Bone-Targeted Nanoparticle Drug Delivery System-Mediated Macrophage Modulation for Enhanced Fracture Healing.

Despite decades of progress, developing minimally invasive bone-specific drug delivery systems (DDS) to improve fracture healing remains a significant clinical challenge. To address this critical therapeutic need, nanoparticle (NP) DDS comprised of poly(styrene-alt-maleic anhydride)-b-poly(styrene) (PSMA-b-PS) functionalized with a peptide that targets tartrate-resistant acid phosphatase (TRAP) and achieves preferential fracture accumulation has been developed. The delivery of AR28, a glycogen synthase kinase-3 beta (GSK3ß) inhibitor, via the TRAP binding peptide-NP (TBP-NP) expedites fracture healing. Interestingly, however, NPs are predominantly taken up by fracture-associated macrophages rather than cells typically associated with fracture healing. Therefore, the underlying mechanism of healing via TBP-NP is comprehensively investigated herein. TBP-NPAR28 promotes M2 macrophage polarization and enhances osteogenesis in preosteoblast-macrophage co-cultures in vitro. Longitudinal analysis of TBP-NPAR28 -mediated fracture healing reveals distinct spatial distributions of M2 macrophages, an increased M2/M1 ratio, and upregulation of anti-inflammatory and downregulated pro-inflammatory genes compared to controls. This work demonstrates the underlying therapeutic mechanism of bone-targeted NP DDS, which leverages macrophages as druggable targets and modulates M2 macrophage polarization to enhance fracture healing, highlighting the therapeutic benefit of this approach for fractures and bone-associated diseases.

Integrating osteoimmunology and nanoparticle-based drug delivery systems for enhanced fracture healing.

Fracture healing is a complex interplay of molecular and cellular mechanisms lasting from days to weeks. The inflammatory phase is the first stage of fracture healing and is critical in setting the stage for successful healing. There has been growing interest in exploring the role of the immune system and novel therapeutic strategies, such as nanoparticle drug delivery systems in enhancing fracture healing. Advancements in nanotechnology have revolutionized drug delivery systems to the extent that they can modulate immune response during fracture healing by leveraging unique physiochemical properties. Therefore, understanding the intricate interactions between nanoparticle-based drug delivery systems and the immune response, specifically macrophages, is essential for therapeutic efficacy. This review provides a comprehensive overview of the relationship between the immune system and nanoparticles during fracture healing. Specifically, we highlight the influence of nanoparticle characteristics, such as size, surface properties, and composition, on macrophage activation, polarization, and subsequent immune responses. IMPACT STATEMENT: This review provides valuable insights into the interplay between fracture healing, the immune system, and nanoparticle-based drug delivery systems. Understanding nanoparticle-macrophage interactions can advance the development of innovative therapeutic approaches to enhance fracture healing, improve patient outcomes, and pave the way for advancements in regenerative medicine.

Reduction of leukemic burden via bone-targeted nanoparticle delivery of an inhibitor of C-chemokine (C-C motif) ligand 3 (CCL3) signaling.

Leukemias are challenging diseases to treat due, in part, to interactions between leukemia cells and the bone marrow microenvironment (BMME) that contribute significantly to disease progression. Studies have shown that leukemic cells secrete C-chemokine (C-C motif) ligand 3 (CCL3), to disrupt the BMME resulting in loss of hematopoiesis and support of leukemic cell survival and proliferation. In this study, a murine model of blast crisis chronic myelogenous leukemia (bcCML) that expresses the translocation products BCR/ABL and Nup98/HoxA9 was used to determine the role of CCL3 in BMME regulation. Leukemic cells derived from CCL3-/- mice were shown to minimally engraft in a normal BMME, thereby demonstrating that CCL3 signaling was necessary to recapitulate bcCML disease. Further analysis showed disruption in hematopoiesis within the BMME in the bcCML model. To rescue the altered BMME, therapeutic inhibition of CCL3 signaling was investigated using bone-targeted nanoparticles (NP) to deliver Maraviroc, an inhibitor of C-C chemokine receptor type 5 (CCR5), a CCL3 receptor. NP-mediated Maraviroc delivery partially restored the BMME, significantly reduced leukemic burden, and improved survival. Overall, our results demonstrate that inhibiting CCL3 via CCR5 antagonism is a potential therapeutic approach to restore normal hematopoiesis as well as reduce leukemic burden within the BMME.

