Triggered Release of Ampicillin from Metallic Implant Coatings for Combating Periprosthetic Infections.

Periprosthetic infections caused by Staphylococcus aureus (S. aureus) pose unique challenges in orthopedic surgeries, in part due to the bacterium's capacity to invade surrounding bone tissues besides forming recalcitrant biofilms on implant surfaces. We previously developed prophylactic implant coatings for the on-demand release of vancomycin, triggered by the cleavage of an oligonucleotide (Oligo) linker by micrococcal nuclease (MN) secreted by the Gram-positive bacterium, to eradicate S. aureus surrounding the implant in vitro and in vivo. Building upon this coating platform, here we explore the feasibility of extending the on-demand release to ampicillin, a broad-spectrum aminopenicillin ß-lactam antibiotic that is more effective than vancomycin in killing Gram-negative bacteria that may accompany S. aureus infections. The amino group of ampicillin was successfully conjugated to the carboxyl end of an MN-sensitive Oligo covalently integrated in a polymethacrylate hydrogel coating applied to titanium alloy pins. The resultant Oligo-Ampicillin hydrogel coating released the ß-lactam in the presence of S. aureus and successfully cleared nearby S. aureus in vitro. When the Oligo-Ampicillin-coated pin was delivered to a rat femoral canal inoculated with 1000 cfu S. aureus, it prevented periprosthetic infection with timely on-demand drug release. The clearance of the bacteria from the pin surface as well as surrounding tissue persisted over 3 months, with no local or systemic toxicity observed with the coating. The negatively charged Oligo fragment attached to ampicillin upon cleavage from the coating did diminish the antibiotic's potency against S. aureus and Escherichia coli (E. coli) to varying degrees, likely due to electrostatic repulsion by the anionic surfaces of the bacteria. Although the on-demand release of the ß-lactam led to adequate killing of S. aureus but not E. coli in the presence of a mixture of the bacteria, strong inhibition of the colonization of the remaining E. coli on hydrogel coating was observed. These findings will inspire considerations of alternative broad-spectrum antibiotics, optimized drug conjugation, and Oligo linker engineering for more effective protection against polymicrobial periprosthetic infections.

Viscoelasticity of a carbon nanotube-laden air-water interface.

The viscoelasticity of a carbon nanotube (CNT)-laden air-water interface was characterized using two different experimental methods. The first experimental method used a Langmuir-Pockels (LP) trough coupled with a pair of oscillating barriers. The second method is termed the Bicone-Trough (BT) method, where a LP trough was custom-built and fit onto a rheometer equipped with a bicone fixture to standardize the preparation and conditioning of a particle-laden interface especially at high particle coverages. The performance of both methods was evaluated by performing Fast Fourier Transform (FFT) analysis to calculate the signal-to-noise ratios (SNR). Overall, the rheometer-based BT method offered better strain control and considerably higher SNRs compared to the Oscillatory Barriers (OB) method that oscillated barriers with relatively limited positional and speed control. For a CNT surface coverage of 165 mg/m2 and a frequency of 100 mHz, the interfacial shear modulus obtained from the OB method increased from 39 to 57 mN/m as the normal strain amplitude increased from 1 to 3%. No linear viscoelastic regime was experimentally observed for a normal strain as small as 0.5%. In the BT method, a linear regime was observed below a shear strain of 0.1%. The interfacial shear modulus decreased significantly from 96 to 2 mN/m as the shear strain amplitude increased from 0.025 to 10%.

Numerical study of drop dynamics for inkjet based 3D printing of pharmaceutical tablets.

