Development of optical probes for in vivo imaging of polarized macrophages during foreign body reactions

Uptake of Cyclodextrin Nanoparticles by Macrophages is Dependent on Particle Size and Receptor-Mediated Interactions

Physiochemical properties of nanoparticles, such as their size and chemical composition, dictate their interaction with professional phagocytes of the innate immune system. Macrophages, in particular, are key regulators of the immune microenvironment that heavily influence particle biodistribution as a result of their uptake. This attribute enables macrophage-targeted delivery, including for phenotypic modulation. Saccharide-based materials, including polyglucose polymers and nanoparticles, are efficient vehicles for macrophage-targeted delivery. Here, we investigate the influence of particle size on cyclodextrin nanoparticle (CDNP) uptake by macrophages and further examine the receptor-mediated interactions that drive macrophage-targeted delivery. We designed and synthesized CDNPs ranging in size from 25 nm to >100 nm in diameter. Increasing particle size was correlated with greater uptake by macrophages in vitro. Both scavenger receptor A1 and mannose receptor were critical mediators of macrophage-targeted delivery, inhibition of which reduced the extent of uptake. Finally, we investigated the cellular bioavailability of drug-loaded CDNPs using a model anti-inflammatory drug, celastrol, which demonstrated that drug bioactivity is improved by CDNP loading relative to free drug alone. This study thus elucidates the interactions between the polyglucose nanoparticles and macrophages, thereby facilitating their application in macrophage-targeted drug delivery that has applications in the context of tissue injury and repair.

Tailoring biomaterials and applications targeting tumor-associated macrophages in cancers

Tumor-associated macrophages (TAMs) play a critical role in supporting tumor growth and metastasis, taming host immunosurveillance, and augmenting therapeutic resistance. As the current treatment paradigms for cancers are generally insufficient to exterminate cancer cells, anti-cancer therapeutic strategies targeting TAMs have been developed. Since TAMs are highly heterogeneous and the pro-tumoral functions are mediated by phenotypes with canonical surface markers, TAM-associated materials exert anti-tumor functions by either inhibiting polarization to the pro-tumoral phenotype or decreasing the abundance of TAMs. Furthermore, TAMs in association with the immunosuppressive tumor microenvironment (TME) and tumor immunity have been extensively exploited in mounting evidence, and could act as carriers or accessory cells of anti-tumor biomaterials. Recently, a variety of TAM-based materials with the capacity to target and eliminate cancer cells have been increasingly developed for basic research and clinical practice. As various TAM-based biomaterials, including antibodies, nanoparticles, RNAs, etc., have been shown to have potential anti-tumor effects reversing the TME, in this review, we systematically summarize the current studies to fully interpret the specific properties and various effects of TAM-related biomaterials, highlighting the potential clinical applications of targeting the crosstalk among TAMs, tumor cells, and immune cells in anti-cancer therapy.

Insight into the bioabsorption of Fe-based materials and their current developments in bone applications

Iron (Fe) and Fe-based materials have been vigorously explored in orthopedic applications in the past decade mainly owing to their promising mechanical properties including high yield strength, elastic modulus and ductility. Nevertheless, their corrosion products and low corrosion kinetics are the major concerns that need to be improved further despite their appealing mechanical strengths. The current studies on porous Fe-based scaffolds show an improved corrosion rate but the in vitro biocompatibility is still problematic in general. Unlike the Mg implants, the biodegradation and bioabsorption of Fe-based implants are still not well described. This vague issue could implicate the development of Fe-based materials as potential medical implants as they have not reached the clinical trial stage yet. Thus, there is a need to understand in-depth the Fe corrosion behavior and its bioabsorption mechanism to facilitate the material design of Fe-based scaffolds and further improve its biocompatibility. This manuscript provides an important insight into the basic bioabsorption of the multi-ranged Fe-based corrosion products with a review of the latest progress on the corrosion & in vitro biocompatibility of porous Fe-based scaffolds together with the remaining challenges and the perspective on the future direction.

