Validation of electrochemical device setup for detection of dual antibiotic drug release from hydrogel.

Due to antimicrobial resistance that occurs throughout the world, antibiotic-releasing hydrogel with at least two drugs that synergistically treat stubborn bacteria is preferable for infection prevention. Hydrogel can serve as a drug reservoir to gradually release drugs in a therapeutic window to effectively treat microorganisms with minimal side effects. The study and development of drug releasing hydrogels requires a reliable, straightforward, cost-effective, fast, and low labor-intensive drug detection technique. In this study, we validate the electrochemical technique and device setup for real-time determination of dual antibacterial drugs released from a hydrogel. Concentrations of two representative antibacterial drugs, tetracycline (TC) and chloramphenicol (CAP), were determined using square wave voltammetry (SWV) mode that yields the lower limit of detection at 2.5 µM for both drugs. Measurement accuracy and repeatability were verified by 36 known drug combination concentrations. Capability in long-term measurement was confirmed by the measurement stability which was found to last for at least 72 h. Stirring was revealed as one of the significant factors for accurate real-time detection. Real-time measurement was ultimately performed to demonstrate the determination of multiple drug releases from a drug releasing hydrogel and validated by high-performance liquid chromatography (HPLC). All the results support that the electrochemical technique with the proposed device design and setup can be used to accurately and simultaneously determine dual drugs that are released from a hydrogel in real-time.

Drug-Releasing Tannic Acid-Mediated Adhesive PEG Hydrogel for Porous Titanium Implants.

Porous titanium implants are commonly utilized for orthopedic surgery because they can mimic the mechanical properties and porous structure of human bone. However, the bioinertness of titanium (Ti) has been reported to obstruct biointegration processes, resulting in slower bone repair. Here, we propose a localized drug delivery system on Ti surfaces using adhesive hydrogel to enhance biological-Ti interactions. The hydrogel was fabricated from polyethylene glycol (PEG), which was cross-linked by the complex of tannic acid (TA) and 1,4-phenylenediboronic acid (PDBA) and stabilized by bovine serum albumin (BSA). The hydrogel was formed and attached to a Ti plate to investigate stability, biodegradability, controlled drug release, and biocompatibility. The stability and biodegradability of the hydrogel could be tuned by adjusting the concentrations of BSA and TA. The hydrogel lasted and remained adhered to the Ti surface after being submerged in PBS for at least 15 days. The controlled release of strontium ranelate (SrRan) and the release mechanism depended on the amount of TA since it was found to govern the hydrogel integrity and pore size. Additionally, in vitro biocompatibility was validated using L929 fibroblast and MC3T3-E1 osteoblast cells that showed greater than 70% viability. The adhesive hydrogel was further studied by injecting it into a 3D-printed Ti-scaffold that contained a porous structure mimicking natural human bone. The hydrogel completely filled and adhered to the inner porous structure of the scaffold. The biodegradation and drug release of the hydrogel in the scaffold occurred at a slower rate, suggesting sustainable drug release that is suitable for bone cell regeneration. The overall results in biodegradability, controlled drug release, and biocompatibility demonstrate the great potential of the drug-releasing TA-mediated adhesive PEG hydrogel as a Ti-enhancing biomaterial that supports osseointegration.

Injectable Poly(ethylene glycol) Hydrogels Cross-Linked by Metal-Phenolic Complex and Albumin for Controlled Drug Release.

Injectable hydrogel is advantageous as a drug reservoir for controlled drug release since its injectability provides minimally invasive access to internal tissues and irregular-shaped target sites. Herein, we fabricated pH-responsive injectable hydrogels constructed of a supramolecular cross-link network, which contained tannic acid (TA), Fe(III), poly(ethylene glycol) (PEG), and bovine serum albumin (BSA) for controlled drug release. The hydrogel precursors rapidly turned into a gel when co-injected with NaOH in a time scale of seconds. The hydrogel properties and drug release profiles are all tunable by adjusting the concentrations of BSA, NaOH, and doxorubicin (DOX). The Young's moduli range from 3.19 ± 0.93 to 43.24 ± 1.37 kPa that match internal soft tissues. The hydrogel lasts more than 3 weeks and gradually releases doxorubicin up to 123.6 ± 1.7 µg at pH 6.4. The results of the physical properties and drug release suggest supramolecular interactions that correspond to Fourier transform infrared (FTIR) results. In vitro cytotoxicity was also assessed using L929 cells, and the results demonstrated the material biocompatibility. The tunable properties, controlled release profiles, and biocompatibility of injectable poly(ethylene glycol) hydrogels support that they have great potential as a drug-releasing material for localized treatments.

Controlled Release of Small Molecules from Elastomers for Reducing Epidermal Downgrowth in Percutaneous Devices.

