The effect of CD47 modified polymer surfaces on inflammatory cell attachment and activation

Formation and biological activities of foreign body giant cells in response to biomaterials

The integration of biomaterials in medical applications triggers the foreign body response (FBR), a multi-stage immune reaction characterized by the formation of foreign body giant cells (FBGCs). Originating from the fusion of monocyte/macrophage lineage cells, FBGCs are pivotal participants during tissue-material interactions. This review provides an in-depth examination of the molecular processes during FBGC formation, highlighting signaling pathways and fusion mediators in response to both exogenous and endogenous stimuli. Moreover, a wide range of material-specific characteristics, such as surface chemical and physical properties, has been proven to influence the fusion of macrophages into FBGCs. Multifaceted biological activities of FBGCs are also explored, with emphasis on their phagocytic capabilities and extracellular secretory functions, which profoundly affect the vascularization, degradation, and encapsulation of the biomaterials. This review further elucidates the heterogeneity of FBGCs and their diverse roles during FBR, as demonstrated by their distinct behaviors in response to different materials. By presenting a comprehensive understanding of FBGCs, this review intends to provide strategies and insights into optimizing biocompatibility and the therapeutic potential of biomaterials for enhanced stability and efficacy in clinical applications. STATEMENT OF SIGNIFICANCE: As a hallmark of the foreign body response (FBR), foreign body giant cells (FBGCs) significantly impact the success of implantable biomaterials, potentially leading to complications such as chronic inflammation, fibrosis, and device failure. Understanding the role of FBGCs and modulating their responses are vital for successful material applications. This review provides a comprehensive overview of the molecules and signaling pathways guiding macrophage fusion into FBGCs. By elucidating the physical and chemical properties of materials inducing distinct levels of FBGCs, potential strategies of materials in modulating FBGC formation are investigated. Additionally, the biological activities of FBGCs and their heterogeneity in responses to different material categories in vivo are highlighted in this review, offering crucial insights for improving the biocompatibility and efficacy of biomaterials.

Attachment of Fibrinogen on Ion Beam Treated Polyurethane

Protein-stable coverage of the artificial implant is a key problem for biocompatibility. In the present study, a protein layer was attached covalently to a polyurethane surface treated by an ion beam. A plasma system consisting of a vacuum chamber (0.8 Pa pressure) with a high voltage electrode powered by a short pulse (20 μS pulse duration and 200 Hz pulse repetition) generator was designed. Polyurethane with a formulation certified as a material for medical implants was treated by nitrogen ions with an energy of 20 keV and 5 × 1014-1016 ions/cm2 fluence range. Wettability measurements, X-ray photoelectron, Raman, Fourier transform infrared attenuated total reflection, and ellipsometry spectra showed a significant change in the structure of the surface layer of the treated polyurethane. The surface of the treated polyurethane contained a carbonised layer containing condensed aromatic clusters with terminal free radicals. The surface energy of polyurethane surface increased from 33 to 65 mJ/m2. The treated polyurethane surface became capable of adsorbing and chemically binding protein (fibrinogen). The designed system for ion beam treatment can be used for surface activation of biomedical polymer devices, where a total protein coverage is required.

Covalently grafted human serum albumin coating mitigates the foreign body response against silicone implants in mice

Implantable biomaterials and biosensors are integral components of modern medical systems but often encounter hindrances due to the foreign body response (FBR). Herein, we report an albumin coating strategy aimed at addressing this challenge. Using a facile and scalable silane coupling strategy, human serum albumin (HSA) is covalently grafted to the surface of polydimethylsiloxane (PDMS) implants. This covalently grafted albumin coating remains stable and resistant to displacement by other proteins. Notably, the PDMS with covalently grafted HSA strongly resists the fibrotic capsule formation following a 180-day subcutaneous implantation in C57BL/6 mice. Furthermore, the albumin coating led to reduced recruitment of macrophages and triggered a mild immune activation pattern. Exploration of albumin coatings sourced from various mammalian species has shown that only HSA exhibited a promising anti-FBR effect. The albumin coating method reported here holds the potential to improve and extend the function of silicone-based implants by mitigating the host responses to subcutaneously implanted biomaterials.

Hypercholesterolemia exacerbates in-stent restenosis in rabbits: Studies of the mitigating effect of stent surface modification with a CD47-derived peptide

BACKGROUND AND AIMS

Hypercholesterolemia (HC) has previously been shown to augment the restenotic response in animal models and humans. However, the mechanistic aspects of in-stent restenosis (ISR) on a hypercholesterolemic background, including potential augmentation of systemic and local inflammation precipitated by HC, are not completely understood. CD47 is a transmembrane protein known to abort crucial inflammatory pathways. Our studies have examined the interrelation between HC, inflammation, and ISR and investigated the therapeutic potential of stents coated with a CD47-derived peptide (pepCD47) in the hypercholesterolemic rabbit model.

METHODS

PepCD47 was immobilized on metal foils and stents using polybisphosphonate coordination chemistry and pyridyldithio/thiol conjugation. Cytokine expression in buffy coat-derived cells cultured over bare metal (BM) and pepCD47-derivatized foils demonstrated an M2/M1 macrophage shift with pepCD47 coating. HC and normocholesterolemic (NC) rabbit cohorts underwent bilateral implantation of BM and pepCD47 stents (HC) or BM stents only (NC) in the iliac location.

RESULTS

A 40 % inhibition of cell attachment to pepCD47-modified compared to BM surfaces was observed. HC increased neointimal growth at 4 weeks post BM stenting. These untoward outcomes were mitigated in hypercholesterolemic rabbits treated with pepCD47-derivatized stents. Compared to NC animals, inflammatory cytokine immunopositivity and macrophage infiltration of peri-strut areas increased in HC animals and were attenuated in HC rabbits treated with pepCD47 stents.

CONCLUSIONS

Augmented inflammatory responses underlie severe ISR morphology in hypercholesterolemic rabbits. Blockage of initial platelet and leukocyte attachment to stent struts through CD47 functionalization of stents mitigates the pro-restenotic effects of hypercholesterolemia.

Nanoparticle delivery through the BBB in central nervous system tuberculosis

Recent advances in Nanotechnology have revolutionized the production of materials for biomedical applications. Nowadays, there is a plethora of nanomaterials with potential for use towards improvement of human health. On the other hand, very little is known about how these materials interact with biological systems, especially at the nanoscale level, mainly because of the lack of specific methods to probe these interactions. In this review, we will analytically describe the journey of nanoparticles (NPs) through the brain, starting from the very first moment upon injection. We will preliminarily provide a brief overlook of the physicochemical properties of NPs. Then, we will discuss how these NPs interact with the body compartments and biological barriers, before reaching the blood-brain barrier (BBB), the last gate guarding the brain. Particular attention will be paid to the interaction with the biomolecular, the bio-mesoscopic, the (blood) cellular, and the tissue barriers, with a focus on the BBB. This will be framed in the context of brain infections, especially considering central nervous system tuberculosis (CNS-TB), which is one of the most devastating forms of human mycobacterial infections. The final aim of this review is not a collection, nor a list, of current literature data, as it provides the readers with the analytical tools and guidelines for the design of effective and rational NPs for delivery in the infected brain.

