Synthesis and properties of photocross-linked poly(propylene fumarate) scaffolds

The photocross-linking of poly(propylene fumarate) (PPF) to form porous scaffolds for bone tissue engineering applications was investigated. PPF was cross-linked using the photoinitiator bis(2,4,6-trimethylbenzoyl) phenylphosphine oxide (BAPO) and exposure to 30 min of long wavelength ultraviolet (UV) light. The porous photocross-linked PPF scaffolds (6.5 mm diameter cylinders) were synthesized by including a NaCl porogen (70, 80, and 90 wt% at cross-linking) prior to photocross-linking. After UV exposure, the samples were placed in water to remove the soluble porogen, revealing the porous PPF scaffold. As porogen leaching has not been used often with cross-linked polymers, and even more rarely with photoinitiated cross-linking, a study of the efficacy of this strategy and the properties of the resulting material was required. Results show that the inclusion of a porogen does not significantly alter the photoinitiation process and the resulting scaffolds are homogeneously cross-linked throughout their diameter. It was also shown that porosity can be generally controlled by porogen content and that scaffolds synthesized with at least 80 wt% porogen possess an interconnected pore structure. Compressive mechanical testing showed scaffold strength to decrease with increasing porogen content. The strongest scaffolds with interconnected pores had an elastic modulus of 2.3+/-0.5 MPa and compressive strength at 1% yield of 0.11+/-0.02 MPa. This work has shown that a photocross-linking/porogen leaching technique is a viable method to form porous scaffolds from photoinitiated materials.

Quinol:fumarate oxidoreductases and succinate:quinone oxidoreductases: phylogenetic relationships, metal centres and membrane attachment

A comprehensive phylogenetic analysis of the core subunits of succinate:quinone oxidoreductases and quinol:fumarate oxidoreductases is performed, showing that the classification of the enzymes as type A to E based on the type of the membrane anchor fully correlates with the specific characteristics of the two core subunits. A special emphasis is given to the type E enzymes, which have an atypical association to the membrane, possibly involving anchor subunits with amphipathic helices. Furthermore, the redox properties of the SQR/QFR proteins are also reviewed, stressing out the recent observation of redox-Bohr effect upon haem reduction, observed for the Desulfovibrio gigas and Rhodothermus marinus enzymes, which indicates a direct protonation event at the haems or at a nearby residue. Finally, the possible contribution of these enzymes to the formation/dissipation of a transmembrane proton gradient is discussed, considering recent experimental and structural data.

Purification, crystallisation and preliminary crystallographic studies of succinate:ubiquinone oxidoreductase from Escherichia coli

A membrane protein complex, succinate dehydrogenase (SQR) from Escherichia coli has been purified and crystallised. This enzyme is composed of four subunits containing FAD, three iron-sulphur clusters and one haem b as prosthetic groups. The obtained crystals belong to the hexagonal space group P6(3) with the unit-cell dimensions of a=b=123.8 A and c=214.6 A. An asymmetric unit of the crystals contains one SQR monomer (M(r) 120 kDa). A data set is now available at 4.0 A resolution with 88.1% completeness and 0.106 R(merge). We have obtained a molecular replacement solution that shows sensible molecular packing, using the soluble domain of E. coli QFR (fumarate reductase) as a search model. The packing suggests that E. coli SQR is a crystallographic trimer rather than a dimer as observed for the E. coli QFR.

Synthesis and characterization of triblock copolymers of methoxy poly(ethylene glycol) and poly(propylene fumarate)

