Stent Application Research Articles

Negative Poisson's Ratio Material Structure Based on 3D Printing and Its Application in Medical Field

First of all, the overall framework of 3D printing is briefly introduced, including the basic principles of the additive manufacturing process, the classification and summary of the seven processes. Secondly, the common negative Poisson's ratio structure is introduced. Compared with the conventional structure, the negative Poisson's ratio structure has stronger energy absorption capacity, better fracture resistance and better indentation resistance, which are its advantages in printing manufacturing. Finally, 3D printing, the application of negative Poisson's ratio structure and the combination of the two are introduced from the different perspective of medical field, for example, the application of cardiovascular stent, biomedical material structure preparation, and lumbar disc implants. This paper suggests that the structural design of negative Poisson's ratio in 3D printing guides the development of new application directions in the medical field. Negative Poisson's ratio materials have a wide range of applications, not only in the medical field but also in mechanical equipment, automotive manufacturing, aerospace, and other high-tech industries.

Clinical efficacy of mini-percutaneous nephrolithotomy versus retrograde intrarenal surgery for the management of upper urinary tract calculus (1–2.5 cm) in children ≤10 years of age

With improvements in endoscopic surgery, open surgical procedures for urinary system stones have cleared the path for the use of less invasive treatment modalities in patients with pediatric kidney stone disease. Extracorporeal shock wave lithotripsy (ESWL), percutaneous nephrolithotomy (PCNL), and retrograde intrarenal surgery (RIRS) are among the treatment options available. To prospectively evaluate the outcomes of mini-percutaneous nephrolithotomy and retrograde intrarenal surgery (RIRS) for children ≤10 years of age with upper urinary tract calculus (1-2.5cm). Sixty pediatric patients with single or multiple renal stones (1-2.5cm in diameter) were collected prospectively and equally divided into two groups to undergo RIRS or mini-PCNL. The operative and postoperative outcomes of both groups were analyzed. The groups' mean ages and genders were comparable. The mean stone size for the RIRS group was 1.86cm and 1.69cm for the PCNL group (P=0.449). The PCNL group had statistically longer mean fluoroscopy and hospitalization times. The stone-free rates (SFRs) after a single procedure were 27 (90%) in the PCNL group and 25 (83.33%) in the RIRS group (P=0.706). The UAS was placed in 13 (43.33%) patients in the RIRS group. In the RIRS group, 14 (46.67%) children required preoperative DJ stent application to passively dilate the ureteric orifice. As regard post DJ stenting, 13 (46%) cases applied DJ in the mini PCNL group. major complications were observed in either group. Minor complication (Clavien 1-3) rates were 16.66% and 13.33% for the PCNL and RIRS groups, respectively. There were no differences found between the RIRS and mini-PCNL groups regarding operative time. The mean cost of RIRS was $703.96 and $537.03 for the mini-PCNL. According to the results of this study, mini-PCNL and RIRS are effective procedures for treating renal stones in children up to 2.5cm with comparable success and complication rates. Hospital stay, radiation exposure, and fluoroscopy time are significantly lower in RIRS than in the mini PCNL technique. Although RIRS is effective, a major disadvantage is the greater requirement for JJ stent insertion either before or after the procedure and the consequent need for a second procedure for removal.

Drug-Eluting Balloon for Coronary In-Stent Restenosis: Could it be an Emerging Strategy?

Despite significant improvement in PCI, including drug-eluting stent (DES) applications, in-stent restenosis (ISR) remains a problem. ISR is challenging to manage. Repeat stenting with bare metal stent (BMS), repeat stenting with DES and bioresorbable vascular scaffolds is primarily used to prevent and treat ISR. Current European guidelines recommend DES or a drug-eluting balloon (DEB) to treat ISR with a Class I indication. However, its use in coronary artery interventions has not yet been approved in the United States. DEB allows the application of the antiproliferative drug to the ISR site without leaving an additional layer of stent strut. Studies show that DEB is superior to plain balloon alone and comparable to DES in ISR treatment. They are increasingly preferred due to their good therapeutic effect in preventing intimal proliferation and restenosis. This review aims to provide an overview on the feasibility of using DEB in ISR management based on current knowledge

The quality of life after keratinized mucosa augmentation around dental implants using xenogenic collagen matrix with or without stent.

