In Vivo Imaging of Composite Hydrogel Scaffold Degradation Using CEST MRI and Two-Color NIR Imaging

Insights into Non-Metallic Magnetic Resonance Imaging Contrast Agents: Advances and Perspectives

Traditional metal-based magnetic resonance imaging contrast agents (MRI CAs), such as gadolinium, iron, and manganese, have made significant advancements in diagnosing major diseases. However, their potential toxicity due to long-term accumulation in the brain and bones raises safety concerns. In contrast, non-metallic MRI CAs, which can produce a nuclear magnetic resonance effect, show great promise in MRI applications due to their adaptable structure and function, good biocompatibility, and excellent biodegradability. Nevertheless, the development of non-metallic MRI CAs is slow due to the inherent low magnetic sensitivity of organic compounds, their rapid metabolism, and susceptibility to reduction. Designing effective multifunctional organic compounds for high-sensitivity MRI remains a challenge. In this discussion, the mechanisms of various non-metallic MRI CAs are explored and an overview of their current status, highlighting both their advantages and potential drawbacks, is provided. The key strategies for creating high-performance MRI CAs are summarized and how different synthetic approaches affect the performance of non-metallic MRI Cas is evaluated. Last, the challenges and future prospects for these promising non-metallic MRI CAs are addressed.

Design Chemical Exchange Saturation Transfer Contrast Agents and Nanocarriers for Imaging Proton Exchange in Vivo

Chemical exchange saturation transfer magnetic resonance imaging (CEST MRI) enables the imaging of many endogenous and exogenous compounds with exchangeable protons and protons experiencing dipolar coupling by using a label-free approach. This provides an avenue for following interesting molecular events in vivo by detecting the natural protons of molecules, such as the increase in amide protons of proteins in brain tumors and the concentration of drugs reaching the target site. Neither of these detections require metallic or radioactive labels and thus will not perturb the molecular events happening in vivo. Yet, magnetization transfer processes such as chemical exchange and dipolar coupling of protons are sensitive to the local environment. Hence, the use of nanocarriers could enhance the CEST contrast by providing a relatively high local concentration of contrast agents, considering the portion of the protons available for exchange, optimizing the exchange rate, and utilizing molecular interactions. This review provides an overview of these factors to be considered for designing efficient CEST contrast agents (CAs), and the molecular events that can be imaged using CEST MRI during disease progression and treatment, as well as the nanocarriers for drug delivery and distribution for the evaluation of treatments.

Advances in Injectable Hydrogels Based on Diverse Gelation Methods for Biomedical Imaging

The injectable hydrogels can deliver the loads directly to the predetermined sites and form reservoirs to increase the enrichment and retention of the loads in the target areas. The preparation and injection of injectable hydrogels involve the sol-gel transformation of hydrogels, which is affected by factors such as temperature, ions, enzymes, light, mechanics (self-healing property), and pH. However, tracing the injection, degradation, and drug release from hydrogels based on different ways of gelation is a major concern. To solve this problem, contrast agents are introduced into injectable hydrogels, enabling the hydrogels to be imaged under techniques such as fluorescence imaging, photoacoustic imaging, magnetic resonance imaging, and radionuclide imaging. This review details methods for causing the gelation of imageable hydrogels; discusses the application of injectable hydrogels containing contrast agents in various imaging techniques, and finally explores the potential and challenges of imageable hydrogels based on different modes of gelation.

Hydrogel in the Treatment of Traumatic Brain Injury

The high prevalence of traumatic brain injury (TBI) poses an important global public health challenge. Current treatment modalities for TBI primarily involve pharmaceutical interventions and surgical procedures; however, the efficacy of these approaches remains limited. In the field of regenerative medicine, hydrogels have garnered significant attention and research efforts. This review provides an overview of the existing landscape and pathological manifestations of TBI, with a specific emphasis on delineating the therapeutic potential of hydrogels incorporated with various bioactive agents for TBI management. Particularly, the review delves into the utilization and efficacy of hydrogels based on extracellular matrix (ECM), stem cell-loaded, drug-loaded, self-assembled peptide structures or conductive in the context of TBI treatment. These applications are shown to yield favorable outcomes such as tissue damage mitigation, anti-inflammatory effects, attenuation of oxidative stress, anti-apoptotic properties, promotion of neurogenesis, and facilitation of angiogenesis. Lastly, a comprehensive analysis of the merits and constraints associated with hydrogel utilization in TBI treatment is presented, aiming to steer and advance future research endeavors in this domain.

A Futuristic Development in 3D Printing Technique Using Nanomaterials with a Step Toward 4D Printing

3D bioprinting has shown great promise in tissue engineering and regenerative medicine for creating patient-specific tissue scaffolds and medicinal devices. The quickness, accurate imaging, and design targeting of this emerging technology have excited biomedical engineers and translational medicine researchers. Recently, scaffolds made from 3D bioprinted tissue have become more clinically effective due to nanomaterials and nanotechnology. Because of quantum confinement effects and high surface area/volume ratios, nanomaterials and nanotechnological techniques have unique physical, chemical, and biological features. The use of nanomaterials and 3D bioprinting has led to scaffolds with improved physicochemical and biological properties. Nanotechnology and nanomaterials affect 3D bioprinted tissue engineered scaffolds for regenerative medicine and tissue engineering. Biomaterials and cells that respond to stimuli change the structural shape in 4D bioprinting. With such dynamic designs, tissue architecture can change morphologically. New 4D bioprinting techniques will aid in bioactuation, biorobotics, and biosensing. The potential of 4D bioprinting in biomedical technologies is also discussed in this article.

Immunoregulation in Skull Defect Repair with a Smart Hydrogel Loaded with Mesoporous Bioactive Glasses

Skull defect repair is a complex and critical medical challenge, and there is an urgent need to develop multifunctional tissue engineering scaffolds for skull regeneration. The success of bone tissue engineering depends on the construction of scaffolds that can regulate the immune microenvironment of bone regeneration and mimic the liquid crystal and viscoelastic properties of natural bone extracellular matrix. Hence, a smart hydrogel (PEGDA5/AM15/CLC-BMP-4@MBG) with good biocompatibility and the ability to modulate the wound immune microenvironment has been developed for the repair of skull defects. The hydrogel consists of chitin liquid crystal hydrogel (PEGDA5/AM15/CLC) and mesoporous bioactive glasses (MBGs) loaded with bone morphogenetic protein-4 (BMP-4). The liquid crystal hydrogel not only offers the necessary biological support and mechanical properties but also maintains the stability of the liquid crystal state, facilitating adhesion and regeneration of surrounding bone tissue. In addition, BMP-4@MBG intelligently regulates the release rate of BMP-4 in response to changes in wound microenvironment, thus effectively promoting the transformation of macrophages from M1 to M2 macrophages. At the same time, Ca2+ and Si4+ released by MBG degradation and BMP-4 synergically promote bone repair process. The PEGDA5/AM15/CLC-BMP-4@MBG hydrogel shows excellent immunomodulatory and osteogenic properties of bone microenvironment and is a promising scaffold material for bone tissue engineering.

