Bioabsorbable Implants Research Articles

Three-dimensional semiquantitative evaluation of reactive emphysema in magnesium implant models

Background Magnesium alloys have great potentials as bioabsorbable implants, whereas the difficulty in evaluating hydrogen gas produced in the degradation process has hindered their research and development. In this study, we investigated the possibility of industrial microfocus X-ray computed tomography (micro-CT) for the precise evaluation of subcutaneous emphysematous changes in a rabbit implantation model. Methods Magnesium plates with/without porous venting were implanted under skin defects on the backs of rabbits. The graft sites were examined by industrial micro-CT after sacrificing. The captured images were reconstructed three-dimensionally for volumetric analyses. The tissues of the graft site were also examined in the traditional histological investigation. Results We were able to image and numerate the shape and volume of subcutaneous emphysema using industrial micro-CT. The volume of emphysema was suppressed by pores punched in samples, and this trend increased as the number of pores increased. In the traditional histological examination, inflammatory changes were observed, but the emphysema could not be measured quantitatively. Conclusions Industrial micro-CT imaging makes it possible to visualize and evaluate magnesium-induced subcutaneous emphysema in animal experiment. This cross-border technology has the potential to be widely applied to other life science fields.

Semi-quantitative elemental imaging of corrosion products from bioabsorbable Mg vascular implants in vivo

While metal materials historically have served as permanent implants and were designed to avoid degradation, next generation bioabsorbable metals for medical devices such as vascular stents are under development, which would elute metal ions and corrosion byproducts into tissues. The fate of these eluted products and their local distribution in vascular tissue largely under studied. In this study, we employ a high spatial resolution spectrometric imaging modality, laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOF-MS) to map the metal distribution, (herein refered to as laser ablation mapping, or LAM) from Mg alloys within the mouse vascular system and approximate their local concentrations. We used a novel rare earth element bearing Mg alloy (WE22) wire implanted within the abdominal aorta of transgenic hypercholesterolemic mice (APOE−/−) to simulate a bioabsorbable vascular prosthesis for up to 30 days. We describe qualitatively and semi-quantitatively implant-derived corrosion product presence throughout the tissue cross sections, and their approximate concentrations within the various vessel structures. Additionally, we report the spatial changes of corrosion products, which we postulate are mediated by phagocytic inflammatory cells such as macrophages (MΦ’s).

Degradation of Unsintered Hydroxyapatite and Poly-L-Lactide Composite Sheets In Vivo and In Vitro.

Bioabsorbable sheet-shaped implants made of forged composites of unsintered hydroxyapatite and poly-L-lactide (F-u-HA/PLLA) have been used for orbital fracture repair with good results. This is the first report using multiple specimens implanted in the human orbit to demonstrate the biodegradation and loss of strength of F-u-HA/PLLA sheets. Among the patients who underwent various facial fracture repairs with F-u-HA/PLLA sheets implanted in their orbits, those whose sheets were subsequently extracted were included in the study. Viscosity-average molecular weight, crystallinity, and bending strength of the extracted implants were measured. An in vitro degradation test was also performed for comparison. Among the 111 patients who underwent F-u-HA/PLLA sheet implantation, 13 subsequently underwent surgical extraction of implants; the majority were due to secondary correction of complex fractures. One patient developed an infection; none developed foreign body reactions. Overall, 11 specimens from 10 patients with consent were examined. The time from implantation to extraction ranged from 43 to 632 days (median: 210d). Compared with the results of the in vitro degradation test, the viscosity-average molecular weight and bending strength had a slower decrease. The F-u-HA/PLLA sheets retained more than 50% of their initial bending strength after 12 months. Crystallinity varied widely. F-u-HA/PLLA sheets implanted in human orbits did not degrade faster than those of in vitro testing. Sheet-shaped implants made of forged composites of unsintered hydroxyapatite and poly-L-lactide can be considered appropriate reconstructive materials for orbital fractures as they retained sufficient strength to support the orbital contents at 12 months postoperatively, and no case of delayed foreign body reactions was observed.