Stress or injury induces cellular plasticity in salivary gland acinar cells.

Salivary gland function is severely disrupted by radiation therapy used to treat patients diagnosed with head and neck cancer and by Sjögren's syndrome. The resulting condition, which results in xerostomia or dry mouth, is due to irreversible loss of the secretory acinar cells within the major salivary glands. There are presently no treatments for the resolution of xerostomia. Cell-based approaches could be employed to repopulate acinar cells in the salivary gland but investigations into potential therapeutic strategies are limited by the challenges of maintaining and expanding acinar cells in vitro. We investigate the encapsulation of salivary gland cell aggregates within PEG hydrogels as a means of culturing secretory acinar cells. Lineage tracing was used to monitor the fate of acinar cells isolated from murine submandibular gland (SMG). Upon initial formation in vitro, SMG aggregates comprise both acinar and duct cells, with the majority cells of acinar origin. With longer culture times, acinar cells significantly decreased the expression of specific markers and activated the expression of keratins normally found in duct cells. A similar acinar-to-duct cell transition was also observed in vivo, following duct ligation injury. These results indicate that under conditions of stress (mechanical and enzymatic isolation from glands) or injury (duct ligation), salivary gland acinar cells exhibit plasticity to adopt a duct cell phenotype.

Delivery of RNAi-Based Therapeutics for Bone Regeneration.

PURPOSE OF REVIEW: The clinical significance, target pathways, recent successes, and challenges that preclude translation of RNAi bone regenerative approaches are overviewed. RECENT FINDINGS: RNA interference (RNAi) is a promising new therapeutic approach for bone regeneration by stimulating or inhibiting critical signaling pathways. However, RNAi suffers from significant delivery challenges. These challenges include avoiding nuclease degradation, achieving bone tissue targeting, and reaching the cytoplasm for mRNA inhibition. Many drug delivery systems have overcome stability and intracellular localization challenges but suffer from protein adsorption that results in clearance of up to 99% of injected dosages, thus severely limiting drug delivery efficacy. While RNAi has myriad promising attributes for use in bone regenerative applications, delivery challenges continue to plague translation. Thus, a focus on drug delivery system development is critical to provide greater delivery efficiency and bone targeting to reap the promise of RNAi.

In Vivo Translation of Peptide-Targeted Drug Delivery Systems Discovered by Phage Display.

Therapeutic compounds with narrow therapeutic windows and significant systemic side effects benefit from targeted drug delivery strategies. Peptide-protein interactions are often exploited for targeting, with phage display a primary method to identify high-affinity peptide ligands that bind cell surface and matrix bound receptors preferentially expressed in target tissues. After isolating and sequencing high-binding phages, peptides are easily synthesized and chemically modified for incorporation into drug delivery systems, including peptide-drug conjugates, polymers, and nanoparticles. This review describes the phage display methodology to identify targeting peptide sequences, strategies to functionalize drug carriers with phage-derived peptides, specific examples of drug carriers with in vivo translation, and limitations and future applications of phage display to drug delivery.

Multivalent Presentation of Peptide Targeting Groups Alters Polymer Biodistribution to Target Tissues.

