Biomaterials Science Blog

This study identifies new surfaces optimized for human pluripotent stem cell expansion using a high-throughput polymer microarray chip.

The biomaterials community is moving toward using high-throughput tools to evaluate cell-material interactions at an unprecedented rate. For instance, polymer microarrays have become popular for identifying candidate surfaces that elicit a desired biological response. Using a single microarray chip, low volumes of polymer solution are deposited in a grid-like format using robotic ink-jet or contact printing. The chip is polymerized to manufacture a polymer microarray. After fabricating the microarray, cells are deposited directly onto the spots of the chip and cultured to determine materials that support a specific cell phenotype.

At the Laboratory of Biophysics and Surface Analysis at the University of Nottingham, Celiz et al. evaluated human pluripotent stem cell growth on a polymer microarray containing 141 varieties of (meth)acrylate and (meth)acrylamide photo-curable polymers. To maximize the diversity of the microarray, monomers containing a variety of nitrogen, fluorine, oxygen, aromatic, and aliphatic side chains were utilized.  Monomers were selected on their ability to be photo-polymerized by UV irradiation. The surface chemistry after polymerization was assessed using ToF-SIMS, and water contact angle measurements determined the surface wettability of each spot.

Partial least squares analysis (PLS) was utilized to correlate surface chemistry and wettability to identify surfaces that would yield high human pluripotent stem cell (hPSC) adhesion. Of the 141 surfaces screened in the array, 47 polymers supported hPSC attachment. Interestingly, no relationship was observed between surface wettability and cell adhesion, indicating wettability of a surface is not sufficient to predict hPSC adhesion. PLS analysis subsequently identified correlations between polymer surface chemistry and experimental hPSC adhesion. Additional experiments confirmed that increased protein adsorption on specific polymer spots was a contributor to cell adhesion to the polymer surface.

Collectively, the polymer array developed in this study was able to operate as a high-throughput tool to identify surfaces amenable to hPSC adhesion. Moving forward, polymer microarrays have the potential to identify a broad library of surfaces capable of supporting sustained hPSC growth and pluripotency.

Chemically diverse polymer microarrays and high throughput surface characterization: a method for discovery of materials for stem cell culture
A. D. Celiz, J. G. W. Smith, A. K. Patel, R. Langer, D. G. Anderson, D. A. Barrett, L. E. Young, M. C. Davies, C. Denning and M. R. Alexander
Biomater. Sci., 2014, Advance Article DOI: 10.1039/C4BM00054D

Brian Aguado is currently a Ph.D. Candidate and NSF Fellow in the Biomedical Engineering department at Northwestern University. He holds a B.S. degree in Biomechanical Engineering from Stanford University and a M.S. degree in Biomedical Engineering from Northwestern University. Read more about Brian’s research publications here.

Follow the latest journal news on Twitter @BioMaterSci or go to our Facebook page.

Researchers have demonstrated that controlling nanoparticle shape and packing can impact how cancer therapeutics interact with cells.

Photodynamic therapy is an innovative emerging therapy for cancer.  This therapeutic modality consists of introducing light-activated molecules known as ‘photosensitizers’ into cancer cells.  When activated with light, these photosensitizers are able to produce toxic molecules within the cells (also known as reactive oxygen species or ROS) that can eventually cause cancer cell death.  Photosensitizers are often introduced into the cells using nanoparticle carriers. In order for effective cell death to occur, ROS must be formed within the nanoparticles and then diffuse out of the nanoparticles into the cells.

In this article, Chu et al. have designed silica-based nanocarriers that can control how photosensitizers interact with cells. They previously found that when photosensitizer-loaded nanoparticles were packed more densely, the amount of ROS that was released decreased.  In contrast, more loosely packed nanoparticles allowed for greater release of ROS into cells. In this study, the researchers designed a third type of nanoparticle consisting of a gold nanorod coated with dense silica. They found that this third type of nanoparticle released photosensitizers much more efficiently than the either densely packed or loosely packed silica-only particles. They also discovered that the nanorod-based particles produced a different distribution of ROS as compared to the loose or dense silica-only particles. When cells were treated with these nanoparticles, loosely-packed silica particles and the nanorod-based particles demonstrated dramatic decreases in cell-viability due to the action of the photosensitizers. Further, while the silica-based loose and dense particles caused cells to die via a programmed cell death (apoptotic) route, the nanorod-based particles caused cell death via cell injury resulting in premature cell death (necrosis).

