Graft copolymerization of glycerol 1,3-diglycerolate diacrylate onto poly(3-hydroxyoctanoate) to improve physical properties and biocompatibility

Glycerol 1,3-diglycerol diacrylate-grafted poly(3-hydroxyoctanoate) (GDD-g-PHO) copolymers were prepared by heating homogeneous solutions of PHO, GDD monomer and benzoylperoxide initiator. Experiments showed that GDD was successfully grafted onto the PHO chains and that the resulting copolymers had enhanced thermal properties and mechanical strengths. The surfaces and the bulk of GDD-g-PHO copolymers became more hydrophilic as the GDD grafting density in the copolymer increased. Measurements of the growth of Chinese hamster ovary cells and the adsorption of blood proteins and platelets in vitro showed that biocompatibility was also enhanced by grafting of GDD groups. These results indicate that the GDD-g-PHO copolymers are promising materials for biocompatible biomedical applications.     

Enzyme immobilization on ultrafine cellulose fibers via poly(acrylic acid) electrolyte grafts

Ultrafine cellulose fiber (diameter 200-400 nm) surfaces were grafted with polyacrylic acid (PAA) via either ceric ion initiated polymerization or methacrylation of cellulose with methacrylate chloride (MACl) and subsequent free-radical polymerization of acrylic acid. PAA grafts by ceric ion initiated polymerization increased with increasing reaction time (2-24 h), monomer (0.3-2.4 M), and initiator (1-10 mM) concentrations, and spanned a broad range from 5.5-850%. PAA grafts on the methacrylated cellulose fibers also increased with increasing molar ratios of MACl to cellulosic hydroxyl groups (MACl/OH, 2-6.4) and monomer acrylic acid (AA) to initiator potassium persulfate (KPS) ratios ([AA]/[KPS], 1.5-6), and were in a much narrower range between 12.8% and 29.4%. The adsorption of lipase (at 1 mg/ml lipase and pH 7) and the activity of adsorbed lipase (pH 8.5, 30 degrees C), in both cases decreased with increasing PAA grafts. The highest adsorption and activity of the lipase on the ceric ion initiated grafted fibers were 1.28 g/g PAA and 4.3 U/mg lipase, respectively, at the lowest grafting level of 5.5% PAA, whereas they were 0.33 g/g PAA and 7.1 U/mg lipase, respectively, at 12.8% PAA grafts on the methacrylated and grafted fibers. The properties of the grafted fibers and the absorption behavior and activity of lipase suggest that the PAA grafts are gel-like by ceric-initiated reaction and brush-like by methacrylation and polymerization. The adsorbed lipase on the ceric ion-initiated grafted surface possessed greatly improved organic solvent stability over the crude lipase. The adsorbed lipases exhibited 0.5 and 0.3 of the initial activity in the second and third assay cycles, respectively.     

Dextran-conjugated tetrathiatriarylmethyl radicals as biocompatible spin probes for EPR spectroscopy and imaging

Tetrathiatriarylmethyl (TAM) radicals represent soluble paramagnetic probes for biomedical electron paramagnetic resonance (EPR)-based spectroscopy and imaging. There is an increasing demand in the development of multifunctional, biocompatible and targeted trityl probes hampered by the difficulties in derivatization of the TAM structure. We proposed a new straightforward synthetic strategy using click chemistry for the covalent conjugation of the TAM radical with a water-soluble biocompatible carrier exemplified here by dextran. A set of dextran-grafted probes varied in the degrees of Finland trityl radical loading and dextran modification by polyethelene glycol has been synthesized. The EPR spectrum of the optimized macromolecular probe exhibits a single narrow line with high sensitivity to oxygen and has advantages over the unbound Finland trityl of being insensitive to interactions with albumin. In vivo EPR imaging of tissue oxygenation performed in breast tumor-bearing mouse using dextran-grafted probe demonstrates its utility for preclinical oximetric applications.     