Quaternary Zinc Alloys with Magnesium, Calcium and Strontium after Hydrostatic Extrusion-Microstructure and Its Impact on Mechanical and Corrosion Properties.

The development of bioabsorbable implants from Zn alloys is one of the main interests in the new generation of biomaterials. The main drawbacks of Zn-based materials are their insufficient mechanical properties. In the presented studies, a quaternary alloy composed of zinc with magnesium (0.2-1 wt. %), calcium (0.1-0.5 wt. %) and strontium (0.05-0.5 wt. %) was prepared by gravity casting followed by hot extrusion and then by hydrostatic extrusion. Microstructural characterization using scanning electron microscopy (SEM) and X-ray diffraction (XRD) phase analysis was performed. The mechanical properties were examined, using static tensile tests. Corrosion properties were analyzed using immersion tests. Samples were immersed in Hanks' solution (temperature = 37 °C, pH = 7.4) for 14 days. All alloys were subjected after corrosion to SEM observations on the surface and cross-section. The corrosion rate was also calculated. The microstructure of the investigated quaternary alloy consists of the α-Zn grains and intermetallic phases Mg2Zn11, CaZn13 and SrZn13 with different grain sizes and distribution, which impacted both mechanical and corrosion properties. Thanks to the alloying by the addition of Mg, Ca, and Sr and plastic deformation using hydrostatic extrusion, outstanding mechanical properties were obtained along with improvement in uniformity of corrosion rate.

Harmonizing microstructures and enhancing mechanical resilience: Novel powder metallurgy approach for Zn–Mg alloys

Zinc alloys are recognised for their excellent biocompatibility and favourable corrosion rates, making them suitable for bioabsorbable implants. However, their mechanical properties necessitate improvement to fulfil the rigorous requirements of biomedical applications. This research focuses on engineering pseudo-harmonic structures within zinc alloys through a comprehensive method combining mechanical alloying, spark plasma sintering, and hot extrusion techniques. This fabrication process results in a composite material characterised by a soft core surrounded by a continuous, three-dimensional, ultrafine-grained hard shell. The experiment involved blending pure zinc with Zn–1Mg alloy powder, leading to the formation of both ductile zinc and fine-grained Zn–1Mg regions. While the Mg2Zn11 intermetallic phase was found to enhance the alloy's mechanical strength, the presence of oxide shells adversely affected the material's properties. The elimination of these shells via hot extrusion markedly improved the alloy's tensile strength, reaching an average value of tensile strength of 333 ± 7 MPa. This study provides significant insights into the material engineering of zinc-based alloys for biodegradable implant applications, demonstrating a viable approach to optimising their mechanical performance.

Analysis of Using Bioabsorbable Implants in Orthopedic and Trauma Surgery in a Chilean Children's Hospital

Analysis of Using Bioabsorbable Implants in Orthopedic and Trauma Surgery in a Chilean Children's Hospital

Mechanical Properties and Corrosion Rate of ZnAg3 as a Novel Bioabsorbable Material for Osteosynthesis.

Osteosynthesis in fracture treatment typically uses hardware that remains in the patient's body, which brings a permanent risk of negative side effects such as foreign body reactions or chronic inflammation. Bioabsorbable materials, however, can degrade and slowly be replaced by autologous bone tissue. A suitable material is requested to offer great biocompatibility alongside excellent mechanical properties and a reasonable corrosion rate. Zinc-silver alloys provide these characteristics, which makes them a promising candidate for research. This study investigated the aptitude as a bioabsorbable implant of a novel zinc-silver alloy containing 3.3 wt% silver (ZnAg3). Here, the tensile strength as well as the corrosion rate in PBS solution (phosphate buffered solution) of ZnAg3 were assessed. Furthermore, shear tests, including fatigue and quasi-static testing, were conducted with ZnAg3 and magnesium pins (MAGNEZIX®, Syntellix AG, Hannover, Germany), which are already in clinical use. The detected corrosion rate of 0.10 mm/year for ZnAg3 was within the proposed range for bioabsorbable implants. With a tensile strength of 237.5 ± 2.12 MPa and a shear strength of 144.8 ± 13.2 N, ZnAg3 satisfied the mechanical requirements for bioabsorbable implants. The fatigue testing did not show any significant difference between ZnAg3 and magnesium pins, whereas both materials withstood the cyclic loading. Thus, the results support the assumption that ZnAg3 is qualified for further investigation.