These experiments suggest that controlling the composition and shape of the nanoparticles that carry photosensitizers to cancer cells can alter both the number of cancer cells killed as well as the mechanism by which the cells die. This work has implications for future photodynamic therapeutic strategies.

Debanti Sengupta recently completed her PhD in Chemistry from Stanford University.  She is currently a Siebel postdoctoral scholar at the University of California, Berkeley.

Follow the latest journal news on Twitter @BioMaterSci or go to our Facebook page.

The cerebellum is a region in the brain responsible for regulating motor control and cognitive functions such as attention and language. During development of the cerebellum (and of other tissues), cells interact with the surrounding microenvironment known as the extracellular matrix (ECM). These neuron-ECM interactions regulate neuronal differentiation, growth, formation of synapses, and neurite outgrowth. Specifically, ECM components including collagen and laminin-1 (lam-1) are known to regulate the alignment, migration, and neurite outgrowth of Purkinje cells (PCs). However, the dual signaling roles of collagen and laminin-1 during cerebellar tissue development have not been fully explored.

Dr. Shantanu Sur, a postdoctoral fellow in Prof. Samuel Stupp’s laboratory at Northwestern University, has collaborated with Dr. Thomas Launey at the RIKEN Brain Science Institute in Japan to explore cerebellar tissue development using biomaterial hydrogels. Sur has developed an artificial matrix consisting of collagen and synthetic peptide amphiphile (PA) molecules presenting IKVAV, the peptide on laminin-1 responsible for cell adhesion and neurite outgrowth. Sur et al. evaluated the spatiotemporal expression of lam-1 and collagen in rat cerebellums during PC development (embryonic to post-natal) using histology and immunostaining. Given the changes in the ratio of lam-1 to collagen during PC formation and growth, these results suggest the dynamic involvement of these ECM proteins in forming the neural architecture of the cerebellum.

Using a biomimetic approach to mimic the critical lam-1 to collagen ratio, Sur proceeded to model the dynamic nature of the ECM during PC development with a synthetic collagen-PA hydrogel. Collagen (types I-V) and IKVAV-PA molecules were mixed together in solution at varying concentrations and gelled using ammonia vapor. This simple method allowed Sur to evaluate the density of PC growth, axon guidance, and dendrite morphology in gels using a wide array of collagen and IKVAV-PA concentrations. Strikingly, effects on PC phenotype were observed as a function of the collagen:IKVAV-PA ratio and not the absolute concentrations of each ECM component within the matrix.

Sur comments that the hybrid matrix provides an easily tunable environment to enable the in vitro testing of the role of ECM signals on neuronal maturation. “Our study shows that the optimal ECM-derived cues for neurons change at specific stages of development,” Sur says. “This observation will drive us to work on the design of a dynamic matrix where the extracellular signals delivered to the neuron can be tuned spatiotemporally.” Additionally, the collagen/IKVAV-PA gels may be used to identify cell-ECM interactions during the development of other tissue types, given the simplicity of the technique.

Collectively, this study demonstrates the exciting use of engineered matrices to evaluate spatiotemporal cell-ECM interactions, with the hopes to further elucidate mechanisms of tissue development.

Synergistic regulation of cerebellar Purkinje neuron development by laminin epitopes and collagen on an artificial hybrid matrix construct
Shantanu Sur, Mustafa O. Guler, Matthew J. Webber, Eugene T. Pashuck, Masao Ito, Samuel I. Stupp, and Thomas Launey
Biomater. Sci., 2014, Advance Article, DOI: 10.1039/C3BM60228A

Brian Aguado is currently a Ph.D. Candidate and NSF Fellow in the Biomedical Engineering department at Northwestern University. He holds a B.S. degree in Biomechanical Engineering from Stanford University and a M.S. degree in Biomedical Engineering from Northwestern University. Read more about Brian’s research publications here.

