Specificity of anti-dna antibodies in SLE—II. Relative contribution of backbone,secondary structure and nucleotide sequence to DNA binding

Fine specificity of a population of anti-DNA antibodies which bound both ssDNA and dsDNA with apparently equal affinity was studied in two SLE plasma. Sensitivity of DNA binding to increasing sodium chloride concentration indicated that electrostatic interactions occurred between antibody and phosphate moieties of DNA. Secondary nucleic acid structure was important to DNA binding as double-stranded synthetic deoxynucleotide polymers were more effective inhibitors than their substituent single-stranded polymers. Nucleotide bases were also found to play a role in recognition of DNA by these cross-reactive antibodies, as ssDNA binding was sensitive to increasing temperature which caused unstacking of the nucleotide bases. Differing patterns of reactivity with synthetic deoxynucleotide polymers with similar secondary structures but different nucleotide compositions further indicated the importance of nucleotide bases to dsDNA binding by cross-reactive anti-DNA antibodies in SLE plasma.     

Thermoresponsive UCST‐Type Behavior of Interpolymer Complexes of Poly(ethylene glycol) and Poly(poly(ethylene glycol) methacrylate) Brushes with Poly(acrylic acid) in Isopropanol

Upper critical solution temperature (UCST)‐type thermoresponsive behavior of poly(ethylene glycol)–poly(acrylic acid) (PEG–PAA) and poly(poly(ethylene glycol) methacrylate)–poly(acrylic acid) (PPEGMA–PAA) interpolymer complexes has been observed in isopropanol. For these investigations, PPEGMA and PAA with various average molecular weights have been synthesized by atom transfer radical polymerization. It has been found that both the PEG and PPEGMA have lower cloud point temperatures (T _cp) than its mixed polymer solutions with PAA, whereas PAA does not show such behavior in the investigated temperature range. These findings indicate the reversible formation of interpolymer complexes with variable structure and composition in the solutions of the polymer mixtures in isopropanol. Increasing the ethylene glycol/acrylic acid molar ratio or the molecular weight of either the PAA or the H‐acceptor PEG component of the interpolymer complexes increases the UCST‐type cloud point temperatures of these interpolymer systems. The polymer–polymer interactions by hydrogen bonds between PAA and PEG or PPEGMA and the correlations between T _cp and structural parameters of the components revealed in the course of these investigations may be utilized for exploring well‐defined UCST‐type material systems for various applications.

     

Simultaneous isolation of cytoplasmic endoribonuclease and exoribonuclease of Trypanosoma brucei

An endoribonuclease and an exoribonuclease have been isolated simultaneously from the cytoplasm of Trypanosoma brucei by hydroxyapatite column chromatography. The endoribonuclease produced oligonucleotides from poly(adenylic acid) with 5'-phosphate and 3'-OH termini. The exoribonuclease produced only ribonucleoside 5'-phosphates from poly(adenylic acid). The relative rates of degradation of synthetic homopolynucleotides by the endoribonuclease under standard conditions were in the order poly(adenylic acid) greater than poly(uridylic acid) poly(cytidylic acid); for the exoribonuclease the order was poly(adenylic acid) poly(uridylic acid) greater than poly(cytidylic acid). Natural transfer and ribosomal RNAs were also degraded by both enzymes, while DNA was resistant to them. The optimal pH of activity for each enzyme was 7.5-8.0. Both ribonucleases require Ca2+ for maximum enzymatic activity.     

Synthesis and properties of novel block copolymers containing poly(lactic-glycolic acid) and poly(ethyleneglycol) segments

A synthetic process for obtaining high-molecular-weight block copolymers containing poly(lacticglycolic acid) and poly(ethylene glycol) segments has been established. This process involves the reaction of poly(ethylene glycols) with phosgene, followed by polycondensation of the resulting ,ω-bis (chloroformates) with poly(lactic-glycolic acid) oligomers. The copolymers have been characterized for their molecular weight, solubility properties, water absorption and preliminarily thermal behaviour. All evidence points to the conclusion that the process described is a general one, enabling biodegradable polymers to be obtained tailor-made according to specific requirements.     

