Biomedical subjects

Surya K Mallapragada

Publications and source records attributed to Surya K Mallapragada.

15 recordsLinked to original sources

PubMed2007

Thermoresponsive reversible behavior of multistimuli pluronic-based pentablock copolymer at the air-water interface.

Surface behavior of the pH- and thermoresponsive amphiphilic ABCBA pentablock copolymer has been studied with respect to the environmental conditions. We demonstrate that the pentablock copolymer poly((diethylaminoethyl methacrylate)-b-(ethylene oxide)-b-(propylene oxide)-b-(ethylene oxide)-b-(diethylaminoethyl methacrylate)) possesses reversible temperature changes at the air-water interface in a narrow pH range of the water subphase. Significant diversity in the surface morphology of pentablock copolymer monolayers at different pH and temperatures observed were related to the corresponding reorganization of central and terminal blocks. Remarkable reversible variations of the surface pressure observed for the Langmuir monolayers at pH 7.4 in the course of heating and cooling between 27 and 50 degrees C is associated with conformational transformations of terminal blocks crossing the phase line in the vicinity of the lower critical solution temperature point. The observed thermoresponsive surface behavior can be exploited for modeling of the corresponding behavior of pentablock copolymers adsorbed onto various biointerfaces for intracellular delivery for deeper understanding of stimuli-responsive transformations relevant to controlled drug and biomolecules release and retention.

Journal Article↗

PubMed2007

Investigation of in vitro biocompatibility of novel pentablock copolymers for gene delivery.

Novel pentablock copolymers of poly(diethylaminoethylmethacrylate) (PDEAEM), poly(ethylene oxide) (PEO), and poly(propylene oxide) (PPO), (PDEAEM-b-PEO-b-PPO-b-PEO-b-PDEAEM), were synthesized as vectors for gene delivery, and were tested for their biocompatibility on SKOV3 (human ovarian carcinoma) and A431 (human epidermoid cancer) cell lines under different in vitro conditions using various assays to elucidate the mechanism of cell death. These copolymers form micelles in aqueous solutions and can be tuned for their cytotoxicity by tailoring the weight percentage of their cationic component, PDEAEM. Copolymers with higher PDEAEM content were found to be more cytotoxic, though their polyplexes were less toxic than the polycations alone. Pentablock copolymers displayed higher cell viability than commercially available ExGen 500 at similar N:P ratios. While cell death with ExGen was found to be accompanied by an early loss of cell membrane integrity, pentablock copolymers caused very little membrane leakage. Caspase-3/7 assay confirmed that none of these polymers induced apoptosis in the cells. These pentablock copolymers form thermo-reversible gels at physiological temperatures, thereby enabling controlled gene delivery. Toxicity of the polymer gels was tested using an agarose-matrix, simulating an in vivo tumor model where injected polyplex gels would dissolve to release polyplexes, diffusing through tumor mass to reach the target cells. Twenty five weight percent of copolymer gels were found to be nontoxic or mildly cytotoxic after 24 h incubation. Transfection efficiency of the copolymers was found to be critically correlated to cytotoxicity and depended on DNA dose, polymer concentration, and N:P ratios. Transgene expression obtained was comparable to that of ExGen, but ExGen exhibited greater cell death.

Caspase 3↗

PubMed2007

Drug release from pH-responsive thermogelling pentablock copolymers.

A novel pH-dependent injectable sustained delivery system was developed by utilizing a cationic pentablock copolymer that exhibits a thermoreversible sol-gel transition. Aqueous solutions of the pentablock copolymer, consisting of poly(2-diethylaminoethyl-methyl methacrylate)-poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)-poly(2-diethylaminoethyl-methyl methacrylate) (PDEAEM(25)-PEO(100)-PPO(65)-PEO(100)-PDEAEM(25)) exhibit temperature and pH dependent micellization due to the lower critical solution temperature of the PPO blocks and the polyelectrolyte character of the PDEAEM blocks, respectively. Aqueous solutions of the copolymers above 12 wt % are free flowing liquids at room temperature and form elastic physical hydrogels reversibly above 37 degrees C. Hydrophobic probe absorbance studies indicate that pentablock copolymer micelles increase the solubility of sparingly soluble drugs. Solutions of the pentablock copolymer that form gels at body temperature exhibit sustained zero-order release in in vitro experiments. The release rates of model drugs and proteins were significantly influenced by the pH of the release media, thereby making these polymers ideal candidates for modulated drug delivery.

