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Synovial fluid lubricates articular joints by forming a hydrated layer between the cartilage surfaces. In degenerative joint diseases like osteoarthritis (OA), the synovial fluid is compromised, which leads to less effective innate lubrication and exacerbated cartilage degeneration. Studies over the years have led to the development of partially or fully synthetic biolubricants to reduce the coefficient of friction with cartilage in knee joints. Cartilage-adhering, hydrated lubricants are particularly important to provide cartilage lubrication and chondroprotection under high normal load and slow speed. Here, we report the development of a hyaluronic acid (HA)-based lubricant functionalized with cationic branched poly-l-lysine (BPL) molecules that bind to cartilage via electrostatic interactions. We surmised that the electrostatic interactions between the BPL-modified HA molecules (HA-BPL) and the cartilage facilitate localization of the HA molecules to the cartilage surface. The number of BPL molecules on the HA backbone was varied to determine the optimal grafting density for cartilage binding and HA localization. Collectively, our results show that our HA-BPL molecules adhered readily to cartilage and were effective as a lubricant in cartilage-on-cartilage shear measurements where the modified HA molecules significantly reduce the coefficient of friction compared to phosphate-buffered saline or HA alone. This proof-of-concept study shows how the incorporation of cartilage adhering moieties, such as cationic molecules, can be used to enhance cartilage binding and lubrication properties of HA.

Bone tissue undergoes continuous remodeling viaosteoclast-mediated bone resorption and osteoblast-mediated bone formation. An imbalance in this process with enhanced osteoclastic activity can lead to excessive bone resorption, resulting in bone thinning. Once activated, osteoclasts bind to the bone surface and acidify the local niche. This acidic environment could serve as a potential trigger for the delivery of therapeutic agents into the osteoporotic bone tissue. To this end, we developed a pH-responsive nanocarrier-based drug delivery system that binds to the bone tissue and delivers an osteoanabolic molecule, adenosine. Adenosine is incorporated into a hyaluronic acid (HA)-based nanocarrier through a pH-sensitive ketal group. The HA-nanocarrier is further functionalized with alendronate moieties to improve binding to the bone tissues. Systemic administration of the nanocarrier containing adenosine attenuated bone loss in ovariectomized mice and showed comparable bone qualities to that of healthy mice. Delivery of osteoanabolic small molecules that can contribute to bone formation and inhibit excessive osteoclast activity by leveraging the tissue-specific milieu could serve as viable therapeutics for osteoporosis.

Preventing bacterial biofilm formation on medical devices and implants in vivo still remains a daunting task. Current antibacterial coatings to combat implant-associated infections are generally composed of toxic metals or nondegradable polymers and involve multistep surface modifications. Here, we present a charge-switchable antibacterial and antibiofilm coating based on water-insoluble cationic hydrophobic polymers that are soluble in organic solvents and can be noncovalently coated onto different surfaces. Toward this, a library of quaternary polyethylenimine (QPEI) polymers with an amide or ester group in their pendant alkyl chain was developed. These QPEIs are shown to hydrolyze from active cationic to nontoxic zwitterionic polymers under acidic or enzymatic conditions. Notably, polymers with both zwitterionic and cationic groups, obtained upon partial hydrolysis of QPEIs, are shown to retain their antibacterial activity with much lower toxicity toward mammalian cells. Furthermore, the zwitterionic polymer, a fully hydrolyzed product of the QPEIs, is shown to be nontoxic to mammalian cells in vitro as well as in vivo. The QPEIs, when coated onto surfaces, kill bacteria and prevent formation of biofilms. In an in vivo mice model, the QPEI-coated medical grade catheter is shown to reduce methicillin-resistant Staphylococcus aureuscontamination both on the catheter surface and in the adjacent tissues (99.99% reduction compared to a noncoated catheter). Additionally, biofilm formation is inhibited on the catheter surface with negligible inflammation in the adjacent tissue. The above results thus highlight the importance of these polymers to be used as effective antibacterial coatings in biomedical applications.

