Gallbladder Cancer Risk and Indigenous South American Mapuche Ancestry: Instrumental Variable Analysis Using Ancestry-Informative Markers.

A strong association between the proportion of indigenous South American Mapuche ancestry and the risk of gallbladder cancer (GBC) has been reported in observational studies. Chileans show the highest incidence of GBC worldwide, and the Mapuche are the largest indigenous people in Chile. We set out to assess the confounding-free effect of the individual proportion of Mapuche ancestry on GBC risk and to investigate the mediating effects of gallstone disease and body mass index (BMI) on this association. Genetic markers of Mapuche ancestry were selected based on the informativeness for assignment measure, and then used as instrumental variables in two-sample Mendelian randomization analyses and complementary sensitivity analyses. Results suggested a putatively causal effect of Mapuche ancestry on GBC risk (inverse variance-weighted (IVW) risk increase of 0.8% per 1% increase in Mapuche ancestry proportion, 95% CI 0.4% to 1.2%, p = 6.7 × 10-5) and also on gallstone disease (3.6% IVW risk increase, 95% CI 3.1% to 4.0%), pointing to a mediating effect of gallstones on the association between Mapuche ancestry and GBC. In contrast, the proportion of Mapuche ancestry showed a negative effect on BMI (IVW estimate -0.006 kg/m2, 95% CI -0.009 to -0.003). The results presented here may have significant implications for GBC prevention and are important for future admixture mapping studies. Given that the association between the individual proportion of Mapuche ancestry and GBC risk previously noted in observational studies appears to be free of confounding, primary and secondary prevention strategies that consider genetic ancestry could be particularly efficient.

Prophylactic platelet transfusion and risk of bleeding associated with ultrasound-guided central venous access in patients with severe thrombocytopenia.

BACKGROUND: Reported risk of bleeding complications after central catheter access in patients with thrombocytopenia is highly variable. Current guidelines recommend routine prophylactic platelet (PLT) transfusion before central venous catheter placement in patients with severe thrombocytopenia. Nevertheless, the strength of such recommendations is weak and supported by observational studies including few patients with very low PLT counts (<20 × 109 /L). This study aims to assess the risk of bleeding complications related to using or not using prophylactic PLT transfusion before ultrasound-guided central venous access in patients with very low PLT counts. METHODS: This was a retrospective cohort study of patients with very low PLT counts (<20 × 109 /L) subjected to ultrasound-guided central venous catheterization between January 2011 and November 2019 in a university hospital. Bleeding complications were graded according to the Common Terminology Criteria for Adverse Events. A multivariate logistic regression was conducted to assess the risk of major and minor bleeding complications comparing patients who did or did not receive prophylactic PLT transfusion for the procedure. Multiple imputation by chained equations was used to handle missing data. A two-tailed p < 0.05 was considered statistically significant. RESULTS: Among 221 patients with very low PLT counts, 72 received prophylactic PLT transfusions while 149 did not. Baseline characteristics were similar between transfused and nontransfused patients. No major bleeding events were identified, while minor bleeding events were recognized in 35.7% of patients. Multivariate logistic regression analysis showed no significant differences in bleeding complications between patients who received prophylactic PLT transfusions and those who did not (odds ratio 0.83, 95% confidence interval 0.45-1.55, p = 0.567). Additional complete case and sensitivity analyses yielded results similar to those of the main analysis. CONCLUSIONS: In this single-center retrospective cohort study of ultrasound-guided central venous access in patients with very low PLT counts, no major bleeding was identified, and prophylactic PLT transfusions did not significantly decrease minor bleeding events.

Complications associated with the use of radial arterial catheters in relation to their length: Does size matter?

