Post by lilsissy on Dec 6, 2009 22:37:12 GMT -5
simplfied ,
www.strangehorizons.com/2001/20010305/plastic.shtml
Living tissue can be broken into separate cells which can be persuaded to grow and divide in petri dishes incubated at body temperature with the right nutrients. However, even when they will grow in a layer one cell thick over the bottom of a petri dish, the cells will not grow back together to form the tissue they came from, whether it was an artery or a bone or even something relatively simple like skin.
The secret of getting cells to build tissues turns out to lie in the extracellular matrix -- a "living web" of proteins, polysaccharides and proteoglycans that cells both stick to and secrete as they grow into tissues like skin and cartilage. The exact components of the extracellular matrix differ between tissues. For instance, the extracellular matrix of bone also includes hydroxyapatite (a mineral containing calcium, phosphate, and bound water) for strength. If an extracellular matrix is provided for cells in cell culture they will often grow into it, absorbing it and secreting proteins and polysaccharides to "remodel" it for their own use, multiplying to fill it and produce living tissue.
However, because extracellular matrix is so complex, it is difficult to reproduce. It can be approximated with mixtures of proteins like collagen or elastin which are normally found in the extracellular matrix, or fibrin, which causes blood clotting. However, if these proteins come from human tissue (for example, the pooled blood products used until recently to make surgical fibrin "glue"), they may transfer disease from one of the donors to the patient. If they come from animals, patients may develop an immune response to the foreign proteins that remain in the newly grown tissue.
Luckily cells will often be happy with a synthetic extracellular matrix of something easier to obtain and purify. Among other things, they will accept several types of biodegradable plastics. Once they have an extracellular matrix substitute, many types of cells will happily grow on it (and into it, and through it, if it's properly porous), secreting extracellular matrix proteins and breaking down the plastic as they go, until they produce a piece of tissue the same size and shape as the plastic "scaffold" but composed of living cells and newly secreted extracellular matrix. In several cases it has been possible to layer two types of tissue to produce a simple organ, like a blood vessel (a tube of smooth muscle cell tissue lined with a layer of endothelial cells) or a urinary bladder (a "balloon" of smooth muscle tissue lined with urothelial cells).
Jen
www3.interscience.wiley.com/journal/118626164/abstract?CRETRY=1&SRETRY=0
Ectopic Calcification as Abnormal Biomineralization
ABSTRACT
Abstract: Vascular calcification is observed frequently in hemodialysis patients. The guidelines for kidney disease outcomes quality initiative recommend a strict control of serum calcium and phosphorus concentrations. Calcium–phosphorus product in extracellular fluids is almost at an oversaturation level in dialysis patients and in healthy individuals as well, but crystallization of hydroxyapatite does not occur in healthy individuals. Presumably, some systemic mechanism that has yet to be defined works to block the formation of hydroxyapatite crystals in healthy individuals, whereas in dialysis patients this defense mechanism is disrupted in hard tissues, leading to progressive biomineralization. Matrix vesicles released from specialized mesenchymal cells such as osteoblasts, play a central role in disrupting the putative defense mechanism against calcification. Matrix vesicles are internally in a highly favorable environment for progressive calcification, and essentially a nidus for hydroxyapatite crystal nucleation and its external growth through disruption of the defense mechanism. Osteoblastic cells release matrix vesicles that form initial crystal hydroxyapatite by condensation of phosphate and calcium, referred to as matrix vesicle calcification. Hydroxyapatite crystals break through vesicular membranes to reach a nearby collagen fiber network and form a continuous layer of calcified bone matrix. Thereafter follows the formation of additive bone matrix by osteoblasts and the advance of the calcification front. Therefore, ectopic calcification arises mechanistically from: (i) disruption of a systemic defense mechanism against calcification; and (ii) appearance of osteoblast-like cells in hard tissues that normally are localized in soft tissues. Abnormal accumulation of calcium/inorganic phosphate in dialysis patients is accounted for by the former disruption of systemic defense mechanism against calcification, and arterial calcification in dialysis patients by the latter osteoblast-like cells transformed from tunica media or vascular smooth-muscle cells.