Heterostereocomplex Crystallization and Homocrystallization From the Melt in Blends of Substituted and Unsubstituted Poly(lactide)s

Poly(L ‐2‐hydroxybutyrate) [P(L ‐2HB)] and poly(D ‐lactide) (PDLA) in their blends were phase separated to form P(L ‐2HB)‐ and PDLA‐enriched domains, and heterostereocomplex (HTSC) crystallization occurred at the interface between these domains. In the blends, HTSC crystallites were formed at crystallization temperature (T_c) = 80–160 °C, and their exclusive formation without the formation of other crystalline species was observed at T_c of 150 or 160 °C. The effects of polymer blend ratio on the types of formed crystalline species were very small due to the phase separation of the blends. The presence of a small amount of P(L ‐2HB) decreased the low limit of crystallizable T_c of PDLA homocrystallites from 80 to 60 °C. The equilibrium melting temperature of HTSC crystallites was 257.6 °C.     

Stereocomplex Crystallization of Star‐Shaped 4‐Armed Equimolar Stereo Diblock Poly(lactide)s with Different Molecular Weights: Isothermal Crystallization from the Melt

The isothermal crystallization of star‐shaped four‐armed equimolar stereo diblock poly(lactide) (4‐LD) polymers with different molecular weights is investigated. Solely stereocomplex (SC) crystallites are formed in all equimolar 4‐LD polymers, irrespective of molecular weight and crystallization temperature (T_c). The wide‐angle X‐ray diffractometry, differential scanning calorimetry, and polarized optical microscopy results for crystalline species, crystallinity, and maximum radial growth rate of spherulites values indicate that both branching and diblock architectures disturb the SC crystallization and spherulites growth of equimolar 4‐LD polymers, and the disturbance effect is larger for branching architecture than for diblock architecture. The equilibrium melting temperature (T_m⁰) values are 181.9–266.0 °C, which are comparable with or lower than the value reported earlier (279 °C). The crystallite growth geometries of equimolar of 4‐LD polymers are independent of molecular weight and T_c.

     

A Unique Meta‐Form Structure in the Stereocomplex of Poly(D‐lactic acid) with Low‐Molecular‐Weight Poly(L‐lactic acid)

The crystalline structure and crystallization behavior of PLLA crystals in a 1:1 w/w mixture of low‐MW PLLA with high‐MW PDLA were analyzed using WAXD, DSC, and SAXS. Under cold crystallization, homopolymeric PLLA, appearing as a meta crystal, was discovered in the PDLA/LMW‐PLLA blend. The meta‐ and α′ crystal forms of PLLA were found to form on crystallization at a T_cc of 85–95 °C and the α crystal PLLA formed at 100 ≤ T_cc < 120 °C. The meta‐crystal PLLA may be incorporated in the stereocomplexed PDLA/LMW‐PLLA lamellar region. During heating, the meta‐crystal PLLA first partially melted and then repacked directly into the α crystal PLLA without going through the less‐stable α′ form.

     

SEC Analysis of Poly(Acrylic Acid) and Poly(Methacrylic Acid)

The accurate characterization of molar‐mass distributions of poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) by size‐exclusion chromatography (SEC) is addressed. Two methods are employed: direct aqueous‐phase SEC on P(M)AA and THF‐based SEC after esterification of P(M)AA to the associated methyl esters, P(M)MA. P(M)AA calibration standards, P(M)AA samples prepared by pulsed‐laser polymerization (PLP), and PAA samples prepared by reversible addition‐fragmentation chain transfer (RAFT) are characterized in a joint initiative of seven laboratories, with satisfactory agreement achieved between the institutions. Both SEC methods provide reliable results for PMAA. In the case of PAA, close agreement between the two SEC methods is only observed for samples prepared by RAFT polymerization with weight‐average molar mass between 80 000 and 145 000 g mol^?1 and for standards with peak molar masses below 20 000 g mol^?1. For standards with higher molar masses and for PLP‐prepared PAA, the values from THF‐based SEC are as much as 40% below the molar masses determined by aqueous‐phase SEC. This discrepancy may be due to branching or degradation of branched PAA during methylation. While both SEC methods can be recommended for PMAA, aqueous‐phase SEC should be used for molar‐mass analysis of PAA unless the sample is not branched.