Human CD47-Derived Cyclic Peptides Enhance Engulfment of mAb-Targeted Melanoma by Primary Macrophages

CD47 on healthy cells, cancer cells, and even engineered particles can inhibit phagocytic clearance by binding SIRPα on macrophages. To mimic and modulate this interaction with peptides that could be used as soluble antagonists or potentially as bioconjugates to surfaces, we made cyclic "nano-Self" peptides based on the key interaction loop of human CD47. Melanoma cells were studied as a standard preclinical cancer model and were antibody-opsonized to adhere to and activate engulfment by primary mouse macrophages. Phagocytosis in the presence of soluble peptides showed cyclic > wildtype > scrambled activity, with the same trend observed with human cells. Opsonized cells that were not engulfed adhered tightly to macrophages, with opposite trends to phagocytosis. Peptide activity is nonetheless higher in human versus mouse assays, consistent with species differences in CD47-SIRPα. Small peptides thus function as soluble antagonists of a major macrophage checkpoint.

Suppressing or Enhancing Macrophage Engulfment through the Use of CD47 and Related Peptides

Foreign particles and microbes are rapidly cleared by macrophages in vivo, although many key aspects of uptake mechanisms remain unclear. "Self" cells express CD47 which functions as an anti-phagocytic ligand for SIRPα on macrophages, particularly when pro-phagocytic ligands such as antibodies are displayed in parallel. Here, we review CD47 and related "Self" peptides as modulators of macrophage uptake. Nanoparticles conjugated with either CD47 or peptides derived from its SIRPα binding site can suppress phagocytic uptake by macrophages in vitro and in vivo, with similar findings for CD47-displaying viruses. Drugs, dyes, and genes as payloads thus show increased delivery to targeted cells. On the other hand, CD47 expression by cancer cells enables such cells to evade macrophages and immune surveillance. This has motivated development of soluble antagonists to CD47-SIRPα, ranging from blocking antibodies in the clinic to synthetic peptides in preclinical models. CD47 and peptides are thus emerging as dual-use phagocytosis modulators against diseases.

Applications of Extracellular Vesicles in Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a localized expansion of the abdominal aorta which can lead to lethal complication as the rupture of aortic wall. Currently there is still neither competent method to predict the impending rupture of aneurysm, nor effective treatment to arrest the progression of small and asymptomatic aneurysms. Accumulating evidence has confirmed the crucial role of extracellular vesicles (EVs) in the pathological course of AAA, acting as important mediators of intercellular communication. Given the advantages of intrinsic targeting properties, lower toxicity and fair stability, EVs show great potential to serve as biomarkers, therapeutic agents and drug delivery carriers. However, EV therapies still face several major challenges before they can be applied clinically, including off-target effect, low accumulation rate and rapid clearance by mononuclear phagocyte system. In this review, we first illustrate the roles of EV in the pathological process of AAA and evaluate its possible clinical applications. We also identify present challenges for EV applications, highlight different strategies of EV engineering and constructions of EV-like nanoparticles, including EV display technology and membrane hybrid technology. These leading-edge techniques have been recently employed in multiple cardiovascular diseases and their promising application in the field of AAA is discussed.

Less phagocytosis of viral vectors by tethering with CD47 ectodomain

Many viral vectors, which are effective when administrated in situ, lack efficacy when delivered intravenously. The key reason for this is the rapid clearance of the viruses from the blood circulation via the immune system before they reach target sites. Therefore, avoiding their clearance by the immune system is essential. In this study, lentiviral vectors were tethered with the ectodomain of self-marker protein CD47 to suppress phagocytosis via interacting with SIRPα on the outer membrane of macrophage cells. CD47 ectodomain and core-streptavidin fusion gene (CD47ED-coreSA) was constructed into pET-30a(+) plasmid and transformed into Lemo21 (DE3) competent E. coli cells. The expressed CD47ED-coreSA chimeric protein was purified by cobalt-nitrilotriacetate affinity column and characterized by SDS-PAGE and western blot. The purified chimeric protein was anchored on biotinylated lentivirus via biotin-streptavidin binding. The CD47ED-capped lentiviruses encoding GFP were used to infect J774A.1 macrophage cells to assess the impact on phagocytosis. Our results showed that the overexpressed CD47ED-coreSA chimeric protein was purified and bound on the surface of biotinylated lentivirus which was confirmed via immunoblotting assay. The process to produce biotinylated lentivirus did not affect native viral infectivity. It was shown that the level of GFP expression in J774A.1 macrophages transduced with CD47ED-lentiviruses was threefold lower in comparison to control lentiviruses, indicating an antiphagocytic effect triggered by the interaction of CD47ED and SIRPα. Through the test of blocking antibodies against CD47ED and/or SIRPα, it was confirmed that the phagocytosis inhibition was mediated through the CD47ED-SIRPα axis signaling. In conclusion, surface immobilization of CD47ED on lentiviral vectors inhibits their phagocytosis by macrophages. The chimeric protein of CD47 ectodomain and core-streptavidin is effective in mediating the surface binding and endowing the lentiviral nanoparticles with the antiphagocytic property.

Biocompatibility Evolves: Phenomenology to Toxicology to Regeneration

The word "biocompatibility," is inconsistent with the observations of healing for so-called biocompatible biomaterials. The vast majority of the millions of medical implants in humans today, presumably "biocompatible," are walled off by a dense, avascular, crosslinked collagen capsule, hardly suggestive of life or compatibility. In contrast, one is now seeing examples of implant biomaterials that lead to a vascularized reconstruction of localized tissue, a biological reaction different from traditional biocompatible materials that generate a foreign body capsule. Both the encapsulated biomaterials and the reconstructive biomaterials qualify as "biocompatible" by present day measurements of biocompatibility. Yet, this new generation of materials would seem to heal "compatibly" with the living organism, where older biomaterials are isolated from the living organism by the dense capsule. This review/perspective article will explore this biocompatibility etymological conundrum by reviewing the history of the concepts around biocompatibility, today's standard methods for assessing biocompatibility, a contemporary view of the foreign body reaction and finally, a compendium of new biomaterials that heal without the foreign body capsule. A new definition of biocompatibility is offered here to address advances in biomaterials design leading to biomaterials that heal into the body in a facile manner.

Antifibrotic strategies for medical devices

A broad range of medical devices initiate an immune reaction known as the foreign body response (FBR) upon implantation. Here, collagen deposition at the surface of the implant occurs as a result of the FBR, ultimately leading to fibrous encapsulation and, in many cases, reduced function or failure of the device. Despite significant efforts, the prevention of fibrotic encapsulation has not been realized at this point in time. However, many next-generation medical technologies including cellular therapies, sensors and devices depend on the ability to modulate and control the FBR. For these technologies to become viable, significant advances must be made in understanding the underlying mechanism of this response as well as in the methods modulating this response. In this review, we highlight recent advances in the development of materials and coatings providing a reduced FBR and emphasize key characteristics of high-performing approaches. We also provide a detailed overview of the state-of-the-art in strategies relying on controlled drug release, the surface display of bioactive signals, materials-based approaches, and combinations of these approaches. Finally, we offer perspectives on future directions in this field.