Drug delivery to bone is challenging, whereby drug distribution is commonly <1% of injected dose, despite development of several bone-targeted drug delivery systems specific to hydroxyapatite. These bone-targeted drug delivery systems still suffer from poor target cell localization within bone, as at any given time overall bone volume is far greater than acutely remodeling bone volume, which harbors relevant cell targets (osteoclasts or osteoblasts). Thus, there exists a need to target bone-acting drugs specifically to sites of bone remodeling. To address this need, this study synthesized oligo(ethylene glycol) copolymers based on a peptide with high affinity to tartrate-resistant acid phosphatase (TRAP), an enzyme deposited by osteoclasts during the bone resorption phase of bone remodeling, which provides greater specificity relevant for bone cell drugging. Gradient and random peptide orientations, as well as polymer molecular weights, were investigated. TRAP-targeted, high molecular weight (Mn) random copolymers exhibited superior accumulation in remodeling bone, where fracture accumulation was observed for at least 1 week and accounted for 14% of tissue distribution. Intermediate and low Mn random copolymer accumulation was lower, indicating residence time depends on Mn. High Mn gradient polymers were cleared, with only 2% persisting at fractures after 1 week, suggesting TRAP binding depends on peptide density. Peptide density and Mn are easily modified in this versatile targeting platform, which can be applied to a range of bone drug delivery applications.

Diblock Copolymer Hydrophobicity Facilitates Efficient Gene Silencing and Cytocompatible Nanoparticle-Mediated siRNA Delivery to Musculoskeletal Cell Types.

pH-responsive diblock copolymers provide tailorable nanoparticle (NP) architecture and chemistry critical for siRNA delivery. Here, diblock polymers varying in first (corona) and second (core) block molecular weight (Mn), corona/core ratio, and core hydrophobicity (%BMA) were synthesized to determine their effect on siRNA delivery in murine tenocytes (mTenocyte) and murine and human mesenchymal stem cells (mMSC and hMSCs, respectively). NP-mediated siRNA uptake, gene silencing, and cytocompatibility were quantified. Uptake is positively correlated with first block Mn in mTenocytes and hMSCs (p ≤ 0.0005). All NP resulted in significant gene silencing that was positively correlated with %BMA (p < 0.05) in all cell types. Cytocompatibility was reduced in mTenocytes compared to MSCs (p < 0.0001). %BMA was positively correlated with cytocompatibility in MSCs (p < 0.05), suggesting stable NP are more cytocompatible. Overall, this study shows that NP-siRNA cytocompatibility is cell type dependent, and hydrophobicity (%BMA) is the critical diblock copolymer property for efficient gene silencing in musculoskeletal cell types.

Poly(styrene-alt-maleic anhydride)-based diblock copolymer micelles exhibit versatile hydrophobic drug loading, drug-dependent release, and internalization by multidrug resistant ovarian cancer cells.

Amphiphilic diblock copolymers of poly(styrene-alt-maleic anhydride)-b-poly(styrene) (PSMA-b-PS) and poly(styrene-alt-maleic anhydride)-b-poly(butyl acrylate) (PSMA-b-PBA) were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerizations. Polymers were well-controlled with respect to molecular weight evolution and polydispersity indices (PDI < 1.2). Additionally, RAFT allowed for control of diblock compositions (i.e., ratio of hydrophilic PSMA blocks to hydrophobic PS/PBA blocks) and overall molecular weight, which resulted in reproducible self-assembly of diblocks into micelle nanoparticles with diameters of 20-100 nm. Parthenolide (PTL), a hydrophobic anticancer drug, was loaded and released from the micelles. The highest loading and prolonged release of PTL was observed from predominantly hydrophobic PSMA-b-PS micelles (e.g., PSMA100-b-PS258), which exhibited the most ordered hydrophobic environment for more favorable core-drug interactions. PSMA100-b-PS258 micelles were further loaded with doxorubicin (DOX), as well as two hydrophobic fluorescent probes, nile red and IR-780. While PTL released quantitatively within 24 h, DOX, IR-780, and nile red showed release over 1 week, suggesting stronger drug-core interactions and/or hindrance due to less favorable drug-solvent interactions. Finally, uptake and intracellular localization of PSMA100-b-PS258 micelles by multidrug resistant (MDR) ovarian cancer cells was observed by transmission electron microscopy (TEM). Additionally, in vitro analyses showed DOX-loaded PSMA-b-PS micelles exhibited greater cytotoxicity to NCI/ADR RES cells than equivalent free DOX doses (75% reduction in cell viability by DOX-loaded micelles compared to 40% reduction in viability by free DOX at 10 µM DOX), likely due to avoidance of MDR mechanisms that limit free hydrophobic drug accumulation. The ability of micelles to achieve intracellular delivery via avoidance of MDR mechanisms, along with the versatility of chemical constituents and drug loading and release rates, offer many advantages for a variety of drug delivery applications.

