INJECTABLE HYDROGELS AS BIOMATERIALS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 186

(A) (B)

Figure 6.3. A. Hydrogel implant after photopolymerizing in the subcutaneous tissue for 3
weeks. B. Construct containing stem cells encapusulated in PEG hydrogel containing HA and
TGF-B3.

PEG to provide cell-matrix interactions. A study investigated the feasibility of
incorporating cell-adhesive peptide sequences to PEG-based hydrogels to bio-
logically modulate cell adhesion. PEG macromers containing peptide sequence
Arg-Gly- Asp (RGD) as well as macromers containing RGD and its synergy site
Pro-His-Ser-Arg-Asn linked via a polyglycine sequence were used in the study to
recapitulate the native spacing of the cell adhesive protein, fi bronectin. The
biologically - modifi ed gels showed signifi cant increase in osteoblast cell adhesion,
proliferation and phenotype expression, compared to cells encapsulated in un-
modifi ed PEG gel [Benoit and Anseth, 2005]. Similarly, several other biologically
active injectable gels based on degradable PEG have also been developed for
tissue engineering applications [Nuttleman et al., 2005; Salinas et al., 2007; Hwang
et al., 2006; Lee et al., 2006].
Anseth et al., have demonstrated the effi cacy of injectable photogelling PEG-
based degradable hydrogels as protein delivery vehicles. The ability to modulate
drug release kinetics by engineering appropriate macromers and cross-linking
densities has been demonstrated [Anseth et al., 2002].
Since delivery of plasmid DNA that encodes therapeutic proteins offer
several advantages over protein delivery, studies were performed to evaluate the
feasibility of delivering DNA using injectable photo cross-linkable gels [Quick
and Anseth, 2003]. The advantages of plasmid DNA over proteins include the
greater stability of DNA in a wide range of environments, better processability
as the same procedure can be applied for administrating a wide range of plasmids
that encodes for different proteins, more control over protein release in vivo , and
considerable ease of production and purifi cation of plasmid DNA. An injectable
DNA delivery system would allow the local administration of plasmid DNA,
thereby avoiding systemic interactions which signifi cantly reduce the effi ciency
of the process. Apart from these advantages, the localized, sustained delivery
of DNA enables continuous transfections leading to prolonged foreign gene