Amphiphilic block copolymers were synthesized by transesterification of hydrophilic methoxy poly(ethylene glycol) (mPEG) and hydrophobic poly(propylene fumarate) (PPF) and characterized. Four block copolymers were synthesized with a 2:1 mPEG:PPF molar ratio and mPEGs of molecular weights 570, 800, 1960, and 5190 and PPF of molecular weight 1570 as determined by NMR. The copolymers synthesized with mPEG of molecular weights 570 and 800 had 1.9 and 1.8 mPEG blocks per copolymer, respectively, as measured by NMR, representing an ABA-type block copolymer. The number of mPEG blocks of the copolymer decreased with increasing mPEG block length to as low as 1.5 mPEG blocks for copolymer synthesized with mPEG of molecular weight 5190. At a concentration range of 5-25 wt % in phosphate-buffered saline, copolymers synthesized with mPEG molecular weights of 570 and 800 possessed lower critical solution temperatures (LCST) between 40 and 45 degrees C and between 55 and 60 degrees C, respectively. Aqueous solutions of copolymer synthesized with mPEG 570 and 800 also experienced thermoreversible gelation. The sol-gel transition temperature was dependent on the sodium chloride concentration as well as the mPEG block length. The copolymer synthesized from mPEG 570 had a transition temperature between 40 and 20 degrees C with salt concentrations between 1 and 10 wt %, while the sol-gel transition temperatures of the copolymer synthesized from mPEG molecular weight 800 were higher in the range 75-30 degrees C with salt concentrations between 1 and 15 wt %. These novel thermoreversible copolymers are the first biodegradable copolymers with unsaturated double bonds along their macromolecular chain that can undergo both physical and chemical gelation and hold great promise for drug delivery and tissue engineering applications.

A theoretical study of the effect of a tetraalkylammonium counterion on the hydrogen bond strength in Z-hydrogen maleate

High-level ab initio calculations (B3LYP/6-31+G and QCISD(T)/6-311+G**) were carried out to resolve the disagreement between recent experimental and computational estimates of the relative strength of the intramolecular hydrogen bond in Z-hydrogen maleate anion with respect to the normal hydrogen bond in maleic acid. The computational estimates for the strength of the intramolecular hydrogen bond in the gas-phase maleate anion are in a range of 14-28 kcal/mol depending on the choice of the reference structure. Computational data suggest that the electrostatic influence of a counterion such as a tetraalkylammonium cation can considerably weaken the hydrogen bonding interaction (by 1.5-2 times) in the complexed hydrogen maleate anion relative to that in the naked anion. The estimated internal H-bonding energies for a series of Z-maleate/R4N+ salts (R = CH3, C2H5, CH3CH2CH2CH2) range from 8 to 13 kcal/mol. The calculated energy differences between the E- and Z-hydrogen maleates complexed to Me4N+, Et4N+, and Bu4N+ cation are 4.9 (B3LYP/6-31+G(d,p)) and 5.7 and 5.8 kcal/mol (B3LYP/6-31G(d)). It is also demonstrated that the sodium cation exerts a similar electrostatic influence on the hydrogen bond strength in bifluoride anion (FHF-). The present study shows that while low-barrier short hydrogen bonds can exist in the gas phase (the barrier for the hydrogen transfer in maleate anion is only 0.2 kcal/mol at the QCISD(T)/6-311+G//QCISD/6-31+G level), whether they can also be strong in condensed media or not depends on how their interactions with their immediate environment affect their strength.

A diffusible analogue of N(3)-(4-methoxyfumaroyl)-L-2,3-diaminopropanoic acid with antifungal activity

N(3)-(4-Methoxyfumaroyl)-L-2,3-diaminopropanoic acid (FMDP), a specific and potent inactivator of glucosamine-6-phosphate (GlcN-6-P) synthase from Candida albicans, exhibits relatively poor anticandidal activity, with an MIC value amounting to 50 microg ml(-1) (200 microM). Uptake of FMDP into C. albicans cells follows saturation kinetics and is sensitive to the action of metabolic inhibitors, thus indicating the active transport mechanism. However, the acetoxymethyl ester of FMDP penetrates the fungal cell membrane by free diffusion and is rapidly hydrolysed by C. albicans cytoplasmic enzymes to release the free FMDP. This mechanism gives rise to continuous accumulation of the enzyme inhibitor and results in higher antifungal activity of the FMDP ester (MIC=3.1 microg ml(-1), 10 microM). These results show that the 'pro-drug' approach can be successfully applied for the enhancement of antifungal activity of glutamine analogues that inhibit GlcN-6-P synthase.