Evaluation of adipogenesis over time using a novel bioabsorbable implant without the addition of exogenous cells or growth factors

BackgroundBreast reconstruction is crucial for patients who have undergone mastectomy for breast cancer. Our bioabsorbable implants comprising an outer poly-l-lactic acid mesh and an inner component filled with collagen sponge promote and retain adipogenesis in vivo without the addition of exogenous cells or growth factors. In this study, we evaluated adipogenesis over time histologically and at the gene expression level using this implant in a rodent model. MethodsThe implants were inserted in the inguinal and dorsal regions of the animals. At 1, 3, 6, and 12 months post-operation, the weight, volume, and histological assessment of all newly formed tissue were performed. We analyzed the formation of new adipose tissue using multiphoton microscopy and RNA sequencing. ResultsBoth in the inguinal and dorsal regions, adipose tissue began to form 1 month post-operation in the peripheral area. Angiogenesis into implants was observed until 3 months. At 6 months, microvessels matured and the amount of newly generated adipose tissue peaked and was uniformly distributed inside implants. The amount of newly generated adipose tissue decreased from 6 to 12 months but at 12 months, adipose tissue was equivalent to the native tissue histologically and in terms of gene expression. ConclusionsOur bioabsorbable implants could induce normal adipogenesis into the implants after subcutaneous implantation. Our implants can serve as a novel and safe material for breast reconstruction without requiring exogenous cells or growth factors.

Metastable FeMg particles for controlling degradation rate, mechanical properties, and biocompatibility of Poly(l-lactic) acid (PLLA) for orthopedic applications

Poly(l-lactic) acid (PLLA) is commonly used in bioabsorbable medical implants, but it suffers from slow degradation rate and rapid decline in mechanical properties for orthopedic applications. To address this drawback, recent research has explored the use of Mg as a filler for PLLA, resulting in composites with improved degradation rate and cytocompatibility compared to neat PLLA. In this study, FeMg powder particles were proposed as fillers for PLLA to investigate the potential of PLLA/FeMg composites for bioabsorbable implants. Cylinder specimens of PLLA, PLLA/Fe, PLLA/Mg and PLLA/FeMg were prepared using solvent casting followed by thermo-molding. The microstructure, thermal behavior, in vitro degradation behavior in simulated body fluid, mechanical properties and cytocompatibility of these composites were examined. The results indicate that the presence of FeMg particles prevents the deterioration of the composite mechanical properties, at least up to 14 days. Once a certain amount of degradation of the composite is reached, the degradation is faster than that of PLLA. Direct cytotoxicity assays revealed that pre-osteoblast MC3T3-E1 cells successfully adhered to and proliferated on the PLLA/FeMg surface. The inclusion of a low percentage of Mg into the Fe lattice not only accelerated the degradation rate of Fe but also improved its cytocompatibility. The enhanced degradation rate, mechanical properties, and osteoconductive properties of this composite make it a promising option for temporary orthopedic biomedical devices.

