Biomaterials25(2004)887–894 Arapid-curingalginategelsystem:utilityinperiosteum-derived cartilagetissueengineering MollyM.Stevens a ,HalaF.Qanadilo a ,RobertLanger a ,V.PrasadShastri b, * a Department of Chemical Engineering, Massachusetts Institute of Technology (MIT), 45 Carleton Street, Cambridge, MA 02139, USA b Department of Materials Science and Engineering, School of Medicine, University of Pennsylvania, 3231 Walnut Street, Philadelphia, PA 19104, USA Received16March2003;accepted14July2003 Abstract In this study, we have developed a rapid-curing alginate gel system and demonstrated its utility as a scaffold for periosteum- derived chondrogenesis for articular cartilage tissue engineering applications. A homogeneous mechanically stable gel was formulatedbyinducinggelationofa2%(w/v)solutionofahighGcontentalginate(65–75%G)witha75mm solutionofCaCl 2 . Thegelexhibitednear-elasticbehavioratlowlevelsofdeformation(15%, R 2 ¼ 0:996),Young’smodulusof0.1770.01MPa,and rapidgelationkinetics(o1mintocompletion).Theinvitrocellcultureofchondrocytesinthegelyieldedalginate/cellconstructs thatlackedthecontinuous,interconnectedcollagen/proteoglycannetworkofhyalinecartilage.Inaddition,wehavedemonstrated thatthisgelsystemiscapableofsupportingperiosteum-derivedchondrogenesis.Weobservedthatwhenwhole-tissueexplantsof periosteum were cultured in vitro within the gel, after 6 weeks, significant quantities (>50%) of the total area of the periosteal explantswascomposedofcartilagethatwashyaline-likeinappearanceandcontainedcartilage-specificproteoglycansandtype-II collagen.Itisenvisionedthatsuchexplantscouldbetransplantedorregeneratedinvivowithinthebiodegradablealginatematrix forthetreatmentofpartialorfull-thicknessdefectsinarticularcartilage.Importantly,theinjectabledeliveryofthegelcouldbeused infillingcomplexdefectsinthearticularsurfaceviaminimallyinvasiveprocedures. r 2003PublishedbyElsevierLtd. Keywords: Alginate;Chondrocyte;Cartilagetissueengineering;Transforminggrowthfactor(TGF) 1. Introduction Alginates are naturally derived polysaccharide block copolymers composed of regions of sequential b-d- mannuronicacidmonomers(M-blocks),regionsof a-l- guluronic acid (G-blocks), and regions of interspersed MandGunits(see Fig.1).ThelengthoftheM-andG- blocks and sequential distribution along the polymer chainvariesdependingonthesourceofthealginate [1]. Alginates undergo reversible gelation in aqueous solu- tion under mild conditions through interaction with divalent cations such as Ca 2+ that can cooperatively bind between the G-blocks of adjacent alginate chains creatingionicinterchainbridges [2]. Alginate gels have been extensively studied for cartilagetissueengineeringapplicationsasamatrixfor cellularencapsulationandculture [3–6].Thealginategel allows chondrocytes to maintain their normal differ- entiatedphenotypeandsynthesizemacromoleculessuch as cartilage-specific proteoglycans and collagens [7–9]. However,intheinvitroenvironment,evenafterseveral weeksofculture,suchalginate/cellconstructsappearto lackthecontinuous,interconnectedcollagen/proteogly- can network found in hyaline cartilage and have thus not found applicability clinically in the treatment of defectsinthearticularsurface [10]. Weproposethatthecultureofperiostealtissuewithin analginategelmatrixmaybeofutilityinthegeneration of cartilaginous constructs to treat articular cartilage defects. It is well established that culturing rabbit periosteuminagarosegelinthepresenceoftransform- ing growth factor-b1 (TGF-b1) promotes chondrogen- esis, due to the proliferation and differentiation of the chondrogenic precursor cells located in the cambium layeroftheperiosteum [11,12].However,tothebestof our knowledge, the use of more biocompatible gels to ARTICLE IN PRESS *Corresponding author. Tel.: +1-215-590-7524; fax: +1-215-590- 6633. E-mail address: shastriv@seas.upenn.edu(V.PrasadShastri). 0142-9612/$-seefrontmatter r 2003PublishedbyElsevierLtd. doi:10.1016/j.biomaterials.2003.07.002