffusion of Ca and O, leading to a structural change from lamellar network to nanocrystalline MgO. In contrast to the fast corrosion rate of the lamellar structure, the primary Mg phase slowly changes into nanocrystalline MgO through surface corrosion by O supplied along the lamellar networks. The rapid interdiffusion induces an inhomogeneous Ca distribution and interestingly leads to the formation of a transient CaO phase, which acts as a selective leaching path for Ca. In addition, the outgoing Ca with P from body fluids forms needle-type calcium phosphates similar to hydroxyl apatite at interior and surface of the implant, providing an active biological environment for bone mineralization.

Load-bearing capacity and biological allowable limit of biodegradable metal based on degradation rate in vivo.

In this study, a newly developed Mg-Ca-Zn alloy for low degradation rate and surface erosion properties was evaluated. The compressive, tensile, and fatigue strength were measured before implantation. The degradation behavior was evaluated by analyzing the microstructure and local hardness of the explanted specimen. Mean and maximum degradation rates were measured using micro CT equipment from 4-, 8-, and 16- week explants, and the alloy was shown to display surface erosion properties. Based on these characteristics, the average and minimum load bearing capacities in tension, compression, and bending modes were calculated. According to the degradation rate and references of recommended dietary intakes (RDI), the Mg-Ca-Zn alloy appears to be safe for human use.

Effect of shear force on intervertebral disc (IVD) degeneration: an in vivo rat study.

Mechanical stress on the intervertebral disc (IVD) may contribute significantly to IVD degeneration, although its pathomechanism has not been fully understood. The purpose of this study was to test the hypothesis that sustained application of static shear force would result in IVD degeneration with minimum injury. We applied shear force on the rat lumbar spine (L5-L6) using a custom-designed loading device for 1 or 2 weeks. Degenerative changes such as nucleus pulposus cavity loss and border disruption were observed from the histology sections, indicating that the application of sustained dorsoventral shear force on the L6 vertebra induced degeneration of the IVDs in L5-L6 and adjacent levels of motion segment in 1 and 2 weeks. The findings of the present study could be useful for gaining a more relevant understanding of the biomechanical load factors of IVD degeneration not only for enabling better therapeutic interventions but also reducing the risk of low back injury.

Spinal muscles can create compressive follower loads in the lumbar spine in a neutral standing posture.

The ligamentous spinal column buckles under compressive loads of even less than 100N. Experimental results showed that under the follower load constraint, the ligamentous lumbar spine can sustain large compressive loads without buckling, while at the same time maintaining its flexibility reasonably well. The purpose of this study was to investigate the feasibility of follower loads produced by spinal muscles in the lumbar spine in a quiet standing posture. A three-dimensional static model of the lumbar spine incorporating 232 back muscles was developed and utilized to perform the optimization analysis in order to find the muscle forces, and compressive follower loads (CFLs) along optimum follower load paths (FLPs). The effect of increasing external loads on CFLs was also investigated. An optimum solution was found which is feasible for muscle forces producing minimum CFLs along the FLP located 11 mm posterior to the curve connecting the geometrical centers of the vertebral bodies. Activation of 30 muscles was found to create CFLs with zero joint moments in all intervertebral joints. CFLs increased with increasing external loads including FLP deviations from the optimum location. Our results demonstrate that spinal muscles can create CFLs in the lumbar spine in a neutral standing posture in vivo to sustain stability. Therefore, its application in experimental and numerical studies concerning loading conditions seems to be suitable for the attainment of realistic results.

Wear-corrosion performance of Si-DLC coatings on Ti-6Al-4V substrate.

Si-incorporated diamond-like carbon (Si-DLC) coatings ranging from 0 to 2 at % Si were deposited on Ti-alloy substrate by means of radio frequency plasma-assisted chemical vapor deposition (r.f. PACVD) technique, using a mixture of benzene (C(6)H(6)) and silane (SiH(4)) as the reaction gas. The synergy in wear and corrosion of Si-DLC coatings was investigated by tribological and electrochemical techniques. The electrolyte used in this test to simulate the corrosive environment of body fluid was a 0.89 wt % NaCl solution of pH 7.4 at 37 degrees C. This study provides quantitative data for the assessment of the effect of Si incorporation on the synergistic effect between wear and corrosion in the simulated body fluid environment. In conclusion, tribological and electrochemical measurements showed that the Si-DLC films could improve wear-corrosion resistance in the simulated body fluid environment owing to the lower friction coefficient, corrosion rate, delamination area, and water uptake.

Biomechanical evaluation of cervical double-door laminoplasty using hydroxyapatite spacer.

STUDY DESIGN: In vitro three-dimensional kinematic changes after double-door cervical laminoplasty, with and without spacer, and laminectomy were studied in a human cadaveric model. OBJECTIVES: To evaluate the effects of multilevel double-door laminoplasty and laminectomy as compared with the intact and to assess the influence of the spinous process spacer on the stability of the cervical spine. SUMMARY OF BACKGROUND DATA: Double-door type cervical laminoplasty has been widely used in the treatment of multisegmental stenotic conditions. However, its biomechanical advantages over laminectomy remain controversial. Also, the biomechanical effects of spacers between the split laminae have not been investigated. METHODS: Using fresh cadaveric C2-T1 specimens, sequential injuries were created in the following order: intact, double-door laminoplasty (C3-C6) with insertion of hydroxyapatite spacers, laminoplasty without spacer, and laminectomy. Motions of each vertebra in each injury status were measured in six loading modes: flexion, extension, right and left lateral bending, and right and left axial rotation.RESULTS Cervical laminectomy showed significant increase in motion compared with intact control in flexion [25% (P < 0.001)], extension [19% (P < 0.05)], and axial rotation [24% (P < 0.001)] at maximum load. Double-door laminoplasty with hydroxyapatite spacer indicated no significant difference in motion in all loading modes compared with intact. Laminoplasty without spacer showed intermediate values between laminoplasty with spacer and laminectomy in all loading modes. Initial slack of each injury status showed trends similar to that of maximum load, although mean percent changes of laminectomy and laminoplasty without spacer were greater than that of maximum load. CONCLUSIONS: Double-door laminoplasty with hydroxyapatite spacer appears to restore the motion of the decompressed segment back to its intact state in all loading modes. The use of HA spacers well contributes to maintaining the total stiffness of cervical spine. In contrast, laminectomy seems to have potential leading postoperative deformity or instability.

The biomechanical effects of multilevel posterior foraminotomy and foraminotomy with double-door laminoplasty.

The aim of this study is to evaluate the biomechanical effects of multilevel foraminotomy and foraminotomy with double-door laminoplasty compared with foraminotomy with laminectomy. Using fresh human cadaveric specimens (C2-T1), sequential injuries were created in the following order: intact, bilateral foraminotomies (C3-C4, C4-C5, C5-C6), laminoplasty (C3-C6) using hydroxyapatite spacer, removal of the spacers, and laminectomy. Changes in the rotations of each vertebra in each injury status were measured in six loading modes: flexion, extension, right and left lateral bending, and right and left axial rotation. Foraminotomy alone and following laminoplasty showed no significant differences in motion compared with intact except in axial rotation. After removal of the spacers and following laminectomy, the motion increased significantly in flexion and axial rotation. The ranges of initial slack showed similar trends when compared with the results at maximum load. Clinical implications of these observations are presented.