Animals↗

PubMed2006

Amphiphilic polyanhydrides for protein stabilization and release.

The overall goal of this research is to design novel amphiphilic biodegradable systems based on polyanhydrides for the stabilization and sustained release of peptides and proteins. Accordingly, copolymers of the anhydrides, 1,6-bis(p-carboxyphenoxy)hexane (CPH) and 1,8-bis(p-carboxyphenoxy)-3,6-dioxaoctane (CPTEG), which are monomer-containing oligomeric ethylene glycol moieties, have been synthesized. Microspheres of different CPTEG:CPH compositions have been fabricated by two non-aqueous methods: solid/oil/oil double emulsion and cryogenic atomization. The ability of this amphiphilic polymeric system to stabilize model proteins (i.e., lysozyme and ovalbumin) was investigated. The structure of both the encapsulated as well as the released protein was monitored using gel electrophoresis, circular dichroism, and fluorescence spectroscopy. It was found that the CPTEG:CPH system preserves the structural hierarchy of the encapsulated proteins. Activity studies of the released protein indicate the CPTEG:CPH system retains the biological activity of the released protein. These results are promising for future in vivo studies, which involve the design of novel biodegradable polyanhydride carriers for the stabilization and sustained release of therapeutic peptides and proteins.

Amino Acid Sequence↗

PubMed2006

Directed growth and selective differentiation of neural progenitor cells on micropatterned polymer substrates.

Directional growth and differentiation of adult rat hippocampal progenitor cells (AHPCs) were investigated on micropatterned polymer substrates in vitro. Astrocytes or AHPCs cultured on micropatterned polystyrene substrates chemically modified with laminin exhibited over 75% alignment in the groove direction. AHPCs co-cultured with astrocytes preferentially acquired neuronal morphology, with nearly double the percentage of cells expressing class III beta-tubulin on the micropatterned half of the substrate, as opposed to the planar half of the substrate, or compared to those growing in the absence of astrocytes. This indicates that substrate three-dimensional topography, in synergy with chemical (laminin) and biological (astrocytes) guidance cues, facilitates neuronal differentiation of the AHPCs. Through multi-dimensional cell-cell interactions, this environment provides spatial control selectively enhancing neuronal differentiation and neurite alignment on topographically different regions of the same substrate. Integrating these cues is important in understanding and controlling neural stem cell differentiation and designing scaffolds for guided nerve regeneration.

Animals↗

PubMed2006

Supramolecular self-assembly of multiblock copolymers in aqueous solution.

A unique pH-dependent phase behavior from a copolymer micellar solution to a collapsed hydrogel with micelles ordered in a hexagonal phase was observed. Small-angle neutron scattering (SANS) was used to follow the pH-dependent structural evolution of micelles formed in a solution of a pentablock copolymer consisting of poly((diethylaminoethyl methacrylate)-b-(ethylene oxide)-b-(propylene oxide)-b-(ethylene oxide)-b-(diethylaminoethyl methacrylate)) (PDEAEM25-b-PEO100-b-PPO65-b-PEO100-b-PDEAEM25). Between pH 3.0 and pH 7.4, we observed the presence of charged spherical micelles. Increasing the pH of the micelle solution above pH 7.4 resulted in increasing the size of the micelles due to the increasing hydrophobicity of the PDEAEM blocks above their pKa of 7.6. The increase in size of the spherical micelles resulted in a transition to a cylindrical micelle morphology in the pH range 8.1-10.5, and at pH >11, the copolymer solution undergoes macroscopic phase separation. Indeed, the phase separated copolymer sediments and coalesces into a hydrogel structure that consists of 25-35 wt % water. Small-angle X-ray scattering (SAXS) clearly indicated that the hydrogel has a hexagonal ordered phase. Interestingly, the process is reversible, as lowering of the pH below 7.0 leads to rapid dissolution of the solid into homogeneous solution. We believe that the hexagonal structure in the hydrogel is a result of the organization of the cylindrical micelles due to the increased hydrophobic interactions between the micelles at 70 degrees C and pH 11. Thus we have developed a pH-/temperature-dependent, reversible hierarchically self-assembling block copolymer system with structures spanning nano- to microscale dimensions.

Journal Article↗

PubMed2006

Synthesis and characterization of novel polyanhydrides with tailored erosion mechanisms.