We present vancomycin-loaded dual-function injectable hydrogel that delivers antibiotic locally suitable for treatment of infections in avascular or necrotic tissues. The syringe-deliverable gels were developed using polydextran aldehyde and an inherently antibacterial polymer N-(2-hydroxypropyl)-3-trimethylammonium chitosan chloride along with vancomycin. The antibiotic was primarily encapsulated via reversible imine bonds formed between vancomycin and polydextran aldehyde in the hydrogel which allowed sustained release of vancomycin over an extended period of time in a pH-dependent manner. Being inherently antibacterial, the gels displayed excellent efficacy against bacteria due to dual mode of action (killing bacteria upon contact as well as by releasing antibiotics into surroundings). Upon subcutaneous implantation, the gel was shown to kill methicillin-resistant Staphylococcus aureus(>99.999%) when bacteria were introduced directly into the gel as well as at distal site from the gel in a mice model. These materials thus represent as novel noninvasive drug-delivery device suitable for local antibiotic therapy.

Polymer–silver nanocomposites have emerged as an integral weapon to combat device-related infections. However, synthesis of the nanocomposites still remains a major challenge that often involves two-step process in which silver nanoparticles are synthesized ex situ. Additionally, polymers used in the nanocomposites are commonly not antimicrobial and biodegradable thus often lack bioactivity and biocompatibility. Herein we report highly active dual-function polymer-silver nanocomposites consisting of an inherently antimicrobial and biodegradable polymer in one-pot. A simple method of in situ reduction of a silver salt was employed to synthesize the silver nanoparticles (5–15 nm) from silver para-toluenesulfonate in which the intrinsically biodegradable and antimicrobial polymer N,N-dimethyl-N-hexadecyl ammonium chitin tosylate acted as reducing as well as stabilizing agent. The nanocomposite with the water-insoluble and organo-soluble polymer was simply painted onto surfaces via facile noncovalent immobilization. Notably, composite-coated surfaces inactivated both drug-sensitive and drug-resistant bacteria including pathogenic fungi at a much faster rate than polymer alone. The composites released active silver ions over an extended period of time and displayed remarkably long-lasting activity. In addition, surfaces coated with composites effectively inhibited both bacterial and fungal biofilm formation. Further, upon coating on catheter, the nanocomposites reduced methicillin-resistant Staphylococcus aureus(MRSA) burden both on catheter (>99.99% reduction) and in tissues surrounding the catheter (>99.999% reduction) in a mice model. These novel nanomaterials that showed negligible hemolysis toward human erythrocytes might be used as safe and effective antimicrobial coatings in biomedical device applications.

Radiotherapy remains a common treatment modality for cancer despite skeletal complications. However, there are currently no effective treatments for radiation-induced bone loss, and the consequences of radiotherapy on skeletal progenitor cell (SPC) survival and function remain unclear. After radiation, leptin receptor–expressing cells, which include a population of SPCs, become localized to hypoxic regions of the bone and stabilize the transcription factor hypoxia-inducible factor-2α (HIF-2α), thus suggesting a role for HIF-2α in the skeletal response to radiation. Here, we conditionally knocked out HIF-2α in leptin receptor–expressing cells and their descendants in mice. Radiation therapy in littermate control mice reduced bone mass; however, HIF-2α conditional knockout mice maintained bone mass comparable to nonirradiated control animals. HIF-2α negatively regulated the number of SPCs, bone formation, and bone mineralization. To test whether blocking HIF-2α pharmacologically could reduce bone loss during radiation, we administered a selective HIF-2α inhibitor called PT2399 (a structural analog of which was recently FDA-approved) to wild-type mice before radiation exposure. Pharmacological inhibition of HIF-2α was sufficient to prevent radiation-induced bone loss in a single-limb irradiation mouse model. Given that ~90% of patients who receive a HIF-2α inhibitor develop anemia because of off-target effects, we developed a bone-targeting nanocarrier formulation to deliver the HIF-2α inhibitor to mouse bone, to increase on-target efficacy and reduce off-target toxicities. Nanocarrier-loaded PT2399 prevented radiation-induced bone loss in mice while reducing drug accumulation in the kidney. Targeted inhibition of HIF-2α may represent a therapeutic approach for protecting bone during radiation therapy.