Nanoparticle-mediated gene silencing confers radioprotection to salivary glands in vivo.

Radiation treatment of head and neck cancers causes irreversible damage of the salivary glands (SG). Here, we introduce a preclinical mouse model for small-interfering RNA (siRNA)-based gene silencing to provide protection of SG from radiation-induced apoptosis. Novel, pH-responsive nanoparticles complexed with siRNAs were introduced into mouse submandibular glands (SMG) by retroductal injection to modulate gene expression in vivo. To validate this approach, we first targeted Nkcc1, an ion transporter that is essential for saliva secretion. Nkcc1 siRNA delivery resulted in efficient knockdown, as quantified at the mRNA and the protein levels, and the functional result of Nkcc1 knockdown phenocopied the severe decrease in saliva secretion, characteristic of the systemic Nkcc1 gene knockout. To establish a strategy to prevent apoptotic cell loss due to radiation damage, siRNAs targeting the proapoptotic Pkcδ gene were administered into SMG before ionizing radiation. Knockdown of Pkcδ not only reduced the number of apoptotic cells during the acute phase of radiation damage, but also markedly improved saliva secretion at 3 months in irradiated animals, indicating that this treatment confers protection from hyposalivation. These results demonstrate that nanoparticle delivery of siRNAs targeting a proapoptotic gene is a localized, nonviral, and effective means of conferring radioprotection to the SGs.

Advancing Bone-Targeted Drug Delivery: Leveraging Biological Factors and Nanoparticle Designs to Improve Therapeutic Efficacy.

Designing targeted drug delivery systems to effectively treat bone diseases ranging from osteoporosis to nonunion bone defects remains a significant challenge. Previously, nanoparticles (NPs) self-assembled from diblock copolymers of poly(styrene-alt-maleic anhydride)-b-poly(styrene) (PSMA-b-PS) delivering a Wnt agonist were shown to effectively target bone and improve healing via the introduction of a peptide with high affinity to tartrate-resistant acid phosphatase (TRAP), an enzyme deposited by the osteoclasts during bone remodeling. Despite these promising results, the underlying biological factors governing targeting and subsequent drug delivery system (DDS) design parameters have not been examined to enable the rational design to improve bone selectivity. Therefore, this work investigated the effect of target ligand density, the treatment window after injury, specificity of TRAP binding peptide (TBP), the extent of TRAP deposition, and underlying genetic factors (e.g., mouse strain differences) on TBP-NP targeting. Data based on in vitro binding studies and in vivo biodistribution analyses using a murine femoral fracture model suggest that TBP-NP-TRAP interactions and TBP-NP bone accumulation were ligand-density-dependent; in vitro, TRAP affinity was correlated with ligand density up to the maximum of 200,000 TBP ligands/NP, while NPs with 80,000 TBP ligands showed 2-fold increase in fracture accumulation at day 21 post injury compared with that of untargeted or scrambled controls. While fracture accumulation exhibited similar trends when injected at day 3 compared to that at day 21 postfracture, there were no significant differences observed between TBP-functionalized and control NPs, possibly due to saturation of TRAP by NPs at day 3. Leveraging a calcium-depletion diet, TRAP deposition and TBP-NP bone accumulation were positively correlated, confirming that TRAP-TBP binding leads to TBP-NP bone accumulation in vivo. Furthermore, TBP-NP exhibited similar bone accumulation in both C57BL/6 and BALB/c mouse strains versus control NPs, suggesting the broad applicability of TBP-NP regardless of the underlying genetic differences. These studies provide insight into TBP-NP design, mechanism, and therapeutic windows, which inform NP design and treatment strategies for fractures and other bone-associated diseases that leverage TRAP, such as marrow-related hematologic diseases.

