Advances in Fabrication Technologies for the Development of Next-Generation Cardiovascular Stents

Coronary artery disease is the most prevalent cardiovascular disease, claiming millions of lives annually around the world. The current treatment includes surgically inserting a tubular construct, called a stent, inside arteries to restore blood flow. However, due to lack of patient-specific design, the commercial products cannot be used with different vessel anatomies. In this review, we have summarized the drawbacks in existing commercial metal stents which face problems of restenosis and inflammatory responses, owing to the development of neointimal hyperplasia. Further, we have highlighted the fabrication of stents using biodegradable polymers, which can circumvent most of the existing limitations. In this regard, we elaborated on the utilization of new fabrication methodologies based on additive manufacturing such as three-dimensional printing to design patient-specific stents. Finally, we have discussed the functionalization of these stent surfaces with suitable bioactive molecules which can prove to enhance their properties in preventing thrombosis and better healing of injured blood vessel lining.

A polydiolcitrate-MoS2 composite for 3D printing Radio-opaque, Bioresorbable Vascular Scaffolds

Implantable polymeric biodegradable devices, such as biodegradable vascular stents or scaffolds, cannot be fully visualized using standard X-ray-based techniques, compromising their performance due to malposition after deployment. To address this challenge, we describe composites of methacrylated poly(1,12 dodecamethylene citrate) (mPDC) and MoS2 nanosheets to fabricate novel X-ray visible radiopaque and photocurable liquid polymer-ceramic composite (mPDC-MoS2). The composite was used as an ink with micro continuous liquid interface production (μCLIP) to fabricate bioresorbable vascular scaffolds (BVS). Prints exhibited excellent crimping and expansion mechanics without strut failures and, importantly, required X-ray visibility in air and muscle tissue. Notably, MoS2 nanosheets displayed physical degradation over time in a PBS environment, indicating the potential for producing bioresorbable devices. mPDC-MoS2 is a promising bioresorbable X-ray-visible composite material suitable for 3D printing medical devices, particularly vascular scaffolds or stents, that require non-invasive X-ray-based monitoring techniques for implantation and evaluation. This innovative composite system holds significant promise for the development of biocompatible and highly visible medical implants, potentially enhancing patient outcomes and reducing medical complications.

Engineering Analysis of Non-Braided Polycaprolactone Bioresorbable Flow Diverters for Aneurysms

This paper reports a nonbraided, bioresorbable polycaprolactone (PCL) flow diverter (FD) for the endovascular treatment of aneurysms. Bioresorbable FDs can reduce the risk associated with the permanent metallic FDs as they are resorbed by the body after curing of aneurysms. PCL FDs were designed and fabricated using an in-house hybrid electromelt spinning-fused deposition fabrication unit. Flow diverter's properties, surface qualities, and mechanical characteristics of PCL FDs of 50%, 60%, and 70% porosities were studied using scanning electron microscope (SEM), atomic force microscopy (AFM), and high precision universal testing machine (UTM). The deployability through a clinically relevant catheter was demonstrated in a PDMS aneurysm model. The angiographic visibility of the developed PCL FDs was evaluated using BaSO4 and Bi2O3 coatings of various concentration. The average strut thicknesses were 74.12 ± 6.63 μm, 63.07 ± 1.26 μm, and 56.82 ± 2.09 μm for PCL FDs with 50%, 60%, and 70% porosities, respectively. They average pore areas for the 50%, 60% and 70% porosities FDs were 0.055 ± 0.0056 mm2, 0. 0605 ± 0.0065 mm2, and 0.0712 ± 0.012 mm2, respectively. The surface quality was great with an RMS roughness value of 14.45 nm. The tensile, radial strength, and flexibility were found to be satisfactory and comparable to the nonbraided coronary stents. The developed PCL FDs were highly flexible and demonstrated to be deployable through conventional delivery system as low as 4 Fr catheters in a PDMS aneurysm model. The visibility under X-ray increases with the increasing concentration of coating materials BaSO4 and Bi2O3. The visibility intensity was slightly higher with Bi2O3 coating of PCL FDs. The overall results of the engineering analysis of the developed nonbraided PCL FDs are promising.

In Vitro Degradation of 3D-Printed Poly(L-lactide-Co-Glycolic Acid) Scaffolds for Tissue Engineering Applications

The creation of scaffolds for cartilage tissue engineering has faced significant challenges in developing constructs that can provide sufficient biomechanical support and offer suitable degradation characteristics. Ideally, such tissue-engineering techniques necessitate the fabrication of scaffolds that mirror the mechanical characteristics of the articular cartilage while degrading safely without damaging the regenerating tissues. The aim of this study was to create porous, biomechanically comparable 3D-printed scaffolds made from Poly(L-lactide-co-glycolide) 85:15 and to assess their degradation at physiological conditions 37 °C in pH 7.4 phosphate-buffered saline (PBS) for up to 56 days. Furthermore, the effect of scaffold degradation on the cell viability and proliferation of human bone marrow mesenchymal stem cells (HBMSC) was evaluated in vitro. To assess the long-term degradation of the scaffolds, accelerated degradation tests were performed at an elevated temperature of 47 °C for 28 days. The results show that the fabricated scaffolds were porous with an interconnected architecture and had comparable biomechanical properties to native cartilage. The degradative changes indicated stable degradation at physiological conditions with no significant effect on the properties of the scaffold and biocompatibility of the scaffold to HBMSC. Furthermore, the accelerated degradation tests showed consistent degradation of the scaffolds even in the long term without the notable release of acidic byproducts. It is hoped that the fabrication and degradation characteristics of this scaffold will, in the future, translate into a potential medical device for cartilage tissue regeneration.

Benchtop proof of concept and comparison of iron- and magnesium-based bioresorbable flow diverters

OBJECTIVE

Bioresorbable flow diverters (BRFDs) could significantly improve the performance of next-generation flow diverter technology. In the current work, magnesium and iron alloy BRFDs were prototyped and compared in terms of porosity/pore density, radial strength, flow diversion functionality, and resorption kinetics to offer insights into selecting the best available bioresorbable metal candidate for the BRFD application.

METHODS

BRFDs were constructed with braided wires made from alloys of magnesium (MgBRFD) or iron (FeBRFD). Pore density and crush resistance force were measured using established methods. BRFDs were deployed in silicone aneurysm models attached to flow loops to investigate flow diversion functionality and resorption kinetics in a simulated physiological environment.

RESULTS

The FeBRFD exhibited higher pore density (9.9 vs 4.3 pores/mm2) and crush resistance force (0.69 ± 0.05 vs 0.53 ± 0.05 N/cm, p = 0.0765, n = 3 per group) than the MgBRFD, although both crush resistances were within the range previously reported for FDA-approved flow diverters. The FeBRFD demonstrated greater flow diversion functionality than the MgBRFD, with significantly higher values of established flow diversion metrics (mean transit time 159.6 ± 11.9 vs 110.9 ± 1.6, p = 0.015; inverse washout slope 192.5 ± 9.0 vs 116.5 ± 1.5, p = 0.001; n = 3 per group; both metrics expressed as a percentage of the control condition). Last, the FeBRFD was able to maintain its braided structure for > 12 weeks, whereas the MgBRFD was almost completely resorbed after 5 weeks.

CONCLUSIONS

The results of this study demonstrated the ability to manufacture BRFDs with magnesium and iron alloys. The data suggest that the iron alloy is the superior material candidate for the BRFD application due to its higher mechanical strength and lower resorption rate relative to the magnesium alloy.

Safe and effective profile of the VSTENT bioresorbable polymer sirolimus-eluting stent in the treatment of patients with de novo coronary artery lesions: a prospective, cohort, multicenter study

Background

The drug-eluting stent was a significant stride forward in the development of enhanced therapeutic therapy for coronary intervention, with three generations of increased advancement. VSTENT is a newly developed stent manufactured in Vietnam that aims to provide coronary artery patients with a safe, effective, and cost-efficient option. The purpose of this trial was to determine the efficacy and safety of a new bioresorbable polymer sirolimus-eluting stent called VSTENT.

Methods

This is a prospective, cohort, multicenter research in 5 centers of Vietnam. A prespecified subgroup received intravascular ultrasound (IVUS) or optical coherence tomography (OCT) imaging. We determined procedure success and complications during index hospitalization. We monitored all participants for a year. Six-month and 12-month rates of major cardiovascular events were reported. All patients had coronary angiography after 6 months to detect late lumen loss (LLL). Prespecified patients also had IVUS or OCT performed.