The substitution of missing teeth with implants is a dependable and anticipated therapeutic approach. Despite numerous studies affirming long-term success rates, there exists a spectrum of potential biological and aesthetic complications. The primary objective of this study was to assess patient responses subsequent to surgical interventions, with a specific emphasis on the utilization of xenogenic collagen matrix (XCM), both with and without the application of a stent secured over healing abutments, in the context of keratinized gingival mucosa augmentation. The principal aim was to evaluate and draw comparisons between the clinical outcomes resulting from these two procedural approaches, with a particular focus on critical parameters encompassing post-operative complications, patient comfort, and the overall efficacy in achieving successful keratinized tissue augmentation. Sixty patients were selected for this study. The patients were divided into three groups: A, B, and a control group, with each group comprising 20 participants. We used XCM in experimental group A, XCM covered with surgical stent in experimental group B, and free gingival graft (FGG) in the control group. After the surgical procedure, patients were required to complete a visual analogue scale (VAS) questionnaire for post-operative complications, and a quality of life (QOL) questionnaire on days 1, 3, and 7. Patients in the experimental groups A and B demonstrated markedly improved outcomes when compared with the control group. Assessments conducted on days 1, 3, and 7 demonstrated diminished levels of pain, bleeding, and swelling in both experimental groups, with experimental group B showing the least discomfort. The incorporation of XCM, either with or without stents, was associated with a reduction in analgesic consumption, underscoring its favorable influence on post-operative comfort, notwithstanding the exception of halitosis in experimental group B. Using XCM with or without a stent for keratinized tissue augmentation has better post-operative outcomes associated with reduced swelling, bleeding, and pain based on the QOL survey. This study provides data to support the clinical application of XCM and stents.

Mechanical properties of an improved flexible auxetic metamaterial and its application in self-expanding vascular stents

Auxetic metamaterials have shown great significance in the field of cardiovascular stents, but improving their applicability remains an issue. Here, we develop a type of improved auxetic metamaterial called the Re-entrant-Arrow-Snake (RAS) structure by adding arrow-shaped and snake-shaped structures to the Re-entrant (RE) structure. We first systematically study its in-plane elastic properties and compression behaviors. It is observed that the RAS structure exhibits improved vertical stiffness, horizontal flexibility, and clear auxetic effect in the vertical direction. The influence of the additional structures on the deformation pattern and the stability is also discussed by the in-plane compression analysis. Furthermore, we propose a new self-expanding (SE) vascular stent named RAS-SE based on the RAS structure. Numerical analysis demonstrates that the RAS-SE stent possesses enhanced dual-plateau radial force, negative foreshortening behavior, and improved bending flexibility, indicating better deployment performance and support in clinical applications. Biomechanical studies also show that axial deformation caused by the auxetic effect of the RAS-SE stent only slightly increases stress damage to plaque without affecting stress damage of the intima. This study further expands the application of metamaterials in SE vascular stents, and the proposed RAS structure shows high applicability on the SE stent, thus warranting further attention.

Safety of single-use flexible ureteroscopy for dusting of upper urinary tract calculi in children

BackgroundFlexible ureteroscopy offers numerous advantages, such as increased reach, superior stone-free rate, reduced risk of bleeding, minimal surgical trauma, and faster recovery time. There are few studies discussing the effectiveness of single-use flexible ureteroscopy in children, and none so far have addressed its safety. This study aims to evaluate the effectiveness and safety of a single-use flexible ureteroscope for treating upper urinary tract stones in children.MethodsThis study included children with single upper urinary tract stones measuring less than 2 cm who underwent single-use flexible ureteroscopy between October 2020 and January 2023. We assessed the following patient characteristics: age, gender, stone type, size, position, pre and postoperative stent placements, use of a ureteral access sheath, stone-free rate, operation duration, and the rate of complications. A patient was considered stone-free if there were no residual stone particles larger than 3 mm after surgery.ResultsFlexible ureteroscopy and holmium laser lithotripsy were undertaken for 44 participants, with an average age of 8.5 years (range: 2–16 years). The typical stone size was 14 mm (range: 6–20 mm). The average operation time was 74 min (range 35–110 min). Ureteral access sheaths were used in 81.8% (36 out of 44) of procedures. After a single FURS session, 86.36% (38 out of 44) of patients achieved stone-free status. Postoperative JJ stent application was noted in 86.4% (38 out of 44) of patients. Complications were categorized using the Calvien system, revealing that 25% (11 out of 44) of patients experienced mild hematuria, colic, and low-grade fever (Calvien I). No severe side effects like mucosal avulsion or ureteral perforation were reported.ConclusionIn the short-term, single-use flexible ureteroscopy is a safe and effective method for managing single renal and proximal ureteric stones, measuring 2 cm or less, in children.

