Surya K. Mallapragada

Vaccine adjuvants: Current challenges and future approaches

For humans, companion animals, and food producing animals, vaccination has been touted as the most successful medical intervention for the prevention of disease in the twentieth century. However, vaccination is not without problems. With the development of new and less reactogenic vaccine antigens, which take advantage of molecular recombinant technologies, also comes the need for more effective adjuvants that will facilitate the induction of adaptive immune responses. Furthermore, current vaccine adjuvants are successful at generating humoral or antibody mediated protection but many diseases currently plaguing humans and animals, such as tuberculosis and malaria, require cell mediated immunity for adequate protection. A comprehensive discussion is presented of current vaccine adjuvants, their effects on the induction of immune responses, and vaccine adjuvants that have shown promise in recent literature.

Oriented Schwann cell growth on micropatterned biodegradable polymer substrates

This paper investigates the influence of substrate-mediated chemical and physical guidance on the growth and alignment of Schwann cells in vitro. Novel techniques were developed to fabricate microgrooves with adsorbed proteins on biodegradable polymer substrates made of poly(D,L-lactic acid). Compression molding and solvent-casting were used to transfer micropatterns from quartz and silicon substrates onto biodegradable polymer films. Laminin was selectively adsorbed onto the grooves and rat sciatic Schwann cells were seeded on the substrates. Laminin was found to improve adhesion of Schwann cells on the substrates. The microgrooves were found to cause the Schwann cells to align along the direction of the grooves. The groove width influenced Schwann cell alignment the most, while groove depth did not seem to play a significant role. The degradation of the grooves in the solvent cast films was much slower than those in the compression-molded films, making them the preferred substrates for Schwann cell culture.

Dissolution mechanism of semicrystalline poly(vinyl alcohol) in water

Changes occurring in the degree of crystallinity and lamellar thickness distribution of poly(vinyl alcohol) (PVA) samples during dissolution in water were investigated. PVA samples of three different molecular weights were crystallized by annealing at 90, 110, and 120°C. The initial degrees of crystallinity measured by differential scanning calorimetry (DSC) and by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) varied from 43 to 60% and the average lamellar thicknesses measured by DSC ranged from 50 to 400 A. PVA dissolution was followed at 25, 35, and 45°C from 30 s up to 195 min. Lamellar thicknesses were determined as a function of dissolution time using DSC. There was an initial drastic decrease in the degree of crystallinity, which leveled off to a fairly constant value before reaching zero by the time the polymer dissolved completely. Increase in molecular weight led to lesser number of crystals, but with larger average lamellar thickness, which were more stable in the presence of water. Increase in crystallization temperature or decrease in dissolution temperature led to larger average lamellar thickness. Based on these findings, a dissolution mechanism involving unfolding of the polymer chains of the crystal was proposed.

Multifunctional nanoparticles for targeted delivery of immune activating and cancer therapeutic agents.

Nanoparticles (NPs) have been extensively investigated for applications in both experimental and clinical settings to improve delivery efficiency of therapeutic and diagnostic agents. Most recently, novel multifunctional nanoparticles have attracted much attention because of their ability to carry diverse functionalities to achieve effective synergistic therapeutic treatments. Multifunctional NPs have been designed to co-deliver multiple components, target the delivery of drugs by surface functionalization, and realize therapy and diagnosis simultaneously. In this review, various materials of diverse chemistries for fabricating multifunctional NPs with distinctive architectures are discussed and compared. Recent progress involving multifunctional NPs for immune activation, anticancer drug delivery, and synergistic theranostics is the focus of this review. Overall, this comprehensive review demonstrates that multifunctional NPs have distinctive properties that make them highly suitable for targeted therapeutic delivery in these areas.

Synergistic Effects of Physical and Chemical Guidance Cues on Neurite Alignment and Outgrowth on Biodegradable Polymer Substrates

This article demonstrates that directional outgrowth of neurites is promoted by applying a combination of physical and chemical cues to biodegradable polymer substrates. Films of poly-D,L-lactic acid and poly(lactide-co-glycolide) were micropatterned to form grooves on substrate surfaces, using novel indirect transfer techniques developed specifically for biodegradable polymers that cannot be micropatterned directly. Laminin was selectively adsorbed in the grooves. Whole and dissociated dorsal root ganglia were seeded on the substrates and neurite outgrowth and alignment along the microgrooves were measured. The microgrooves provide physical guidance, whereas laminin provides chemical cues to the neurons. The groove depth and spacing were found to significantly influence neurite alignment. The presence of laminin was found to promote neurite adhesion and outgrowth along the grooves. Using a combination of optimized physical and chemical cues, excellent spatial control of directional neurite outgrowth, with up to 95% alignment of neurites, was obtained. The synergistic effect of physical and chemical guidance cues was found to be more effective than individual cues in promoting directional outgrowth of neurites.

Micropatterned Schwann cell-seeded biodegradable polymer substrates significantly enhance neurite alignment and outgrowth.

Biomimetic strategies were employed to promote directional outgrowth of neurites in vitro by using a synergistic combination of physical, chemical, and cellular cues. Compression molded and solvent cast biodegradable polymer substrates made of poly(D,L-lactic acid) were micropatterned to form grooves on the substrate surfaces. Laminin was localized in the grooves, and rat sciatic Schwann cells were seeded on the substrates. Whole as well as dissociated rat dorsal root ganglia were seeded on the substrates along with Schwann cells, and neurite outgrowth and alignment were measured. The micropatterns provide physical guidance, laminin provides chemical cues, and the Schwann cells provide biological cues to the axons. The presence of Schwann cells in the grooves was found to promote neurite alignment as well as outgrowth and help the neurites orient even on shallower grooves and exhibit continued alignment even as the grooves degrade. The synergistic combination of physical, chemical, and cellular guidance enabled greater than 98% alignment of neurites and accelerated outgrowth of neurites in the direction of the microgrooves.

