(210f) Antibacterial and Angiogenic Multifunctional Adhesives for the Treatment of Chronic Wounds

Antibacterial and Angiogenic Multifunctional
Adhesives for the Treatment of Chronic Wounds " new roman>

Bahram Saleh^1,2, Thomas J. Webster^1,2*

text-align:center;line-height:normal">¹Department of Chemical Engineering,
Northeastern University, Boston, MA 02115

text-align:center;line-height:normal">²Nanomedicine Science and Technology Center,
Northeastern University, Boston, MA 02115

text-align:center;line-height:normal">

Statement of Purpose: Diabetes mellitus is an important health
problem that affects millions of people worldwide. Diabetic patients suffer
from skin chronic wounds, which do not heal in a timely and orderly fashion.
These wounds are characterized by impaired vascularization, uncontrolled
inflammation, and bacterial infection. In particular, excessive inflammation
impairs the healing process, reduces the protective role of immune cells, and
could lead to bacterial infection. On the other hand, bacterial colonization exacerbates
prolonged inflammation and causes tissue injury due to the interaction of the
host with multiplying bacteria. Moreover, the decreased blood supply to full thickness wounds impairs the
immune response by reducing the infiltration of leukocytes and macrophages at
early stages of inflammation. Therefore,
there is an unmet clinical need to develop innovative therapeutic strategies to
overcome these overlaping challenges in chronic wounds. We designed a
biocompatible, biodegradable, and photocrosslinkable
adhesive hydrogels by introducing mussel adhesive moiety (catechol) and
methacrylic anhydride (MA) to a naturally derived polymer, gelatin. Also, we
developed an antimicrobial-hybrid Zinc-Oxide@Gold (ZnO@Au) tetrapods. By dispersion
of these tetrapods in the 3D networks of the hydrogels
we attain nanocomposite hydrogels that can be applied readily on the wound site
and be crosslinked in a few seconds. Moreover, ZnO@Au
tetrapods can enhance angiogenesis in the wound area
according to proangiogenic properties of ZnO.

Methods: " new roman>
Antimicrobial and angiogenic tetrapods were
synthesized using a wet chemical route and coated with PEG-DA (dopamine
conjugated to 500 kDa polyethyleneglycol)
to conclude water soluble tetrapods. Catechol
modified photocrosslinkable pre-polymer for the
hydrogel formation was synthesized in two consecutive reactions. The
crosslinking reagents BOP ((Benzotriazol-1-yloxy) tris(dimethylamino)phosphonium
hexafluorophosphate) and HOBt (Hydroxybenzotriazole)
were used to conjugate catechol groups to the gelatin backbone and then
catechol modified gelatin was precipitated and washed in excess acetone. Next,
the catechol modified gelatin was dissolved in carbonate/bicarbonate buffer
(pH=9.5) and methacrylated in a direct reaction with
methacrylic anhydride. To prevent the undesired crosslinking during the
reaction, we performed the reactions under an inert atmosphere of nitrogen.
Different concentrations of tetrapods were mixed with
hydrogel precursors in PBS (phosphate buffer saline), containing triethanolamine
and N-vinylcaprolactam. Eosin Y disodium salt was
dissolved separately in phosphate buffer saline and used as the photoinitiator. The tetrapod/hydrogel precursor solution
was then mixed with Eosin Y and photopolymerized. The adhesive properties of hydrogels
were assessed using standardized tests (e.g., ASTM F2392-04), and compared to
commercially available tissue adhesives such as Evicel
and Coseal, Colony counting test was performed using
different concentration of tetrapods and tetrapods in hydrogels to assess the antimicrobial
properties of them. Human dermal fibroblast (HDF) cells were used as model
cells to measure the cytotoxicity of the tetrapods. Next,
hydrogels were formed on the membrane of transwell
inserts, and the inserts were placed into the wells containing the human umbilical
vein cells (HUVECs). The intensity of CD31 expression on HUVECs was quantified
from fluorescent images of anti-CD31 stained cells.

Results: font-family:" minor-latin new roman>
We first synthesized tetrapod loaded adhesive hydrogels using varying
concentrations of tetrapods. We optimized the
mechanical and physical properties of the engineered adhesives for skin tissue
regeneration (elastic modulus of around 130 kPa, extensibility more than 100).
Our results showed strong adhesion of tetrapod loaded hydrogels in a wound
closure test using pig skin as substrate. The adhesion strength of the
tetrapod/hydrogels (148.4 ± 14.5 font-family:" minor-latin new roman>kPa)
was significantly higher than those commercially available adhesives, Evicel Calibri;mso-fareast-theme-font:minor-latin">® 11.0pt;font-family:" minor-latin new roman>
(i.e., 26.3 ± 4.7 kPa) and Coseal minor-latin">® (19.4 ± 17.3 kPa).  Tetrapods showed antibacterial activity against different
multidrug resistant bacteria strains in the concentration as low as 10 minor-latin">µg/ml. Quantification of the
intensity of fluorescently labeled CD31 on HUVECs demonstrated around 1400
times increase in the expression of CD31, as compared to control HUVECs
incubated in culture media, at day 1 and 3 of treatment with tetrapods.

Conclusions: 11.0pt;font-family:" minor-latin new roman>
Our results demonstrated that the engineered hydrogels can be potentially used
as a multifunctional adhesive, with the ability to control infection, promote
angiogenesis, and consequently tissue healing. In addition, due to its strong
adhesion to skin and rapid closure of the wound, engineered hydrogels can cover
skin wounds in any shape and size, especially in cases that no suture can be
used.