Thermosensitive Exosome-Liposome Hybrid Nanoparticle-Mediated Chemoimmunotherapy for Improved Treatment of Metastatic Peritoneal Cancer

Metastatic peritoneal carcinoma (mPC) is a deadly disease without effective treatment. To improve treatment of this disease, a recently developed hyperthermic intraperitoneal chemotherapy (HIPEC) has emerged as the standard of care. However, the efficacy of this approach is limited by inefficient drug penetration and rapidly developed drug resistance. Herein, a nanotechnology approach is reported that is designed to improve drug delivery to mPC and to augment the efficacy of HIPEC through delivery of chemoimmunotherapy. First, the drug delivery efficiency of HIPEC is determined and it is found that chemotherapy agents cannot be efficiently delivered to large tumors nodules. To overcome the delivery hurdle, genetically engineered exosomes-thermosensitive liposomes hybrid NPs, or gETL NPs, are then synthesized, and it is demonstrated that the NPs after intravenous administration efficiently penetrates into mPC tumors and releases payloads at the hypothermia condition of HIPEC. Last, it is shown that, when granulocyte-macrophage colony-stimulating factor (GM-CSF) and docetaxel are co-delivered, gETL NPs effectively inhibit tumor development and the efficacy is enhanced when HIPEC is co-administered. The study provides a strategy to improve drug delivery to mPCs and offers a promising approach to improve treatment of the disease through combination of locoregional delivery of HIPEC and systemic delivery of chemoimmunotherapy via gETL NPs.

Mechanobiology of Macrophages: How Physical Factors Coregulate Macrophage Plasticity and Phagocytosis

In addition to their early-recognized functions in host defense and the clearance of apoptotic cell debris, macrophages play vital roles in tissue development, homeostasis, and repair. If misregulated, they steer the progression of many inflammatory diseases. Much progress has been made in understanding the mechanisms underlying macrophage signaling, transcriptomics, and proteomics, under physiological and pathological conditions. Yet, the detailed mechanisms that tune circulating monocytes/macrophages and tissue-resident macrophage polarization, differentiation, specification, and their functional plasticity remain elusive. We review how physical factors affect macrophage phenotype and function, including how they hunt for particles and pathogens, as well as the implications for phagocytosis, autophagy, and polarization from proinflammatory to prohealing phenotype. We further discuss how this knowledge can be harnessed in regenerative medicine and for the design of new drugs and immune-modulatory drug delivery systems, biomaterials, and tissue scaffolds.

Blockade of macrophage adhesion to CD200-treated polystyrene culture surface

CD200 is an anti-inflammatory transmembrane glycoprotein in the immunoglobulin superfamily. The interaction of CD200 and its receptor CD200R has shown to inhibit inflammatory response of myeloid cells to foreign materials. The purpose of this study is to create a CD200 immobilized biomaterial surface through polydopamine coating to suppress macrophage cell adhesion and reduce inflammatory cytokine secretion accordingly by macrophages. In this study, tissue-culture treated polystyrene (TCPS) surface was modified with biotin through polydopamine coating. Purified CD200-streptavidin fusion protein was then immobilized onto the biotinylated TCPS surface through the high affinity between biotin and streptavidin. Mouse J774A.1 macrophages were seeded on CD200-immobilized TCPS surface to evaluate the effect of CD200 on preventing macrophage attachment. The effects of CD200-immobilized TCPS surface on pro-inflammatory cytokine secretion from J774A.1 macrophages were measured by enzyme-linked immunosorbent assay. As a result, CD200-immobilized TCPS surface suppressed macrophage attachment for up to 9 hr. The level of IL-6 and TNF-α secreted from J774A.1 macrophages interacted with CD200-coated TCPS surface was reduced by 36.3% and 32.4%, respectively.

Development of an immunosuppressive camouflage-coating platform with nanocellulose and cell membrane vesicles

Biomedical devices trigger immune responses when implanted in the body, as they are treated as foreign bodies. To avoid inflammatory responses and enhance the biocompatibility of biomedical devices, advanced coating technology that can modulate immune responses is essential. As a part of the immune response in the body, autologous cells evade attack from macrophages using CD47 ligands that function as markers for self. Inspired by this self-recognition system, we developed a camouflage coating for biomaterial surfaces using cell membrane vesicles that could suppress inflammatory responses. In this study, we used monocyte-derived cell membrane vesicles expressing CD47 for coating nanocellulose-coated substrates. Our data showed that presentation of CD47 to macrophages elicited negative signal transduction for immunosuppression. Further, for coating, we used cell membrane vesicles and plant-derived nanofibers. We observed that the supporting layer of cellulose nanofibers physically fixed cell membrane vesicles and provided hydrophilic surfaces to the polystyrene substrate. Based on CD47 signaling, cell membrane vesicle coating suppressed the inflammatory responses of stimulated macrophages. Camouflaging biomaterial surfaces with cell-derived components might serve as an advanced coating platform to suppress inflammatory responses and enhance tissue integrity for biomedical devices after implantation.

Studies of combined NO-eluting/CD47-modified polyurethane surfaces for synergistic enhancement of biocompatibility

The blood compatibility of various intravascular (IV) devices (e.g., catheters, sensors, etc.) is compromised by activation of platelets that can cause thrombus formation and device failure. Such devices also carry a high risk of microbial infection. Recently, nitric oxide (NO) releasing polymers/devices have been proposed to reduce these clinical problems. CD47, a ubiquitously expressed transmembrane protein with proven anti-inflammation/anti-platelet properties when immobilized on polymeric surfaces, is a good candidate to complement NO release in both effectiveness and longevity. In this work, we successfully appended CD47 peptides (pepCD47) to the surface of biomedical grade polyurethane (PU) copolymers. SIRPα binding and THP-1 cell attachment experiments strongly suggested that the pepCD47 retains its biological properties when bound to PU films. In spite of the potentially high reactivity of NO toward various amino acid residues in CD47, the efficacy of surface-immobilized pepCD47 to prevent inflammatory cell attachment was not inhibited after being subjected to a high flux of NO for three days, demonstrating excellent compatibility of the two species. We further constructed a CD47 surface immobilized silicone tubing filled with NO releasing S-nitrosoglutathione/ascorbic acid (GSNO/AA) solution for synergistic biocompatibility evaluation. Via an ex vivo Chandler loop model, we demonstrate for the first time that NO release and CD47 modification could function synergistically at the blood/material interface and produce greatly enhanced anti-inflammatory/anti-platelet effects. This concept should be readily implementable to create a new generation of thromboresistant/antimicrobial implantable devices.

