Co association of mucus modulating agents and nanoparticles for mucosal drug delivery

Orally-administered nanomedicine systems targeting colon inflammation for the treatment of inflammatory bowel disease: latest advances

Inflammatory bowel disease (IBD) is a chronic and idiopathic condition that results in inflammation of the gastrointestinal tract, leading to conditions such as ulcerative colitis and Crohn's disease. Commonly used treatments for IBD include anti-inflammatory drugs, immunosuppressants, and antibiotics. Fecal microbiota transplantation is also being explored as a potential treatment method; however, these drugs may lead to systemic side effects. Oral administration is preferred for IBD treatment, but accurately locating the inflamed area in the colon is challenging due to multiple physiological barriers. Nanoparticle drug delivery systems possess unique physicochemical properties that enable precise delivery to the target site for IBD treatment, exploiting the increased permeability and retention effect of inflamed intestines. The first part of this review comprehensively introduces the pathophysiological environment of IBD, covering the gastrointestinal pH, various enzymes in the pathway, transport time, intestinal mucus, intestinal epithelium, intestinal immune cells, and intestinal microbiota. The second part focuses on the latest advances in the mechanism and strategies of targeted delivery using oral nanoparticle drug delivery systems for colitis-related fields. Finally, we present challenges and potential directions for future IBD treatment with the assistance of nanotechnology.

Impact of mucus modulation by N-acetylcysteine on nanoparticle toxicity

Human respiratory mucus is a biological hydrogel that forms a protective barrier for the underlying epithelium. Modulation of the mucus layer has been employed as a strategy to enhance transmucosal drug carrier transport. However, a drawback of this strategy is a potential reduction of the mucus barrier properties, in particular in situations with an increased exposure to particles. In this study, we investigated the impact of mucus modulation on its protective role. In vitro mucus was produced by Calu-3 cells, cultivated at the air-liquid interface for 21 days and used for further testing as formed on top of the cells. Analysis of confocal 3D imaging data revealed that after 21 days Calu-3 cells secrete a mucus layer with a thickness of 24 ± 6 μm. Mucus appeared to restrict penetration of 500 nm carboxyl-modified polystyrene particles to the upper 5-10 μm of the layer. Furthermore, a mucus modulation protocol using aerosolized N-acetylcysteine (NAC) was developed. This treatment enhanced the penetration of particles through the mucus down to deeper layers by means of the mucolytic action of NAC. These findings were supported by cytotoxicity data, indicating that intact mucus protects the underlying epithelium from particle-induced effects on membrane integrity. The impact of NAC treatment on the protective properties of mucus was probed by using 50 and 100 nm amine-modified and 50 nm carboxyl-modified polystyrene nanoparticles, respectively. Cytotoxicity was only induced by the amine-modified particles in combination with NAC treatment, implying a reduced protective function of modulated mucus. Overall, our data emphasize the importance of integrating an assessment of the protective function of mucus into the development of therapy approaches involving mucus modulation.

Nanocarriers transport across the gastrointestinal barriers: The contribution to oral bioavailability via blood circulation and lymphatic pathway

Oral administration is the preferred route of drug delivery in clinical practice due to its noninvasiveness, safety, convenience, and high patient compliance. The gastrointestinal tract (GIT) plays a crucial role in facilitating the targeted delivery of oral drugs. However, the GIT presents multiple barriers that impede drug absorption, including the gastric barrier in the stomach and the mucus and epithelial barriers in the intestine. In recent decades, nanotechnology has emerged as a promising approach for overcoming these challenges by utilizing nanocarrier-based drug delivery systems such as liposomes, micelles, polymeric nanoparticles, solid lipid nanoparticles, and inorganic nanoparticles. Encapsulating drugs within nanocarriers not only protects them from degradation but also enhances their transport and absorption across the GIT, ultimately improving oral bioavailability. The aim of this review is to elucidate the mechanisms underlying nanocarrier-mediated transportation across the GIT into systemic circulation via both the blood circulation and lymphatic pathway.

