Temporary Implants Research Articles

A study on setting of the fatigue limit of temporary dental implants.

A temporary dental implant is a medical device which is temporarily used to support a prosthesis such as an artificial tooth used for restoring patient's masticatory function during implant treatment. It is implanted in the oral cavity to substitute for the role of tooth. Due to the aging and westernization of current Korean society, the number of tooth extraction and implantation procedures is increasing, leading to an increase in the use and development of temporary dental implants. Because an implant performs a masticatory function in place of a tooth, a dynamic load is repeatedly put on the implant. Thus, the fatigue of implants is reported to be the most common causes of the fracture thereof. According to the investigation and analysis of the current domestic and international standards, the standard for fatigue of implant fixtures is not separately specified. Although a test method for measuring the fatigue is suggested in an ISO standard, it is a standard for permanent dental implants. Most of the test standards for Korean manufacturers and importers apply 250 N or more based on the guidance for the safety and performance evaluation of dental implants. Therefore, this study is intended to figure out the fatigue standard which can be applied to temporary dental implants when measuring the fatigue according to the test method suggested in the permanent dental implant standard. The results determined that suitable fatigue standards of temporary dental implants should be provided by each manufacturer rather than applying 250 N. This study will be useful for the establishment of the fatigue standards and fatigue test methods of the manufacturers and importers of temporary dental implants.

Dissolvable batteries made of silk

A flexible battery made of silk films could power temporary medical sensors and implants in the body and then harmlessly melt away once its work is done (ACS Energy Lett. 2017, DOI: 10.1021/acsenergylett.7b00012). Caiyun Wang and Gordon G. Wallace of the University of Wollongong and colleagues made thin silk films for the battery by dissolving the protein fibroin, derived from silkworm cocoons, in water. They spread the solution in a mold and peeled off ultrathin sheets of silk after the water evaporated. To make a solid electrolyte for the battery, the researchers infused a piece of the silk film with the ionic liquid choline nitrate, a molten salt that conducts ions. Depositing a magnesium alloy on another piece of silk formed an anode, and depositing gold on still another piece formed a cathode. The team assembled the battery by sandwiching the electrolyte film between the two electrode films. The postage-stamp-sized,

Study of Transport Properties of Polyelectrolyte-Cellulose Acetate Membranes

The rapid and uncontrollable corrosion of Mg and Mg based alloys is one of the main obstacles in the development of Mg based temporal implant materials1,2; the potentially harmful corrosion products leading to the increase of local pH and release of H2 gas to the surrounding tissues are especially problematic. Therefore, the control over the dissolution rate and release of corrosion products is of high importance if Mg based materials are to be used as temporary biomedical implants. Earlier, the authors have developed a weak polyelectrolyte-cellulose acetate membrane (poly(N,N-dimethylaminoethyl methacrylate)-cellulose acetate=PDMAEMA:CA membrane), which can simultaneously control the dissolution rate of Mg as well as protect the surrounding environment from the high pH increase and H2 gas3. In the present study, scanning electrochemical microscope (SECM) was used to investigate the transport properties of these membranes in more details. The results show that the PDMAEMA content controls the permeability of the membrane but also, a surprising time-dependent behaviour was observed: the permeability of the PDMAEMA:CA membranes decreased as a function of time and ellipsometer results showed that this behaviour is not related to the swelling of the membrane. Instead, the time-dependent behaviour might be an indicator of the conformational change of PDMAEMA molecules – either due to the screening of charges or change in degree of ionisation - blocking the membrane pores and this results in a change in permeability as a function of time. A material with such a time-dependent behaviour is an extremely interesting candidate when designing smart and responsive coatings and membranes for temporal biomedical implants. (1) F. Witte, N. Hort, C. Vogt, S. Cohen, K. U. Kainer, R. Willumeit, F. Feyerabend, Current Opinion in Solid State and Materials Science, 2008, 12, 63-72. (2) S. Virtanen, Mater. Sci. Eng. B, 2011, 176, 1600-1608. (3) K. Yliniemi, B. P. Wilson, F. Singer, S. Höhn, E. Kontturi S. Virtanen, ACS Applied Materials and Interfaces, 2014, 6, 22393-22399.