Interest in 3D printing has been growing rapidly especially in pharmaceutical industry due to its multiple advantages such as manufacturing versatility, personalization of medicine, scalability, and cost effectiveness. Inkjet based 3D printing gained special attention after FDA's approval of Spritam® manufactured by Aprecia pharmaceuticals in 2015. The precision and printing efficiency of 3D printing is strongly influenced by the dynamics of ink/binder jetting, which further depends on the ink's fluid properties. In this study, Computational Fluid Dynamics (CFD) has been utilized to study the drop formation process during inkjet-based 3D printing for piezoelectric and thermal printhead geometries using Volume of Fluid (VOF) method. To develop the CFD model commercial software ANSYS-Fluent was used. The developed CFD model was experimentally validated using drop watcher setup to record drop progression and drop velocity. During the study, water, Fujifilm model fluid, and Amitriptyline drug solutions were evaluated as the ink solutions. The drop properties such as drop volume, drop diameter, and drop velocity were examined in detail in response to change ink solution properties such as surface tension, viscosity, and density. A good agreement was observed between the experimental and simulation data for drop properties such as drop volume and drop velocity.

Modulating On-Demand Release of Vancomycin from Implant Coatings via Chemical Modification of a Micrococcal Nuclease-Sensitive Oligonucleotide Linker.

Periprosthetic infections are one of the most serious complications in orthopedic surgeries, and those caused by Staphylococcus aureus (S. aureus) are particularly hard to treat due to their tendency to form biofilms on implants and their notorious ability to invade the surrounding bones. The existing prophylactic local antibiotic deliveries involve excessive drug loading doses that could risk the development of drug resistance strains. Utilizing an oligonucleotide linker sensitive to micrococcal nuclease (MN) cleavage, we previously developed an implant coating capable of releasing covalently tethered vancomycin, triggered by S. aureus-secreted MN, to prevent periprosthetic infections in the mouse intramedullary (IM) canal. To further engineer this exciting platform to meet broader clinical needs, here, we chemically modified the oligonucleotide linker by a combination of 2'-O-methylation and phosphorothioate modification to achieve additional modulation of its stability/sensitivity to MN and the kinetics of MN-triggered on-demand release. We found that when all phosphodiester bonds within the oligonucleotide linker 5'-carboxy-mCmGTTmCmG-3-acrydite, except for the one between TT, were replaced by phosphorothioate, the oligonucleotide (6PS) stability significantly increased and enabled the most sustained release of tethered vancomycin from the coating. By contrast, when only the peripheral phosphodiester bonds at the 5'- and 3'-ends were replaced by phosphorothioate, the resulting oligonucleotide (2PS) linker was cleaved by MN more rapidly than that without any PS modifications (0PS). Using a rat femoral canal periprosthetic infection model where 1000 CFU S. aureus was inoculated at the time of IM pin insertion, we showed that the prophylactic implant coating containing either 0PS- or 2PS-modified oligonucleotide linker effectively eradicated the bacteria by enabling the rapid on-demand release of vancomycin. No bacteria were detected from the explanted pins, and no signs of cortical bone changes were detected in these treatment groups throughout the 3 month follow-ups. With an antibiotic tethering dose significantly lower than conventional antibiotic-bearing bone cements, these coatings also exhibited excellent biocompatibility. These chemically modified oligonucleotides could help tailor prophylactic anti-infective coating strategies to meet a range of clinical challenges where the risks for S. aureus prosthetic infections range from transient to long-lasting.

Pilot-scale binder jet 3D printing of sustained release solid dosage forms.

The additive nature and versatility of 3D printing show great promise in the rapid prototyping of solid dosage forms for clinical trials and mass customization for personalized medicine applications. This paper reports the formulation and process development of sustained release solid dosage forms, termed "printlets", using a pilot-scale binder jetting (BJT) 3D printer and acetaminophen (APAP) as the model drug. With the inclusion of hydroxypropyl methylcellulose (HPMC) as a release retardant polymer in the print powder, the drug release time of APAP increased considerably from minutes to hours. However, given the swelling propensity of HPMC, a thicker layer of powder must be laid down during printing to avoid any shape distortion of the printlets. For a fixed print volume, the level of binder saturation (i.e., ratio between the liquid binder and powder in the as-printed sample) is inversely proportional to the thickness of the spread powder layer. An increase in the spread powder layer inadvertently resulted in a lower level of binder saturation and consequently weaker printlets. By increasing the level of binder saturation with jetting from more print heads, the mechanical strength of printlets containing 18% HPMC was successfully restored. The resultant printlets have a drug release time of 3.5 h and a breaking force of 12.5 kgf that is comparable to the fast-disintegrating printlets containing no HPMC and surpasses manually pressed tablets with the same HPMC content.

