Facile Synthesis of Chitosan-Based Hydrogels and Microgels through Thiol-Ene Photoclick Cross-Linking.

Polysaccharide-based microgels are effective vectors for the delivery of biopharmaceutics and functional components in tissue engineering due to their bioactivity and biocompatibility. Currently, the synthesis of chemically cross-linked microgels typically requires long reaction times and a high-energy input and are low yielding due to low volumes of the water phase used. Herein, we report the synthesis of norbornene-derived chitosan (CS-nbn-COOH), which can undergo rapid gelation in the presence of a thiolated cross-linker through the highly efficient thiol-ene photoclick reaction. This water-soluble photo-cross-linkable derivative, synthesized on scale via a single step from native chitosan and commercially available carbic anhydride, represents the first example of a norbornene-functionalized CS to the best of our knowledge. Microgels with controlled cross-linking densities and diameters varying between 100 and 400 nm were obtained via a low-energy water-in-oil nanoemulsion templating method at room temperature, with photo-cross-linking initiated in a flow reactor powered with a domestic UV-A lamp, a method that is suitable for the scale-up synthesis of the microgels. We also demonstrate that the resulting microgels were nontoxic to human dermofibroblasts (HDF) cell lines and that residual norbornene groups could be reacted in a late stage through tetrazine ligation, highlighting the potential of these microgels as scaffolds for functional nanomaterials with biomedical applications.

Cerebral White Matter Maturation Patterns in Preterm Infants: An MRI T2 Relaxation Anisotropy and Diffusion Tensor Imaging Study.

BACKGROUND AND PURPOSE: Preterm birth is associated with worse neurodevelopmental outcome, but brain maturation in preterm infants is poorly characterized with standard methods. We evaluated white matter (WM) of infant brains at term-equivalent age, as a function of gestational age at birth, using multimodal magnetic resonance imaging (MRI). METHODS: Infants born very preterm (<32 weeks gestation) and late preterm (33-36 weeks gestation) were scanned at 3 T at term-equivalent age using diffusion tensor imaging (DTI) and T2 relaxometry. MRI data were analyzed using tract-based spatial statistics, and anisotropy of T2 relaxation was also determined. Principal component analysis and linear discriminant analysis were applied to seek the variables best distinguishing very preterm and late preterm groups. RESULTS: Across widespread regions of WM, T2 is longer in very preterm infants than in late preterm ones. These effects are more prevalent in regions of WM that myelinate earlier and faster. Similar effects are obtained from DTI, showing that fractional anisotropy (FA) is lower and radial diffusivity higher in the very preterm group, with a bias toward earlier myelinating regions. Discriminant analysis shows high sensitivity and specificity of combined T2 relaxometry and DTI for the detection of a distinct WM development pathway in very preterm infants. T2 relaxation is anisotropic, depending on the angle between WM fiber and magnetic field, and this effect is modulated by FA. CONCLUSIONS: Combined T2 relaxometry and DTI characterizes specific patterns of retarded WM maturation, at term equivalent age, in infants born very preterm relative to late preterm.

Neonatal outcomes of pregnancies affected by haemolytic disease of the foetus and newborn and managed with intrauterine transfusion: a service evaluation.

BACKGROUND: This study, conducted in the tertiary Foetal Medicine Unit at St Michael's Hospital, Bristol, was designed to obtain information regarding neonatal outcomes of pregnancies affected by haemolytic disease of the foetus and newborn and managed by intrauterine transfusion, and to determine whether a change in intrauterine transfusion protocol in 2004 had improved safety. The new protocol included attendance of two Foetal Medicine Unit consultants, foetal sedation and use of the intrahepatic vein as an alternative route to placental cord insertion if deemed safer. MATERIALS AND METHODS: Data for pregnancies affected by haemolytic disease of the foetus and newborn as a result of haemolytic red cell alloimmunisation and managed with intrauterine transfusion at St Michael's Hospital between 1999 and 2009 were retrospectively collected using local databases, and medical note review. RESULTS: Overall, 256 relevant intrauterine transfusions were performed. The median number of intrauterine transfusions per pregnancy was two. Ninety-three per cent of the live deliveries had 5-minute APGAR scores ≥9 and 98% were admitted to a Neonatal Intensive Care Unit/Special Care Baby Unit, requiring phototherapy (96%), top-up transfusions (44%: 23.2% immediate, 13.4% late, 7.3% both), and exchange transfusion (37%). An association was found between increased intrauterine transfusion number and reduced phototherapy duration and hospital admission: each additional intrauterine transfusion reduced the duration of phototherapy by 16% (95% CI: 0.72-0.98), and Neonatal Intensive Care Unit/Special Care Baby Unit admission by 44% (95% CI: 0.48-0.66). Following the change in intrauterine transfusion protocol, there was a significant reduction in the number of emergency Caesarean sections occurring directly after an intrauterine transfusion (n =5 vs 0; P =0.02). The foetal loss rate within 48 hours of an intrauterine transfusion was 1.9% per pregnancy, or 0.8% per intrauterine transfusion: no losses occurred under the new protocol (n =3 vs 0; P = NS). DISCUSSION: Although the majority of neonates required admission to a Neonatal Intensive Care Unit/Special Care Baby Unit and phototherapy, the medium-term outcomes were positive. Importantly, the safety of the intrauterine transfusion procedure has improved significantly since the change in protocol.

Amniotic fluid index in low-risk, post-dates pregnancies.