The usefulness of bioabsorbable magnesium implants in addition to metal plates in the treatment of complex distal radius fractures

Purpose: The aim of this study was to determine whether normal plating yields comparable outcomes to plating using additional bioabsorbable screws or wires for complex distal radial fractures.Methods: Among 80 patients with complex distal radius fractures treated between January 2018 and March 2021, 45 were studied retrospectively and divided into two groups as follows: group A (n=23) received a plate, and group B (n=22) received a plate with a bioresorbable screw or wire. Radiological studies evaluated the period of bone union, radial length, inclination, and resorption of the bioresorbable screws or wires after surgery. The Disabilities of the Arm, Shoulder, and Hand (DASH) score was examined for clinical evaluation, and complications were compared between the two groups.Results: The two groups showed similar distributions in sex, age, injury mechanism, diabetes mellitus, smoking, and mean follow-up period; however, there were no statistically significant differences in the period of bone union and maintenance of reduction (radial length, inclination, and volar tilt). The DASH score averaged 14.8 and 13.2 points in groups A and B, respectively, showing no significant difference in complications (nonunion, malunion, infection, and arthritis).Conclusion: Regardless of the use of additional bioresorbable screws or wires, reduction in distal radius fractures in both groups yielded good results. Plating with additional bioresorbable screws or wires may be a suitable fixation method to compensate for the shortcomings of metal implants in complex distal radius fractures.

Fentanyl-induced respiratory depression in rodents is inhibited by bioabsorbable, subcutaneous naltrexone implants at 3.5 months.

The aim of this study is to determine if extended-release, bioabsorbable, subcutaneous naltrexone (NTX) implants inhibit respiratory depression after an IV injection of fentanyl. Bioabsorbable implants fabricated from two different release-controlling polymers, poly-D-L-lactide (PDLLA) and polycaprolactone (PCL), alone (placebo) or containing NTX, were subcutaneously implanted in Sprague Dawley rats. After 3.5 months of implantation, the rodents were administered an IV bolus of fentanyl through the tail vein. The placebo implant rats received a dose of 4 micrograms (mcg) - (10 mcg/kg/dose), while the NTX implanted animals received a dose of 8 mcg (20 mcg/kg/dose). The minimum active dose of fentanyl that caused a > 50 ± 2% depression in the respiration rate in the placebo implanted rodents was 4 mcg. The respiration rate of the placebo implanted rats dropped from 208 ± 14 breaths/minute at predose, to 84 ± 12 breaths/minute (p = 0.0003) at 2 min. In contrast, all NTX implanted animals easily tolerated twice the dose of 8 mcg of fentanyl without any significant reduction in respiration rate. The mean respiration rate = increased from 164 ± 22 breaths/minute at predose to 178 ± 17 breaths/minute (p = 0.24) at 2 min. The mean plasma concentrations of NTX, 3.5 months after implantation, ranged from 7.4 (±1.1) ng/mL to 80.3 (±37.5) ng/mL. Bioabsorbable implants containing NTX effectively blocked fentanyl-induced respiratory depression in rodents as compared with placebo implants, 3.5 months after implantation.

Designing organic-inorganic hybrid coating from composite and structures for the tribological property and corrosion resistance of Mg alloys

Magnesium alloys are promising materials for the regeneration of bioabsorbable implants, but restricted by its poor tribological property and the rapid corrosion. In this work, a robust organic–inorganic hybrid coating was fabricated on the surface of Mg-Nd-Zn-Zr alloys through a combination of chemical assembly technique of hydroxylated boron nitride (BNO) and plasma-enhanced chemical vapour deposition of vinyltriethoxysilane. The obtained hybrid coating simultaneously enhanced anti-wear and anti-corrosion properties in both the dry friction and simulated body fluid (SBF)-condition friction. The wear rates of the Mg alloy modified by BNO/siloxane hybrid coating were significantly reduced by 97.3% and 96.4% under dry and SBF conditions, respectively. This step-by-step coating modification method is applicable to various shapes of magnesium alloys and hence displays great potential in implant application.