Development of a pilot-scale HuskyJet binder jet 3D printer for additive manufacturing of pharmaceutical tablets.

This paper reports a custom-built binder jet 3D printer for pilot-scale manufacturing of pharmaceutical tablets. The printer is equipped with high-throughput piezoelectric inkjet print heads and allows direct control of several key process parameters, including the build layer thickness, amount of jetted liquid binder, and powder spreading rate. The effects of these parameters on the properties of the as-printed tablets were studied using a powder mixture of lactose monohydrate and Kollidon® VA64 (KL) and an aqueous binder containing 5% of KL. The appropriate processing windows for two different powder spreading rates were identified, and the final properties of the printed samples were explained using a dimensionless "degree of overlap" parameter which is defined as the ratio between the penetrating depth of the binder into the powder and the build layer thickness. Lastly, 10% of indomethacin was added to the powder feedstock as a model drug. Drug-loaded tablets were produced at a rate of 32 tablets/min, having an average breaking force of 9.4 kgf, a friability of 2.5%, and an average disintegration time of 8 s. These properties are comparable to commercially available tablets and represent one of the best values reported in the literature of 3D printed tablets thus far.

Toward Long-Term Accurate and Continuous Monitoring of Nitrate in Wastewater Using Poly(tetrafluoroethylene) (PTFE)-Solid-State Ion-Selective Electrodes (S-ISEs).

Long-term accurate and continuous monitoring of nitrate (NO3-) concentration in wastewater and groundwater is critical for determining treatment efficiency and tracking contaminant transport. Current nitrate monitoring technologies, including colorimetric, chromatographic, biometric, and electrochemical sensors, are not feasible for continuous monitoring. This study addressed this challenge by modifying NO3- solid-state ion-selective electrodes (S-ISEs) with poly(tetrafluoroethylene) (PTFE, (C2F4)n). The PTFE-loaded S-ISE membrane polymer matrix reduces water layer formation between the membrane and electrode/solid contact, while paradoxically, the even more hydrophobic PTFE-loaded S-ISE membrane prevents bacterial attachment despite the opposite approach of hydrophilic modifications in other antifouling sensor designs. Specifically, an optimal ratio of 5% PTFE in the S-ISE polymer matrix was determined by a series of characterization tests in real wastewater. Five percent of PTFE alleviated biofouling to the sensor surface by enhancing the negative charge (-4.5 to -45.8 mV) and lowering surface roughness (Ra: 0.56 ± 0.02 nm). It simultaneously mitigated water layer formation between the membrane and electrode by increasing hydrophobicity (contact angle: 104°) and membrane adhesion and thus minimized the reading (mV) drift in the baseline sensitivity ("data drifting"). Long-term accuracy and durability of 5% PTFE-loaded NO3- S-ISEs were well demonstrated in real wastewater over 20 days, an improvement over commercial sensor longevity.

Binder-Jet 3D Printing of Indomethacin-laden Pharmaceutical Dosage Forms.