Results

The rate of device success was 100% (95% CI: 98.3-100%; P<0.001). Major cardiovascular events were 4.7% (95% CI: 1.9-9.4%; P<0.001). The LLL over quantitative coronary angiography (QCA) was 0.08±0.19 mm (95% CI: 0.05-0.10; P<0.001) in the in-stent segment and 0.07±0.31 mm (95% CI: 0.03-0.11; P=0.002) in 5 mm within the two ends of the stent segment. The LLL recorded by IVUS and OCT at 6 months was 0.12±0.35 mm (95% CI: 0.01-0.22; P=0.028) and 0.15±0.24 mm (95% CI: 0.02-0.28; P=0.024), respectively.

Conclusions

This study's device success rates were perfect. IVUS and OCT findings on LLL were favorable at 6-month follow-up. One-year follow-up showed low in-stent restenosis (ISR) and target lesion revascularization (TLR) rates, reflecting few significant cardiovascular events. VSTENT's safety and efficacy make it a promising percutaneous intervention option in developing nations.

High Adherence of Oral Streptococcus to Polylactic Acid Might Explain Implant Infections Associated with PLA Mesh Implantation

The aim of this study was to evaluate and compare the biofilm formation properties of common pathogens associated with implant-related infections on two different implant material types. Bacterial strains tested in this study were Staphylococcus aureus, Streptococcus mutans, Enterococcus faecalis, and Escherichia coli. Implant materials tested and compared were PLA Resorb × polymer of Poly DL-lactide (PDLLA) comprising 50% poly-L-lactic acid and 50% poly-D-lactic acid) and Ti grade 2 (tooled with a Planmeca CAD-CAM milling device). Biofilm assays were done with and without saliva treatment to evaluate the effect of saliva on bacterial adhesion and to mimic the intraoral and extraoral surgical routes of implant placement, respectively. Five specimens of each implant type were tested for each bacterial strain. Autoclaved material specimens were first treated with 1:1 saliva-PBS solution for 30 min, followed by washing of specimens and the addition of bacterial suspension. Specimens with bacterial suspension were incubated for 24 h at 37 °C for biofilm formation. After 24 h, non-adhered bacteria were removed, and specimens were washed, followed by removal and calculation of adhered bacterial biofilm. S. aureus and E. faecalis showed more attachment to Ti grade 2, whereas S. mutans showed higher adherence to PLA in a statistically significant manner. The salivary coating of specimens enhanced the bacterial attachment by all the bacterial strains tested. In conclusion, both implant materials showed significant levels of bacterial adhesion, but saliva treatment played a vital role in bacterial attachment, therefore, saliva contamination of the implant materials should be minimized and considered when placing implant materials inside the body.

Self-powered, light-controlled, bioresorbable platforms for programmed drug delivery

Degradable polymer matrices and porous scaffolds provide powerful mechanisms for passive, sustained release of drugs relevant to the treatment of a broad range of diseases and conditions. Growing interest is in active control of pharmacokinetics tailored to the needs of the patient via programmable engineering platforms that include power sources, delivery mechanisms, communication hardware, and associated electronics, most typically in forms that require surgical extraction after a period of use. Here we report a light-controlled, self-powered technology that bypasses key disadvantages of these systems, in an overall design that is bioresorbable. Programmability relies on the use of an external light source to illuminate an implanted, wavelength-sensitive phototransistor to trigger a short circuit in an electrochemical cell structure that includes a metal gate valve as its anode. Consequent electrochemical corrosion eliminates the gate, thereby opening an underlying reservoir to release a dose of drugs by passive diffusion into surrounding tissue. A wavelength-division multiplexing strategy allows release to be programmed from any one or any arbitrary combination of a collection of reservoirs built into an integrated device. Studies of various bioresorbable electrode materials define the key considerations and guide optimized choices in designs. In vivo demonstrations of programmed release of lidocaine adjacent the sciatic nerves in rat models illustrate the functionality in the context of pain management, an essential aspect of patient care that could benefit from the results presented here.

Preparation, physicochemical characterization, and in vitro and in vivo osteogenic evaluation of a bioresorbable, moldable, hydroxyapatite/poly(caprolactone-co-lactide) bone substitute

Use of bioresorbable artificial bone substitutes is anticipated for bone augmentation in dental implant surgery because they are relatively economical and uniform in quality compared to heterogeneous bone. In this study, a new shapable, rubbery, bioresorbable bone substitute was developed. The material was prepared by ultrasonically dispersing hydroxyapatite (HA) particles throughout a poly (caprolactone-co-lactide) (PCLLA) rubbery matrix. Physiochemical properties of the bone substitute including its composition, deformability, anti-collapse ability, degradation behavior, and in vitro and in vivo osteogenic ability were evaluated. Results revealed that HA/PCLLA, which consists of homogeneously dispersed HA particles and a rubbery matrix composed of PCLLA, possesses a deformable capacity. The result of the mass retention rate of the material indicated an excellent durability in an aqueous environment. Further, the effects of HA/PCLLA on cell functions and bone-regenerated performance were evaluated in vitro and in vivo. The results showed that HA/PCLLA had enhanced proliferative capacity, and ability to undergo osteogenic differentiation and mineralization in vitro. It was also found that HA/PCLLA had an appropriate degradation rate to induce consecutive new bone formation without collapse at the early stage in vivo, as well as the ability to maintain the contour of the bone-grafting area, which is comparable to the deproteinized bovine bone mineral. These results indicated that HA/PCLLA is a promising bioresorbable bone substitute with properties that meet clinical requirements, including deformability, resistance to collapse in an aqueous environment, appropriate early-stage degradation rate, biocompatibility, osteogenic bioactivity and the capacity to regenerate bone tissue with favorable contour.

Evaluation of Topology Optimization Using 3D Printing for Bioresorbable Fusion Cages: A Biomechanical Study in a Porcine Model

STUDY DESIGN

Preclinical biomechanical study of topology optimization versus standard ring design for bioresorbable poly-ε-caprolactone (PCL) cervical spine fusion cages delivering bone morphogenetic protein-2 (BMP-2) using a porcine model.

OBJECTIVE

The aim was to evaluate range of motion (ROM) and bone fusion, as a function of topology optimization and BMP-2 delivery method.

SUMMARY OF BACKGROUND DATA

3D printing technology enables fabrication of topology-optimized cages using bioresorbable materials, offering several advantages including customization, and lower stiffness. Delivery of BMP-2 using topology optimization may enhance the quality of fusion.

METHODS

Twenty-two 6-month-old pigs underwent anterior cervical discectomy fusion at one level using 3D printed PCL cages. Experimental groups (N=6 each) included: Group 1: ring design with surface adsorbed BMP-2, Group 2: topology-optimized rectangular design with surface adsorbed BMP-2, and Group 3: ring design with BMP-2 delivery via collagen sponge. Additional specimens, two of each design, were implanted without BMP-2, as controls. Complete cervical segments were harvested six months postoperatively. Nanocomputed tomography was performed to assess complete bony bridging. Pure moment biomechanical testing was conducted in all three planes, separately. Continuous 3D motions were recorded and analyzed.

RESULTS

Three subjects suffered early surgical complications and were not evaluated. Overall, ROM for experimental specimens, regardless of design or BMP-2 delivery method, was comparable, with no clinically significant differences among groups. Among experimental specimens at the level of the fusion, ROM was <1.0° in flexion and extension, indicative of fusion, based on clinically applied criteria for fusion of <2 to 4°. Despite the measured biomechanical stability, using computed tomography evaluation, complete bony bridging was observed in 40% of the specimens in Group 1, 50% of Group 2, 100% of Group 3, and none of the control specimens.

CONCLUSION

A topology-optimized PCL cage with BMP-2 is capable of resulting in an intervertebral fusion, similar to a conventional ring-based design of the same bioresorbable material.

Natural Coatings and Surface Modifications on Magnesium Alloys for Biomedical Applications

Magnesium (Mg) alloys have great potential in biomedical applications due to their incomparable properties regarding other metals, such as stainless steels, Co-Cr alloys, and titanium (Ti) alloys. However, when Mg engages with body fluids, its degradation rate increases, inhibiting the complete healing of bone tissue. For this reason, it has been necessary to implement protective coatings to control the rate of degradation. This review focuses on natural biopolymer coatings used on Mg alloys for resorbable biomedical applications, as well as some modification techniques implemented before applying natural polymer coatings to improve their performance. Issues such as improving the corrosion resistance, cell adhesion, proliferation, and biodegradability of natural biopolymers are discussed through their basic comparison with inorganic-type coatings. Emphasis is placed on the expected biological behavior of each natural polymer described, to provide basic information as a reference on this topic.

