PMC:4996398 / 34617-36411 JSONTXT

{"project":"2_test","denotations":[{"id":"27600217-24880568-69475948","span":{"begin":515,"end":517},"obj":"24880568"},{"id":"27600217-11759015-69475949","span":{"begin":539,"end":541},"obj":"11759015"},{"id":"27600217-8021988-69475950","span":{"begin":542,"end":544},"obj":"8021988"}],"text":"3.2. Delayed Gelation Systems\nDelayed gelation systems where gels are formed inside the body (in situ) allow implantation with less invasive surgery which is easier to deliver since they will exactly fill tissue voids and defects. The mixture of gel forming ions suspended or dissolved in an alginate solution is, along with internal gelation principles, the basis of delayed gelation. Examples include mixing of an alginate solution with a suspension of calcium alginate particles [95], calcium carbonate and GDL [96] or calcium sulfate [97,98].\nA promising approach for tissue engineering of hyaline cartilage is utilization of human mesenchymal stem cells (hMSCs). The most sufficient chondrogenic differentiation is obtained in 3D culture systems. A novel model system for 3D chondrogenic differentiation of hMSCs has recently been described [95]. Here, cells were entrapped in an alginate hydrogel formed as calcium ions diffused from calcium alginate particles subsequent to mixture with a solution of sodium alginate (see principle in Figure 9). This technology, also known as “self-gelling” alginate, allows homogeneous distribution of the cells within a hydrogel of defined size and shape. The study demonstrated how hMSCs were differentiated resulting in up-regulation of a large number of genes associated with hyaline chondrogenesis which, for example, may be used to repair potential lesions of hyaline cartilage [95].\nFigure 9 Principle of delayed gelling of a hydrogel made from alginate only [99]. By mixing a sodium alginate solution with a dispersion of insoluble calcium alginate, using for example connected syringes, a homogeneous hydrogel can be made. Upon mixing, gel forming ions rearrange between insoluble and soluble alginate molecules resulting in gel formation.\n\n3"}