BACKGROUND: Radial arterial catheters (RAC) are commonly used in emergency services and intensive care units (ICU) for continuous invasive monitoring of blood pressure and arterial blood gas sampling. Complications associated with RAC are rare. Regarding length of RAC catheters and complications, few studies were found in the literature. The present study seeks to provide health care professionals with scientific evidence to select an optimal length of RAC, based on the difference in the incidence of complications between ultrasound-guided catheters of the same diameter but different lengths. METHODS: Observational, descriptive, retrospective study. Patients older than 17 years admitted to the emergency department or ICU were included. RAC were placed with diameters of 20 gauge, between 5 and 8 cm (Arrow-Teleflex), and 22 gauge diameters between 4 and 8 cm (Vygon). Univariate analysis was made to determine behavior of the numerical variables. Normality of variables was determined through a Shapiro-Wilk-test. Qualitative variables were expressed in percentages, quantitative variables in means and standard deviation, or with median and quartiles in the case of a non-normal distribution. Chi-square or Fisher method was used for qualitative variables and the t-test for symmetric quantitative variables. Asymmetric distributions were processed with the Mann-Whitney U test. A value p < 0.05 was considered statistically significant. The statistical analysis was performed with Stata 14.1 program. RESULTS: About 793 RAC were placed between 2016 and 2019 were included, median age was 60 (37-73) (RIQ) years, 49% male. Complications were reported in all groups on average 17.5%, the most frequent being dysfunction/occlusion of the catheter. Given complications of the same diameter and different catheter lengths, there were no statistical differences between groups. CONCLUSION: Selecting one length or another with a catheter of the same diameter does not have statistically significant differences, in terms of the complications this device may cause-meaning that size does not matter.

Supervivencia a 30 días y 1 año de pacientes con muerte súbita con posterior colocación de dispositivo cardíaco implantable en un hospital de alta complejidad / Patients with sudden cardiac death receiving an implantable cardiac device: survival at 30 days and one year

Background: The use of implantable cardiac devices in patients with sudden cardiac arrest has contributed to their survival. Aim: To determine the survival rate at 30 days and one year after hospital discharge of patients who had a cardiac arrest with subsequent placement of an implantable cardiac device. Material and Methods: Twenty-three patients older than 18 years who presented sudden extra-institutional or intra-institutional death with subsequent implantation of an implantable cardiac device and whose survival was recorded at 30 days and one year, were included. A univariate analysis was performed. Results: Eighteen patients had an extra institutional cardiac arrest. All patients were discharged alive. We could not ascertain the health status of one patient at follow-up. Twenty-one patients had a Cerebral Performance Category (CPC) of 1 at discharge. One patient died of a stroke within 30 days and one patient died due to an arrhythmic electrical storm one year later. Twenty patients survived at least one year after hospital discharge. Conclusions: Survival at 30 days and one year, was high in patients with sudden death or cardiac arrest who required intracardiac devices.

[Patients with sudden cardiac death receiving an implantable cardiac device: survival at 30 days and one year]. / Supervivencia a 30 días y 1 año de pacientes con muerte súbita con posterior colocación de dispositivo cardíaco implantable en un hospital de alta complejidad.

BACKGROUND: The use of implantable cardiac devices in patients with sudden cardiac arrest has contributed to their survival. AIM: To determine the survival rate at 30 days and one year after hospital discharge of patients who had a cardiac arrest with subsequent placement of an implantable cardiac device. MATERIAL AND METHODS: Twenty-three patients older than 18 years who presented sudden extra-institutional or intra-institutional death with subsequent implantation of an implantable cardiac device and whose survival was recorded at 30 days and one year, were included. A univariate analysis was performed. RESULTS: Eighteen patients had an extra institutional cardiac arrest. All patients were discharged alive. We could not ascertain the health status of one patient at follow-up. Twenty-one patients had a Cerebral Performance Category (CPC) of 1 at discharge. One patient died of a stroke within 30 days and one patient died due to an arrhythmic electrical storm one year later. Twenty patients survived at least one year after hospital discharge. CONCLUSIONS: Survival at 30 days and one year, was high in patients with sudden death or cardiac arrest who required intracardiac devices.

Right main bronchus rupture associated with blunt chest trauma: a case report.