Activation of the low oxygen affinity-inducing potential of the Asn108(beta)-->Lys mutation of Hb-Presbyterian on intramolecular alpha alpha-fumaryl cross-bridging

The Asn108 beta-->Lys mutation in hemoglobin (HbPresbyterian mutation) endows a low O(2) affinity-inducing propensity to the protein. Introduction of a fumaryl cross-bridge between its two alpha 99 lysine residues also induces a low O(2) affinity into HbA. We have now engineered an alpha alpha-fumaryl cross-bridge into Hb-Presbyterian to determine the synergy or additivity, if any, that can be achieved between these two low O(2) affinity-inducing structural perturbations. Despite the presence of the additional epsilon-amino group of Lys108(beta) within the central cavity, the epsilon-amino group of Lys99(alpha alpha) of deoxy Hb-Presbyterian retained high selectivity for alpha alpha-fumaryl cross-bridging, with an overall efficiency comparable to that with HbA. The alpha alpha-fumaryl cross-linking of Hb-Presbyterian reduced its O(2) affinity much more significantly than that observed with HbA, indicating a synergy between the two low O(2) affinity-inducing structural perturbations. Apparently, the alpha alpha-fumaryl cross-bridge in Hb-Presbyterian activates part of the latent low O(2) affinity-inducing potential of Lys108(beta) that is generally activated in the presence of chloride. The synergy between the Asn108(beta)-->Lys mutation and the alpha alpha-fumaryl cross-bridging was conserved in the presence of chloride, but not in the presence of DPG. Furthermore, in the presence of chloride and DPG, alpha alpha-fumaryl Hb-Presbyterian accessed a low O(2) affinity T-state that is accessed by HbA, alpha alpha-HbA and Hb-Presbyterian only in the presence of IHP. Isoelectric focusing analysis suggested that the alpha alpha-fumaryl cross-linking of Hb-Presbyterian induces changes in the ionization behavior of one or more of the functional groups neighboring Lys99(alpha) and Lys108(beta) [presumably His103(alpha) and/or Glu101(beta)] to compensate for the extra positive charge of Lys108(beta). Molecular modeling studies identified two potential chloride binding sites per alpha beta dimer within the middle of the central cavity of alphaalpha-fumaryl HbA involving residues His103(alpha), Arg104(beta) and Asn108(beta). The affinity of these sites is increased in alpha alpha-fumaryl Hb-Presbyterian as a result of the Asn108(beta)-->Lys mutation. Thus, the results of the present study suggest that the enhanced neutralization of the positive charges in the middle of the central cavity of Hb achieved by these two electrostatic modifications, one (the alpha alpha-fumaryl cross-bridge) acting directly and the other (the Presbyterian mutation) acting indirectly through the mediation of chloride ion binding, facilitates the alpha alpha- fumaryl-Hb Presbyterian to access a low O(2) affinity T-state structure much more readily than either Hb-Presbyterian or alpha alpha-fumaryl HbA.

Glutathione depletion in rat hepatocytes: a mixture toxicity study with alpha, beta-unsaturated esters

1. Glutathione (GSH) depletion is often reported as an early cytotoxic effect, caused by many reactive organic chemicals. In the present study, GSH depletion in primary rat hepatocytes was used as an in vitro effect-equivalent to measure the toxic potency of alpha,beta-unsaturated esters (acrylates and methacrylates). 2. When these compounds were administered as a mixture, GSH depletion was dose additive. The result of the mixture study shows that GSH depletion may be a useful effect-equivalent for the risk assessment of mixtures of alpha,beta-unsaturated esters. 3. To get more insight in the underlying mechanisms of GSH depletion, the metabolism of two esters was investigated in greater detail. One of them, allyl methacrylate, was metabolized to acrolein. This metabolic pathway can explain the high potency of allyl methacrylate to deplete GSH despite its low intrinsic chemical reactivity.

Probing the active site of L-aspartate oxidase by site-directed mutagenesis: role of basic residues in fumarate reduction