To keep up-to-date with all the latest research, sign-up to our RSS feed or Table of contents

Engineering tissue mimics in vitro using cells and materials is one of the core goals of biomaterials science. To develop a tailored cell culture environment, natural and/or synthetic hydrogels are used to mimic the extracellular matrix. Cells are embedded in a hydrogel matrix in a process known as “encapsulation.” During encapsulation, polymers in solution are chemically or physically cross-linked to immobilize cells in a mesh-like structure. The cell-loaded hydrogels are subsequently used for various regenerative medicine applications.

Researchers at the University of Maryland have developed a novel encapsulation technique for embedding cells in hydrogel materials. Instead of passively encapsulating cells in the polymer mesh, cells serve as “active structural elements” and are connected to the polymer chains. Using hydrophobically-modified (hm) alginate and chitosan, hydrophobic regions along the polymer chains are physically embedded in the hydrophobic cell membrane. The cells serve as struts to link together the polymer mesh. Rheological studies were performed to confirm the sol-gel transition when hm-polymers were combined to form gels (unmodified polymer controls did not form gels). To show the versatility of the system, various cell types were used to form gels with hm-alginate and hm-chitosan, including human umbilical vein endothelial cells (HUVECs), MCF7 breast cancer cells, and blood cells.

Analogous to building block toys such as Legos, the non-covalent hm-polymer and cell interactions are reversible with the addition of excess hydrophobic binding “pockets.” Using α-cyclodextrin, the gels are immediately transformed into free-flowing solutions (confirmed using rheology). The α-cyclodextrin serves to sequester the hydrophobic tails of the hm-polymer and gently release the cells from the mesh. Interestingly, α-cyclodextrin does not affect cell viability because the molecule is not large enough to bind two-tailed lipids of the cell membrane. Viability of the cells was confirmed before and after the gentle release from the gel, indicating that cell membranes remained unharmed during the gel reversal process.

Taken together, hm-polymers could serve as a unique technique to embed and release cells from a hydrogel matrix. Using cells as building blocks is highly desirable for several applications including 3D cell culture models and injectable cell therapies.

Reversible gelation of cells using self-assembling hydrophobically-modified biopolymers: toward self-assembly of tissue
Vishal Javvaji, Matthew B. Dowling, Hyuntaek Oh, Ian M. White and Srinivasa R. Raghavan
Biomater. Sci., 2014, Advance Article, DOI: 10.1039/C4BM00017J

Brian Aguado is currently a Ph.D. Candidate and NSF Fellow in the Biomedical Engineering department at Northwestern University. He holds a B.S. degree in Biomechanical Engineering from Stanford University and a M.S. degree in Biomedical Engineering from Northwestern University. Read more about Brian’s research publications here.

To keep up-to-date with all the latest research, sign-up to our RSS feed or Table of contents

The ability to control neuronal behavior and growth is highly sought among researchers interested in neuro-regenerative medicine.  Over the past two decades, it has become widely accepted that modifications in a substrate’s physical surface topography can influence the growth patterns of seeded neurites.  However, the advent of techniques that are capable of fabricating nano-textured surfaces has revealed that the magnitude of this influence may be much greater than originally thought.  In this paper, a group of scientists from KAIST review a number of recent advances in the development of nano-topographies which can influence neuronal behavior.

Many of these advances revolve around improving neural adhesion, providing directional guidance for axonal growth, and accelerating the speed of neurite outgrowth.  Numerous groups have become interested in using nanowire arrays to improve neuron adhesion, eliminating the need for any additional surface coating.  In a 2010 Nano Letters publication, Xie et al. were able to demonstrate the creation of a silicon nanopillar array that could selectively pin cortical neurons to desired locations.  Any cells that were seeded onto, or later came into contact with the nanopillars became immobilized, enabling a long-term observational study of their electrical activity.  Other groups have found that nanofiber bundles make excellent scaffolding materials for neurons and can be used to direct and align neurite growth.  In addition, when compared to planar surfaces, nanofiber-based substrates were shown to increase the speed at which initial neurite formation occurred.

