Heart Valve Tissue Engineering: Concepts, Approaches, Progress, and Challenges

Potential applications of tissue engineering in regenerative medicine range from structural tissues to organs with complex function. This review focuses on the engineering of heart valve tissue, a goal which involves a unique combination of biological, engineering, and technological hurdles. We emphasize basic concepts, approaches and methods, progress made, and remaining challenges. To provide a framework for understanding the enabling scientific principles, we first examine the elements and features of normal heart valve functional structure, biomechanics, development, maturation, remodeling, and response to injury. Following a discussion of the fundamental principles of tissue engineering applicable to heart valves, we examine three approaches to achieving the goal of an engineered tissue heart valve: (1) cell seeding of biodegradable synthetic scaffolds, (2) cell seeding of processed tissue scaffolds, and (3) in-vivo repopulation by circulating endogenous cells of implanted substrates without prior in-vitro cell seeding. Lastly, we analyze challenges to the field and suggest future directions for both preclinical and translational (clinical) studies that will be needed to address key regulatory issues for safety and efficacy of the application of tissue engineering and regenerative approaches to heart valves. Although modest progress has been made toward the goal of a clinically useful tissue engineered heart valve, further success and ultimate human benefit will be dependent upon advances in biodegradable polymers and other scaffolds, cellular manipulation, strategies for rebuilding the extracellular matrix, and techniques to characterize and potentially non-invasively assess the speed and quality of tissue healing and remodeling

Desempenho reprodutivo, características do pelame e taxa de sudação em vacas da raça Braford Effects of hair coat traits and sweating rate on reproductive performance of Braford cows

Foram investigados os efeitos das características do pelame e da taxa de sudação (TS) sobre o intervalo de partos (IEP, n = 423) e os dias para o parto (DPP, n = 1.202) de vacas da raça Braford criadas em sistema extensivo em região tropical úmida no Mato Grosso do Sul, Brasil. As análises foram realizadas pelo método dos quadrados mínimos considerando para intervalo de partos os seguintes efeitos das classes de idade da vaca ao parto: grupo genético; pai; e regressão sobre a refletância da superfície da capa (R), a espessura da capa (E), o comprimento dos pêlos (C), o número de pêlos por unidade de área (N), o diâmetro dos pêlos (D) e a taxa de sudação. Para dias para o parto, foram considerados os efeitos: R, E, C, N, D, TS, divididos em classes; grupo genético; idade no início da estação de monta; e pai. Os componentes de variância e co-variância foram estimados pelo método de Máxima Verossimilhança Restrita sob o modelo touro. As características adaptativas não foram importantes para a variação do intervalo de parto e dos dias para o parto, mas a taxa de sudação apresentou efeito importante sobre dias ao parto. As estimativas de herdabilidade foram quase nulas para IEP e DPP e maiores para as características adaptativas (E = 0,16 ± 0,09; C = 0,18 ± 0,09; N = 0,08 ± 0,06; D = 0,12 ± 0,07; R = 0,30 ± 0,12; TS = 0,10 ± 0,06). Os resultados obtidos para as correlações genéticas de IEP e DPP com TS e entre as características do pelame indicaram que a seleção simultânea para menores valores de C pode ser favorável à redução do intervalo de partos. Em geral, as correlações genéticas entre TS, IEP e DPP apresentaram elevado erro-padrão. Considerando os resultados deste estudo e a importância das características do pelame e da sudação, confirma-se a necessidade de se estudarem as correlações genéticas entre as características adaptativas e o desempenho reprodutivo para o progresso da adaptação de bovinos da raça Braford no Brasil.<br>This study aimed to evaluate the effects of hair coat traits (thickness (T), reflectance (R), length (L), diameter (D) and number of hairs per unit area (N)) and sweating rate (SR) on calving interval (CI, n = 423) and days to calving (DC, n = 1202) of Braford cows raised in Mato Grosso do Sul State, Brazil. Data were analyzed by least squares and the model for CI included the effects of age class of cow, genetic group, sire and regression on R, T, L, N, D and SR. For days to calving the following effects were considered: R, T, L, N, D, TS divided in classes; regressions on genetic group, age at the beginning of breeding season and sire. Variance and covariance components were estimated by REML. Hair coat traits and SR traits were not statistically significant for CI, but the SR effect was statistically significant on DC. The heritability estimates were practically null for CI and DC and ranged from 0.08 to 0.30 for adaptive characteristics (T = 0.16 ± 0.09; L = 0.18 ± 0.09; N = 0.08 ± 0.06; D = 0.12 ± 0.07; R = 0.30 ± 0.12; SR = 0.10 ± 0.06). Overall, estimates of genetic correlations between pair of traits (hair coat, sweating rate, CI and DC) were characterized by high standard errors. Additional data is required to obtain accurate estimates of genetic correlations among hair coat traits, sweating rate and reproductive performance of Braford cows in Brazil