Intranasal delivery of stem cells labeled by nanoparticles in neurodegenerative disorders: Challenges and opportunities

Neurodegenerative disorders occur through progressive loss of function or structure of neurons, with loss of sensation and cognition values. The lack of successful therapeutic approaches to solve neurologic disorders causes physical disability and paralysis and has a significant socioeconomic impact on patients. In recent years, nanocarriers and stem cells have attracted tremendous attention as a reliable approach to treating neurodegenerative disorders. In this regard, nanoparticle-based labeling combined with imaging technologies has enabled researchers to survey transplanted stem cells and fully understand their fate by monitoring their survival, migration, and differentiation. For the practical implementation of stem cell therapies in the clinical setting, it is necessary to accurately label and follow stem cells after administration. Several approaches to labeling and tracking stem cells using nanotechnology have been proposed as potential treatment strategies for neurological diseases. Considering the limitations of intravenous or direct stem cell administration, intranasal delivery of nanoparticle-labeled stem cells in neurological disorders is a new method of delivering stem cells to the central nervous system (CNS). This review describes the challenges and limitations of stem cell-based nanotechnology methods for labeling/tracking, intranasal delivery of cells, and cell fate regulation as theragnostic labeling. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease.

FOF1-ATPase Motor-Embedded Chromatophore as Drug Delivery System: Extraction, Cargo Loading Ability and Mucus Penetration Ability

Mucosal drug delivery permits direct and prompt drug absorption, which is capable of reducing undesirable decomposition that occurs before absorption. However, mucus clearance of those mucosal drug delivery systems strongly retards their actual application. Herein, we propose chromatophore nanoparticles embedded with FOF1-ATPase motors to promote mucus penetration. The FOF1-ATPase motor-embedded chromatophores were firstly extracted from Thermus thermophilus by using a gradient centrifugation method. Then, the model drug (curcumin) was loaded onto the chromatophores. The drug loading efficiency and entrapment efficiency were optimized by using different loading approaches. The activity, motility, stability and mucus permeation of the drug-loaded chromatophore nanoparticles were thoroughly investigated. Both the in vitro and in vivo studies revealed that the FOF1-ATPase motor-embedded chromatophore successfully enhanced mucus penetration glioma therapy. This study indicates that the FOF1-ATPase motor-embedded chromatophore is a promising alternative as a mucosal drug delivery system.

Palmitic acid- and cysteine-functionalized nanoparticles overcome mucus and epithelial barrier for oral delivery of drug

Nanoparticles (NPs) used for oral administration have greatly improved drug bioavailability and therapeutic efficacy. Nevertheless, NPs are limited by biological barriers, such as gastrointestinal degradation, mucus barrier, and epithelial barrier. To solve these problems, we developed the PA-N-2-HACC-Cys NPs loaded with anti-inflammatory hydrophobic drug curcumin (CUR) (CUR@PA-N-2-HACC-Cys NPs) by self-assembled amphiphilic polymer, composed of the N-2-Hydroxypropyl trimethyl ammonium chloride chitosan (N-2-HACC), hydrophobic palmitic acid (PA), and cysteine (Cys). After oral administration, the CUR@PA-N-2-HACC-Cys NPs had good stability and sustained release under gastrointestinal conditions, followed by adhering to the intestine to achieve drug mucosal delivery. Additionally, the NPs could penetrate mucus and epithelial barriers to promote cellular uptake. The CUR@PA-N-2-HACC-Cys NPs could open tight junctions between cells for transepithelial transport while striking a balance between mucus interaction and diffusion through mucus. Notably, the CUR@PA-N-2-HACC-Cys NPs improved the oral bioavailability of CUR, which remarkably relieved colitis symptoms and promoted mucosal epithelial repair. Our findings proved that the CUR@PA-N-2-HACC-Cys NPs had excellent biocompatibility, could overcome mucus and epithelial barriers, and had significant application prospects for oral delivery of the hydrophobic drugs.

Effects of prophylactic antibiotics administration on barrier properties of intestinal mucosa and mucus from preterm born piglets