Clinical Outcomes of 3D-Printed Bioresorbable Scaffolds for Bone Tissue Engineering-A Pilot Study on 126 Patients for Burrhole Covers in Subdural Hematoma

Burrhole craniostomy is commonly performed for subdural hematoma (SDH) evacuation, but residual scalp depressions are often cosmetically suboptimal for patients. OsteoplugTM, a bioresorbable polycaprolactone burrhole cover, was introduced by the National University Hospital, Singapore, in 2006 to cover these defects, allowing osseous integration and vascular ingrowth. However, the cosmetic and safety outcomes of OsteoplugTM-C-the latest (2017) iteration, with a chamfered hole for subdural drains-remain unexplored. Data were collected from a single institution from April 2017 to March 2021. Patient-reported aesthetic outcomes (Aesthetic Numeric Analog (ANA)) and quality of life (EQ-5D-3L including Visual Analog Scale (VAS)) were assessed via telephone interviews. Clinical outcomes included SDH recurrence, postoperative infections, and drain complications. OsteoplugTM-C patients had significantly higher satisfaction and quality of life compared to those without a burrhole cover (ANA: 9 [7, 9] vs. 7 [5, 8], p = 0.019; VAS: 85 [75, 90] vs. 70 [50, 80], p = 0.021), and the absence of a burrhole cover was associated with poorer aesthetic outcomes after multivariable adjustment (adjusted OR: 4.55, 95% CI: 1.09-22.68, p = 0.047). No significant differences in other clinical outcomes were observed between OsteoplugTM-C, OsteoplugTM, or no burrhole cover. Our pilot study supports OsteoplugTM-C and its material polycaprolactone as suitable adjuncts to burrhole craniostomy, improving cosmetic outcomes while achieving comparable safety outcomes.

Biocompatibility and Degradation Behavior of Molybdenum in an In Vivo Rat Model

The biocompatibility and degradation behavior of pure molybdenum (Mo) as a bioresorbable metallic material (BMM) for implant applications were investigated. In vitro degradation of a commercially available Mo wire (ø250 µm) was examined after immersion in modified Kokubo's SBF for 28 days at 37 °C and pH 7.4. For assessment of in vivo degradation, the Mo wire was implanted into the abdominal aorta of female Wistar rats for 3, 6 and 12 months. Microstructure and corrosion behavior were analyzed by means of SEM/EDX analysis. After explantation, Mo levels in serum, urine, aortic vessel wall and organs were investigated via ICP-OES analysis. Furthermore, histological analyses of the liver, kidneys, spleen, brain and lungs were performed, as well as blood count and differentiation by FACS analysis. Levels of the C-reactive protein were measured in blood plasma of all the animals. In vitro and in vivo degradation behavior was very similar, with formation of uniform, non-passivating and dissolving product layers without occurrence of a localized corrosion attack. The in vitro degradation rate was 101.6 µg/(cm2·d) which corresponds to 33.6 µm/y after 28 days. The in vivo degradation rates of 12, 33 and 36 µg/(cm2·d) were observed after 3, 6 and 12 months for the samples properly implanted in the aortic vessel wall. This corresponds with a degradation rate of 13.5 µm/y for the 12-month cohort. However, the magnitude of degradation strongly depended on the implant site, with the wires incorporated into the vessel wall showing the most severe degradation. Degradation of the implanted Mo wire neither induced an increase in serum or urine Mo levels nor were elevated Mo levels found in the liver and kidneys compared with the respective controls. Only in the direct vicinity of the implant in the aortic vessel wall, a significant amount of Mo was found, which, however, was far below the amounts to be expected from degrading wires. No abnormalities were detected for all timepoints in histological and blood analyses compared to the control group. The C-reactive protein levels were similar between all the groups, indicating no inflammation processes. These findings suggest that dissolved Mo from a degrading implant is physiologically transported and excreted. Furthermore, radiographic and µCT analyses revealed excellent radiopacity of Mo in tissues. These findings and the unique combination with its extraordinary mechanical properties make Mo an interesting alternative for established BMMs.

A novel gradient and multilayered sheet with a silk fibroin/polyvinyl alcohol core-shell structure for bioabsorbable arterial grafts

Bioabsorbable arterial grafts can potentially improve patency and neovessel formation; however, their application in clinical settings has not been realized. In this study, we developed bioabsorbable gradient sheets based on silk fibroin (SF) and polyvinyl alcohol (PVA) with a core-shell nanofibrous structure. This gradient sheet was expected to promote vascular remodeling while we maintained its physical properties and a gradual degrading process from the luminal surface. ESP was conducted at various flow rates for SF and PVA to achieve the multilayer gradient structure. Furthermore, the elasticity of the gradient sheet could be increased by increasing the PVA flow rate; however, this reduced the tensile strength of the core-shell fibers. Notably, the physical properties of the gradient sheet did not degrade even after 7 days of immersion in a phosphate buffer saline solution, which indicates that the structure could maintain its structural integrity while resisting arterial pressure. In vitro experiments revealed that the number of endothelial cells attached to the SF/PVA sheet was notably higher than that on the cell-culture dish. The gradient sheets were implanted in rat abdominal aortas and explanted after 14 days to confirm acute-phase patency and vascular remodeling. The gradient sheets constructed with SF composed of polyurethane and PVA improved the ease of handling of the material, and these sheets resulted in a favorable vascular remodeling outcome. Our results strongly suggest that the SF/PVA-based gradient sheets described in this study can serve as a novel design for bioabsorbable arterial grafts upon further modifications.

Drug Release and Pharmacokinetic Evaluation of Novel Implantable Mometasone Furoate Matrices in Rabbit Maxillary Sinuses

BACKGROUND

Intranasal corticosteroid sprays (INCSs) used to treat chronic rhinosinusitis are suboptimal due to limited penetration into the middle meatus, rapid clearance, and poor patient compliance. A bioresorbable drug matrix, developed with the XTreo^TM drug delivery platform, may overcome the limitations of INCS by providing continuous dosing over several months.

OBJECTIVE

To evaluate the in vitro drug release and in vivo pharmacokinetics of novel mometasone furoate (MF) matrices in a rabbit dorsal maxillary osteotomy model.

METHODS

XTreo^TM matrices were formulated to consistently elute MF for up to 6 months. Matrices were surgically placed bilaterally into the maxillary sinuses of New Zealand White (NZW) rabbits. Tissue and plasma MF concentrations were measured to assess the in vivo drug delivery. The in vivo and in vitro drug release kinetics of the matrices were quantified and compared to those of rabbits receiving daily Nasonex^® MF nasal sprays.

RESULTS

XTreo^TM matrices self-expanded upon deployment to conform to the irregular geometry of the maxillary sinus cavities in the NZW rabbits. Sustained release of MF was demonstrated in vitro and in vivo for 2 MF matrices of distinct release durations and an in vitro-in vivo correlation was established. Therapeutic levels of MF in local tissues were measured throughout the intended dosing durations. In contrast to the variable peaks and troughs of daily nasal sprays, sustained dosing via a single administration of MF matrices was confirmed by quantifiable plasma MF concentrations over the intended dosing duration.

CONCLUSION

The XTreo^TM MF matrices provided targeted and efficient dosing to local sinus tissues that was superior to INCS. Sustained drug release was confirmed both in vitro and in vivo. The novel XTreo^TM technology may provide precisely tuned, long-lasting drug delivery to sinus tissues with a single treatment.

In Vitro and In Vivo Biosafety Analysis of Resorbable Polyglycolic Acid-Polylactic Acid Block Copolymer Composites for Spinal Fixation

Herein, spinal fixation implants were constructed using degradable polymeric materials such as PGA–PLA block copolymers (poly(glycolic acid-b-lactic acid)). These materials were reinforced by blending with HA-g-PLA (hydroxyapatite-graft-poly lactic acid) and PGA fiber before being tested to confirm its biocompatibility via in vitro (MTT assay) and in vivo animal experiments (i.e., skin sensitization, intradermal intracutaneous reaction, and in vivo degradation tests). Every specimen exhibited suitable biocompatibility and biodegradability for use as resorbable spinal fixation materials.

Two-year follow-up of bioresorbable vascular scaffolds in severe infra-popliteal arterial disease

OBJECTIVES

To assess the safety, efficacy, and durability of the Absorb bioresorbable vascular scaffold in predominantly complex, infra-popliteal lesions for the management of chronic limb ischemia at two-year clinical follow-up. Bioresorbable vascular scaffold are biodegradable scaffolds that provide short-term vascular support before undergoing intravascular degradation. A recent trial reported excellent 36-month vessel patency rates in simple infrapopliteal arterial lesions treated with Absorb bioresorbable vascular scaffold.

METHODS

This single-center, retrospective study evaluated the use of the Absorb bioresorbable vascular scaffold (everolimus impregnated poly-L-lactic scaffold) in patients with infra-popliteal peripheral arterial disease (PAD) with respect to safety (thrombosis and TIMI bleeding), technical success, and freedom from clinically driven target vessel failure at 24 months.