Cationic small molecular biocides have been developed as promising antibiofilm agents because of their tunability in chemical structures and their ability to disrupt established biofilms. However, the impact of biocides in antibiofilm treatment is largely limited due to the lack of an effective delivery system that can ensure sustained release of biocides at the target site. Herein we report a biocide-encapsulated antibacterial and antibiofilm hydrogel that acts as an efficient delivery vehicle for the biocide and eradicates matured bacterial biofilm. The hydrogels are prepared using dextran methacrylate (Dex-MA), a biocompatible and photopolymerizable polymer, and a nontoxic cationic biocide with two cationic charges, two nonpeptidic amide bonds, and optimized amphiphilicity, which is capable of eradicating established bacterial biofilms. The gels, prepared via direct loading of the biocide and with highly controllable amounts, display 100% activity against both drug-sensitive and drug-resistant bacteria such as methicillin-resistant Staphylococcus aureus(MRSA). Importantly, the gels are shown to release the biocide and kill bacteria for an extended period of time (until day 5). When being treated with the established bacterial biofilms, the released biocide from the gel is shown to completely eradicate establishedS. aureus, Escherichia coli, and MRSA biofilms, the most common biofilm forming bacteria that cause severe infections (e.g., skin infections, urinary tract infections, etc.) in humans. Moreover, the gels were shown to annihilate preformed MRSA biofilm with >99.99% bacterial reduction under in vitroand in vivoconditions in a superficial MRSA infection model in mice. Notably, when tested, excellent skin compatibility is observed for these materials in various animal models such as a rat model of acute dermal toxicity, guinea pig model of skin sensitization, and rabbit model of skin irritation. The biocompatible antibacterial and antibiofilm hydrogels developed herein thus might be useful in treating bacterial biofilm associated infections, especially topical infections.

Two component injectable hydrogels that cross-link in situ have been used as noninvasive wound-filling devices, i.e., sealants. These materials carry a variety of functions at the wound sites, such as sealing leaks, ceasing unwanted bleeding, binding tissues together, and assisting in wound healing processes. However, commonly used sealants typically lack antibacterial properties. Since bacterial infection at the wound site is very common, bioadhesive materials with intrinsic antibacterial properties are urgently required. Herein, we report a biocompatible injectable hydrogel with inherent bioadhesive, antibacterial, and hemostatic capabilities suitable for wound sealing applications. The hydrogels were developed in situ from an antibacterial polymer, N-(2-hydroxypropyl)-3-trimethylammonium chitosan chloride (HTCC), and a bioadhesive polymer, polydextran aldehyde. The gels were shown to be active against both Gram-positive and Gram-negative bacteria, including drug-resistant ones such as methicillin-resistant Staphylococcus aureus(MRSA), vancomycin-resistant Enterococcus faecium(VRE), and β-lactam-resistant Klebsiela pneumoniae. Mechanistic studies revealed that the gels killed bacteria upon contact by disrupting the membrane integrity of the pathogen. Importantly, the gels were shown to be efficacious in preventing sepsis in a cecum ligation and puncture (CLP) model in mice. While only 12.5% of animals survived in the case of mice with punctured cecam but with no gel on the punctured area (control), 62.5% mice survived when the adhesive gel was applied to the punctured area. Furthermore, the gels were also shown to be effective in facilitating wound healing in rats and ceasing bleeding from a damaged liver in mice. Notably, the gel showed negligible toxicity toward human red blood cells (only 2–3% hemolysis) and no inflammation to the surrounding tissue upon subcutaneous implantation in mice, thus proving it as a safe and effective antibacterial sealant.

Bacterial colonization and subsequent formation of biofilms onto surfaces of medical devices and implants is a major source of nosocomial infections. Most antibacterial coatings to combat infections are either metal-based or nondegradable-polymer-based and hence limited by their nondegradability and unpredictable toxicity. Moreover, to combat infections effectively, the coatings are required to display simultaneous antibacterial and antibiofilm activity. Herein we report biocompatible and biodegradable coatings based on organo-soluble quaternary chitin polymers which were immobilized noncovalently onto surfaces as bactericidal paint. The polycationic paint was found to be active against both drug-sensitive and -resistant bacteria such as methicillin-resistant Staphylococcus aureus(MRSA), vancomycin-resistant Enterococcus faecium(VRE), and β-lactam-resistant Klebsiella pneumoniae. The cationic polymers were shown to interact with the negatively charged bacterial cell membrane and disrupt the membrane integrity, thereby causing leakage of intracellular constituents and cell death upon contact. Importantly, surfaces coated with the polymers inhibited formation of biofilms against both Gram-positive S. aureusand Gram-negative E. coli, two of the most clinically important bacteria that form biofilms. Surfaces coated with the polymers displayed negligible toxicity against human erythrocytes and embryo kidney cells. Notably, the polymers were shown to be susceptible toward lysozyme. Furthermore, subcutaneous implantation of polymer discs in rats led to 15–20% degradation in 4 weeks thereby displaying their biodegradability. In a murine model of subcutaneous infection, polymer-coated medical-grade catheter reduced MRSA burden by 3.7 log compared to that of noncoated catheter. Furthermore, no biofilm development was observed on the coated catheters under in vivoconditions. The polycationic materials thus developed herein represent a novel class of safe and effective coating agents for the prevention of device-associated infections.