Influence of molecular configuration on the passage of macromolecules across the glomerular capillary wall

The influence of molecular configuration on the filtration of macromolecules across glomerular capillary walls was examined by comparing fractional clearances of two uncharged polysaccharides of distinctly different molecular configuration in the Munich-Wistar rat. The macromolecules employed were dextran, a slightly branched polymer of glucopyranose, and ficoll, a highly cross-linked copolymer of sucrose and epichlorohydrin. Differences in effective shape between these two polymers were determined from measurements of several physical properties of aqueous solutions containing either dextran or ficoll. It was found that dextran is best represented as a prolate ellipsoid with axial ratios of 4, 9, and 16 for molecules with Stokes-Einstein radii of 22, 32, and 40 A, respectively. On the other hand, ficoll is more closely approximated as spherical since the axial ratio was found to be between 1 and 2 for all molecular sizes. Fractional clearances of dextran and ficoll ranging in effective radius from 18 to 44 A were determined in each of seven Munich-Wistar rats. Fractional clearances of dextran were found to be greater than those of ficoll, the difference being significant for molecular radii ranging from 24 to 44 A. In addition, as shown previously for dextran, ficoll was found to be neither secreted nor reabsorbed by the renal tubules. These results, therefore, suggest that in addition to molecular size and charge, molecular configuration is also a determinant of the filtration of macromolecules across the glomerular capillary wall.     

Methods for the topographical patterning and patterned surface modification of hydrogels based on hydroxyethyl methacrylate

Hydrogels have gained broad acceptance as a class of biocompatible materials. In this paper, we report the topographic patterning and regiospecific functionalization of hydrogel surfaces. Both photolithography and soft lithography are combined in a hybrid process to form these topographic features. By functionalization of a base layer surface followed by lithographic patterning steps, it is possible to introduce chemical functions to specific regions of the patterned surface. The model systems investigated were based on 2-hydroxyethyl methacrylate (HEMA), which is well-known for its low toxicity and widespread use in biomedical applications. Tests of Ni-NTA modified hydrogel surfaces showed successful binding of fluorescently labeled proteins to selected regions of the patterned hydrogel surface. These processes can be expanded to a wide range of monomer systems.     

Thermal stability of immobilized enzymes circular dichroism, fluorescence and kinetic measurements of alpha-chymotrypsin attached to soluble carriers.

The temperature-induced unfolding of alpha-chymotrypsin and of chymotrypsin covalently bound to two soluble transparent carriers, dextran and a copolymer of maleic acid anhydride and acrylic acid, has been studied by tryptophan fluorescence emission, circular dichroic and kinetic measurements. It has been shown that the structural and functional properties of the enzyme when bound to the anionic copolymer are strongly influenced by electrostatic interactions. A number of reference experiments with anionic polyelectrolytes and the hydrogenated monomers of the copolymer suggest that these changes are brought about by the cooperative ion pair formation between protein and polyanionic matrix.     

Fabricating Superhydrophobic Polymeric Materials for Biomedical Applications

Superhydrophobic materials, with surfaces possessing permanent or metastable non-wetted states, are of interest for a number of biomedical and industrial applications. Here we describe how electrospinning or electrospraying a polymer mixture containing a biodegradable, biocompatible aliphatic polyester (e.g., polycaprolactone and poly(lactide-co-glycolide)), as the major component, doped with a hydrophobic copolymer composed of the polyester and a stearate-modified poly(glycerol carbonate) affords a superhydrophobic biomaterial. The fabrication techniques of electrospinning or electrospraying provide the enhanced surface roughness and porosity on and within the fibers or the particles, respectively. The use of a low surface energy copolymer dopant that blends with the polyester and can be stably electrospun or electrosprayed affords these superhydrophobic materials. Important parameters such as fiber size, copolymer dopant composition and/or concentration, and their effects on wettability are discussed. This combination of polymer chemistry and process engineering affords a versatile approach to develop application-specific materials using scalable techniques, which are likely generalizable to a wider class of polymers for a variety of applications.     

