Gd(III)-Gold Nanoconjugates Provide Remarkable Cell Labeling for High Field Magnetic Resonance Imaging

Engineered Nonviral Protein Cages Modified for MR Imaging

Diagnostic medical imaging utilizes magnetic resonance (MR) to provide anatomical, functional, and molecular information in a single scan. Nanoparticles are often labeled with Gd(III) complexes to amplify the MR signal of contrast agents (CAs) with large payloads and high proton relaxation efficiencies (relaxivity, r1). This study examined the MR performance of two structurally unique cages, AaLS-13 and OP, labeled with Gd(III). The cages have characteristics relevant for the development of theranostic platforms, including (i) well-defined structure, symmetry, and size; (ii) the amenability to extensive engineering; (iii) the adjustable loading of therapeutically relevant cargo molecules; (iv) high physical stability; and (v) facile manufacturing by microbial fermentation. The resulting conjugates showed significantly enhanced proton relaxivity (r1 = 11-18 mM-1 s-1 at 1.4 T) compared to the Gd(III) complex alone (r1 = 4 mM-1 s-1). Serum phantom images revealed 107% and 57% contrast enhancements for Gd(III)-labeled AaLS-13 and OP cages, respectively. Moreover, proton nuclear magnetic relaxation dispersion (1H NMRD) profiles showed maximum relaxivity values of 50 mM-1 s-1. Best-fit analyses of the 1H NMRD profiles attributed the high relaxivity of the Gd(III)-labeled cages to the slow molecular tumbling of the conjugates and restricted local motion of the conjugated Gd(III) complex.

Multinuclear MRI in Drug Discovery

The continuous development of magnetic resonance imaging broadens the range of applications to newer areas. Using MRI, we can not only visualize, but also track pharmaceutical substances and labeled cells in both in vivo and in vitro tests. ¹H is widely used in the MRI method, which is determined by its high content in the human body. The potential of the MRI method makes it an excellent tool for imaging the morphology of the examined objects, and also enables registration of changes at the level of metabolism. There are several reports in the scientific publications on the use of clinical MRI for in vitro tracking. The use of multinuclear MRI has great potential for scientific research and clinical studies. Tuning MRI scanners to the Larmor frequency of a given nucleus, allows imaging without tissue background. Heavy nuclei are components of both drugs and contrast agents and molecular complexes. The implementation of hyperpolarization techniques allows for better MRI sensitivity. The aim of this review is to present the use of multinuclear MRI for investigations in drug delivery.

The electrostatic confinement of aquated monocationic Gd(III) complex-molecules within the inner core of porous silica nanoparticles creates a highly efficient T1 contrast agent for magnetic resonance imaging

Contrast-agent enhanced magnetic resonance imaging (MRI) has been under continuous investigation for the conspicuous imaging of lesions and the early-stage detection of tumors. To achieve the development of a T₁-weighted contrast agent with a high relaxivity value, herein, porous silica nanoparticles that had internalized about 20 aquated cationic Gd(III) complexes (1) of the hexadentate hydroxyethyl-appended picolinate-based ligand H₂hbda were demonstrated. Complex 1 exhibited a longitudinal relaxivity value per mM Gd(III) ions, r₁, of 9.05 mM^-1 s^-1 (pH 7.4, 37 °C, 1.41 T), which increased to 86.41 mM^-1 s^-1 because of the grafting of complex 1 in the inner core of porous silica nanospheres through electrostatic interactions between the anionic silica surface and the cationic complex 1 molecules. A further augmentation in the relaxivity value to 118.32 mM^-1 s^-1 was realized because of the interaction of the complex 1@SiO₂NPs with serum albumin protein. The synthesized nanosystem was impervious to physiologically available anions (HPO₄^2- and HCO₃^1-) and also kinetically inert, as evidenced via a transmetallation experiment in the presence of Zn(II) ions. The developed complex-incorporated nanomaterial was bio- and hemo-compatible. Cellular uptake measurements employing HeLa cells and the concentration-dependent enhancement in the brightness of in vitro phantom images, recorded under a clinical scanner at 1.5 T, demonstrated that the developed biocompatible 1@SiO₂NP complex has promising diagnostic applications as a T₁-weighted MRI contrast agent.