Toward Fully Automated Personalized Orthopedic Treatments: Innovations and Interdisciplinary Gaps

Personalized orthopedic devices are increasingly favored for their potential to enhance long-term treatment success. Despite significant advancements across various disciplines, the seamless integration and full automation of personalized orthopedic treatments remain elusive. This paper identifies key interdisciplinary gaps in integrating and automating advanced technologies for personalized orthopedic treatment. It begins by outlining the standard clinical practices in orthopedic treatments and the extent of personalization achievable. The paper then explores recent innovations in artificial intelligence, biomaterials, genomic and proteomic analyses, lab-on-a-chip, medical imaging, image-based biomechanical finite element modeling, biomimicry, 3D printing and bioprinting, and implantable sensors, emphasizing their contributions to personalized treatments. Tentative strategies or solutions are proposed to address the interdisciplinary gaps by utilizing innovative technologies. The key findings highlight the need for the non-invasive quantitative assessment of bone quality, patient-specific biocompatibility, and device designs that address individual biological and mechanical conditions. This comprehensive review underscores the transformative potential of these technologies and the importance of multidisciplinary collaboration to integrate and automate them into a cohesive, intelligent system for personalized orthopedic treatments.

Dynamic monitoring soft tissue healing via visualized Gd-crosslinked double network MRI microspheres

By integrating magnetic resonance-visible components with scaffold materials, hydrogel microspheres (HMs) become visible under magnetic resonance imaging(MRI), allowing for non-invasive, continuous, and dynamic monitoring of the distribution, degradation, and relationship of the HMs with local tissues. However, when these visualization components are physically blended into the HMs, it reduces their relaxation rate and specificity under MRI, weakening the efficacy of real-time dynamic monitoring. To achieve MRI-guided in vivo monitoring of HMs with tissue repair functionality, we utilized airflow control and photo-crosslinking methods to prepare alginate-gelatin-based dual-network hydrogel microspheres (G-AlgMA HMs) using gadolinium ions (Gd (III)), a paramagnetic MRI contrast agent, as the crosslinker. When the network of G-AlgMA HMs degrades, the cleavage of covalent bonds causes the release of Gd (III), continuously altering the arrangement and movement characteristics of surrounding water molecules. This change in local transverse and longitudinal relaxation times results in variations in MRI signal values, thus enabling MRI-guided in vivo monitoring of the HMs. Additionally, in vivo data show that the degradation and release of polypeptide (K2 (SL)6 K2 (KK)) from G-AlgMA HMs promote local vascular regeneration and soft tissue repair. Overall, G-AlgMA HMs enable non-invasive, dynamic in vivo monitoring of biomaterial degradation and tissue regeneration through MRI, which is significant for understanding material degradation mechanisms, evaluating biocompatibility, and optimizing material design.

Preparation of Hematoporphyrin-Poly(Lactic Acid) Nanoparticles Encapsulated Perfluoropentane/Salicylic Acid for Enhanced US/CEST MR Bimodal Imaging

Background

Medical imaging modalities, such as magnetic resonance imaging (MRI), ultrasound, and fluorescence imaging, have gained widespread acceptance in clinical practice for tumor diagnosis. Each imaging modality has its own unique principles, advantages, and limitations, thus necessitating a multimodal approach for a comprehensive disease understanding of the disease process. To enhance diagnostic precision, physicians frequently integrate data from multiple imaging modalities, driving research advancements in multimodal imaging technology research.

Methods

In this study, hematoporphyrin-poly (lactic acid) (HP-PLLA) polymer was prepared via ring-opening polymerization and thoroughly characterized using FT-IR, 1H-NMR, XRD, and TGA. HP-PLLA based nanoparticles encapsulating perfluoropentane (PFP) and salicylic acid were prepared via emulsion-solvent evaporation. Zeta potential and mean diameter were assessed using DLS and TEM. Biocompatibility was evaluated via cell migration, hemolysis, and cytotoxicity assays. Ultrasonic imaging was performed with a dedicated apparatus, while CEST MRI was conducted using a 7.0 T animal scanner.

Results

We designed and prepared a novel dual-mode nanoimaging probe SA/PFP@HP-PLLA NPs. PFP enhanced US imaging, while salicylic acid bolstered CEST imaging. With an average size of 74.43 ± 1.12 nm, a polydispersity index of 0.175 ± 0.015, and a surface zeta potential of -64.1 ± 2.11 mV. These NPs exhibit excellent biocompatibility and stability. Both in vitro and in vivo experiments confirmed the SA/PFP@HP-PLLA NP's ability to improve tumor characterization and diagnostic precision.

Conclusion

The SA/PFP@HP-PLLA NPs demonstrate promising dual-modality imaging capabilities, indicating their potential for preclinical and clinical use as a contrast agent.

NIR light-facilitated bone tissue engineering

In the last decades, near-infrared (NIR) light has attracted considerable attention due to its unique properties and numerous potential applications in bioimaging and disease treatment. Bone tissue engineering for bone regeneration with the help of biomaterials is currently an effective means of treating bone defects. As a controlled light source with deeper tissue penetration, NIR light can provide real-time feedback of key information on bone regeneration in vivo utilizing fluorescence imaging and be used for bone disease treatment. This review provides a comprehensive overview of NIR light-facilitated bone tissue engineering, from the introduction of NIR probes as well as NIR light-responsive materials, and the visualization of bone regeneration to the treatment of bone-related diseases. Furthermore, the existing challenges and future development directions of NIR light-based bone tissue engineering are also discussed. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement.