Stability and bioactivity of pepCD47 attachment on stainless steel surfaces

In-stent restenosis (ISR) and late stent thrombosis are the major complications associated with the use of metal stents and drug eluting stents respectively. Our lab previously investigated the use of peptide CD47 in improving biocompatibility of bare metal stents in a rat carotid stent model and our results demonstrated a significant reduction in platelet deposition and ISR. However, this study did not characterize the stability of the pepCD47 on metal surfaces post storage, sterilization and deployment. Thus, the objective of the present study was 1) to test the stability of the peptide post - storage, sterilization, exposure to shear and mechanical stress and 2) to begin to expand our current knowledge of pepCD47 coated metal surfaces into the preclinical large animal rabbit model. Our results show that the maximum immobilization density of pepCD47 on metal surfaces is approximately 350 ng/cm². 100% of the pepCD47 was retained on the metal surface post 24 weeks of storage at 4 °C, exposure to physiological shear stress, and mechanical stress of stent expansion. The bioactivity of the pepCD47 was found to be intact post 24 weeks of storage and ethylene oxide sterilization. Finally our ex vivo studies demonstrated that compared to bare metal the rabbit pepCD47 coated surfaces showed - 45% reduced platelet adhesion, a 10-fold decrease in platelet activation, and 93% endothelial cell retention. Thus, our data suggests that pepCD47 coating on metal surfaces is stable and rabbit pepCD47 shows promising preliminary results in preventing thrombosis and not inhibiting the growth of endothelial cells. STATEMENT OF SIGNIFICANCE: Biocompatibility of bare metal stents is a major challenge owing to the significantly high rates of in-stent restenosis. Previously we demonstrated that peptide CD47 functionalization improves the biocompatibility of bare metal stents in rat model. A similar trend was observed in our ex vivo studies where rabbit blood was perfused over the rabbit pepCD47 functionalized surfaces. These results provide valuable proof of concept data for future in vivo rabbit model studies. In addition, we investigated stability of the pepCD47 on metal surface and observed that pepCD47 coating is stable over time and resistant to industrially relevant pragmatic challenges.

Is CD47 a potentially promising therapeutic target in cardiovascular diseases? - Role of CD47 in cardiovascular diseases

CD47 (cluster of differentiation 47) is a ubiquitously expressed transmembrane protein that belongs to the immunoglobulin superfamily. CD47 is both a receptor for the matricellular protein thrombospondin-1 (TSP-1) and a ligand for signal-regulatory protein alpha (SIRPα). Suppression of CD47 activity enhances angiogenesis and blood flow, restores phagocytosis by macrophages, improves ischemic tissue survival, attenuates ischemia reperfusion injury, and reverses atherosclerotic plaque formation. In conclusion, these observations suggest a pathogenic role of CD47 in the development of cardiovascular diseases (CVDs) and indicate that CD47 might be a potentially promising molecular target for treating CVDs. Herein, we highlight the role of CD47 in the CVD pathogenesis and discuss the potential clinical application by targeting CD47 for treating CVDs.

Stealth functionalization of biomaterials and nanoparticles by CD47 mimicry

Polymeric biomaterials and nanoparticles (NPs) have shown a potential to be widely used for medical purposes. Functional limits of their biocompatibility depend on cellular and molecular responses between host and their artificial surfaces. Accordingly, medical devices of polymer biomaterials like endovascular stents, cardiopulmonary bypass circuits, and prostheses, may trigger inflammation or can be rejected by host due to the induction of immune responses. Furthermore, the main restriction to the use of NPs for medical purposes is their short in vivo circulation time because of their rapid clearance via the reticuloendothelial system. Various methods are under investigation to produce bioinert biomaterials and NPs. Currently, PEGylation and camouflaging are the most common approaches to enhance their biocompatibility. However, the disadvantages and limitations of these methods are leading to research new strategies. The CD47 molecule is well known as a widely expressed cellular surface receptor activating the transudction of the ''don't-eat-me'' signal. This review elaborates on the role of CD47 in the immune system and the application of CD47 mimicry peptides to produce bioinert biomaterials and NPs.

Bijel-templated implantable biomaterials for enhancing tissue integration and vascularization

Mitigation of the foreign body response (FBR) and successful tissue integration are essential to ensuring the longevity of implanted devices and biomaterials. The use of porous materials and coatings has been shown to have an impact, as the textured surfaces can mediate macrophage interactions with the implant and influence the FBR, and the pores can provide space for vascularization and tissue integration. In this study, we use a new class of implantable porous biomaterials templated from bicontinuous interfacially jammed emulsion gels (bijels), which offer a fully percolating, non-constricting porous network with a uniform pore diameter on the order of tens of micrometers, and surfaces with consistent curvature. We demonstrate that these unique morphological features, inherent to bijel-templated materials (BTMs), can enhance tissue integration and vascularization, and reduce the FBR. Cylindrical polyethylene glycol diacrylate (PEGDA) BTMs, along with PEGDA particle-templated materials (PTMs), and non-templated materials (NTMs), were implanted into the subcutaneous space of athymic nude mice. After 28 days, implants were retrieved and analyzed via histological techniques. Within BTMs, blood vessels of increased size and depth, changes in collagen deposition, and increased presence of pro-healing macrophages were observed compared to that of PTM and NTM implants. Bijel templating offers a new route to biomaterials that can improve the function and longevity of implantable devices. STATEMENT OF SIGNIFICANCE: All implanted biomaterials are subject to the foreign body response (FBR) which can have a detrimental effect on their efficacy. Altering the surface chemistry can decrease the FBR by limiting the amount of proteins adsorbed to the implant. This effect can be enhanced by including pores in the biomaterial to allow new tissue growth as the implant becomes integrated in the body. Here, we introduce a new class of self-assembled biomaterials comprising a fully penetrating, non-constricting pore phase with hyperbolic (saddle) surfaces for enhanced tissue integration. These unique morphological characteristics result in dense blood vessel formation and favorable tissue response properties demonstrated in a four-week implantation study.

Biomaterials: Been There, Done That, and Evolving into the Future

Biomaterials as we know them today had their origins in the late 1940s with off-the-shelf commercial polymers and metals. The evolution of materials for medical applications from these simple origins has been rapid and impactful. This review relates some of the early history; addresses concerns after two decades of development in the twenty-first century; and discusses how advanced technologies in both materials science and biology will address concerns, advance materials used at the biointerface, and improve outcomes for patients.