Early intervention and short-duration treatments with antibiotics in premature infants are reported to reduce the incidence of necrotizing enterocolitis (NEC), a terrible disease with severe inflammation and impaired intestinal barrier properties. Yet, it is unclear how antibiotics exposure, as well as route of administration used for dosing, can minimize the risk of NEC. With this study, we aimed to investigate if and how administration of antibiotics may affect the barrier properties of intestinal mucosa and mucus. We compared how parenteral (PAR) and a combination of enteral and parenteral (ENT+PAR) ampicillin and gentamicin given to preterm born piglets within 48 h after birth affected both barrier and physical properties of ex vivo small intestinal mucosa and mucus. Permeation of the markers mannitol, metoprolol, and fluorescein-isothiocyanate dextran of 4 kDa (FD4) and 70 kDa (FD70) through the mucosa and mucus was evaluated. For all markers, permeation through the mucosa and mucus collected from PAR piglets tended to be reduced when compared to that observed using untreated piglets. In contrast, permeation through the mucosa and mucus collected from ENT+PAR piglets tended to be similar to that observed for untreated piglets. Additionally, rheological measurements on the mucus from PAR piglets and ENT+PAR piglets displayed a decreased G' and G'/G" ratio and decreased viscosity at 0.4 s^-1 as well as lower stress stability compared to the mucus from untreated piglets.

Airway mucus in pulmonary diseases: Muco-adhesive and muco-penetrating particles to overcome the airway mucus barriers

Airway mucus is a complex viscoelastic gel that provides a defensive physical barrier and shields the airway epithelium by trapping inhaled foreign pathogens and facilitating their removal via mucociliary clearance (MCC). In patients with respiratory diseases, such as chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF), non-CF bronchiectasis, and asthma, an increase in crosslinking and physical entanglement of mucin polymers as well as mucus dehydration often alters and typically reduces mucus mesh network pore size, which reduces neutrophil migration, decreases pathogen capture, sustains bacterial infection, and accelerates lung function decline. Conventional aerosol particles containing hydrophobic drugs are rapidly captured and removed by MCC. Therefore, it is critical to design aerosol delivery systems with the appropriate size and surface chemistry that can improve drug retention and absorption with the goal of increased efficacy. Biodegradable muco-adhesive particles (MAPs) and muco-penetrating particles (MPPs) have been engineered to achieve effective pulmonary delivery and extend drug residence time in the lungs. MAPs can be used to target mucus as they get trapped in airway mucus by steric obstruction and/or adhesion. MPPs avoid muco-adhesion and are designed to have a particle size smaller than the mucus network, enhancing lung retention of particles as well as transport to the respiratory epithelial layer and drug absorption. In this review, we aim to provide insight into the composition of airway mucus, rheological characteristics of airway mucus in healthy and diseased subjects, the most recent techniques to study the flow dynamics and particle diffusion in airway mucus (in particular, multiple particle tracking, MPT), and the advancements in engineering MPPs that have contributed to improved airway mucus penetration, lung distribution, and retention.

Mechanisms and strategies to enhance penetration during intravesical drug therapy for bladder cancer

Bladder cancer (BCa) is one of the most prevalent cancers worldwide. The effectiveness of intravesical therapy for bladder cancer, however, is limited due to the short dwell time and the presence of permeation barriers. Considering the histopathological features of BCa, the permeation barriers for drugs to transport across consist of a mucus layer and a nether tumor physiological barrier. Mucoadhesive delivery systems or mucus-penetrating delivery systems are developed to enhance their retention in or penetration across the mucus layer, but delivery systems that are capable of mucoadhesion-to-mucopenetration transition are more efficient to deliver drugs across the mucus layer. For the tumor physiological barrier, delivery systems mainly rely on four types of penetration mechanisms to cross it. This review summarizes the classical and latest approaches to intravesical drug delivery systems to penetrate BCa.

Precise oral delivery systems for probiotics: A review

Probiotics have several health benefits to the host. However, low pH in the stomach, various digestive enzymes and bile salts in the intestine threaten their viability and function. Thus, probiotics need to be protected during gastric transit to address challenges associated with low viability and impaired function. At present, probiotic delivery systems with different trigger mechanisms have been constructed to successfully introduce numerous high-viability probiotics to the intestine. On this basis, the application of non-targeted/targeted probiotic delivery systems in different gut microenvironment and the adjuvant therapeutic effect of probiotic delivery systems on other disease were discussed in detail. It is important to also note that most of the current studies in this area focused on non-targeted probiotic delivery systems. Moreover, changes in intestinal microenvironment under disease state and discontinuous distribution of disease site limit their development. Thus, emphasis were made on the optimization of non-targeted probiotic delivery systems and the necessity of designing more precisely targeted ones.

