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Objective:To evaluate the physicochemical properties, degradation and drug release behaviour, cytocompatibility and bacteriostatic properties in vitro of porous magnesium alloy scaffolds containing vancomycin/poly(lactic-co-glycolic acid) (PLGA). Methods:Porous magnesium scaffolds (Mg-2Zn-0.3Ca) were prepared using the template replication technique. The MgF 2 surface layer was obtained by high temperature fluorination. The vancomycin/PLGA porous magnesium alloy drug-loaded scaffolds were obtained by homogeneous lifting after submersion in a dichloromethane solution of PLGA containing vancomycin hydrochloride. According to the products at each stage of the preparation (scaffolds of magnesium alloy, magnesium fluoride alloy, PLGA coated magnesium fluoride alloy, and vancomycin/PLGA magnesium fluoride alloy), they were divided into an Mg group, an MgF 2 group, a PLGA group, and a vancomycin/PLGA group. Immediately after preparation, the material science characterization, degradation rate, drug release rate, antibacterial properties, hemocompatibility, and cell proliferation and differentiation ability of the scaffolds were measured and evaluated. Results:Vancomycin-loaded magnesium alloy scaffolds were successfully prepared with an average porosity of 66.39%. Their degradation rate [(0.540±0.102) mm/year] was significantly lower than that of the Mg ones [(10.048±0.297) mm/year] ( P<0.05). Their pH of degradation in Hank equilibrium salt solution was close to the physiological pH. Their release of vancomycin was fast in the first 48 h and gradually slowed down after 48 h. Their cumulative drug concentration reached a maximum of 43 mg/L at d 11; their vancomycin was still released slowly after d 11. The antimicrobial rate in the vancomycin/PLGA group (97.89%±0.28%) was significantly higher than that in the Mg group (74.92%±2.20%), the MgF 2 group (78.46%±2.59%) and the PLGA group (61.08%±4.21%) ( P<0.05). Their hemolysis rate (0.55%) was much lower than the requirement of ISO 10993-4 (5%). The extract liquid from them promoted the proliferation of rat bone marrow mesenchymal stem cells (BMSCs), showing a gradually increased proliferation rate from d1 (104.80%±5.13%) to d3 (112.36%±2.07%) and d7 (127.79%±4.61%). The calcium nodules in BMSCs were significantly increased at d 14, with an OD value of absorbance of 1.189±0.020, significantly higher than that in the Mg group (0.803±0.020), the MgF 2 group (0.878±0.028) and the PLGA group (0.887±0.026) ( P<0.05). Conclusion:Vancomycin/PLGA-loaded porous magnesium alloy scaffolds exhibit good material properties, antibacterial properties, biocompatibility and osteogenic properties in vitro.
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BACKGROUND: It has been confirmed that some biomedical magnesium alloy products have antibacterial properties, but the specific antibacterial mechanism is still unclear. OBJECTIVE: To investigate the antibacterial properties of biomedical Jiao Da Bio-Magnesium scaffold in vitro and explore possible mechanism. METHODS: Jiao Da Bio-Magnesium porous scaffold material extract was prepared. As the most common bacteria causing orthopedic implants infection, Escherichia coli and Staphylococcus aureus were selected for testing. The bacteriostasis rate was quantitatively evaluated by contact culture of the extraction solution. The bacteriostasis performance of the material was qualitatively evaluated by observing the bacterial morphology through scanning electron microscope. The alkaline phosphatase, conductivity, potassium ion, nucleic acid and protein content in bacterial extracellular liquid environment were detected. The possible antibacterial mechanism of Jiao Da Bio-Magnesium porous scaffold material extract was preliminarily explored. RESULTS AND CONCLUSION: (1) The bacteriostasis rate of Jiao Da Bio-Magnesium porous scaffold extract cultured with Escherichia coli for 12 hours ranged from 56.23% to 79.72%, while the Staphylococcus aureus group ranged from 62.34% to 76.07%. (2) Under scanning electron microscope, wizened form, smaller volume and scarcer distribution were observed. (3) The material extract had no effect on the content of alkaline phosphatase in the extracellular environment of the two bacteria, but increased the electrical conductivity and potassium ion content in the extracellular environment of the two bacteria. (4) The material extract had no effect on the content of nucleic acid and protein in the extracellular environment of Escherichia coli, and increased the content of nucleic acid and protein in the extracellular environment of Staphylococcus aureus. (5) The material extract could inhibit the nucleic acid content of the two bacteria, but had no effect on the soluble protein content of Escherichia coli cells, and inhibited the synthesis of soluble protein in Staphylococcus aureus cells. (6) Results suggested that Jiao Da Bio-Magnesium porous scaffold material has certain antibacterial properties in vitro, and the inhibitory effect on Staphylococcus aureus is stronger than that on Escherichia coli. The possible antibacterial mechanism is speculated that it can change the permeability of bacterial cell membrane and affect the synthesis of bacterial nucleic acids and proteins.
