Enhanced visualization of biodegradable polymeric vascular scaffolds by incorporation of gold, silver and magnetite nanoparticles

Nanotechnology in tissue engineering: expanding possibilities with nanoparticles

Tissue engineering is a multidisciplinary field that merges engineering, material science, and medical biology in order to develop biological alternatives for repairing, replacing, maintaining, or boosting the functionality of tissues and organs. The ultimate goal of tissue engineering is to create biological alternatives for repairing, replacing, maintaining, or enhancing the functionality of tissues and organs. However, the current landscape of tissue engineering techniques presents several challenges, including a lack of suitable biomaterials, inadequate cell proliferation, limited methodologies for replicating desired physiological structures, and the unstable and insufficient production of growth factors, which are essential for facilitating cell communication and the appropriate cellular responses. Despite these challenges, there has been significant progress made in tissue engineering techniques in recent years. Nanoparticles hold a major role within the realm of nanotechnology due to their unique qualities that change with size. These particles, which provide potential solutions to the issues that are met in tissue engineering, have helped propel nanotechnology to its current state of prominence. Despite substantial breakthroughs in the utilization of nanoparticles over the past two decades, the full range of their potential in addressing the difficulties within tissue engineering remains largely untapped. This is due to the fact that these advancements have occurred in relatively isolated pockets. In the realm of tissue engineering, the purpose of this research is to conduct an in-depth investigation of the several ways in which various types of nanoparticles might be put to use. In addition to this, it sheds light on the challenges that need to be conquered in order to unlock the maximum potential of nanotechnology in this area.

Development of 3D Printed Biodegradable, Entirely X-ray Visible Stents for Rabbit Carotid Artery Implantation

Biodegradable stents are considered a promising strategy for the endovascular treatment of cerebrovascular diseases. The visualization of biodegradable stents is of significance during the implantation and long-term follow-up. Endowing biodegradable stents with X-ray radiopacity can overcome the weakness of intrinsic radioparency of polymers. Hence, this work focuses on the development of an entirely X-ray visible biodegradable stent (PCL-KIO3) composed of polycaprolactone (PCL) and potassium iodate via physical blending and 3D printing. The in vitro results show that the introduction of potassium iodate makes the 3D-printed PCL stents visualizable under X-ray. So far, there is inadequate study about polymeric stent visualization in vivo. Therefore, PCL-KIO3 stents are implanted into the rabbit carotid artery to evaluate the biosafety and visibility performance. During stent deployment, the visualization of the PCL-KIO3 stent effectively helps to understand the position and dilation status of stents. At 6-month follow-up, the PCL-KIO3 stent could still be observed under X-ray and maintains excellent vessel patency. To sum up, this study demonstrates that PCL-KIO3 stent may provide a robust strategy for biodegradable stent visualization.

A Facile Composite Strategy to Prepare a Biodegradable Polymer Based Radiopaque Raw Material for "Visualizable" Biomedical Implants

Enabling a biodegradable polymer radiopaque under X-ray is much desired for many medical devices. Physical blending of a present biodegradable polymer and a commercialized medical contrast agent is convenient yet lacks comprehensive fundamental research. Herein, we prepared a biodegradable polymer-based radiopaque raw material by blending poly(l-lactic acid) (PLLA or simply PLA) and iohexol (IHX), where PLA constituted the continuous phase and IHX particles served as the dispersed phase. The strong X-ray adsorption of IHX enabled the composite radiopaque; the hydrolysis of the polyester and the water solubility of the contrast agent enabled the composite biodegradable in an aqueous medium. The idea was confirmed by in vitro characterizations of the resultant composite, in vivo subcutaneous implantation in rats up to 6 months, and the clear visualization of a part of a biodegradable occluder in a Bama piglet under X-ray. We also found that the crystallization of PLA was significantly enhanced in the presence of the solid particles, which should be taken into consideration in the design of an appropriate biomaterial composite because crystallization degree influences the biodegradation rate and mechanical property of a material to a large extent. We further tried to introduce a small amount of poly(vinylpyrrolidone) into the blend of PLA and IHX. Compared to the bicomponent composite, the tricomponent one exhibited decreased modulus and increased elongation at break and tensile strength. This paves more ways for researchers to select appropriate raw materials according to the regenerated tissue and the application site.