Although the benefits of nano-textured substrates are clear, the mechanism by which neurons translate these physical cues into biological signals is still something of a mystery.  However, many of the reviewed papers suggest that actin filaments and focal adhesions (FA) play a major role.  One group found that f-actin often forms networks which resemble the shape of the underlying surface topography and that the impairment of f-actin polymerization completely erases any ability neurons have to respond to nanotopographical cues.  Other groups have demonstrated that the size of FA is proportional to the degree of neuronal alignment with underlying surface structures.  An increase in alignment leads to a larger FA which ultimately results in a more stable neurite attachment.

Regardless of the mechanism, it has become clear in recent years that nanotopography is an important parameter for the controlled manipulation of neuronal behavior.  In this mini-review, Kim et al. are able to provide an interesting overview on the progress that has already been made within this area.

Neurons on nanometric topographies: insights into neuronal behaviors in vitro
M. Kim, M. Park, K. Kang, and I.S. Choi.
Biomater. Sci., 2014, 2, 148-155 DOI: 10.1039/C3BM60255A

Ellen Tworkoski is a guest web-writer for Biomaterials Science.  She is currently a graduate student in the biomedical engineering department at Northwestern University (Evanston, IL, USA).

Follow the latest journal news on Twitter @BioMaterSci or go to our Facebook page.

To keep up-to-date with all the latest research, sign-up to our RSS feed or Table of contents alert.

According to the World Health Organization, cardiovascular disease causes 17.3 million deaths worldwide, with projections reaching 23.3 million deaths by the year 2030. Unfortunately, heart attack patients still have limited therapeutic options, commonly relying on left ventricular assist devices (LVADs) and heart transplantation. To provide more modern therapies, physicians have turned to tissue engineers to develop biomaterials that enable local regeneration of the heart to restore function and ideally improve the quality of life for the patient.

Professor Karen Christman’s lab at the University of California – San Diego (UCSD) is exploring methods to fabricate injectable hydrogels for cardiac repair. In the present study, the lab has developed human myocardial matrix (HMM), and compared the material properties of HMM to previously fabricated porcine myocardial matrix (PMM). The materials are made directly from the decellularized extracellular matrix (ECM) from human and porcine hearts. The decellularized matrices are composed of the natural structural proteins found in the heart, which make the ideal environment needed to promote cardiac cell growth and maturation.

To produce HMM, seven human hearts with a patient age range of 41-69 years were decellularized using sodium dodecyl sulfate (SDS) and a series of lyophilization, milling, and digestion steps.  Due to the dramatic patient-to-patient variability between hearts, over 50% of the HMM solutions were not able to self-assemble into hydrogels at physiological conditions, unlike self-assembling PMM hydrogels. The irreproducibility of HMM hydrogel fabrication is likely due to differences in protein composition between HMM and PMM. Using mass spectrometry to identify the proteins present in the decellularized matrices, the authors showed that porcine and human hearts have inherent differences in their matrix composition.

Although HMM did not produce hydrogels reproducibly, the matrix was still useful for in vitro cell culture protocols. Using PMM and HMM as coatings for cell culture plates, increased proliferation of rat aortic smooth muscle cells (RASMCs) and human coronary artery endothelial cells (HCAECs) was observed on HMM coated plates compared to PMM coated plates. Additionally, cell cultured on both HMM and PMM matrices showed increased expression of early cardiac transcription factor markers in human fetal cardiomyocyte progenitor cells (hCMPCs). This result indicates that biochemical cues from the HMM and PMM proteins may enhance early stages of cardiomyocyte differentiation.

Even though HMM was shown to not be a likely candidate for clinical translation due to large variability between samples, PMM injectable hydrogels are still a promising alternative for improving cardiac repair in vivo. Additionally, HMM materials may be used for future in vitro cell culture and cardiomyocyte differentiation protocols.