Models using native tracheobronchial mucus in the context of pulmonary drug delivery research: Composition, structure and barrier properties

Mucus covers all wet epithelia and acts as a protective barrier. In the airways of the lungs, the viscoelastic mucus meshwork entraps and clears inhaled materials and efficiently removes them by mucociliary escalation. In addition to physical and chemical interaction mechanisms, the role of macromolecular glycoproteins (mucins) and antimicrobial constituents in innate immune defense are receiving increasing attention. Collectively, mucus displays a major barrier for inhaled aerosols, also including therapeutics. This review discusses the origin and composition of tracheobronchial mucus in relation to its (barrier) function, as well as some pathophysiological changes in the context of pulmonary diseases. Mucus models that contemplate key features such as elastic-dominant rheology, composition, filtering mechanisms and microbial interactions are critically reviewed in the context of health and disease considering different collection methods of native human pulmonary mucus. Finally, the prerequisites towards a standardization of mucus models in a regulatory context and their role in drug delivery research are addressed.

In Vitro Comparative Study of Solid Lipid and PLGA Nanoparticles Designed to Facilitate Nose-to-Brain Delivery of Insulin

The brain insulin metabolism alteration has been addressed as a pathophysiological factor underlying Alzheimer's disease (AD). Insulin can be beneficial in AD, but its macro-polypeptide nature negatively influences the chances of reaching the brain. The intranasal (IN) administration of therapeutics in AD suggests improved brain-targeting. Solid lipid nanoparticles (SLNs) and poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs) are promising carriers to deliver the IN-administered insulin to the brain due to the enhancement of the drug permeability, which can even be improved by chitosan-coating. In the present study, uncoated and chitosan-coated insulin-loaded SLNs and PLGA NPs were formulated and characterized. The obtained NPs showed desirable physicochemical properties supporting IN applicability. The in vitro investigations revealed increased mucoadhesion, nasal diffusion, and drug release rate of both insulin-loaded nanocarriers over native insulin with the superiority of chitosan-coated SLNs. Cell-line studies on human nasal epithelial and brain endothelial cells proved the safety IN applicability of nanoparticles. Insulin-loaded nanoparticles showed improved insulin permeability through the nasal mucosa, which was promoted by chitosan-coating. However, native insulin exceeded the blood-brain barrier (BBB) permeation compared with nanoparticulate formulations. Encapsulating insulin into chitosan-coated NPs can be beneficial for ensuring structural stability, enhancing nasal absorption, followed by sustained drug release.

Liposomes for oral delivery of protein and peptide-based therapeutics: challenges, formulation strategies, and advances

Throughout the past decade, there has been a rapid growth in the development of protein/peptide-based therapeutics. These therapeutics have found widespread applications in the treatment of cancer, infectious diseases, and other metabolic disorders owing to their several desirable attributes, such as reduced toxicity, diverse biological activities, high specificity, and potency. Most protein/peptide-based drugs are still administered parenterally, and there is an unprecedented demand in the pharmaceutical industry to develop oral delivery routes to increase patient acceptability and convenience. Recent advancements in nanomedicine discoveries have led to the development of several nano and micro-particle-based oral delivery platforms for protein/peptide-based therapeutics and among these, liposomes have emerged as a prominent candidate. Liposomes are spherical vesicles composed of one or more phospholipid bilayers enclosing a core aqueous phase. Their unique amphiphilic nature enables encapsulation of a diverse range of bioactives/drugs including both hydrophobic and hydrophilic compounds for delivery. Against this backdrop, this review provides an overview of the current approaches and challenges associated with the routes and methods of oral administration of protein/peptide-based therapeutics by using liposomes as a potential vehicle. First, the conventional and innovative liposome formation approaches have been discussed along with their applications. Next, the challenges associated with current approaches for oral delivery of protein and peptide-derived therapeutics have been thoroughly addressed. Lastly, we have critically reviewed the potential of liposomes utilization as vehicles for oral delivery of proteins emphasizing the current status and future directions in this area.

