Chemistry Reference
In-Depth Information
possible formation of bacterial colonies, or to maintain the action of analgesics for
controlled period of time. HA can have, if compared to other polymers already
employed as coating films, the potentiality of antifouling properties, thanks to
its poor ability to allow bacteria adhesion. In this patent, in particular, HA-g
polyesters are proposed to form, at the opportune concentration in aqueous envi-
ronment, physical hydrogels with proper rheological behavior to be, just before the
surgical intervention, mixed with drug solution and then applied on prosthesis
surface [
62
,
63
].
8.3.2 HA-Graft-Synthetic Polymers to Obtain Scaffolds
for Tissue Engineering
Thanks to its structural and bio-inductive role in the ECM, HA finds a wide
application for the production of scaffolds to support cell growth or to obtain
their delivery to a damaged tissue or organ. Most of the examples employ HA
graft copolymers to change physicochemical properties of starting HA, with the aim
to improve hydrolytic and mechanic resistance or to produce self-assembled physi-
cal hydrogels or to obtain copolymers with peculiar solubility in organic solvents
better suitable for processing strategies.
Examples in regenerative medicine include the induction of chondrocytes
expansion and differentiation or [
64
] the employ of in situ implantable HA-based
biomaterials to delivery mesenchymal stem cells for the treatment of full-thickness
defects [
65
]. Physical hydrogels, obtained by aqueous dispersion of HA-alkyl chain
derivatives, for instance, HA-C12 and HA-C18, were proposed as biomaterials to
delivery primary chondrocytes into full-thickness articular defects [
66
].
Dispersions of such copolymers in physiological solution at concentration equal
to 1 % w/v produced viscoelastic injectable hydrogels that were loaded into rat
articular cartilage defects and tested for their property to improve cartilage repair in
comparison with hybrid sponges made of Alginate/HA and Alginate/HAC18.
Authors demonstrated that physical hydrogels made of HA-C18 copolymer were
suitable to stimulate bone regeneration; however, better results, in terms of GAG
and collagen neosynthesis, were obtained with implants made of HA-C18 and
Alginate. Major concerns about the use of physical HA hydrogels are
however related to the lower stability due to a possible dissolution in the aqueous
fluids if compared with chemically cross-linked HA-based materials. Burdick
and colleagues designed HA photocrosslinkable hydrogels for cartilage regeneration
obtained mixing in different ratio-methacrylated HA (HA-MA) derivatives
and HA-g-polycaprolactone-methacrylated (HA-g-PCL-MA) derivatives
(see
Scheme
8.9
)[
67
].
Compared to the photocrosslinked HA-MA derivatives, HA-g-PCL-MA cross-
linked derivatives allow a faster degradation due to the hydrolysis of the grafted
polyester. Indeed HA-methacrylated cross-linked hydrogels are characterized by a