     

In vivo evaluation of nerve guidance channels of PTMC/PLLA porous biomaterial

Introduction

Peripheral nerve disruptions, frequently occurring during limb injuries, give rise to serious complications of patients recovery resulting from limitations in neural tissue regeneration capabilities. To overcome this problem bridging techniques utilizing guidance channels gain their importance. Biodegradable polymeric tubes seem to be more prospective then non-degradable materials – no necessity of implant removal and possibilities of release of incorporated drugs or biologically active agents that may support nerve regeneration process are the main advantages.

Material and methods

Polymer blend of commercial poly(L-lactic acid) (PLLA) and in-house synthesized poly(trimethylene carbonate) (PTMC) were processed in an organic solvent – phase inversion process on a supporting rod – to form a guidance porous tube of 1.1 mm inner diameter. In vivo experiments on rat''s cut femoral nerve by using either the tubes or end-to-end suturing (control group) involved 22 and 19 rats, respectively. Motor recovery of operated limbs, neuroma occurrence and histopathology of explanted nerves were evaluated after 30, 60 and 90 days of implantation.

Results

Motor recovery of the limbs was of similar rate for the two animal groups. The neuroma formation was evident in over 90% control specimens, while for the bridging group it was less than 40% of all evaluable samples (p = 0.0022). Biocompatibility of applied materials was affirmed by moderate tissue response.

Conclusions

Application of the biodegradable PLLA/PTMC polymeric tubes effectively supports regeneration of discontinued nerves. The applied material prevents neuroma formation, by reducing the scar tissue formation time and, thus, accelerating the process of neural tissue restoration.     

Attempts to map the structure and degradation characteristics of aliphatic polyesters derived from lactic and glycolic acids

During the past 5 years, important advances have been accomplished in the understanding of the fate of aliphatic polyesters derived from lactic acid (LA) and glycolic acid (GA) in aqueous media. Hydrolysis of solid LA/GA polymers is now regarded as dependent upon a diffusion-reaction mechanism. Faster central degradation, degradation-induced composition, and morphology changes are three of the most important findings which appeared to be composition-dependent as deduced from the behavior of different LA/GA polymers. An attempt is made to generalize these findings to the whole family and to elaborate a map which could be used to predict degradation characteristics of LA/GA polymers from their initial composition and morphology.     

聚乙二醇单甲醚-聚(D,L-乳酸)嵌段共聚物的研究

采用熔融缩聚反应合成一系列聚（D，L-乳酸）（PDLLA）／聚乙二醇单甲醚（mPEG）两亲性二嵌段共聚物（PEDLLA），采用IR、^1H-NMR、DSC、WAXD和TEM等手段分析和研究PEDLLA的结构与性能。实验结果表明，PEDLLA的结构和组成与设计相一致，结晶度和熔点均低于均聚物，且随着PEDLLA中PDLLA含量的增加，mPEG嵌段熔点降低，随着PDLLA嵌段相对分子质量的增大，PEDLLA降解速率增大。载药纳米粒呈核壳结构，载药量达30％。     

Biodegradation of PLA/GA polymers: increasing complexity

The degradation of aliphatic polyesters derived from lactic and glycolic acids (PLA/GA) depends on many factors. It has been found recently that the interior of large size devices degrades faster than the outer zone. A qualitative model has been proposed to account for this heterogeneous degradation. It is based on diffusion-reaction phenomena combined with the well-known autocatalytic effect of carboxylic chain ends. This contribution recalls the present understanding of the hydrolytic degradation of PLA/GA polymers and emphasizes its complexity on the basis of the influence of secondary factors such as the presence of a basic load, namely, gentamycin, in poly(lactic acid) matrices, and the presence of long stereoregular sequences in poly( -lactic acid) macromolecules. Biomaterials (1994) 15,1209–1213     

聚乳酸－乙醇酸共聚物合成与降解

本文对聚乳酸-乙醇酸(PLGA)的合成制备的多种方法进行了阐述,对聚乳酸-乙醇酸(PLGA)的降解性能和降解机理进行了概述.     