Enhancing nanoparticle penetration through airway mucus to improve drug delivery efficacy in the lung

Introduction: Airway mucus gel layer serves as a key delivery barrier that limits the performance of inhaled drug delivery nanoparticles. Conventional nanoparticles are readily trapped by the airway mucus and rapidly cleared from the lung via mucus clearance mechanisms. These nanoparticles cannot distribute throughout the lung airways, long-reside in the lung and/or reach the airway epithelium. To address this challenge, strategies to enhance particle penetration through the airway mucus have been developed and proof-of-concept has been established using mucus model systems..Areas covered: In this review, we first overview the biochemical and biophysical characteristics that render the airway mucus a challenging delivery barrier. We then introduce strategies to improve particle penetration through the airway mucus. Specifically, we walk through two classes of approaches, including modification of physicochemical properties of nanoparticles and modulation of barrier properties of airway mucus.Expert opinion: State-of-the-art strategies to overcome the airway mucus barrier have been introduced and experimentally validated. However, data should be interpreted in the comprehensive context of therapeutic delivery from the site of administration to the final destination to determine clinically-relevant approaches. Further, safety should be carefully monitored, particularly when it comes to mucus-altering strategies that may perturb physiological functions of airway mucus.

Comparing the permeability of human and porcine small intestinal mucus for particle transport studies

The gastrointestinal mucus layer represents the last barrier between ingested food or orally administered pharmaceuticals and the mucosal epithelium. This complex gel structure plays an important role in the process of small intestinal absorption. It provides protection against hazardous particles such as bacteria but allows the passage of nutrients and drug molecules towards the intestinal epithelium. In scientific research, mucus from animal sources is usually used to simulate difficult-to-obtain human small intestinal mucus for investigating the intramucus transport of drug delivery systems or food nanoparticles. However, there is a lack of evidence the human mucus can be reliably substituted by animal counterparts for human-relevant transport models. In this report, a procedure for collecting human mucus has been described. More importantly, the permeability characteristics of human and porcine small intestinal mucus secretions to sub-micron sized particles have been compared under simulated intestinal conditions. Negatively charged, 500 nm latex beads were used in multiple-particle tracking experiments to examine the heterogeneity and penetrability of mucus from different sources. Diffusion of the probe particles in adult human ileal mucus and adult pig jejunal and ileal mucus revealed no significant differences in microstructural organisation or microviscosity between the three mucus types (P > 0.05). In contrast to this interspecies similarity, the intraspecies comparison of particle diffusivity in the mucus obtained from adult pigs vs. 2-week old piglets showed better penetrability of the piglet mucus. The mean Stokes–Einstein viscosity of the piglet jejunal mucus was approx. two times lower than the viscosity of the pig jejunal mucus (P < 0.05). All mucus structures were also visualised by scanning electron microscopy. This work validates the use of porcine small intestinal mucus collected from fully-grown pigs for studying colloidal transport of sub-micron sized particles in mucus under conditions mimicking the adult human small intestinal environment.

Uptake of silica particulate drug carriers in an intestine-on-a-chip: towards a better in vitro model of nanoparticulate carrier and mucus interactions

Micro and nano-particulate carriers have potential to increase bioavailability of oral drugs, but must first overcome the mucus barrier of the intestinal epithelium to facilitate absorption and entry to systemic circulation. We report on mucus-silica nanoparticulate carrier interactions in an in vitro intestine-on-a-chip (IOAC) microfluidic model. Caco-2 cells cultured within the IOAC model recapitulate the morphology of the human intestinal epithelium that is currently lacking in traditional static Transwell models. Fine control over the cell culture conditions produced a mucus layer, previously problematic to achieve without employing cell co-culture. The microdevice design also allowed for direct imaging of silica particulate carrier (40-700 nm) uptake through the mucus and cellular monolayer. PEGylated particulate carriers penetrated more readily through the mucus layer compared to non-PEGylated particulate carriers while larger particulate carriers tended to retard particulate carrier penetration through a dense mucus mesh. This was confirmed via imaging flow cytometry and UV-fluorescence spectroscopy. The IOAC also demonstrated the ability to mimic intestinal peristaltic fluidic conditions, which in turn affects the particulate carrier uptake. This in vitro IOAC model has potential to directly elucidate mucus interactions and uptake mechanisms for a range of drug carrier systems.