Biodegradation behavior of magnesium and ZK60 alloy in artificial urine and rat models

In this work, the biodegradable and histocompatibility properties of pure Mg and ZK60 alloy were investigated as new temporary implants for urinary applications. The corrosion mechanism in artificial urine was proposed using electrochemical impedance spectroscopy and potentiodynamic polarization tests. The corrosion potential of pure magnesium and ZK60 alloy were −1820 and −1561 mV, respectively, and the corrosion current densities were 59.66 ± 6.41 and 41.94 ± 0.53 μA cm−2, respectively. The in vitro degradation rates for pure Mg and ZK60 alloy in artificial urine were 0.382 and 1.023 mm/y, respectively, determined from immersion tests. The ZK60 alloy degraded faster than the pure Mg in both artificial urine and in rat bladders (the implants of both samples are ø 3 mm × 5 mm). Histocompatibility evaluations showed good histocompatibility for the pure Mg and ZK60 alloy during the 3 weeks post-implantation in rat bladders, and no harm was observed in the bladder, liver and kidney tissues. The results provide key information on the degradation properties and corrosion mechanism of pure Mg and ZK60 alloy in the urinary system.

Mechanical behaviour of biodegradable AZ31 magnesium alloy after long term in vitro degradation

Biodegradable magnesium alloys including AZ31 are exciting candidates for temporary implants as they eliminate the requirement for surgical removal, yet have higher mechanical properties than degradable polymers. However, the very long term mechanical properties and degradation of these alloys have not been fully characterized. The tensile, bending and corrosion behaviour of biodegradable AZ31 Mg alloy specimens have been investigated for up to 9months in vitro in phosphate buffered saline (PBS).Small AZ31 Mg specimens showed a significant drop in bend yield strength and modulus after 3months in vitro degradation and an average mass loss of 6.1%. Larger dumbbell specimens showed significant drops in tensile strength from 251.96±3.53MPa to 73.5±20.2MPa and to 6.43±0.9MPa and in modulus from 47.8±5.6GPa to 25.01±3.4GPa and 2.36±0.89GPa after 3 and 9months respectively. These reductions were accompanied by an average mass loss of 18.3% in 9months.Degradation rate for the small and large specimens followed similar profiles with immersion time, with peak degradation rates of 0.1747gm−2h−1 and 0.0881gm−2h−1, and average rates of 0.1038gm−2h−1 and 0.0397gm−2h−1 respectively. SEM fractography and polished specimen cross-sections revealed corrosion pits, cracks and corrosion induced defects. These data indicate the potential of AZ31 Mg for use in implants that require medium term degradation with load bearing mechanical properties.

Biodegradable Metallic Materials for Temporary Medical Implants

Biodegradable Mg, Zn and Fe alloys are currently studied as prospective biomaterials for temporary medical implants like stents for repairing damaged blood vessels and devices (screws and plates) for fixing fractured bones. In the present paper, novel Mg-, Zn- and Fe-biodegradable alloys are proposed. Advantages and disadvantages of the three kinds of alloys are demonstrated regarding the mechanical performance, in vitro corrosion behavior and biocompatibility.

Influence of Calcium on the Structure and Mechanical Properties of Biodegradable Zinc Alloys

In this work, Zn-1.5Mg-0.5Ca alloy was studied. The alloy composition was chosen according to the results of our previous work that was focused on the research of biodegradable materials. The mechanical properties of such cast alloy are similar to the characteristics of human bones. Moreover, Zn-1.5Mg alloy itself satisfies biocompatibility requirements. The main goal of this work was to improve the mechanical properties of this alloy. A small addition of calcium affected both the alloy microstructure and mechanical properties. Light microscope and scanning electron microscope were used for the analysis of microstructure. After calcium addition, secondary phases were visible in observed micrographs; their composition was verified by XRD. Mechanical properties (Vickers hardness, compressive and tensile tests) were studied and compared with the Zn-1.5Mg alloy prepared in our previous work. Based on presented results, Zn-1.5Mg-0.5Ca alloy is intended for use in medicine as a suitable material for temporary implants.