Ductal Stenting in Low-Resource Environments.

Duct-dependent pulmonary circulation has traditionally been addressed by the Blalock-Taussig-Thomas shunts (BTTS). Recently, catheter-based alternatives such as ductal stenting have emerged as a particularly advantageous option, especially in resource-constrained settings. This article delves into the nuances of ductal stenting within low-resource environments, highlighting its relative ease of application, reduced morbidity, and cost-effectiveness as key factors in its favor. Comparisons in mortality between the two procedures are however likely to be confounded by selection biases. Ductal stenting appears to be particularly beneficial for palliating older infants and children with cyanotic congenital heart disease and diminished pulmonary blood flow who present late. Additionally, it serves as a valuable tool for left ventricular training in late-presenting transposition with an intact ventricular septum. A meticulous pre-procedure echocardiographic assessment of anatomy plays a pivotal role in planning access and hardware, with additional imaging seldom required for this purpose. The adaptation of adult coronary hardware has significantly enhanced the technical feasibility of ductal stenting. However, challenges such as low birth weight and sepsis specifically impact the performance of ductal stenting and patient recovery in low-resource environments. There is potential for systematic application of quality improvement processes to optimize immediate and long-term outcomes of ductal stenting. There is also a need to prospectively examine the application of ductal stenting in low-resource environments through multi-center registries.

“Through-stent enterography”: first experience with a novel technique intended to improve safety in endosonography-guided gastroenterostomy

Background and AimsEndosonographic-guided gastroenterostomy (EUS-GE) is a novel technique to manage symptoms of gastric outlet obstruction. Major challenges are the high mobility of intestinal loops and the transient loss of endosonographic visibility during the puncture. This can lead to stent-misdeployment, which can be associated with potentially fatal adverse events. By injecting contrast medium through the guidewire-channel of the lumen apposing metal stent (LAMS) application system under fluoroscopic guidance, a positive enterogram can confirm the position of the stent inside the intestinal lumen before its deployment. The aim of this study was to describe this novel technique and to assess its feasibility. MethodsThe data of 39 consecutive patients undergoing EUS-GE with “through-stent-enterography” between July 2020 and March 2022 were retrospectively collected and analyzed. Primary endpoint was to assess the technical success. Secondary endpoints were to assess adverse events, rate of reinterventions and clinical success. ResultsTechnical success was achieved in all cases (n=39). In two cases a second puncture was required to place the stent successfully. In one case, misdeployment could be avoided after a negative enterogram. In the other case, misdeployment occurred despite a positive enterogram a reintervention was needed. Clinical success was achieved in 92.3% (n=36). No major adverse events or mortalities were encountered. Conclusions“Through-stent-enterography” after the puncture to confirm the correct position of the stent in the small bowel is a novel and simple technique, which can potentially reduce the risk of misdepolyment of the stent.