Long term observation of de novo adipogenesis using novel bioabsorbable implants with larger size in a porcine model

IntroductionThe regeneration of adipose tissue in patients after breast cancer surgery would be desirable without the use of growth factors or cells to avoid potential recurrence and metastasis. We reported that prolate spheroidal-shaped poly-L-lactic acid (PLLA) mesh implants of approximately 18-mm polar diameter and 7.5-mm greatest equatorial diameter containing collagen sponge (CS) would be replaced by regenerated adipose tissue after implantation, thereby suggesting an innovative method for breast reconstruction. Our study aimed to evaluate the adipose tissue regeneration ability of implant aggregates in a porcine model. MethodsWe prepared implant aggregates consisting of thirty PLLA mesh implants containing CS packed in a woven poly (glycolic acid) bag. The implant aggregates were inserted under the mammary glands in the porcine abdomen for a year. Single and double groups were classified by inserting either one or two implant aggregates on each side of the abdomen, respectively. ResultsIn both groups, the volume of the implant aggregates decreased over time, and the formation of adipose tissue peaked between 6 and 9 months. Histologically, the formation of adipose tissue was confirmed in the area that was in contact with native adipose tissue. ConclusionsOur implant aggregates could induce the autologous adipose tissue after long term implantation in vivo, without the use of any growth factor or cell treatment, presenting a potential novel method of breast reconstruction.

Magnesium Alloys Processed by Severe Plastic Deformation (SPD) for Biomedical Applications: An Overview

Ultra-fine grained and even nanostructured magnesium alloys obtained by processing with methods of severe plastic deformation (SPD) are promising biomaterials for absorbable orthopaedic implants due to their enhanced mechanical properties, adequate corrosion resistance and biocompatibility. This paper presents an overview of the impact of the most important SPD methods – equal-channel angular pressing (ECAP) and high-pressure torsion (HPT) – on microstructure refinement and improvement of the mechanical properties of magnesium alloys intended for medical implants. Several selected groups of magnesium alloys which have the potential for use as bioabsorbable implants are discussed. The presented results of many years of research indicate the beneficial effect of SPD methods on obtaining ultra-fine and even nanostructures of magnesium alloys with improved mechanical and better functional properties, which are necessary for bioabsorbable implants.

Biocompatibility Assessment of Zinc Alloys as a New Potential Material for Bioabsorbable Implants for Osteosynthesis.

In the last several years, zinc and its alloys have come into focus as bioabsorbable materials by qualifying themselves with an excellent corrosion rate, mechanical properties, anti-bacterial effects. and considerable biocompatibility. In this study, the biocompatibility of zinc-silver alloys containing 3.3 wt% silver (ZnAg3) was assessed by evaluating their cell viability, the proliferation rate, and the cell toxicity. Two alloys were investigated in which one was phosphated and the other was non-phosphated. The alloys were tested on human osteoblasts (hOb), which are, to a large extent, responsible for bone formation and healing processes. The performance of the phosphated alloy did not differ significantly from the non-phosphated alloy. The results showed a promising biocompatibility with hOb for both alloys equally in all conducted assays, qualifying ZnAg3 for further investigations such as in vivo studies.

Low-Profile Cartilage Repair With Knotless All-Suture Anchors: Surgical Technique

Osteochondral and pure chondral lesions of the knee are common after patellar dislocations. There are multiple described techniques for the fixation of these lesions, including metallic screws, bioabsorbable screws, bioabsorbable implants, and suture devices. The purpose of this article is to describe a surgical technique for surgical fixation of a lateral condyle chondral lesion using knotless all-suture anchors, with second-look knee arthroscopy illustrating healing of the cartilage repair.

Cardiovascular Safety and Benefits of Testosterone Implant Therapy in Postmenopausal Women: Where Are We?

