Of the storage modulus within the linear visco

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of the storage modulus within the linear visco-elastic rangealso represents the strength of the material, i.e. the force thatwithstands deformation (G0LVER=mean of G0within thelinear visco-elastic range). As shown in Fig.5the strengthof the gels could be controlled by the DM of the precursormolecules and by the mass fraction applied. G0correlatedpositively with increases in the DM and also with increasesin polymer concentration.In contrast to many hydrogels described in literature[3234],theGel-MAAmgelspreparedinthisstudyachieved G0in the medium kPa range. G0of the strongestgels prepared was 368 kPa. Moduli of various natural tis-sues also range in the kPa area, e.g. canine kidney cortexand medulla with*10 kPa [17], or human nasal cartilagewith234 kPa [18,19].Hyalinecartilage, oneofthestrongest hydrogel materials, holds G0=*800 kPa [20].Therefore, the highly crosslinked Gel-MAAm hydrogelsdescribed in this study are considered to be promisingmaterial systems with a view to the generation of tissueengineering matrices at the ‘‘stiffer end’’ of soft tissues.3.6 In vitro cytocompatibilityWith regard to applications in e.g. Advanced TherapyMedicinal Products (ATMPs) preliminary in vitro cyto-compatibilitytestingwasperformed,investigatingmaterialextractsanddirectcell-materialinteractionswith porcine chondrocytes. For direct cell-material con-tact cells were seeded onto Gel-MAAm2gels with dif-ferent gelatin mass fractions. Cell adhesion, cell viabilityand cell confluency were evaluated by performing live/dead staining on day one (d 1) and on day six (d 6).Figure6shows representative fluorescence images of thestained cells and Fig.7gives the results of the countingof viable cells on the hydrogels. Very few dead cellsweredetectedonthegelsindependentofthemassfraction. Cytotoxicity assays according to extract testingsbased on DIN EN ISO 10993-5 were carried out andconfirmed the favorable cytocompatibility of the Gel-MAAm hydrogels (Fig.8).Chondrocyteadhesion(d 1)wasweakestonthe10 wt% hydrogels and increased with increasing gelatincontent. Cell spreading was rarely observed on 10 wt%gels (round shaped cells) but increased with increasinggelatin content (flat cells). As gelatin provides RGDmotifs,assuminglythenumberofRGDmotifswasincreased as the increase of the gelatin mass fraction wasincreased. This might have accounted for the improvedadhesion of chondrocytes to the gels of higher massfraction. Yet, various authors have shown that materialproperties such as the material strength also influencedcellbehavior[3537].Therefore,thedifferencesinmaterial strength may have also played a role in the cells’adhesion preferences. Evaluation of the cells on day six(d 6) revealed that the cell spreading had increased whilethecellnumberremainedfairlyunchangedonthehydrogels (Fig.7). The non-proliferative behavior mightbe considered to confirm the cytocompatibility of thematerial for chondrocytes, which natively stay in a qui-escent state. We therefore conclude that Gel-MAAmhydrogels are potential biomaterials for medical applica-

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Term
Spring
Professor
Berrettoni
Tags
Test, crosslinked hydrogels

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