Heart failure prognosis over time: how the prognostic role of oxygen consumption and ventilatory efficiency during exercise has changed in the last 20 years

Aims: Exercise-derived parameters, specifically peak exercise oxygen uptake (peak VO 2 ) and minute ventilation/carbon dioxide relationship slope (VE/VCO 2 slope), have a pivotal prognostic value in heart failure (HF). It is unknown how the prognostic threshold of peak VO 2 and VE/VCO 2 slope has changed over the last 20 years in parallel with HF prognosis improvement. Methods and results: Data from 6083 HF patients (81% male, age 61 ± 13 years), enrolled in the MECKI score database between 1993 and 2015, were retrospectively analysed. By enrolment year, four groups were generated: group 1 1993–2000 (n = 440), group 2 2001–2005 (n = 1288), group 3 2006–2010 (n = 2368), and group 4 2011–2015 (n = 1987). We compared the 10-year survival of groups and analysed how the overall risk (cardiovascular death, urgent heart transplantation, or left ventricular assist device implantation) changed over time according to peak VO 2 and VE/VCO 2 slope and to major clinical and therapeutic variables. At 10 years, a progressively higher survival from group 1 to group 3 was observed, with no further improvement afterwards. A 20% risk for peak VO 2 15 mL/min/kg (95% confidence interval 16–13), 9 (11–8), 4 (4–2) and 5 (7–4) was observed in group 1, 2, 3, and 4, respectively, while the VE/VCO 2 slope value for a 20% risk was 32 (37–29), 47 (51–43), 59 (64–55), and 57 (63–52), respectively. Conclusions: Heart failure prognosis improved over time up to 2010 in a HF population followed by experienced centres. The peak VO 2 and VE/VCO 2 slope cut-offs identifying a definite risk progressively decreased and increased over time, respectively. The prognostic threshold of peak VO 2 and VE/VCO 2 slope must be updated whenever HF prognosis improves

Heart failure prognosis over time: how the prognostic role of oxygen consumption and ventilatory efficiency during exercise has changed in the last 20 years

Aims: Exercise-derived parameters, specifically peak exercise oxygen uptake (peak VO 2 ) and minute ventilation/carbon dioxide relationship slope (VE/VCO 2 slope), have a pivotal prognostic value in heart failure (HF). It is unknown how the prognostic threshold of peak VO 2 and VE/VCO 2 slope has changed over the last 20 years in parallel with HF prognosis improvement. Methods and results: Data from 6083 HF patients (81% male, age 61 \ub1 13 years), enrolled in the MECKI score database between 1993 and 2015, were retrospectively analysed. By enrolment year, four groups were generated: group 1 1993\u20132000 (n = 440), group 2 2001\u20132005 (n = 1288), group 3 2006\u20132010 (n = 2368), and group 4 2011\u20132015 (n = 1987). We compared the 10-year survival of groups and analysed how the overall risk (cardiovascular death, urgent heart transplantation, or left ventricular assist device implantation) changed over time according to peak VO 2 and VE/VCO 2 slope and to major clinical and therapeutic variables. At 10 years, a progressively higher survival from group 1 to group 3 was observed, with no further improvement afterwards. A 20% risk for peak VO 2 15 mL/min/kg (95% confidence interval 16\u201313), 9 (11\u20138), 4 (4\u20132) and 5 (7\u20134) was observed in group 1, 2, 3, and 4, respectively, while the VE/VCO 2 slope value for a 20% risk was 32 (37\u201329), 47 (51\u201343), 59 (64\u201355), and 57 (63\u201352), respectively. Conclusions: Heart failure prognosis improved over time up to 2010 in a HF population followed by experienced centres. The peak VO 2 and VE/VCO 2 slope cut-offs identifying a definite risk progressively decreased and increased over time, respectively. The prognostic threshold of peak VO 2 and VE/VCO 2 slope must be updated whenever HF prognosis improves