Biomedical subjects

R J Beiler

Publications and source records attributed to R J Beiler.

7 recordsLinked to original sources

PubMed2002

Application of magnetic resonance microscopy to tissue engineering: a polylactide model.

Absorbable polymers are unique materials that find application as temporary scaffolds in tissue engineering. They are often extremely sensitive to histological processing and, for this reason, studying fragile, tissue-engineered constructs before implantation can be quite difficult. This research investigates the use of noninvasive imaging using magnetic resonance microscopy (MRM) as a tool to enhance the assessment of these cellular constructs. A series of cellular, polylactide constructs was developed and analyzed using a battery of tests, including MRM. Distribution of rat aortic smooth muscle cells within the scaffolds was compared as one example of a tissue engineering MRM application. Cells were loaded in varying amounts using static and dynamic methods. It was found that the cellular component was readily identified and the polymer microstructure readily assessed. Specifically, the MRM results showed a heterogeneous distribution of cells due to static loading and a homogenous distribution associated with dynamic loading, results that were not visible through biochemical tests, scanning electron microscopy, or histological evaluation independently. MRM also allowed differentiation between different levels of cellular loading. The current state of MRM is such that it is extremely useful in the refinement of polymer processing and cell seeding methods. This method has the potential, with technological advances, to be of future use in the characterization of cell-polymer interactions.

Absorbable Implants↗

PubMed2000

Central leptin regulates the UCP1 and ob genes in brown and white adipose tissue via different beta-adrenoceptor subtypes.

The three known subtypes of beta-adrenoreceptors (beta(1)-AR, beta(2)-AR, and beta(3)-AR) are differentially expressed in brown and white adipose tissue and mediate peripheral responses to central modulation of sympathetic outflow by leptin. To assess the relative roles of the beta-AR subtypes in mediating leptin's effects on adipocyte gene expression, mice with a targeted disruption of the beta(3)-adrenoreceptor gene (beta(3)-AR KO) were treated with vehicle or the beta(1)/beta(2)-AR selective antagonist, propranolol (20 microgram/g body weight/day) prior to intracerebroventricular (ICV) injections of leptin (0.1 microgram/g body weight/day). Leptin produced a 3-fold increase in UCP1 mRNA in brown adipose tissue of wild type (FVB/NJ) and beta(3)-AR KO mice. The response was unaltered by propranolol in wild type mice, but was completely blocked by this antagonist in beta(3)-AR KO mice. In contrast, ICV leptin had no effect on leptin mRNA in either epididymal or retroperitoneal white adipose tissue (WAT) from beta(3)-AR KOs. Moreover, propranolol did not block the ability of exogenous leptin to reduce leptin mRNA in either WAT depot site of wild type mice. These results demonstrate that the beta(3)-AR is required for leptin-mediated regulation of ob mRNA expression in WAT, but is interchangeable with the beta(1)/beta(2)-ARs in mediating leptin's effect on UCP1 mRNA expression in brown adipose tissue.

Adipose Tissue↗

PubMed2000

Comparative study of seeding methods for three-dimensional polymeric scaffolds.

Development of tissue-engineered devices may be enhanced by combining cells with porous absorbable polymeric scaffolds before implantation. The cells are seeded throughout the scaffolds and allowed to proliferate in vitro for a predetermined amount of time. The distribution of cells throughout the porous material is one critical component determining success or failure of the tissue-engineered device. This can influence both the successful integration of the device with the host tissue as well as the development of a vascularized network throughout the entire scaffold volume. This research sought to compare different seeding and proliferation methods to select an ideal method for a polyglycolide/aortic endothelial cell system. Two seeding environments, static and dynamic, and three proliferation environments, static, dynamic, and bioreactor, were analyzed, for a total of six possible methods. The six seeding and proliferation combinations were analyzed following a 1-week total culture time. It was determined that for this specific system, dynamic seeding followed by a dynamic proliferation phase is the least promising method and dynamic seeding followed by a bioreactor proliferation phase is the most promising.

Animals↗

PubMed2000

Differential regulation of leptin expression and function in A/J vs. C57BL/6J mice during diet-induced obesity.

Obesity-resistant (A/J) and obesity-prone (C57BL/6J) mice were weaned onto low-fat (LF) or high-fat (HF) diets and studied after 2, 10, and 16 wk. Despite consuming the same amount of food, A/J mice on the HF diet deposited less carcass lipid and gained less weight than C57BL/6J mice over the course of the study. Leptin mRNA was increased in white adipose tissue (WAT) in both strains on the HF diet but to significantly higher levels in A/J compared with C57BL/6J mice. Uncoupling protein 1 (UCP1) and UCP2 mRNA were induced by the HF diet in brown adipose tissue (BAT) and WAT of A/J mice, respectively, but not in C57BL/6J mice. UCP1 mRNA was also significantly higher in retroperitoneal WAT of A/J compared with C57BL/6J mice. The ability of A/J mice to resist diet-induced obesity is associated with a strain-specific increase in leptin, UCP1, and UCP2 expression in adipose tissue. The findings indicate that the HF diet does not compromise leptin-dependent regulation of adipocyte gene expression in A/J mice and suggest that maintenance of leptin responsiveness confers resistance to diet-induced obesity.

Adipose Tissue↗

PubMed2000

Absorbable mesh aids in development of discrete, tissue-engineered constructs.

Absorbable mesh was investigated as a potential containment material in which to house discrete, small, tissue-engineered constructs. The mesh was fashioned into bags of varying shapes and consistent volumes. Cells were cultivated on porous, collagen beads, and the tissue constructs were placed into the bags. The mechanical integrity of the bags and feasibility of the design was tested in vitro. The bags successfully maintained their integrity as the cells developed on the collagen matrices. Furthermore, their porosity allowed access of nutrients and waste products to and from the developing tissue. Having demonstrated feasibility of processing, the next step is to optimize the cell culture specifications and materials design.

Absorbable Implants↗

PubMed1999

The development of an embedding technique for polylactide sponges.

The use of absorbable polymeric biomaterials is increasing in the field of tissue engineering. These polymeric scaffolds provide mechanical strength and shape as the engineered tissue forms. Histological analysis is an important part of the development of an appropriate polymeric construct, because it allows the analysis of the cell/material interaction. Unfortunately, routine paraffin processing often degrades these absorbable polymers, and routine staining can dissolve the remnants. This research sought to develop a histological procedure that would retain the polymer structure. Two processing procedures, paraffin and glycol methacrylate, were tested on three in vitro groups of poly-L-lactide sponges, high cell density seeding, low cell density seeding, and a control. The paraffin processing caused shrinkage and degradation of the polymer, and staining dissolved the remnants. The glycol methacrylate processing minimized damage to the polymer even after staining.

Animals↗

PubMed1999

Parameters affecting cellular adhesion to polylactide films.

Absorbable biomaterials have been recently incorporated into the field of tissue engineering. Little work has been performed, even with the clinically acceptable absorbables, concerning their tissue promoting capability or lack, thereof. Furthermore, the relative attractions of cells to these implants may be largely disguised by the presence of serum. This research involved the development of an adhesion assay to compare the adhesion behavior of two cell types to two different polylactides in a serum free environment. The results showed that the attachment behavior depends not only on the cell or the polymer but a combination of the two.

Animals↗