Removal of Non-Specifically Bound Proteins Using Rayleigh Waves Generated on ST-Quartz Substrates

Label-free biosensors are plagued by the issue of non-specific protein binding which negatively affects sensing parameters such as sensitivity, selectivity, and limit-of-detection. In the current work, we explore the possibility of using the Rayleigh waves in ST-Quartz devices to efficiently remove non-specifically bound proteins via acoustic streaming. A coupled-field finite element (FE) fluid structure interaction (FSI) model of a surface acoustic wave (SAW) device based on ST-Quartz substrate in contact with a liquid loading was first used to predict trends in forces related to SAW-induced acoustic streaming. Based on model predictions, it is found that the computed SAW body force is sufficient to overcome adhesive forces between particles and a surface while lift and drag forces prevent reattachment for a range of SAW frequencies. We further performed experiments to validate the model predictions and observe that the excitation of Rayleigh SAWs removed non-specifically bound (NSB) antigens and antibodies from sensing and non-sensing regions, while rinsing and blocking agents were ineffective. An amplified RF signal applied to the device input disrupted the specific interactions between antigens and their capture antibody as well. ST-quartz allows propagation of Rayleigh and leaky SH-SAW waves in orthogonal directions. Thus, the results reported here could allow integration of three important biosensor functions on a single chip, i.e., removal of non-specific binding, mixing, and sensing in the liquid phase.

Using containerless methods to develop amorphous pharmaceuticals

BACKGROUND

Many pipeline drugs have low solubility in their crystalline state and require compounding in special dosage forms to increase bioavailability for oral administration. The use of amorphous formulations increases solubility and uptake of active pharmaceutical ingredients. These forms are rapidly gaining commercial importance for both pre-clinical and clinical use.

METHODS

Synthesis of amorphous drugs was performed using an acoustic levitation containerless processing method and spray drying. The structure of the products was investigated using in-situ high energy X-ray diffraction. Selected solvents for processing drugs were investigated using acoustic levitation. The stability of amorphous samples was measured using X-ray diffraction. Samples processed using both spray drying and containerless synthesis were compared.

RESULTS

We review methods for making amorphous pharmaceuticals and present data on materials made by containerless processing and spray drying. It was shown that containerless processing using acoustic levitation can be used to make phase-pure forms of drugs that are known to be difficult to amorphize. The stability and structure of the materials was investigated in the context of developing and making clinically useful formulations.

CONCLUSIONS

Amorphous compounds are emerging as an important component of drug development and for the oral delivery of drugs with low solubility. Containerless techniques can be used to efficiently synthesize small quantities of pure amorphous forms that are potentially useful in pre-clinical trials and for use in the optimization of clinical products.

GENERAL SIGNIFICANCE

Developing new pharmaceutical products is an essential enterprise to improve patient outcomes. The development and application of amorphous pharmaceuticals to increase absorption is rapidly gaining importance and it provides opportunities for breakthrough research on new drugs. There is an urgent need to solve problems associated with making formulations that are both stable and that provide high bioavailability. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo.

Non-equilibrium effects evidenced by vibrational spectra during the coil-to-globule transition in poly(N-isopropylacrylamide) subjected to an ultrafast heating-cooling cycle

Molecular dynamics simulations in conjunction with finite element calculations are used to explore the conformational dynamics of a thermo-sensitive oligomer, namely poly(N-isopropylacrylamide) (PNIPAM), subjected to an ultra-fast heating-cooling cycle. Finite element (FE) calculations were used to predict the temperature profile resulting from laser-induced heating of the polymer-aqueous system. The heating rate (∼0.6 K ps(-1)) deduced from FE calculations was used to heat an aqueous solution of PNIPAM consisting of 30 monomeric units (30-mer) from 285 K to 315 K. Non-equilibrium effects arising from the ultra-fast heating-cooling cycle results in a hysteresis during the coil-to-globule transition. The corresponding atomic scale conformations were characterized by monitoring the changes in the vibrational spectra, which provided a reliable metric to study the coil-to-globule transition in PNIPAM and vice-versa across the LCST. The vibrational spectra of bonds involving atoms from the oligomer backbone and the various side-groups (amide I, amide II, and the isopropyl group of PNIPAM) of the oligomers were analyzed to study the conformational changes in the oligomer corresponding to the observed hysteresis. The differences in the vibrational spectra calculated at various temperatures during heating and cooling cycles were used to understand the coil-to-globule and globule-to-coil transitions in the PNIPAM oligomer and identify the changes in the relative interactions between various atoms in the backbone and in the side groups of the oligomer with water. The shifts in the computed vibrational spectral peaks and the changes in the intensity of peaks for the different regions of PNIPAM, seen across the LCST during the heating cycle, are in good agreement with previous experimental studies. The changes in the radius of gyration (Rg) and vibrational spectra for amide I and amide II regions of PNIPAM suggest a clear coil-to-globule transition at ∼301 K during the heating cycle from 285 K to 315 K. During the heating cycle, a comparison of the vibrational spectra of isopropyl groups in PNIPAM at 285 K and 315 K suggests dehydration of the isopropyl moieties at 315 K. This implies that the oligomer-water interactions are dominant below the LCST whereas oligomer-oligomer interactions pre-dominate above the LCST. On the other hand, during the cooling cycle minor changes in the Rg and vibrational spectra of the PNIPAM oligomer in going from 315 K to 285 K indicate that the interactions between oligomer-oligomer and between the oligomer and water are less perturbed during the cooling cycle. Our simulations suggest that the observed hysteresis is a consequence of ultrafast heating-cooling kinetics, which allows insufficient relaxation times for the solvated oligomer.

Fabrication of Poly(ethylene glycol) Hydrogel Structures for Pharmaceutical Applications using Electron beam and Optical Lithography

Soft-polymer based microparticles are currently being applied in many biomedical applications, ranging from bioimaging and bioassays to drug delivery carriers. As one class of soft-polymers, hydrogels are materials, which can be used for delivering drug cargoes and can be fabricated in controlled sizes. Among the various hydrogel-forming polymers, poly(ethylene glycol) (PEG) based hydrogel systems are widely used due to their negligible toxicity and limited immunogenic recognition. Physical and chemical properties of particles (i.e., particle size, shape, surface charge, and hydrophobicity) are known to play an important role in cell-particle recognition and response. To understand the role of physicochemical properties of PEG-based hydrogel structures on cells, it is important to have geometrically precise and uniform hydrogel structures. To fabricate geometrically uniform structures, we have employed electron beam lithography (EBL) and ultra-violet optical lithography (UVL) using PEG or PEG diacrylate polymers. These hydrogel structures have been characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), optical microscopy, and attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) confirming control of chemistry, size, and shape.