(604c) Engineering an Adhesive and Injectable Cryogel Scaffold

Engineering An
Adhesive And Injectable Cryogel Scaffold

Devyesh Rana¹,
Samantha Johnson², Thibault Colombani¹, Nasim Annabi^1,3,4,
Sidi A. Bencherif^1,2,5,6

¹Department of Chemical Engineering,
Northeastern University, Boston, MA, USA. ²Department
of Bioengineering, Northeastern University, Boston, MA, USA. ³ Biomaterials Innovation Research Center, Brigham
and Women’s Hospital, Harvard Medical School, Boston, MA, USA. ⁴Harvard-MIT
Division of Health Sciences and Technology, Massachusetts Institute of
Technology, Cambridge, MA, USA. ⁵Harvard John A. Paulson School of
Engineering and Applied Sciences, Harvard University, Cambridge, USA. ⁶Sorbonne
University, UTC CNRS UMR 7338, Biomechanics and Bioengineering (BMBI),
University of Technology of Compiègne, Compiègne, France.

Introduction

In
the United States, 17.1 million people underwent cosmetic procedures in 2016 with
approximately 90% being minimally invasive injectable procedures for scar
revisions, tumor removals, breast reconstruction, among other conditions [1].
Subsequently, minimally invasive (injectable) procedures are in high demand
because it is safer, non-invasive, less painful, and less expensive resulting
in a $15 billion market in 2016 [2]. Biopolymers, such as hyaluronic acid (HA)
and gelatin, have recently become popular in soft tissue augmentation [3]. Especially,
polymers that can polymerize at subfreezing temperatures to form macroporous
cryogels are promising. Cryogels, similar to hydrogels, can be loaded with
cells or therapeutic agents; however, unlike hydrogels, possess elastic
sponge-like matrices with shape-retention properties, and can be molded into
any shape or size depending on defect geometry [4]. Macroporous cryogels can be
used as dermal fillers and 3D scaffolds for tissue regeneration. However, implantable
biomaterials face a number of challenges, such as poor biointegration, limited tissue
regeneration, and poor anchoring to target tissues, which may be improved by
increasing their adhesion to the surrounding native tissues [5]. To improve tissue
adhesion of biomaterials, an interest in naturally-inspired bioadhesive
biopolymers, including dopamine (DOPA)-conjugated polymers has risen [6]. However,
many strategies neglect the mechanism of oxidation of DOPA during its polymerization,
whereby reactive oxygen species (ROS) are formed – compromising bioadhesion and
causing toxicity. Therefore, this project aims to develop a ROS-free injectable
bioadhesive cryogel scaffold, comprised of HA and gelatin conjugated with
mussel-inspired polydopamine (PDA).  

Materials
& Methods

HA, gelatin, DOPA, and L-glutathione (GSH) were
obtained from Sigma Aldrich and used without further purification. Methacryloyl
gelatin (GelMA) and methacrylated HA (HAGM) were prepared according to previously
described procedures [4, 7, 8]. HAGM and acrylated DOPA (ADOPA) or GelMA and ADOPA
were cryopolymerized at -20°C in an aqueous solution containing a free radical
initiator system. Mechanical and adhesion properties were tested using an
Instron 5944 mechanical tester. Cell studies (Live/Dead, Actin/Dapi, Presto
Blue, flow cytometry) were assessed using NIH 3T3 fibroblast cells and isolated
T Cells from murine splenocytes.

Results
& Discussion

Our preliminary results on the compressive properties
of HAGM-co-ADOPA and GelMA-co-ADOPA cryogels indicate that the
compressive moduli are proportional to the total polymer content. However,
increasing the fraction of ADOPA did not significantly impact the compressive
moduli (Figure 1a). Moreover, due to the macroporous nature of cryogels, up to
80% gel compression was achieved, enabling their injection through an 18G
needle. Adhesive properties were determined using an American Society for
Testing and Materials wound closure standard F2458-05 for adhesives. Our data
show that increasing polymer concentration does not significantly alter
adhesion; however, increasing ADOPA concentration drastically improves adhesion
strength (Figure 1b). Furthermore, cell studies with GSH, a substance that was
introduced to prevent DOPA oxidation showed over 80% cell viability of both T
Cells and 3T3 cells, unlike 0-10% viability without the antioxidant.

Conclusion

We have developed a non-invasive bioinspired cryogel
scaffold with optimized physical properties for soft tissue engineering, while
minimizing negative side effects of dopamine oxidation. Including antioxidants
in the gel formulation could further improve the adhesive performance of
DOPA-containing hydrogels which may enhance tissue biointegration and
regeneration. 

Figure 1. Mechanical and adhesive properties of HAGM-co-ADOPA
and GelMA-co-ADOPA cryogels at varying concentrations of ADOPA. a) Compressive
moduli for HAGM-co-ADOPA and GelMA-co-ADOPA cryogels show no significant change
in moduli as ADOPA content increases. b) Adhesion strength as measured by wound
closure test for both types of cryogels show an increase in adhesion strength
as ADOPA content increases.

Acknowledgments

N.A.
acknowledges the support from the American Heart Association (AHA,
16SDG31280010), and National Institutes of Health (NIH) (R01EB023052;
R01HL140618), Northeastern University, and the startup funds provided by the
Department of Chemical Engineering, College of Engineering at Northeastern
University. S.B. acknowledges the support from Northeastern University Seed
Grant/Proof of Concept Tier 1 Research Grant.

References

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