Functional Imaging in Wounds: Imaging Modalities of Today and Tomorrow

Wound care is a multidisciplinary field with significant economic burden to our healthcare system. Not only does wound care cost the US healthcare system $20 billion annually, but wounds also remarkably impact the quality of life of patients; wounds pose significant risk of mortality, as the five-year mortality rate for diabetic foot ulcers (DFUs) and ischemic ulcers is notably higher compared to commonly encountered cancers such as breast and prostate. Although it is important to measure how wounds may or may not be improving over time, the only relative "marker" for this is wound area measurement-area measurements can help providers determine if a wound is on a healing or non-healing trajectory. Because wound area measurements are currently the only readily available "gold standard" for predicting healing outcomes, there is a pressing need to understand how other relative biomarkers may play a role in wound healing. Currently, wound care centers across the nation employ various techniques to obtain wound area measurements; length and width of a wound can be measured with a ruler, but this carries a high amount of inter- and intrapersonal error as well as uncertainty. Acetate tracings could be used to limit the amount of error but do not account for depth, thereby making them inaccurate. Here, we discuss current imaging modalities and how they can serve to accurately measure wound size and serve as useful adjuncts in wound assessment. Moreover, new imaging modalities are also discussed and how up-and-coming technologies can provide important information on "biomarkers" for wound healing.

Tumor-Associated Macrophages-Implications for Molecular Oncology and Imaging

Tumor-associated macrophages (TAMs) represent the largest group of leukocytes within the tumor microenvironment (TME) of solid tumors and orchestrate the composition of anti- as well as pro-tumorigenic factors. This makes TAMs an excellent target for novel cancer therapies. The plasticity of TAMs resulting in varying membrane receptors and expression of intracellular proteins allow the specific characterization of different subsets of TAMs. Those markers similarly allow tracking of TAMs by different means of molecular imaging. This review aims to provides an overview of the origin of tumor-associated macrophages, their polarization in different subtypes, and how characteristic markers of the subtypes can be used as targets for molecular imaging and theranostic approaches.

Targeted Imaging of CD206 Expressing Tumor-Associated M2-like Macrophages Using Mannose-Conjugated Antibiofouling Magnetic Iron Oxide Nanoparticles

Although tumor-associated macrophages (TAMs) have been shown to promote cancer progression, their roles in tumor development and resistance to therapy remain to be fully understood, mainly because of the lack of a good approach to evaluate the dynamic changes of heterogeneous macrophages in their residing microenvironment. Here, we report an approach of using antibiofouling PEG-b-AGE polymer-coated iron oxide nanoparticles (IONPs) for targeted imaging of mannose receptor (CD206)-expressing M2-like TAMs. Antibiofouling polymer coatings block non-specific phagocytosis of IONPs by different cells but enable ligand-mediated CD206⁺ M2-like macrophage targeting after surface functionalizing with mannose (Man-IONP). Costaining tissue sections of the 4T1 mouse mammary tumors using an anti-CD206 antibody and fluorescent dye (TRITC)-labeled Man-IONP showed 94.7 ± 4.5% colocalization of TRITC-Man-IONPs with the anti-CD206 antibody. At 48 h after intravenous (i.v.) injection of Man-IONPs, magnetic resonance imaging of mice bearing orthotopic 4T1 mammary tumors showed a significantly larger IONP-induced decrease of the transverse relaxation time (T ₂) in tumors with 29.4 ± 1.5 ms compared to 12.3 ± 3.6 ms in tumors that received non-targeted IONP probes (P < 0.001). Immunofluorescence-stained tumor tissue sections collected at 6, 18, and 24 h after i.v. administration of the nanoprobes revealed that Man-IONPs specifically targeted CD206⁺ M2-like macrophages in various tumor areas at all time points, while nonconjugated IONPs were absent in the tumor after 18 h. Thus, antibiofouling Man-IONPs demonstrated the capability of explicitly imaging CD206⁺ M2-like macrophages in vivo and potentials for investigating the dynamics of macrophages in the tumor microenvironment and delivering therapeutics targeting M2-like TAMs.