Current Strategies to Enhance Delivery of Drugs across the Blood–Brain Barrier

The blood–brain barrier (BBB) has shown to be a significant obstacle to brain medication delivery. The BBB in a healthy brain is a diffusion barrier that prevents most substances from passing from the blood to the brain; only tiny molecules can pass across the BBB. The BBB is disturbed in specific pathological illnesses such as stroke, diabetes, seizures, multiple sclerosis, Parkinson’s disease, and Alzheimer’s disease. The goal of this study is to offer a general overview of current brain medication delivery techniques and associated topics from the last five years. It is anticipated that this review will stimulate readers to look into new ways to deliver medications to the brain. Following an introduction of the construction and function of the BBB in both healthy and pathological conditions, this review revisits certain contested questions, such as whether nanoparticles may cross the BBB on their own and if medications are selectively delivered to the brain by deliberately targeted nanoparticles. Current non-nanoparticle options are also discussed, including drug delivery via the permeable BBB under pathological circumstances and the use of non-invasive approaches to improve brain medication absorption.

High-Relaxivity Molecular MRI Contrast Agent to Target Gb3-Expressing Cancer Cells

Targeted contrast agents (CAs) can improve magnetic resonance imaging (MRI) for accurate cancer diagnosis. In this work, we used the Shiga toxin B-subunit (STxB) as a targeting agent, which binds to Gb3, a glycosphingolipid highly overexpressed on the surface of tumor cells. We developed STxB-targeted MRI probes from cyclic peptide scaffolds functionalized with six to nine monoamide DO3A[Gd(III)] chelates. The influence of structural constraints on the longitudinal relaxivity (r₁) of the CAs has been studied. The cyclic peptide carrying nine monoamide DO3A[Gd(III)] exhibited a r₁ per compound of 32 and 93 mM^-1s^-1 at 9.4 and 1.5 T, respectively. Its conjugation to the pentameric STxB protein led to a 70 kDa compound with a higher r₁ of 150 and 475 mM^-1 s^-1 at 9.4 and 1.5 T, respectively. Specific accumulation and cellular distribution of this conjugate in Gb3-expressing cancer cells were demonstrated using immunofluorescence microscopy and quantified by an inductively coupled plasma-mass spectrometry dosage of Gd(III). Such an agent should enable the in vivo detection by MRI of tumors expressing Gb3 receptors.

Recent Development of Gold Nanoparticles as Contrast Agents for Cancer Diagnosis

Simple Summary

The development of nanotechnology has brought revolution to the diagnosis and therapy of diseases, with a high precision and efficacy. Because nanoparticles can integrate multifunctions together including imaging, targeting, and therapeutics, they are more efficient than the standalone diagnostic or therapeutic entities. Among which, gold nanoparticles are most extensively investigated due to their excellent biocompatibility, versatility and ease of functionalization. Excepting the using of gold nanoparticles as vehicles for therapeutics delivery, they are also good candidates as contrast agents for imaging diagnosis, from magnetic resonance imaging, CT and nuclear imaging, fluorescence imaging, photoacoustic imaging to X-ray fluorescence imaging. We summarize their recent applications in these imaging modalities and challenges for their clinical translation.

Abstract

The last decade has witnessed the booming of preclinical studies of gold nanoparticles (AuNPs) in biomedical applications, from therapeutics delivery, imaging diagnostics, to cancer therapies. The synthetic versatility, unique optical and electronic properties, and ease of functionalization make AuNPs an excellent platform for cancer theranostics. This review summarizes the development of AuNPs as contrast agents to image cancers. First, we briefly describe the AuNP synthesis, their physical characteristics, surface functionalization and related biomedical uses. Then we focus on the performances of AuNPs as contrast agents to diagnose cancers, from magnetic resonance imaging, CT and nuclear imaging, fluorescence imaging, photoacoustic imaging to X-ray fluorescence imaging. We compare these imaging modalities and highlight the roles of AuNPs as contrast agents in cancer diagnosis accordingly, and address the challenges for their clinical translation.