Optimization and characterization of dextran membranes prepared by electrospinning

Dextran is soluble in both water and organic solvents, so it could be a versatile biomacromolecule for preparing nanofibrous electrospun membranes by blending with either water-soluble bioactive agents or hydrophobic biodegradable polymers for biomedical applications. We have formulated electrospun dextran membranes, and the effects of various processing parameters on the membrane properties were investigated. It was found that uniform nanofibrous dextran membranes could be formed by using water, DMSO/water, and DMSO/DMF mixtures as solvents through adjusting the processing conditions (solution concentration, voltage, and the distance between the electrode and the collecting plate). When water was used as a solvent, up to 10% (w/w) of bovine serum albumin (BSA) or lysozyme could be directly incorporated into the dextran electrospun membrane without compromising its morphology. No significant effect of the electrospinning process on lysozyme activity was observed. The composite electrospun membranes consisting of poly(D,L-lactide-co-glycolide) (PLGA) and dextran were obtained using DMSO/DMF (50/50, volume ratio) mixture as solvents. For cross-linking the electrospun membrane, dextran was modified by substitution of methacrylate groups at the hydroxyl sites. It was found that the electrospun membranes prepared from methacrylated dextran can be cured by UV irradiation in the presence of 1% of 2,2-dimethoxy-2-phenylacetophenone (DMPA) as a photoinitiator.     

Photocrosslinkable biodegradable responsive hydrogels as drug delivery systems

Recently, controlled release from biocompatible materials has received much attention for biomedical applications. Due to their biocompatibility and biodegradability, glucopyranosides such as dextran appear as promising polymeric materials if one is able to regulate their rheological properties and the encapsulation/release efficiency. In this work graft polymer hydrogels from dextran and N-isopropylacrylamide (NIPAAm) were prepared and characterized.Dextran molecules were modified with 2-isocyanatoethylmethacrylate (IEMA) in order to obtain a polymer with carbon double bonds. Urethane linkages resulted from the reaction between hydroxyl groups (OH) of the dextran and isocyanate groups (NCO) of the IEMA. The obtained polymer was then crosslinked by UV irradiation in the presence of the photoinitiating agent Irgacure 2959 by CIBA^®. The drug Ondansetron^® was entrapped in the final system and its release profile was determined at 25 and 37 °C.The characterization of the materials was accomplished by: ATR-FTIR (Attenuated Total Reflectance-Fourier Transform Infrared) spectroscopy, elemental analysis, lower critical solution temperature (LCST) determination, swelling behaviour evaluation, determination of surface energy by contact angle measurement and drug delivery profile studies.     

Short interfering RNA delivered by a hybrid nanoparticle targeting VEGF: Biodistribution and anti-tumor effect

BackgroundThe use of RNA interference (iRNA) therapy has proved to be an interesting target therapy for the cancer treatment; however, siRNAs are unstable and quickly eliminated from the bloodstream. To face these barriers, the use of biocompatible and efficient nanocarriers emerges as an alternative to improve the success application of iRNA to the cancer, including breast cancer.ResultsA hybrid nanocarrier composed of calcium phosphate as the inorganic phase and a block copolymer containing polyanions as organic phase, named HNPs, was developed to deliver VEGF siRNA into metastatic breast cancer in mice. The particles presented a rounded shape by TEM images with average size measured by DLS suitable and biocompatible for biomedical applications. The XPS and EDS spectra confirmed the hybrid composition of the nanoparticles. Moreover, after intravenous administration, the particles accumulated mainly in the tumor site and kidneys, which demonstrates the tumor targeting accumulation through the Enhanced Permeability and Retention Effect (EPR). A significant decrease in size of the tumors treated with the nanoparticles containing siVEGF (HNPs-siVEGF) was observed and the reduction was related to enhanced tumor accumulation of siRNA as well as in vivo VEGF silencing at gene and protein levels.ConclusionThe hybrid system prepared was successful in promoting the RNAi effect in vivo with very low toxicity.General significanceThis study shows the valuable development of a hybrid nanoparticle carrying VEGF siRNA, as well as their tumor targeting, accumulation and reduction in mice triple-negative breast cancer.     

