Biomedical subjects

R L Sah

Publications and source records attributed to R L Sah.

59 records · Page 4Linked to original sources

PubMedDate not supplied

Video microscopy to quantitate the inhomogeneous equilibrium strain within articular cartilage during confined compression.

The objectives of this study were to develop a method to quantitate the displacement and strain fields within articular cartilage during equilibrium confined compression, and to use the method to determine the variation of the equilibrium confined compression modulus with depth from the articular surface in bovine cartilage. The method made use of fluorescently labeled chondrocyte nuclei as intrinsic fiducial markers. Articular cartilage was harvested from the patellofemoral groove of adult bovines and trimmed to rectangular blocks 5 mm long, 0.76 mm wide, and 500 microns deep with the articular surface intact. Test specimens were stained with the DNA binding dye Hoechst 33258, placed in a custom confined compression chamber, and viewed with an epifluorescence microscope equipped for video image acquisition. Image processing was used to localize fluorescing chondrocyte nuclei in uncompressed and compressed (approximately 17%) specimens, allowing determination of the intra-tissue displacement profile. Strain was determined as the slope of linear regression fits of the displacement data in four sequential 125-microns-thick layers. Equilibrium strains varied 6.1-fold from the articular surface through 500 microns of cartilage depth, with the greatest compressive strain in the superficial 125-microns layer and the least compressive strain in the two deepest 125-microns layers. Thus, the four successive 125-microns layers have moduli that are 0.44 (superficial), 1.07, 2.39, and 2.67 (deep) times the apparent modulus for a 500-microns thick cartilage sample assumed to be homogeneous.

Animals↗

PubMedDate not supplied

Formulation of PEG-based hydrogels affects tissue-engineered cartilage construct characteristics.

The limited supply of cartilage tissue with appropriate sizes and shapes needed for reconstruction and repair has stimulated research in the area of hydrogels as scaffolds for cartilage tissue engineering. In this study we demonstrate that poly(ethylene glycol) (PEG)-based semi-interpenetrating (sIPN) network hydrogels, made with a crosslinkable poly(ethylene glycol)-dimethacrylate (PEGDM) component and a non-crosslinkable interpenetration poly(ethylene oxide) (PEO) component, and seeded with chondrocytes support cartilage construct growth having nominal thicknesses of 6 mm and relatively uniform safranin-O stained matrix when cultured statically, unlike constructs grown with prefabricated macroporous scaffolds. Even though changing the molecular weight of the PEO from 100 to 20 kDa reduces the viscosity of the precursor polymer solution, we have demonstrated that it does not appear to affect the histological or biochemical characteristics of cartilaginous constructs. Extracellular matrix (ECM) accumulation and the spatial uniformity of the ECM deposited by the embedded chondrocytes decreased, and hydrogel compressive properties increased, as the ratio of the PEGDM:PEO in the hydrogel formulation increased (from 30:70 to 100:0 PEGDM:PEO). Total collagen and glycosaminoglycan contents per dry weight were highest using the 30:70 PEGDM:PEO formulation (24.4+/-3.5% and 7.1+/-0.9%, respectively). The highest equilibrium compressive modulus was obtained using the 100:0 PEGDM:PEO formulation (0.32+/-0.07 MPa), which is similar to the compressive modulus of native articular cartilage. These results suggest that the versatility of PEG-based sIPN hydrogels makes them an attractive scaffold for tissue engineering of cartilage.

Journal Article↗

PubMedDate not supplied

The effects of hyaluronan on tissue healing after meniscus injury and repair in a rabbit model.

To assess the effect of hyaluronan on meniscus injury and repair, we had 35 mature New Zealand White rabbits undergo bilateral meniscus injury and repair (19 in the peripheral region, and 16 in the inner region). A longitudinal tear was created in the medial meniscus and repaired with horizontally placed nylon sutures. The left knee joint received intraarticular injections of hyaluronan 1 week after surgery and once a week for 5 weeks. The right knees were injected with phosphate-buffered saline (the carrier vehicle of the hyaluronan). Twelve weeks after repair, tears in the peripheral region showed gross and histologic evidence of healing, with no difference between the vehicle- and hyaluronan-treated menisci. Biochemically, the ratio of reducible collagen cross-links in the hyaluronan-treated menisci was significantly higher than in the vehicle-treated menisci, indicating greater level of collagen remodeling. Biomechanically the vehicle- and hyaluronan-treated menisci demonstrated similarly high tearing load and fracture toughness. In the inner region, poor healing response was observed grossly and histologically in both treatment groups. Water content in the hyaluronan-treated menisci was significantly lower than in the vehicle-treated menisci, indicating a lower level of swelling. Hyaluronan treatment stimulated collagen remodeling in the peripheral region and inhibited swelling of the meniscus repaired in the inner region.

Adjuvants, Immunologic↗

PubMedDate not supplied

Static and dynamic compression regulate cartilage metabolism of PRoteoGlycan 4 (PRG4).

The boundary lubrication function of articular cartilage is mediated in part by molecules at the articular surface and in synovial fluid, encoded by Prg4. The objective of this study was to determine whether static and dynamic compression regulate PRG4 biosynthesis by cartilage explants. Articular cartilage disks were harvested to include the articular surface from immature bovines. Some disks were subjected to 24 h (day 1) of loading, followed by 72 h (days 2-4) of free-swelling culture to assess chondrocyte responses following unloading. Loading consisted of 6 or 100 kPa of static compression, with or without superimposed dynamic compression (10 or 300 kPa peak amplitude, 0.01 Hz). Other disks were cultured free-swelling as controls. PRG4 secretion into culture medium was inhibited by all compression protocols during day 1. Following unloading, cartilage previously subjected to dynamic compression to 300 kPa exhibited a rebound effect, secreting more PRG4 than did controls, while cartilage previously subjected to 100 kPa static loading secreted less PRG4. Immunohistochemistry revealed that all compression protocols also affected the number of cells expressing PRG4. The paradigm that mechanical stimuli regulate biosynthesis in cartilage appears operative not only for load bearing matrix constituents, but also for PRG4 molecules mediating lubrication.

Animals↗

PubMedDate not supplied

Septicemic proteus infection in Japanese quail chicks (Coturnix coturnix japonica).

Proteus infection was incriminated as the cause of severe depression, coma, and high mortality in successive broods of quail chicks. The pathological lesions comprised congestion of lungs, liver, and kidneys and mucus exudation in the trachea. The organism, isolated from the heart blood and lungs of affected chicks, was identified on biochemical tests as Proteus mirabilis. Pathogenicity of the isolate was tested in young albino mice and week-old quail chicks, which succumbed to infection within 48 hours of inoculation. Association of P. mirabilis with septicemic disease in Japanese quails has apparently been demonstrated for the first time.

Animals↗