The effect of cisplatin on the nanoscale structure of aqueous PEO-PPO-PEO micelles of varying hydrophilicity observed using SAXS

Effect of Acetaminophen on Poloxamer 407 Micelles and Hydrogels: The Relationship between Structural and Physical Properties

Poloxamer hydrogel possesses thermosensitive sol-gel transition characteristics and is widely used as a drug-controlled-release carrier for topical or injectable formulations. In this study, the effect of loading of a drug, acetaminophen (ACE), on the physical and structural properties of poloxamer 407 (P407) micelles and hydrogels was investigated. Differential scanning calorimetry measurements revealed that ACE reduced the critical micelle temperature and enthalpy of micellization of P407 solutions. The P407 micellization was promoted by ACE incorporation. Rheometry showed that ACE increased the sol-gel transition temperature and reduced the gel strength of P407. In situ small-angle X-ray scattering (SAXS) using synchrotron radiation revealed that ACE altered the structure of P407 micelles and their packing in the P407 gels. As ACE concentration increased, the P407 micelle packing changed from a face-centered cubic phase to a body-centered cubic phase. Furthermore, ACE disordered the micelle packing structure and induced the formation of an amorphous phase. Structural analysis of the P407 micelle packing indicated that ACE reduced the aggregation number (Nagg) of P407 micelles in the gels. The SAXS study for diluted P407 solutions revealed that ACE reduced the P407 micelle size and its uniformity. The structural changes in P407 micelles by ACE loading (e.g., the reduction of Nagg, size, and size uniformity) would alter the micelle packing structure. It was found that these structural changes of micelle packing, especially the formation of an amorphous phase, could destabilize the P407 gel. As a result, the physical properties of P407 gels, such as gelation temperature and gel strength, were changed. This relationship between the structure and physical property of drug-loaded P407 gels was well-explained by correlating the micelle and gel structures. The mechanistic understanding of the change in the physical properties of P407 gels by drug loading is essential for the effective development of poloxamer gel formulations.

Impact of small molecule and reverse poloxamer addition on the micellization and gelation mechanisms of poloxamer hydrogels

Poloxamer 407 (P407) is widely used for targeted drug-delivery because it exhibits thermoresponsive gelation behavior near body temperature, stemming from a disorder-to-order transition. Hydrophobic small molecules can be encapsulated within P407; however, these additives often negatively impact the rheological properties and lower the gelation temperatures of the hydrogels, limiting their clinical utility. Here we investigate the impact of adding two BAB reverse poloxamers (RPs), 25R4 and 31R1, on the thermal transitions, rheological properties, and assembled structures of P407 both with and without incorporated small molecules. By employing a combination of differential scanning calorimetry (DSC), rheology, and small-angle x-ray scattering (SAXS), we determine distinct mechanisms for RP incorporation. While 25R4 addition promotes inter-micelle bridge formation, the highly hydrophobic 31R1 co-micellizes with P407. Small molecule addition lowers thermal transition temperatures and increases the micelle size, while RP addition mitigates the decreases in modulus traditionally associated with small molecule incorporation. This fundamental understanding yields new strategies for tuning the mechanical and structural properties of the hydrogels, enabling design of drug-loaded formulations with ideal thermal transitions for a range of clinical applications.

A meta-analysis of bone cement mediated antibiotic release: Overkill, but a viable approach to eradicate osteomyelitis and other infections tied to open procedures

A number of clinical studies have highlighted the success of antibiotics formulated at concentrations between 0 and 6% w/w into bone cements to address localized infections. Separately, some commercial manufacturers have produced gentamycin-infused bone cement mixtures as a countermeasure to infection. The anecdotal evidence suggests that antibiotic infused cements can help eradicate or delay the onset of infections. Quantifying the functionality of that response is more challenging. We have surveyed the literature to identify studies in which controlled drug release or mechanical behavioral assessments have been conducted on drug-infused cements. The focus here is on vancomycin (VAN) in part due to its higher potency relative to gentamycin and its more common usage for staph infections. Takeaways from the limited pool of research studies indicate that large fractions (>99%) of the infused vancomycin remain sequestered in the cement and aren't bioavailable after solidification. Antibiotic fluence ranged from 1 to 283 μg/cm²hr. The initial strength of the various antibiotic loaded samples as produced were 52-96 MPa. Simulated exposures in a fluid environment by submersion reduced the antibiotic loaded strengths between 3 and 29%. Some strength measurements were noted below the ASTM F451 standard for acrylic bone cement although drug releasing spacers likely have different requirements. The glassy behavior of the cured cement led to both vancomycin and gentamicin having low permeability and a burst response. Smaller drug molecules and more gel-like immobilization matrices with lower glass transition temperatures offer higher potential for larger and more comprehensive drug bioavailability.

Polymeric micelles in drug delivery: An insight of the techniques for their characterization and assessment in biorelevant conditions

Polymeric micelles, i.e. aggregation colloids formed in solution by self-assembling of amphiphilic polymers, represent an innovative tool to overcome several issues related to drug administration, from the low water-solubility to the poor drug permeability across biological barriers. With respect to other nanocarriers, polymeric micelles generally display smaller size, easier preparation and sterilization processes, and good solubilization properties, unfortunately associated with a lower stability in biological fluids and a more complicated characterization. Particularly challenging is the study of their interaction with the biological environment, essential to predict the real in vivo behavior after administration. In this review, after a general presentation on micelles features and properties, different characterization techniques are discussed, from the ones used for the determination of micelles basic characteristics (critical micellar concentration, size, surface charge, morphology) to the more complex approaches used to figure out micelles kinetic stability, drug release and behavior in the presence of biological substrates (fluids, cells and tissues). The techniques presented (such as dynamic light scattering, AFM, cryo-TEM, X-ray scattering, FRET, symmetrical flow field-flow fractionation (AF4) and density ultracentrifugation), each one with their own advantages and limitations, can be combined to achieve a deeper comprehension of polymeric micelles in vivo behavior. The set-up and validation of adequate methods for micelles description represent the essential starting point for their development and clinical success.