Haemodynamics of stent-mounted neural interfaces in tapered and deformed blood vessels

The endovascular neural interface provides an appealing minimally invasive alternative to invasive brain electrodes for recording and stimulation. However, stents placed in blood vessels have long been known to affect blood flow (haemodynamics) and lead to neointimal growth within the blood vessel. Both the stent elements (struts and electrodes) and blood vessel wall geometries can affect the mechanical environment on the blood vessel wall, which could lead to unfavourable vascular remodelling after stent placement. With increasing applications of stents and stent-like neural interfaces in venous blood vessels in the brain, it is necessary to understand how stents affect blood flow and tissue growth in veins. We explored the haemodynamics of a stent-mounted neural interface in a blood vessel model. Results indicated that blood vessel deformation and tapering caused a substantial change to the lumen geometry and the haemodynamics. The neointimal proliferation was evaluated in sheep implanted with an endovascular neural interface. Analysis showed a negative correlation with the mean Wall Shear Stress pattern. The results presented here indicate that the optimal stent oversizing ratio must be considered to minimise the haemodynamic impact of stenting.

Novel application of lumen-apposing metal stent for management of malignant recto-sigmoid stricture with fistula

Video 1Demonstration of novel application of lumen-apposing metal stent for management of a malignant recto-sigmoid junction stricture with fistula.

Recent development and future application of biodegradable ureteral stents.

Ureteral stenting is a common clinical procedure for the treatment of upper urinary tract disorders, including conditions such as urinary tract infections, tumors, stones, and inflammation. Maintaining normal renal function by preventing and treating ureteral obstruction is the primary goal of this procedure. However, the use of ureteral stents is associated with adverse effects, including surface crusting, bacterial adhesion, and lower urinary tract symptoms (LUTS) after implantation. Recognizing the need to reduce the complications associated with permanent ureteral stent placement, there is a growing interest among both physicians and patients in the use of biodegradable ureteral stents (BUS). The evolution of stent materials and the exploration of different stent coatings have given these devices different roles tailored to different clinical needs, including anticolithic, antibacterial, antitumor, antinociceptive, and others. This review examines recent advances in BUS within the last 5 years, providing an in-depth analysis of their characteristics and performance. In addition, we present prospective insights into the future applications of BUS in clinical settings.

Research on theoretical and experimental investigations of burr formation mechanism in micro-milling process of medical ploy-l-lactide

Medical grade poly-l-lactide (PLLA) has been widely applied for medical devices and consumables, e.g. biodegradable cardiovascular stents and surgical thread, due to its excellent biocompatibility. High-speed micro-milling technology shows great potential in high-precision and high-quality manufacturing of material PLLA, while it usually produces problems such as material burrs and defects. There is few research and analysis on the material removal mechanism and theory in the micro-milling process of polymers, and thus this paper aims to investigate the burr formation mechanism and processing quality in micro-milling process of medical PLLA. Firstly, a novel thermal-mechanical coupled theoretical model was proposed by considering the minimum cutting thickness and cutting-edge radius size effects, which can reveal the plastic flow law during micro-milling process of polymer material. This model was used to calculate the burr width at up and down milling sides of cutting area. Then material characterization and micro-milling experiments on two types of PLLA with different molecular weights were carried out to validate the established theoretical model, and further the micro-milling parameters were optimized to achieve the control of material burr formation and growth. As a result, a cardiovascular stent was fabricated by micro-milling with the optimized parameters (spindle speed of 25,000 rpm, feed rate of 100 mm/min and axial depth of cut of 5 μm), and the stents obtained significantly high surface quality. These results suggest that the proposed theoretical model has great advantages in the high-quality micro-milling of medical material PLLA. This work provides a potential stent manufacture technique in the development and clinical application of bioresorbable polymeric stents.

Anti-fibrotic and anti-stricture effects of biodegradable biliary stents braided with dexamethasone-impregnated sheath/core structured monofilaments