RESULTS

31 patients (51.6% male) with a median age of 67 years with predominantly advanced infra-popliteal disease were treated with 49 bioresorbable vascular scaffold in 41 vessels. The mean stenosis was 94% (80-100), with 49% of lesions being chronic thrombotic occlusions. No scaffold thrombosis or peri-procedural bleeding was observed. Procedural success was achieved in all patients; 93.5% of patients experienced freedom from clinically driven target vessel failure at 24 months, driven by one revascularization and one amputation. Primary patency was 96.7% at 12 months and 87.1% at 24 months. All patients were alive at 12 and 24 months.

CONCLUSIONS

At 24 months, our study found that patients with predominantly advanced infra-popliteal PAD who were treated with Absorb bioresorbable vascular scaffold reported improved clinical status and a low and durable rate of clinically driven target vessel failure extending out to 24 months.

Cytocompatibility Evaluation of a Novel Series of PEG-Functionalized Lactide-Caprolactone Copolymer Biomaterials for Cardiovascular Applications

Although the use of bioresorbable materials in stent production is thought to improve long-term safety compared to their durable counterparts, a recent FDA report on the 2-year follow-up of the first FDA-approved bioresorbable vascular stent showed an increased occurrence of major adverse cardiac events and thrombosis in comparison to the metallic control. In order to overcome the issues of first generation bioresorbable polymers, a series of polyethylene glycol-functionalized poly-L-lactide-co-ε-caprolactone copolymers with varying lactide-to-caprolactone content is developed using a novel one-step PEG-functionalization and copolymerization strategy. This approach represents a new facile way toward surface enhancement for cellular interaction, which is shown by screening these materials regarding their cyto- and hemocompatibility in terms of cytotoxicity, hemolysis, platelet adhesion, leucocyte activation and endothelial cell adhesion. By varying the lactide-to-caprolactone polymer composition, it is possible to gradually affect endothelial and platelet adhesion which allows fine-tuning of the biological response based on polymer chemistry. All polymers developed were non-cytotoxic, had acceptable leucocyte activation levels and presented non-hemolytic (<2% hemolysis rate) behavior except for PLCL-PEG 55:45 which presented hemolysis rate of 2.5% ± 0.5. Water contact angles were reduced in the polymers containing PEG functionalization (PLLA-PEG: 69.8° ± 2.3, PCL-PEG: 61.2° ± 7.5) versus those without (PLLA: 79.5° ± 3.2, PCL: 76.4° ± 10.2) while the materials PCL-PEG550, PLCL-PEG550 90:10 and PLCL-PEG550 70:30 demonstrated best endothelial cell adhesion. PLLA-PEG550 and PLCL-PEG550 70:30 presented as best candidates for cardiovascular implant use from a cytocompatibility perspective across the spectrum of testing completed. Altogether, these polymers are excellent innovative materials suited for an application in stent manufacture due to the ease in translation of this one-step synthesis strategy to device production and their excellent in vitro cyto- and hemocompatibility.

Materials and Orthopedic Applications for Bioresorbable Inductively Coupled Resonance Sensors

Bioresorbable passive resonance sensors based on inductor-capacitor (LC) circuits provide an auspicious sensing technology for temporary battery-free implant applications due to their simplicity, wireless readout, and the ability to be eventually metabolized by the body. In this study, the fabrication and performance of various LC circuit-based sensors are investigated to provide a comprehensive view on different material options and fabrication methods. The study is divided into sections that address different sensor constituents, including bioresorbable polymer and bioactive glass substrates, dissolvable metallic conductors, and atomic layer deposited (ALD) water barrier films on polymeric substrates. The manufactured devices included a polymer-based pressure sensor that remained pressure responsive for 10 days in aqueous conditions, the first wirelessly readable bioactive glass-based resonance sensor for monitoring the complex permittivity of its surroundings, and a solenoidal coil-based compression sensor built onto a polymeric bone fixation screw. The findings together with the envisioned orthopedic applications provide a reference point for future studies related to bioresorbable passive resonance sensors.

Comparison of Contemporary Drug-eluting Coronary Stents - Is Any Stent Better than the Others?

Percutaneous coronary intervention (PCI) with implantation of a metallic drug-eluting stent (DES) is the mainstay of treatment in patients with significant coronary artery disease or acute coronary syndromes. DESs comprise a metallic platform and an anti-proliferative drug, usually released from a polymer coating. A wide range of DESs, differing in platform, polymer or drug, are currently available for clinical use. Although there are significant differences in the physical, biological and pharmacological properties of contemporary DESs, it remains unclear whether these impact meaningfully on clinical outcomes for patients undergoing PCI. Numerous randomised clinical trials have compared DESs in recent years, but these trials are typically designed to show non-inferiority, rather than superiority. Data from meta-analyses have helped to study this in larger populations, but have limitations. Improvement in stent design continues and ongoing work is exploring the effects of new innovations as well as gathering further data on existing devices. This review explores the development, properties and clinical efficacy of current-generation DESs, comparing different types where possible, whilst identifying areas of further work.

Bioabsorbable Versus Titanium Screws in Anterior Cruciate Ligament Reconstruction Using Hamstring Autograft: A Prospective, Randomized Controlled Trial With 13-Year Follow-up

BACKGROUND

Bioabsorbable screws for anterior cruciate ligament reconstruction (ACLR) have been a popular choice, with theoretical advantages in imaging and surgery. Titanium and poly-L-lactic acid with hydroxyapatite (PLLA-HA) screws have been compared, but with less than a decade of follow-up.

PURPOSE/HYPOTHESIS

The purpose was to compare long-term outcomes of hamstring autograft ACLR using either PLLA-HA screws or titanium screws. We hypothesized there would be no difference at 13 years in clinical scores or tunnel widening between PLLA-HA and titanium screw types, along with high-grade resorption and ossification of PLLA-HA screws.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 1.

METHODS

Forty patients undergoing ACLR were randomized to receive either a PLLA-HA screw or a titanium screw for ACL hamstring autograft fixation. Blinded evaluation was performed at 2, 5, and 13 years using the International Knee Documentation Committee score, Lysholm knee score, and KT-1000 arthrometer. Magnetic resonance imaging (MRI) was performed at 2 or 5 years and 13 years to evaluate tunnel volumes, ossification around the screw, graft integration, and cyst formation. Computed tomography (CT) of patients with PLLA-HA was performed at 13 years to evaluate tunnel volumes and intratunnel ossification.

RESULTS

No differences were seen in clinical outcomes at 2, 5, or 13 years between the 2 groups. At 13 years, tibial tunnel volumes were smaller for the PLLA-HA group (2.17 cm³) compared with the titanium group (3.33 cm³; P = .004). By 13 years, the PLLA-HA group had complete or nearly complete resorption on MRI or CT scan.

CONCLUSION

Equivalent clinical results were found between PLLA-HA and titanium groups at 2, 5, and 13 years. Although PLLA-HA screws had complete or nearly complete resorption by 13 years, tunnel volumes remained largely unchanged, with minimal ossification.

Experimental Tests, FEM Constitutive Modeling and Validation of PLGA Bioresorbable Polymer for Stent Applications

The use of bioresorbable polymers such as poly(lactic-co-glycolic acid) (PLGA) in coronary stents can hypothetically reduce the risk of complications (e.g., restenosis, thrombosis) after percutaneous coronary intervention. However, there is a need for a constitutive modeling strategy that combines the simplicity of implementation with strain rate dependency. Here, a constitutive modeling methodology for PLGA comprising numerical simulation using a finite element method is presented. First, the methodology and results of PLGA experimental tests are presented, with a focus on tension tests of tubular-type specimens with different strain rates. Subsequently, the constitutive modeling methodology is proposed and described. Material model constants are determined based on the results of the experimental tests. Finally, the developed methodology is validated by experimental and numerical comparisons of stent free compression tests with various compression speeds. The validation results show acceptable correlation in terms of both quality and quantity. The proposed and validated constitutive modeling approach for the bioresorbable polymer provides a useful tool for the design and evaluation of bioresorbable stents.

Cranial flap fixation in sheep using a resorbable bone adhesive

OBJECTIVE

The authors' goal in this study was to investigate the use of a novel, bioresorbable, osteoconductive, wet-field mineral-organic bone adhesive composed of tetracalcium phosphate and phosphoserine (TTCP-PS) for cranial bone flap fixation and compare it with conventional low-profile titanium plates and self-drilling screws.

METHODS

An ovine craniotomy surgical model was used to evaluate the safety and efficacy of TTCP-PS over 2 years. Bilateral cranial defects were created in 41 sheep and were replaced in their original position. The gaps (kerfs) were completely filled with TTCP-PS (T1 group), half-filled with TTCP-PS (T2 group), or left empty and the flaps fixated by plates and screws as a control (C group). At 12 weeks, 1 year, and 2 years following surgery, the extent of bone healing, local tissue effects, and remodeling of the TTCP-PS were analyzed using macroscopic observations and histopathological and histomorphometric analyses. Flap fixation strength was evaluated by biomechanical testing at 12 weeks and 1 year postoperatively.