Conventional and Recent Trends of Scaffolds Fabrication: A Superior Mode for Tissue Engineering

Tissue regeneration is an auto-healing mechanism, initiating immediately following tissue damage to restore normal tissue structure and function. This falls in line with survival instinct being the most dominant instinct for any living organism. Nevertheless, the process is slow and not feasible in all tissues, which led to the emergence of tissue engineering (TE). TE aims at replacing damaged tissues with new ones. To do so, either new tissue is being cultured in vitro and then implanted, or stimulants are implanted into the target site to enhance endogenous tissue formation. Whichever approach is used, a matrix is used to support tissue growth, known as ‘scaffold’. In this review, an overall look at scaffolds fabrication is discussed, starting with design considerations and different biomaterials used. Following, highlights of conventional and advanced fabrication techniques are attentively presented. The future of scaffolds in TE is ever promising, with the likes of nanotechnology being investigated for scaffold integration. The constant evolvement of organoids and biofluidics with the eventual inclusion of organ-on-a-chip in TE has shown a promising prospect of what the technology might lead to. Perhaps the closest technology to market is 4D scaffolds following the successful implementation of 4D printing in other fields.

Conventional and Recent Trends of Scaffolds Fabrication: A Superior Mode for Tissue Engineering

Tissue regeneration is an auto-healing mechanism, initiating immediately following tissue damage to restore normal tissue structure and function. This falls in line with survival instinct being the most dominant instinct for any living organism. Nevertheless, the process is slow and not feasible in all tissues, which led to the emergence of tissue engineering (TE). TE aims at replacing damaged tissues with new ones. To do so, either new tissue is being cultured in vitro and then implanted, or stimulants are implanted into the target site to enhance endogenous tissue formation. Whichever approach is used, a matrix is used to support tissue growth, known as 'scaffold'. In this review, an overall look at scaffolds fabrication is discussed, starting with design considerations and different biomaterials used. Following, highlights of conventional and advanced fabrication techniques are attentively presented. The future of scaffolds in TE is ever promising, with the likes of nanotechnology being investigated for scaffold integration. The constant evolvement of organoids and biofluidics with the eventual inclusion of organ-on-a-chip in TE has shown a promising prospect of what the technology might lead to. Perhaps the closest technology to market is 4D scaffolds following the successful implementation of 4D printing in other fields.

Iron Oxide Nanoparticles in Regenerative Medicine and Tissue Engineering

In recent years, many promising nanotechnological approaches to biomedical research have been developed in order to increase implementation of regenerative medicine and tissue engineering in clinical practice. In the meantime, the use of nanomaterials for the regeneration of diseased or injured tissues is considered advantageous in most areas of medicine. In particular, for the treatment of cardiovascular, osteochondral and neurological defects, but also for the recovery of functions of other organs such as kidney, liver, pancreas, bladder, urethra and for wound healing, nanomaterials are increasingly being developed that serve as scaffolds, mimic the extracellular matrix and promote adhesion or differentiation of cells. This review focuses on the latest developments in regenerative medicine, in which iron oxide nanoparticles (IONPs) play a crucial role for tissue engineering and cell therapy. IONPs are not only enabling the use of non-invasive observation methods to monitor the therapy, but can also accelerate and enhance regeneration, either thanks to their inherent magnetic properties or by functionalization with bioactive or therapeutic compounds, such as drugs, enzymes and growth factors. In addition, the presence of magnetic fields can direct IONP-labeled cells specifically to the site of action or induce cell differentiation into a specific cell type through mechanotransduction.

From in vitro evaluation to human postmortem pre-validation of a radiopaque and resorbable internal biliary stent for liver transplantation applications

The implantation of an internal biliary stent (IBS) during liver transplantation has recently been shown to reduce biliary complications. To avoid a potentially morbid ablation procedure, we developed a resorbable and radiopaque internal biliary stent (RIBS). We studied the mechanical and radiological properties of RIBS upon in vivo implantation in rats and we evaluated RIBS implantability in human anatomical specimens. For this purpose, a blend of PLA₅₀-PEG-PLA₅₀ triblock copolymer, used as a polymer matrix, and of X-ray-visible triiodobenzoate-poly(ε-caprolactone) copolymer (PCL-TIB), as a radiopaque additive, was used to design X-ray-visible RIBS. Samples were implanted in the peritoneal cavity of rats. The radiological, chemical, and biomechanical properties were evaluated during degradation. Further histological studies were carried out to evaluate the degradation and compatibility of the RIBS. A human cadaver implantability study was also performed. The in vivo results revealed a decline in the RIBS mechanical properties within 3 months, whereas clear and stable X-ray visualization of the RIBS was possible for up to 6 months. Histological analyses confirmed compatibility and resorption of the RIBS, with a limited inflammatory response. The RIBS could be successfully implanted in human anatomic specimens. The results reported in this study will allow the development of trackable and degradable IBS to reduce biliary complications after liver transplantation. STATEMENT OF SIGNIFICANCE: Biliary reconstruction during liver transplantation is an important source of postoperative morbidity and mortality although it is generally considered as an easy step of a difficult surgery. In this frame, internal biliary stent (IBS) implantation is beneficial to reduce biliary anastomosis complications (leakage, stricture). However, current IBS are made of non-degradable silicone elastomeric materials, which leads to an additional ablation procedure involving potential complications and additional costs. The present study provides in vitro and human postmortem implantation data related to the development and evaluation of a resorbable and radiopaque internal biliary stent (RIBS) that could tackle these drawbacks.