Radical-Mediated Degradation of Thiol-Maleimide Hydrogels.

Michael addition between thiol- and maleimide-functionalized molecules is a long-standing approach used for bioconjugation, hydrogel crosslinking, and the functionalization of other advanced materials. While the simplicity of this chemistry enables facile synthesis of hydrogels, network degradation is also desirable in many instances. Here, the susceptibility of thiol-maleimide bonds to radical-mediated degradation is reported. Irreversible degradation in crosslinked materials is demonstrated using photoinitiated and chemically initiated radicals in hydrogels and linear polymers. The extent of degradation is shown to be dependent on initiator concentration. Using a model linear polymer system, the radical-mediated mechanism of degradation is elucidated, in which the thiosuccinimide crosslink is converted to a succinimide and a new thioether formed with an initiator fragment. Using laser stereolithography, high-fidelity spatiotemporal control over degradation in crosslinked gels is demonstrated. Ultimately, this work establishes a platform for controllable, radical-mediated degradation in thiol-maleimide hydrogels, further expanding their versatility as functional materials.

Engineering models of head and neck and oral cancers on-a-chip.

Head and neck cancers (HNCs) rank as the sixth most common cancer globally and result in over 450 000 deaths annually. Despite considerable advancements in diagnostics and treatment, the 5-year survival rate for most types of HNCs remains below 50%. Poor prognoses are often attributed to tumor heterogeneity, drug resistance, and immunosuppression. These characteristics are difficult to replicate using in vitro or in vivo models, culminating in few effective approaches for early detection and therapeutic drug development. Organs-on-a-chip offer a promising avenue for studying HNCs, serving as microphysiological models that closely recapitulate the complexities of biological tissues within highly controllable microfluidic platforms. Such systems have gained interest as advanced experimental tools to investigate human pathophysiology and assess therapeutic efficacy, providing a deeper understanding of cancer pathophysiology. This review outlines current challenges and opportunities in replicating HNCs within microphysiological systems, focusing on mimicking the soft, glandular, and hard tissues of the head and neck. We further delve into the major applications of organ-on-a-chip models for HNCs, including fundamental research, drug discovery, translational approaches, and personalized medicine. This review emphasizes the integration of organs-on-a-chip into the repertoire of biological model systems available to researchers. This integration enables the exploration of unique aspects of HNCs, thereby accelerating discoveries with the potential to improve outcomes for HNC patients.

Development of a nanoparticle-based tendon-targeting drug delivery system to pharmacologically modulate tendon healing.

Satisfactory healing following acute tendon injury is marred by fibrosis. Despite the high frequency of tendon injuries and poor outcomes, there are no pharmacological therapies in use to enhance the healing process. Moreover, systemic treatments demonstrate poor tendon homing, limiting the beneficial effects of potential tendon therapeutics. To address this unmet need, we leveraged our existing tendon healing spatial transcriptomics dataset and identified an area enriched for expression of Acp5 (TRAP) and subsequently demonstrated robust TRAP activity in the healing tendon. This unexpected finding allowed us to refine and apply our existing TRAP binding peptide (TBP) functionalized nanoparticle (NP) drug delivery system (DDS) to facilitate improved delivery of systemic treatments to the healing tendon. To demonstrate the translational potential of this DDS, we delivered niclosamide (NEN), an S100a4 inhibitor. While systemic delivery of free NEN did not alter healing, TBP-NPNEN enhanced both functional and mechanical recovery, demonstrating the translational potential of this approach to enhance the tendon healing process.

TOF-SIMS 3D imaging of native and non-native species within HeLa cells.

In this study, a non-native chemical species, bromodeoxyuridine (BrdU), was imaged within single HeLa cells using time-of-flight secondary ion mass spectrometry (TOF-SIMS). z-corrected 3D images were reconstructed that accurately portray the distribution of intracellular BrdU as well as other intracellular structures. The BrdU was localized to the nucleus of cells, whereas structures composed of CxHyOz(-) species were located in bundles on the periphery of cells. The CxHyOz(-) subcellular features had a spatial resolution at or slightly below a micrometer (900 nm), as defined by the distance between the 16% and 84% intensities in a line scan across the edge of the features. Additionally, important parameters influencing the quality of the HeLa cell 3D images were investigated. Atomic force microscopy measurements revealed that the HeLa cells were sputtered at a rate of approximately 4 nm per 10(13) C60(+) ions/cm(2) at 10 keV and a 45° incident angle. Optimal 3D images were acquired using a Bi3(+) liquid metal ion gun operating in the simultaneous high mass and spatial resolution mode.