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Objective To investigate the feasibility of absorbable magnesium alloy screws in atlantoaxial dislocation fixation. Methods Four kinds of screws with triangular, rectangular, trapezoidal and zigzag thread were designed with WE43 magnesium alloy. The finite element simulation analyses were performed on the screw- polyurethane model and atlantoaxial fixation system model. The stress and displacement distributions on the models were obtained. Results The pull-out force simulations were carried out on four kinds of magnesium alloy screws according to ASTM F543 standard specification. The stresses of screws with triangular, rectangular, trapezoidal and zigzag thread were 146.20, 185.22,194.98, 264.55 MPa, respectively. The pull-out strength of the screw with triangular thread was the largest, and the peak stress was the smallest. The magnesium alloy screw with triangular thread used for atlantoaxial fixation could meet the strength requirements of flexion/extension, rotation and bending of the neck. The peak stress of the screw was reduced by 17.16 MPa after adding hydroxyapatite (HA) coating on the surface, and the stress on the screw was within the range of bonding strength between coating and magnesium alloy substrate. Conclusions Under the same loading condition, the screw with triangular thread has good stability and the best pull-out force performance. After heat treatment, the strength of magnesium alloy screw with triangular thread meets the load-bearing requirements for atlantoaxial dislocation fixation. HA coating on screw surface can optimize mechanical properties of the screw, and there exits good bonding strength between the coating and the screw.
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Objective To study the degradation behavior and mechanical properties of magnesium alloy plate on treatment of tibial fracture in New Zealand rabbits. Methods Thirty-six adult New Zealand rabbits were randomly divided into experimental group (magnesium alloy bone plate group, n=18) and control group (titanium alloy bone plate group, n=18). Tibial fractures in experimental group and control group were fixed with magnesium alloy bone plate and titanium alloy bone plate, respectively. After operation, X-ray, scanning electron microscopy, energy spectrum analysis, weight loss test and four-point bending test were performed in each group to analyze the degradation behavior and mechanical properties of magnesium alloy plate after tibial fracture treatment. Results Magnesium alloy bone plate could be degraded gradually in vivo. The degradation of magnesium alloy bone plate was deepened gradually with the implantation time, and the surface was corroded uniformly. The mechanical properties of magnesium alloy bone plate decreased gradually with the degradation in vivo. Conclusions Magnesium alloy bone plate can degrade gradually with fracture healing in vivo, and its mechanical properties gradually decline, but it can still meet the requirements of fracture internal fixation, and is a kind of good new degradable orthopedic implant material.
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Biodegradable vascular stents have better biocompatibility than drug-eluting stents. The blood vessels are rebuilt and degraded after normal physiological functions are restored. Due to it will not stay in the body for a long time and the patients don't need taking anti-rejection drugs all the time, it becomes the focus of attention in the treatment of coronary heart disease. This article introduced the development history of biodegradable stents and reviewed the research status of several different materials of vascular stents (animals or humans)
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Animals , Humans , Absorbable Implants , Drug-Eluting Stents , StentsABSTRACT
Objective To study the effect of stress on the degradation rate in vitro of novel magnesium alloy bone screw. Methods A three-dimensional （3D） model of the tibia fracture was established using the reverse engineering method. Then, based on the FE model, the in vitro degradation experimental device for bone screws was designed. The stress distribution of the screw by finite element calculation was used as the in vitro experimental load, which effectively improved the accuracy and efficiency of the experiment. The experimental samples were divided into four groups. Group A was treated as control group without force application, while Groups B, C and D were subjected to 150, 250 and 350 N axial forces. The influence of different mechanical environment on the degradation rate in vitro of bone screws was investigated. Finally, combining the stress distributions with the degradation experiment results in vitro, the curve between the stress and the degradation rate in vitro of novel magnesium alloy bone screws was obtained. Results Degradation experiments in vitro showed that Group A had the lowest weight loss and hydrogen production, and the average degradation rate was (0.315±0.005) mm/a. While in the stress groups, the weight loss and hydrogen production increased gradually with the axial force increasing. The average degradation rates of Groups B, C and D were (0.379±0.006), (0.469±0.007) and (0.547±0.009) mm/a, respectively. Conclusions When the novel magnesium alloy bone screw was degraded in mechanical environment, the greater stress on the screw would cause the faster degradation rate in vitro. The obtained relationship between the maximum stress and the average degradation rate in vitro of the novel megnesium alloy bone screw provided data support and theoretical guidance for material selection, design and clinical application of magnesium alloy bone screws.