BACKGROUND: Tracheobronchial injury is one of the least common injuries in the scenario of blunt chest trauma. However, around 81% of patients with airway injury die immediately or before arriving at the emergency department due to tension pneumothorax. It presents with non-specific signs and symptoms challenging prompt diagnosis. CASE PRESENTATION: A 15-year-old adolescent who was riding a bicycle suffered an accident when he fell down a cliff, approximately 5 m deep. Upon admission to the emergency department, he presented with signs of respiratory distress. The airway was secured and a thoracoabdominal angiography was performed. The image reported pneumomediastinum, a small right pneumothorax, areas of pulmonary contusion, and an image of loss of continuity in the anterior superior wall of the right main bronchus highly suggestive of bronchial rupture. The bronchial lesion was then confirmed by fiberoptic bronchoscopy. Taking into account the patient's characteristics, conservative management was chosen, and the patient was transferred to the intensive care unit (ICU) where protective tracheal intubation was performed. CONCLUSIONS: A delay in diagnosis increases the rate of complications, mainly infectious complications and the formation of granulation tissue that could potentially obstruct the airway, impacting the patient's outcome. The first step in the management of these patients is securing the airway, which should be done immediately. The gold standard for the diagnosis and characterization of airway injuries is bronchoscopy as it is the most effective tool to assess topography, extent, and depth of the lesion.

Laparoscopic management of incidental gallbladder cancer.

BACKGROUND: The laparoscopic cholecystectomy has allowed the detection of an increasing number of incidental gallbladder cancers (IGBC). Although laparoscopy is employed in the management of a variety of abdominal tumors, its use in gallbladder cancer is reduced and controversial. This study analyzes the role of laparoscopy in gallbladder cancer with the focus in IGBC. METHOD: We evaluated our prospective series of 51 patients with an IGBC who were treated by laparoscopy between 2006 and 2016 at the Clinica Alemana in Santiago, Chile. RESULTS: The series comprised 7 men and 44 women. Age ranged from 43 to 76 years (mean age 60). Regarding wall involvement, 29 patients had a T2 tumor, which was the most common. 8 and 14 patients had T1b and T3 tumors, respectively. Of the patients, 17 underwent only laparoscopic exploration. This was due to the presence tumor dissemination not being observed in the preoperative staging. 10 patients had to be converted to complete the resection, whereas 24 patients were laparoscopically resected. The quality of the resected material was not different between those who were converted and those who were treated by laparoscopy. In the laparoscopic group, the average number of harvested lymph nodes was 7.9, not statistically different from the converted group. The mean of hospital stay in the laparoscopic group (4.3 days) was significantly lower than the converted group. CONCLUSIONS: Laparoscopy has been shown to be a safe and feasible method for the management of IGBC. This method not only allows for a complete exploration, identifying a previously unseen residual tumor, but also makes it possible to accomplish the same oncology objectives as the open procedure. Therefore, laparoscopy should be considered a valid alternative in the management of IGBC.

Automated measurement of estrogen receptor in breast cancer: a comparison of fluorescent and chromogenic methods of measurement.

Whereas FDA-approved methods of assessment of estrogen receptor (ER) are 'fit for purpose', they represent a 30-year-old technology. New quantitative methods, both chromogenic and fluorescent, have been developed and studies have shown that these methods increase the accuracy of assessment of ER. Here, we compare three methods of ER detection and assessment on two retrospective tissue microarray (TMA) cohorts of breast cancer patients: estimates of percent nuclei positive by pathologists and by Aperio's nuclear algorithm (standard chromogenic immunostaining), and immunofluorescence as quantified with the automated quantitative analysis (AQUA) method of quantitative immunofluorescence (QIF). Reproducibility was excellent (R(2)>0.95) between users for both automated analysis methods, and the Aperio and QIF scoring results were also highly correlated, despite the different detection systems. The subjective readings show lower levels of reproducibility and a discontinuous, bimodal distribution of scores not seen by either mechanized method. Kaplan-Meier analysis of 10-year disease-free survival was significant for each method (Pathologist, P=0.0019; Aperio, P=0.0053, AQUA, P=0.0026); however, there were discrepancies in patient classification in 19 out of 233 cases analyzed. Out of these, 11 were visually positive by both chromogenic and fluorescent detection. In 10 cases, the Aperio nuclear algorithm labeled the nuclei as negative; in 1 case, the AQUA score was just under the cutoff for positivity (determined by an Index TMA). In contrast, 8 out of 19 discrepant cases had clear nuclear positivity by fluorescence that was unable to be visualized by chromogenic detection, perhaps because of low positivity masked by the hematoxylin counterstain. These results demonstrate that automated systems enable objective, precise quantification of ER. Furthermore, immunofluorescence detection offers the additional advantage of a signal that cannot be masked by a counterstaining agent. These data support the usage of automated methods for measurement of this and other biomarkers that may be used in companion diagnostic tests.