Human versus porcine tissue sourcing for an injectable myocardial matrix hydrogel
Todd D. Johnson, Jessica A. DeQuach, Roberto Gaetani, Jessica Ungerleider, Dean Elhag, Vishal Nigam, Atta Behfar, and Karen L. Christman
Biomater. Sci., 2014, Advance Article, DOI: 10.1039/C3BM60283D

Brian Aguado is currently a Ph.D. Candidate and NSF Fellow in the Biomedical Engineering department at Northwestern University. He holds a B.S. degree in Biomechanical Engineering from Stanford University and a M.S. degree in Biomedical Engineering from Northwestern University. Read more about Brian’s research publications here.

To keep up-to-date with all the latest research, sign-up to our RSS feed or Table of contents

Most biological organisms depend on electrical signals to function properly. For instance, neurons are electrically active cells that transmit signals to other neurons using electrical signals known as action potentials. Other electrically active cells such as cardiomyocytes in the heart spontaneously generate electrical signals that regulate normal heart rhythm. Additionally, electrical signals are also known to mediate certain processes such as cell migration and cell division. Knowing that biological organisms rely on electrical signals to function, biomaterials scientists are searching for opportunities on how to use innovative electrically conductive materials to deepen our understanding of fundamental biological processes.

Professor Bozhi Tian and his team at the University of Chicago have recently written a mini-review discussing nanoscale semiconductor devices and how they can revolutionize our understanding of cellular electrophysiology. Semiconductor devices such as silicon nanowire field effect transistors (NWFETs) operate at a sufficient resolution to detect the slightest changes in chemical and electrical signals (down to the pico- and femto- unit scales). These devices could theoretically be used as a low-cost strategy for disease marker detection in the clinic.

Ramya Parameswaran, an MD/PhD student at the University of Chicago and second author on the mini-review, explains that the use of nanoscale semiconductor devices in the clinic is not far away. The authors discuss the development of “multiplex sensing” semiconductor devices seek to replace enzyme-linked immunosorbent assays (ELISA) in the future, with the ability to detect concentrations of proteins, nucleic acids, and other ions within cells simultaneously with one device. “Multiplexing nanomaterials can hopefully soon be used to detect biomarkers such as cancer antigens or other important players involved in disease processes in a rapid fashion,” says Parameswaran. “While clinical trials for devices such as these have not been performed as of yet, the proof of concept exists.” These devices would ultimately accelerate patient diagnosis, and would ideally improve patient treatments for a variety of diseases.

The application of nanoscale semiconductor devices in the tissue-engineering field is also emerging. Nanoscale semiconductors embedded in tissue-engineered implants could be used to record electrical information for monitoring and ensuring proper functionality of the implant. Interestingly, nanoelectronic scaffolds can be used for a variety of tissue targets. “Free-standing nanowire nanoelectronic scaffolds can be interfaced with neurons, smooth muscle cells, and cardiomyocytes to monitor local electrical activity within the hybrid scaffolds,” says Parameswaran. Using these nanoelectronic scaffolds, tissue responses to drug treatments could also be “monitored meticulously,” which is another advantage for accelerating the translation of these devices to the clinic.

This mini-review describes the current status of nanoscale semiconductor devices and how they can advance our understanding of cell electrophysiology. Additionally, these devices could have a transformative role in the design of medical devices and tissue engineering scaffolds for clinical applications.

Nanoscale semiconductor devices as new biomaterials
John Zimmerman, Ramya Parmeswaran, and Bozhi Tian
Biomaterial Sci., Advance Article, DOI: 10.1039/C3BM60280J

Brian Aguado is currently a Ph.D. Candidate and NSF Fellow in the Biomedical Engineering department at Northwestern University. He holds a B.S. degree in Biomechanical Engineering from Stanford University and a M.S. degree in Biomedical Engineering from Northwestern University. Read more about Brian’s research publications here.