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Objective To conduct simulation analysis on support performance of the stent by using finite element method, and optimize structure parameters of the stent by using Kriging surrogate model, so as to provide more scientific guidance for clinical treatment with design and development of the stent. Methods The contact model was established by penalty function method. The generalized variational principle was selected as theoretical basis of the numerical simulation, and the theory of Kriging surrogate model was used for finite element optimization on support stiffness of the stent, so as to study the effect from the number of circumferential support, the length of the support and the initial diameter on support performance of the stent. Results With the increase of the number of circumferential support or the length of the support, the support performance showed the decreasing tendency; with the increase of the initial diameter, the support performance showed the increasing tendency. From seven stents by using the theory of Kriging surrogate model, it was concluded that structural parameters of the optimal stent were: the number of circumferential support was six, the length of the support was 1.15 mm, and the initial diameter was 1.65 mm. Conclusions The numerical result agreed well with the experimental data and the error was smaller than 5%, and the error rate of experimental repeatability was within 0.5%, which verified effectiveness and rationality of the finite element analysis. The optimization of support performance provides an important reference for design and exploration of new magnesium alloy stent.
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Objective To observe the degradation time and the intimal hyperplasia of biodegradable magnesium alloy stent (MPM) implanted in the abdominal aorta of experimental rabbits.Methods A total of 24 New Zealand white rabbits were randomly divided into four groups (30 d,60 d,90 d and 180 d) with 6 rabbits in each group.In cach rabbit one MPM stent was implanted in the abdominal aorta at the level of one cm below the left renal artery.Reexamination of abdominal aortography with DSA was separately performed at 30,60,90 and 180 d after stent implantation to check the stent condition.The rabbits of each group were sacrificed at the corresponding scheduled day,the stenting segment of aorta of each rabbit was removed and the specimen was sent for microscopic examination.The experimental results were analyzed with SPSS20.0 software.Results All the 24 experimental rabbits survived.During the follow-up period the stent showed gradual degradation changes,and basically complete degradation was not observed until to 180 days.Meanwhile,the intimal hyperplasia reached its peak at 90 days after implantation.The abdominal aorta remained unobstructed during the whole process of degradation.Conclusion The time of complete degradation for MPM stent is 182 days,which is long enough to meet the needs of vascular positive remodeling.
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Objective To design a new type of biliary stent to be used in the common bile duct probe and evaluate its biocompatibility, safety and effectiveness in a canine model.Methods Magnesium alloy (AZ 31B) was used to make biliary stents.A canine model of acute obstructive jaundice was established by ligating the distal end of the common bile duct.These dogs were divided into two groups with either placement of magnesium stent or not.The incidence of bile duct leakage and survival were evaluated.Meanwhile, we determined the concentration of magnesium in various body fluids and organs, liver function test, and ultrasonic and histological studies.Results The concentrations of magnesium in the blood, feces, liver, heart, brain and lungs were similar between the two groups.Bile leakage rate in experimental group and control group was 0％ and 16.7％, respectively.The mortality was 16.7％ and 33.3％.There were no significant differences in ALP and TBIL between experimental group and control group (P>0.05) before building and bile duct exploration.There were significant differences in ALP andTBIL between the two groups one and three months after bile duct probe (P<0.05).Biliary tract specimens showed obviously anastomotic stenosis performances and expansion performances of extrahepatic biliary in the control group, but in experimental group such changes were not observed.Ultrasonography showed that the patency of biliary anastomosis was good and there was no anastomotic biliary stricture in experimental group.However, progressive stenosis and expansion performances of extrahepatic biliary occurred in control group.There were fewer collagen fibers but more muscle fibers in experimental group than in control group.Conclusion Biliary stent made of magnesium alloy is of good biocompatibility and has the potential to prevent the postoperative stenosis in the common bile duct probe.
