Papers by Alexander Rivera 2
Acta biomaterialia, Sep 15, 2017
Current clinical methods to treat articular cartilage lesions provide temporary relief of the sym... more Current clinical methods to treat articular cartilage lesions provide temporary relief of the symptoms but fail to permanently restore the damaged tissue. Tissue engineering, using mesenchymal stem cells (MSCs) combined with scaffolds and bioactive factors, is viewed as a promising method for repairing cartilage injuries. However, current tissue engineered constructs display inferior mechanical properties compared to native articular cartilage, which could be attributed to the lack of structural organization of the extracellular matrix (ECM) of these engineered constructs in comparison to the highly oriented structure of articular cartilage ECM. We previously showed that we can guide MSCs undergoing chondrogenesis to align using microscale guidance channels on the surface of a two-dimensional (2-D) collagen scaffold, which resulted in the deposition of aligned ECM within the channels and enhanced mechanical properties of the constructs. In this study, we developed a technique to rol...
Tissue engineering is a promising method for long-term repair of cartilage lesions; however, curr... more Tissue engineering is a promising method for long-term repair of cartilage lesions; however, current tissue-engineered cartilage constructs have inferior mechanical properties compared to native cartilage. Other researchers attribute this problem to a lack of an oriented structure in the constructs at the microscale that is present in the native tissue. In this study, we utilized contact guidance to develop constructs with microscale architecture for improved chondrogenesis and function. In this system, we used microscale channels on the scaffold surface to guide mesenchymal stem cells (MSCs) undergoing chondrogenesis to produce oriented extracellular matrix (ECM). Stable channels of varying microscale dimensions were formed in collagen-based and polydimethylsiloxane membranes via a combination of microfabrication and soft-lithography. Human MSCs were selectively seeded in these channels. The chondrogenic potential of MSCs seeded in these channels was investigated by culturing them ...
Micromachines, 2015
Tissue engineering is viewed as a promising option for long-term repair of cartilage lesions, but... more Tissue engineering is viewed as a promising option for long-term repair of cartilage lesions, but current engineered cartilage constructs fail to match the mechanical properties of native tissue. The extracellular matrix of adult human articular cartilage contains highly organized collagen fibrils that enhance the mechanical properties of the tissue. Unlike articular cartilage, mesenchymal stem cell (MSC) based tissue engineered cartilage constructs lack this oriented microstructure and therefore display much lower mechanical strength. The goal of this study was to investigate the effect of biomolecular gradients and shear stress on MSCs undergoing chondrogenesis within a microfluidic device. Via poly(dimethyl siloxane) soft-lithography, microfluidic devices containing a gradient generator were created. Human MSCs were seeded within these chambers and exposed to flow-based transforming growth factor β1 (TGF-β1) gradients. When the MSCs were both confluent and exposed to shear stress, the cells aligned along the flow direction. Exposure to TGF-β1 gradients led to chondrogenesis of MSCs, indicated by positive type II collagen staining. These results, together with a previous study that showed that aligned MSCs produce aligned collagen, suggest that oriented cartilage tissue structures with superior mechanical properties can be obtained by aligning MSCs along the flow direction and exposing MSCs to chondrogenic gradients.
Tissue Engineering Part A, 2013
Tissue engineering is a possible method for long-term repair of cartilage lesions, but current ti... more Tissue engineering is a possible method for long-term repair of cartilage lesions, but current tissue-engineered cartilage constructs have inferior mechanical properties compared to native cartilage. This problem may be due to the lack of an oriented structure in the constructs at the microscale that is present in the native tissue. In this study, we utilize contact guidance to develop constructs with microscale architecture for improved chondrogenesis and function. Stable channels of varying microscale dimensions were formed in collagen-based and polydimethylsiloxane membranes via a combination of microfabrication and soft-lithography. Human mesenchymal stem cells (MSCs) were selectively seeded in these channels. The chondrogenic potential of MSCs seeded in these channels was investigated by culturing them for 3 weeks under differentiating conditions, and then evaluating the subsequent synthesized tissue for mechanical function and by type II collagen immunohistochemistry. We demonstrate selective seeding of viable MSCs within the channels. MSC aligned and produced mature collagen fibrils along the length of the channel in smaller linear channels of widths 25-100 mm compared to larger linear channels of widths 500-1000 mm. Further, substrates with microchannels that led to cell alignment also led to superior mechanical properties compared to constructs with randomly seeded cells or selectively seeded cells in larger channels. The ultimate stress and modulus of elasticity of constructs with cells seeded in smaller channels increased by as much as fourfolds. We conclude that microscale guidance is useful to produce oriented cartilage structures with improved mechanical properties. These findings can be used to fabricate large clinically useful MSC-cartilage constructs with superior mechanical properties.