L-Aspartate oxidase is a very particular oxidase which behaves as a fumarate reductase in anaerobic conditions. Its primary and tertiary structures present remarkable similarity with the soluble fumarate reductase (FRD) from Shewanella frigidimarina and the flavin subunit of the membrane-bound fumarate reductase from Escherichia coli and Wolinella succinogenes. This and other extensive similarities are consistent with the idea that a common catalytic mechanism for the reduction of fumarate operates for all members of this enzyme group and that the key residues involved in the substrate binding and catalysis are conserved. This manuscript reports information about the role of these basic residues in L-aspartate oxidase: R290, R386, H244, and H351. By means of site-directed mutagenesis, R290 and R386 are mutated to Leu and H351 and H244 are mutated both to Ala and Ser. H351, H244, and R386 mutants bind substrate analogues with higher dissociation constants and present lower k(cat)/K(m) values in the reduction of fumarate. Therefore, the results indicate that R386, H244, and H351 are important for the binding of the substrate fumarate and may play an important but not essential role in catalysis. R290, on the contrary, is mainly involved in catalysis and not in substrate binding since its mutation abolishes the catalytic activity without lowering the affinity of the enzyme for the substrate. The redox properties of all the mutants are identical to the wild-type. The findings are consistent with a model of L-aspartate oxidase active site based on the hypothesis proposed for the soluble FRD from S. fridimarina.

Amide and ester derivatives of N3-(4-methoxyfumaroyl)-(S)-2,3-diaminopropanoic acid

Several amide and ester derivatives of a glutamine analogue, N3-(4-methoxyfumaroyl)-(S)-2,3-diaminopropanoic acid (FMDP) (1-8), were synthesized and evaluated for the inhibitory activity in regard to glucosamine-6-phosphate synthase from Candida albicans. The syntheses were accomplished by the reaction of N2-tert-butoxycarbonyl-N3-(4-methoxyfumaroyl)-(S)-2,3-diaminopropanoic acid (BocFMDP) with the corresponding amines to give the FMDP amides (1-4) or with alkyl halides to give corresponding esters of FMDP (5-8). Among the synthesized compounds, the acetoxymethyl ester of FMDP was the most active inhibitor of the enzyme. Its IC50 value compared to that of FMDP (4 microM) was equal to 11.5 microM. The methyl and allyl esters and the N-hexyl-N-methyl-amide of FMDP exhibited a moderate enzyme inhibitory activity.

The simplest supramolecular complexes containing pairs of Mo(2)(formamidinate)(3) units linked with various dicarboxylates: preparative methods, structures, and electrochemistry

Twelve compounds containing two quadruply bonded Mo(2)(DAniF)(3) (DAniF = N,N'-di-p-anisylformamidinate) units linked by dicarboxylate anions have been prepared in high purity and good yields. All of these compounds have been characterized by crystallography and NMR. The dinuclear pairs display electrochemical behavior which is controlled by the nature of the bridging dicarboxylate group. As described by the linkers, the compounds are oxalate, 1; acetylene dicarboxylate, 2; fumarate, 3; tetrafluorophthalate, 4; carborane dicarboxylate, 5; ferrocene dicarboxylate, 6; malonate, 7; succinate, 8; propane-1,3-dicarboxylate, 9; tetrafluorosuccinate, 10; bicyclo[1.1.1]pentane-1,3-dicarboxylate, 11; and trans-1,4-cyclohexanedicarboxylate, 12.

The effect of change in pH on the solubility of iron bis-glycinate chelate and other iron compounds

The effect of a pH change from 2 to 6 was tested on the solubility of ferrous sulfate, ferrous fumarate, iron bis-glycine chelate (Ferrochel) and sodium-iron ethylenediaminetetraacetic acid (NaFeEDTA). It was found that at pH 2 ferrous sulfate, Ferrochel and NaFeEDTA were completely soluble and only 75% of iron from ferrous fumarate was soluble. When pH was raised to 6, iron from amino acid chelate and NaFeEDTA remained completely soluble while solubility from ferrous sulfate and ferrous fumarate decreased 64 and 74%, respectively compared to the amount of iron initially soluble at pH 2. These results suggest that iron solubility from iron bis-glycine chelate and NaFeEDTA is not affected by pH changes within the ranges tested, probably because iron remained associated to the respective compounds.

