No abstract

Coarse powders of acid-insoluble matrix of diaphysis and calvarial parietal bone rapidly and consistently transformed fibroblasts into masses of cartilage and bone containing hemopoietic marrow. The transformant was encapsulated by fibroblasts within 24 hr to form a plaque. Transformation was restricted to the central thicknesses of the plaque. Under the stated conditions the alteration of the phenotype, fibroblast to chondroblast, was an unstable transformation, whereas the phenotype change, fibroblast to osteoblast, was stable. The transformation occurred on a rigid timetable of sequences. Measurements of alkaline phosphatase activity and incorporation of radioactive sulfate, phosphate, and calcium were sensitive and quantitative assays for the appearance of the transformed products, cartilage and bone.The aim of this work was to develop reproducible, rapid, and quantitative methods (a) to induce the fibroblast-chondroblast-osteoblast transformation, and (b) to differentiate the major links in the biological sequence.Long after embryonic differentiation has ceased, fibroblasts still retain the singular potential of transformability (1) into cells of other sorts, an attribute that persists throughout the life of the animal. The visible and biochemical characters are altered so profoundly that we refer to the phenomenon as transformation (2). Approximation of transformant (TF) and competent responding fibroblasts (R) initiates a series of interconnected biological reactions that yield products which we shall designate: Pi, cartilage; P2, bone; P3, hemopoietic bone marrow.Urist discovered that intramuscular transplants of lyophilized segments of demineralized bone (3) or tooth (4) transform fibroblasts to form bone by endochondral ossification in 24-26 days. Chondrogenesis occurs in cell culture (5), as well as in vivo. There are two convenient enzyme assays to study the transformation of the fibroblasts of fascia into cartilage, followed by bone: a. activity of alkaline phosphatase (6); b. determination of the quotient of activity: lactate dehydrogenase/malate dehydrogenase (7).The present experiments consisted of allogeneic transplantation of a weighed amount of sized desiccated powder of acidinsoluble bone matrix to the subcutaneous tissues of young rats. This technique provided a simple, quick, and standardized method to induce the transformation. The biochemical sequences of cartilage and bone in the chain reaction were analyzed by measurement of enzyme activities and incorporation of isotopes in the transformation products. MATERIALS AND METHODSPreparation of Transformant. Manufacture and final storage of all preparations were at room temperature (about 250).When liquids of any sort were used, the biological materials were immersed in the fluids in a jar with a magnetic stirrer, where they were propelled around the vortex created by vigorous stirring.Large adult rats of both sexes were used as donors throughout. The rats were decapitated. Parietal bones of the calvarium were removed and fragmented. ...

No abstract

Morphogenesis is the developmental cascade of pattern formation, body plan establishment, and the architecture of mirror-image bilateral symmetry of many structures and asymmetry of some, culminating in the adult form. Tissue engineering is the emerging discipline of design and construction of spare parts for the human body to restore function based on principles of molecular developmental biology and morphogenesis governed by bioengineering. The three key ingredients for both morphogenesis and tissue engineering are inductive signals, responding stem cells, and the extracellular matrix. Among the many tissues in the human body, bone has considerable powers for regeneration and is a prototype model for tissue engineering based on morphogenesis. Implantation of demineralized bone matrix into subcutaneous sites results in local bone induction. This model mimics sequential limb morphogenesis and permitted the isolation of bone morphogens. Although it is traditional to study morphogenetic signals in embryos, bone morphogenetic proteins (BMPs), the inductive signals for bone, were isolated from demineralized bone matrix from adults. BMPs and related cartilage-derived morphogenetic proteins (CDMPs) initiate, promote, and maintain chondrogenesis and osteogenesis and have actions beyond bone. The symbiosis of bone inductive and conductive strategies are critical for tissue engineering, and is in turn governed by the context and biomechanics. The context is the microenvironment, consisting of extracellular matrix, which can be duplicated by biomimetic biomaterials such as collagens, hydroxyapatite, proteoglycans, and cell adhesion proteins including fibronectins. Thus, the rules of architecture for tissue engineering are an imitation of the laws of developmental biology and morphogenesis, and thus may be universal for all tissues, including bones and joints.