Endoscopic biliary stent insertion has been widely used for the treatment of benign biliary stricture (BBS). Thus, the development of stent materials in the perspectives of structure, mechanical properties, and biocompatibility has been also studied. However, conventional metal and plastic stents have several disadvantages, such as repeated procedures to remove or exchange them, dislodgment, restenosis, biocompatibility, and poor mechanical properties. Sustainable effectiveness, attenuation and prevention of fibrosis, and biocompatibility are key factors for the clinical application of stents to BBS treatment. In addition, loading drugs could show synergistic effects with stents’ own performance. We developed a dexamethasone-eluting biodegradable stent (DBS) consisting of a sheath/core structure with outstanding mechanical properties and sustained release of dexamethasone, which maintained its functions in a BBS duct over 12 weeks in a swine model. The insertion of our DBS not only expanded BBS areas but also healed secondary ulcers as a result of the attenuation of fibrosis. After 16 weeks from the insertion, BBS areas were totally improved, and the DBS was degraded and thoroughly disappeared without re-intervention for stent removal. Our DBS would be an effective clinical tool for non-vascular diseases. Statement of significanceThis study describes the insertion of a drug-eluting biodegradable stent (DBS) into the bile duct. The sheath/core structure of DBS confers substantial durability and a sustained drug release profile. Drug released from the DBS exhibited anti-fibrotic effects without inflammatory responses in both in vitro and in vivo experiments. The DBS maintained its function over 12 weeks after insertion into the common bile duct, expanding benign biliary stricture (BBS) and reducing inflammation to heal secondary ulcers in a swine BBS model. After 16 weeks from the DBS insertion, the DBS thoroughly disappeared without re-intervention for stent removal, resulting in totally improved BBS areas. Our findings not only spotlight the understanding of the sheath/core structure of the biodegradable stent, but also pave the way for the further application for non-vascular diseases.

Melt blending of poly(lactic acid) with biomedically relevant polyurethanes to improve mechanical performance

Minimally invasive surgery procedures are of utmost relevance in clinical practice. However, the associated mechanical stress on the material poses a challenge for new implant developments. In particular PLLA, one of the most widely used polymeric biomaterials, is limited in its application due to its high brittleness and low elasticity. In this context, blending is a conventional method of improving the performance of polymer materials. However, in implant applications and development, material selection is usually limited to the use of medical grade polymers. The focus of this work was to investigate the extent to which blending poly-l-lactide (PLLA) with low contents of a selection of five commercially available medical grade polyurethanes leads to enhanced material properties. The materials obtained by melt blending were characterized in terms of their morphology and thermal properties, and the mechanical performance of the blends was evaluated taking into account physiological conditions. From these data, we found that mixing PLLA with Pellethane 80A is a promising approach to improve the material's performance, particularly for stent applications. It was found that PLLA/Pellethane blend with 10% polyurethane exhibits considerable plastic deformation before fracture, while pure PLLA fractures with almost no deformation. Furthermore, the addition of Pellethane only leads to a moderate reduction in elongation at yield and yield stress. In addition, dynamic mechanical analysis for three different PLLA/Pellethane ratios was performed to investigate thermally induced shape retention and shape recovery of the blends.

Experimental study of a canine model for a newly designed adjustable prefenestration aortic stent graft

When performing thoracic aortic endovascular repair (TEVAR) on lesions of the aortic arch, physician-modified fenestration or in situ fenestration is often used to maintain patent branches. We designed a new adjustable prefenestration aortic stent graft that can both isolate pathologies in the aortic arch and obtain patent branches simultaneously. In this study, we use this new type of stent to perform fenestrated TEVAR in a canine’s aorta. This study aims to evaluate the safety and feasibility of the new device, which may provide preliminary data for potential human application. Eight Labrador Retriever canines underwent fenestrated TEVAR using the new stent device. Digital subtract angiography (DSA) was performed before and after fenestrated TEVAR to evaluate the safety and feasibility of the procedure. For the device deployment, at the “large curvature” side in the endograft, there is a rectangular prefenestration area (2 × 5 cm) without the polytetrafluoroethylene membrane, and at both longer side edges of the fenestration, there are two slide rails. A moveable membrane that covers the same area as the prefenestration area is initially set at the prefenestration position. A stay line is connected from the distal site of the moveable membrane that controls it to the distal position along the slide rail, which releases the fenestration. After the positioning of the prefenestration is determined, the outer sheath of the delivery system is released, and the stay line at the end of the delivery system is pulled outside the body. The animals were divided into a 1-month group (n = 4) and a 3-month group (n = 4) after the fenestrated TEVAR. Computed tomography (CT) was performed before euthanasia, and video of the DSA during the procedures and CT angiography (CTA) images were then studied. The procedure success rate was 100%, but the total survival rate was only 87.5%. There were no aortic-related deaths during follow-up, and during the operation, there were no stent-graft-related accidents. In addition, no stent-graft migrations were observed in the CTA, and all branch arteries were kept patent by the adjustable fenestration. Finally, histological examination and electron microscope results showed no obvious vascular injury or inflammation. Based on the results of this study, we judge the safety and feasibility of the use of the newly designed adjustable prefenestration aortic stent graft in a fenestrated-TEVAR canine model to be acceptable. Our preliminary data may serve as an initial reference for evaluating the potential application of the new stent in humans.