Nanomaterials as potential and versatile platform for next generation tissue engineering applications

Tissue engineering (TE) is an emerging field where alternate/artificial tissues or organ substitutes are implanted to mimic the functionality of damaged or injured tissues. Earlier efforts were made to develop natural, synthetic, or semisynthetic materials for skin equivalents to treat burns or skin wounds. Nowadays, many more tissues like bone, cardiac, cartilage, heart, liver, cornea, blood vessels, and so forth are being engineered using 3-D biomaterial constructs or scaffolds that could deliver active molecules such as peptides or growth factors. Nanomaterials (NMs) due to their unique mechanical, electrical, and optical properties possess significant opportunities in TE applications. Traditional TE scaffolds were based on hydrolytically degradable macroporous materials, whereas current approaches emphasize on controlling cell behaviors and tissue formation by nano-scale topography that closely mimics the natural extracellular matrix. This review article gives a comprehensive outlook of different organ specific NMs which are being used for diversified TE applications. Varieties of NMs are known to serve as biological alternatives to repair or replace a portion or whole of the nonfunctional or damaged tissue. NMs may promote greater amounts of specific interactions stimulated at the cellular level, ultimately leading to more efficient new tissue formation. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2433-2449, 2019.

Nanoparticles in tissue engineering: applications, challenges and prospects

Tissue engineering (TE) is an interdisciplinary field integrating engineering, material science and medical biology that aims to develop biological substitutes to repair, replace, retain, or enhance tissue and organ-level functions. Current TE methods face obstacles including a lack of appropriate biomaterials, ineffective cell growth and a lack of techniques for capturing appropriate physiological architectures as well as unstable and insufficient production of growth factors to stimulate cell communication and proper response. In addition, the inability to control cellular functions and their various properties (biological, mechanical, electrochemical and others) and issues of biomolecular detection and biosensors, all add to the current limitations in this field. Nanoparticles are at the forefront of nanotechnology and their distinctive size-dependent properties have shown promise in overcoming many of the obstacles faced by TE today. Despite tremendous progress in the use of nanoparticles over the last 2 decades, the full potential of the applications of nanoparticles in solving TE problems has yet to be realized. This review presents an overview of the diverse applications of various types of nanoparticles in TE applications and challenges that need to be overcome for nanotechnology to reach its full potential.

Radiopaque Resorbable Inferior Vena Cava Filter Infused with Gold Nanoparticles

Failure to remove a retrievable inferior vena cava (IVC) filter can cause severe complications with high treatment costs. Polydioxanone (PPDO) has been shown to be a good candidate material for resorbable IVC filters. However, PPDO is radioluscent under conventional imaging modalities. Thus, the positioning and integrity of these PPDO filters cannot be monitored by computed tomography (CT) or x-ray. Here we report the development of radiopaque PPDO IVC filters based on gold nanoparticles (AuNPs). Commercially available PPDO sutures were infused with AuNPs. Scanning electron microscopy analysis confirmed the presence of AuNP on the surface of PPDO. Micro-CT and x-ray images of the AuNP-infused PPDO sutures showed significant signal enhancement compared to untreated PPDO sutures. Elemental analysis showed that gold loading exceeded 2000 ppm. Tensile strength and in vitro cytotoxicity showed no significant difference between AuNP-infused and untreated PPDO. In a 10-week stability study, neither the gold content nor the radiopacity of the infused PPDO sutures significantly changed in the first 6 weeks. The increased attenuation of AuNP-infused PPDO sutures indicates their major advantage as a radiopaque resorbable filter material, as the radiopacity allows monitoring of the position and integrity of the filter, thereby increasing its safety and efficacy.

Design, synthesis and ring-opening polymerization of a new iodinated carbonate monomer: a universal route towards ultrahigh radiopaque aliphatic polycarbonates

A universal route towards ultrahigh radiopaque aliphatic polycarbonates was developed based on a new iodinated carbonate monomer.