A Cu@ZIF-8 encapsulated antibacterial and angiogenic microneedle array for promoting wound healing

Skin wounds caused by external injuries remain a serious challenge in clinical practice. Wound dressings that are antibacterial, pro-angiogenic, and have potent regeneration capacities are highly desirable for wound healing. In this study, a minimally invasive and wound-friendly Cu@ZIF-8 encapsulated PEGDA/CMCS microneedle (MN) array was fabricated using the molding method to promote wound healing. The MNs had good biocompatibility, excellent mechanical strength, as well as strong antibacterial properties and pro-angiogenic effects. When incubated with H2O2, Cu@ZIF-8 nanoparticles generated reactive oxygen species, which contributed to their antibacterial properties. Due to the oxidative stress of the cupric ions released from Cu@ZIF-8 and the anti-bacterial capability of the PEGDA/CMCS hydrogel scaffold, such an MN array presents excellent antibacterial activity. Moreover, with the continuous release of Cu ions from the scaffold, such MNs are effective in terms of promoting angiogenesis. With considerable biocompatibility and a minimally invasive approach, the degradable MN array composed of PEGDA/CMCS possessed superior capabilities to continuously and steadily release the loaded ingredients and avoid secondary damage to the wound. Benefiting from these features, the Cu@ZIF-8 encapsulated degradable MN array can dramatically accelerate epithelial regeneration and neovascularization. These results indicated that the combination of Cu@ZIF-8 and degradable MN arrays is valuable in promoting wound healing, which opened a new window for treatment of skin defection.

Development of cationic peptide-based hydrogels loaded with iopamidol for CEST-MRI detection

Peptide-based hydrogels have been recently investigated as materials for biomedical applications like tissue engineering and delivery of drugs and imaging agents. Among the synthetic peptide hydrogelators, the cationic hexapeptides Ac-K1 and Ac-K2 were proposed as scaffolds for bioprinting applications. Here, we report the formulation of Ac-K1 and Ac-K2 hydrogels loaded with iopamidol, an iodinated contrast agent clinically approved for X-ray computed tomography, and more recently identified as an efficient CEST-MRI probe. Iopamidol-loaded hydrogels were soft, injectable and non-toxic both in vitro (on three tumor cell lines: GL261, TS/A and 3T3-NIH) and in vivo (in Balb/c mice inoculated with TS/A breast cancer cells). The in vitro CEST-MRI study evidenced the typical features of the CEST pattern of iopamidol, with a CEST contrast higher than 50%. Due to their injectability and good ability to retain the contrast agent, the herein investigated systems can be considered as promising candidates for the development of smart MRI detectable hydrogels.

Injectable polylysine and dextran hydrogels with robust antibacterial and ROS-scavenging activity for wound healing

Cutaneous wound management remains a major concern due to uncontrolled inflammation and bacterial infection in clinical care. A desirable hydrogel dressing with antibacterial and antioxidative properties can drive wound healing by inhibiting infection and inflammation. Herein, a multifunctional hydrogel based on polylysine-graft-cysteine (EPL-SH)/oxidized dextran (ODex) was fabricated for promoting skin tissue regeneration. The engineered hydrogel possessed versatile properties including tunable gelation time (60-300 s), typical rheological behavior, suitable swelling and degradation progress, injectable and self-healing ability. The unique hydrogels also displayed promising tissue adhesiveness, high cell affinity, excellent antioxidant and antimicrobial activity. Furthermore, the in vivo full-thickness skin defect experiment demonstrated the simple-to-implement injectable hydrogels could significantly promoting wound healing by improving the collagen deposition and angiogenesis. The manufacture of our multifunctional hydrogels dressing affords a new strategy for improving efficacy of cutaneous wound treatment.

Supramolecular Structure and Mechanical Performance of κ-Carrageenan-Gelatin Gel

In this work, by means of complex physicochemical methods the structural features of a composite κ-carrageenan–gelatin system were studied in comparison with initial protein gel. The correlation between the morphology of hydrogels and their mechanical properties was demonstrated through the example of changes in their rheological characteristics. The experiments carried out with PXRD, SAXS, AFM and rheology approaches gave new information on the structure and mechanical performance of κ-carrageenan–gelatin hydrogel. The combination of PXRD, SAXS and AFM results showed that the morphological structures of individual components were not observed in the composite protein–polysaccharide hydrogels. The results of the mechanical testing of initial gelatin and engineered κ-carrageenan–gelatin gel showed the substantially denser parking of polymer chains in the composite system due to a significant increase in intermolecular protein–polysaccharide contacts. Close results were indirectly followed from the SAXS estimations—the driving force for the formation of the common supramolecular structural arrangement of proteins and polysaccharides was the increase in the density of network of macromolecular chains entanglements; therefore, an increase in the energy costs was necessary to change the conformational rearrangements of the studied system. This increase in the macromolecular arrangement led to the growth of the supramolecular associate size and the growth of interchain physical bonds. This led to an increase in the composite gel plasticity, whereas the enlargement of scattering particles made the novel gel system not only more rigid, but also more fragile.

Image-guided intratumoral immunotherapy: Developing a clinically practical technology

Immunotherapy has revolutionized the contemporary oncology landscape, with durable responses possible across a range of cancer types. However, the majority of cancer patients do not respond to immunotherapy due to numerous immunosuppressive barriers. Efforts to overcome these barriers and increase systemic immunotherapy efficacy have sparked interest in the local intratumoral delivery of immune stimulants to activate the local immune response and subsequently drive systemic tumor immunity. While clinical evaluation of many therapeutic candidates is ongoing, development is hindered by a lack of imaging confirmation of local delivery, insufficient intratumoral drug distribution, and a need for repeated injections. The use of polymeric drug delivery systems, which have been widely used as platforms for both image guidance and controlled drug release, holds promise for delivery of intratumoral immunoadjuvants and the development of an in situ cancer vaccine for patients with metastatic cancer. In this review, we explore the current state of the field for intratumoral delivery and methods for optimizing controlled drug release, as well as practical considerations for drug delivery design to be optimized for clinical image guided delivery particularly by CT and ultrasound.