Imaging in Chronic Wound Diagnostics

Significance: Chronic wounds affect millions of patients worldwide, placing a huge burden on health care resources. Although significant progress has been made in the development of wound treatments, very few advances have been made in wound diagnosis. Recent Advances: Standard imaging methods like computed tomography, single-photon emission computed tomography, magnetic resonance imaging, terahertz imaging, and ultrasound imaging have been widely employed in wound diagnostics. A number of noninvasive optical imaging modalities like optical coherence tomography, near-infrared spectroscopy, laser Doppler imaging, spatial frequency domain imaging, digital camera imaging, and thermal and fluorescence imaging have emerged over the years. Critical Issues: While standard diagnostic wound imaging modalities provide valuable information, they cannot account for dynamic changes in the wound environment. In addition, they lack the capability to predict the healing outcome. Thus, there remains a pressing need for more efficient methods that can not only indicate the current state of the wound but also help determine whether the wound is on track to heal normally. Future Directions: Many imaging probes have been fabricated and shown to provide real-time assessment of tissue microenvironment and inflammatory responses in vivo. These probes have been demonstrated to noninvasively detect various changes in the wound environment, which include tissue pH, reactive oxygen species, fibrin deposition, matrix metalloproteinase production, and macrophage accumulation. This review summarizes the creation of these probes and their potential implications in wound monitoring.

Chemokine releasing particle implants for trapping circulating prostate cancer cells

Prostate cancer (PCa) is the most prevalent cancer in U.S. men and many other countries. Although primary PCa can be controlled with surgery or radiation, treatment options of preventing metastatic PCa are still limited. To develop a new treatment of eradicating metastatic PCa, we have created an injectable cancer trap that can actively recruit cancer cells in bloodstream. The cancer trap is composed of hyaluronic acid microparticles that have good cell and tissue compatibility and can extend the release of chemokines to 4 days in vitro. We find that erythropoietin (EPO) and stromal derived factor-1α can attract PCa in vitro. Animal results show that EPO-releasing cancer trap attracted large number of circulating PCa and significantly reduced cancer spreading to other organs compared with controls. These results support that cancer trap may serve as a unique device to sequester circulating PCa cells and subsequently reduce distant metastasis.

Screening for new macrophage therapeutics

Myeloid derived macrophages play a key role in many human diseases, and their therapeutic modulation via pharmacological means is receiving considerable attention. Of particular interest is the fact that these cells are i) dynamic phenotypes well suited to therapeutic manipulation and ii) phagocytic, allowing them to be efficiently targeted with nanoformulations. However, it is important to consider that macrophages represent heterogeneous populations of subtypes with often competing biological behaviors and functions. In order to develop next generation therapeutics, it is therefore essential to screen for biological effects through a combination of in vitro and in vivo assays. Here, we review the state-of-the-art techniques, including both cell based screens and in vivo imaging tools that have been developed for assessment of macrophage phenotype. We conclude with a forward-looking perspective on the growing need for noninvasive macrophage assessment and laboratory assays to be put into clinical practice and the potential broader impact of myeloid-targeted therapeutics.

Mechanical Strength, Biodegradation, and in Vitro and in Vivo Biocompatibility of Zn Biomaterials

Zn-based biomaterials have emerged as promising new types of bioresorbable metallics applicable to orthopedic devices, cardiovascular stents, and other medical applications recently. Compared to other degradable metallic biomaterials (i.e., Mg- or Fe-based), Zn biomaterials have a more appropriate corrosion rate without hydrogen gas evolution. Here, we evaluated the potential of Zn-based metallics as medical implants, both in vitro and in vivo, alongside a standard benchmark Mg alloy, AZ31. The mechanical properties of the pure Zn were not strong enough but were significantly enhanced (microhardness > 70 kg/mm², strength > 220 MPa, elongation > 15%) after alloying with Sr or Mg (1.5 at. %), surpassing the minimal design criteria for load-bearing device applications. The corrosion rate of Zn-based biomaterials was about 0.4 mm/year, significantly slower than that of AZ31. The measured cell viability and proliferation of three different human primary cells fared better for Zn-based biomaterials than AZ31 using both direct and indirect culture methods. Platelet adhesion and activation on Zn-based materials were minimal, significantly less than on AZ31. The hemolysis ratio of red cells (<0.5%) after incubation with Zn-based materials was also well below the ISO standard of 5%. Moreover, Zn-based biomaterials promoted stem cell differentiation to induce the extracellular matrix mineralization process. In addition, in vivo animal testing using subcutaneous, bone, and vascular implantations revealed that the acute toxicity and immune response of Zn-based biomaterials were minimal/moderate, comparable to that of AZ31. No extensive cell death and foreign body reactions were observed. Taken together, Zn-based biomaterials may have a great potential as promising candidates for medical implants.