Dry Transient Electronic Systems by Use of Materials that Sublime

The recent emergence of materials for electronic systems that are capable of programmable self‐destruction and/or bio/eco‐resorption creates the potential for important classes of devices that cannot be easily addressed using conventional technologies, ranging from temporary biomedical implants to enviromentally benign environmental monitors to hardware secure data systems. Although most previous demonstrations rely on wet chemistry to initiate transient processes of degradation/decomposition, options in “dry transient electronic systems” could expand the range of possible uses. The work presented here introduces materials and composite systems in which sublimation under ambient conditions leads to mechanical fragmentation and disintegration of active devices upon disappearance of a supporting substrate, encapsulation layer, interlayer dielectric and/or gate dielectric. Examples span arrays of transistors based on silicon nanomembranes with specialized device designs to solar cells adapted from commercial components.

Early bone formation around immediately loaded implants with nanostructured calcium-incorporated and machined surface: a randomized, controlled histologic and histomorphometric study in the human posterior maxilla.

The aim of this randomized, controlled histologic/histomorphometric study was to compare the early bone formation around immediately loaded implants with nanostructured calcium-incorporated (NCI) and machined (MA) surface, placed in the human posterior maxilla. Fifteen fully edentulous patients (six males; nine females; mean age 57.9±6.7years) were selected for this study. Each patient was installed with two temporary transmucosal implants, with different surfaces: one NCI (test) and one MA (control) implant. All temporary implants were placed in the posterior maxilla, according to a split-mouth design, to help to support an interim complete maxillary denture. After 8weeks, all temporary transmucosal implants were retrieved for histologic/histomorphometric evaluation. The bone-to-implant contact (BIC%) and the bone density (BD%) were calculated. The Wilcoxon matched-pairs signed-rank test was used to evaluate differences (BIC%, BD%) between the surfaces. The level of significance was set at 0.05. Eight weeks after placement, 24 clinically stable implants (12 test, 12 control) were subjected to histologic/histomorphometric evaluation. In the MA implants, the histomorphometric evaluation revealed a mean BIC(±SD)% and BD(±SD)% of 21.2(±4.9)% and 29.8(±7.8)%, respectively. In the NCI implants, the histomorphometric analysis revealed a mean BIC(±SD)% and BD(±SD)% of 39.7(±8.7)% and 34.6(±7.2)%, respectively. A statistically significant difference was found between the two surfaces with regard to BIC% (p<0.001), while no significant difference was found with regard to BD% (p=0.09). The NCI surface seems to increase the peri-implant endosseous healing properties in the native bone of the posterior maxilla, under immediate loading conditions, when compared with the MA surface. Under immediate loading conditions in the human posterior maxilla, the nanostructured calcium-incorporated surface has led to better histologic and histomorphometric results than the machined surface; therefore, the clinical use of implants with nanostructured calcium-incorporated surface may be beneficial in the posterior maxilla, under immediate loading protocol.

Biopolymeric coatings for delivery of antibiotic and controlled degradation of bioresorbable Mg AZ31 alloys

ABSTRACTMagnesium and magnesium alloys are attracting considerable interest as biodegradable materials with high potential for application as temporary implants. The high corrosion rate of Mg-based implants is considered a serious drawback, and it is crucial to design novel surface protection strategies that minimize the detrimental effects of corrosion, while contributing for introducing additional functionalities on the material surface. In this work, a layer-by-layer coating architecture composed of an inner poly(lactic-co-glycolic) acid layer, working as adhesion promoter, and additional polycaprolactone (PCL) layers working as reservoirs for antibiotic (levofloxacin) and for nanohydroxyapatite (nanoHA) particles was applied on the Mg alloy AZ31. The results demonstrate that the composition and number of PCL layers can tailor the biodegradation of the bare magnesium alloy, surface wettability, and the kinetics of release of antibiotic (levofloxacin). The distribution of nanoHA in the coating architecture plays a crucial role on tailoring the desired biocompatible functionalities and corrosion protection of the bare alloy.