GMA grafted sago starch as a reactive component in ultra violet radiation curable coatings

Glycidyl methacrylate (GMA) was successfully grafted onto sago starch using ceric ammonium nitrate as initiator in aqueous medium. The percentage of grafting increased with increasing concentration of GMA monomer in the range studied. A core-shell configuration had been suggested to account for the hydrophobic behavior of the starch-g-GMA. Fourier transform infrared spectral analysis provided evidence of the grafting of GMA onto the starch. The acrylic double bond participated in the grafting onto the polysaccharide backbone with the glycidyl groups remaining unaffected.

The graft copolymer of starch and glycidyl methacrylate (starch-g-GMA) was incorporated into UV curable formulations using a cationic photoinitiator. In general, the addition of starch-g-GMA increased the flexibility of the cured film. The increasing of starch-g-GMA concentration in the coatings formulation increased the hardness of cured films. Gel content of the cured epoxy resin remained unimpaired by the addition of starch-g-GMA. Increasing the photoinitiator concentration in the coating formulations increased the hardness and as expected decreased the flexibility of the cured film. The gel content increased with increasing photoinitiator concentration. Further experiments are in progress to study the biodegradability of coatings.     

Coagulation, hemostasis, and plasma expanders:a quarter century enigma.

Despite more than 2 decades of research, the explanation of the long-known hemostatic failure consequent to the use of some natural and synthetic macromolecular agents as plasma substitutes remains obscure. Conventional clotting parameters are not significantly affected in vivo or in vitro. Dextran, hydroxyethyl starch, and many other colloid macromolecules precipitate Factors I and VIII, fibrin monomer, and perhaps v. W. (von Willebrand) factor(s) from plasma, rendering at least the first three insoluble, in relation to the molecule size and concentration of the colloid, and for dextran, its intrinsic viscosity. The precipitate, rich in Factors VIII and I, redissolves on warming, and reprecipitates on cooling, behaving as a cryo-Factor I. In composition it closely resembles the cryoprecipitate obtained by slow-thawing of plasma. Both clot faster with thrombin than the parent plasma. The amount precipitated from plasma by dextran or hydroxyethyl starch varies very widely from individual to individual. Cryo- of dextran-precipitable material can be obtained by interacting purified Factor I with a miniscule amount of thrombin. Dextran, hydroxyethyl starch, polyvinyl pyrrolidone, some forms of gelatin, and several polyamino acids accelerate thrombin clotting of normal plasma, several dysfibrinogenemic plasmas, or Factor I. Albumin, hemoglobin, some modified gelatins do not. Poor platelet thromboplastic function appears some hours after dextran infusion, associated with morphologic capillary abnormalities that strikingly resemble those in v. W. disease. We postulate that the hemostatic defect associated with the use of plasma substitutes is a form of induced v. W. disease or disseminated intravascular clotting, ensuing from precipitation and removal of v. W. factor(s), Factors VIII and I, microcirculatory abnormality, and platelet malfunction. The latter two supervene some time after administration of dextran. It reported antithrombotic activity is perhaps referable to the same action.     

Compatibilized polymer blends based on PDLLA and PCL for application in bioartificial liver

Porous scaffolds for tissue engineering applications based on poly(D,L-lactide)/poly(epsilon-caprolactone) compatibilized blends are described. The addition of a third polymer, namely poly( D, L-lactide-co-caprolactone) copolymer, has a profound effect on morphological properties of the blends scaffolds. In fact, the copolymer acts as compatibilizing agent and reduces the dimension of the dispersed phase of an order of magnitude. Such effect is function of the polymer composition. The efficiency of scaffolds obtained with poly( D, L-lactide) based blends containing 30% by weight of poly(epsilon-caprolactone) as dispersed phase toward hepatocytes has been tested by several biological assays and we found that they are able to promote a perfect adhesion, proliferation and growth of cells. Moreover, the addition of the copolymer significantly improves the biomedical performance of the scaffold.     