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Objective To study the mechanical properties and degradation behavior of biodegradable silicon-covered magnesium alloy stent in vitro,to investigate the technical feasibility of its implantation into rabbit esophagus and to observe the tissue reaction in vivo.Methods The mechanical compression recovery properties and the degradation behavior of biodegradable silicon-covered magnesium alloy stent were tested in vitro.A total of 30 healthy Holland rabbits were randomly divided into silicon-covered magnesium alloy stent group (n=15) and control group (n=15).For rabbits in the silicon-covered magnesium alloy stent group fluoroscopy-guided insertion of the stent into the lower third segment of esophagus was conducted,while for rabbits in the control group no intervention was adopted.One,2 and 4 weeks after the implantation of the stent,esophagography was performed for all rabbits of both groups,and each time every 5 rabbits from both groups were sacrificed,the specimens were collected and sent for histological examinations.Results In vitro test indicated that biodegradable silicon-covered magnesium alloy stent had good flexibility and elasticity,and in phosphate-buffered saline with pH 4.0 or pH 7.4 it degraded more slowly than bare magnesium alloy stent.In vivo test showed that the stent implantation could be well tolerated by all experimental rabbits.Before stent insertion the esophageal diameter was(9.2±0.8) mm,and at one,2 and 4 weeks after stent insertion the esophageal diameters were (9.7±0.7) mm,(9.6±0.8) mm and (9.6±0.5) mm respectively (P＞0.05).In the silicon-covered magnesium alloy stent group,stent displacement occurred in 6 rabbits in one week (n=l),2weeks (n=1) and 4 weeks (n=4).After stent implantation,the tissue reactions such as esophageal wall injury,collagen deposition,etc.were not obviously different from those in the control group (P＞0.05).Conclusion It is technically feasible to insert silicon-covered magnesium alloy stent into the rabbit's esophagus,the stent can provide sufficient support for at least 2 weeks,the stent displacement rate is low and acceptable,and no severe esophageal wall injury and collagen deposition are observed.
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Objective To analyze and compare the effects of structure parameters on synchronous motor ability between the blood vessel and stent after stent implantation by using finite element method and grey correlation theory. Methods The magnesium alloy stent of S closed-loop type was selected, and 9 models of such stents with different materials, numbers of support in circumferential direction, support lengths and initial diameters were established by using SolidWorks, and these stent models were meshed by using HyperMesh. The synchronous motor ability between the blood vessel and stent after stent implantation was simulated by using ABAQUS, and the influencing factors of different structure parameters on bending stiffness were investigated and compared by using grey correlation theory. Results The effect of materials on stent flexibility was obvious. The flexibility of magnesium alloy stent was the best, and the bending stiffness was 0.958 N•(rad•mm)-1; the best flexibility of stents were those with 5-support in circumferential direction, 1.0 mm-support length, and 1.4 mm-initial diameter, and their bending stiffness was 0.853,0.829 and 1.024 N•(rad•mm)-1, respectively. Conclusions The flexibility of magnesium alloy stent is the best, followed by stainless steel stent, and cobalt-chromium stent ranks last. With the increase of support numbers in circumferential direction, support length and initial diameter, the stent flexibility shows the decreasing tendency; the grey correlation analysis shows that the effect of materials on stent flexibility is the most significant, followed by support numbers in circumferential direction and support length, while initial diameter exerts the smallest influence. The analysis of structure parameter effects on stent flexibility will provide more scientific guidance for stent design and development as well as its intervention treatment in clinic.
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Stent implantation plays a more and more important role in the treatment of benign esophageal stenosis. Metal stents are most commonly used in the clinical practice, which can be classified into permanent stents and temporary retrieval stents. Permanent implantation of metal stents is easy to cause complications such as inflammatory hyperplasia, in-stent restenosis, perforation, bleeding, etc. Temporary retrieval stents should be removed with one week after it is implanted in order to avoid esophageal scar tissue repair and in-stent tissue hyperplasia, which can cause difficulty in its removing and produce higher recurrence rate of esophageal restenosis. Clinically, drug-eluting stents have already been used in cardiovascular system procedures, but at present the gastrointestinal drug-eluting stents are still in development and animal experiment stage. Biodegradable magnesium alloy stents have been widely employed in cardiovascular system procedures. With the rapid development of biological engineering materials, drug-eluting magnesium alloy stent has become a hot spot and the frontier in research field. This paper aims to make a comprehensive review about the current research status and prospect of the drug-eluting magnesium alloy stents, focusing on the stent technology, stent molding, coating modification, and the treatment of drug-eluting.