High strength bioresorbable bone plates: preparation, mechanical properties and in vitro analysis

Biodegradable bone plates were prepared as semi-interpenetrating networks (SIPN) of crosslinked polypropylene fumarate (PPF) within a host matrix of either poly(lactide-co-glycolide)-85:15 (PLGA) or poly(1-lactide-co-d,l-lactide)-70:30 (PLA) using N-vinylpyrrolidone (NVP), ethylene glycol dimethacrylate (EGDMA), 2-hydroxyethyl methacrylate (HEMA), and methyl methacrylate (MMA) as crosslinking agents. Hydroxyapatite (HAP), an inorganic filler material, was used to further augment mechanical strength. The control crosslinking agent (NVP) was replaced partially and totally with other crosslinking agents. The amount of crosslinking agent lost, the characterization change in the mechanical properties and the dimensional stability of the bone plates after in vitro treatment was calculated. The optimum crosslinking agent was selected on the basis of low in vitro release of NVP from SIPN matrix. Bone plates were then prepared using this crosslinking agent at 5 MPa pressure and at temperatures between 100-140 degrees C to determine if there was any augmentation of mechanical properties in the presence of the crosslinked network. In vitro analysis showed that 90% of the crosslinking agent was lost on plates using NVP as a crosslinking agent. This loss was reduced to 50% when NVP was partially replaced with EGDMA or MMA. EGDMA was determined to be superior because (1) its low release as a crosslinking agent, (2) flexural plate strength of 50-67 MPa, (3) flexural modulus of 7-13 GPa, and (4) manufacturability stiffness of 300-600 N/m. HAP-loading resulted in an additional increase in values of mechanical parameters. Substituting PLGA with PLA in the PPF-SIPN did not show any additional improvement of mechanical properties.

Injectable biodegradable polymer composites based on poly(propylene fumarate) crosslinked with poly(ethylene glycol)-dimethacrylate

New injectable, in situ crosslinkable biodegradable polymer composites were investigated consisting of poly(propylene fumarate) (PPF), poly(ethylene glycol)-dimethacrylate (PEG-DMA), and beta-tricalcium phosphate (beta-TCP). We examined the effects of the PEG-DMA/PPF double-bond ratio and beta-TCP content on the crosslinking characteristics of the composites including the maximum crosslinking temperature and the gel point, as well as the properties of the crosslinked composites such as the compressive strength and modulus, and the water-holding capacity. The maximum crosslinking temperature was constant averaging 39.7 degrees C for the composite formulations tested. The gel points varied from 8.0 +/- 1.0 to 12.6 +/- 2.5 min and were not affected by the relative amounts of PEG-DMA. The compressive strength at yield of PEG-DMA/PPF composites without beta-TCP increased from 5.9 +/- 1.0 to 11.2 +/- 2.2 MPa as the double-bond ratio of PEG-DMA/PPF increased from 0.38 to 1.88. An increase in compressive modulus was also observed from 30.2 +/- 3.5 to 58.4 +/- 6.2 MPa for the same range of the PEG-DMA/PPF double-bond ratio. Also, the addition of beta-TCP (33 wt%) enhanced the mechanical properties of all composites. The equilibrium water content of networks without beta-TCP increased from 21.7 +/- 0.2 to 30.6 +/- 0.2% for a double-bond ratio of PEG-DMA/PPF ranging from 0.38 to 1.88. However, the mechanical properties of the swollen composites under compression were smaller than the dry ones. These data demonstrate the feasibility of fabricating injectable biodegradable polymer composites with engineered mechanical properties for orthopedic tissue engineering.

Catalysis in fumarate reductase

In the absence of oxygen many bacteria are able to utilise fumarate as a terminal oxidant for respiration. In most known organisms the fumarate reductases are membrane-bound iron-sulfur flavoproteins but Shewanella species produce a soluble, periplasmic flavocytochrome c(3) that catalyses this reaction. The active sites of all fumarate reductases are clearly conserved at the structural level, indicating a common mechanism. The structures of fumarate reductases from two Shewanella species have been determined. Fumarate, succinate and a partially hydrated fumarate ligand are found in equivalent locations in different crystals, tightly bound in the active site and close to N5 of the FAD cofactor, allowing identification of amino acid residues that are involved in substrate binding and catalysis. Conversion of fumarate to succinate requires hydride transfer from FAD and protonation by an active site acid. The identity of the proton donor has been open to question but we have used structural considerations to suggest that this function is provided by an arginine side chain. We have confirmed this experimentally by analysing the effects of site-directed mutations on enzyme activity. Substitutions of Arg402 lead to a dramatic loss of activity whereas neither of the two active site histidine residues is required for catalysis.