Emerging 3D printing technologies offer an exciting opportunity to create customized 3D objects additively from a digital design file. 3D printing may be further leveraged for personalized medicine, clinical trial, and controlled release applications. A wide variety of 3D printing methods exists, and many studies focus on extrusion-based 3D printing techniques that closely resemble hot melt extrusion. In this paper, we explore different pharmaceutical-grade feedstock materials for creating tablet-like dosage forms using a binder jet 3D printing method. In this method, pharmaceutical-grade powders are repeatedly spread onto a build plate, followed by inkjet printing a liquid binder to selectively bind the powders in a predetermined pattern. The physical properties of the pharmaceutical-grade powders and binders have been characterized and a molding method has been developed to select appropriate powder and binder materials for subsequent printing experiments. There was a correlation between the breaking forces of the molded and printed samples, but no clear correlation was observed for disintegration time, which was primarily controlled by the higher porosity of the printed samples. The breaking force and disintegration properties of as-printed and post-processed samples containing indomethacin as an active pharmaceutical ingredient have been measured and compared with relevant literature data.

Correlation of the hierarchical structure with rheological behavior of polypseudorotaxane gel composed of pluronic and ß-cyclodextrin.

We have identified the hierarchical (primary, secondary, tertiary and quaternary) structures of a polypseudorotaxane (PPR) gel composed of the Pluronic F108 and ß-cyclodextrin system to be ß-cyclodextrin crystalline, lamellar sheets, lamellar stacks and "grains", respectively. The correlation between the rheological properties and the proposed structures under shear flows was rationalized. Alignment of lamellar stacks and reorganization of grain boundaries under shear flows were investigated by rheo-SANS, small angle X-ray scattering and small-angle light scattering. The relaxation of highly aligned lamellar stacks is slow (>2 h) after flow cessation compared to that of the regrouped grains (a few minutes). The main contribution to thixotropic behavior is likely from the faster relaxation of the reorganized grains containing highly oriented lamellar stacks. The comprehensive understanding of structure-function relationship of the PPR gel will facilitate the rational design for its applications.

What causes the anomalous aggregation in pluronic aqueous solutions?

Pluronic (PL) block copolymers have been widely used as delivery carriers, molecular templates for porous media, and process additives for affecting rheological behavior. Unlike most surfactant systems, where unimer transforms into micelle with increased surfactant concentration, anomalous large PL aggregates below the critical micelle concentration (CMC) were found throughout four types of PL (F108, F127, F88 and P84). We characterized their structures using dynamic light scattering and small-angle X-ray/neutron scattering. Molecular dynamics simulations suggest that the PPO segments, though weakly hydrophobic interaction (insufficient to form micelles), promote the formation of large aggregates. Addition of acid or base (e.g. citric acid, acetic acid, HCl and NaOH) in F108 solution significantly suppresses the aggregate formation for up to 20 days due to the repulsion force from the attached H3O+ molecules on the EO segment in both PEO and PL and the reduction of CMC through the salting out effect, respectively.

Correlated changes in structure and viscosity during gelatinization and gelation of tapioca starch granules.

Melting of native tapioca starch granules in aqueous pastes upon heating is observed in situ using simultaneous small- and wide-angle X-ray scattering (SAXS/WAXS) and solution viscometry. Correlated structure and viscosity changes suggest closely associated amylose and amylopectin chains in the semicrystalline layers, and the release of amylose chains for enhanced solution viscosity occurs largely after melting of the semicrystalline structure. Before melting, WAXS results reveal mixed crystals of A- and B-types (∼4:1 by weight), whereas SAXS results indicate that the semicrystalline layers are composed of lamellar blocklets of ca 43 nm domain size, with polydisperse crystalline (≃7.5 nm) and amorphous (≃1.1 nm) layers alternatively assembled into a lamellar spacing of ≃8.6 nm with 20% polydispersity. Upon melting, the semicrystalline lamellae disintegrate into disperse and molten amylopectin nanoclusters with dissolved and partially untangled amylose chains in the aqueous matrix which leads to increased solution viscosity. During subsequent cooling, gelation starts at around 347 K; successively increased solution viscosity coincides with the development of nanocluster aggregation to a fractal dimension ≃2.3 at 303 K, signifying increasing intercluster association through collapsed amylose chains owing to decreased solvency of the aqueous medium with decreasing temperature.