Injectable gels for tissue engineering

Abstract

Recently, tissue engineering approaches using injectable, in situ gel forming systems have been reported. In this review, the gelation processes and several injectable systems that exhibit in situ gel formation at physiological conditions are discussed. Applications of selected injectable systems (alginate, chitosan, hyaluronan, polyethylene oxide/polypropylene oxide) in tissue engineering are also described. Injectable polymer formulation can gel in vivo in response to temperature change (thermal gelation), pH change, ionic cross-linking, or solvent exchange. Kinetics of gelation is directly affected by its mechanism. Injectable formulations offer specific advantages over preformed scaffolds such as: possibility of a minimally invasive implantation, an ability to fill a desired shape, and easy incorporation of various therapeutic agents. Several factors need to be considered before an injectable gel can be selected as a candidate for tissue engineering applications. Apart from tissue-specific cell-matrix interactions, the following gel properties need to be considered: gelation kinetics, matrix resorption rate, possible toxicity of degradation products and their elimination routes, and finally possible interference of the gel matrix with histogenesis. Anat

Cell and organ printing 2: Fusion of cell aggregates in three‐dimensional gels

“…A molecular weight of 510 kD was estimated by gel permeation chromatography (GPC) with a light-scattering detector. The polymer synthesis and characterization are described elsewhere (Gutowska et al, 2001).…”

“…However, up to now this technology was limited to the printing of only 2D tissue constructs. A new opportunity for extending the printing technology to three dimensions is created by the use of thermo-reversible gels (Gutowska et al, 2001). Nontoxic, biodegradable, thermo-reversible gels, which are fluid at 20°C and gel above 32°C, are used as a sort of "paper" on which tissue structures can be printed, and the cells are the "ink."…”

Transient flows in active porous media

“…1). Responsive hydrogels, i.e., hydrophilic polymers embedded and cross-linked into hydrophilic structures [4], can respond to a broad range of stimuli, e.g., pH [5][6][7][8][9][10][11][12][13], temperature [14,15], individual molecules (chemically driven) [16][17][18][19], shear stress [20][21][22][23][24][25], etc., that trigger a change of material properties. In pHinduced responses, hydrogel swelling and deswelling occurs when polymers are ionized by the dynamically changing environmental pH [5].…”

Recent Applications of Polymeric Biomaterials and Stem Cells in Tissue Engineering and Regenerative Medicine

“…27,28 Alginate has been also used extensively in hydrogel form for cell encapsulation and drug delivery, 29 as well as in tissue engineering. 30 Although many advances in alginatebased materials have been reported, translation to clinical applications will require several improvements. The purity of the input algal source is critical, along with the development of validation strategies for alginate extraction and purification processes.…”