RESULTS

No adverse local tissue effects were observed in any group. At 12 weeks, the bone flap fixation strengths in test group 1 (1689 ± 574 N) and test group 2 (1611 ± 501 N) were both statistically greater (p = 0.01) than that in the control group (663 ± 385 N). From 12 weeks to 1 year, the bone flap fixation strengths increased significantly (p < 0.05) for all groups. At 1 year, the flap fixation strength in test group 1 (3240 ± 423 N) and test group 2 (3212 ± 662 N) were both statistically greater (p = 0.04 and p = 0.02, respectively) than that in the control group (2418 ± 1463 N); however, there was no statistically significant difference in the strengths when comparing the test groups at both timepoints. Test group 1 had the best overall performance based on histomorphometric evaluation and biomechanical testing. At 2 years postoperatively, the kerfs filled with TTCP-PS had histological evidence of osteoconduction and replacement of TTCP-PS by bone with nearly complete osteointegration.

CONCLUSIONS

TTCP-PS was demonstrated to be safe and effective for cranial flap fixation in an ovine model. In this study, the bioresorbable, osteoconductive bone adhesive appeared to have multiple advantages over standard plate-and-screw bone flap fixation, including biomechanical superiority, more complete and faster bony healing across the flap kerfs without fibrosis, and the minimization of bone flap and/or hardware migration and loosening. These properties of TTCP-PS may improve human cranial bone flap fixation and cranioplasty.

Three anchor concepts for rotator cuff repair in standardized physiological and osteoporotic bone: a biomechanical study

BACKGROUND

Previous biomechanical studies used single-pull destructive tests in line with the anchor and are limited by a great variability of bone density of cadaver samples. To overcome these limitations, a more physiological test setting was provided using titanium, bioresorbable, and all-suture anchors.

METHODS

In this controlled laboratory study, 3 anchor constructs were divided into 2 groups: physiological and osteoporotic. Sixty standardized artificial bone specimens (=10 for each anchor in each group) were used for biomechanical testing. The anchors were inserted at a 45° angle as during surgery. Cyclic loading for 1000 cycles followed by ultimate load-to-failure (ULTF) testing was performed. Elongation, ultimate load at failure, and the mode of failure were noted.

RESULTS

In the physiological group, the ULTF for the all-suture anchor (mean [standard deviation], 632.9 [96.8 N]) was found to be significantly higher than for the other anchors (titanium, 497.1 [50.5] N, and bioresorbable, 322.4 [3.1 N], P < .0001). The titanium anchor showed a significantly higher ULTF than the bioresorbable anchor (P < .0001). In the osteoporotic group, the all-suture anchor again showed a higher ULTF compared to the bioresorbable anchor (500.9 [50.6] N vs. 315.1 [11.3] N, P < .0001). In the osteoporotic group, cyclic loading revealed a higher elongation after 1000 loading cycles for the bioresorbable (0.40 [0.12] mm) compared to the titanium (0.22 [0.11] mm; P = .01) as well as the all-suture anchor (0.19 [0.15] mm, P = .003).

CONCLUSION

Regarding ULTF, the all-suture anchor outperformed the other anchors in physiological bone, but in osteoporotic bone, significance was reached only compared to the bioresorbable anchor. Although cyclic loading revealed significant differences, these might not be clinically relevant.

Intracoronary Imaging for Assessment of Vascular Healing and Stent Follow-up in Bioresorbable Vascular Scaffolds

Bioresorbable Vascular Scaffolds (BVS) are polymer-based materials implanted in the coronary arteries in order to treat atherosclerotic lesions, based on the concept that once the lesion has been treated, the material of the implanted stent will undergo a process of gradual resorption that will leave, in several years, the vessel wall smooth, free of any foreign material and with its vasomotion restored. However, after the first enthusiastic reports on the efficacy of BVSs, the recently published trials demonstrated disappointing results regarding long-term patency following BVS implantation, which were mainly attributed to technical deficiencies during the stenting procedure. Intracoronary imaging could play a crucial role for helping the operator to correctly implant a BVS into the coronary artery, as well as providing relevant information in the follow-up period. This review aims to summarize the role of intracoronary imaging in the follow-up of coronary stents, with a particular emphasis on the role of intravascular ultrasound and optical coherence tomography for procedural guidance during stent implantation and also for follow-up of bioabsorbable scaffolds.

Photodynamically Active Electrospun Fibers for Antibiotic-Free Infection Control

Antimicrobial biomaterials are critical to aid in the regeneration of oral soft tissue and prevent or treat localized bacterial infections. With the rising trend in antibiotic resistance, there is a pressing clinical need for new antimicrobial chemistries and biomaterial design approaches enabling on-demand activation of antibiotic-free antimicrobial functionality following an infection that are environment-friendly, flexible and commercially viable. This study explores the feasibility of integrating a bioresorbable electrospun polymer scaffold with localized antimicrobial photodynamic therapy (aPDT) capability. To enable aPDT, we encapsulated a photosensitizer (PS) in polyester fibers in the PS inert state, so that the antibacterial function would be activated on-demand via a visible light source. Fibrous scaffolds were successfully electrospun from FDA-approved polyesters, either poly(ε-caprolactone (PCL) or poly[(rac-lactide)-co-glycolide] (PLGA), with encapsulated PS (either methylene blue (MB) or erythrosin B (ER)). These were prepared and characterized with regards to their loading efficiency (UV-vis spectroscopy), microarchitecture (SEM, porometry, and BET (Brunauer-Emmett-Teller) analysis), tensile properties, hydrolytic behavior (contact angle, dye release capability, degradability), and aPDT effect. The electrospun fibers achieved an ∼100 wt % loading efficiency of PS, which significantly increased their tensile modulus and reduced their average fiber diameter and pore size with respect to PS-free controls. In vitro, PS release varied between a burst release profile to limited release within 100 h, depending on the selected scaffold formulation, while PLGA scaffolds displayed significant macroscopic shrinkage and fiber merging, following incubation in phosphate buffered saline solution. Exposure of PS-encapsulated PCL fibers to visible light successfully led to at least a 1 log reduction in Escherichia coli viability after 60 min of light exposure, whereas PS-free electrospun controls did not inactive microbes. This study successfully demonstrates the significant potential of PS-encapsulated electrospun fibers as photodynamically active biomaterial for antibiotic-free infection control.

The Future of Cardiovascular Stents: Bioresorbable and Integrated Biosensor Technology

Cardiovascular disease is the greatest cause of death worldwide. Atherosclerosis is the underlying pathology responsible for two thirds of these deaths. It is the age-dependent process of "furring of the arteries." In many scenarios the disease is caused by poor diet, high blood pressure, and genetic risk factors, and is exacerbated by obesity, diabetes, and sedentary lifestyle. Current pharmacological anti-atherosclerotic modalities still fail to control the disease and improvements in clinical interventions are urgently required. Blocked atherosclerotic arteries are routinely treated in hospitals with an expandable metal stent. However, stented vessels are often silently re-blocked by developing "in-stent restenosis," a wound response, in which the vessel's lumen renarrows by excess proliferation of vascular smooth muscle cells, termed hyperplasia. Herein, the current stent technology and the future of biosensing devices to overcome in-stent restenosis are reviewed. Second, with advances in nanofabrication, new sensing methods and how researchers are investigating ways to integrate biosensors within stents are highlighted. The future of implantable medical devices in the context of the emerging "Internet of Things" and how this will significantly influence future biosensor technology for future generations are also discussed.

Bioresorbable Electrode Array for Electrophysiological and Pressure Signal Recording in the Brain

Medical implantation of an electrocorticography (ECoG) recording system for brain monitoring is an effective clinical tool for seizure focus location and brain disease diagnosis. Planar and flexible ECoG electrodes can minimize the risks of infection and serious inflammatory response, and their good shape adaptability allows the device to fit complex cortex shape and structure to record brain signals with high spatial and temporal resolution. However, these ECoG electrodes require an additional surgery to remove the implant, which imposes potential medical risks. Here, a novel flexible and bioresorbable ECoG device integrated with an intracortical pressure sensor for monitoring swelling of the cortex during operation is reported. The ECoG device is fabricated with poly(l-lactide) and polycaprolactone composite and transient metal molybdenum. In vivo tests on rats show that the ECoG system can record the dynamic changes in brain signals for the different epilepsy stages with high resolution, while the malleable pressure sensor shows a linear relationship between the pressure and resistance in in vitro tests. In vitro degradation experiments show that the ECoG system can work stably for about five days before loss of efficacy, and the whole ECoG system degrades completely in a phosphate buffer solution in about 100 days.

Early natural history of neotissue formation in tissue-engineered vascular grafts in a murine model

Aim: To characterize early events in neotissue formation during the first 2 weeks after vascular scaffold implantation. Materials & methods: Biodegradable polymeric scaffolds were implanted as abdominal inferior vena cava interposition grafts in wild-type mice. Results: All scaffolds explanted at day 1 contained a platelet-rich mural thrombus. Within the first few days, the majority of cell infiltration appeared to be from myeloid cells at the peritoneal surface with modest infiltration along the lumen. Host reaction to the graft was distinct between the scaffold and mural thrombus; the scaffold stimulated an escalating foreign body reaction, whereas the thrombus was quickly remodeled into collagen-rich neotissue. Conclusion: Mural thrombi remodel into neotissue that persistently occludes the lumen of vascular grafts.

Zinc-Based Biomaterials for Regeneration and Therapy

Zinc has been described as the 'calcium of the twenty-first century'. Zinc-based degradable biomaterials have recently emerged thanks to their intrinsic physiological relevance, biocompatibility, biodegradability, and pro-regeneration properties. Zinc-based biomaterials mainly include: metallic zinc alloys, zinc ceramic nanomaterials, and zinc metal-organic frameworks (MOFs). Metallic zinc implants degrade at a desirable rate, matching the healing pace of local tissues, and stimulating remodeling and formation of new tissues. Zinc ceramic nanomaterials are also beneficial for tissue engineering and therapy thanks to their nanostructures and antibacterial properties. MOFs have large surface areas and are easily functionalized, making them ideal for drug delivery and cancer therapy. This review highlights recent developments in zinc-based biomaterials, discusses obstacles to overcome, and pinpoints directions for future research.

Fully Bioabsorbable Capacitor as an Energy Storage Unit for Implantable Medical Electronics

Implantable medical electronic devices are usually powered by batteries or capacitors, which have to be removed from the body after completing their function due to their non-biodegradable property. Here, a fully bioabsorbable capacitor (BC) is developed for life-time implantation. The BC has a symmetrical layer-by-layer structure, including polylactic acid (PLA) supporting substrate, PLA nanopillar arrays, self-assembled zinc oxide nanoporous layer, and polyvinyl alcohol/phosphate buffer solution (PVA/PBS) hydrogel. The as-fabricated BC can not only work normally in air but also in a liquid environment, including PBS and the animal body. Long-term normal work time is achieved to 30 days in PBS and 50 days in Sprague-Dawley (SD) rats. The work time of BC in the liquid environment is tunable from days to weeks by adopting different encapsulations along BC edges. Capacitance retention of 70% is achieved after 3000 cycles. Three BCs in series can light up 15 green light-emitting diodes (LEDs) in vivo. Additionally, after completing its mission, the BC can be fully degraded in vivo and reabsorbed by a SD rat. Considering its performance, the developed BC has a great potential as a fully bioabsorbable power source for transient electronics and implantable medical devices.

Bioabsorbable Capacitors: Fully Bioabsorbable Capacitor as an Energy Storage Unit for Implantable Medical Electronics (Adv. Sci. 6/2019)

Transient electronics provide an effective technology to develop bioabsorbable implantable medical devices (IMDs). In article number 1801625, Yubo Fan, Zhong Lin Wang, Zhou Li, and co‐workers design a new fully bioabsorbable capacitor as an energy storage unit for IMDs. This capacitor achieves good working performance and full biodegradability in animals.

Evaluation of Magnesium-based Medical Devices in Preclinical Studies: Challenges and Points to Consider

Absorbable metallic implants have been under investigation for more than a century. Animal and human studies have shown that magnesium (Mg) alloys can be safely used in bioresorbable scaffolds. Several cardiovascular and orthopedic biodegradable metallic devices have recently been approved for use in humans. Bioresorbable Mg implants present many advantages when compared to bioabsorbable polymer or nonabsorbable metallic implants, including similar strength and mechanical properties as existing implant-grade metals without the drawbacks of permanence or need for implant removal. Imaging visibility is also improved compared to polymeric devices. Additionally, with Mg-based cardiovascular stents, the risk of late stent thrombosis and need for long-term anti-platelet therapy may be reduced as the host tissue absorbs the Mg degradation products and the morphology of the vessel returns to a near-normal state. Absorbable Mg implants present challenges in the conduct of preclinical animal studies and interpretation of pathology data due to their particular degradation process associated with gas production and release of by-products. This article will review the different uses of Mg implants, the Mg alloys, the distinctive degradation features of Mg, and the challenges confronting pathologists at tissue collection, fixation, imaging, slide preparation, evaluation, and interpretation of Mg implants.

Silk Protein Bioresorbable, Drug-Eluting Ear Tubes: Proof-of-Concept

Otitis media with effusion (OEM) is a common pediatric pathology treated with topical fluoroquinolones (ear drops) and tympanoplasty tube, also referred to as ear tube, implantation for middle ear drainage. Commercially available ear tubes are fabricated using poly (lactic-co-glycolic acid) synthetic materials that are associated with long-complications due to premature extrusion. Resorbable materials have emerged as desirable alternatives to reduce extrusion-related complications, but often limited by fast resorption rates. Therefore, resorbable tubes with long-term functional integrity are required for future clinical translation. In this communication, a proof-of-concept study is reported on a bioresorbable and drug-eluting silk ear tube device. Preliminary in vitro assessments reveal time-dependent drug elution and antimicrobial properties, while maintaining long-term functional integrity in vivo. This report provides evidence of a silk ear tube with potential for future clinical translation and OEM treatment.

Bioresorbable Silicon Nanomembranes and Iron Catalyst Nanoparticles for Flexible, Transient Electrochemical Dopamine Monitors

A strategy of materials synthesis, characteristic evaluations, and manufacturing process for a mechanically elastic, biologically safe silicon-based dopamine detector that is designed to be completely transient, i.e., dissolved in water and/or biofluids, potentially in the brain after a desired period of operation, is introduced. Use of inexpensive, bioresorbable iron (Fe)-based nanoparticles (NPs) is one of the attractive choices for efficient catalytic oxidation of dopamine as an alternative for noble, nontransient platinum (Pt) nanoparticles, based on extensive studies of synthesized materials and catalytic reactions. Arrays of transient dopamine sensors validate electrochemical functionality to determine physiological levels of dopamine and to selectively sense dopamine in a variety of neurotransmitters, illuminating feasibilities for a higher level of soft, transient electronic implants integrated with other components of overall system.

3D-Printed PCL/PLA Composite Stents: Towards a New Solution to Cardiovascular Problems

Biodegradable stents (BRS) offer enormous potential but first they must meet five specific requirements: (i) their manufacturing process must be precise; (ii) degradation should have minimal toxicity; (iii) the rate of degradation should match the recovery rate of vascular tissue; (iv) ideally, they should induce rapid endothelialization to restore the functions of vascular tissue, but at the same time reduce the risk of restenosis; and (v) their mechanical behavior should comply with medical requirements, namely, the flexibility required to facilitate placement but also sufficient radial rigidity to support the vessel. Although the first three requirements have been comprehensively studied, the last two have been overlooked. One possible way of addressing these issues would be to fabricate composite stents using materials that have different mechanical, biological, or medical properties, for instance, Polylactide Acid (PLA) or Polycaprolactone (PCL). However, fashioning such stents using the traditional stent manufacturing process known as laser cutting would be impossible. Our work, therefore, aims to produce PCL/PLA composite stents using a novel 3D tubular printer based on Fused Deposition Modelling (FDM). The cell geometry (shape and area) and the materials (PCL and PLA) of the stents were analyzed and correlated with 3T3 cell proliferation, degradation rates, dynamic mechanical and radial expansion tests to determine the best parameters for a stent that will satisfy the five strict BRS requirements. Results proved that the 3D-printing process was highly suitable for producing composite stents (approximately 85⁻95% accuracy). Both PCL and PLA demonstrated their biocompatibility with PCL stents presenting an average cell proliferation of 12.46% and PLA 8.28% after only 3 days. Furthermore, the PCL/PLA composite stents demonstrated their potential in degradation, dynamic mechanical and expansion tests. Moreover, and regardless of the order of the layers, the composite stents showed (virtually) medium levels of degradation rates and mechanical modulus. Radially, they exhibited the virtues of PCL in the expansion step (elasticity) and those of PLA in the recoil step (rigidity). Results have clearly demonstrated that composite PCL/PLA stents are a highly promising solution to fulfilling the rigorous BRS requirements.

Stretchable, Implantable, Nanostructured Flow-Diverter System for Quantification of Intra-aneurysmal Hemodynamics

Random weakening of an intracranial blood vessel results in abnormal blood flow into an aneurysmal sac. Recent advancements show that an implantable flow diverter, integrated with a medical stent, enables a highly effective treatment of cerebral aneurysms by guiding blood flow into the normal vessel path. None of such treatment systems, however, offers post-treatment monitoring to assess the progress of sac occlusion. Therefore, physicians rely heavily on either angiography or magnetic resonance imaging. Both methods require a dedicated facility with sophisticated equipment settings and time-consuming, cumbersome procedures. In this paper, we introduce an implantable, stretchable, nanostructured flow-sensor system for quantification of intra-aneurysmal hemodynamics. The open-mesh membrane device is capable of effective implantation in complex neurovascular vessels with extreme stretchability (500% radial stretching) and bendability (180° with 0.75 mm radius of curvature) for monitoring of the treatment progress. A collection of quantitative mechanics, fluid dynamics, and experimental studies establish the fundamental aspects of design criteria for a highly compliant, implantable device. Hemocompatibility study using fresh ovine blood captures the device feasibility for long-term insertion in a blood vessel, showing less platelet deposition compared to that in existing implantable materials. In vitro demonstrations of three types of flow sensors show quantification of intra-aneurysmal blood flow in a pig aorta and the capability of observation of aneurysm treatment with a great sensitivity (detection limit as small as 0.032 m/s). Overall, this work describes a mechanically soft flow-diverter system that offers an effective treatment of aneurysms with an active monitoring of intra-aneurysmal hemodynamics.

6-Month Clinical and Angiographic Outcomes of a Novel Radiopaque Sirolimus-Eluting Bioresorbable Vascular Scaffold: The FANTOM II Study

OBJECTIVES

The purpose of this study was to evaluate the outcomes of the novel Fantom coronary bioresorbable scaffold at 6 months.

BACKGROUND

The Fantom sirolimus-eluting bioresorbable scaffold incorporates a unique proprietary iodinated, polycarbonate copolymer of tyrosine analogs that is radiopaque, with thin struts (125 μm) that facilitate device delivery and precise target lesion treatment.

METHODS

The 6-month outcomes and performance of the Fantom scaffold were evaluated in 117 patients with single de novo native coronary artery lesions of length ≤20 mm and reference vessel diameter 2.5 to 3.5 mm. The primary angiographic endpoint was mean late lumen loss at 6 months measured by quantitative coronary angiography. Procedural outcomes were categorized as short-term technical success, short-term procedural success, and clinical procedural success. The primary clinical endpoint was major adverse cardiac events at 6 months, the composite of cardiac death, myocardial infarction (MI), or clinically driven target lesion revascularization (TLR).

RESULTS

Short-term technical success, short-term procedural success, and clinical procedural success were achieved in 96.6%, 99.1%, and 99.1% of patients, respectively. Mean 6-month in-stent late lumen loss was 0.25 ± 0.40 mm (n = 100). Binary restenosis was present in 2 patients (2.0%). Major adverse cardiac events within 6 months occurred in 3 patients (2.6%), including no deaths, 2 MIs, and 2 TLRs (1 patient had both an MI and TLR). Scaffold thrombosis occurred in 1 patient (0.9%).

CONCLUSIONS

The clinical results from 117 patients enrolled in cohort A of the multicenter FANTOM II (Safety & Performance Study of the FANTOM Sirolimus-Eluting Bioresorbable Coronary Scaffold) study demonstrate favorable 6-month outcomes of this novel device in the treatment of noncomplex coronary artery disease.

Development of a Polymer-Based Biodegradable Neurovascular Stent Prototype: A Preliminary In Vitro and In Vivo Study

Biodegradable stents are not established in neurovascular interventions. In this study, mechanical, radiological, and histological characteristics of a stent prototype developed for neurovascular use are presented. The elasticity and brittleness of PLA 96/4, PLDL 70/30, PCL, and PLGA 85/15 and 10/90 polymers in in vitro experiments are first analyzed. After excluding the inapt polymers, degradability and mechanical characteristics of 78 PLGA 85/15 and PLGA 10/90 stent prototypes are analyzed. After excluding PLGA 10/90 stents because of rapid loss of mass PLGA 85/15 stents in porcine in vivo experiments are analyzed. Angiographic occlusion rates 7 d, 1 month, 3 months, and 6 months after stent implantation are assessed. Histological outcome measures are the presence of signs of inflammation, endothelialization, and the homogeneity of degradation after six months. One case of stent occlusion occurs within the first 7 d. There is a prominent foreign-body reaction with considerable mononuclear and minor granulocytic inflammation combined with incomplete fragmental degradation of the struts. It is possible to produce a stent prototype with dimensions that fit the typical size of carotid arteries. Major improvements concerning thrombogenicity, degradation, and inflammatory response are required to produce biodegradable stents that are suitable for neurovascular interventions.

Advances in Degradable Embolic Microspheres: A State of the Art Review

Considerable efforts have been placed on the development of degradable microspheres for use in transarterial embolization indications. Using the guidance of the U.S. Food and Drug Administration (FDA) special controls document for the preclinical evaluation of vascular embolization devices, this review consolidates all relevant data pertaining to novel degradable microsphere technologies for bland embolization into a single reference. This review emphasizes intended use, chemical composition, degradative mechanisms, and pre-clinical safety, efficacy, and performance, while summarizing the key advantages and disadvantages for each degradable technology that is currently under development for transarterial embolization. This review is intended to provide an inclusive reference for clinicians that may facilitate an understanding of clinical and technical concepts related to this field of interventional radiology. For materials scientists, this review highlights innovative devices and current evaluation methodologies (i.e., preclinical models), and is designed to be instructive in the development of innovative/new technologies and evaluation methodologies.

Low-Cost Manufacturing of Bioresorbable Conductors by Evaporation-Condensation-Mediated Laser Printing and Sintering of Zn Nanoparticles

Currently, bioresorbable electronic devices are predominantly fabricated by complex and expensive vacuum-based integrated circuit (IC) processes. Here, a low-cost manufacturing approach for bioresorbable conductors on bioresorbable polymer substrates by evaporation-condensation-mediated laser printing and sintering of Zn nanoparticle is reported. Laser sintering of Zn nanoparticles has been technically difficult due to the surface oxide on nanoparticles. To circumvent the surface oxide, a novel approach is discovered to print and sinter Zn nanoparticle facilitated by evaporation-condensation in confined domains. The printing process can be performed on low-temperature substrates in ambient environment allowing easy integration on a roll-to-roll platform for economical manufacturing of bioresorbable electronics. The fabricated Zn conductors show excellent electrical conductivity (≈1.124 × 10⁶ S m^-1 ), mechanical durability, and water dissolvability. Successful demonstration of strain gauges confirms the potential application in various environmentally friendly sensors and circuits.

Tailoring the physicochemical and shape memory properties of the biodegradable polymer poly(glycerol dodecanoate) via curing conditions

A major challenge in the repair and regeneration of soft tissue damage occurring as a result of aging, injury, or disease is recapitulating the biomechanical properties of the native tissue. Ideally, a candidate biomaterial for soft tissue engineering applications should be biocompatible, nonlinearly elastic to match soft tissue mechanical behavior, biodegradable to enable tissue remodeling, and tailorable to achieve a range of nonlinear elastic mechanical properties to match specific soft tissues. In addition, for cardiac and other applications, the biomaterial should have shape memory characteristics to facilitate minimally invasive and/or catheter-based delivery. Poly(glycerol dodecanoate) (PGD) is a shape memory material that has nonlinear elastic properties at body temperature and elastic-plastic behavior at room temperature. In this study, we investigated the effects of curing conditions on the nonlinear elastic, shape memory, and biocompatibility properties of PGD. Increased curing and crosslinking resulted in an increase in both the initial stiffness and the nonlinear strain stiffening behavior of PGD. After shape fixation at 60% strain, 100% shape recovery was achieved within 1 min at body temperature for all conditions tested. Polymer curing had no adverse effects on the cellular biocompatibility or non-hemolytic characteristics of PGD, indicating the potential suitability of these formulations for blood-contacting device applications. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1618-1623, 2017.

Pilot Mouse Study of 1 mm Inner Diameter (ID) Vascular Graft Using Electrospun Poly(ester urea) Nanofibers

An off-the-shelf, small diameter tissue engineered vascular graft (TEVG) would be transformative to surgeons in multiple subspecialties. Herein, the results of a small diameter (ID ≈ 1 mm) vascular graft constructed from resorbable, amino acid-based poly(ester urea) (PEU) are reported. Electrospun PEU grafts of two different wall thicknesses (type A: 250 μm; type B: 350 μm) are implanted as abdominal infra-renal aortic grafts in a severe combined immune deficient/beige mouse model and evaluated for vessel remodeling over one year. Significantly, the small diameter TEVG does not rupture or lead to acute thrombogenic events during the intervals tested. The pilot TEVG in vivo shows long-term patency and extensive tissue remodeling with type A grafts. Extensive tissue remodeling in type A grafts leads to the development of well-circumscribed neovessels with an endothelial inner lining, a neointima containing smooth muscle cells. However, due to slow degradation of the PEU scaffold materials in vivo, the grafts remain after one year. The type B grafts, which have 350 μm thick walls, experience occlusion over the one year interval due to intimal hyperplasia. This study affords significant findings that will guide the design of future generations of small diameter vascular grafts.