Discovering Macrophage Functions Using In Vivo Optical Imaging Techniques

Macrophages are an important component of host defense and inflammation and play a pivotal role in immune regulation, tissue remodeling, and metabolic regulation. Since macrophages are ubiquitous in human bodies and have versatile physiological functions, they are involved in virtually every disease, including cancer, diabetes, multiple sclerosis, and atherosclerosis. Molecular biological and histological methods have provided critical information on macrophage biology. However, many in vivo dynamic behaviors of macrophages are poorly understood and yet to be discovered. A better understanding of macrophage functions and dynamics in pathogenesis will open new opportunities for better diagnosis, prognostic assessment, and therapeutic intervention. In this article, we will review the advances in macrophage tracking and analysis with in vivo optical imaging in the context of different diseases. Moreover, this review will cover the challenges and solutions for optical imaging techniques during macrophage intravital imaging.

Influence of scaffold design on host immune and stem cell responses

The combined culture of isolated stem cells in tissue engineering scaffolds represents a popular strategy for the regeneration of specialized tissues. Despite of improved outcomes in some tissues, this stem cell-seeded tissue engineering strategy has not led to significant tissue regeneration as expected. The lower-than-expected outcome may be caused by overwhelming immune responses to scaffold materials and poor survival of seeded stem cells following implantation. This review is aimed at summarizing the success and failure of this strategy and also shedding some light on new directions to design scaffolds for promoting regenerative responses via autologous stem cells. The first half of this review summarizes the influence of scaffold physical and chemical properties on immune cell responses to scaffold implants. The second half focuses on the influence of scaffold design to alter immune and stem cell responses for achieving desirable tissue regeneration.

Ethylene Glycol - Polyethylene Glycol (EG-PEG) Mixtures: Infrared Spectra Wavelet Cross-Correlation Analysis

Infrared spectra were collected on mixtures of ethylene glycol (EG) and polyethylene glycol 600 (PEG600) as a function of weight fraction from pure EG to pure PEG600. In this paper, it will be shown that while the OH vibrational contribution drastically reduces its center frequency from 3450 cm^-1 to 3300 cm^-1 in the weight fraction range 0-25%, the displacement of the mixture spectral features of the mixtures from ideal behavior, i.e., in the absence of interaction, shows the presence of a non-ideal mixing process. Furthermore, wavelet cross-correlation analysis of the registered pairs of spectra and of the intramolecular O-H stretching contributions reveals how the addition of a small amount of pure EG to PEG600 dramatically influences the structural properties of the polymeric matrix, owing to an increase the intermolecular connectivity. In particular, the wavelet cross-correlation parameters, evaluated between each pair of the registered data as a function of weight fraction, in a linear-logarithmic plot, reveals an inflection point for a weight fraction of about 25% of EG, which confirms that, within the three-dimensional networks of hydrogen-bonded EG-PEG600 molecules, a key role is played by EG in determining an increase in the hydrogen-bond network density.

H2O2-Depleting and O2-Generating Selenium Nanoparticles for Fluorescence Imaging and Photodynamic Treatment of Proinflammatory-Activated Macrophages