Improving Corrosion Resistance and Biocompatibility of Magnesium Alloy by Sodium Hydroxide and Hydrofluoric Acid Treatments

Owing to excellent mechanical property and biodegradation, magnesium-based alloys have been widely investigated for temporary implants such as cardiovascular stent and bone graft; however, the fast biodegradation in physiological environment and the limited surface biocompatibility hinder their clinical applications. In the present study, magnesium alloy was treated by sodium hydroxide (NaOH) and hydrogen fluoride (HF) solutions, respectively, to produce the chemical conversion layers with the aim of improving the corrosion resistance and biocompatibility. The results of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) indicated that the chemical conversion layers of magnesium hydroxide or magnesium fluoride were obtained successfully. Sodium hydroxide treatment can significantly enhance the surface hydrophilicity while hydrogen fluoride treatment improved the surface hydrophobicity. Both the chemical conversion layers can obviously improve the corrosion resistance of the pristine magnesium alloy. Due to the hydrophobicity of magnesium fluoride, HF-treated magnesium alloy showed the relative better corrosion resistance than that of NaOH-treated substrate. According to the results of hemolysis assay and platelet adhesion, the chemical surface modified samples exhibited improved blood compatibility as compared to the pristine magnesium alloy. Furthermore, the chemical surface modified samples improved cytocompatibility to endothelial cells, the cells had better cell adhesion and proliferative profiles on the modified surfaces. Due to the excellent hydrophilicity, the NaOH-treated substrate displayed better blood compatibility and cytocompatibility to endothelial cells than that of HF-treated sample. It was considered that the method of the present study can be used for the surface modification of the magnesium alloy to enhance the corrosion resistance and biocompatibility.

Effect of Immersion in Simulated Body Fluid on the Mechanical Properties and Biocompatibility of Sintered Fe–Mn-Based Alloys

Fe–Mn-based degradable biomaterials (DBMs) are promising candidates for temporary implants such as cardiovascular stents and bone fixation devices. Identifying their mechanical properties and biocompatibility is essential to determine the feasibility of Fe–Mn-based alloys as DBMs. This study presents the tensile properties of two powder metallurgical processed Fe–Mn-based alloys (Fe–28Mn and Fe–28Mn-3Si, in mass percent) as a function of immersion time in simulated body fluid (SBF). In addition, short-term cytotoxicity testing was performed to evaluate the in vitro biocompatibility of the sintered Fe–Mn-based alloys. The results reveal that an increase in immersion duration deteriorated the tensile properties of both the binary and ternary alloys. The tensile properties of the immersed alloys were severely degraded after being soaked in SBF for ≥45 days. The ion concentration in SBF released from the Fe–28Mn-3Si samples was higher than their Fe–28Mn counterparts after 7 days immersion. The preliminary cytotoxicity testing based on the immersed SBF medium after 7 days immersion suggested that both the Fe–28Mn-3Si and Fe–28Mn alloys presented a good biocompatibility in Murine fibroblast cells.

Multiblock High Order Large Eddy Simulation of Powered Fontan Hemodynamics: Towards Computational Surgery.

Children born with only one functional ventricle must typically undergo a series of three surgeries to obtain the so-called Fontan circulation in which the blood coming from the body passively flows from the Vena Cavae (VCs) to the Pulmonary Arteries (PAs) through the Total Cavopulmonary Connection (TCPC). The circulation is inherently inefficient due to the lack of a subpulmonary ventricle. Survivors face the risk of circulatory sequelae and eventual failure for the duration of their lives. Current efforts are focused on improving the outcomes of Fontan palliation, either passively by optimizing the TCPC, or actively by using mechanical support. We are working on a chronic implant that would be placed at the junction of the TCPC, and would provide the necessary pressure augmentation to re-establish a circulation that recapitulates a normal two-ventricle circulation. This implant is based on the Von Karman viscous pump and consists of a vaned impeller that rotates inside the TCPC. To evaluate the performance of such a device, and to study the flow features induced by the presence of the pump, Computational Fluid Dynamics (CFD) is used. CFD has become an important tool to understand hemodynamics owing to the possibility of simulating quickly a large number of designs and flow conditions without any harm for patients. The transitional and unsteady nature of the flow can make accurate simulations challenging. We developed and in-house high order Large Eddy Simulation (LES) solver coupled to a recent Immersed Boundary Method (IBM) to handle complex geometries. Multiblock capability is added to the solver to allow for efficient simulations of complex patient specific geometries. Blood simulations are performed in a complex patient specific TCPC geometry. In this study, simulations without mechanical assist are performed, as well as after virtual implantation of the temporary and chronic implants being developed. Instantaneous flow structures, hepatic factor distribution, and statistical data are presented for all three cases.