Two-Wave Variable Nanotheranostic Agents for Dual-Mode Imaging-Guided Photo-Induced Triple-Therapy for Cancer

Photothermal therapy (PTT) is a promising strategy for cancer treatment, but its clinical application relies heavily on accurate tumor positioning and effective combination. Nanotheranostics has shown superior application in precise tumor positioning and treatment, bringing potential opportunities for developing novel PTT-based therapies. Here, a nanotheranostic agent is proposed to enhance magnetic resonance imaging (MRI)/ near-infrared fluorescence imaging (NIRFI) imaging-guided photo-induced triple-therapy for cancer. Thermosensitive liposomes co-loaded with SPIONs/IR780 and Abemaciclib (SIA-TSLs), peptide ACKFRGD, and click group 2-cyano-6-amino-benzothiazole (CABT) are co-modified on the surface of SIA-TSLs to form SIA-αTSLs. ACKFRGD can be hydrolyzed to expose the 1, 2-thiolamino groups in the presence of cathepsin B in tumors, which click cycloaddition with the cyano group on CABT, resulting in the formation of SIA-αTSLs aggregates. The aggregation of SIA-αTSLs in tumors enhances the MRI/NIRFI imaging capability and enables precise PTT. Photo-induced triple-therapy enhances precision cancer therapy. First, PTT ablates specific tumors and induces ICD via localized photothermal. Second, local tumor heating promotes the rupture of SIA-αTSLs, which release Abemaciclib to block the tumor cell cycle and inhibit Tregs proliferation. Third, injecting GM-CSF into tumor tissue leads to recruitment of dendritic cells and initiation of antitumor immunity. Collectively, these results present a promising nanotheranostic strategy for future cancer therapy.

Amphiphilic and fatigue-resistant organohydrogels for small-diameter vascular grafts

Hydrogels are used in vascular tissue engineering because of their good biocompatibility. However, most natural hydrogels exhibit high swelling ratio, poor mechanical stability, and low durability, which are key limitations for wider applications. Amphiphilic and fatigue-resistant organohydrogels were fabricated here via the click chemical reaction of unsaturated functional microbial polyhydroxyalkanoates and polyethylene glycol diacrylate and a combination of two-dimensional material graphdiyne. These organohydrogels were maintained stable in body fluids over time, and their tensile moduli remained unchanged after more than 2000 cycles of cyclic stretching. The tubular scaffolds presented good biocompatibility and perfusion in vitro. After transplantation in vivo, the vascular grafts exhibited obvious cell infiltration and tissue regeneration, having a higher patency rate than the control group in 3 months. This fabrication method provides a strategy of improving and promoting the application of organohydrogels as implant materials for small-diameter vascular graft.

Molecular imaging nanoprobes for theranostic applications

As a non-invasive imaging monitoring method, molecular imaging can provide the location and expression level of disease signature biomolecules in vivo, leading to early diagnosis of relevant diseases, improved treatment strategies, and accurate assessment of treating efficacy. In recent years, a variety of nanosized imaging probes have been developed and intensively investigated in fundamental/translational research and clinical practice. Meanwhile, as an interdisciplinary discipline, this field combines many subjects of chemistry, medicine, biology, radiology, and material science, etc. The successful molecular imaging not only requires advanced imaging equipment, but also the synthesis of efficient imaging probes. However, limited summary has been reported for recent advances of nanoprobes. In this paper, we summarized the recent progress of three common and main types of nanosized molecular imaging probes, including ultrasound (US) imaging nanoprobes, magnetic resonance imaging (MRI) nanoprobes, and computed tomography (CT) imaging nanoprobes. The applications of molecular imaging nanoprobes were discussed in details. Finally, we provided an outlook on the development of next generation molecular imaging nanoprobes.

Biodegradable Elastomers and Gels for Elastic Electronics

Biodegradable electronics are considered as an important bio-friendly solution for electronic waste (e-waste) management, sustainable development, and emerging implantable devices. Elastic electronics with higher imitative mechanical characteristics of human tissues, have become crucial for human-related applications. The convergence of biodegradability and elasticity has emerged a new paradigm of next-generation electronics especially for wearable and implantable electronics. The corresponding biodegradable elastic materials are recognized as a key to drive this field toward the practical applications. The review first clarifies the relevant concepts including biodegradable and elastic electronics along with their general design principles. Subsequently, the crucial mechanisms of the degradation in polymeric materials are discussed in depth. The diverse types of biodegradable elastomers and gels for electronics are then summarized. Their molecular design, modification, processing, and device fabrication especially the structure-properties relationship as well as recent advanced are reviewed in detail. Finally, the current challenges and the future directions are proposed. The critical insights of biodegradability and elastic characteristics in the elastomers and gel allows them to be tailored and designed more effectively for electronic applications.

Emerging scaffold- and cellular-based strategies for brain tissue regeneration and imaging

Stimulating brain tissue regeneration is a major challenge after central nervous system (CNS) injury, such as those observed from trauma or cerebrovascular accidents. Full regeneration is difficult even when a neurogenesis-associated repair response may occur. Currently, there are no effective treatments to stimulate brain tissue regeneration. However, biomaterial scaffolds are showing promising results, where hydrogels are the materials of choice to develop these supportive scaffolds for cell carriers. Their combination with growth factors, such as brain-derived neurotrophic factor (BDNF), basic fibroblast growth factor (bFGF), or vascular endothelial growth factor (VEGF), together with other cell therapy strategies allows the prevention of further neuronal death and can potentially lead to the direct stimulation of neurogenesis and vascularisation at the injured site. Imaging of the injured site is particularly critical to study the reestablishment of neural cell functionality after brain tissue injury. This review outlines the latest key advances associated with different strategies aiming to promote the neuroregeneration, imaging, and functional recovery of brain tissue.

Graphical abstract

Mapping the acute time course of immune cell infiltration into an ECM hydrogel in a rat model of stroke using 19F MRI

Extracellular matrix (ECM) hydrogel implantation into a stroke-induced tissue cavity invokes a robust cellular immune response. However, the spatio-temporal dynamics of immune cell infiltration into peri-infarct brain tissues versus the ECM-bioscaffold remain poorly understood. We here tagged peripheral immune cells using perfluorocarbon (PFC) nanoemulsions that afford their visualization by ¹⁹F magnetic resonance imaging (MRI). Prior to ECM hydrogel implantation, only blood vessels could be detected using ¹⁹F MRI. Using "time-lapse" ¹⁹F MRI, we established the infiltration of immune cells into the peri-infarct area occurs 5-6 h post-ECM implantation. Immune cells also infiltrated through the stump of the MCA, as well as a hydrogel bridge that formed between the tissue cavity and the burr hole in the skull. Tissue-based migration into the bioscaffold was observed between 9 and 12 h with a peak signal measured between 12 and 18 h post-implantation. Fluorescence-activated cell sorting of circulating immune cells revealed that 9% of cells were labeled with PFC nanoemulsions, of which the vast majority were neutrophils (40%) or monocytes (48%). Histology at 24 h post-implantation, in contrast, indicated that macrophages (35%) were more numerous in the peri-infarct area than neutrophils (11%), whereas the vast majority of immune cells within the ECM hydrogel were neutrophils (66%). Only a small fraction (12%) of immune cells did not contain PFC nanoemulsions, indicating a low type II error for ¹⁹F MRI. ¹⁹F MRI hence provides a unique tool to improve our understanding of the spatio-temporal dynamics of immune cells invading bioscaffolds and effecting biodegradation.