Synthesis, swelling behavior, and biocompatibility of novel physically cross-linked polyurethane-block-poly(glycerol methacrylate) hydrogels

Physically cross-linked novel block copolymer hydrogels with tunable hydrophilic properties for biomedical applications were synthesized by controlled radical polymerization of polyurethane macroiniferter and (2,2-dimethyl-1,3-dioxolane) methyl methacrylate. The block copolymers were converted to hydrogels by the selective hydrolysis of poly[(2,2-dimethyl-1,3-dioxolane) methyl methacrylate] block to poly(glycerol methacrylate). The block copolymerization has been monitored by monomer conversion and molecular weight increase as a function of time. It was observed that the polymerization proceeded with a characteristic "living" behavior where both monomer conversion and molecular weight increased linearly, with increasing reaction time. The resulting hydrogels were investigated for their equilibrium water content (EWC), dynamic water contact angles, swelling kinetics, thermodynamic interaction parameters, plasma protein adsorption, and platelet adhesion. Similar to our previous mechanically responsive hydrogels (Mequanint, K.; Sheardown, H. J. Biomater. Sci. Polym. Ed. 2005, 10, 1303-1318), the present results indicated that block copolymer hydrogels have excellent hydrophilicity and swelling behavior with improved modulus of elasticity. The equilibrium swelling was affected by the hydrolysis time, block length of poly(glycerol methacrylate), temperature, and the presence of soluble salts. Fibrinogen adsorption and platelet adhesion were significantly lower for the hydrogels than for the control polyurethane, whereas albumin adsorption increased for the hydrogels in proportion to the contents of poly(glycerol methacrylate). These hydrogels have potential in a number of biomedical applications such as drug delivery and scaffolds for tissue engineering.     

Semisynthetic hydrophilic polyals

Non-bioadhesive, fully biodegradable soluble polymers would be very instrumental in advanced biomedical applications, such as gene and drug delivery and tissue engineering. However, rational development of such materials is hindered by the complexity of macromolecule interactions with biological milieu. The prevalence of carbohydrates in naturally occurring interface structures suggests an alternative, biomimetic approach. Interface carbohydrates, regardless of their biological function, have common non-signaling substructures (e.g., acetal and ketal groups, secondary and primary alcohols). We hypothesized that hydrophilic polymers (polyals) consisting of acyclic units built of non-signaling carbohydrate substructures would be highly biocompatible and non-bioadhesive, while intrachain acetal or ketal groups would enable nonenzymatic biodegradation upon uptake by cells. Acyclic hydrophilic polyals can be prepared via either polymerization of suitable monomers or lateral cleavage of cyclic polyals (e.g., polysaccharides). In this study, model polyals were produced via lateral cleavage of polyaldoses and polyketoses. Best results were achieved using dextran B-512 as a precursor. The resultant poly[hydroxymethylethylene hydroxymethylformal], in agreement with the hypothesis, demonstrated excellent biological properties and technological flexibility. Materials of this type can potentially have several applications in pharmacology and bioengineering.     

Biological Characteristics of the MG-63 Human Osteosarcoma Cells on Composite Tantalum Carbide/Amorphous Carbon Films

Tantalum (Ta) is a promising metal for biomedical implants or implant coating for orthopedic and dental applications because of its excellent corrosion resistance, fracture toughness, and biocompatibility. This study synthesizes biocompatible tantalum carbide (TaC) and TaC/amorphous carbon (a-C) coatings with different carbon contents by using a twin-gun magnetron sputtering system to improve their biological properties and explore potential surgical implant or device applications. The carbon content in the deposited coatings was regulated by controlling the magnetron power ratio of the pure graphite and Ta cathodes. The deposited TaC and TaC/a-C coatings exhibited better cell viability of human osteosarcoma cell line MG-63 than the uncoated Ti and Ta-coated samples. Inverted optical and confocal imaging was used to demonstrate the cell adhesion, distribution, and proliferation of each sample at different time points during the whole culture period. The results show that the TaC/a-C coating, which contained two metastable phases (TaC and a-C), was more biocompatible with MG-63 cells compared to the pure Ta coating. This suggests that the TaC/a-C coatings exhibit a better biocompatible performance for MG-63 cells, and they may improve implant osseointegration in clinics.     