We discuss the CV safety and efficacy data for subcutaneous testosterone therapy (STT) in postmenopausal women. We also highlight new directions and applications of correct dosages performed in a specialized center. To recommend STT, we propose innovative criteria (IDEALSTT) according to total testosterone (T) level, carotid artery intima-media thickness, and calculated SCORE for a 10-year risk of fatal cardiovascular disease (CVD). Despite all the controversies, hormone replacement therapy (HRT) with T has gained prominence in treating pre and postmenopausal women in the last decades. HRT with silastic and bioabsorbable testosterone hormone implants has gained prominence recently due to its practicality and effectiveness in treating menopausal symptoms and hypoactive sexual desire disorder. A recent publication on the complications of STT, looking at a large cohort of patients over seven years, demonstrated its long-term safety. However, the cardiovascular (CV) risk and safety of STT in women are still controversial.

Comparison of 2 Types of Bioabsorbable Implants Performing The Chevron Osteotomy to Treat Hallux Valgus Deformity: A Randomized Prospective Clinical Study

Comparison of 2 Types of Bioabsorbable Implants Performing The Chevron Osteotomy to Treat Hallux Valgus Deformity: A Randomized Prospective Clinical Study

Combining a Chest Wall Perforator Flap and Bioabsorbable Implant to Facilitate Oncoplastic Breast-conserving Surgery

Oncoplastic breast conservation is classically divided into two approaches: volume displacement and volume replacement (VR). These approaches are important to use when more than 20% of the breast is removed to avoid deformity. Smaller, nonptotic breasts require VR strategies from flaps based off of local chest wall perforators. When larger volumes are required, a flap based off the thoracodorsal artery can be used. Although this flap can replace larger volumes, it usually requires a position change with increased operative time, patient morbidity, and longer recovery while also exhausting a major reconstructive modality. In an effort to avoid this increased operative complexity, we have found that combining a local chest wall perforator flap and bioabsorbable implant, which has been previously shown to be safe and effective in reconstructing partial mastectomy defects, allows for a simpler VR strategy in patients who might otherwise require a more extensive thoracodorsal artery-based flap surgery or a mastectomy. Here, we present 10 cases where we combined flaps based off the lateral, anterior or medial intercostal artery perforators or lateral thoracic artery perforator with a bioabsorbable implant to successfully perform oncoplastic breast conservation in patients who might otherwise be marginal candidates for VR using a local chest wall perforator flap.

Microstructure, mechanical properties and fracture toughness of ECAPed magnesium matrix composite reinforced with hydroxyapatite ceramic particulates for bioabsorbable implants

Employing ceramic particles like hydroxyapatite to fabricate magnesium-based bio-composite has received incredible attention in orthopedic applications due to their bioactivity and biocompatibility. Besides, applying severe plastic deformation methods like equal channel angular pressing (ECAP), in addition to eliminating defects induced by casting, causes the metallurgical and mechanical behavior improvement of Mg/HA bio-composites. In this paper, the combined effects of HA particles and the ECAP process with Bc route on the microstructure, mechanical properties, and fracture toughness behavior of Mg/HA bio-composite fabricated through the electromagnetic and mechanical stir casting method were evaluated. Furthermore, a non-contact digital image correlation (DIC) method was adopted to accurately assess the elastic and plastic parameters and crack propagation during the fracture toughness test. Microstructural observation demonstrated that the addition of HA particles and, subsequently, applying four passes of the ECAP process on the bio-composites not only decreased the grain size by a considerable amount of 92%, but also resulted in a homogenous microstructure. Moreover, according to the results of the mechanical tests, after four-pass ECAP, although the compressive yield stress of Mg/HA bio-composite did not significantly change, the highest tensile yield stress, ultimate tensile, and compressive strength were accomplished. Among all elastic and plastic parameters, the elastic modulus and strength coefficient have continuously risen with adding HA and increasing the number of ECAP passes. However, the strain hardening exponent has decreased noticeably with the addition of HA, and the ECAP process compensated for some of this reduction. In addition, reinforcing magnesium with HA particles and improving the dislocation density caused by increasing the number of ECAP passes has led to increased material resistance against crack growth, wasted energy, and, consequently, fracture toughness. In this case, the four-pass ECAPed bio-composite showed the highest fracture toughness, approximately 28 MPa m0.5, 70% more than the pure Mg.