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Objective To make a preliminary evaluation of the degradation of AZ31 bioabsorbable magnesium alloy stent implanted in the abdominal aorta of experimental rabbits.Methods Twelve AZ31 biodegradable magnesium alloy stents were separately deployed in the infrarenal abdominal aortas of twelve New Zealand white rabbits.Every three experimental rabbits were sacrificed each time at one,two,three and four months after the procedure of stenting.The stenting segment of the aortas were harvested,radiographod and sent for pathologic examination to observe the degradable performance of the stent.Results All animals survived form the operation in the scheduled follow-up period.Radiographically and pathologically,the stents were fully expanded with perfect shape one month after the procedure,and part of the stent struts began to be degraded and fractured in two months,resulting in the loss of its supporting function.Three months after the implantation most stents were corroded.and in four months all the stents become completely destroyed.The estimating time for producing complete degradation of AZ31 magnesium alloy stents in rabbit's aorta was 104.5 days.Conclusion AZ31 bioabsorbable magnesium alloy stents implanted in rabbit abdominal aorta will lose their radial force in two months.How to prolong the functioning time of the implanted stents is the next research target.
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Stent implantation plays an significant role in the interventional therapy, mainly with permanent stent, possessing many disadvantages such as restenosis and inflammatory hyperplasia and can thus hardly be used in children and nonmalignant stenosis. Biodegradable stent has theoretical capability to solve these problems and acquires a bright future. Nowadays, with the development of material industry and manufacture craft, biodegradable stent technique has turned up to be mature in last decades. Through the strict animal experiments and prophase of clinic application, satisfactory result has been acquired. We believe that bioabsorbable stent will be widely used in many benign diseases which would be a good supplement for permanent stent in the near future.
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[Objective]To study the mechanism of magnesium alloy degradation and bone formation at the bone-implant interface after implanting a magnesium alloy into rat femur.[Method]SD rats femur were filled with magnesium alloy stick.Nine weeks later,animals were killed and femur were retrieved.Systematic investigations on the surface morphology,composition,structure of bone-implant were performed by means of metallurgical microscope,scanning electron microscopy(SEM),and energy dispersive spectrum(EDS).Decalcified sections were prepared,and histologic examination was carried out.[Result]The bone response happened both on the surface of surrounding bone and the surface of magnesium alloy degradation layer while magnesium alloy degradating in rat femur.It was formed three layers at the interface of bone-implant: the metal layer,the degradation layer,and the new bone layer.Discontinuity connective tissue could be seen on the new bone layer but no inflammatory cells were found.[Conclusion]The new bone response at the interface of bone-implant is consistent with normal bone tissue.Magnesium alloys have good characters of degradation ability,osteogenesis ability,and histocompatibility.And the rate of degradation is corresponding to the rate of new bone formation.
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[Objective]To observe mouse osteoblasts vitality,histomorphology and growing development in vitro co-culture combined with magnesium alloys,confirm the biocompatibility of magnesium alloys and osteoblasts,and try to find out the possibility of magnesium alloys to be a new type of bone surgery implant material.[Method]Mouse osteoblasts were checked by Gomori and Von kossa stained,cultured and developed in vitro.Then the osteoblasts were mixed with magnesium alloys in a cell density of 3?104/ml.After 24、48、72 hours co-culture,the surface of magnesium alloys were observed by scanning electron microscopy(SEM) and confocal microscopy to find the change of osteoblasts.[Result]After culture in vitro,the osteoblasts well developed,and expressed stable character.After co-culture with magnesium alloys,the cells adhered and proliferated on the surface of alloys very well from SEM and confocal microscopy observation,which showed the osteoblasts had great activity and reproduce capability.[Conclusion]Magnesium alloys showed good biocompatibility and bone conduction capability with mouse osteoblasts,so the magnesium alloy is very possible to be a new type of bone surgery implant material.