Design of novel poly(L-lactide)-based shape memory multiblock copolymers for biodegradable esophageal stent application

Esophageal cancer is a globally prevalent malignancy known for its extremely aggressive nature and high fatality rates. However, the conventional stents used in its treatment pose limitations including rigidity, non-degradability, and a lack of anti-inflammatory action. Shape memory multiblock copolymer stents (SMBS) have attracted considerable attention because of their distinctive characteristics. Nonetheless, achieving a variety of key functionalities, such as biocompatibility, biodegradability, thermoresponsiveness (body temperature, 37 °C), water responsiveness (biofluid), flexibility, and robustness, in a simple polymer system for practical applications still presents a significant problem. Herein, a versatile SMBS that is capable of delivering all the aforementioned key functionalities is proposed. This SMBS can efficiently be prepared via a rapid two-step strategy, leveraging the shape memory effect (SME) of a poly(L-lactide) (PLA)-based physical crosslinking network programmed into specific shapes. The proposed stent design incorporates bio-based PLA with flexible and hydrophilic polyethylene glycol (PEG), resulting in PEG-PLA multiblock copolymers with tunable transition temperatures (31.90–54.60 °C), effectively covering the body temperature (37 °C). Additionally, PEG-PLA exhibited a wide range of water uptake ratio of 41 % to 328 % and satisfactory elongation at break (142.8 % to 1920.6 %), and desired pH-dependent and simulated gastrointestinal biodegradability. Specifically, PEG4000PLA1500 displayed excellent body temperature-triggered (with a recovery rate of 99.5 %) and water-triggered dual SME, which allowed it to potentially be fabricated into on-demand synchronous shape memory and drug-release functional SMBS for esophageal stenosis therapy. The results of this study indicate that the proposed SMBS holds substantial potential for biomedical applications.

Polish Society of Biomechanics Morecki&Fidelus Award Winner: Comparison of two polymers PDO and PLLA/PCL in application of urological stent for the treatment of male urethral stenosis.

Purpose: The primary objective of the conducted research was to develop an urological stent design for the treatment of male ure-thral stenosis. Given the variable loading conditions inside the urethra, the proposed stent should maintain normal tissue kinetics and obstruct the narrowed lumen. The suitable selection for the stent material significantly influences the regeneration and proper remodeling of the urethral tissues. Methods: In this work, the mechanical characteristics of some polymer materials were studied, including: polydi-oxanone (PDO) and poly(L-lactide) (PLLA)/polycaprolactone (PCL) composite. The obtained mechanical properties for static tensile testing of the materials, allowed the determination of such parameters as Young's modulus (E), tensile strength (R m) and yield strength (R e). Subsequently, the design of a urological stent was developed, for which a numerical analysis was carried out to check the behaviour of the stent during varying loads prevailing in the urethra. Result: The research indicated that PDO has better mechanical properties than the proposed PLLA/PCL composite. The numerical analysis results suggested that the developed stent design can be successfully used in the treatment of male urethral stenosis. The obtained stress and strain distributions in the numerical analysis confirm that the PDO material can be used as a material for an urological stent. Conclusions: The biodegradable polymers can be successfully used in urology. Their advantages over solid materials are their physicochemical properties, the ability to manipulate the rate and time of degradation and the easy availability of materials and manufacturing technology.

