Mechanical properties and degradation of drug eluted bioresorbable vascular scaffolds prepared by three-dimensional printing technology

Long-term outcomes following bioresorbable vascular scaffolds

INTRODUCTION

The higher scaffold thrombosis rates observed with the first-generation bioresorbable scaffolds (BRSs) compared to conventional drug-eluting stents were likely due in part to bioresorbable polymers having insufficient radial strength, necessitating larger strut profiles. Meta-analysis of the long-term outcomes from the first-generation Absorb bioresorbable vascular scaffold (BVS) showed that this period of excess risk ended at 3 years. Therefore, current attention has been focused on improving early outcomes by increasing the scaffold's tensile strength and reducing strut thickness.

AREAS COVERED

This review summaries the lessons learned from the first-generation BRS. It updates the long-term clinical outcomes of trials evaluating the ABSORB BVS and metallic alloy-based BRS. In addition, it reviews the next-generation BRSs manufactured in Asia.

EXPERT OPINION

Critical areas to improve the performance and safety of biodegradable scaffolds include further development in material science, surface modification, delivery systems, and long-term follow-up studies.

Investigation of 3D Printed Bioresorbable Vascular Scaffold Crimping Behavior

The rise in additive manufacturing (AM) offers myriad opportunities for 3D-printed polymeric vascular scaffolds, such as customization and on-the-spot manufacturing, in vivo biodegradation, incorporation of drugs to prevent restenosis, and visibility under X-ray. To maximize these benefits, informed scaffold design is critical. Polymeric bioresorbable vascular scaffolds (BVS) must undergo significant deformation prior to implantation in a diameter-reduction process known as crimping which enables minimally invasive surgery. Understanding the behavior of vascular scaffolds in this step provides twofold benefits: first, it ensures the BVS is able to accommodate stresses occurring during this process to prevent failure, and further, it provides information on the radial strength of the BVS, a key metric to understanding its post-implant performance in the artery. To capitalize on the fast manufacturing speed AM provides, a low time cost solution for understanding scaffold performance during this step is necessary. Through simulation of the BVS crimping process in ABAQUS using experimentally obtained bulk material properties, we have developed a qualitative analysis tool which is capable of accurately comparing relative performance trends of varying BVS designs during crimping in a fraction of the time of experimental testing, thereby assisting in the integration of informed design into the additive manufacturing process.

Clinical situations for which 3D Printing is considered an appropriate representation or extension of data contained in a medical imaging examination: vascular conditions

BACKGROUND

Medical three-dimensional (3D) printing has demonstrated utility and value in anatomic models for vascular conditions. A writing group composed of the Radiological Society of North America (RSNA) Special Interest Group on 3D Printing (3DPSIG) provides appropriateness recommendations for vascular 3D printing indications.

METHODS

A structured literature search was conducted to identify all relevant articles using 3D printing technology associated with vascular indications. Each study was vetted by the authors and strength of evidence was assessed according to published appropriateness ratings.

RESULTS

Evidence-based recommendations for when 3D printing is appropriate are provided for the following areas: aneurysm, dissection, extremity vascular disease, other arterial diseases, acute venous thromboembolic disease, venous disorders, lymphedema, congenital vascular malformations, vascular trauma, vascular tumors, visceral vasculature for surgical planning, dialysis access, vascular research/development and modeling, and other vasculopathy. Recommendations are provided in accordance with strength of evidence of publications corresponding to each vascular condition combined with expert opinion from members of the 3DPSIG.

CONCLUSION

This consensus appropriateness ratings document, created by the members of the 3DPSIG, provides an updated reference for clinical standards of 3D printing for the care of patients with vascular conditions.

Investigation of 3D Printed Bioresorbable Vascular Scaffold Crimping Behavior

The rise in additive manufacturing (AM) offers myriad opportunities for 3D-printed polymeric vascular scaffolds, such as customization and on-the-spot manufacturing, in vivo biodegradation, incorporation of drugs to prevent restenosis, and visibility under X-ray. To maximize these benefits, informed scaffold design is critical. Polymeric bioresorbable vascular scaffolds (BVS) must undergo significant deformation prior to implantation in a diameter-reduction process known as crimping which enables minimally invasive surgery. Understanding the behavior of vascular scaffolds in this step provides twofold benefits: first, it ensures the BVS is able to accommodate stresses occurring during this process to prevent failure, and further, it provides information on the radial strength of the BVS, a key metric to understanding its post-implant performance in the artery. To capitalize on the fast manufacturing speed AM provides, a low time cost solution for understanding scaffold performance during this step is necessary. Through simulation of the BVS crimping process in ABAQUS using experimentally obtained bulk material properties, we have developed a qualitative analysis tool which is capable of accurately comparing relative performance trends of varying BVS designs during crimping in a fraction of the time of experimental testing, thereby assisting in the integration of informed design into the additive manufacturing process.

