Consequently, many materials used in tissue engineering are biodegradable. For example, a cross-linked chitosan that was minimally toxic to mesothelial cells in vitro caused marked adhesions when placed in the peritoneum ( 11).Ī basic concept in tissue engineering is that the scaffold performs a time-limited architectural or other function but that, being foreign to the natural environment, it will disappear once that function has been fulfilled, leaving behind a viable purely biologic system. Of note, a material's apparent lack of cytotoxicity does not necessarily predict biocompatibility. Even quite benign matrices, adequate for drug delivery in sensitive environments such as the peritoneum can be composed of relatively cytotoxic precursors ( 9, 10). Therefore, it is important to be aware of the potential toxicity of the materials' breakdown products, as well as of residual unreacted cross-linking agents ( e.g., glutaraldehyde), reactive groups on polymers ( e.g., aldehydes, amides, hydrazides), and similar issues. Similarly, the material must be neither cytotoxic nor systemically toxic. Conversely, inflammation can lead to invasion of the construct by host cells, with untoward consequences for the transplanted cells. For example, the inflammatory reaction to relatively benign polymers such as the α-hydroxy acids ( 7), together with the acidosis that results from their breakdown, can lead to bony destruction and development of draining fistulae ( 8) here, the absolute mass of the biomaterial may play a role. Local tissue reaction to the biomaterial of a construct may be harmful to the host and/or the construct, even in the absence of immune-mediated reaction to nonautologous cellular material. For example, a formulation that is biocompatible in subcutaneous tissue might not be so in nerve or in the peritoneum ( 6). Despite this broad spectrum of potential materials, there are certain generic properties that are desirable.īiocompatibility is clearly important, although it is important to note that “biocompatibility” is not an intrinsic property of a material, but depends on the biologic environment and the leeway that exists with respect to tissue reaction. injection or minimally invasive procedure), the nature of any bioactive molecules that might be released, the need for surface functionalization, the needs of the cell types of interest in terms of porosity, and other issues. The type of materials used is also dependent on the anticipated mode of application (open implantation vs. In others, looser networks may be needed or even preferable. For example, relatively strong mechanical properties may be required in situations where the device may be subjected to weight-loading or strain, or where maintenance of a specific cyto-architecture is needed. The breadth of materials used in tissue engineering arises from the multiplicity of anatomical locations, cell types, and special applications that apply. There are also functional or structural classifications, such as whether they are hydrogels ( 1), injectable ( 2), surface modified ( 3, 4), capable of drug delivery ( 5), by specific application, and so on. The basic types of biomaterials used in tissue engineering can be broadly classified as synthetic polymers, which includes relatively hydrophobic materials such as the α-hydroxy acid, polyanhydrides, and others naturally occurring polymers, such as complex sugars (hyaluronan, chitosan) and inorganics (hydroxyapatite).
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |