Degradable and Removable Tough Adhesive Hydrogels

The development of tough adhesive hydrogels has enabled unprecedented adhesion to wet and moving tissue surfaces throughout the body, but they are typically composed of nondegradable components. Here, a family of degradable tough adhesive hydrogels containing ≈90% water by incorporating covalently networked degradable crosslinkers and hydrolyzable ionically crosslinked main-chain polymers is developed. Mechanical toughness, adhesion, and degradation of these new formulations are tested in both accelerated in vitro conditions and up to 16 weeks in vivo. These degradable tough adhesives are engineered with equivalent mechanical and adhesive properties to nondegradable tough adhesives, capable of achieving stretches >20 times their initial length, fracture energies >6 kJ m-2 , and adhesion energies >1000 J m-2 . All degradable systems show complete degradation within 2 weeks under accelerated aging conditions in vitro and weeks to months in vivo depending on the degradable crosslinker selected. Excellent biocompatibility is observed for all groups after 1, 2, 4, 8, and 16 weeks of implantation, with minimal fibrous encapsulation and no signs of organ toxicity. On-demand removal of the adhesive is achieved with treatment of chemical agents which do not cause damage to underlying skin tissue in mice. The broad versatility of this family of adhesives provides the foundation for numerous in vivo indications.

Novelty preferences and cocaine-associated cues influence regions associated with the salience network in juvenile female rats

Preferences for novel environments (novelty-seeking) is a risk factor for addiction, with little known about its underlying circuitry. Exposure to drug cues facilitates addiction maintenance, leading us to hypothesize that exposure to a novel environment activates a shared neural circuitry. Stimulation of the D1 receptor in the prelimbic cortex increases responsivity to drug-associated environments. Here, we use D1 receptor overexpression in the prelimbic cortex to probe brain responses to novelty-preferences (in a free-choice paradigm) and cocaine-associated odors following place conditioning. These same cocaine-conditioned odors were used to study neural circuitry with Blood Oxygen Level Dependent (BOLD) activity. D1 overexpressing females had deactivated BOLD signals related to novelty-preferences within the insula cortex and amygdala and activation in the frontal cortex and dopamine cell bodies. BOLD responses to cocaine cues were also sensitive to D1. Control females demonstrated a place preference for cocaine environments with no significant BOLD response, while D1 overexpressing females demonstrated a place aversion and weak BOLD responses to cocaine-conditioned odor cues within the insula cortex. For comparison, we provide data from an earlier study with juvenile males overexpressing D1 that show a strong preference for cocaine and elevated BOLD responses. The results support the use of a pharmacological manipulation (e.g., D1 overexpression) to probe the neural circuitry downstream from the prelimbic cortex.

A novel two-component, expandable bioadhesive for exposed defect coverage: Applicability to prenatal procedures

BACKGROUND/PURPOSE

We sought to test select properties of a novel, expandable bioadhesive composite that allows for enhanced adhesion control in liquid environments.

METHODS

Rabbit fetuses (n = 23) underwent surgical creation of spina bifida on gestational day 22-25 (term 32-33 days). Defects were immediately covered with a two-component tough adhesive consisting of a hydrogel made of a double network of ionically crosslinked alginate and covalently crosslinked polyacrylamide linked to a bridging chitosan polymer adhesive. Animals were euthanized prior to term for different analyses, including hydraulic pressure testing.

RESULTS

Hydrogels remained adherent in 70% (16/23) of the recovered fetuses and in all of the last 14 fetuses as the procedure was optimized. Adherent hydrogels showed a median two-fold (IQR: 1.7-2.4) increase in area at euthanasia, with defect coverage confirmed by ultrasound and histology. The median maximum pressure to repair failure was 15 mmHg (IQR: 7.8-55.3), exceeding reported neonatal cerebrospinal fluid pressures.

CONCLUSIONS

This novel bioadhesive composite allows for selective, stable attachment of an alginate-polyacrylamide hydrogel to specific areas of the spina bifida defect in a fetal rabbit model, while the hydrogel expands with the defect over time. It could become a valuable alternative for the prenatal repair of spina bifida and possibly other congenital anomalies.

TYPE OF STUDY

N/A (animal and laboratory study).

LEVEL OF EVIDENCE

N/A (animal and laboratory study).

Essential and sex-specific effects of mGluR5 in ventromedial hypothalamus regulating estrogen signaling and glucose balance

The ventromedial hypothalamus (VMH) plays chief roles regulating energy and glucose homeostasis and is sexually dimorphic. We discovered that expression of metabotropic glutamate receptor subtype 5 (mGluR5) in the VMH is regulated by caloric status in normal mice and reduced in brain-derived neurotrophic factor (BDNF) mutants, which are severely obese and have diminished glucose balance control. These findings led us to investigate whether mGluR5 might act downstream of BDNF to critically regulate VMH neuronal activity and metabolic function. We found that mGluR5 depletion in VMH SF1 neurons did not affect energy balance regulation. However, it significantly impaired insulin sensitivity, glycemic control, lipid metabolism, and sympathetic output in females but not in males. These sex-specific deficits are linked to reductions in intrinsic excitability and firing rate of SF1 neurons. Abnormal excitatory and inhibitory synapse assembly and elevated expression of the GABAergic synthetic enzyme GAD67 also cooperate to decrease and potentiate the synaptic excitatory and inhibitory tone onto mutant SF1 neurons, respectively. Notably, these alterations arise from disrupted functional interactions of mGluR5 with estrogen receptors that switch the normally positive effects of estrogen on SF1 neuronal activity and glucose balance control to paradoxical and detrimental. The collective data inform an essential central mechanism regulating metabolic function in females and underlying the protective effects of estrogen against metabolic disease.