Advances in the One-Step Approach of Polymeric Materials Using Enzymatic Techniques

The formulation in which biochemical enzymes are administered in polymer science plays a key role in retaining their catalytic activity. The one-step synthesis of polymers with highly sequence-controlled enzymes is a strategy employed to provide enzymes with higher catalytic activity and thermostability in material sustainability. Enzyme-catalyzed chain growth polymerization reactions using activated monomers, protein-polymer complexation techniques, covalent and non-covalent interaction, and electrostatic interactions can provide means to develop formulations that maintain the stability of the enzyme during complex material processes. Multifarious applications of catalytic enzymes are usually attributed to their efficiency, pH, and temperature, thus, progressing with a critical structure-controlled synthesis of polymer materials. Due to the obvious economics of manufacturing and environmental sustainability, the green synthesis of enzyme-catalyzed materials has attracted significant interest. Several enzymes from microorganisms and plants via enzyme-mediated material synthesis have provided a viable alternative for the appropriate synthesis of polymers, effectively utilizing the one-step approach. This review analyzes more and deeper strategies and material technologies widely used in multi-enzyme cascade platforms for engineering polymer materials, as well as their potential industrial applications, to provide an update on current trends and gaps in the one-step synthesis of materials using catalytic enzymes.

Bioresorbable Nonwoven Patches as Taxane Delivery Systems for Prostate Cancer Treatment

Prostate cancer is the second most common cancer in males. In the case of locally advanced prostate cancer radical prostatectomy is one of the first-line therapy. However, recurrence after resection of the tumor can appear. Drug-eluting bioresorbable implants acting locally in the area of the tumor or the resection margins, that reduce the risk of recurrence would be advantageous. Electrospinning offers many benefits in terms of local delivery so fiber-forming polyesters and polyestercarbonates which are suitable to be drug-loaded were used in the study to obtain CTX or DTX-loaded electrospun patches for local delivery. After a fast verification step, patches based on the blend of poly(glycolide-ε-caprolactone) and poly(lactide-glycolide) as well as patches obtained with poly(lactide-glycolide- ε-caprolactone) were chosen for long-term study. After three months, 60% of the drug was released from (PGCL/PLGA) + CTX and it was selected for final, anticancer activity analysis with the use of PC-3 and DU145 cells to establish its therapeutic potential. CTX-loaded patches reduced cell growth to 53% and 31% respectively, as compared to drug-free patches. Extracts from drug-free patches showed excellent biocompatibility with the PC-3 cell line. Cabazitaxel-loaded bioresorbable patches are a promising drug delivery system for prostate cancer therapy.

Moisture adsorption by decellularized bovine pericardium collagen matrices studied by terahertz pulsed spectroscopy and solid immersion microscopy

In this paper, terahertz (THz) pulsed spectroscopy and solid immersion microscopy were applied to study interactions between water vapor and tissue scaffolds-the decellularized bovine pericardium (DBP) collagen matrices, in intact form, cross-linked with the glutaraldehyde or treated by plasma. The water-absorbing properties of biomaterials are prognostic for future cell-mediated reactions of the recipient tissue with the scaffold. Complex dielectric permittivity of DBPs was measured in the 0.4-2.0 THz frequency range, while the samples were first dehydrated and then exposed to water vapor atmosphere with 80.0 ± 5.0% relative humidity. These THz dielectric measurements of DBPs and the results of their weighting allowed to estimate the adsorption time constants, an increase of tissue mass, as well as dispersion of these parameters. During the adsorption process, changes in the DBPs' dielectric permittivity feature an exponential character, with the typical time constant of =8-10 min, the transient process saturation at =30 min, and the tissue mass improvement by =1-3%. No statistically-relevant differences between the measured properties of the intact and treated DBPs were observed. Then, contact angles of wettability were measured for the considered DBPs using a recumbent drop method, while the observed results showed that treatments of DBP somewhat affects their surface energies, polarity, and hydrophilicity. Thus, our studies revealed that glutaraldehyde and plasma treatment overall impact the DBP-water interactions, but the resultant effects appear to be quite complex and comparable to the natural variability of the tissue properties. Such a variability was attributed to the natural heterogeneity of tissues, which was confirmed by the THz microscopy data. Our findings are important for further optimization of the scaffolds' preparation and treatment technologies. They pave the way for THz technology use as a non-invasive diagnosis tool in tissue engineering and regenerative medicine.