Efficacy of Osteoconductive Ceramics in Bioresorbable Screws for Anterior Cruciate Ligament Reconstruction: A Prospective Intrapatient Comparative Study

Background:

Osteoconductive additives are used in resorbable interference screws for anterior cruciate ligament (ACL) reconstruction to improve graft incorporation and mitigate adverse effects. There are no published studies that compare biological performances of bioresorbable and biocomposite screws without artifacts due to different follow-up times and intrinsic patient characteristics.

Purpose/Hypothesis:

The purpose of this study was to evaluate the efficacy of osteoconductive agents in bioresorbable screws for ACL reconstruction at minimum follow-up of 2 years by intrapatient comparison. The hypothesis was that osteoconductive ceramics would result in slower resorption, improved ossification, and less tunnel widening.

Study Design:

Cohort study; Level of evidence, 2.

Methods:

A total of 28 ACL reconstructions at 2 centers were randomly assigned into 2 comparable groups: (1) the graft was fixed in the tibia using standard bioresorbable screws and in the femur using biocomposite screws with osteoconductive agents (biphasic calcium phosphate), and (2) the graft was fixed in the femur using a standard bioresorbable screw and in the tibia using a biocomposite screw with osteoconductive agents.

Results:

Twenty-seven patients completed evaluations at 29.9 ± 4.0 months. Resorption was complete for more bioresorbable (81%) than biocomposite (37%) screws (P = .0029), whereas satisfactory ossification was observed in more biocomposite (52%) than bioresorbable (15%) screws (P = .0216). The tunnel shape was normal in more biocomposite (81%) than bioresorbable (48%) screws (P = .0126), and marked cortical formation was twice more frequent for biocomposite (78%) than bioresorbable (37%) screws (P = .0012). Bioresorbable screws exhibited faster resorption in the femur (P = .0202) but not in the tibia (not significant). Conversely, biocomposite screws demonstrated better ossification, less tunnel widening, and more cortical formation in the tibia (P < .0001, P = .0227, and P < .0001, respectively) but not in the femur (not significant for all).

Conclusion:

Osteoconductive additives can reduce the extent of resorption while improving ossification, reducing tunnel widening, and increasing cortical formation.

Clinical Relevance:

The benefits of osteoconductive agents justify their associated costs for ACL reconstruction, particularly in the tibia.

Feasibility study of sustained-release travoprost punctum plug for intraocular pressure reduction in an Asian population

Purpose

To investigate the efficacy and safety of a punctum plug-based sustained drug release system for a prostaglandin analog, travoprost (OTX-TP), for intraocular pressure (IOP) reduction in an Asian population.

Methods

This is an initial feasibility, prospective, single-arm study involving 26 eyes and a bioresorbable punctum plug containing OTX-TP. An OTX-TP was placed in the vertical portion of the superior or inferior canaliculus of patients with primary open-angle glaucoma or ocular hypertension. The main outcome measure was the IOP-lowering efficacy of OTX-TP at 3 (8 am) and 10, 20, and 30 days (8 am, 10 am, and 4 pm), compared to baseline.

Results

A total of 26 OTX-TP were inserted for 17 subjects. The mean (standard deviation) age was 57.2 (13.8) years. At 10 days, all plugs were still present, and the IOP reduction from baseline was 6.2 (23%), 5.4 (21%), and 7.5 mmHg (28%) at 8 am, 10 am, and 4 pm, respectively. At 10 days, the mean IOP (standard error of mean) was 21.2 (1.2), 20.4 (0.8), and 19.7 (1.0) at 8 am, 10 am, and 4 pm, respectively, showing no discernible IOP trend during the course of the day. At 30 days, plug retention had declined to 42%, and the overall IOP reduction had decreased to 16%.

Conclusion

The sustained-release OTX-TP is able to reduce IOP by 24% (day 10) and 15.6% (day 30), respectively. It is a potentially well-tolerable ocular hypotensive for glaucoma patients with a history of poor compliance.

Non-viral approaches for direct conversion into mesenchymal cell types: Potential application in tissue engineering

Acquiring adequate number of cells is one of the crucial factors to apply tissue engineering strategies in order to recover critical-sized defects. While the reprogramming technology used for inducing pluripotent stem cells (iPSCs) opened up a direct path for generating pluripotent stem cells, a direct conversion strategy may provide another possibility to obtain desired cells for tissue engineering. In order to convert a somatic cell into any other cell type, diverse approaches have been investigated. Conspicuously, in contrast to traditional viral transduction method, non-viral delivery of conversion factors has the merit of lowering immune responses and provides safer genetic manipulation, thus revolutionizing the generation of directly converted cells and its application in therapeutics. In addition, applying various microenvironmental modulations have potential to ameliorate the conversion of somatic cells into different lineages. In this review, we discuss the recent progress in direct conversion technologies, specifically focusing on generating mesenchymal cell types.

Degradation and Characterization of Resorbable Phosphate-Based Glass Thin-Film Coatings Applied by Radio-Frequency Magnetron Sputtering

Quinternary phosphate-based glasses of up to 2.67 μm, deposited by radio-frequency magnetron sputtering, were degraded in distilled water and phosphate-buffered saline (PBS) to investigate their degradation characteristics. Magnetron-sputtered coatings have been structurally compared to their compositionally equivalent melt-quenched bulk glass counterparts. The coatings were found to have structurally variable surfaces to melt-quenched glass such that the respective bridging oxygen to nonbridging oxygen bonds were 34.2% to 65.8% versus 20.5% to 79.5%, forming metaphosphate (PO3)(-) (Q(2)) versus less soluble (P2O7)(4-) (Q(1)) and (PO4)(3-) (Q(0)), respectively. This factor led to highly soluble coatings, exhibiting a t(1/2) degradation dependence in the first 2 h in distilled water, followed by a more characteristic linear profile because the subsequent layers were less soluble. Degradation was observed to preferentially occur, forming voids characteristic of pitting corrosion, which was confirmed by the use of a focused ion beam. Coating degradation in PBS precipitated a (PO3)(-) metaphosphate, an X-ray amorphous layer, which remained adherent to the substrate and seemingly formed a protective diffusion barrier, which inhibited further coating degradation. The implications are that while compositionally similar, sputter-deposited coatings and melt-quenched glasses are structurally dissimilar, most notably, with regard to the surface layer. This factor has been attributed to surface etching of the as-deposited coating layer during deposition and variation in the thermal history between the processes of magnetron sputtering and melt quenching.

Tunable release of ophthalmic therapeutics from injectable, resorbable, thermoresponsive copolymer scaffolds

The sustained release of ophthalmic therapeutics to the posterior segment of the eye is a challenge. Injectable polymer materials have the potential to reduce injection frequency by providing long term therapeutic delivery. Copolymers with varying N-isopropylacrylamide, acrylamide (AAm), acrylic acid N-hydroxysuccinimide, and (r)-α-acryloyloxy-β,β-dimethyl-γ-butyrolactone (DBA) were synthesized by RAFT polymerization to develop injectable, resorbable, and thermoresponsive copolymer scaffolds. Upon injection into physiological conditions, these copolymers undergo a temperature induced gelation to form a drug releasing scaffold. Modification of the copolymer's AAm/DBA ratio and molecular weight afforded significant and precise control over the scaffold's physical properties and subsequent drug release profile. Hydrolytic DBA ring-opening enables redissolution of the copolymers for clearance from the body. Precise control over the drug release profile from these copolymer scaffolds by simple alteration of composition and molecular weight provides an efficient method to customize the minimally invasive delivery of therapeutics to the posterior segment of the eye. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 53-62, 2017.

Bioresorbable Electronic Stent Integrated with Therapeutic Nanoparticles for Endovascular Diseases

Implantable endovascular devices such as bare metal, drug eluting, and bioresorbable stents have transformed interventional care by providing continuous structural and mechanical support to many peripheral, neural, and coronary arteries affected by blockage. Although effective in achieving immediate restoration of blood flow, the long-term re-endothelialization and inflammation induced by mechanical stents are difficult to diagnose or treat. Here we present nanomaterial designs and integration strategies for the bioresorbable electronic stent with drug-infused functionalized nanoparticles to enable flow sensing, temperature monitoring, data storage, wireless power/data transmission, inflammation suppression, localized drug delivery, and hyperthermia therapy. In vivo and ex vivo animal experiments as well as in vitro cell studies demonstrate the previously unrecognized potential for bioresorbable electronic implants coupled with bioinert therapeutic nanoparticles in the endovascular system.