Sleep-disordered breathing and nocturnal hypoxemia in young adults with sickle cell disease

Sleep-disordered breathing (SDB) is reported in up to 69% of adolescents and children with sickle cell disease (SCD) [1], but data regarding the prevalence of SDB in adults with SCD are limited. In order to obtain a preliminary assessment of the frequency and degree of sleep-related hypoxemia and potential associations with cardiovascular function in adults with SCD, we conducted overnight sleep studies, 6-min walk tests, echocardiograms, and hematologic and chemistry panels, calculated the Pittsburgh sleep quality index (PSQI), and conducted fatigue- and health-related quality-of-life measurement in 20 young adults with SCD visiting a sickle cell clinic for routine care. Sleep apnea, defined as an apnea-hypopnea index (AHI) > 5 events/h, was found in 50% of patients. Traditional clinical indicators, such as obesity, the presence of snoring, and reported sleep complaints, did not reliably differentiate them. The patients with AHI > 5 had higher mean systolic blood pressure (p = 0.03), evidence of impaired left ventricular diastolic function (i.e., increased mitral valve E/A ratio, p = 0.05), a trend toward higher reduction in 6-min walk distances (p = 0.06), and lower health-related quality-of-life scores (p ≤ 0.01). Three of nine patients with more severe anemia (total Hb < 9.0) showed nocturnal hypoxemia in the absence of sleep apnea. As prolonged and frequent hypoxemic episodes likely increase risks for vaso-occlusive, cardiovascular, and neurologic complications of SCD, these results suggest that the prevalence and severity of SDB should be investigated further in studies of larger patient populations. If confirmed, these findings could identify opportunities to prevent or reduce nocturnal hypoxia and improve outcomes.

Negative priming, attention, and discriminating the present from the past

Priming effects have been used widely as a tool to study attentional processes. However, inferences regarding attention depend on how priming effects are interpreted. In the case of negative priming, an activation-based framework for interpreting priming suggests that attention inhibits the representation of prime distractors and that this inhibition is measured in performance to subsequent probes. Data summarized in this article point out that negative priming does not depend on selection of one of two primes and that attentional influences during retrieval play an important role in determining negative priming. Also, two experiments are described that demonstrate a correlation between priming effects and knowledge of the relation between primes and probes. We suggest that negative priming is not determined directly by a process of ignoring, but instead occurs because a repeated probe is less temporally distinct when ignored as a prime than when attended.

Acute lymphoidic leukemia in a patient with thrombocytopenia/absent radii (Tar) syndrome

PURPOSE

Patients with thrombocytopenia, absent radii (TAR) syndrome have a spontaneous amelioration of thrombocytopenia after infancy. No individual with the syndrome has been reported to develop subsequent bone marrow disease.

PATIENTS AND METHODS

We report a child with TAR syndrome who developed acute lymphoidic leukemia.

RESULTS AND CONCLUSIONS

The TAR syndrome may predispose patients to other forms of marrow disease (as do other inherited marrow failure diseases). Additional cases are needed to confirm this hypothesis.

Brain injuries among infants, children, adolescents, and young adults

Blunt and penetrating force injuries to the brain constitute an enormous public health problem. If a child or young adult survives a moderate or severe brain injury, there is a strong likelihood of a lifetime of physical and mental impairment as well as tremendous economic and social impact on the family. The magnitude of this problem has only been recently appreciated, yet many questions on the causes and short- or long-term outcomes remain unanswered. One conclusion is clear: prevention is the best solution, but information on the nature of the brain injury, exposure factors, and effectiveness of countermeasures is incomplete. We sought to summarize certain basic epidemiological data on brain injuries in infants, children, adolescents, and young adults as well as findings on incidence of brain injury and current data on demographics and risk factors. We also estimated disability and person-years of life lost from brain injuries and highlight the value of helmets as a countermeasure for several exposures to head injury.

A primate model (Macaca mulatta) to study the pharmacokinetics of heparin and its fractions

We have extensively studied the hemostatic parameters and the responses to the anticoagulant action of heparin and its fractions in the primate model (M. mulatta) and found these to be identical to those obtained in humans. The functional properties of antithrombin III, alpha 2-antiplasmin, and platelet factor 4 were also identical to humans in amidolytic and coagulant assays. Human antibodies against FPA, B beta 15-42 peptide, platelet factor 4, and thromboxane B2 reacted with the primate antigen, and assays were developed to measure these parameters in primates. Infusion of activated prothrombin complex concentrates (more than 100 U/kg/day) on a continual basis up to 3 days resulted in a hypercoagulable state manifested by an elevation of FPA, thromboxane B2, and changes in the thrombelastographic patterns. Similarly, infusion of homologous primate serum also resulted in a hypercoagulable state, as was evident by a sharp increase in the FPA levels. The antithrombotic effects of intravenous and subcutaneous administration of heparin, its low molecular fraction, and their constituents were studied after intravenous and subcutaneous injections. The low molecular weight fractions showed the most effective antithrombotic effects, whereas somewhat milder protection was observed with the starting material and highly anionic fraction. The prolongation of global tests, such as the APTT, TT, and changes in the thromboelastogram did not correlate with the reduction in the blood markers of hypercoagulable state. A modified simplate bleeding time method was used to study the effect of heparin and its fractions on the bleeding profile of heparin fractions. The components of fibrinolytic systems were also measurable in both the clot-based and amidolytic methods to predict the profibrinolytic actions of heparin fractions in its mode. These studies suggest that plasma markers, such as the platelet release proteins, products of thrombin activation, and prostaglandin metabolites, may provide better indices in the monitoring of the antithrombotic actions of newer heparins and antithrombotic drugs. Studies suggest that the pathophysiologic responses after a thrombogenic trigger in the primate model are close to humans, and drug modulation of these may provide relevant clinical information. This model provides the most similar preclinical model to study the actions of heparin fractions.

A modified stasis thrombosis model to study the antithrombotic actions of heparin and its fractions

The original stasis thrombosis model of Wessler has been modified. Numerous thrombogenic agents were evaluated for their pathophysiologic effects and were classified in terms of stasis clot in the jugular vein. Alterations produced in coagulation parameters, such as the PT, APTT, thrombin time, activated recalcification time (Hemachron), and thrombelastographic pattern were recorded. Since the pathophysiologic activation of the hemostatic system varies considerably in different diseases, a proper animal model along with a proper type of thrombogenic trigger should be carefully selected to produce pathogenesis and to study the therapeutic responses of heparin and its derivatives. In the modified stasis thrombosis model, besides monitoring the formation of the jugular vein stasis clot, it is proposed that the following tests may be useful to establish hypercoagulable states: Functional levels of various coagulation factors, platelet counts, fibrinogen levels, and whole blood activated clotting times. The nature of activation processes in each thrombogenic challenge should be carefully analyzed in terms of pathways involved; for example, the administration of heterologous serum (such as human, monkey) to rabbits produces anaphylactoid reactions, including hemolysis, thrombocytopenia, clinical chemistry abnormalities (enzymes), and many problems that may involve the complement and immune systems. All previous data obtained using heterologous sera as a thrombogenic trigger are of questionable value as to the efficacy of some of the antithrombotic agents tested against it. In addition to the species and the thrombogenic challenge, the following factors may contribute significantly to the pathophysiologic response and its alteration by various agents: (1) Composition of the thrombogenic agent; (2) effect of preparatory drugs, such as anesthetics, on the hemostatic parameters; (3) alterations on injection time, volume, osmolarity, and temperature; (4) variations in the circulation time of the thrombogenic agent and stasis time of the ligated jugular vein stasis segment; and (5) blood sample collection and handling. Since the kallikrein-kinin cascade is closely associated with the coagulation and the fibrinolytic network, a systemic monitoring of blood pressure may provide information on the effect of thrombogenic agents on hemodynamics.(ABSTRACT TRUNCATED AT 400 WORDS)

Platelet activation by human pancreatic fluid

The effects of human pancreatic fluid (HPF) on platelet aggregation and activation were studied. HPF, obtained at operation from nine patients with chronic pancreatitis and two with pancreas cancer, was pooled, lyophilized, and adjusted to a concentration of 1 mg protein/cc of 0.9% saline after dialysis. Platelet aggregation was evaluated by measuring platelet count after iv administration of HPF to five rabbits in concentrations ranging from 0.2 to 2.0 mg/kg. Platelet activation was evaluated by adding 0.1-ml aliquots of pooled HPF in various concentrations to 0.9 ml of human platelet-rich plasma. After a 15-min incubation at 37 degrees C, the platelets were removed by centrifugation and the supernatant examined for platelet-release products. Serotonin was measured by high-performance liquid chromatography (HPLC) and platelet factor 4 and thromboxane B2 were measured by radioimmunoassay. A significant decrease in rabbit platelet count signifying platelet aggregation was seen after iv administration of 1.0 mg/kg (P less than 0.05) and 2.0 mg/kg (P less than 0.001) HPF. Platelet activation was confirmed by a significant increase (P less than 0.05) in serotonin, platelet factor 4, and thromboxane B2 at almost all concentrations of HPF. This study indicates that HPF induces platelet aggregation and activation and suggests that platelet contact with pancreatic exocrine fluid may have both local and systemic effects that are important in the pathophysiology of acute pancreatitis.