Enhancement of Anhydrous Proton Conductivity of Poly(vinylphosphonic acid)–Poly(2,5‐benzimidazole) Membranes via In Situ Polymerization

Polymer electrolyte membranes (PEMs) are synthesized via in situ polymerization of vinylphosphonic acid (VPA) within a poly(2,5‐benzimidazole) (ABPBI) matrix. The characterization of the membranes is carried out by using Fourier transform infrared (FTIR) spectroscopy for the interpolymer interactions, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) for the thermal properties, and scanning electron microscopy (SEM) for the morphological properties. The physicochemical characterizations suggest the complexation between ABPBI and PVPA and the formation of homogeneous polymer blends. Proton conductivities in the anhydrous state (150 °C) measured by using impedance spectroscopy are considerable, at up to 0.001 and 0.002 S cm^?1 for (1:1) and (1:2) molar ratios, respectively. These conductivities indicate significant improvements (>1000×) over the physically blended samples. The results shown here demonstrate the great potential of in situ preparation for the realization of new PEM materials in future high‐temperature and non‐humidified polymer electrolyte membrane fuel cell (PEMFC) applications.

     

Preparation and mineralization of a biocompatible double network hydrogel

Double network (DN) hydrogels have shown favorable toughness and strength and been harnessed as scaffolding materials in tissue engineering, particularly, mineralized DN hydrogels may be potential scaffolds in bone tissue engineering. In this paper, DN hydrogels were fabricated from poly(ethylene glycol) diacrylate (PEGDA) and methacrylated poly(γ-glutamic acid) (mPGA). This DN hydrogel not only showed excellent mechanical properties but also good cytocompatibility as evidenced by the characterizations in terms of swelling ratio, mechanical strength/modulus, and cytotoxicity. Further, the DN hydrogels were subjected to mineralization in simulated body fluid, during which hydroxyapatite or analogues formed within the DN hydrogels; the DN hydrogels may be potentially harnessed as bone tissue engineering scaffold.     

A Comparative Study on Electrokinetic Properties of Boronic Acid Derivative Polymers in Aqueous and Nonaqueous Media

Semiconducting poly(3‐aminophenylboronic acid) (PABA) and poly(thiophene‐3‐boronic acid) (PTBA) nanoparticles are synthesized using KIO₃ and (NH4)₂S₂O₈ as initiators, respectively; and structural, morphological, and surface characterizations are carried out by various well‐known techniques. Electrokinetic properties of PABA and PTBA dispersions are determined by zeta (ζ)‐potential measurements in aqueous medium by taking the effects of pH, various electrolytes, surfactants, and temperature into account. Colloidally stable range of +30 mV ≤ ζ ≤ ?30 mV is obtained in the presence of NaCl and Na₂SO₄ for PABA and PTBA, respectively. Addition of anionic surfactant, sodium dodecyl sulfate, to PABA and PTBA dispersions shifts the ζ‐potentials to more negative values and enhances their colloidal stabilities. ζ‐Potential values of PABA increase with rising temperature, whereas almost no change is observed for PTBA at elevated temperatures up to 65 °C. ζ‐Potentials of PABA and PTBA dispersions in silicone oil with the absence and presence of Triton X‐100 are also determined to be high.

     

Collagen-based new bioartificial polymeric materials

Bioartificial polymeric materials, based on blends of biological and synthetic polymers, have been proposed as new materials for applications in the biomedical field. They should usefully combine the biocompatibility of the biological component with the physical and mechanical properties of the synthetic component. Blends of collagen with either poly(vinyl alcohol) or poly(acrylic acid) have been prepared by mixing aqueous solutions of the two polymers. Differential scanning calorimetry and dynamic mechanical thermal analysis has been carried out to investigate the miscibility properties of the polymers and the mechanical behaviour of the blends. Biomaterials (1994) 15, 1229–1233