Experimental investigation and mathematical modeling of Pluronic® F127 gel dissolution: drug release in stirred systems

We have examined the dissolution of Pluronic F127 gels in a USP dissolution apparatus under stirred conditions, and simultaneously monitored the release of model drugs from these gels. The drugs selected were propranolol HCl, metronidazole and cephalexin. Our results show that drug release is zero-order and is controlled by the dissolution of the gel for all the drugs, under various conditions of temperature, F127 concentration, drug concentration, and for stirring speeds between 20 and 80 rpm. The addition of inorganic salts has no significant effect on dissolution rate or drug release. Increasing F127 concentration in the gel decreases gel dissolution and drug release rates. We have developed a predictive mathematical model based on the assumption that uptake of water into the gel and subsequent disentanglement of F127 micelles control gel dissolution. There is good agreement between experimental results and model predictions for stirring speeds above 20 rpm. As stirring speed is decreased to 20 rpm and below, there are discrepancies between actual and predicted values, presumably due to a significant diffusion component that contributes to drug release.

Synergistic effects of micropatterned biodegradable conduits and Schwann cells on sciatic nerve regeneration

This paper describes a novel biodegradable conduit that provides a combination of physical, chemical and biological cues at the cellular level to facilitate peripheral nerve regeneration. The conduit consists of a porous poly(D,L-lactic acid) (PDLLA) tubular support structure with a micropatterned inner lumen. Schwann cells were pre-seeded into the lumen to provide additional trophic support. Conduits with micropatterned inner lumens pre-seeded with Schwann cells (MS) were fabricated and compared with three types of conduits used as controls: M (conduits with micropatterned inner lumens without pre-seeded Schwann cells), NS (conduits without micropatterned inner lumens pre-seeded with Schwann cells) and N (conduits without micropatterned inner lumens, without pre-seeded Schwann cells). The conduits were implanted in rats with 1 cm sciatic nerve transections and the regeneration and functional recovery were compared in the four different cases. The number or size of regenerated axons did not vary significantly among the different conduits. The time of recovery, and the sciatic function index, however, were significantly enhanced using the MS conduits, based on qualitative observations as well as quantitative measurements using walking track analysis. This demonstrates that biodegradable micropatterned conduits pre-seeded with Schwann cells that provide a combination of physical, chemical and biological guidance cues for regenerating axons at the cellular level offer a better alternative for repairing sciatic nerve transactions than conventional biodegradable conduits.

Materials-Based Strategies for Multi-Enzyme Immobilization and Co-Localization: A Review

Immobilized enzymes as biocatalysts have great potential both scientifically and industrially because of their technological and economic importance. Their highly efficient catalytic mechanisms and reusability have made them excellent candidates for green and sustainable applications. Previous studies have primarily focused on single enzyme immobilization. However, there are many situations where a single enzyme cannot completely catalyze reactions and multiple enzymes working together in a cascade are needed. It is very challenging to efficiently drive the multi‐step reaction toward the desired direction, which is especially true when reactive intermediates are present. Nature overcomes this limitation through the use of multi‐enzyme complexes (MECs) to promote the overall catalytic efficiency, which has inspired researchers to synthesize artificial MECs to controllably enhance the production of the desired compounds in multi‐step reaction cascades in vitro. The most common approaches to synthesize artificial MECs are to use genetic engineering techniques to create fusion proteins or to co‐localize multiple enzymes on suitable carriers. This review focuses on the latter with a particular emphasis on materials‐based approaches to enzyme co‐localization, which builds on techniques developed for single enzyme immobilization. The attachment techniques used in single enzyme immobilization are also effective in multiple enzyme co‐localization, which has a direct impact on the overall enzyme orientation and activity. For carrier‐based strategies, the platforms developed for single enzyme immobilization are also appropriate for attaching and co‐localizing multiple enzymes. However, the involvement of multiple components in co‐localization brings many challenges. The properties of different enzymes makes co‐localization complicated when selecting attachment techniques and platforms to preserve enzymatic activity, because the structure and function of each component enzyme needs to be taken into consideration to preserve the overall enzyme activity. In addition, the relative position of the multiple enzymes in a confined space plays a significant role in the interactions between different enzymes, which makes spatial control important for co‐localization. This review focuses on the potential of materials‐based approaches for multiple enzyme co‐localization for the design of sustainable multi‐enzyme biocatalysts. A critical analysis of the attachment techniques and carriers platforms that have been used in enzyme immobilization and multi‐enzyme co‐localization in vitro is provided. Biotechnol. Bioeng. 2014;111: 209–222.

Understanding drug release from poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) gels.

Experimental and mathematical studies were performed to understand the release mechanism of small molecular weight compounds from poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) polymer gels (trademarked Pluronic by BASF Corp.) of various concentrations. Studies of the diffusion coefficient of solutes in the polymer gels were performed using a novel technique to predict movement of drugs within the gel as release occurs. Studies were also performed to determine the diffusion coefficient of water in the polymer gel, as it is this parameter that controls the dissolution rate of the polymer, and in turn, the drug release rate. A model was formulated and solved numerically to determine the controlling release mechanism. By parameter modification, this algorithm for determining the overall mass of drug released from a drug loaded gel can be used for a number of drugs and for a wide range of initial polymer concentrations. Drug release data were obtained with a novel experimental setup and were used to verify the accuracy of the overall solution of the model. The results of the model indicate that although the rate of polymer dissolution ultimately controls the drug release, about 5% of the release is due to diffusion at the gel/liquid interface, giving rise to a slightly non-linear release. It was also found that agitation speed greatly affects the dissolution rates of these polymer gels.