Two-dimensional patterns of poly(N-isopropylacrylamide) microgels to spatially control fibroblast adhesion and temperature-responsive detachment.

Thermoresponsive poly(N-isopropyl acrylamide) (PNIPAM) microgels were patterned on polystyrene substrates via dip coating, creating cytocompatible substrates that provided spatial control over cell adhesion. This simple dip-coating method, which exploits variable substrate withdrawal speeds forming particle suspension stripes of densely packed PNIPAM microgels, while spacings between the stripes contained sparsely distributed PNIPAM microgels. The assembly of three different PNIPAM microgel patterns, namely, patterns composed of 50 µm stripe/50 µm spacing, 50 µm stripe/100 µm spacing, and 100 µm stripe/100 µm spacing, was verified using high-resolution optical micrographs and ImageJ analysis. PNIPAM microgels existed as monolayers within stripes and spacings, as revealed by atomic force microscopy (AFM). Upon cell seeding on PNIPAM micropatterned substrates, NIH3T3 fibroblast cells preferentially adhered within spacings to form cell patterns. Three days after cell seeding, cells proliferated to form confluent cell layers. The thermoresponsiveness of the underlying PNIPAM microgels was then utilized to recover fibroblast cell sheets from substrates simply by lowering the temperature without disrupting the underlying PNIPAM microgel patterns. Harvested cell sheets similar to these have been used for multiple tissue engineering applications. Also, this simple, low-cost, template-free dip-coating technique can be utilized to micropattern multifunctional PNIPAM microgels, generating complex stimuli-responsive substrates to study cell-material interactions and allow drug delivery to cells in a spatially and temporally controlled manner.

Emerging ideas: Engineering the periosteum: revitalizing allografts by mimicking autograft healing.

BACKGROUND: To fulfill the need for large volumes, devitalized allografts are used to treat massive bone defects despite a 60%, 10-year postimplantation fracture rate. Allograft healing is inferior to autografts where the periosteum orchestrates remodeling. HYPOTHESIS: By augmenting allografts with a tissue engineered periosteum consisting of tunable and degradable, poly(ethylene glycol) (PEG) hydrogels for mesenchymal stem cell (MSC) transplantation, the functions critical for periosteum-mediated healing will be identified and emulated. METHOD OF STUDY: PEG hydrogels will be designed to emulate periosteum-mediated autograft healing to revitalize allografts. We will exploit murine femoral defect models for these approaches. Critical-sized, 5-mm segmental defects will be created and filled with decellularized allograft controls or live autograft controls. Alternatively, defects will be treated with our experimental approaches: decellularized allografts coated with MSCs transplanted via degradable PEG hydrogels to mimic progenitor cell densities and persistence during autograft healing. Healing will be evaluated for 9 weeks using microcomputed tomography, mechanical testing, and histologic analysis. If promising, MSC densities, hydrogel compositions, and genetic methods will be used to isolate critical aspects of engineered periosteum that modulate healing. Finally, hydrogel biochemical characteristics will be altered to initiate MSC and/or host-material interactions to further promote remodeling of allografts. SIGNIFICANCE: This approach represents a novel tissue engineering strategy whereby degradable, synthetic hydrogels will be exploited to emulate the periosteum. The microenvironment, which will mediate MSC transplantation, will use tunable PEG hydrogels for isolation of critical allograft revitalization factors. In addition, hydrogels will be modified with biochemical cues to further augment allografts to reduce or eliminate revision surgeries associated with allograft failures.

Impact of Nanoparticle Physicochemical Properties on Protein Corona and Macrophage Polarization.