We have designed a new synthesis route to create polyanhydrides based on monomers that contain hydrophilic entities within highly hydrophobic backbones. The method results in polyanhydrides that can be easily processed into drug-containing tablets. The synthesis, characterization, and erosion studies of polyanhydride copolymers based on 1,6-bis(p-carboxyphenoxy)hexane (CPH), which is highly hydrophobic, and 1,8-bis(p-carboxyphenoxy)-3,6-dioxaoctane (CPTEG), which has hydrophilic oligomeric ethylene glycol segments in the monomer unit, was performed using a combination of molecular spectroscopy, thermal analysis, gravimetry, and scanning electron microscopy. The studies demonstrate that by increasing the CPH content in the CPTEG:CPH copolymers, the erosion of the system can be tailored from bulk-eroding to surface-eroding mechanism. These systems have promise as protein carriers.

Biocompatible Materials↗

PubMed2005

Synthesis of novel biodegradable polyanhydrides containing aromatic and glycol functionality for tailoring of hydrophilicity in controlled drug delivery devices.

Aromatic diacids were synthesized from chlorinated triethylene or pentaethylene glycols and p-hydroxy benzoic acid. The diacids were acetylated with acetic anhydride to produce homopolymers of polyanhydrides for controlled release applications such as the stabilization of proteins and drugs. Adding ethylene glycol segments into the acid monomer allows tailoring of the hydrophobicity of the polyanhydrides, which in turn dictates the solubility of molecules within the polymer matrix and degradation rate of the polymer. The glycol containing polyanhydrides were characterized by NMR, GPC, DSC and dissolution testing. The release characteristics and mechanism of the new polyanhydrides were evaluated using hydrophilic and hydrophobic dyes.

Absorbable Implants↗

PubMed2004

Novel cationic pentablock copolymers as non-viral vectors for gene therapy.

New cationic pentablock copolymers of poly(diethylaminoethylmethacrylate) (PDEAEM), poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO)--PDEAEM-b-PEO-b-PPO-b-PEO-b-PDEAEM--synthesized in our laboratory were investigated for their potential as non-viral vectors for gene therapy. Agarose gel studies showed that the copolymers effectively condensed plasmid DNA to form polyplexes, and also protected plasmids against nuclease degradation. Light scattering and transmission electron microscopy were used to analyze the apparent size, molecular weight and morphology of these polyplexes. Lactate dehydrogenase assay was employed to find the cytotoxicity limits of the polymers and polyplexes on a human ovarian cancer cell line. The polymers showed much less cytotoxicity than commercially available ExGen 500 (linear polyethyleneimine). By changing the relative lengths of the blocks in the copolymers, it was found that the cytotoxicity of these copolymers could be tailored. The micellar structures of these copolymers in aqueous solutions and their pH-sensitive protonation were added advantages. In vitro transfection efficiencies of the polymers using green fluorescent protein (pEGFP-N1) and luciferase (pRL-CMV) reporter genes were found comparable to ExGen 500. Besides, aqueous solutions of these pentablock copolymers have been shown to exhibit thermodynamic phase transitions and thermoreversible gelation, a quality that could allow subcutaneous/intramuscular injections of these polymers for controlled gene delivery over time.

Cations↗

PubMed2004

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.

Absorbable Implants↗

PubMed2002

The effect of salts on the micellization temperature of aqueous poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) solutions and the dissolution rate and water diffusion coefficient in their corresponding gels.

Studies were performed to examine the effect of ionic salts on phase transitions, dissolution rates, and diffusion coefficients of water in gels of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) with polymer concentrations ranging from 22 to 32% w/w and salt concentrations ranging from 0 to 1.5% w/w. Salts tested include Na(3)PO(4), Na(2)SO(4), Na(2)HPO(4), NaH(2)PO(4), NaCH(3)CO(2), NaCl, and KI. Micellization transition temperatures were obtained using differential scanning calorimetry. The dissolution rates were obtained by measurement of the surface erosion rates, and diffusion coefficients were obtained by using a method to analyze the intrusion of water into the aqueous gels. It was found that salts had no effect on the dissolution rate of the polymer gels into deionized water. However, when the salt concentration in the aqueous dissolution media was adjusted to match the concentration in the gels, the dissolution rate of the polymer gel decreased with increasing salt concentration. The salts also had a profound effect on the critical micellization temperature (CMT) and the diffusion coefficient of water within the gel. The diffusion coefficient and CMT decreased in the presence of salts. The magnitude of these effects was comparable to their placement on the Hofmeister, or lyotropic series for salts. The effects of polymer and salt concentrations on the CMT were quantified, and a single correlation was proposed to predict the micellization temperatures for a wide range of salt and polymer concentrations.