A self-complementary, self-assembling microsphere system: application for intravenous delivery of the antiepileptic and neuroprotectant compound felbamate

Felbamate (FBM) is a novel antiepileptic drug (AED) and neuroprotectant (NP) compound that interacts with strychnine-insensitive (SI) glycine receptors in brain (IC(50) = 374 microM). FBM concentrations required to interact with SI glycine receptors are consistent with brain levels following oral and intraperitoneal administration of AED and NP doses. Because of the solubility limits of FBM, an intravenous (iv) form has not been developed. Nevertheless, an iv form could be important for the treatment of disorders such as status epilepticus and neuronal damage due to hypoxic/ischemic events. Substituted diketopiperazines precipitate in acid to form microspherical particles of uniform size ( approximately 2 microm). The microsphere system entraps drugs on precipitation and dissolves near physiological pH to release the drug cargo. Therefore, microspheres were used to produce an iv formulation of FBM. Mice were administered the FBM/microsphere (20-60 mg/kg FBM) and tested for protection against tonic extension seizures using maximal electroshock. The FBM/microsphere was effective in a time- and dose-dependent manner following iv administration. The median effective dose (ED(50)) for protection against MES seizures at 30 min was 27.2 mg/kg [95% confidence interval (CI) = 20.8-33.4, slope = 6.5]. The ED(50) for minimal motor impairment at 30 min was 167 mg/kg (95% CI = 155-177, slope = 28.1). Thus, the feasibility of encapsulating FBM or similar aqueous insoluble compounds in a microsphere system with delivery by the iv route for treatment of epilepsy and various central nervous system disorders has been clearly demonstrated. Studies were performed in accordance with the Guide for the Care and Use of Laboratory Animals.

Role of malonate in chickpeas

Analysis of the content and distribution of organic acids in chickpea plants (Cicer arietinum L.) showed that malonate was the most abundant acid in roots and nodules, whereas malate was the main acid in leaves and stems. The highest concentration of malonate in roots was in the apices. Malonate metabolism did not appear to be directly related to abiotic stress. We suggest that malonate has a role as a defensive chemical in roots and nodules of chickpeas.

Improved osteoconduction of cortical bone grafts by biodegradable foam coating

Alteration of the geometrical surface configuration of cortical bone allografts may improve incorporation into host bone. A porous biodegradable coating that would maintain immediate structural recovery and subsequently allow normal graft healing and remodeling by promoting bony ingrowth could provide an osteoconductive surface scaffold. We investigated the feasibility of augmenting cortical bone grafts with osteoconductive biodegradable polymeric scaffold coatings. Three types of bone grafts were prepared: Type I--cortical bone without coating (control), Type II--cortical bone coated with PLGA-foam, Type III--cortical bone coated with PPF-foam. The grafts were implanted into the rat tibial metaphysis (16 animals for each type of bone graft). Post-operatively the animals were sacrificed at 2 weeks and 4 weeks (8 animals for each type of bone graft at each time point). Histologic and histomorphometric analysis of grafts showed that the amount of new bone forming around the foam-coated grafts was significantly higher than in the control group (uncoated; p < 0.02). Although both foam formulations were initially equally osteoconductive, PLGA-based foam coatings appeared to have degraded at two weeks postoperatively, whereas PPF-based foam coatings were still present at 4 weeks postoperatively. While significant resorption was present in control allografts with little accompanying reactive new bone formation, PLGA-coated bone grafts showed evidence of bone resorption and subsequent bony ingrowth earlier than those coated with PPF-based foams suggesting that PPF-coated cortical bone grafts were longer protected against host reactions resulting in bone resorption.