Propuesta de evaluación de estrategias de afrontamiento ante la enfermedad crónica en adolescentes / Strategies of coping with chronic illness in adolescents

Objetivo Desarrollar un instrumento destinado a evaluar las estrategias de afrontamiento ante la enfermedad crónica en población adolescente. Sujetos y método Con base a una revisión teórica y entrevistas semiestructuradas a adolescentes, se construye un cuestionario que es finalmente evaluado por jueces expertos en tanto comprensión, pertinencia y viabilidad. Resultados Se propone una escala compuesta por 60 reactivos agrupados en 12 familias de afrontamiento. Conclusión La escala puede ser una herramienta útil para un clínico al entregar información clave sobre la vivencia y las formas de afrontar la enfermedad en un adolescente.

Objective To develop a tool to evaluate coping strategies for chronic illness in adolescents. Subjects and method Based on a theoretical review and semi-structured interviews with adolescents, a questionnaire was prepared that was finally evaluated by judges experienced in in understanding, relevance and viability. Results A scale is proposed that consists of 60 items grouped into 12 coping families. Conclusion The scale may be a useful clinical tool to provide key information about the experience and ways to cope with illness in adolescents.

[Strategies of coping with chronic illness in adolescents]. / Propuesta de evaluación de estrategias de afrontamiento ante la enfermedad crónica en adolescentes.

OBJECTIVE: To develop a tool to evaluate coping strategies for chronic illness in adolescents. SUBJECTS AND METHOD: Based on a theoretical review and semi-structured interviews with adolescents, a questionnaire was prepared that was finally evaluated by judges experienced in in understanding, relevance and viability. RESULTS: A scale is proposed that consists of 60 items grouped into 12 coping families. CONCLUSION: The scale may be a useful clinical tool to provide key information about the experience and ways to cope with illness in adolescents.

In situ tumor PD-L1 mRNA expression is associated with increased TILs and better outcome in breast carcinomas.

PURPOSE: Blockade of the PD-1/PD-L1 axis emerged as a promising new therapeutic option for cancer that has resulted in lasting responses in metastatic renal, lung carcinomas, and melanomas. Tumor PD-L1 protein expression may predict response to drugs targeting this pathway. Measurement of PD-L1 protein is limited by the lack of standardized immunohistochemical methods and variable performance of antibodies. Our goal was to correlate PD-L1 mRNA expression with clinical variables in primary breast carcinomas. EXPERIMENTAL DESIGN: The fluorescent RNAscope paired-primer assay was used to quantify in situ PD-L1 mRNA levels in 636 stage I-III breast carcinomas on two sets of tissue microarrays [YTMA128 (n = 238) and YTMA201 (n = 398)]. Tumor-infiltrating lymphocytes (TIL) were assessed by hematoxylin/eosin stain and quantitative fluorescence. RESULTS: On YTMA128 and YTMA201, 55.7% and 59.5% of cases showed PD-L1 mRNA expression, respectively. Higher PD-L1 mRNA expression was significantly associated with increased TILs (P = 0.04) but not with other clinical variables. Elevated TILs (scores 2 and 3+) occurred in 16.5% on YTMA128 and 14.8% on YTMA201 and was associated with estrogen receptor-negative status (P = 0.01 on YTMA128 and 0.0001 on YTMA201). PD-L1 mRNA expression was associated with longer recurrence-free survival (log-rank P = 0.01), which remained significant in multivariate analysis including age, tumor size, histologic grade, nodal metastasis, hormone receptor, HER2 status, and the extent of TILs (HR, 0.268; CI, 0.099-0.721; P = 0.009). CONCLUSIONS: PD-L1 mRNA expression is identified in nearly 60% of breast tumors and it is associated with increased TILs and improved recurrence-free survival. These observations support the evaluation of PD-1/PD-L1-targeted therapies in breast cancer.