Stabilization of dry protein coatings with compatible solutes

Exposure of protein modified surfaces to air may be necessary in several applications. For example, air contact may be inevitable during the implantation of biomedical devices, for analysis of protein modified surfaces, or for sensor applications. Protein coatings are very sensitive to dehydration and can undergo significant and irreversible alterations of their conformations upon exposure to air. With the use of two compatible solutes from extremophilic bacteria, ectoine and hydroxyectoine, the authors were able to preserve the activity of dried protein monolayers for up to >24 h. The protective effect can be explained by the preferred exclusion model; i.e., the solutes trap a thin water layer around the protein, retaining an aqueous environment and preventing unfolding of the protein. Horseradish peroxidase (HRP) immobilized on compact TiO₂ was used as a model system. Structural differences between the compatible solute stabilized and unstabilized protein films, and between different solutes, were analyzed by static time-of-flight secondary ion mass spectrometry (ToF-SIMS). The biological activity difference observed in a colorimetric activity assay was correlated to changes in protein conformation by application of principal component analysis to the static ToF-SIMS data. Additionally, rehydration of the denatured HRP was observed in ToF-SIMS with an exposure of denatured protein coatings to ectoine and hydroxyectoine solutions.

Incorporation of a Ligand Peptide for Immune Inhibitory Receptor LAIR-1 on Biomaterial Surfaces Inhibits Macrophage Inflammatory Responses

Leukocyte-associated immunoglobulin-like receptor-1 (LAIR-1) is an inhibitory receptor broadly expressed on immune cells, with its ligands residing within the extracellular matrix protein collagen. In this study, surfaces are modified with a LAIR-1 ligand peptide (LP), and it is observed that macrophages cultured on LAIR-1 LP-conjugated surfaces exhibit significantly reduced secretion of inflammatory cytokines in response to proinflammatory stimuli that reflect an injured environment. These downregulated mediators include TNF-α, MIP-1α, MIP-1β, MIP-2, RANTES, and MIG. Knockdown of LAIR-1 using siRNA abrogates this inhibition of cytokine secretion, supporting the specificity of the inhibitory effect to this receptor. These results are the first to demonstrate that integration of LAIR-1 ligands with biomaterials could suppress inflammatory responses.

Co-coating of receptor-targeted drug nanocarriers with anti-phagocytic moieties enhances specific tissue uptake versus non-specific phagocytic clearance

Nanocarriers (NCs) help improve the performance of therapeutics, but their removal by phagocytes in the liver, spleen, tissues, etc. diminishes this potential. Although NC functionalization with polyethylene glycol (PEG) lowers interaction with phagocytes, it also reduces interactions with tissue cells. Coating NCs with CD47, a protein expressed by body cells to avoid phagocytic removal, offers an alternative. Previous studies showed that coating CD47 on non-targeted NCs reduces phagocytosis, but whether this alters binding and endocytosis of actively-targeted NCs remains unknown. To evaluate this, we used polymer NCs targeted to ICAM-1, a receptor overexpressed in many diseases. Co-coating of CD47 on anti-ICAM NCs reduced macrophage phagocytosis by ∼50% for up to 24 h, while increasing endothelial-cell targeting by ∼87% over control anti-ICAM/IgG NCs. Anti-ICAM/CD47 NCs were endocytosed via the CAM-mediated pathway with efficiency similar (0.99-fold) to anti-ICAM/IgG NCs. Comparable outcomes were observed for NCs targeted to PECAM-1 or transferrin receptor, suggesting broad applicability. When injected in mice, anti-ICAM/CD47 NCs reduced liver and spleen uptake by ∼30-50% and increased lung targeting by ∼2-fold (∼10-fold over IgG NCs). Therefore, co-coating NCs with CD47 and targeting moieties reduces macrophage phagocytosis and improves targeted uptake. This strategy may significantly improve the efficacy of targeted drug NCs.

CD47-retargeted oncolytic adenovirus armed with melanoma differentiation-associated gene-7/interleukin-24 suppresses in vivo leukemia cell growth

Our previous studies have suggested that harboring a soluble coxsackie-adenovirus receptor-ligand (sCAR-ligand) fusion protein expression cassette in the viral genome may provide a universal method to redirect oncolytic adenoviruses to various membrane receptors on cancer cells resisting to serotype 5 adenovirus infection. We report here a novel oncolytic adenovirus vector redirected to CD47+ leukemia cells though carrying a sCAR-4N1 expression cassette in the viral genome, forming Ad.4N1, in which 4N1 represents the C-terminal CD47-binding domain of thrombospondin-1. The infection and cytotoxicity of Ad.4N1 in leukemia cells were determined to be mediated by the 4N1-CD47 interaction. Ad.4N1 was further engineered to harbor a gene encoding melanoma differentiation-associated gene-7/interleukin-24 (mda-7/IL-24), forming Ad.4N1-IL24, which replicated dramatically faster than Ad.4N1, and elicited significantly enhanced antileukemia effect in vitro and in a HL60/Luc xenograft mouse model. Our data suggest that Ad.4N1 could act as a novel oncolytic adenovirus vector for CD47+ leukemia targeting gene transfer, and Ad.4N1 harboring anticancer genes may provide novel antileukemia agents.

Modulation of Immune Responses by Particulate Materials

Many biomaterials that are in both preclinical and clinical use are particulate in nature and there is a growing appreciation that the physicochemical properties of materials have a significant impact on their efficacy. The ability of particulates to modulate adaptive immune responses has been recognized for the past century but it is only in recent decades that a mechanistic understanding of how particulates can regulate these responses has emerged. It is now clear that particulate characteristics including size, charge, shape and porosity can influence the scale and nature of both the innate and adaptive immune responses. The potential to tailor biomaterials in order to regulate the type of innate immune response induced, offers significant opportunities in terms of designing systems with increased immune-mediated efficacy.

Receptor-targeted drug delivery: current perspective and challenges

Receptor-targeted drug delivery has been extensively explored for active targeting. However, the scarce clinical applications of such delivery systems highlight the implicit hurdles in development of such systems. These hurdles begin with lack of knowledge of differential expression of receptors, their accessibility and identification of newer receptors. Similarly, ligand-specific challenges range from proper choice of ligand and conjugation chemistry, to release of drug/delivery system from ligand. Finally, nanocarrier systems, which offer improved loading, biocompatibility and reduced premature degradation, also face multiple challenges. This review focuses on understanding these challenges, and means to overcome such challenges to develop efficient, targeted drug-delivery systems.

The use of CD47-modified biomaterials to mitigate the immune response

Addressing the aberrant interactions between immune cells and biomaterials represents an unmet need in biomaterial research. Although progress has been made in the development of bioinert coatings, identifying and targeting relevant cellular and molecular pathways can provide additional therapeutic strategies to address this major healthcare concern. To that end, we describe the immune inhibitory motif, receptor-ligand pairing of signal regulatory protein alpha and its cognate ligand CD47 as a potential signaling pathway to enhance biocompatibility. The goals of this article are to detail the known roles of CD47-signal regulatory protein alpha signal transduction pathway and to describe how immobilized CD47 can be used to mitigate the immune response to biomaterials. Current applications of CD47-modified biomaterials will also be discussed herein.

