Type I collagen fibers

Silver, F. H., Christiansen, D. L., Snowhill, P. B., and Chen, Y. (2001). Transition from viscous to elastic-based dependency of mechanical properties of self-assembled type I collagen fibers./. Appl. Polymer Sci. 79, 134-142. 

The reticular layer of basement membrane in a tissue such as the skin contains a variety of matrix structures. Strands of basement membrane may project down to type I collagen fibers. Anchoring fibers, banded fibers composed of type VII collagen, extend into the basement mem-... 

Figure 7.7. Total, elastic, and viscous stress-strain curves for uncrosslinked self-assembled type I collagen fibers.Total (open squares), elastic (filled diamonds), and viscous (filled squares) stress-strain curves for self-assembled uncrosslinked collagen fibers obtained from incremental stress-strain measurements at a strain rate of 10%/min. The fibers were tested immediately after manufacture and were not aged at room temperature. Error bars represent one standard deviation of the mean value for total and viscous stress components. Standard deviations for the elastic stress components are similar to those shown for the total stress but are omitted to present a clearer plot. The straight line for the elastic stress-strain curve closely overlaps the line for the viscous stress-strain curve. Note that the viscous stress-strain curve is above the elastic curve suggesting that viscous sliding is the predominant energy absorbing mechanism for uncrosslinked collagen fibers.

Figure 7.9. Relationship between mechanical properties and fibril length (L) for self-assembled collagen fibers. Plot of UTS (A) and elastic slope (B) versus L in im for self-assembled type I collagen fibers stretched in tension at strain rate of 50%/min. Points with fibril lengths less than 20 pm are for uncrosslinked self-assembled type I collagen fibers and the points above 20 pm are for crosslinked fibers. The correlation coefficient for the best fit line is given by R2.

Figure 8.5. Plots of elastic modulus versus mineral content (b) and days of mineralization (a) from incremental stress-strain tests performed on mineralized self-assembled type I collagen fibers. Slopes were obtained from the straight portions of the elastic and viscous stress-strain curves.

Type El fibers (fetal, reticular and vascular collagen) are delicate compared with type I fibers. In the fetus, type IE collagen is incorporated within the type I collagen to impart the greater flexibility critical for fetal development. After birth, the delicate type El collagen fibers contribute to reticular fibers and also type I collagen fibers that are present in cardiovascular and lymphoid tissues and also beneath epithelial basal cell layers, muscles, and nervous tissue Schwann cells. 

Type VII collagen is a non-fibrous, anchoring fibril that binds large type I collagen fibers in the stroma to the lamina densa section of the basal lamina. Type VII procollagen... 

For mineralization, the normal, metastable state is adjusted by nucleation, measured by the seed and solubility tests. The seed test measures amount of solid apatite required to precipitate Ca2+ and HP042- ion concentrations exceeding their solubility product. The solubility test measures the minimal concentrations of Ca2+ and HP042- necessary to induce precipitation. Type I collagen fibers nucleate bone formation as the concentrations of Ca2+... 

Osteoblasts secrete osteoid, a matrix rich in type I collagen fibers and vesicles. Precipitation of calcium phosphate is inhibited by a high concentration of pyrophosphate in stromal interstitial fluids, and a high concentration also of albumin and citrate in blood plasma. Pyrophosphate is derived from (1) transport out of the cytosol, and (2) synthesis from nucleoside triphosphates in the stromal interstitial fluid that permeates the osteoid matrix. Precipitation occurs only when calcium and phosphate ions are taken up into vesicles whose inner membrane is composed of phosphatidylserine. The high concentration of calcium and phosphate ions in the vesicle is mediated by annexin and type HI Pi Na-dependent transporters. This overwhelms the pyrophosphate and nucleation occurs. As the precipitate grows and ruptures the membrane, tissue-nonspecific alkaline phosphatase is activated to remove pyrophosphate from the osteoid matrix fluid so that calcium phosphate precipitates around phosphorylated serine residues within the collagen fibers. 

Fibrous Aligned type i collagen fibers Compressive, tensile hoop, and shear stresses -i -fli... 

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