Novel O/W nanoemulsions for nasal administration: Structural hints in the selection of performing vehicles with enhanced mucopenetration

We propose novel oil-in-water nanoemulsions (O/W NEs) including PEGylated surfactants and chitosan, showing good biocompatibility and optimization for nasal administration of drugs or vaccines. The transmucosal route has been shown to be ideal for a fast and efficient absorption and represents a viable alternative when the oral administration is problematic. The critical structural features in view of optimal encapsulation and transmucosal delivery were assessed by characterizing the NEs with complementary scattering techniques, i.e. dynamic light scattering (DLS), small angle X-ray (SAXS) and neutron scattering (SANS). Combined results allowed for selecting the formulations with the best suited structural properties and in addition establishing their propensity to enter the mucus barrier. To this scope, mucin was used as a model system and the effect of adding chitosan to the NEs, as adjuvant, was investigated. Remarkably, the presence of chitosan had a positive impact on the diffusion of the NE particles through the mucin matrix. We can infer that chitosan-mucin interaction induces density inhomogeneity and an increase in the pore size within the gel matrix that enhances the PEGylated NEs mobility. The coupling of mucoadhesive and mucopenetrating agents is shown to be a promising strategy for innovative transmucosal delivery systems.

Delivery of tacrolimus with cationic lipid-assisted nanoparticles for ulcerative colitis therapy

Oral drug delivery with nanoparticles has demonstrated great potential for drugs with poor bioavailability. Efficient delivery is possible by overcoming both the mucus and epithelial barrier of the gastrointestinal tract (GIT). Cationic lipid-assisted nanoparticles (CLANs), which are composed of amphiphilic block copolymers and cationic lipids, have been well studied and have been proved beneficial for drug delivery. In this study, CLANs prepared by poly(ethylene glycol)-block-poly(lactic acid) (PEG-b-PLA) and 1,2-dioleoyl-3-trimethylammonium-propanechloride (DOTAP) or N,N-bis(2-hydroxyethyl)-N-methyl-N-(2-cholesteryloxycarbonyl aminoethyl)ammoniumbromide (BHEM-Chol) were used for oral delivery of tacrolimus (FK506) for ulcerative colitis treatment. The average size of these nanoparticles is around 110 nm and the zeta-potential is 35 mV. These nanoparticles maintained their size in buffer solutions of pH 1.2 and 6.8, and slowly release the encapsulated drug. CLANs can be accumulated in the colon and transported through the epithelium in the colitis model by dextran sulfate sodium salt (DSS), leading to attenuation of DSS-induced colitis.

Modulating intestinal mucus barrier for nanoparticles penetration by surfactants

Improving peroral delivery efficiency is always a persistent goal for both small-molecule and macromolecular drug development. However, intestinal mucus barrier which greatly impedes drug-loaded nanoparticles penetration is commonly overlooked. Therefore, in this study, taking fluorescent labeled PLGA (poly (lactic-co-glycolic acid)) nanoparticles as a tool, the influence of anionic and nonionic surfactants on mucus penetration ability of nanoparticles and their mucus barrier regulating ability were studied. The movement of PLGA nanoparticles in mucus was tracked by multiple particles tracking method (MPT). Alteration of mucus properties by addition of surfactants was evaluated by rheology and morphology study. Rat intestinal villus penetration study was used to further evaluate penetration enhancement of nanoparticles. The effective diffusivities of the nanoparticles in surfactants pretreated mucus were increased by 2–3 times and the mucus barrier regulating capacity was also surfactant type dependent. Sodium dodecyl sulfate (SDS) increased the complex viscosity and viscoelastic properties of mucus, but poloxamer presented a decreased trend. Tween 80 maintained the rheological property of the mucus. With the mucus barrier regulated by surfactants, the penetration of nanoparticles in intestinal villus was obviously increased. In summary, the mucus penetration ability of nanoparticles could be enhanced by altering mucus microenvironment with surfactants. Tween 80 which largely retains the original mucus rheology and morphology properties may be a promising candidate for facilitating nanoparticle penetration through the mucus barrier with good safety profile.

Selective permeability of mucus barriers

Mucus is a hydrogel that exhibits complex selective permeability, permitting the passage of some particles while restricting the passage of other particles including important therapeutics. In this review, we discuss biochemical mechanisms underlying mucus penetration and mucus binding, emphasizing the importance of steric, electrostatic, and hydrophobic interactions. We discuss emerging techniques for engineering nanoparticle surface chemistries for mucus penetration as well as recent advances in tuning mucus interactions with small molecule, peptide, or protein therapeutics. Finally, we highlight recent work suggesting that mucus permeability can serve as a biomarker for disease and physiological states such as pregnancy.