Cytocompatibility and early inflammatory response of human endothelial cells in direct culture with Mg-Zn-Sr alloys.

Magnesium (Mg) alloys specifically designed for biodegradable implant applications have been the focus of biomedical research since the early 2000s. Physicochemical properties of Mg alloys make these metallic biomaterials excellent candidates for temporary biodegradable implants in orthopedic and cardiovascular applications. As Mg alloys continue to be investigated for biomedical applications, it is necessary to understand whether Mg-based materials or the alloying elements have the intrinsic ability to direct an immune response to improve implant integration while avoiding cell-biomaterial interactions leading to chronic inflammation and/or foreign body reactions. The present study utilized the direct culture method to investigate for the first time the in vitro transient inflammatory activation of endothelial cells induced by the degradation products of Zn-containing Mg alloys.

Corrosion of nanostructured and ultrafine-grained metallic implant materials

Nanostructured metallic materials are increasingly investigated for numerous biomedical implant applications. They offer benefits of high strength with enough ductility and often possess superior biocompatibility. Several materials processing routes involving severe plastic deformation of candidate materials lead to bulk nanostructured and surface nanostructured metals. Literature is replete with studies claiming their superior mechanical behaviour and biocompatibility in terms of wettability, cell adhesion and proliferation. In spite of their metallic properties, permanent metallic implants with an expected life span of 15 years or more, often break down prematurely and corrosion of some form is a common cause or trigger. Therefore, in order to ensure reliable performance of newly developed nanostructured metal implants in service, it is necessary to understand their electrochemical degradation behaviour. Concerns stem from adverse reactions from corrosion products, desired longevity of long term implants, and biodegradability of temporary implants. Present review covers the developments in this domain.

Glass-like cerium sol-gel coatings on AZ31B magnesium alloy for controlling the biodegradation of temporary implants

Mg alloys are a good alternative to be used as biodegradable and resorbable implants, but its rate of degradation in the body is too fast. In this work, two types of coatings are studied to control the corrosion speed and to improve the corrosion resistance of magnesium alloy in simulated physiological environment. First, glass-like cerium-based coatings (CexOy) were prepared using cerium nitrate and various complexing agents, deposited by dip-coating and heat treated at 250 °C for 10 min. On the other side, a silica sol was prepared by acid catalysis with ethyltriethoxysilane (TEOS) and deposited by dip-coating on the CexOy coatings. The characterizations of single (CexOy) and double layer (CexOy/SiO2) coatings included adhesion tests and wettability by contact angle measurements. Furthermore, immersion tests were performed using the simulated body fluid (SBF) at 37 °C assessing the change in pH, hydrogen evolution and mass loss of the coated and uncoated alloys as a function of the immersion time. The coated substrates showed suitable adhesion behaviour and SBF tests demonstrated that degradation speed of the substrate is reduced by the deposition of the coatings.

P20. Reduction of post-implant planning time of temporary I-125 LDR implants

Introduction Groote Schuur Hospital has a well-established low-dose rate (LDR) brachytherapy programme using I-125 seeds. Temporary implants in and around the eye, tongue, floor of mouth, palate or for keloid scars are custom-made for each individual. A pre-implant plan is done to determine seed positions and activities, while a post-implant plan is done to determine the actual dose distributions in the patient. Method and materials The pre-implant plans generally consist of a number of trains loaded with I-125 seeds in a geometry specified by the oncologist. Different activity seeds are used to create an optimal pre-implant dose distribution. Post-implant plans are currently worked out on orthogonal X-rays. The magnification factor is determined from specially placed brass rings and each seed has to be individually matched on each X-ray. This is a very time-consuming task, especially for implants with large seed numbers. Once the seeds have been identified, the correct activities have to be assigned to each seed. An investigation is under way to find a more efficient way of determining the seed co-ordinates from a post-implant CT scan. Results Initial investigations show that this is a feasible alternative in many cases for determining the seed co-ordinates. The 3D viewing option of the CT data also helps in assigning the seed activities. This may not be a suitable alternative for all implants, especially for some of the orbital implants that have a lead disk inserted under the eye lid for shielding purposes, and also to hold additional seeds. The lead disc, as well as the clamped ends of the seed trains, introduce artefacts on the CT scans, possibly obscuring individual seeds. Conclusion In cases where this post-planning option proves to be a suitable alternative, post-planning times are reduced significantly.