Programmed death ligand-1 expression in non-small cell lung cancer.

Recent strategies targeting the interaction of the programmed cell death ligand-1 (PD-L1, B7-H1, CD274) with its receptor, PD-1, resulted in promising activity in early phase clinical trials. In this study, we used various antibodies and in situ mRNA hybridization to measure PD-L1 in non-small cell lung cancer (NSCLC) using a quantitative fluorescence (QIF) approach to determine the frequency of expression and prognostic value in two independent populations. A control tissue microarray (TMA) was constructed using PD-L1-transfected cells, normal human placenta and known PD-L1-positive NSCLC cases. Only one of four antibodies against PD-L1 (5H1) validated for specificity on this TMA. In situ PD-L1 mRNA using the RNAscope method was similarly validated. Two cohorts of NSCLC cases in TMAs including 340 cases from hospitals in Greece and 204 cases from Yale University were assessed. Tumors showed PD-L1 protein expression in 36% (Greek) and 25% (Yale) of the cases. PD-L1 expression was significantly associated with tumor-infiltrating lymphocytes in both cohorts. Patients with PD-L1 (both protein and mRNA) expression above the detection threshold showed statistically significant better outcome in both series (log-rank P=0.036 and P=0.027). Multivariate analysis showed that PD-L1 expression was significantly associated with better outcome independent of histology. Measurement of PD-L1 requires specific conditions and some commercial antibodies show lack of specificity. Expression of PD-L1 protein or mRNA is associated with better outcome. Further studies are required to determine the value of this marker in prognosis and prediction of response to treatments targeting this pathway.

Expresión y amplificación del gen HER2 en el cáncer gástrico avanzado / HER2 gene amplification and overexpression in advanced gastric cancer

Background:Overexpression/amplification of the HER2 gene in advanced gastric cancer is a predictor of response to adjuvant therapy with monoclonal antibodies.Aim: To determine the frequency of HER2 gene overexpression and amplificationin advanced gastric cancer. Material and Methods: One hundred nine advancedgastric cancer biopsy specimens, from 76 men and 33 women aged 67 ± 14 and 62± 12 years respectively, were selected. Three histological patterns (diffuse, intestinaland mixed) were recognized. Automated immunohistochemistry was performedwith monoclonal c-erbB-2 (NCL-356) Novocastra. Fluorescent in situ hybridization (FISH) for HER2 was performed in positive cases. Results: In 39% of cases,immunohistochemical staining was negative. It was 1+, 2+ and 3+ positive in 15,36 and 11% of cases, respectively. It was positive in 16% and 3% of intestinal typeand mixed carcinomas, respectively. It was negative in all diffuse carcinomas. FISHwas performed in 39 (2 +) cases and in 11 (3 +) cases. The gene amplification waspositive in two (2 +) and 11 (3 +) cases (11.9%). The overall concordance betweenimmunohistochemical staining and in situ hybridization was 85%. Conclusions: Inadvanced gastric cancer, HER2 gene overexpression or amplification was observed in11% and 12% of cases, respectively.

[HER2 gene amplification and overexpression in advanced gastric cancer]. / Expresión y amplificación del gen HER2 en el cáncer gástrico avanzado.