The elevated infection rise associated with indwelling devices can compromise the performance of percutaneous devices and increase the risk of complications. High infection rates are associated with both the high bacterial load on the skin and epidermal downgrowth at the interface of the indwelling material. Here, we propose a drug-eluting material that promotes local dermal regeneration to reduce epidermal downgrowth. Mesoporous elastomeric matrices composed of naturally occurring monomers were prepared by a combination of photo- and thermal-crosslinking. Elastomeric devices loaded with conjugated linoleic acids (CLA), a class of small molecules that promote local anti-inflammatory responses, can deliver these compounds for 7 d (DCLA-elastomer = 3.94 × 10-9 cm2/s, 95% CI [3.12 × 10-9, 4.61 × 10-9]). In a mouse model, CLA-eluting elastomeric matrices increase the M2 population (5.0 × 103 ± 1.4 × 103 cells/cm2), compared to blank devices (3.8 × 103 ± 2.2 × 103 cells/cm2), and also reduce skin contraction (98.9 ± 6.4%), compared to blank devices (70.9 ± 9.3%) at 7 d. Dermal downgrowth is also attenuated at 14 d (60.4 ± 32.4 µm) compared to blank devices (171.7 ± 93.8 µm). CLA-eluting elastomers are therefore a viable strategy to reduce epidermal downgrowth in percutaneous devices.

Lithography-free fabrication of reconfigurable substrate topography for contact guidance.

Mammalian cells detect and respond to topographical cues presented in natural and synthetic biomaterials both in vivo and in vitro. Micro- and nano-structures influence the adhesion, morphology, proliferation, migration, and differentiation of many phenotypes. Although the mechanisms that underpin cell-topography interactions remain elusive, synthetic substrates with well-defined micro- and nano-structures are important tools to elucidate the origin of these responses. Substrates with reconfigurable topography are desirable because programmable cues can be harmonized with dynamic cellular responses. Here we present a lithography-free fabrication technique that can reversibly present topographical cues using an actuation mechanism that minimizes the confounding effects of applied stimuli. This method utilizes strain-induced buckling instabilities in bilayer substrate materials with rigid uniform silicon oxide membranes that are thermally deposited on elastomeric substrates. The resulting surfaces are capable of reversible of substrates between three distinct states: flat substrates (A = 1.53 ± 0.55 nm; Rms = 0.317 ± 0.048 nm); parallel wavy grating arrays (A∥= 483.6 ± 7.8 nm; λ∥= 4.78 ± 0.16 µm); perpendicular wavy grating arrays (A⊥= 429.3 ± 5.8 nm; λ⊥= 4.95 ± 0.36 µm). The cytoskeleton dynamics of 3T3 fibroblasts in response to these surfaces was measured using optical microscopy. Fibroblasts cultured on dynamic substrates that are switched from flat to topographic features (FLAT-WAVY) exhibit a robust and rapid change in gross morphology as measured by a reduction in circularity from 0.30 ± 0.13 to 0.15 ± 0.08 after 5 min. Conversely, dynamic substrate sequences of FLAT-WAVY-FLAT do not significantly alter the gross steady-state morphology. Taken together, substrates that present topographic structures reversibly can elucidate dynamic aspects of cell-topography interactions.

Biologically derived soft conducting hydrogels using heparin-doped polymer networks.

The emergence of flexible and stretchable electronic components expands the range of applications of electronic devices. Flexible devices are ideally suited for electronic biointerfaces because of mechanically permissive structures that conform to curvilinear structures found in native tissue. Most electronic materials used in these applications exhibit elastic moduli on the order of 0.1-1 MPa. However, many electronically excitable tissues exhibit elasticities in the range of 1-10 kPa, several orders of magnitude smaller than existing components used in flexible devices. This work describes the use of biologically derived heparins as scaffold materials for fabricating networks with hybrid electronic/ionic conductivity and ultracompliant mechanical properties. Photo-cross-linkable heparin-methacrylate hydrogels serve as templates to control the microstructure and doping of in situ polymerized polyaniline structures. Macroscopic heparin-doped polyaniline hydrogel dual networks exhibit impedances as low as Z = 4.17 Ω at 1 kHz and storage moduli of G' = 900 ± 100 Pa. The conductivity of heparin/polyaniline networks depends on the oxidation state and microstructure of secondary polyaniline networks. Furthermore, heparin/polyaniline networks support the attachment, proliferation, and differentiation of murine myoblasts without any surface treatments. Taken together, these results suggest that heparin/polyaniline hydrogel networks exhibit suitable physical properties as an electronically active biointerface material that can match the mechanical properties of soft tissues composed of excitable cells.