Osteoarthritis and Cartilage, 2010
Animals, 2020
A study was conducted at the Escuela Superior Politècnica de Chimborazo, Ecuador, to evaluate the... more A study was conducted at the Escuela Superior Politècnica de Chimborazo, Ecuador, to evaluate the influence of litter size of guinea pigs (Cavia porcellus) on their development and to establish the economic profitability of the production system. Forty-eight animals were used, distributed into litters of two, three, and four rodents per litter, with a balanced diet and green fresh alfalfa for the weaning, growth, and fattening stage, the rodents and litters were randomly selected, applying the statistical model completely randomly and evaluating different variables across 120 days. The litters of three guinea pigs obtained the best productive responses and economic profitability. With respect to sex, the males presented better productive behavior, greater economic increase, and less cost, evidencing that mixed feeding influences the number of guinea pigs per birth in terms of growth and development. The results serve to improve guinea pig meat production for the rural population.
Sleep
Introduction Sleep disturbance is a transdiagnostic risk factor that is so prevalent among emergi... more Introduction Sleep disturbance is a transdiagnostic risk factor that is so prevalent among emerging adults it is considered to be a public health epidemic. For emerging adults, who are already at greater risk for psychopathology, the COVID-19 pandemic has disrupted daily routines, potentially changing sleep patterns and heightening risk factors for the emergence of affective dysregulation, and consequently mood-related disturbances. This study aimed to determine whether variability in sleep patterns across a 3-month period was associated with next-day positive and negative affect, and affective dynamics, proximal affective predictors of depressive symptoms among young adults during the pandemic. Methods College student participants (N=20, 65% female, Mage=19.80, SDage=1.0) wore non-invasive wearable devices (the Oura ring https://ouraring.com/) continuously for a period of 3-months, measuring sleep onset latency, sleep efficiency, total sleep, and time spent in different stages of s...
BACKGROUND Sleep disturbance is a transdiagnostic risk factor so prevalent among young adults it ... more BACKGROUND Sleep disturbance is a transdiagnostic risk factor so prevalent among young adults it is considered a public health epidemic, exacerbated by the COVID-19 pandemic. Sleep may contribute to mental health via affect dynamics. Prior literature on contribution of sleep to affect is largely based on correlational studies or experiments that do not generalize to the daily lives of young adults. Furthermore, the literature examining the associations between sleep variability and affect dynamics remains scant. OBJECTIVE In an ecologically valid context, using an intensive longitudinal design, we aimed to assess the daily and long-term associations between sleep patterns and affect dynamics among young adults during the COVID-19 pandemic. METHODS College student participants (N=20, 65% female) wore an Oura ring continuously for 3-months to measure sleep patterns, such as average and variability in total sleep time (TST), wake after sleep onset (WASO), sleep efficiency (SE), and sle...
BACKGROUND The year 2020 has been challenging for many, particularly for young adults who have be... more BACKGROUND The year 2020 has been challenging for many, particularly for young adults who have been adversely affected by the COVID-19 pandemic. Emerging adulthood is a developmental phase with significant changes in the patterns of daily living; it is a risky phase for the onset of major mental illness. College students during the pandemic face significant risk, potentially losing several protective factors (eg, housing, routine, social support, job, and financial security) that are stabilizing for mental health and physical well-being. Individualized multiple assessments of mental health, referred to as multimodal personal chronicles, present an opportunity to examine indicators of health in an ongoing and personalized way using mobile sensing devices and wearable internet of things. OBJECTIVE To assess the feasibility and provide an in-depth examination of the impact of the COVID-19 pandemic on college students through multimodal personal chronicles, we present a case study of an...
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Papers by Alexander Rivera 2