In Vivo Imaging of Implanted Hyaluronic Acid Hydrogel Biodegradation

Although the use of stem cell therapy for central nervous system (CNS) repair has shown considerable promise, it is still limited by the immediate death of a large fraction of transplanted cells owing to cell handling procedures, injection stress and host immune attack leading to poor therapeutic outcomes. Scaffolding cells in hydrogels is known to protect cells from such immediate death by shielding them from mechanical damage and by averting an immune attack after transplantation. Implanted hydrogels must eventually degrade and facilitate a safe integration of the graft with the surrounding host tissue. Hence, serial monitoring of hydrogel degradation in vivo is pivotal to optimize hydrogel compositions and overall therapeutic efficacy of the graft. We present here methods and protocols to use chemical exchange saturation transfer magnetic resonance imaging (CEST MRI) as a non-invasive, label-free imaging paradigm to monitor the degradation of composite hydrogels made up of thiolated gelatin (Gel-SH), thiolated hyaluronic acid (HA-SH), and poly (ethylene glycol) diacrylate (PEGDA), of which the stiffness and CEST contrast can be fine-tuned by simply varying the composite concentrations and mixing ratios. By individually labeling Gel-S and HA-S with two distinct near-infrared (NIR) dyes, multispectral monitoring of the relative degradation of the components can be used for long-term validation of the CEST MRI findings.

PLGA/β-TCP composite scaffold incorporating cucurbitacin B promotes bone regeneration by inducing angiogenesis

Objectives

Vascularization is an essential step in successful bone tissue engineering. The induction of angiogenesis in bone tissue engineering can be enhanced through the delivery of therapeutic agents that stimulate vessel and bone formation. In this study, we show that cucurbitacin B (CuB), a tetracyclic terpene derived from Cucurbitaceae family plants, facilitates the induction of angiogenesis in vitro.

Methods

We incorporated CuB into a biodegradable poly (lactide-co-glycolide) (PLGA) and β-tricalcium phosphate (β-TCP) biomaterial scaffold (PT/CuB) Using 3D low-temperature rapid prototyping (LT-RP) technology. A rat skull defect model was used to verify whether the drug-incorporated scaffold has the effects of angiogenesis and osteogenesis in vivo for the regeneration of bone defect. Cytotoxicity assay was performed to determine the safe dose range of the CuB. Tube formation assay and western blot assay were used to analyze the angiogenesis effect of CuB.

Results

PT/CuB scaffold possessed well-designed bio-mimic structure and improved mechanical properties. CuB was linear release from the composite scaffold without affecting pH value. The results demonstrated that the PT/CuB scaffold significantly enhanced neovascularization and bone regeneration in a rat critical size calvarial defect model compared to the scaffold implants without CuB. Furthermore, CuB stimulated angiogenic signaling via up-regulating VEGFR2 and VEGFR-related signaling pathways.

Conclusion

CuB can serve as promising candidate compound for promoting neovascularization and osteogenesis, especially in tissue engineering for repair of bone defects.

The translational potential of this article

This study highlights the potential use of CuB as a therapeutic agent and strongly support its adoption as a component of composite scaffolds for tissue-engineering of bone repair.

Physical Gold Nanoparticle-Decorated Polyethylene Glycol-Hydroxyapatite Composites Guide Osteogenesis and Angiogenesis of Mesenchymal Stem Cells

In this study, polyethylene glycol (PEG) with hydroxyapatite (HA), with the incorporation of physical gold nanoparticles (AuNPs), was created and equipped through a surface coating technique in order to form PEG-HA-AuNP nanocomposites. The surface morphology and chemical composition were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–Vis spectroscopy (UV–Vis), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and contact angle assessment. The effects of PEG-HA-AuNP nanocomposites on the biocompatibility and biological activity of MC3T3-E1 osteoblast cells, endothelial cells (EC), macrophages (RAW 264.7), and human mesenchymal stem cells (MSCs), as well as the guiding of osteogenic differentiation, were estimated through the use of an in vitro assay. Moreover, the anti-inflammatory, biocompatibility, and endothelialization capacities were further assessed through in vivo evaluation. The PEG-HA-AuNP nanocomposites showed superior biological properties and biocompatibility capacity for cell behavior in both MC3T3-E1 cells and MSCs. These biological events surrounding the cells could be associated with the activation of adhesion, proliferation, migration, and differentiation processes on the PEG-HA-AuNP nanocomposites. Indeed, the induction of the osteogenic differentiation of MSCs by PEG-HA-AuNP nanocomposites and enhanced mineralization activity were also evidenced in this study. Moreover, from the in vivo assay, we further found that PEG-HA-AuNP nanocomposites not only facilitate the anti-immune response, as well as reducing CD86 expression, but also facilitate the endothelialization ability, as well as promoting CD31 expression, when implanted into rats subcutaneously for a period of 1 month. The current research illustrates the potential of PEG-HA-AuNP nanocomposites when used in combination with MSCs for the regeneration of bone tissue, with their nanotopography being employed as an applicable surface modification approach for the fabrication of biomaterials.