Review on Computer-Aided Design and Manufacturing of Drug Delivery Scaffolds for Cell Guidance and Tissue Regeneration

In the last decade, additive manufacturing (AM) processes have updated the fields of biomaterials science and drug delivery as they promise to realize bioengineered multifunctional devices and implantable tissue engineering (TE) scaffolds virtually designed by using computer-aided design (CAD) models. However, the current technological gap between virtual scaffold design and practical AM processes makes it still challenging to realize scaffolds capable of encoding all structural and cell regulatory functions of the native extracellular matrix (ECM) of health and diseased tissues. Indeed, engineering porous scaffolds capable of sequestering and presenting even a complex array of biochemical and biophysical signals in a time- and space-regulated manner, require advanced automated platforms suitable of processing simultaneously biomaterials, cells, and biomolecules at nanometric-size scale. The aim of this work was to review the recent scientific literature about AM fabrication of drug delivery scaffolds for TE. This review focused on bioactive molecule loading into three-dimensional (3D) porous scaffolds, and their release effects on cell fate and tissue growth. We reviewed CAD-based strategies, such as bioprinting, to achieve passive and stimuli-responsive drug delivery scaffolds for TE and cancer precision medicine. Finally, we describe the authors' perspective regarding the next generation of CAD techniques and the advantages of AM, microfluidic, and soft lithography integration for enhancing 3D porous scaffold bioactivation toward functional bioengineered tissues and organs.

Current perspectives on bioresorbable scaffolds in coronary intervention and other fields

Introduction: The first-generation bioresorbable scaffolds (BRSs) had a large strut profile to compensate for the insufficient radial strength of bioresorbable polymer materials, resulting in higher scaffold thrombosis rates than conventional drug-eluting stents. To improve the clinical safety and efficacy, the new generation BRSs have been improved by optimal structure design, post-processing of bioresorbable polymer materials, or altering bioresorbable metallic alloys.Areas covered: This review summarizes the lessons learned from the first-generation BRS, updates the clinical outcomes of trials evaluating ABSORB bioresorbable vascular scaffold at long-term and bioresorbable metallic alloy-based devices, and examines recent outcomes of BRS treated in STEMI patients. This review also provides an overview of the current clinical data of seven BRSs manufactured in Asia, and of the BRSs extended application in other clinical arenas.Expert opinion: Drawbacks of the first-generation BRSs need to be addressed by the next generation of these stents with novel materials and technologies. Clinical research, including randomized controlled trials, are required to further evaluate BRSs application in coronary artery disease. The encouraging results of BRSs innovation applied in the peripheral arteries and gastrointestinal tracts support other potential clinical applications of BRS technology.

Dual-encapsulated biodegradable 3D scaffold from liposome and waterborne polyurethane for local drug control release in breast cancer therapy

Compared with the traditional chemotherapy by injection, local release of drugs in the lesion area is a more efficient and less harmful treatment for solid tumors. However, the selection of appropriate drug carrier and controlled release of chemotherapy drugs are still great challenges. Herein, a kind of dual-encapsulated three-dimensional (3D) scaffold is designed for local drug release via blending the paclitaxel (PTX) loaded phospholipid liposomes with waterborne polyurethane (PU) by freeze-drying. The controlled release of paclitaxel is carried out through two simultaneous procedures. First, liposomes encapsulated in polyurethane scaffold can slowly release by water absorption and degradation of polyurethane. Then paclitaxel encapsulated in liposomes can also be released into water. Compared with the polyurethane scaffold which directly encapsulated paclitaxel, dual-encapsulated scaffold has slower initial release amount and maintain higher concentration of paclitaxel in later stage. Moreover, the protection of the phospholipid layer can prevent paclitaxel from being quickly decomposed and cleared, which could greatly improve the bioavailability and therapeutic effect of paclitaxel. Cell experiment results can be seen that dual-encapsulated scaffold not only has higher inhibition rate to the breast cancer MCF7 cells, but also has less damage to normal tissue cells. It provides a more effective platform for the local drug therapy in the treatment of tumors.[Formula: see text].