Poly(carbonate-ester)s of dihydroxyacetone and lactic acid as potential biomaterials

The synthesis of new polymeric biomaterials using biocompatible building blocks is important for the advancement of the biomedical field. We report the synthesis of statistically random poly(carbonate-ester)s derived from lactic acid and dihydroxyacetone by ring-opening polymerization. The monomer mole feed ratio and initiator concentration were adjusted to create various copolymer ratios and molecular weights. A dimethoxy acetal protecting group was used to stabilize the dihydroxyacetone and was removed using elemental iodine and acetone at reflux to produce the final poly(lactide-co-dihydroxyacetone) copolymers. The characteristics of the copolymers in their protected and deprotected forms were characterized by (1)H NMR, (13)C NMR, GPC, TGA, and DSC. Hydrolytic degradation of the deprotected copolymers was tracked over an 8-week time frame. The results show that faster degradation occurred with increased carbonate content in the copolymer backbone. The degradation pattern of the copolymers was visualized using SEM and revealed a trend toward surface erosion as the primary mode of degradation.     

Biocompatibility and antimicrobial activity of poly(3-hydroxyoctanoate) grafted with vinylimidazole

Vinylimidazole-grafted poly(3-hydroxyoctanoate) (VI-g-PHO) copolymers were prepared by heating homogeneous solutions of PHO, VI monomer, and benzoylperoxide initiator. The Fourier transform infrared spectroscopy attenuated total reflection and electron spectroscopy for chemical analyses showed that VI was successfully grafted onto the PHO chains. The surfaces and the bulk of VI-g-PHO copolymers became more hydrophilic as the VI grafting density in the copolymer increased. Measurements of the growth of Chinese hamster ovary cells and the adsorption of blood proteins and platelets in vitro showed that biocompatibility was also enhanced by grafting of VI groups. Antimicrobial activity of the VI-g-PHO copolymers was studied against Escherichia coli, Staphylococcus aureus, and Candida albicans. Treatment of each culture suspension with 2.0% (w/v) copolymers for 12h resulted in >90% reduction in viable cell counts against all test microorganisms. These results indicate that the VI-g-PHO copolymers are promising materials for biomedical applications, as they exhibited both biocompatibility and broad spectrum antimicrobial activity.     

Recent Progress in Polyhydroxyalkanoates‐Based Copolymers for Biomedical Applications

In recent years, naturally biodegradable polyhydroxyalkanoate (PHA) monopolymers have become focus of public attentions due to their good biocompatibility. However, due to its poor mechanical properties, high production costs, and limited functionality, its applications in materials, energy, and biomedical applications are greatly limited. In recent years, researchers have found that PHA copolymers have better thermal properties, mechanical processability, and physicochemical properties relative to their homopolymers. This review summarizes the synthesis of PHA copolymers by the latest biosynthetic and chemical modification methods. The modified PHA copolymer could greatly reduce the production cost with elevated mechanical or physicochemical properties, which can further meet the practical needs of various fields. This review further summarizes the broad applications of modified PHA copolymers in biomedical applications, which might shred lights on their commercial applications.     

Synthesis and characterization of thermoset biodegradable elastomers based on star-poly(epsilon-caprolactone-co-D,L-lactide)

Biodegradable elastomers represent a useful class of biomaterials. In this paper, we synthesize thermoset elastomers by utilizing the living nature of ring-opening polymerization of a star copolymer of D,L-lactide and epsilon-caprolactone initiated with glycerol and catalyzed by stannous 2-ethylhexanoate. The star copolymers were synthesized of varying molecular weight and monomer composition and cross-linked by compression molding using a dilactone, bis(epsilon-caprolactone-4-yl)propane dissolved in epsilon-caprolactone monomer. The elastomers were then characterized by differential scanning calorimetry and uniaxial tensile testing and their physical properties related to the nature of the star copolymer prepolymers. The results demonstrate a means of predictably altering the elastomer physical properties by adjusting the star copolymer prepolymer initial molecular weight and monomer ratio.