Maximizing Magnetic Resonance Contrast in Gd(III) Nanoconjugates: Investigation of Proton Relaxation in Zirconium Metal-Organic Frameworks

Gadolinium(III) nanoconjugate contrast agents (CAs) provide significant advantages over small-molecule complexes for magnetic resonance imaging (MRI), namely increased Gd(III) payload and enhanced proton relaxation efficiency (relaxivity, r₁). Previous research has demonstrated that both the structure and surface chemistry of the nanomaterial substantially influence contrast. We hypothesized that inserting Gd(III) complexes in the pores of a metal-organic framework (MOF) might offer a unique strategy to further explore the parameters of nanomaterial structure and composition, which influence relaxivity. Herein, we postsynthetically incorporate Gd(III) complexes into Zr-MOFs using solvent-assisted ligand incorporation (SALI). Through the study of Zr-based MOFs, NU-1000 (nano and micronsize particles) and NU-901, we investigated the impact of particle size and pore shape on proton relaxivity. The SALI-functionalized Gd nano NU-1000 hybrid material displayed the highest loading of the Gd(III) complex (1.9 ± 0.1 complexes per node) and exhibited the most enhanced proton relaxivity (r₁ of 26 ± 1 mM^-1 s^-1 at 1.4 T). Based on nuclear magnetic relaxation dispersion (NMRD) analysis, we can attribute the performance of Gd nano NU-1000 to the nanoscale size of the MOF particles and larger pore size that allows for rapid water exchange. We have demonstrated that SALI is a promising method for incorporating Gd(III) complexes into MOF materials and identified crucial design parameters for the preparation of next generation Gd(III)-functionalized MOF MRI contrast agents.

Combined Magnetic Resonance Imaging and Photodynamic Therapy Using Polyfunctionalised Nanoparticles Bearing Robust Gadolinium Surface Units

A robust dithiocarbamate tether allows novel gadolinium units based on DOTAGA (q=1) to be attached to the surface of gold nanoparticles (2.6-4.1 nm diameter) along with functional units offering biocompatibility, targeting and photodynamic therapy. A dramatic increase in relaxivity (r₁ ) per Gd unit from 5.01 mm^-1  s^-1 in unbound form to 31.68 mm^-1  s^-1 (10 MHz, 37 °C) is observed when immobilised on the surface due to restricted rotation and enhanced rigidity of the Gd complex on the nanoparticle surface. The single-step synthetic route provides a straightforward and versatile way of preparing multifunctional gold nanoparticles, including examples with conjugated zinc-tetraphenylporphyrin photosensitizers. The lack of toxicity of these materials (MTT assays) is transformed on irradiation of HeLa cells for 30 minutes (PDT), leading to 75 % cell death. In addition to passive targeting, the inclusion of units capable of actively targeting overexpressed folate receptors illustrates the potential of these assemblies as targeted theranostic agents.

Dual Imaging Gold Nanoplatforms for Targeted Radiotheranostics

Gold nanoparticles (AuNPs) are interesting for the design of new cancer theranostic tools, mainly due to their biocompatibility, easy molecular vectorization, and good biological half-life. Herein, we report a gold nanoparticle platform as a bimodal imaging probe, capable of coordinating Gd³⁺ for Magnetic Resonance Imaging (MRI) and ⁶⁷Ga³⁺ for Single Photon Emission Computed Tomography (SPECT) imaging. Our AuNPs carry a bombesin analogue with affinity towards the gastrin releasing peptide receptor (GRPr), overexpressed in a variety of human cancer cells, namely PC3 prostate cancer cells. The potential of these multimodal imaging nanoconstructs was thoroughly investigated by the assessment of their magnetic properties, in vitro cellular uptake, biodistribution, and radiosensitisation assays. The relaxometric properties predict a potential T₁- and T₂- MRI application. The promising in vitro cellular uptake of ⁶⁷Ga/Gd-based bombesin containing particles was confirmed through biodistribution studies in tumor bearing mice, indicating their integrity and ability to target the GRPr. Radiosensitization studies revealed the therapeutic potential of the nanoparticles. Moreover, the DOTA chelating unit moiety versatility gives a high theranostic potential through the coordination of other therapeutically interesting radiometals. Altogether, our nanoparticles are interesting nanomaterial for theranostic application and as bimodal T₁- and T₂- MRI / SPECT imaging probes.

Gold nanomaterials functionalised with gadolinium chelates and their application in multimodal imaging and therapy

An overview of recent progress in the design of gadolinium-functionalised gold nanoparticles for use in MRI, multimodal imaging and theranostics.