Enhanced biocompatibility of CD47-functionalized vascular stents

The effectiveness of endovascular stents is hindered by in-stent restenosis (ISR), a secondary re-obstruction of treated arteries due to unresolved inflammation and activation of smooth muscle cells in the arterial wall. We previously demonstrated that immobilized CD47, a ubiquitously expressed transmembrane protein with an established role in immune evasion, can confer biocompatibility when appended to polymeric surfaces. In present studies, we test the hypothesis that CD47 immobilized onto metallic surfaces of stents can effectively inhibit the inflammatory response thus mitigating ISR. Recombinant CD47 (recCD47) or a peptide sequence corresponding to the Ig domain of CD47 (pepCD47), were attached to the surfaces of both 316L-grade stainless steel foils and stents using bisphosphonate coordination chemistry and thiol-based conjugation reactions to assess the anti-inflammatory properties of CD47-functionalized surfaces. Initial in vitro and ex vivo analysis demonstrated that both recCD47 and pepCD47 significantly reduced inflammatory cell attachment to steel surfaces without impeding on endothelial cell retention and expansion. Using a rat carotid stent model, we showed that pepCD47-functionalized stents prevented fibrin and platelet thrombus deposition, inhibited inflammatory cell attachment, and reduced restenosis by 30%. It is concluded that CD47-modified stent surfaces mitigate platelet and inflammatory cell attachment, thereby disrupting ISR pathophysiology.

Interplay between Cellular and Molecular Inflammatory Mediators in Lung Cancer

Inflammation is a component of the tumor microenvironment and represents the 7th hallmark of cancer. Chronic inflammation plays a critical role in tumorigenesis. Tumor infiltrating inflammatory cells mediate processes associated with progression, immune suppression, promotion of neoangiogenesis and lymphangiogenesis, remodeling of extracellular matrix, invasion and metastasis, and, lastly, the inhibition of vaccine-induced antitumor T cell response. Accumulating evidence indicates a critical role of myeloid cells in the pathophysiology of human cancers. In contrast to the well-characterized tumor-associated macrophages (TAMs), the significance of granulocytes in cancer has only recently begun to emerge with the characterization of tumor-associated neutrophils (TANs). Recent studies show the importance of CD47 in the interaction with macrophages inhibiting phagocytosis and promoting the migration of neutrophils, increasing inflammation which can lead to recurrence and progression in lung cancer. Currently, therapies are targeted towards blocking CD47 and enhancing macrophage-mediated phagocytosis. However, antibody-based therapies may have adverse effects that limit its use.

Healing with medical implants: The body battles back

Disease or inflammation can have substantial impact on biomaterials performance and the loosely defined term "biocompatibility" (Oliva et al., this issue).

Biomolecular strategies to modulate the macrophage response to implanted materials

The material-induced foreign body response is a major challenge for implanted medical devices. This review highlights recent developments in biomimetic approaches to create biomaterials that mitigate the host response to biomaterials. Specifically, we will describe strategies in which biomaterials are decorated with endogenously expressed biomolecules that naturally modulate the function of immune cells. These include molecules that directly bind to and interact with immune cells, as well as molecules that control complement activation or thrombosis and indirectly modulate immune cell function. We provide perspective on how these approaches may impact the design of materials for medical devices and tissue engineering.

Thiol click modification of cyclic disulfide containing biodegradable polyurethane urea elastomers

Although the thiol click reaction is an attractive tool for postpolymerization modification of thiolmers, thiol groups are easily oxidized, limiting the potential for covalent immobilization of bioactive molecules. In this study, a series of biodegradable polyurethane elastomers incorporating stable cyclic disulfide groups was developed and characterized. These poly(ester urethane)urea (PEUU-SS) polymers were based on polycaprolactone diol (PCL), oxidized dl-dithiothreitol (O-DTT), lysine diisocyanate (LDI), or butyl diisocyanate (BDI), with chain extension by putrescine. The ratio of O-DTT:PCL was altered to investigate different levels of potential functionalization. PEG acrylate was employed to study the mechanism and availability of both bulk and surface click modification of PEUU-SS polymers. All synthesized PEUU-SS polymers were elastic with breaking strengths of 38-45 MPa, while the PEUU-SS(LDI) polymers were more amorphous, possessing lower moduli and relatively small permanent deformations versus PEUU-SS(BDI) polymers. Variable bulk click modification of PEUU-SS(LDI) polymers was achieved by controlling the amount of reduction reagent, and rapid reaction rates occurred using a one-pot, two-step process. Likewise, surface click reaction could be carried out quickly under mild, aqueous conditions. Furthermore, a maleimide-modified affinity peptide (TPS) was successfully clicked on the surface of an electrospun PEUU-SS(BDI) fibrous sheet, which improved endothelial progenitor cell adhesion versus corresponding unmodified films. The cyclic disulfide containing biodegradable polyurethanes described provide an option for cardiovascular and other soft tissue regenerative medicine applications where a temporary, elastic scaffold with designed biofunctionality from a relatively simple click chemistry approach is desired.

Strategies for delivery of therapeutics into the central nervous system for treatment of lysosomal storage disorders

Lysosomal storage disorders (LSDs) are a group of about fifty life-threatening conditions caused by genetic defects affecting lysosomal components. The underscoring molecular deficiency leads to widespread cellular dysfunction through most tissues in the body, including peripheral organs and the central nervous system (CNS). Efforts during the last few decades have rendered a remarkable advance regarding our knowledge, medical awareness, and early detection of these genetic defects, as well as development of several treatment modalities. Clinical and experimental strategies encompassing enzyme replacement, gene and cell therapies, substrate reduction, and chemical chaperones are showing considerable potential in attenuating the peripheral pathology. However, a major drawback has been encountered regarding the suboptimal impact of these approaches on the CNS pathology. Particular anatomical and biochemical constraints of this tissue pose a major obstacle to the delivery of therapeutics into the CNS. Approaches to overcome these obstacles include modalities of local administration, strategies to enhance the blood-CNS permeability, intranasal delivery, use of exosomes, and those exploiting targeting of transporters and transcytosis pathways in the endothelial lining. The later two approaches are being pursued at the time by coupling therapeutic agents to affinity moieties and drug delivery systems capable of targeting these natural transport routes. This approach is particularly promising, as using paths naturally active at this interface may render safe and effective delivery of LSD therapies into the CNS.

CD47 Enhances In Vivo Functionality of Artificial Antigen-Presenting Cells

PURPOSE

Artificial antigen-presenting cells, aAPC, have successfully been used to stimulate antigen-specific T-cell responses in vitro as well as in vivo. Although aAPC compare favorably with autologous dendritic cells in vitro, their effect in vivo might be diminished through rapid clearance by macrophages. Therefore, to prevent uptake and minimize clearance of aAPC by macrophages, thereby increasing in vivo functionality, we investigated the efficiency of "don't eat me" three-signal aAPC compared with classical two-signal aAPC.

EXPERIMENTAL DESIGN

To generate "don't eat me" aAPC, CD47 was additionally immobilized onto classical aAPC (aAPC(CD47+)). aAPC and aAPC(CD47+) were analyzed in in vitro human primary T-cell and macrophage cocultures. In vivo efficiency was compared in a NOD/SCID T-cell proliferation and a B16-SIY melanoma model.