Post-Stroke Timing of ECM Hydrogel Implantation Affects Biodegradation and Tissue Restoration

Extracellular matrix (ECM) hydrogel promotes tissue regeneration in lesion cavities after stroke. However, a bioscaffold's regenerative potential needs to be considered in the context of the evolving pathological environment caused by a stroke. To evaluate this key issue in rats, ECM hydrogel was delivered to the lesion core/cavity at 7-, 14-, 28-, and 90-days post-stroke. Due to a lack of tissue cavitation 7-days post-stroke, implantation of ECM hydrogel did not achieve a sufficient volume and distribution to warrant comparison with the other time points. Biodegradation of ECM hydrogel implanted 14- and 28-days post-stroke were efficiently (80%) degraded by 14-days post-bioscaffold implantation, whereas implantation 90-days post-stroke revealed only a 60% decrease. Macrophage invasion was robust at 14- and 28-days post-stroke but reduced in the 90-days post-stroke condition. The pro-inflammation (M1) and pro-repair (M2) phenotype ratios were equivalent at all time points, suggesting that the pathological environment determines macrophage invasion, whereas ECM hydrogel defines their polarization. Neural cells (neural progenitors, neurons, astrocytes, oligodendrocytes) were found at all time points, but a 90-days post-stroke implantation resulted in reduced densities of mature phenotypes. Brain tissue restoration is therefore dependent on an efficient delivery of a bioscaffold to a tissue cavity, with 28-days post-stroke producing the most efficient biodegradation and tissue regeneration, whereas by 90-days post-stroke, these effects are significantly reduced. Improving our understanding of how the pathological environment influences biodegradation and the tissue restoration process is hence essential to devise engineering strategies that could extend the therapeutic window for bioscaffolds to repair the damaged brain.

Detecting and Monitoring Hydrogels with Medical Imaging

Hydrogels, water-swollen polymer networks, are being applied to numerous biomedical applications, such as drug delivery and tissue engineering, due to their potential tunable rheologic properties, injectability into tissues, and encapsulation and release of therapeutics. Despite their promise, it is challenging to assess their properties in vivo and crucial information such as hydrogel retention at the site of administration and in situ degradation kinetics are often lacking. To address this, technologies to evaluate and track hydrogels in vivo with various imaging techniques have been developed in recent years, including hydrogels functionalized with contrast generating material that can be imaged with methods such as X-ray computed tomography (CT), magnetic resonance imaging (MRI), optical imaging, and nuclear imaging systems. In this review, we will discuss emerging approaches to label hydrogels for imaging, review the advantages and limitations of these imaging techniques, and highlight examples where such techniques have been implemented in biomedical applications.

Imaging Self-Healing Hydrogels and Chemotherapeutics Using CEST MRI at 3 T

Imaging hydrogel-based local drug delivery to the brain after tumor resection has implications for refining treatments, especially for brain tumors with poor prognosis and high recurrence rate. Here, we developed a series of self-healing chitosan-dextran (CD)-based hydrogels for drug delivery to the brain. These hydrogels are injectable, self-healing, mechanically compatible, and detectable by chemical exchange saturation transfer magnetic resonance imaging (CEST MRI). CD hydrogels have an inherent CEST contrast at 1.1 ppm, which decreases as the stiffness increases. We further examined the rheological properties and CEST contrast of various chemotherapeutic-loaded CD hydrogels, including gemcitabine (Gem), doxorubicin, and procarbazine. Among these formulations, Gem presented the best compatibility with the rheological (G': 215.3 ± 4.5 Pa) and CEST properties of CD hydrogels. More importantly, the Gem-loaded CD hydrogel generated another CEST readout at 2.2 ppm (11.6 ± 0.1%) for monitoring Gem. This enabled independent and simultaneous imaging of the drug and hydrogel integrity using a clinically relevant 3 T MRI scanner. In addition, the Gem-loaded CD hydrogel exhibited a longitudinal antitumor efficacy of Gem over a week in vitro. Furthermore, the CD hydrogel could be visualized by CEST after brain injection with a contrast of 7.38 ± 2.31%. These natural labels on both the chemotherapeutics and hydrogels demonstrate unique image-guided local drug delivery for brain applications.

Noninvasive Three-Dimensional In Situ and In Vivo Characterization of Bioprinted Hydrogel Scaffolds Using the X-ray Propagation-Based Imaging Technique

Hydrogel-based three-dimensional (3D) bioprinting has been illustrated as promising to fabricate tissue scaffolds for regenerative medicine. Notably, bioprinting of hydrated and soft 3D hydrogel scaffolds with desired structural properties has not been fully achieved so far. Moreover, due to the limitations of current imaging techniques, assessment of bioprinted hydrogel scaffolds is still challenging, yet still essential for scaffold design, fabrication, and longitudinal studies. This paper presents our study on the bioprinting of hydrogel scaffolds and on the development of a novel noninvasive imaging method, based on synchrotron propagation-based imaging with computed tomography (SR-PBI-CT), to study the structural properties of hydrogel scaffolds and their responses to environmental stimuli both in situ and in vivo. Hydrogel scaffolds designed with varying structural patterns were successfully bioprinted through rigorous printing process regulations and then imaged by SR-PBI-CT within physiological environments. Subjective to controllable compressive loadings, the structural responses of scaffolds were visualized and characterized in terms of the structural deformation caused by the compressive loadings. Hydrogel scaffolds were later implanted in rats as nerve conduits for SR-PBI-CT imaging, and the obtained images illustrated their high phase contrast and were further processed for the 3D structure reconstruction and quantitative characterization. Our results show that the scaffold design and printing conditions play important roles in the printed scaffold structure and mechanical properties. More importantly, our obtained images from SR-PBI-CT allow us to visualize the details of hydrogel 3D structures with high imaging resolution. It demonstrates unique capability of this imaging technique for noninvasive, in situ characterization of 3D hydrogel structures pre- and post-implantation in diverse physiological milieus. The established imaging platform can therefore be utilized as a robust, high-precision tool for the design and longitudinal studies of hydrogel scaffold in tissue engineering.

Zn-MOF Encapsulated Antibacterial and Degradable Microneedles Array for Promoting Wound Healing

An infected skin wound caused by external injury remains a serious challenge in clinical practice. Wound dressings with the properties of antibacterial activity and potent regeneration capacity are highly desirable for wound healing. In this paper, a degradable, ductile, and wound-friendly Zn-MOF encapsulated methacrylated hyaluronic acid (MeHA) microneedles (MNs) array is fabricated through the molding method for promoting wound healing. Due to the damage capability against the bacteria capsule and oxidative stress of the zinc ion released from the Zn-MOF, such MNs array presents excellent antibacterial activity, as well as considerable biocompatibility. Besides, the degradable MNs array composed of photo-crosslinked MeHA possesses the superior capabilities to continuously and steadily release the loaded active ingredients and avoid secondary damage to the wound. Moreover, the low molecular weight hyaluronic acid (HA) generated by hydrolysis of MeHA is also conducive to tissue regeneration. Benefiting from these features, it has been demonstrated that the Zn-MOF encapsulated degradable MNs array can dramatically accelerate epithelial regeneration and neovascularization. These results indicate that the combination of MOFs and degradable MNs array is of great value for promoting wound healing.