OBJECTIVE: To determine normal values for amniotic fluid index (AFI) in uncomplicated post-dates singleton pregnancies and compare it to current reference ranges. POPULATION: Four hundred and forty-eight women with singleton, uncomplicated pregnancies, presenting for post-dates assessment (gestation 40+0 to 42+0 weeks) between January 1, 2004 and June 30, 2005. METHODS: Ultrasound assessment of liquor to calculate the AFI. RESULTS: The mean and standard deviation for AFI in the sample was 9.86 (SD 3.4), which is significantly different to the mean of the currently used reference range (mean 11.6, SD 3.9, p < 0.0001). The 5th percentile in this population was 4.6 cm. CONCLUSIONS: This study has demonstrated lower mean and 5th percentile values for AFI in post-dates pregnancies than current reference ranges. It has the largest published UK study population, and can therefore be used as a reference range in similar populations, which is likely to reduce unnecessary obstetric interventions.

Prognosis of spina bifida in the era of prenatal diagnosis and termination of pregnancy.

OBJECTIVE: To evaluate the current outcome of a selected prenatally diagnosed spina bifida group. MATERIALS AND METHODS: We analyzed and followed up 74 cases of prenatally diagnosed spina bifida. RESULTS: Termination of pregnancy was chosen in 72% of the cases and 28% were live-born. Chromosomal defects were identified in 16%, although only 1.6% in isolated cases. Of the 21 live births, 3 died in the neonatal period. The other 18 (86%) were all alive after an average follow-up of 3 years and 6 months (range 5 months to 7 years and 4 months). From this group 11% are wheelchair-dependent, 87% of the patients older than 2 years of age are walking, 33% have had cerebral shunting and 72% have normal neurodevelopment. There was a better outcome in patients with closed defects; however, the rates of neuropathic bladder (50%) remain a concern. CONCLUSIONS: Even with prenatal diagnosis and a tendency towards apparently less severe defects in the cases in which the pregnancies continue, the prognosis in terms of morbidity needs to remain guarded.

A small-angle neutron scattering and rheology study of the composite of chitosan and gelatin.

The composite chitosan/gelatin solutions and films formed from these solutions were studied by rheological measurements, SANS and tensile tests. The relationship between the inter-molecule interactions with microstructure, rheological behaviour of a solution and eventually the mechanical performance of formed films was established. It was found that the complex formed between chitosan and gelatin was mainly through hydrogen bond but the size of the structure was also affected by electrostatic repulsions. The local structure (correlation length) and the global structure (large inhomogeneous structure size) in the composite solutions were found to be highly correlated to each other. It was also found that the interactions between these two polymers in solution were closely related to the mechanical properties of the formed films. This work will enable one to design films with desired mechanical properties through the combination of different polymers at optimum weight ratios.

Determinants of flow along arterio-arterial anastomoses in monochorionic placentae by dynamic computer modelling of chorionic plate vasculature.

OBJECTIVES: To investigate anatomical and physiological determinants of inter-fetal transfusion along arterio-arterial (AA) anastomoses in monochorionic placentae. METHODS: A computer model of chorionic arterial vasculature was constructed in QuickBASIC using data collected from experimentation and the published literature. After validating the model, the influence of various physiological and anatomical variables on anastomotic flow rates was examined. RESULTS: AA anastomotic flow rates were significantly related to changes in fetal mean arterial pressure (p < 0.0001) and heart rate (p < 0.0005). AA flow rates were also related to the imbalance in number of arterio-venous (AV) anastomoses, to placental territory share, and to the branch number of the AA anastomosis (AAAs) from the chorionic arterial tree. CONCLUSIONS: Net blood flow and direction along AA anastomoses are influenced by fetal cardiac output, by the presence of compensatory AV anastomoses, and by the branch number of the chorionic arteries connected by the anastomosis. This study provides insight into the determinants of chronic transfusional imbalance as well as acute inter-fetal transfusion.

Optimal interval between middle cerebral artery velocity measurements when monitoring pregnancies complicated by red cell alloimmunization.

OBJECTIVE: To evaluate the optimal interval between middle cerebral artery (MCA) Doppler measurements when monitoring pregnancies complicated by red cell alloimmunization. METHODS: Thirty-nine fetal blood samplings (FBS) performed on 24 pregnant women with red blood cell alloimmunization followed up using both MCA peak systolic velocity and time-averaged mean velocity measurements on weekly basis. RESULTS: In total, 65.5 and 37.5% of women with moderate or severe fetal anemia had abnormal MCA Doppler values 1 and 2 weeks, respectively, before FBS was performed. CONCLUSIONS: A weekly assessment of women at risk for fetal anemia is optimal in most of the cases even though 35.5% of cases of moderate or severe fetal anemia are expected to have normal Doppler measurements the week before the decision of doing an FBS is made.

Safety of fetal blood sampling by cordocentesis in fetuses with single umbilical arteries.

OBJECTIVES: To examine the safety of cordocentesis in fetuses with single umbilical arteries. METHODS: Retrospective analysis of all cases of cordocenteses in fetuses with single umbilical arteries over a five-year period at one centre. We analysed the records for pregnancy details, outcomes, and procedure-related complications, and compared these to similar data for cordocenteses procedures performed, during the same period, for similar indications in fetuses with three-vessel cords. RESULTS: Twenty-nine eligible cases were identified. All procedures were performed for the indication of fetal structural abnormalities, and seven fetuses (24%) had abnormal karyotypes. The median gestational age at the time of the procedure was 21 weeks (range 19-34 weeks). There were no procedure-related fetal losses but the umbilical artery was inadvertently punctured in one case, resulting in prolonged bradycardia with spontaneous recovery. These outcomes compare favourably to those of a total of 134 cordocenteses procedures in fetuses with three-vessel cords. CONCLUSION: Cordocentesis in cases with single umbilical arteries does not appear to carry more risk than in cases with three-vessel cord, and should continue to be performed by adequately trained specialists when indicated. Extra care should be undertaken to avoid puncturing the umbilical artery.