Evaluation of Stent Applications for Upper Gastrointestinal Disorders

Aim: Gastrointestinal stents are predominantly used for palliating malignant dysphagia in patients with esophageal cancer when surgical intervention is deemed inappropriate. This research aims to elucidate the diagnostic and follow-up processes of patients who underwent stent placement for upper gastrointestinal system pathologies at our clinic. Method: A retrospective analysis assessed 61 patients who received stents for upper gastrointestinal tract stenosis due to various causes. Patient demographics, including age and gender, underlying pathology, benign-malignant status, location of the pathology, prior surgical or bougie dilation interventions, post-stent survival status, and, if applicable, the duration between the procedure and decease, were evaluated. Patient health records were accessed from the hospital's electronic medical database. Results: Pre-stent bougie dilation was performed in 26.2% (n=16) of patients, while pre-stent surgery was undertaken in 41% (n=25). Repeat stenting was necessitated in 6.6% (n=4) of cases. Of the patients, 86.9% (n=53) succumbed to their condition, while 13.1% (n=8) survived. Post-stent survival times for deceased patients after stent surgery ranged from 0 to 55 months, with a median survival time of two months. Surviving patients exhibited varied post-stent durations between 65 and 122 months, with a mean stent utilization period of 101 months. A statistically significant correlation was observed between pre-stent surgery and survival status, indicating a higher surgery rate in patients who survived than those who did not (p<0.05).

Effect of laser power on microstructure and mechanical properties of pure Zn fabricated via laser powder bed fusion

The preparation of biodegradable pure Zn porous scaffolds using additive manufacturing technology has great potential for application. However, the mechanical properties of pure Zn are not sufficient for the clinical application of stents. An object of this paper was to investigate the effect of laser power on microstructural evolution and tensile properties of pure Zn fabricated via laser powder bed fusion (LPBF). The results demonstrated that the temperature gradient and heat storage were the main factors determining the microstructure. The formation of columnar grains was due to the high temperature gradient in the early printing stage, and the equiaxed grains in the middle and top region were attributed to the heat storage induced recrystallization and columnar-to-equiaxed transition (CET), respectively. In addition, as the laser power increased from 40 W to 60 W, the recrystallization degree increased, and the Kernel average misorientation value and Taylor factor decreased gradually, resulting in a significant increase in the ductility. The mechanical properties were maximized at the laser power of 60 W and the scanning rate of 150 mm/s (yield strength, tensile strength and elongation of samples can reach 82.02 MPa, 116.20 MPa and 37.16 %, respectively). This work provides theoretical support for optimizing the mechanical properties of LPBF Zn-based materials by microstructural regulation.

Developing austenitic high-manganese high-carbon steels for biodegradable stent applications: Microstructural and mechanical studies

Fully degradable stents that temporarily support healing tissue can solve potential long-term complications associated with permanent implants. In this study, we investigate austenitic high-manganese high-carbon steels as promising candidates for such biodegradable stent applications. The microstructural characteristics and mechanical properties of the Fe–Mn–C steels were systematically analysed to assess their suitability for this purpose. A series of four austenitic Fe–Mn–C steels with varying manganese (15 and 30 wt%) and carbon (0.6–1.0 wt%) content were processed by vacuum induction casting, annealing and hot forging. Microstructural analysis was performed, and the hot forged materials were further evaluated using ultrasound, macro hardness, and (stopped) quasi-static tensile tests to assess stent-related parameters. In contrast to the as-cast state, the hot forged steels exhibited high chemical homogeneity, as was found by energy-dispersive X-ray spectroscopy (EDXS). Electron backscatter diffraction (EBSD) revealed comparability between the four steels regarding their annealing twin fractions and grain size distributions. An austenitic microstructure was revealed for all modifications by transmission X-ray diffraction (XRD), except Fe–15Mn–0.6C, which displayed a minor ε–martensite fraction. Reducing manganese from 30 to 15 wt% resulted in favourable effects, including a higher Young's modulus, lowered offset yield strength, and an increased ultimate tensile strength due to larger strain hardening while preserving a high total elongation. However, reducing the carbon content to 0.6 wt% diminished the mechanical performance due to reduced solid solution strengthening and the ε–martensite formation. Among the investigated steels, the novel Fe–15Mn–0.8C alloy exhibited the most attractive combination of the studied properties for potential stent applications.