In Vivo Imaging of Allografted Glial-Restricted Progenitor Cell Survival and Hydrogel Scaffold Biodegradation

Transplanted glial-restricted progenitor (GRP) cells have potential to focally replace defunct astrocytes and produce remyelinating oligodendrocytes to avert neuronal death and dysfunction. However, most central nervous system cell therapeutic paradigms are hampered by high initial cell death and a host anti-graft immune response. We show here that composite hyaluronic acid-based hydrogels of tunable mechanical strengths can significantly improve transplanted GRP survival and differentiation. Allogeneic GRPs expressing green fluorescent protein and firefly luciferase were scaffolded in optimized hydrogel formulations and transplanted intracerebrally into immunocompetent BALB/c mice followed by serial in vivo bioluminescent imaging and chemical exchange saturation transfer magnetic resonance imaging (CEST MRI). We demonstrate that gelatin-sensitive CEST MRI can be exploited to monitor hydrogel scaffold degradation in vivo for ∼5 weeks post transplantation without necessitating exogenous labeling. Hydrogel scaffolding of GRPs resulted in a 4.5-fold increase in transplanted cell survival at day 32 post transplantation compared to naked cells. Histological analysis showed significant enhancement of cell proliferation as well as Olig2⁺ and GFAP⁺ cell differentiation for scaffolded cells compared to naked cells, with reduced host immunoreactivity. Hence, hydrogel scaffolding of transplanted GRPs in conjunction with serial in vivo imaging of cell survival and hydrogel degradation has potential for further advances in glial cell therapy.

Cancer theranostic platforms based on injectable polymer hydrogels

Theranostic platforms that combine therapy with diagnosis not only prevent the undesirable biological responses that may occur when these processes are conducted separately, but also allow individualized therapies for patients. Polymer hydrogels have been employed to provide well-controlled drug release and targeted therapy in theranostics, where injectable hydrogels enable non-invasive treatment and monitoring with a single injection, offering greater patient comfort and efficient therapy. Efforts have been focused on applying injectable polymer hydrogels in theranostic research and clinical use. This review highlights recent progress in the design of injectable polymer hydrogels for cancer theranostics, particularly focusing on the elements/components of theranostic hydrogels, and their cross-linking strategies, structures, and performance with regard to drug delivery/tracking. Therapeutic agents and tracking modalities that are essential components of the theranostic platforms are introduced, and the design strategies, properties and applications of the injectable hydrogels developed via two approaches, namely chemical bonds and physical interactions, are described. The theranostic functions of the platforms are highly dependent on the architecture and components employed for the construction of hydrogels. Challenges currently presented by theranostic platforms based on injectable hydrogels are identified, and prospects of acquiring more comfortable and personalized therapies are proposed.

Novel Hydrogel Scaffolds Based on Alginate, Gelatin, 2-Hydroxyethyl Methacrylate, and Hydroxyapatite

Hydrogel scaffolding biomaterials are one of the most attractive polymeric biomaterials for regenerative engineering and can be engineered into tissue mimetic scaffolds to support cell growth due to their similarity to the native extracellular matrix. The novel, versatile hydrogel scaffolds based on alginate, gelatin, 2-hydroxyethyl methacrylate, and inorganic agent hydroxyapatite were prepared by modified cryogelation. The chemical composition, morphology, porosity, mechanical properties, effects on cell viability, in vitro degradation, in vitro and in vivo biocompatibility were tested to correlate the material’s composition with the corresponding properties. Scaffolds showed an interconnected porous microstructure, satisfactory mechanical strength, favorable hydrophilicity, degradation, and suitable in vitro and in vivo biocompatible behavior. Materials showed good biocompatibility with healthy human fibroblast in cell culture, as well as in vivo with zebrafish assay, suggesting newly synthesized hydrogel scaffolds as a potential new generation of hydrogel scaffolding biomaterials with tunable properties for versatile biomedical applications and tissue regeneration.

Capturing the Real-Time Hydrolytic Degradation of a Library of Biomedical Polymers by Combining Traditional Assessment and Electrochemical Sensors

We have developed an innovative methodology to overcome the lack of techniques for real-time assessment of degradable biomedical polymers at physiological conditions. The methodology was established by combining polymer characterization techniques with electrochemical sensors. The in vitro hydrolytic degradation of a series of aliphatic polyesters was evaluated by following the molar mass decrease and the mass loss at different incubation times while tracing pH and l-lactate released into the incubation media with customized miniaturized electrochemical sensors. The combination of different analytical approaches provided new insights into the mechanistic and kinetics aspects of the degradation of these biomedical materials. Although molar mass had to reach threshold values for soluble oligomers to be formed and specimens' resorption to occur, the pH variation and l-lactate concentration were direct evidence of the resorption of the polymers and indicative of the extent of chain scission. Linear models were found for pH and released l-lactate as a function of mass loss for the l-lactide-based copolymers. The methodology should enable the sequential screening of degradable polymers at physiological conditions and has potential to be used for preclinical material's evaluation aiming at reducing animal tests.

Medical imaging of tissue engineering and regenerative medicine constructs

Advancement of tissue engineering and regenerative medicine (TERM) strategies to replicate tissue structure and function has led to the need for noninvasive assessment of key outcome measures of a construct's state, biocompatibility, and function. Histology based approaches are traditionally used in pre-clinical animal experiments, but are not always feasible or practical if a TERM construct is going to be tested for human use. In order to transition these therapies from benchtop to bedside, rigorously validated imaging techniques must be utilized that are sensitive to key outcome measures that fulfill the FDA standards for TERM construct evaluation. This review discusses key outcome measures for TERM constructs and various clinical- and research-based imaging techniques that can be used to assess them. Potential applications and limitations of these techniques are discussed, as well as resources for the processing, analysis, and interpretation of biomedical images.