Design and Synthesis of Gold-Gadolinium-Core-Shell Nanoparticles as Contrast Agent: a Smart Way to Future Nanomaterials for Nanomedicine Applications

INTRODUCTION

The development of biopolymers for the synthesis of Gd(III) nanoparticles, as therapeutics, could play a key role in nanomedicine. Biocompatible polymers are not only used for complex monovalent biomolecules, but also for the realization of multivalent active targeting materials as diagnostic and/or therapeutic hybrid nanoparticles. In this article, it was reported for the first time, a novel synthesis of Gd(III)-biopolymer-Au(III) complex, acting as a key ingredient of core-shell gold nanoparticles (Gd(@AuNPs).

MATERIAL AND METHODS

The physical and chemical evaluation was carried out by spectroscopic analytical techniques (Raman spectroscopy, UV-visible and TEM). The theoretical characterization by DFT (density functional theory) analysis was carried out under specific conditions to investigate the interaction between the Au and the Gd precursors, during the first nucleation step. Magnetic features with relaxivity measurements at 7T were also performed as well as cytotoxicity studies on hepatocyte cell lines for biocompatibility studies. The in vivo detailed dynamic biodistribution studies in mice to characterize the potential applications for biology as MRI contrast agents were then achieved.

RESULTS

Physical-chemical evaluation confirms the successful design and reaction supposed. Viabilities of TIB-75 (hepatocytes) cells were evaluated using Alamar blue cytotoxic tests with increasing concentrations of nanoparticles. In vivo biodistribution studies were then accomplished to assess the kinetic behavior of the nanoparticles in mice and characterize their stealthiness property after intravenous injection.

CONCLUSION

We demonstrated that Gd@AuNPs have some advantages to display hepatocytes in the liver. Particularly, these nanoconjugates give a good cellular uptake of several quantities of Gd@NPs into cells, while preserving a T1 contrast inside cells that provide a robust in vivo detection using T1-weighted MR images. These results will strengthen the role of gadolinium as complex to gold in order to tune Gd(@AuNPs) as an innovative diagnostic agent in the field of nanomedicine.

Water-Soluble Nanoconjugate for Enhanced Cellular Delivery of Receptor-Targeted Magnetic Resonance Contrast Agents

ProGlo is an efficient steroid receptor-targeted magnetic resonance (MR) imaging contrast agent (CA). It has been shown to bind to the progesterone receptor (PR) and produce enhanced image contrast in PR-positive cells and tissues in vitro and in vivo. However, the hydrophobicity of the steroid targeting domain of ProGlo (logP = 1.4) limits its formulation and delivery at clinically relevant doses. In this work, a hydrophobic moiety was utilized to drive efficient adsorption onto nanodiamond (ND) clusters to form a water-soluble nanoconstruct (logP = -2.4) with 80% release in 8 h under biological conditions. In cell culture, the ND-ProGlo construct delivered increased concentrations of ProGlo to target cells compared to ProGlo alone. Importantly, these results were accomplished without the use of solvents such as DMSO, providing a significant advance toward formulating ProGlo for translational applications. Biodistribution studies confirm the delivery of ProGlo to PR(+) tissues with enhanced efficacy over untargeted controls. These results demonstrate the potential for a noncovalent ND-CA construct as a general strategy for solubilizing and delivering hydrophobic targeted MR CAs.

Molecular Magnetic Resonance Imaging with Gd(III)-Based Contrast Agents: Challenges and Key Advances

In an era of personalized medicine, the clinical community has become increasingly focused on understanding diseases at the cellular and molecular levels. Magnetic resonance imaging (MRI) is a powerful imaging modality for acquiring anatomical and functional information. However, it has limited applications in the field of molecular imaging due to its low sensitivity. To expand the capability of MRI to encompass molecular imaging applications, we introduced bioresponsive Gd(III)-based magnetic resonance contrast agents (GBCAs) in 1997. Since that time, many research groups across the globe have developed new examples of bioresponsive GBCAs. These contrast agents have shown great promise for visualizing several biochemical processes, such as gene expression, neuronal signaling, and hormone secretion. They are designed to be conditionally retained, or activated, in vivo in response to specific biochemical events of interest. As a result, an observed MR signal change can serve as a read-out for molecular events. A significant challenge for these probes is how to utilize them for noninvasive diagnostic and theranostic applications. This Perspective focuses on the design strategies that underlie bioresponsive probes, and describes the key advances made in recent years that are facilitating their application in vivo and ultimately in clinical translation. While the field of bioresponsive agents is embryonic, it is clear that many solutions to the experimental and clinical radiologic problems of today will be overcome by the probes of tomorrow.