RESULTS

This study demonstrates that aAPC(CD47+) in coculture with human macrophages show a CD47 concentration-dependent inhibition of phagocytosis, whereas their ability to generate and expand antigen-specific T cells was not affected. Furthermore, aAPC(CD47+)-generated T cells displayed equivalent killing abilities and polyfunctionality when compared with aAPC-generated T cells. In addition, in vivo studies demonstrated an enhanced stimulatory capacity and tumor inhibition of aAPC(CD47+) over normal aAPC in conjunction with diverging biodistribution in different organs.

CONCLUSIONS

Our data for the first time show that aAPC functionalized with CD47 maintain their stimulatory capacity in vitro and demonstrate enhanced in vivo efficiency. Thus, these next-generation aAPC(CD47+) have a unique potential to enhance the application of the aAPC technology for future immunotherapy approaches.

Nanocomposited silicone hydrogels with a laser-assisted surface modification for inhibiting the growth of bacterial biofilm

Compared to the commercial silicone catheters, the nanocomposited silicone hydrogel with a laser-assisted surface modification can reduce the growth of bacteria from 1.20 × 10⁶ CFU cm⁻² to 3.69 × 10⁵ CFU cm⁻², almost an order of magnitude.

Biodegradable poly(ester urethane)urea elastomers with variable amino content for subsequent functionalization with phosphorylcholine

While surface modification is well suited for imparting biomaterials with specific functionality for favorable cell interactions, the modification of degradable polymers would be expected to provide only temporary benefit. Bulk modification by incorporating pendant reactive groups for subsequent functionalization of biodegradable polymers would provide a more enduring approach. Towards this end, a series of biodegradable poly(ester urethane)urea elastomers with variable amino content (PEUU-NH2 polymers) were developed. Carboxylated phosphorycholine was synthesized and conjugated to the PEUU-NH2 polymers for subsequent bulk functionalization to generate PEUU-PC polymers. Synthesis was verified by proton nuclear magnetic resonance, X-ray photoelectron spectroscopy and attenuated total reflection Fourier transform infrared spectroscopy. The impact of amine incorporation and phosphorylcholine conjugation was shown on mechanical, thermal and degradation properties. Water absorption increased with increasing amine content, and further with PC conjugation. In wet conditions, tensile strength and initial modulus generally decreased with increasing hydrophilicity, but remained in the range of 5-30 MPa and 10-20 MPa, respectively. PC conjugation was associated with significantly reduced platelet adhesion in blood contact testing and the inhibition of rat vascular smooth muscle cell proliferation. These biodegradable PEUU-PC elastomers offer attractive properties for applications as non-thrombogenic, biodegradable coatings and for blood-contacting scaffold applications. Further, the PEUU-NH2 base polymers offer the potential to have multiple types of biofunctional groups conjugated onto the backbone to address a variety of design objectives.

Addressing the Inflammatory Response to Clinically Relevant Polymers by Manipulating the Host Response Using ITIM Domain-Containing Receptors

Tissue contacting surfaces of medical devices initiate a host inflammatory response, characterized by adsorption of blood proteins and inflammatory cells triggering the release of cytokines, reactive oxygen species (ROS) and reactive nitrogen species (RNS), in an attempt to clear or isolate the foreign object from the body. This normal host response contributes to device-associated pathophysiology and addressing device biocompatibility remains an unmet need. Although widespread attempts have been made to render the device surfaces unreactive, the establishment of a completely bioinert coating has been untenable and demonstrates the need to develop strategies based upon the molecular mechanisms that define the interaction between host cells and synthetic surfaces. In this review, we discuss a family of transmembrane receptors, known as immunoreceptor tyrosine-based inhibitory motif (ITIM)-containing receptors, which show promise as potential targets to address aberrant biocompatibility. These receptors repress the immune response and ensure that the intensity of an immune response is appropriate for the stimuli. Particular emphasis will be placed on the known ITIM-containing receptor, Signal Regulatory Protein Alpha (SIRPhα), and its cognate ligand CD47. In addition, this review will discuss the potential of other ITIM-containing proteins as targets for addressing the aberrant biocompatibility of polymeric biomaterials.

The use of the ex vivo Chandler Loop Apparatus to assess the biocompatibility of modified polymeric blood conduits

The foreign body reaction occurs when a synthetic surface is introduced to the body. It is characterized by adsorption of blood proteins and the subsequent attachment and activation of platelets, monocyte/macrophage adhesion, and inflammatory cell signaling events, leading to post-procedural complications. The Chandler Loop Apparatus is an experimental system that allows researchers to study the molecular and cellular interactions that occur when large volumes of blood are perfused over polymeric conduits. To that end, this apparatus has been used as an ex vivo model allowing the assessment of the anti-inflammatory properties of various polymer surface modifications. Our laboratory has shown that blood conduits, covalently modified via photoactivation chemistry with recombinant CD47, can confer biocompatibility to polymeric surfaces. Appending CD47 to polymeric surfaces could be an effective means to promote the efficacy of polymeric blood conduits. Herein is the methodology detailing the photoactivation chemistry used to append recombinant CD47 to clinically relevant polymeric blood conduits and the use of the Chandler Loop as an ex vivo experimental model to examine blood interactions with the CD47 modified and control conduits.

Vascular targeting of nanocarriers: perplexing aspects of the seemingly straightforward paradigm

Targeted nanomedicine holds promise to find clinical use in many medical areas. Endothelial cells that line the luminal surface of blood vessels represent a key target for treatment of inflammation, ischemia, thrombosis, stroke, and other neurological, cardiovascular, pulmonary, and oncological conditions. In other cases, the endothelium is a barrier for tissue penetration or a victim of adverse effects. Several endothelial surface markers including peptidases (e.g., ACE, APP, and APN) and adhesion molecules (e.g., ICAM-1 and PECAM) have been identified as key targets. Binding of nanocarriers to these molecules enables drug targeting and subsequent penetration into or across the endothelium, offering therapeutic effects that are unattainable by their nontargeted counterparts. We analyze diverse aspects of endothelial nanomedicine including (i) circulation and targeting of carriers with diverse geometries, (ii) multivalent interactions of carrier with endothelium, (iii) anchoring to multiple determinants, (iv) accessibility of binding sites and cellular response to their engagement, (v) role of cell phenotype and microenvironment in targeting, (vi) optimization of targeting by lowering carrier avidity, (vii) endocytosis of multivalent carriers via molecules not implicated in internalization of their ligands, and (viii) modulation of cellular uptake and trafficking by selection of specific epitopes on the target determinant, carrier geometry, and hydrodynamic factors. Refinement of these aspects and improving our understanding of vascular biology and pathology is likely to enable the clinical translation of vascular endothelial targeting of nanocarriers.