In Vitro and In Vivo Study of a Novel Nanoscale Demineralized Bone Matrix Coated PCL/β-TCP Scaffold for Bone Regeneration

Bone defects remains a challenge for surgeons. Bone graft scaffold can fill the defect and enhance the bone regeneration. Demineralized bone matrix (DBM) is an allogeneic bone graft substitute, which can only be used as a filling material rather than a structural bone graft. Coating of the scaffolds with nanoscale DBM may enhance the osteoinductivity or osteoconductivity. Herein the lyophilization method is presented to coat the nano-DBM on surface of the porous polycaprolactone (PCL)/β-tricalcium phosphate (β-TCP) scaffolds fabricated by 3D printing technology. The morphology, elastic modulus, in vitro cell biocompatibility, and in vivo performance are investigated. Scanning electron microscope (SEM) shows DBM particle clusters with size of 200-500 nm are observed on scaffolds fibers after coating. MC3T3-E1 cells on nano-DBM coated PCL/β-TCP scaffold show better activity than on PCL/β-TCP scaffold. In vivo tests show better infiltration of new bone tissue in nano-DBM coated PCL/β-TCP scaffold than PCL/β-TCP scaffold via the interface. These results show the presence of nano-DBM coating on PCL/β-TCP scaffold could enhance the attachment, proliferation, and viability of cells and benefit for the new bone formation surrounding and deep inside the scaffolds. Nano-DBM could potentially be used as a new kind of biomaterial for bone defect treatment.

NIR fluorescence for monitoring in vivo scaffold degradation along with stem cell tracking in bone tissue engineering

Stem cell-based tissue engineering has the potential to use as an alternative for autologous tissue grafts; however, the contribution of the scaffold degradation along with the transplanted stem cells to in vivo tissue regeneration remains poorly understood. Near-infrared (NIR) fluorescence imaging has great potential to monitor implants while avoiding autofluorescence from the adjacent host tissue. To utilize NIR imaging for in vivo monitoring of scaffold degradation and cell tracking, we synthesized 800-nm emitting NIR-conjugated PCL-ran-PLLA-ran-PGA (ZW-PCLG) copolymers with three different degradation rates and labeled 700-nm emitting lipophilic pentamethine (CTNF127) on the human placental stem cells (CT-PSCs). The 3D bioprinted hybrid constructs containing the CT-PSC-laden hydrogel together with the ZW-PCLG scaffolds demonstrate that NIR fluorescent imaging enables tracking of in vivo scaffold degradation and stem cell fate for bone regeneration in a rat calvarial bone defect model. This NIR-based monitoring system can be effectively utilized to study cell-based tissue engineering applications.

19F magnetic resonance imaging enabled real-time, non-invasive and precise localization and quantification of the degradation rate of hydrogel scaffolds in vivo

The degradation behavior of hydrogel scaffolds is closely related to the controlled release of bioactive agents and matching with the proliferative demands of newly generated tissues. However, the current methods cannot provide precise localization and track the degradation of individual hydrogel scaffolds in vivo, despite superficial or volumetric information. Here, for the first time, we presented the use of ¹⁹F magnetic resonance imaging (¹⁹F MRI) to precisely monitor the localization and quantify the degradation rate of implantable or injectable hydrogels in a real-time and noninvasive manner, with no interference of endogenous background signals and limitation of penetration depth. The total voxel and content in the region of interest (ROI) were linearly correlated to the injection amount, providing exact three-dimensional (3D) stereoscopic and two-dimensional (2D) anatomical information in the meantime. Moreover, a computational algorithm was established to present the real-time degradation rate in vivo as a function of time, which was implemented directly from the ¹⁹F MRI dataset. In addition, labelling with a zwitterionic ¹⁹F contrast agent demonstrated a facile and general applicability for multiple types of materials with no influence on their original gelation properties as well as ¹⁹F NMR properties in the hydrogel matrix. Therefore, this ¹⁹F MRI method offers a new approach to non-invasively track the degradation rate of hydrogel scaffolds in vivo in a precise localization and accurate quantification way, which will suffice the need for the evaluation of implants at deep depths in large animals or human objects.

Bionic Detectors Based on Low-Bandgap Inorganic Perovskite for Selective NIR-I Photon Detection and Imaging

Fluorescence imaging with photodetectors (PDs) toward near-infrared I (NIR-I) photons (700-900 nm), the so-called "optical window" in organisms, has provided an important path for tracing biological processes in vivo. With both excitation photons and fluorescence photons in this narrow range, a stringent requirement arises that the fluorescence signal should be efficiently differentiated for effective sensing, which cannot be fulfilled by common PDs with a broadband response such as Si-based PDs. In this work, delicate optical microcavities are designed to develop a series of bionic PDs with selective response to NIR-I photons, the merits of a narrowband response with a full width at half maximum (FWHM) of <50 nm, and tunability to cover the NIR-I range are highlighted. Inorganic halide perovskite CsPb_0.5 Sn_0.5 I₃ is chosen as the photoactive layer with comprehensive bandgap and film engineering. As a result, these bionic PDs offer a signal/noise ratio of ≈10⁶ , a large bandwidth of 543 kHz and an ultralow detection limit of 0.33 nW. Meanwhile, the peak responsivity (R) and detectivity (D*) reach up to 270 mA W^-1 and 5.4 × 10¹⁴ Jones, respectively. Finally, proof-of-concept NIR-I imaging using the PDs is demonstrated to show great promise in real-life application.

CEST MRI detectable liposomal hydrogels for multiparametric monitoring in the brain at 3T

Adjuvant treatment using local drug delivery is applied in treating glioblastoma multiforme (GBM) after tumor resection. However, there are no non-invasive imaging techniques available for tracking the compositional changes of hydrogel-based drug treatment.

Methods: We developed Chemical Exchange Saturation Transfer Magnetic Resonance Imaging (CEST MRI) detectable and injectable liposomal hydrogel to monitor these events in vivo at 3T clinical field. Mechanical attributes of these hydrogels and their in vitro and in vivo CEST imaging properties were systematically studied.

Results: The MRI detectable hydrogels were capable of generating multiparametric readouts for monitoring specific components of the hydrogel matrix simultaneously and independently. Herein, we report, for the first time, CEST contrast at -3.4 ppm provides an estimated number of liposomes and CEST contrast at 5 ppm provides an estimated amount of encapsulated drug. CEST contrast decreased by 1.57% at 5 ppm, while the contrast at -3.4 ppm remained constant over 3 d in vivo, demonstrating different release kinetics of these components from the hydrogel matrix. Furthermore, histology analysis confirmed that the CEST contrast at -3.4 ppm was associated with liposome concentrations.

Conclusion: This multiparametric CEST imaging of individual compositional changes in liposomal hydrogels, formulated with clinical-grade materials at 3T and described in this study, has the potential to facilitate the refinement of adjuvant treatment for GBM.