Gold nanomaterials as key suppliers in biological and chemical sensing, catalysis, and medicine

BACKGROUND

Gold nanoparticles (AuNPs) with unique physicochemical properties have received a great deal of interest in the field of biological, chemical and biomedical implementations. Despite the widespread use of AuNPs in chemical and biological sensing, catalysis, imaging and diagnosis, and more recently in therapy, no comprehensive summary has been provided to explain how AuNPs could aid in developing improved sensing and catalysts systems as well as medical settings.

SCOPE OF REVIEW

The chemistry of Au-based nanosystems was followed by reviewing different applications of Au nanomaterials in biological and chemical sensing, catalysis, imaging and diagnosis by a number of approaches, and finally synergistic combination therapy of different cancers. Afterwards, the clinical impacts of AuNPs, future application of AuNPs, and opportunities and challenges of AuNPs application were also discussed.

MAJOR CONCLUSIONS

AuNPs show exclusive colloidal stability and are considered as ideal candidates for colorimetric detection, catalysis, imaging, and photothermal transducers, because their physicochemical properties can be tuned by adjusting their structural dimensions achieved by the different manufacturing methods.

GENERAL SIGNIFICANCE

This review provides some details about using AuNPs in sensing and catalysis applications as well as promising theranostic nanoplatforms for cancer imaging and diagnosis, and sensitive, non-invasive, and synergistic methods for cancer treatment in an almost comprehensive manner.

Polyfunctionalised Nanoparticles Bearing Robust Gadolinium Surface Units for High Relaxivity Performance in MRI

The first example of an octadentate gadolinium unit based on DO3A (hydration number q=1) with a dithiocarbamate tether has been designed and attached to the surface of gold nanoparticles (around 4.4 nm in diameter). In addition to the superior robustness of this attachment, the restricted rotation of the Gd complex on the nanoparticle surface leads to a dramatic increase in relaxivity (r₁ ) from 4.0 mm^-1  s^-1 in unbound form to 34.3 mm^-1  s^-1 (at 10 MHz, 37 °C) and 22±2 mm^-1  s^-1 (at 63.87 MHz, 25 °C) when immobilised on the surface. The one-pot synthetic route provides a straightforward and versatile way of preparing a range of multifunctional gold nanoparticles. The incorporation of additional surface units for biocompatibility (PEG and thioglucose units) and targeting (folic acid) leads to little detrimental effect on the high relaxivity observed for these non-toxic multifunctional materials. In addition to the passive targeting attributed to gold nanoparticles, the inclusion of a unit capable of targeting the folate receptors overexpressed by cancer cells, such as HeLa cells, illustrates the potential of these assemblies.

Investigation of nanoparticle immobilized cellulase: nanoparticle identity, linker length and polyphenol hydrolysis

Cellulase containing nanobiocatalysts have been useful as an extraction tool based on their ability to disrupt plant cell walls. In this work, we investigate the effect of nanoparticle composition and chemical linkage towards immobilized cellulase activity. Cellulase nanoconstructs have been prepared, characterized and compared for their loading efficiencies with standard assays and enzyme kinetics and correlate well with the cognate loading efficiencies. Application of the cellulase-immobilized nanoparticles on onion skins results in release of a distinctive composition of polyphenols. The aglycosidic form of quercetin is the dominant product of onion skin hydrolysis affected by cellulase nanobiocatalysts. Chitosan-coated iron oxide nanoparticles with APTES-conjugated cellulase are found to be most effective for polyphenol release and for transformation of glycosidic to aglycosidic form of quercetin. These results shed light on the activity of immobilized cellulase beyond their role in cell wall disruption and are important for the practical application of cellulase nanobiocatalysts.

Nitroxide-radicals-modified gold nanorods for in vivo CT/MRI-guided photothermal cancer therapy

Purpose

This article presents a report of the synthesis, characterization, and biomedical application of nitroxide-radicals-modified gold nanorods (Au-TEMPO NRs) for imaging-guided photothermal cancer therapy.

Patients and methods

Au nanorods were synthesized through seed-mediated growth method, 4-Amino-TEMPO was added and the reaction proceeded under magnetic stirring.