Infusion of iodine-based contrast agents into poly(p-dioxanone) as a radiopaque resorbable IVC filter

To determine the feasibility of infusing resorbable inferior vena cava (IVC) filter with iodine-based contrast agents to produce a radiopaque, computed tomography (CT)-visible IVC filter. Infused poly(p-dioxanone) (PPDO) was obtained by incubating PPDO in different concentrations of 4-iodobenzoyl chloride (IBC) and 2,3,5-triiodobenzoic acid (TIBA). Characterizations of infused and nascent PPDO were done using elemental analysis, micro-CT, tensile strength analysis, scanning electron microscopy, and differential scanning calorimetry. Elemental analysis showed percentage loading of 1.07 ± 0.08 for IBC and 0.73 ± 0.01 for TIBA. The iodine loading remained the same within 2 weeks for TIBA but decreased to about 80 % with IBC when subjected to physiological conditions. Micro-CT images showed increased attenuation of the infused PPDO compared with the nascent PPDO. The Hounsfield unit values for infused and nascent sutures were 110 ± 40 and 153 ± 53 for PPDO infused with 2 mg/mL IBC and TIBA, respectively, but only 11.35 ± 2 for nascent PPDO. In contrast the HU for bone was 116 ± 37. Tensile strength analysis showed maximum loads of 1.01 ± 0.43 kg and 10.02 ± 0.54 kg for IBC and TIBA, respectively, and 10.10 ± 0.64 kg for nascent PPDO. Scanning electron microscopy showed that the morphology of the PPDO surface did not change after coating and preliminary cytotoxicity assay showed no killing effect on Hela cells. PPDO infused with a contrast agent is significantly more radiopaque than nascent PPDO on micro-CT imaging. This radiopacity could allow the position and integrity of infused resorbable IVC filter to be monitored while it is in place, thus increasing its safety and efficacy as a medical device.

Nanoparticles for imaging: top or flop?

Nanoparticles are frequently suggested as diagnostic agents. However, except for iron oxide nanoparticles, diagnostic nanoparticles have been barely incorporated into clinical use so far. This is predominantly due to difficulties in achieving acceptable pharmacokinetic properties and reproducible particle uniformity as well as to concerns about toxicity, biodegradation, and elimination. Reasonable indications for the clinical utilization of nanoparticles should consider their biologic behavior. For example, many nanoparticles are taken up by macrophages and accumulate in macrophage-rich tissues. Thus, they can be used to provide contrast in liver, spleen, lymph nodes, and inflammatory lesions (eg, atherosclerotic plaques). Furthermore, cells can be efficiently labeled with nanoparticles, enabling the localization of implanted (stem) cells and tissue-engineered grafts as well as in vivo migration studies of cells. The potential of using nanoparticles for molecular imaging is compromised because their pharmacokinetic properties are difficult to control. Ideal targets for nanoparticles are localized on the endothelial luminal surface, whereas targeted nanoparticle delivery to extravascular structures is often limited and difficult to separate from an underlying enhanced permeability and retention (EPR) effect. The majority of clinically used nanoparticle-based drug delivery systems are based on the EPR effect, and, for their more personalized use, imaging markers can be incorporated to monitor biodistribution, target site accumulation, drug release, and treatment efficacy. In conclusion, although nanoparticles are not always the right choice for molecular imaging (because smaller or larger molecules might provide more specific information), there are other diagnostic and theranostic applications for which nanoparticles hold substantial clinical potential.

Radiopaque poly(ε-caprolactone) as additive for X-ray imaging of temporary implantable medical devices

A family of radiopaque PCL, poly(ε-caprolactone-co-α-triiodobenzoate-ε-caprolactone), has been designed, used and evaluated as macromolecular contrast agent for X-ray imaging of implantable polymeric biomaterials.

Taking a deep look: modern microscopy technologies to optimize the design and functionality of biocompatible scaffolds for tissue engineering in regenerative medicine

This review focuses on modern nonlinear optical microscopy (NLOM) methods that are increasingly being used in the field of tissue engineering (TE) to image tissue non-invasively and without labelling in depths unreached by conventional microscopy techniques. With NLOM techniques, biomaterial matrices, cultured cells and their produced extracellular matrix may be visualized with high resolution. After introducing classical imaging methodologies such as µCT, MRI, optical coherence tomography, electron microscopy and conventional microscopy two-photon fluorescence (2-PF) and second harmonic generation (SHG) imaging are described in detail (principle, power, limitations) together with their most widely used TE applications. Besides our own cell encapsulation, cell printing and collagen scaffolding systems and their NLOM imaging the most current research articles will be reviewed. These cover imaging of autofluorescence and fluorescence-labelled tissue and biomaterial structures, SHG-based quantitative morphometry of collagen I and other proteins, imaging of vascularization and online monitoring techniques in TE. Finally, some insight is given into state-of-the-art three-photon-based imaging methods (e.g. coherent anti-Stokes Raman scattering, third harmonic generation). This review provides an overview of the powerful and constantly evolving field of multiphoton microscopy, which is a powerful and indispensable tool for the development of artificial tissues in regenerative medicine and which is likely to gain importance also as a means for general diagnostic medical imaging.