(275e) Multicomponent Polymer Networks Enhance Mechanical Properties and Cellular Response of Hydrogel Scaffolds for Cartilage Tissue Engineering

A wide variety of hydrogel networks are under
investigation as scaffolds to support the repair and regeneration of a variety
of tissues because they provide a three-dimensional environment for cells with
water contents comparable to the native extracelullar
matrix.  However, hydrogels made of
single components typically do not have either the mechanical properties or
cellular interaction that adequately mimic the native ECM.  The approach taken in this work is to
use multiple polymeric components to more closely capture the key features of
the ECM necessary to provide the mechanical response and cytocompatibility
needed to improve cellular response for cartilage tissue engineering.

In this work, synthetic and biological polymers of
established utility in tissue engineering are combined in different fashions to
obtain desirable combinations of mechanical and biological responses.  The primary approach taken is to use
interpenetrating networks (IPNs) of agarose and poly(ethylene glycol) diacrylate
(PEGDA)  to provide mechanical
strength while supplementing the network with methacrylated
chondroitin sulfate (MCS) or other glycosaminoglycans
to improve the biological response. 
In a related approach, PEGDA is used as a crosslinker
for MCS to create a strong yet biodegradable scaffold in a single synthesis
step.

IPNs are created by encapsulating porcine
chondrocytes in thermally gelling agarose, followed
by soaking in a solution of PEGDA and MCS which is
subsequently photopolymerized to form a copolymer
network which interpenetrates the agarose constructs.
Crosslinked MCS gels are made in a similar fashion
but by photopolymerizing a solution of MCS with PEGDA
along with chondrocytes in a single step. 

For unconfined compression of hydrogel disks, the IPN
displayed a 4-fold increase in shear modulus relative to a pure PEG-DA network
(39.9 vs. 9.9 kPa) and a 4.9-fold increase relative
to a pure agarose network (8.2 kPa).
PEGDA and IPN compressive failure strains were found to be 71±17 and 74±17
percent, respectively, while pure agarose gels failed
around 15 percent strain. Similar mechanical property improvements were seen in
IPN gels with encapsulated chondrocytes.  Live/Dead assays demonstrated that the viability
of IPN-encapsulated chondrocytes was over 90% initially, but viability while in
culture drops to 45% 3 weeks after encapsulation. However, inclusion of MCS
with the PEGDA solution links it to the PEGDA network, and 3
week viability was then raised to 70%.  A continuous increase in GAG content
over this time was also observed in these networks. In principle, these IPNs
could be made biodegradable by inclusion of degradable linkers.  However, another route to degradable with
synthesized in a single step was to make a gel from a solution of  10 –
15% MCS and 1 – 3% PEGDA  (w/v%).  The combination of MCS and PEGDA substantially
increased the Young's modulus and fracture stress of MCS gel to levels
comparable to the IPNs.  The MCS
network would also be biodegradable over time while releasing lower molecular
PEG fragments that can ultimately cleared from the body.

This work was supported by the NIH
(1 R21 EB008783-01, 5 P20 RR 16475-08), and the NSF (IOS 0726425 and DMR 0805264).