Macrophages have a pivotal role in chronic inflammatory diseases (CIDs), so imaging and controlling activated macrophage is critical for detecting and reducing chronic inflammation. In this study, photodynamic selenium nanoparticles (SeNPs) with photosensitive and macrophage-targeting bilayers were developed. The first layer of the photosensitive macromolecule was composed of a conjugate of a photosensitizer (rose bengal, RB) and a thiolated chitosan (chitosan-glutathione), resulting in a plasmonic coupling-induced red shift and broadening of RB absorption bands with increased absorption intensity. Electron paramagnetic resonance (EPR) and diphenylanthracene (DPA) quenching studies revealed that the SeNPs that were coated with the photosensitive layer were more effective than RB alone in producing singlet oxygen (¹O₂) under photoirradiation. The second layer of the activated macrophage-targetable macromolecule was synthesized by conjugation of hyaluronic acid with folic acid using an ethylenediamine linker. Proinflammatory-activated macrophages rapidly internalized the SeNPs that were covered with the targeting ligand, exhibiting a much stronger fluorescence signal of the SeNPs than did the nonactivated macrophages. Since proinflammatory-activated macrophage was known to generate a substantial amount of H₂O₂ while the inflamed site generally caused inflammation-associated tissue hypoxia, the SeNPs were further modified with O₂ self-sufficient function for photodynamic therapy. Catalase was immobilized on the SeNPs by the formation of disulfide bonds. Intracellular reduction of disulfide bonds induced the subsequent release of catalase, which catalyzed the decomposition of H₂O₂. The H₂O₂-depleting and O₂-generating photodynamic SeNPs efficiently killed activated macrophages and quenched the intracellular H₂O₂ and NO that are associated with inflammation. The SeNPs may have potential as a theranostic nanomaterial to image and control the activation of macrophages.

Directing immunomodulation using biomaterials for endogenous regeneration

Stem cell therapy and tissue engineering hold considerable potential for innovative and transformative strategies to repair damaged tissue form and function. Although many approaches are adopting ex vivo expanded cells for transplantation, an alternative is to manipulate the biomaterial-host interactions that recruit the patients' own stem cells endogenously for regeneration. There are several considerations in targeting the biomaterial-host interactions therapeutically, not the least of which is the biomimetic design of extracellular matrix (ECM)-mimicking materials and the administration of navigation cues and small molecules that target specific aspects of the native healing cascades to stimulate homing of endogenous stem cells and, thereafter, their expansion and differentiation. A sequence of coordinated interactions between the local niche cells and implanted biomaterials offers signals and sign posts that may instruct the cells traveling toward the injured tissues. Furthermore, stem cell function is critically influenced by extrinsic signals provided by the niche as well as by the implanted biomaterials. Novel strategies harnessing growth factors and immunological cues to design materials not only can modulate the behavior of stem cells but also can alter innate and adaptive immunity in a controlled manner. We envisage that successful and safe endogenous regeneration will involve at least three aspects, i.e., homing of sufficient stem cells, controlling cell fate determination, and blunting host immune responses to outside biomaterial devices. Improving our understanding of the biological and physicochemical signals of biomimetic biomaterials that govern immunomodulation for in situ tissue regeneration, particularly context-dependent macrophage (Mφ) polarization, will lead to a concurrent improvement in clinical outcomes.

Extended culture of macrophages from different sources and maturation results in a common M2 phenotype

Inflammatory responses to biomaterials heavily influence the environment surrounding implanted devices, often producing foreign-body reactions. The macrophage is a key immunomodulatory cell type consistently associated with implanted biomaterials and routinely used in short-term in vitro cell studies of biomaterials aiming to reproduce host responses. Inconsistencies within these studies, including differently sourced cells, different durations of culture, and assessment of different activation markers, lead to many conflicting results in vitro that confound consistency and conclusions. We hypothesize that different experimentally popular monocyte-macrophage cell types have intrinsic in vitro culture-specific differences that yield conflicting results. Recent studies demonstrate changes in cultured macrophage cytokine expression over time, leading to the hypothesis that changes in macrophage phenotype also occur in response to extended culture. Here, macrophage cells of different transformed and primary-derived origins were cultured for 21 days on model polymer biomaterials. Cell type-based differences in morphology and cytokine/chemokine expression as well as changes in cell surface biomarkers associated with differentiation stage, activation state, and adhesion were compared. Results reflect consistent macrophage development toward an M2 phenotype via up-regulation of the macrophage mannose receptor for all cell types following 21-day extended culture. Significantly, implanted biomaterials experiencing the foreign-body response and encapsulation in vivo often elicit a shift toward an analogous M2 macrophage phenotype. In vitro "default" of macrophage cultures, regardless of lineage, to this M2 state in the presence of biomaterials at long culture periods is not recognized, but has important implications to in vitro modeling of in vivo host response.