Enhanced in Vitro and in Vivo Performance of Mg-Zn-Y-Nd Alloy Achieved with APTES Pretreatment for Drug-Eluting Vascular Stent Application.

Bioabsorbable magnesium alloys are becoming prominent as temporary functional implants, as they avoid the risks generated by permanent metallic implants such as persistent inflammation and late restenosis. Nevertheless, the overfast corrosion of Mg alloys under physiological conditions hinders their wider application as medical implant materials. Here we investigate a simple one-step process to introduce a cross-linked 3-amino-propyltrimethoxysilane (APTES) silane physical barrier layer on the surface of Mg-Zn-Y-Nd alloys prior to electrostatic spraying with rapamycin-eluting poly(lactic-co-glycolic acid) (PLGA) layer. Surface microstructure was characterized by scanning electron microscope and Fourier transform infrared spectroscopy. Nanoscratch test verified the superior adhesion strength of PLGA coating in the group pretreated with APTES. Electrochemical tests combined with long-term immersion results suggested that the preferable in vitro anticorrosion behavior could be achieved by dense APTES barrier. Cell morphology and proliferation data demonstrated that APTES pretreated group resulted in remarkably preferable compatibility for both human umbilical vein endothelial cells and vascular smooth muscle cells. On the basis of excellent in vitro mechenical property, the animal study on the APTES pretreated Mg-Zn-Y-Nd stent implanted into porcine coronary arteries confirmed benign tissue compatibility as well as re-endothelialization without thrombogenesis or in-stent restenosis at six-month followup.

CO2-rich atmosphere strongly affects the degradation of Fe-21Mn-1C for biodegradable metallic implants

For decades, biomaterials used as implants saved the life or improved its quality for millions around the globe. Biodegradable metals constitute a new class of biomaterials especially designed for temporary implants. Fe-based biodegradable metals are an important sub-class, but their development is limited by their tendency to degrade faster in vitro than in vivo. Blood is known to contain a high CO2 concentration. This is susceptible to form various carbonates with different stability, thus affecting and potentially decrease the material degradation rate. Therefore, this work investigates the influence of CO2 on the static degradation of Fe-21Mn-1C alloy in modified Hanks' solution. Results clearly evidenced that the presence of CO2 led to different degradation patterns and rates. Indeed, in 5% CO2 atmosphere, the degradation layer exhibited uniform, compact and dense manganese carbonate crystals, whereas, under ambient atmosphere, amorphous iron phosphorous compounds were dominant.

Influence of surface pre-treatment on the cytocompatibility of a novel biodegradable ZnMg alloy

Degradable zinc-based alloys with an appropriate corrosion rate are promising materials for the preparation of temporary orthopaedic implants. Previously, we prepared and characterised a novel Zn1.5Mg alloy. This paper is focused on the characterisation of this alloy after a surface pre-treatment, which should mimic processes occurring in vivo.The samples of the Zn1.5Mg alloy were immersed in a simulated body fluid (SBF) at 37°C for 14days in order to form a protective layer of corrosion products. Thereafter, these samples were used for the corrosion rate determination, an indirect in vitro cytotoxicity test, as well as for a direct contact test and were compared with the non-treated samples. The protective layer was characterized by SEM and its chemical composition was determined by EDS and XPS analysis.The corrosion rate was significantly decreased after the pre-incubation. The protective layer of corrosion products was rich in Ca and P. The pre-incubated samples exhibited increased cytocompatibility in the indirect test (metabolic activity of L929 cells was above 70%) and we also observed osteoblast-like cell growth directly on the samples during the contact tests. Thus, the pre-incubation in SBF leading to improved cytocompatibility could represent more appropriate model to in vivo testing.