In vitro corrosion of ZEK100 plates in Hank's Balanced Salt Solution

Enhancing bone formation using absorbable AZ31B magnesium alloy membranes during distraction osteogenesis: A new material study

Purpose

To investigate whether the use of absorble AZ31B magnesium alloys over distraction gaps improves the quality and quantity of regenerated bone better than the use of Collagen membranes.

Methods

Fifteen mixed-breed dogs were randomly divided into the experimental (n = 10) and control (n = 5) groups. In the experimental group, two devices were implanted along the mandible; one side with absorble AZ31B and the other side with Collagen. The control animals did not undergo osteotomy or distraction. After a consolidation time of two months, 30 specimens were harvested, and newly created bone was identified using CBCT and micro-CT.

Results

The Collagen membranes were absorbed completely, and the AZ31B membranes became irregular and rough. Mandible length was successfully extended approximately 1 cm. More bone formation was found after using AZ31B than Collagen, and there was a significant difference in width reduction between experimental sites treated with AZ31B (0.11 ± 0.04 cm) and Collagen (0.42 ± 0.06 cm) (p < 0.05). Trabecular thickness was also significantly higher in AZ31B (0.338 ± 0.08 cm) and control (0.417 ± 0.05 cm) than Collagen (0.178 ± 0.04 cm) (p < 0.05).

Conclusion

An AZ31B membrane barrier is biocompatible and absorbable which can maintain the distraction gap and provide support to the attached osteoprogenitors by providing space for them to proliferate.

Characterization and Evaluation of Composite Biomaterial Bioactive Glass-Polylactic Acid for Bone Tissue Engineering Applications

The limitations associated with the clinical use of autographs and allografts are driving efforts to develop relevant and applicable biomaterial substitutes. In this research, 3D porous scaffolds composed of bioactive glass (BG) obtained through the sol-gel technique and polylactic acid (PLA) synthesized via lactic acid (LA) ring-opening polymerization were prepared by the gel-pressing technique. Two different weight compositions were evaluated, namely, BG70-PLA30 and BG30-PLA70. The structure and morphology of the resulting scaffolds were analysed by FTIR, XRD, SEM, and under ASTM F1635 standard characterizations. The results confirmed that BG promotes the formation of a hydroxy-carbonated apatite (HAp) layer on composites when immersed in simulated body fluid (SBF). Biodegradability evaluations were carried out according to the ISO 10993-13:2010 standard. In addition, electrochemical evaluations were performed in both Hank's and SBF solutions at 37 °C in order to analyse the degradation of the material. This evaluation allowed us to observe that both samples showed an activation mechanism in the early stages followed by pseudo-passivation due to physical bioactive glass characteristics, suggesting an improvement in the formation of the HAp nucleation. The described composites showed excellent resistance to degradation and outstanding suitability for bone tissue engineering applications.

In Vitro Investigation on Degradable Mg-Based Biomaterial under the Impact of the Serum Glycoprotein Fetuin

Biomedical applications of magnesium (Mg) and its alloys are generally dependent on their degradation behavior in vivo. Despite its attractive properties, which make Mg suitable for orthopedic applications, the in vivo material-tissue (bone, blood, and lymph tissues) interaction is not yet fully understood. To investigate the influence of major serum proteins on the degradation, this study focused on fetuin, which is one of the major non-collagenous plasma proteins and which is essential for biomineralization. This study used a physiological setup to investigate the influence of fetuin on the degradation behavior of pure Mg in the presence of calcium (Ca). Extruded pure Mg samples were immersed under cell culture conditions in Hank’s balanced salt solution (HBSS) under defined Ca regimes. The results showed a significant decrease in the degradation rate (DR) when both fetuin and Ca were present in an immersion medium as compared to media where they were not simultaneously present. A possible reason for this behavior was the forming of a dense, protein-degradation products protection barrier at the material surface. Furthermore, the limitation of freely available Ca might be a reason for a decreased degradation. The cultivation of primary osteoblasts (pOB) was possible at the fetuin-coated Mg-surface without additional serum supplementation.

Degradation rates and products of pure magnesium exposed to different aqueous media under physiological conditions

As magnesium and many of its alloys are a promising class of degradable implant materials, a thorough understanding of their degradation under physiological conditions is a key challenge in the field of biomaterial science. In order to increase the predictive power of in vitro studies, it is necessary to imitate the in vivo conditions, track the decomposition process and identify the products that form during the degradation pathway. In this in vitro study, slices of pure magnesium were exposed to Hank’s Balanced Salt Solution (HBSS), Dulbecco’s Modified Eagle Medium (DMEM) and simulated body fluid (SBF), respectively, under cell culture conditions, which included CO

Influence of Surrounding Cations on the Surface Degradation of Magnesium Alloy Implants under a Compressive Pressure

The effect of cations in the surrounding solutions on the surface degradation of magnesium alloys, a well-recognized biodegradable biomaterial, has been neglected compared with the effect of anions in the past. To better simulate the compressive environment where magnesium alloys are implanted into the body as a cardiovascular stent, a device is designed and employed in the test so that a pressure, equivalent to the vascular pressure, can be directly applied to the magnesium alloy implants when the alloys are immersed in a medium containing one of the cations (K(+), Na(+), Ca(2+), and Mg(2+)) found in blood plasma. The surface degradation behaviors of the magnesium alloys in the immersion test are then investigated using hydrogen evolution, mass loss determination, electron microscopy, pH value, and potentiodynamic measurements. The cations are found to promote the surface degradation of the magnesium alloys with the degree decreased in the order of K(+) > Na(+) > Ca(2+) > Mg(2+). The possible mechanism of the effects of the cations on the surface degradation is also discussed. This study will allow us to predict the surface degradation of magnesium alloys in the physiological environment and to promote the further development of magnesium alloys as biodegradable biomaterials.