Diffusion↗

PubMed2002

Al-Cu-Fe quasicrystal/ultra-high molecular weight polyethylene composites as biomaterials for acetabular cup prosthetics.

Polymer composites of Al-Cu-Fe quasicrystals and ultra-high molecular weight polyethylene (UHMWPE) were investigated for use in acetabular cup prosthetics. The wear properties of the Al-Cu-Fe/UHMWPE samples and a 440 steel ball counterface were measured. The mechanical strength of the Al-Cu-Fe/UHMWPE composites was compared to UHMWPE and alumina/UHMWPE. The biocompatibility of the composite material was tested using a direct contact cytotoxicity assay. Al-Cu-Fe/UHMWPE demonstrated lower volume loss after wear and higher mechanical strength than UHMWPE. This composite material also showed no increase in counterface wear or cytotoxicity relative to UHMWPE. These combined results demonstrate that Al-Cu-Fe/UHMWPE composites are promising candidate materials for acetabular cup prosthetics.

3T3 Cells↗

PubMed2002

Synthesis and characterization of injectable, water-soluble copolymers of tertiary amine methacrylates and poly(ethylene glycol) containing methacrylates.

Several homopolymers and copolymers of 2-(diethylamino)ethyl methacrylate (DEAEM) and poly(ethylene glycol) methyl ether methacrylate (PEGMEM) were synthesized using anionic polymerization initiated by potassium t-butoxide. The polymers were characterized by average molecular weight, polydispersity and monomeric unit composition. A very narrow molecular weight distribution was achieved with a well-controlled composition. The glass transition temperatures and compositions of the copolymers followed a Gordon-Taylor relationship. The water solubility and biocompatibility of the copolymers was compared to their parent homopolymers to determine if the addition of a poly(ethylene glycol) group was sufficient to solubilize the polymers in aqueous buffer solutions and to increase the biocompatibility of the polymers. These water-soluble, injectable cationic copolymers have potential applications in gene delivery as well as other biomaterial applications.

Amines↗

PubMedDate not supplied

Problem-based learning biotechnology courses in chemical engineering.

We have developed a series of upper undergraduate/graduate lecture and laboratory courses on biotechnological topics to supplement existing biochemical engineering, bioseparations, and biomedical engineering lecture courses. The laboratory courses are based on problem-based learning techniques, featuring two- and three-person teams, journaling, and performance rubrics for guidance and assessment. Participants initially have found them to be difficult, since they had little experience with problem-based learning. To increase enrollment, we are combining the laboratory courses into 2-credit groupings and allowing students to substitute one of them for the second of our 2-credit chemical engineering unit operations laboratory courses.

Biotechnology↗

PubMedDate not supplied

Parallel synthesis and high throughput dissolution testing of biodegradable polyanhydride copolymers.

We have demonstrated that polycondensation reactions can be carried out in a combinatorial fashion and that the polymer library can be screened at high throughput using a rapid prototyping technique to fabricate multiwell substrates. A linearly varying compositional library of 100 different biodegradable polyanhydride random copolymers that are promising carriers for controlled drug delivery was designed, fabricated, and characterized by IR microscopy within a few hours. The polyanhydride copolymer library was based on 1,6-bis(p-carboxyphenoxy)hexane (CPH) and sebacic anhydride (SA) and was characterized with infrared microspectroscopy to determine the composition within each well. Since degradation and release rates depend on copolymer composition, we also developed new high-throughput methods to investigate drug release from this library of copolymers by designing specific wells for each task. A subset of this library was chosen, and a substrate was designed and fabricated to enable the synthesis and monitoring of dye dissolution from a range of polyanhydride copolymers in a parallel fashion using a CCD camera. Multisample substrates were fabricated with a novel rapid prototyping method that consists of an organic solvent-resistant array of 10 x 10 microwells of 2-muL volume each. The libraries were deposited with a custom-built liquid dispensing system consisting of a series of computer-controlled volume-dispensing pumps and XYZ motion stages. The parallel dye dissolution study displayed a decreasing rate of release with increasing CPH content. This result agrees with previously published data for dye release from poly(CPH-co-SA) copolymers. The methodology described in this work is amenable to numerous applications in the arenas of high-throughput polymer synthesis and characterization.

Biodegradation, Environmental↗