To keep up-to-date with all the latest research, sign-up to our RSS feed or Table of contents

One of the primary goals within the field of hard tissue engineering is to create biomaterials that can both promote osteoblast proliferation and support the natural bone mineralization process.  In this study, a trio of researchers at the University of Louisiana at Lafayette has developed a promising, layered hybrid system that contains hydroxyapatite (HAP), chitosan (CS), and graphene oxide (GO).  The GO base provides mechanical strength and biocompatibility while the surface layer which is composed of HAP, a natural constituent of bone, has a high bioactivity.  The intermediate chitosan layer further strengthens the hybrid biomaterial and, perhaps more importantly, has been shown to promote more homogeneous mineralization that mimics the natural biomineralization process.

In order to test the bone forming capabilities of this hybrid material the group soaked it, along with two control materials (HAP-GO and pure GO), in simulated body fluid for three weeks.  Each substrate was then incubated with MC3T3-E1 pre-osteoblast cells.  Among the three biomaterials, the HAP-CS-GO hybrid produced the highest levels of cell proliferation and expansion.   It also induced the greatest expression levels of vinculin, actin, and fibronectin, proteins that are essential for cell adhesion, cytoskeletal organization, and osteoblast morphogenesis and mineralization.  The hybrid material also demonstrated a highly significant increase in mineralized area and bone nodule formation compared to either of the two controls.  This was primarily attributed to the strong electrostatic interactions between the functional groups in the CS-GO base and the calcium ions present in solution.

Overall the hybrid HAP-CS-GO material was able to favorably modulate cellular activity in a way that was conducive to bone formation, making it a promising candidate for future bone tissue engineering applications.   However, as the authors have highlighted, there is room for improvement.  A reoccurring issue that many bone tissue engineering materials, including this novel hybrid material, have faced is an inability to attain the proper ratio of mineral deposit to cellular matrix in the regenerated tissue.  This mineral to matrix ratio has been shown to be relatively high in healthy, intact bone (~4.35-5) but was observed in a significantly lower amount (1.76) in the HAP-CS-GO material.  Nonetheless, the hybrid biomaterial reported in this study represents a promising direction forward in the field of bone tissue engineering.

The synergistic effect of a hybrid graphene oxide-chitosan system and biomimetic mineralization on osteoblast functions
D. Depan, T. C. Pesacreta and R. D. K. Misra
Biomater. Sci., 2014, 2, 264-274 DOI: 10.1039/C3BM60192G

Ellen Tworkoski is a guest web-writer for Biomaterials Science.  She is currently a graduate student in the biomedical engineering department at Northwestern University (Evanston, IL, USA).

Follow the latest journal news on Twitter @BioMaterSci or go to our Facebook page.

To keep up-to-date with all the latest research, sign-up to our RSS feed or Table of contents alert.

This paper by Sunami et al. studies the impact of 3D patterning on cells, and shows that cells grown on 3D micropatterns respond by changing their migration speed, their proliferation rate, and their expression of actin.

It is standard laboratory practice to grow cells outside the body on flat tissue culture plates.  However, cells inside the body are surrounded by other cells and connective tissue organized in three dimensions.  It is therefore very important to develop culture platforms for cells that more accurately capture a cell’s microenvironment inside the body. 

In this paper, the authors developed a three-dimensional culture platform that could be modified to study the properties of fibroblasts (skin cells) in culture. The authors changed only one factor – the area of the three-dimensional triangles that the cells were cultured on – to study the impact of 3D micropatterned areas on fibroblasts. The resultant surfaces that they used were about as adhesive as a smooth glass surface.  Interestingly, they found that fibroblast spreading was very different on surfaces with different areas, with maximum cell spreading observed on a surface with an intermediate pattern area.  The cells primarily adhered to the upper surface of the 3D micropatterns. Further, the density of the cells was also dependent on the micropattern area – as micropattern area increased, the density of the cells correspondingly increased as well. The cells also proliferated faster on surfaces with larger micropattern areas, while cell proliferation slowed on smaller triangles. The authors then used timelapse microscopy to study how these cells migrated over time, and found that while cells migrated more slowly on all of the micropatterned surfaces as compared to a completely flat surface, migration was slowest on the micropatterns with the smallest areas. Similarly, the authors found that f-actin expression was increased on the patterns with the largest areas. The authors hypothesize that this may mean that cells experience less mechanical stress as pattern size decreases.