Magnesium degradation as determined by artificial neural networks

Magnesium degradation under physiological conditions is a highly complex process in which temperature, the use of cell culture growth medium and the presence of CO2, O2 and proteins can influence the corrosion rate and the composition of the resulting corrosion layer. Due to the complexity of this process it is almost impossible to predict the parameters that are most important and whether some parameters have a synergistic effect on the corrosion rate. Artificial neural networks are a mathematical tool that can be used to approximate and analyse non-linear problems with multiple inputs. In this work we present the first analysis of corrosion data obtained using this method, which reveals that CO2 and the composition of the buffer system play a crucial role in the corrosion of magnesium, whereas O2, proteins and temperature play a less prominent role.

Effect of biologically relevant ions on the corrosion products formed on alloy AZ31B: an improved understanding of magnesium corrosion

Simulated physiological solutions mimicking human plasma have been utilized to study the in vitro corrosion of biodegradable metals. However, corrosion and corrosion product formation are different for different solutions with varied responses and, hence, the prediction of in vivo degradation behavior is not feasible based on these studies alone. This paper reports the role of physiologically relevant salts and their concentrations on the corrosion behavior of a magnesium alloy (AZ31B) and subsequent corrosion production formation. Immersion tests were performed for three different concentrations of Ca(2+), HPO4(2-), HCO3(-) to identify the effect of each ion on the corrosion of AZ31B assessed at 1, 3 and 10 days. Time-lapse morphological characterization of the samples was performed using X-ray computed tomography and scanning electron microscopy. The chemical composition of the surface corrosion products was determined by electron dispersive X-ray spectroscopy and X-ray diffraction. The results show that: (1) calcium is not present in the corrosion product layer when only Cl(-) and OH(-) anions are available; (2) the presence of phosphate induces formation of a densely packed amorphous magnesium phosphate corrosion product layer when HPO4(2-) and Cl(-) are present in solution; (3) octacalcium phosphate and hydroxyapatite (HAp) are deposited on the surface of the magnesium alloy when HPO4(2-) and Ca(2+) are present together in NaCl solution (this coating limits localized corrosion and increases general corrosion resistance); (4) addition of HCO3(-) accelerates the overall corrosion rate, which increases with increasing bicarbonate concentration; (5) the corrosion rate decreases due to the formation of insoluble HAp on the surface when HCO3(-), Ca(2+), and HPO4(2-) are present together.

Comparative in vitro study and biomechanical testing of two different magnesium alloys

In this in vitro study, magnesium plates of ZEK100 and MgCa0.8 alloy similar to common titanium alloy osteosynthesis plates were investigated as degradable biomedical materials with a focus on primary stability. Immersion tests were performed in Hank's Balanced Salt Solution at 37. The bending strength of the samples was determined using the four-point bending test according to ISO 9585:1990. The initial strength of the noncorroded ZEK100 plate was 11% greater than that of the MgCa0.8 plate; both were approximately 65% weaker than a titanium plate. The bending strength was determined after 48 and 96 h of immersion in Hank's Balanced Salt Solution; both magnesium alloys decreased by approximately 7% after immersion for 96 h. The degradation rate and the Mg(2+) release of ZEK100 were lower than those of MgCa0.8. Strong pitting and filiform corrosion were observed in the MgCa0.8 samples after 96 h of immersion. The surface of the ZEK100 plates exhibited only small areas of filiform corrosion. The results of this in vitro study indicate that the ZEK100 alloy may be more suitable for biomedical applications.

Biodegradable magnesium-based screw clinically equivalent to titanium screw in hallux valgus surgery: short term results of the first prospective, randomized, controlled clinical pilot study

Purpose

Nondegradable steel-and titanium-based implants are commonly used in orthopedic surgery. Although they provide maximal stability, they are also associated with interference on imaging modalities, may induce stress shielding, and additional explantation procedures may be necessary. Alternatively, degradable polymer implants are mechanically weaker and induce foreign body reactions. Degradable magnesium-based stents are currently being investigated in clinical trials for use in cardiovascular medicine. The magnesium alloy MgYREZr demonstrates good biocompatibility and osteoconductive properties. The aim of this prospective, randomized, clinical pilot trial was to determine if magnesium-based MgYREZr screws are equivalent to standard titanium screws for fixation during chevron osteotomy in patients with a mild hallux valgus.

Methods

Patients (n=26) were randomly assigned to undergo osteosynthesis using either titanium or degradable magnesium-based implants of the same design. The 6 month follow-up period included clinical, laboratory, and radiographic assessments.

Results

No significant differences were found in terms of the American Orthopaedic Foot and Ankle Society (AOFAS) score for hallux, visual analog scale for pain assessment, or range of motion (ROM) of the first metatarsophalangeal joint (MTPJ). No foreign body reactions, osteolysis, or systemic inflammatory reactions were detected. The groups were not significantly different in terms of radiographic or laboratory results.

Conclusion

The radiographic and clinical results of this prospective controlled study demonstrate that degradable magnesium-based screws are equivalent to titanium screws for the treatment of mild hallux valgus deformities.