The continuous rise of antimicrobial resistance and the dearth of new antibiotics in the clinical pipeline raise an urgent call for the development of potent antimicrobial agents. Cationic chitosan derivatives, N-(2-hydroxypropyl)-3-trimethylammonium chitosan chlorides (HTCC), have been widely studied as potent antibacterial agents. However, their systemic structure–activity relationship, activity toward drug-resistant bacteria and fungi, and mode of action are very rare. Moreover, toxicity and efficacy of these polymers under in vivoconditions are yet to be established. Herein, we investigated antibacterial and antifungal efficacies of the HTCC polymers against multidrug resistant bacteria including clinical isolates and pathogenic fungi, studied their mechanism of action, and evaluated cytotoxic and antimicrobial activities in vitroand in vivo. The polymers were found to be active against both bacteria and fungi (MIC = 125–250 μg/mL) and displayed rapid microbicidal kinetics, killing pathogens within 60–120 min. Moreover, the polymers were shown to target both bacterial and fungal cell membrane leading to membrane disruption and found to be effective in hindering bacterial resistance development. Importantly, very low toxicity toward human erythrocytes (HC50= >10000 μg/mL) and embryo kidney cells were observed for the cationic polymers in vitro. Further, no inflammation toward skin tissue was observed in vivofor the most active polymer even at 200 mg/kg when applied on the mice skin. In a murine model of superficial skin infection, the polymer showed significant reduction of methicillin-resistant Staphylococcus aureus(MRSA) burden (3.2 log MRSA reduction at 100 mg/kg) with no to minimal inflammation. Taken together, these selectively active polymers show promise to be used as potent antimicrobial agents in topical and other infections.

Extracellular adenosine plays a key role in promoting bone tissue formation. Local delivery of adenosine could be an effective therapeutic strategy to harness the beneficial effect of extracellular adenosine on bone tissue formation following injury. Herein, we describe the development of an injectable in situ curing scaffold containing microgel-based adenosine delivery units. The two-component scaffold includes adenosine-loaded microgels and functionalized hyaluronic acid (HA) molecules. The microgels were generated upon copolymerization of 3-acrylamidophenylboronic acid (3-APBA)- and 2-aminoethylmethacrylamide (2-AEMA)-conjugated HA (HA-AEMA) in an emulsion suspension. The PBA functional groups were used to load the adenosine molecules. Mixing of the microgels with the HA polymers containing clickable groups, dibenzocyclooctyne (DBCO) and azide (HA-DBCO and HA-Azide), resulted in a 3D scaffold embedded with adenosine delivery units. Application of the in situ curing scaffolds containing adenosine-loaded microgels following tibial fracture injury showed improved bone tissue healing in a mouse model as demonstrated by the reduced callus size, higher bone volume, and increased tissue mineral density compared to those treated with the scaffold without adenosine. Overall, our results suggest that local delivery of adenosine could potentially be an effective strategy to promote bone tissue repair.

Convergent advances in the field of soft matter, macromolecular chemistry, and engineering have led to the development of biomaterials that possess autonomous, adaptive, and self‐healing characteristics similar to living systems. These rationally designed biomaterials can surpass the capabilities of their parent material. Herein, the modification of hyaluronic acid (HA) to exhibit self‐healing properties is described, and its physical and biological function both in vitro and in vivo is studied. The in vitro findings showed that self‐healing HA designed to undergo self‐repair improves lubrication, enhances free radical scavenging, and attenuates enzymatic degradation compared to unmodified HA. Longitudinal imaging following intraarticular injection of self‐healing HA shows improved in vivo retention despite its low molecular weight. Concomitant with these functions, intraarticular injection of self‐healing HA mitigates anterior cruciate ligament injury‐mediated cartilage degeneration in rodents. This proof‐of‐concept study shows how incorporation of functional properties such as self‐healing can be used to surpass the existing capabilities of biolubricants. Modification of low molecular weight hyaluronic acid (HA) to exhibit self‐healing properties enhances its in vivo longevity and lubrication function. Concomitant with these functions, intraarticular injection of self‐healing HA mitigates joint injury‐mediated cartilage degeneration in rodents following anterior cruciate ligament transection.