Enzymatic degradation of hyaluronan hydrogels with different
capacity for in situ bio-mineralization
Science for Life Laboratory, Division of
Polymer Chemistry, Department of
om, Uppsala University,
College of Chemistry and Materials Science,
Northwest University, Xi’an, Shaanxi
710069, People’s Republic of China
Dmitri Ossipov, Science for Life Laboratory,
Division of Polymer Chemistry, Department
om, Uppsala University,
European Community’s Seventh Frame-
work Programme (BIODESIGN)
In situ cross-linked hyaluronan (HA) hydrogels with different capacities for biomineralization were
prepared and their enzymatic degradation was monitored. Covalent incorporation of bisphospho-
nates (BPs) into HA hydrogel results in the increased stiffness of the hydrogel in comparison with
the unmodified HA hydrogel of the same cross-linking density. The rate of enzymatic degradation
of HABP hydrogel was significantly lower than the rate of degradation of control HA hydrogel in
vitro. This effect is observed only in the presence of calcium ions that strongly bind to the matrix-
anchored BP groups and promote further mineralization of the matrix. The degradation of the
hydrogels was followed by noninvasive fluorescence measurements enabled after mild and chemo-
selective labeling of cross-linkable HA derivatives with a fluorescent tag.
biomineralization, bone tissue engineering, degradation, fluorescent labeling, hyaluronan hydrogel
Bone is mainly composed of mineral (nanostructured hydroxyapatite)
and collagen fibers along with a fraction of other proteins and polysac-
As a supporting tissue of our human body, bone undergoes
constant remodeling throughout our life time.
Although bone has the
ability for self-healing, it is insufficient in case of large bone defects.
Regeneration of bone in such cases represents a challenge for orthope-
dic and reconstructive surgeons. Autologous bone grafting is consid-
ered as the “gold standard” in bone replacement.
However, a limited
supply of bone grafts, long complicated surgical procedures, and con-
comitant complications are the drawbacks that drive the research to
find alternative solutions to bone grafting. Bone tissue engineering
(BTE) is a promising technology that has a potential to substitute for
the current clinical procedures in bone regeneration/substitution.
Engineering of bone requires cells that can produce bone (bone
progenitor cells), a scaffold that provides mechanical support for the
cells, and signaling molecules such as bone morphogenetic proteins
(BMP-2 and BMP-7) that instruct the progenitor cells to differentiate
into bone cells.
Mechanical properties for a BTE scaffold should
ideally match those of the bone as well as the scaffold should be nei-
ther toxic to the cells nor giving inflammatory response to the host. In
addition to biocompatibility, the scaffold should be osteoconductive,
provide the biomaterial–cell interaction (adhesion), conduct the cell
migration and proliferation.
Importantly, the scaffold should resorb in
concert with the new tissue growth.
Study of factors that influence
the rate of degradation is therefore important for the design of an ideal
The requirement of biodegradability has determined the focus of
majority of studies on degradable polymers, both natural biomacromo-
lecules (collagen, silk fibroin, hyaluronic acid, chitosan, etc.)
synthetic polymers such as polylactide (PLA),
colic acid) (PLGA).
Hyaluronan (HA) is a natural polysaccharide com-
ponent of extracellular matrix which was widely used in the treatment
of cartilage disease.
Relying on its biocompatibility, cross-linked hya-
luronan (HA hydrogels) was widely studied for tissue (bone, cartilage)
engineering as a matrix for cells cultures, a delivery vehicle for growth
factors, or a combination thereof. Though natural HA is antiadhesive
and not bone conductive, chemical modifications of this biopolymer
can impart the required properties and make HA hydrogels more effec-
tive for BTE.
Bisphosphonates (BPs) are analogous of pyrophos-
phate, in which the bridging oxygen is replaced by carbon atom.
First, bisphosphonates were discovered as molecules that suppress
bone resorption and were then used as drugs for osteoporotic
Because of its high affinity to bone mineral hydroxyapatite,
bisphosphonates have also been considered as bone-targeting groups
Liyang Shi and Yu Zhang contributed equally to this study.
2017 Wiley Periodicals, Inc.
Received: 17 May 2017
Revised: 24 October 2017
Accepted: 31 October 2017