Results

With a mean length of 39.2 nm and an average aspect ratio of approximately 3.85, Au-TEMPO NRs showed good photothermal ability when they were irradiated by 808-nm laser. Au-TEMPO NRs could be stored in PBS for more than 1 month, showed no cytotoxicity against both tumor and normal cells at a concentration of up to 3 mg/mL, and functioned as a dual-mode contrast agent for CT/magnetic resonance (MR) imaging in vitro and in vivo, due to their high X-ray attenuation of Au and good r1 relaxivity of nitroxide radicals. Further, they had a long retention time (~4 hours) in the main organs, which enabled a long CT/MR imaging time window for diagnosis. Bio-distribution results revealed that these Au-TEMPO NRs passively aggregated in the liver and spleen. After irradiation by 808-nm laser, Au-TEMPO NRs could ablate the solid tumor in 4T1 tumor-bearing mice, which implied they were a potential theranostic agent for dual-mode imaging and photothermal cancer therapy.

Conclusion

This type of Au-TEMPO NRs with the abilities of CT/MR imaging and photothermal therapy, can play an active role in imaging-guided photothermal cancer therapy.

Accomplishments and challenges in stem cell imaging in vivo

Stem cell therapies have demonstrated promising preclinical results, but very few applications have reached the clinic owing to safety and efficacy concerns. Translation would benefit greatly if stem cell survival, distribution and function could be assessed in vivo post-transplantation, particularly in patients. Advances in molecular imaging have led to extraordinary progress, with several strategies being deployed to understand the fate of stem cells in vivo using magnetic resonance, scintigraphy, PET, ultrasound and optical imaging. Here, we review the recent advances, challenges and future perspectives and opportunities in stem cell tracking and functional assessment, as well as the advantages and challenges of each imaging approach.

A Markedly Improved Synthetic Approach for the Preparation of Multifunctional Au-DNA Nanoparticle Conjugates Modified with Optical and MR Imaging Probes

We describe a new, and vastly superior approach for labeling spherical nucleic acid conjugates (SNAs) with diagnostic probes. SNAs have been shown to provide the unique ability to traverse the cell membrane and deliver surface conjugated DNA into cells while preserving the DNA from nuclease degradation. Our previous work on preparing diagnostically labeled SNAs was labor intensive, relatively low yielding, and costly. Here, we describe a straightforward and facile preparation for labeling SNAs with optical and MR imaging probes with significantly improved physical properties. The synthesis of Gd(III) labeled DNA Au nanoparticle conjugates is achieved by sequential conjugation of 3'-thiol-modified oligonucleotides and cofunctionalization of the particle surface with the subsequent addition of 1,2 diothiolate modified chelates of Gd(III) (abbreviated: DNA-Gd^III@AuNP). This new generation of SNA conjugates has a 2-fold increase of DNA labeling and a 1.4-fold increase in Gd(III) loading compared to published constructs. Furthermore, the relaxivity ( r₁) is observed to increase 4.5-fold compared to the molecular dithiolane-Gd(III) complex, and 1.4-fold increase relative to previous particle constructs where the Gd(III) complexes were conjugated to the oligonucleotides rather than directly to the Au particle. Importantly, this simplified approach (2 steps) exploits the advantages of previous Gd(III) labeled SNA platforms; however, this new approach is scalable and eliminates modification of DNA for attaching the contrast agent, and the particles exhibit improved cell labeling.

Chemistry and engineering of cyclodextrins for molecular imaging

Cyclodextrins (CDs) are naturally occurring cyclic oligosaccharides bearing a basket-shaped topology with an "inner-outer" amphiphilic character. The abundance of hydroxyl groups enables CDs to be functionalized with multiple targeting ligands and imaging elements. The imaging time, and the payload of different imaging elements, can be tuned by taking advantage of the commercial availability of CDs with different sizes of the cavity. This review aims to offer an outlook of the chemistry and engineering of CDs for the development of molecular probes. Complexation thermodynamics of CDs, and the corresponding implications for probe design, are also presented with examples demonstrating the structural and physiochemical roles played by CDs in the full ambit of molecular imaging. We hope that this review not only offers a synopsis of the current development of CD-based molecular probes, but can also facilitate translation of the incremental advancements from the laboratory to real biomedical applications by illuminating opportunities and challenges for future research.