Augmentation of osteoinduction with a biodegradable poly(propylene glycol-co-fumaric acid) bone graft extender. A histologic and histomorphometric study in rats

We investigated the feasibility of enhancing the regeneration of skeletal tissues by augmenting bone grafts with a composite biodegradable bone graft extender material based on the polymer poly(propylene fumarate), PPF. The material was mixed with autograft and allograft and placed directly into a cylindrical metaphyseal defect made in the rat tibia. These formulations were compared to defects without any graft material, autografts, allografts and PPF alone. Nine animals were included in each group. Animals were sacrificed at 1 and 4 weeks postoperatively. Implantation sites were then evaluated using histologic and histomorphometric methods. Results of this study showed that defects did not heal in sham operated animals. In the experimental groups, there was early new woven bone formation in the autograft group with near complete healing of the defect at four weeks. When PPF was used alone, gradual ingrowth of new bone was seen. Mixing of the PPF bone graft extender with either allograft or autograft material resulted in enhancement of new bone formation with both allo- and autograft. However, significantly more new bone formation than in the autograft group was only seen when the PPF bone graft extender was mixed with fresh autograft. Histomorphometry corroborated these findings. Results of this study suggest that a PPF-based material may be used to increase the volume of smaller amounts of bone grafts supporting the concept of "bone graft extenders" by application of engineered biodegradable porous scaffolds.

Marrow stromal osteoblast function on a poly(propylene fumarate)/beta-tricalcium phosphate biodegradable orthopaedic composite

The objective of this study was to assess the osteoconductivity of a poly(propylene fumarate)/beta-tricalcium phosphate (PPF/beta-TCP) composite in vitro. We examined whether primary rat marrow stromal cells would attach, proliferate, and express differentiated osteoblastic function when seeded on PPF/beta-TCP substrates. Attachment studies showed that a confluent monolayer of cells had adhered to the substrates within an 8 h time frame for marrow stromal cells seeded at confluent numbers. Proliferation and differentiated function of the cells were then investigated for a period of 4 weeks for an initial seeding density of 42,000 cells/cm2. Rapid proliferation during the first 24 h as determined by 3H-thymidine incorporation was mirrored by an initial rapid increase in total cell number by DNA assay. A lower proliferation rate and a gradual increase in cell number persisted for the remainder of the study, resulting in a final cell number of 128,000 cells/cm2. Differentiated cell function was assessed by measuring alkaline phosphatase (ALP) activity and osteocalcin (OC) production throughout the time course. Both markers of osteoblastic differentiation increased significantly over a 4-week period. By day 28, cells grown on PPF/beta-TCP reached a maximal ALP activity of 11 (+/- 1) x 10(-7) micromol/min/cell, while the OC production reached 40 (+/- 1) x 10(-6) ng/cell. These data show that a PPF/beta-TCP composite exhibits in vitro osteoconductivity similar to or better than that of control tissue culture polystyrene.

Mechanical properties of a biodegradable bone regeneration scaffold

Poly (Propylene Fumarate) (PPF), a novel, bulk erosion, biodegradable polymer, has been shown to have osteoconductive effects in vivo when used as a bone regeneration scaffold (Peter, S. J., Suggs, L. J., Yaszemski, M. J., Engel, P. S., and Mikos, A. J., 1999, J. Biomater. Sci. Polym. Ed., 10, pp. 363-373). The material properties of the polymer allow it to be injected into irregularly shaped voids in vivo and provide mechanical stability as well as function as a bone regeneration scaffold. We fabricated a series of biomaterial composites, comprised of varying quantities of PPF, NaCl and beta-tricalcium phosphate (beta-TCP), into the shape of right circular cylinders and tested the mechanical properties in four-point bending and compression. The mean modulus of elasticity in compression (Ec) was 1204.2 MPa (SD 32.2) and the mean modulus of elasticity in bending (Eb) was 1274.7 MPa (SD 125.7). All of the moduli were on the order of magnitude of trabecular bone. Changing the level of NaCl from 20 to 40 percent, by mass, did not decrease Ec and Eb significantly, but did decrease bending and compressive strength significantly. Increasing the beta-TCP from 0.25 g/g PPF to 0.5 g/g PPF increased all of the measured mechanical properties of PPF/NVP composites. These results indicate that this biodegradable polymer composite is an attractive candidate for use as a replacement scaffold for trabecular bone.

Application of the BIRD sandwich for the rapid and accurate determination of (1)H-(1)H NMR coupling constants in higher order spin systems

A method is presented that allows for the convenient and reliable determination of (1)H-(1)H NMR coupling constants in higher order or symmetrically coupled spin systems. The method can be applied on any programmable FT-NMR spectrometer and is demonstrated here on micromole quantities of sample in a standard 5-mm NMR tube.