Macrophages, the major component of the mononuclear phagocyte system, uptake and clear systemically administered nanoparticles (NPs). Therefore, leveraging macrophages as a druggable target may be advantageous to enhance NP-mediated drug delivery. Despite many studies focused on NP-cell interactions, NP-mediated macrophage polarization mechanisms are still poorly understood. This work aimed to explore the effect of NP physicochemical parameters (size and charge) on macrophage polarization. Upon exposure to biological fluids, proteins rapidly adsorb to NPs and form protein coronas. To this end, we hypothesized that NP protein coronas govern NP-macrophage interactions, uptake, and subsequent macrophage polarization. To test this hypothesis, model polystyrene NPs with various charges and sizes, as well as NPs relevant to drug delivery, were utilized. Data suggest that cationic NPs potentiate both M1 and M2 macrophage markers, while anionic NPs promote M1-to-M2 polarization. Additionally, anionic polystyrene nanoparticles (APNs) of 50 nm exhibit the greatest influence on M2 polarization. Proteomics was pursued to further understand the effect of NPs physicochemical parameters on protein corona, which revealed unique protein patterns based on NP charge and size. Several proteins impacting M1 and M2 macrophage polarization were identified within cationic polystyrene nanoparticles (CPNs) corona, while APNs corona included fewer M1 but more M2-promoting proteins. Nevertheless, size impacts protein corona abundance but not identities. Altogether, protein corona identities varied based on NP surface charge and correlated to dramatic differences in macrophage polarization. In contrast, NP size differentially impacts macrophage polarization, which is dominated by NP uptake level rather than protein corona. In this work, specific corona proteins were identified as a function of NP physicochemical properties. These proteins are correlated to specific macrophage polarization programs and may provide design principles for developing macrophage-mediated NP drug delivery systems.

Zwitterionic peptides: Tunable next-generation stealth nanoparticle modifications.

Adsorption of proteins to nanoparticles (NPs), a complex process that results in a protein corona, is controlled by NP surface properties that define NP interactions in vivo. Efforts to control adsorbed protein quantity through surface modification have led to improvements in circulation time or biodistribution. Still, current approaches have yet to be identified to control adsorbed protein identities within the corona. Here, we report the development and characterization of diverse zwitterionic peptides (ZIPs) for NP anti-fouling surface functionalization with specific and controllable affinity for protein adsorption profiles defined by ZIP sequence. Through serum exposure of ZIP-conjugated NPs and proteomics analysis of the resulting corona, we determined that protein adsorption profiles depend not on the exact composition of the ZIPs but on the sequence and order of charges along the sequence (charge motif). These findings pave the way for developing tunable ZIPs to orchestrate specific ZIP-NP protein adsorption profiles as a function of ZIP charge motif to better control cell and tissue specificity and pharmacokinetics and provide new tools for investigating relationships between protein corona and biological function. Furthermore, overall ZIP diversity enabled by the diversity of amino acids may ameliorate adaptive immune responses.

Drug Delivery Approaches to Improve Tendon Healing.

Tendon injuries disrupt the transmission of forces from muscle to bone, leading to chronic pain, disability, and a large socioeconomic burden. Tendon injuries are prevalent; there are over 300,000 tendon repair procedures a year in the United States to address acute trauma or chronic tendinopathy. Successful restoration of function after tendon injury remains challenging clinically. Despite improvements in surgical and physical therapy techniques, the high complication rate of tendon repair procedures motivates the use of therapeutic interventions to augment healing. While many biological and tissue engineering approaches have attempted to promote scarless tendon healing, there is currently no standard clinical treatment to improve tendon healing. Moreover, the limited efficacy of systemic delivery of several promising therapeutic candidates highlights the need for tendon-specific drug delivery approaches to facilitate translation. This review article will synthesize the current state-of-the-art methods that have been used for tendon-targeted delivery through both systemic and local treatments, highlight emerging technologies used for tissue-specific drug delivery in other tissue systems, and outline future challenges and opportunities to enhance tendon healing through targeted drug delivery.