Influence of the pattern size of micropatterned scaffolds on cell morphology, proliferation, migration and F-actin expression
Hiroshi Sunami, Ikuko Yokota and Yasuyuki Igarashi
Biomater. Sci., 2014, Advance Article DOI: 10.1039/C3BM60237K

Debanti Sengupta recently completed her PhD in Chemistry from Stanford University.  She is currently a Siebel postdoctoral scholar at the University of California, Berkeley.  

Follow the latest journal news on Twitter @BioMaterSci or go to our Facebook page.

One of the goals of tissue engineers is to manufacture “spare body parts” made of cells and biomaterials to repair damaged or diseased tissues. A current challenge for commercializing cell-biomaterial constructs is maintaining their viability during shipping and/or storage. The storage of cells in liquid suspension is relatively simple with the use of common cryoprotectants (such as dimethyl sulfoxide), but current preservation methods for large cell-biomaterial constructs yield low cell viability in comparison.  More effective preservation methods for cell-biomaterial constructs are needed to produce “off the shelf” tissue engineered products and accelerate the translation of tissue engineered products to the clinic.

In a current study conducted at the Japan Advanced Institute of Science and Technology (JAIST), researchers developed a dextran-based polyampholyte (charged polymer) hydrogel with cryoprotective properties. First, dextran polymers were functionalized with azide groups (azide-Dex) to provide sites for crosslinking. Then, positively charged amine groups were introduced on the dextran using poly-L-lysine to form azide-amino-Dex. To add negatively charged carboxyl groups, succinic anhydride was added at various concentrations to azide-amino-Dex to convert amine groups to carboxyl groups. This newly formed dextran polyampholyte (azide-Dex-PA) polymer was utilized for cryopreservation studies. After encapsulating and freezing cells with various azide-Dex-PA solutions, cell viability post-cryopreservation was shown to increase with higher concentrations of azide-Dex-PA. Viability was also dependent on the ratio of amine and carboxyl groups on the polymer, indicating that the cryoprotective properties of the polyampholyte are likely due to polymer charge.

The azide groups on the azide-Dex-PA were utilized to crosslink the dextran polyampholytes to form hydrogels. After synthesizing alkyne-functionalized dextran with dibenzylcyclooctyne (DBCO-Dex), the two components were mixed with cells to form hydrogels with azide-alkyne click chemistry. Encapsulated cells in the hydrogel were cryopreserved, thawed, and evaluated for viability. Compared to the 0% viability observed with collagen hydrogel and non-polyampholyte dextran hydrogel controls, the dextran polyampholyte hydrogels substantially increased cell viability to 93-94%. The increased viability post-cryopreservation may be due to the polyampholyte polymer adsorbing onto the cell membrane, providing a polymer “shell” of protection during thawing. Images of cells coated with FITC labeled azide-Dex-PA provide evidence to support this hypothesis.

All in all, dextran polyampholyte hydrogels have cryoprotective properties, and are able to preserve cell viability during the cryopreservation process. The dramatic increase in cell viability post-cryopreservation justifies future studies for using these hydrogels for preserving larger cell-biomaterial constructs for long term storage.

Hydrogelation of dextran-based polyampholytes with cryoprotective properties via click chemistry
Minkle Jain, Robin Rajan, Suong-Hyu Hyon, and Kazuaki Matsumura
Biomaterials Science, 2014, Advance Article DOI: 10.1039/C3BM60261C

Brian Aguado is currently a Ph.D. Candidate and NSF Fellow in the Biomedical Engineering department at Northwestern University. He holds a B.S. degree in Biomechanical Engineering from Stanford University and a M.S. degree in Biomedical Engineering from Northwestern University. Read more about Brian’s research publications here.

To keep up-to-date with all the latest research, sign-up to our RSS feed or Table of contents