Polymeric nanotherapeutics: clinical development and advances in stealth functionalization strategies

Long-circulating polymeric nanotherapeutics have garnered increasing interest in research and in the clinic owing to their ability to improve the solubility and pharmacokinetics of therapeutic cargoes. Modulation of carrier properties promises more effective drug localization at the disease sites and can lead to enhanced drug safety and efficacy. In the present review, we highlight the current development of polymeric nanotherapeutics in the clinic. In light of the importance of stealth properties in therapeutic nanoparticles, we also review the advances in stealth functionalization strategies and examine the performance of different stealth polymers in the literature. In addition, we discuss the recent development of biologically inspired "self" nanoparticles, which present a differing stealth concept from conventional approaches.

Liposome-like Nanostructures for Drug Delivery

Liposomes are a class of well-established drug carriers that have found numerous therapeutic applications. The success of liposomes, together with recent advancements in nanotechnology, has motivated the development of various novel liposome-like nanostructures with improved drug delivery performance. These nanostructures can be categorized into five major varieties, namely: (1) polymer-stabilized liposomes, (2) nanoparticle-stabilized liposomes, (3) core-shell lipid-polymer hybrid nanoparticles, (4) natural membrane-derived vesicles, and (5) natural membrane coated nanoparticles. They have received significant attention and have become popular drug delivery platforms. Herein, we discuss the unique strengths of these liposome-like platforms in drug delivery, with a particular emphasis on how liposome-inspired novel designs have led to improved therapeutic efficacy, and review recent progress made by each platform in advancing healthcare.

Hemocompatibility of Chitosan/poly(acrylic acid) Grafted Polyurethane Tubing

The activation and adhesion of platelets or whole blood exposed to chitosan (CH) grafted surfaces is used to evaluate the hemocompatibility of biomaterials. The biomaterial surfaces are polyurethane (PU) tubes grafted with an inner poly(acrylic acid) (PAA) and an outer CH or quaternary ammonium modified CH (CH-Q) brush. The CH, CH-Q and PAA grafted layers were characterized by ellipsometry and fluorescence microscopy. Material wear tests demonstrate that CH (CH-Q) is stably grafted onto PU tubes upon exposure to saline solution for 7 days. Using quartz-crystal microbalances with dissipation (QCM-D), in-situ adsorption of blood plasma proteins on CH and CH-Q compared to a silicon oxide control was measured. The QCM-D results showed that the physically adsorbed plasma protein layer on CH-Q and CH surfaces is softer and more viscous than the protein layer on the SiO2 surface. The CH-Q layer thus has the weakest interaction with plasma proteins. Whole blood and platelet adhesion was reduced by ~92% on CH-Q, which showed the weakest interaction with plasma protein but more viscous adsorbed plasma protein layer, compared to SiO2. Last, to examine the biologic response of platelets and neutrophils to biomaterial surfaces, CH (CH-Q)/PAA, PAA and PU tubes were tested using a Chandler Loop apparatus as an ex vivo model and flow cytometry. The blood adhesion and biologic response results showed that CH and CH-Q reduced adhesion and activation of platelets and neutrophils and improved hemocompatibility relative to other surfaces (PU and PAA). Our studies demonstrated that the properties of physically adsorbed plasma protein layer on biomaterial surfaces correlates with blood coagulation on biomaterial surfaces.

Intracellular signaling mechanisms associated with CD47 modified surfaces

We have previously established that recombinant CD47 can ameliorate the inflammatory response to synthetic polymeric surfaces. Here, we begin to profile, at the transcriptional, translational and cell signaling level, the inflammatory cell response when blood interacts with CD47 modified polyvinyl chloride (PVC) (CD47-PVC). We used qPCR arrays to compare transcriptional changes between human whole blood exposed to CD47-PVC or PVC. Transcription of IL1F5, IL1F10, IL17F, CCL3, CCL8, CCL28, CXCL12, and CXCL13 was upregulated in blood exposed to PVC, compared to CD47-PVC. The increase in CCL3 and CCL8 transcription correlated with an increase in the chemokines' presence in the plasma. Exposure of blood to CD47-PVC resulted in an increase, compared to PVC, in transcription of CCL2, CCL4, CCL20, CXCL1, TGFβ3, GDF3, GDF10, CD40LG, and TNFSF10. CD47-PVC exposure resulted in an increase of the following matrix metalloproteinase related genes: MMP1, MMP7, MMP13, and MMP16. Phosflow cytometry, and assays examining transcription factor binding, cell attachment, and genome-wide chromatin association indicated that members of the JAK-STAT signaling pathway, particularly JAK2 and STAT5, mediate inflammatory cell interactions with CD47-PVC. Our data demonstrate that differential molecular responses to CD47 involve downregulation of cytokines, upregulation of MMPs, and JAK/STAT signaling mechanisms.

Hyaluronan and dextran modified tubes resist cellular activation with blood contact

This study was undertaken to evaluate the effects of thin film hyaluronic acid and dextran surface coatings to blunt cellular activation in a laboratory model of extracorporeal blood circulation. The inner lumen surface of polyurethane (PU) and poly(vinyl) chloride (PVC) tubing was grafted with hyaluronic acid and dextran. Surfaces were characterized for the presence of the grafted layer using ellipsometry, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Persistence of the surface layer was maintained for up to 5 days of continuous exposure to shear flow using a Chandler loop apparatus. The Chandler loop method was used to study human whole blood activation activity. Whole blood aggregometry and flow cytometry measures of CD18, CD62L, CD62P, Annexin V and myeloperoxidase performed on blood samples exposed to the tubing for up to three hours were complemented by scanning electron microscopy (SEM) analysis of adherent cells and state of activation. In these studies commercial hospital products and uncoated PVC and PU tubes were used as controls. We found that hyaluranized PU and PVC conferred the greatest resistance to blood activation and that dextranization of the PU and PU tubing also provided significant diminution of the bioresponses measured. Based on our findings, we suggest that surface coating with hyaluronic acid or dextran acts as a potent shield from blood cellular activation during forms of extracorporeal circulation.

'Marker-of-self' functionalization of nanoscale particles through a top-down cellular membrane coating approach

We investigate the 'marker-of-self' functionalization of nanoparticles through coating of natural RBC membranes. The membrane translocation approach is shown to be highly efficient and bestows nanoparticles with correctly oriented and functional immunomodulatory proteins such as CD47 at equivalent density to natural RBCs.

Minimal "Self" peptides that inhibit phagocytic clearance and enhance delivery of nanoparticles

Foreign particles and cells are cleared from the body by phagocytes that must also recognize and avoid clearance of "self" cells. The membrane protein CD47 is reportedly a "marker of self" in mice that impedes phagocytosis of self by signaling through the phagocyte receptor CD172a. Minimal "Self" peptides were computationally designed from human CD47 and then synthesized and attached to virus-size particles for intravenous injection into mice that express a CD172a variant compatible with hCD47. Self peptides delay macrophage-mediated clearance of nanoparticles, which promotes persistent circulation that enhances dye and drug delivery to tumors. Self-peptide affinity for CD172a is near the optimum measured for human CD172a variants, and Self peptide also potently inhibits nanoparticle uptake mediated by the contractile cytoskeleton. The reductionist approach reveals the importance of human Self peptides and their utility in enhancing drug delivery and imaging.