This shows he familar stacked rings we often see,
www.swri.org/3pubs/ttoday/fall98/bone.htm
www.strangehorizons.com/2001/20010305/plastic.shtml
Living tissue can be broken into separate cells which can be persuaded to grow and divide in petri dishes incubated at body temperature with the right nutrients. However, even when they will grow in a layer one cell thick over the bottom of a petri dish, the cells will not grow back together to form the tissue they came from, whether it was an artery or a bone or even something relatively simple like skin.
The secret of getting cells to build tissues turns out to lie in the extracellular matrix -- a "living web" of proteins, polysaccharides and proteoglycans that cells both stick to and secrete as they grow into tissues like skin and cartilage. The exact components of the extracellular matrix differ between tissues. For instance, the extracellular matrix of bone also includes hydroxyapatite (a mineral containing calcium, phosphate, and bound water) for strength. If an extracellular matrix is provided for cells in cell culture they will often grow into it, absorbing it and secreting proteins and polysaccharides to "remodel" it for their own use, multiplying to fill it and produce living tissue.
However, because extracellular matrix is so complex, it is difficult to reproduce. It can be approximated with mixtures of proteins like collagen or elastin which are normally found in the extracellular matrix, or fibrin, which causes blood clotting. However, if these proteins come from human tissue (for example, the pooled blood products used until recently to make surgical fibrin "glue"), they may transfer disease from one of the donors to the patient. If they come from animals, patients may develop an immune response to the foreign proteins that remain in the newly grown tissue.
Luckily cells will often be happy with a synthetic extracellular matrix of something easier to obtain and purify. Among other things, they will accept several types of biodegradable plastics. Once they have an extracellular matrix substitute, many types of cells will happily grow on it (and into it, and through it, if it's properly porous), secreting extracellular matrix proteins and breaking down the plastic as they go, until they produce a piece of tissue the same size and shape as the plastic "scaffold" but composed of living cells and newly secreted extracellular matrix. In several cases it has been possible to layer two types of tissue to produce a simple organ, like a blood vessel (a tube of smooth muscle cell tissue lined with a layer of endothelial cells) or a urinary bladder (a "balloon" of smooth muscle tissue lined with urothelial cells).
Jen
www3.interscience.wiley.com/journal/118626164/abstract?CRETRY=1&SRETRY=0
Ectopic Calcification as Abnormal Biomineralization
ABSTRACT
Abstract: Vascular calcification is observed frequently in hemodialysis patients. The guidelines for kidney disease outcomes quality initiative recommend a strict control of serum calcium and phosphorus concentrations. Calcium–phosphorus product in extracellular fluids is almost at an oversaturation level in dialysis patients and in healthy individuals as well, but crystallization of hydroxyapatite does not occur in healthy individuals. Presumably, some systemic mechanism that has yet to be defined works to block the formation of hydroxyapatite crystals in healthy individuals, whereas in dialysis patients this defense mechanism is disrupted in hard tissues, leading to progressive biomineralization. Matrix vesicles released from specialized mesenchymal cells such as osteoblasts, play a central role in disrupting the putative defense mechanism against calcification. Matrix vesicles are internally in a highly favorable environment for progressive calcification, and essentially a nidus for hydroxyapatite crystal nucleation and its external growth through disruption of the defense mechanism. Osteoblastic cells release matrix vesicles that form initial crystal hydroxyapatite by condensation of phosphate and calcium, referred to as matrix vesicle calcification. Hydroxyapatite crystals break through vesicular membranes to reach a nearby collagen fiber network and form a continuous layer of calcified bone matrix. Thereafter follows the formation of additive bone matrix by osteoblasts and the advance of the calcification front. Therefore, ectopic calcification arises mechanistically from: (i) disruption of a systemic defense mechanism against calcification; and (ii) appearance of osteoblast-like cells in hard tissues that normally are localized in soft tissues. Abnormal accumulation of calcium/inorganic phosphate in dialysis patients is accounted for by the former disruption of systemic defense mechanism against calcification, and arterial calcification in dialysis patients by the latter osteoblast-like cells transformed from tunica media or vascular smooth-muscle cells.
This shows he familar stacked rings we often see,
www.swri.org/3pubs/ttoday/fall98/bone.htm