BACKGROUND: Overexpression/amplification of the HER2 gene in advanced gastric cancer is a predictor of response to adjuvant therapy with monoclonal antibodies. AIM: To determine the frequency of HER2 gene overexpression and amplification in advanced gastric cancer. MATERIAL AND METHODS: One hundred nine advanced gastric cancer biopsy specimens, from 76 men and 33 women aged 67 ± 14 and 62 ± 12 years respectively, were selected. Three histological patterns (diffuse, intestinal and mixed) were recognized. Automated immunohistochemistry was performed with monoclonal c-erbB-2 (NCL-356) Novocastra. Fluorescent in situ hybridization (FISH) for HER2 was performed in positive cases. RESULTS: In 39% of cases, immunohistochemical staining was negative. It was 1+, 2+ and 3+ positive in 15, 36 and 11% of cases, respectively. It was positive in 16% and 3% of intestinal type and mixed carcinomas, respectively. It was negative in all diffuse carcinomas. FISH was performed in 39 (2 +) cases and in 11 (3 +) cases. The gene amplification was positive in two (2 +) and 11 (3 +) cases (11.9%). The overall concordance between immunohistochemical staining and in situ hybridization was 85%. CONCLUSIONS: In advanced gastric cancer, HER2 gene overexpression or amplification was observed in 11% and 12% of cases, respectively.

Electric Field Controlled Self-Assembly of Hierarchically Ordered Membranes.

Self-assembly in the presence of external forces is an adaptive, directed organization of molecular components under nonequilibrium conditions. While forces may be generated as a result of spontaneous interactions among components of a system, intervention with external forces can significantly alter the final outcome of self-assembly. Superimposing these intrinsic and extrinsic forces provides greater degrees of freedom to control the structure and function of self-assembling materials. In this work we investigate the role of electric fields during the dynamic self-assembly of a negatively charged polyelectrolyte and a positively charged peptide amphiphile in water leading to the formation of an ordered membrane. In the absence of electric fields, contact between the two solutions of oppositely charged molecules triggers the growth of closed membranes with vertically oriented fibrils that encapsulate the polyelectrolyte solution. This process of self-assembly is intrinsically driven by excess osmotic pressure of counterions, and the electric field is found to modify the kinetics of membrane formation, and also its morphology and properties. Depending on the strength and orientation of the field we observe a significant increase or decrease of up to nearly 100% in membrane thickness, as well as the controlled rotation of nanofiber growth direction by 90 degrees, resulting in a significant increase in mechanical stiffness. These results suggest the possibility of using electric fields to control structure in self-assembly processes involving diffusion of oppositely charged molecules.

Optimal emergency personnel allocation after a natural disaster.

OBJECTIVE: Little work has been devoted to the links between natural disasters, subsequent Emergency Medical Services (EMS) network utilization, triage, and public awareness. The aim of this study was to investigate the types and distribution of emergency calls recorded after each South Florida hurricane during the 2005 season, identifying target areas for public health education, and emergency personnel use and training. DESIGN: Retrospective database review. SETTING: Miami-Dade Fire Rescue (MDFR) emergency dispatch headquarters. PATIENTS, PARTICIPANTS: All persons making 911 phone calls to the MDFR emergency dispatch headquarters in the 3 days before and after category 3 or higher hurricanes during 2005. INTERVENTIONS: None. RESULTS: There were 192,363 emergencies reported in 2005. The mean number of 911 emergencies reported per day for the 3 days before and after Katrina was 503 +/- 26 and 819 +/- 105, respectively (p = 0.007). The mean number for Wilma was 533 +/- 42 before and 800 +/- 63 after (p = 0.004). However, Rita had no impact on the number of 911 emergencies reported. Katrina resulted in a statistically significant increase in 911 calls for breathing (p = 0.03), convulsions and seizures (p = 0.02), and hazardous situations (p = 0.04). Rita led to an increase in convulsions and seizures (p = 0.03). Lastly, Wilma caused a rise in breathing emergencies (p = 0.02) and hazardous situations (p = 0.02). CONCLUSIONS: This study suggests that 911 calls regarding respiratory complaints, convulsions, seizures, and hazardous situations can be expected to significantly increase after a hurricane. Educational initiatives, EMS resource allocation, and modified triage systems designed to target these areas may limit EMS system-wide strain and improve health outcomes following natural disasters.

Paracordoma recidivante en la mano de un niño. Comunicación de un caso y revisión de la literatura / Recurring parachordoma in the hand of a child. A case report and review of the literature

El paracordoma es una neoplasia infrecuente de partes blandas que forma parte del espectro tumor mixto/mioepitelioma. Descrito en la década de 1950, se han comunicado 64 casos, 10 de los cuales corresponden a niños. El rango etario es amplio, con una media en la cuarta década. El paracordoma es morfológicamente similar al cordoma, pero su localización es extraaxial, preferentemente en la porción proximal de las extremidades, y posee un patrón inmunohistoquímico característico. Esta neoplasia es de crecimiento lento y localmente agresivo, pero se han informado casos con metástasis. Se presenta un niño de 8 años con un paracordoma de un año de evolución en la mano izquierda, que recidivó a los 6 meses de la cirugía inicial(AU)

Parachordoma is an unusual soft tissue tumour, falling within the mixed tumor/myoepithelioma spectrum. Only 64 cases have been reported since it was first described in 1950; of these 10 occurred in children. The overall age range is broad but the majority of patients are between 40 and 50 years old. Morphologically it is similar to chordoma but with an extraaxial location, occurring most frequently in the proximal limbs. Furthermore, it shows a different pattern with immunostaining. It is a slow growing tumour with local invasion, although metastases have been reported. We present a case of parachordoma in an 8 year old boy who presented with a slow growing mass in his left hand which recurred 6 months post-operatively(AU)

A bioactive self-assembled membrane to promote angiogenesis.

We report here on a bioactive hierarchically structured membrane formed by self-assembly. The membrane is formed with hyaluronic acid and peptide amphiphiles with binding affinity for heparin, and its hierarchical structure contains both an amorphous zone and a layer of fibrils oriented perpendicular to the membrane plane. The design of bioactivity is based on the potential ability to bind and slowly release heparin-binding growth factors. Human mesenchymal stem cells (hMSCs) seeded on these membranes attached and remained viable. Basic fibroblast growth factor (FGF2) and vascular endothelial growth factor (VEGF) were incorporated within the membrane structure prior to self-assembly and released into media over a prolonged period of time (14 days). Using the chicken chorioallantoic membrane (CAM) assay, we also found that these membranes induced a significant and rapid enhancement of angiogenesis relative to controls.

Streptavidin-biotin binding in the presence of a polymer spacer. A theoretical description.

The binding of streptavidin to biotin located at the terminal ends of poly(ethylene oxide) tethered to a planar surface is studied using molecular theory. The theoretical model is applied to mimic experiments (Langmuir 2008, 24, 2472) performed using drop-shape analysis to study receptor-ligand binding at the oil/water interface. Our theoretical predictions show very good agreements with the experimental results. Furthermore, the theory enables us to study the thermodynamic and structural behavior of the PEO-biotin + streptavidin layer. The interfacial structure, shown by the volume fraction profiles of bound proteins and polymers, indicates that the proteins form a thick layer supported by stretched polymers, where the thickness of the layer is greater than the height of the protein. When the polymer spacer is composed of PEO (3000), a thick layer with multilayers of proteins is formed, supported by the stretched polymer chains. It was found that thick multilayers of proteins are formed when long spacers are present or at very high protein surface coverages on short spacers. This shows that the flexibility of the polymer spacer plays an important role in determining the structure of the bound proteins due to their ability to accommodate highly distorted conformations to optimize binding and protein interactions. Protein domains are predicted when the amount of bound proteins is small due to the existence of streptavidin-streptavidin attractive interactions. As the number of proteins is increased, the competition between attractive interactions and steric repulsions determines the stability and structure of the bound layer. The theory predicts that the competition between these two forces leads to a phase separation at higher protein concentrations. The point where this transition happens depends on both spacer length and protein surface coverage and is an important consideration for practical applications of these and other similar systems. If the goal is to maximize protein binding, it is favorable to be above the layer transition, as multiple layers can accommodate greater bound protein densities. On the other hand, if the goal is to use these bound proteins as a linker group to build more complex structures, such as when avidin or streptavidin serves as a linker between two biotinylated polymers or proteins, the optimum is to be below the layer transition such that all bound linker proteins are available for further binding.