Binata Joddar

Biological modifications of materials surfaces with proteins for regenerative medicine

It is very important to modify the surfaces of biomaterials for regulation of cells in the development of regenerative medicine or tissue engineering. Biomaterials are categorized into three primary types, metallic, ceramic, and polymers. Here the biological modification of biomaterial surfaces such as metals, ceramics, and polymers and the effects of such biological modifications are discussed. It is well known that cellular compatibility is regulated by three interactions: one is with extracellular matrices (ECM), second with neighboring cells, and third with soluble biosignals such as growth factors. Biomaterial researchers have immobilized ECM, cell adhesion factors, and growth factors on various materials to regulate cellular functions. Herein, biosignaling of ECM, cell adhesion factors, and growth factors are reviewed and biomaterial designs to activate biosignaling mechanisms are discussed.

Development of functionalized multi-walled carbon-nanotube-based alginate hydrogels for enabling biomimetic technologies.

Alginate is a hydrogel commonly used for cell culture by ionically crosslinking in the presence of divalent Ca2+ ions. However these alginate gels are mechanically unstable, not permitting their use as scaffolds to engineer robust biological bone, breast, cardiac or tumor tissues. This issue can be addressed via encapsulation of multi-walled carbon nanotubes (MWCNT) serving as a reinforcing phase while being dispersed in a continuous phase of alginate. We hypothesized that adding functionalized MWCNT to alginate, would yield composite gels with distinctively different mechanical, physical and biological characteristics in comparison to alginate alone. Resultant MWCNT-alginate gels were porous, and showed significantly less degradation after 14 days compared to alginate alone. In vitro cell-studies showed enhanced HeLa cell adhesion and proliferation on the MWCNT-alginate compared to alginate. The extent of cell proliferation was greater when cultured atop 1 and 3 mg/ml MWCNT-alginate; although all MWCNT-alginates lead to enhanced cell cluster formation compared to alginate alone. Among all the MWCNT-alginates, the 1 mg/ml gels showed significantly greater stiffness compared to all other cases. These results provide an important basis for the development of the MWCNT-alginates as novel substrates for cell culture applications, cell therapy and tissue engineering.

Artificial niche substrates for embryonic and induced pluripotent stem cell cultures

Stem cells possess the ability to self-renew and differentiate into other cell types. In vivo, stem cells reside in their own anatomic niches in a defined physiological environment, from which they are released to differentiate into a required cell type when deemed appropriate. While a resident within the niche, the stem cell receives signals that in turn maintain the cell in a pluripotent state. In addition, the niche also provides nourishment to the cell. Physically, the niche also serves to anchor the cell via various ECM components and cell-adhesion molecules. Therefore, in vitro models that replicate the in vivo niche will lead to a better understanding of stem cell fate and turnover. In turn, this will help inform attempts to culture stem cells in vitro on artificial niche-like substrates. In this review, we have highlighted recent studies describing artificial niche-like substrates used to culture embryonic and induced pluripotent stem cells in vitro.

Sustained delivery of siRNA from dopamine-coated stainless steel surfaces

Dopamine, an adhesive protein can be covalently deposited onto biomaterials. In this study, we evaluated the ability of dopamine-coated surfaces for small interfering RNA (siRNA) immobilization and release. Dopamine was deposited onto 316L stainless steel discs either as a monolayer at acidic pH or as polydopamine at alkaline pH, following which siRNA was immobilized onto these discs. To investigate the RNA interference ability of immobilized siRNA, reduction of luciferase expression in HeLa, and reduction of Egr-1 expression and cell proliferation in human aortic smooth muscle cells (HAoSMCs) were determined. Dopamine treatment of 316L stainless steel discs under both the acidic and alkaline conditions resulted in the deposition of amino (NH2) groups, which enabled electrostatic immobilization of siRNA. The immobilized siRNA was released from both types of coatings, and enhanced the percent suppression of firefly luciferase activity of HeLa significantly up to ~96.5% compared to HeLa on non-dopamine controls (18%). Both the release of siRNA and the percent suppression of firefly luciferase activity were sustained for at least 7 days. In another set of experiments, siRNA sequences targeting to inhibit the activity of the transcription factor Egr-1 were eluted from dopamine-coated surfaces to HAoSMCs. Egr-1 siRNA eluted from dopamine-coated surfaces, significantly reduced the proliferation of HAoSMCs and their protein expression of Egr-1. Therefore, this method of surface immobilization of siRNA onto dopamine-coated surfaces might be effective for nucleic acid delivery from stents.

The effects of covalently immobilized hyaluronic acid substrates on the adhesion, expansion, and differentiation of embryonic stem cells for in vitro tissue engineering

We investigated the in vitro effects of the molecular weight (MW) of hyaluronic acid (HA) on the maintenance of the pluripotency and proliferation of murine embryonic stem (ES) cells. High (1000 kDa) or low (4-8 kDa) MW HA was derivatized using an ultraviolet-reactive compound, 4-azidoaniline, and the derivative was immobilized onto cell culture cover slips. Murine ES cells were cultured on these HA surfaces for 5 days. High-MW HA interacted with murine ES cells via CD44, whereas low-MW HA interacted with these cells mostly via CD168. ES cells grown on both high- and low-MW HA appeared undifferentiated after 3 days. However, more cells adhered, proliferated, and exhibited greater amounts of phospho-p42/44 mitogen-activated-protein-kinase on low- compared with high-MW HA. Expression of Oct-3/4 and phosphorylation of STAT3 were enhanced by ES cells on low-MW HA, not on high-MW HA. After release from HA, cells cultured on low-MW HA in the presence of differentiating medium showed enhanced expression of α-SMA or CD31 compared with cells cultured on high-MW HA. It was concluded that low-MW HA substrates were effective in maintaining murine ES cells in a viable and undifferentiated state, which favors their use in the propagation of ES cells for tissue engineering.

The significance of membrane fluidity of feeder cell-derived substrates for maintenance of iPS cell stemness

The biological activity of cell-derived substrates to maintain undifferentiated murine-induced pluripotent stem (iPS) cells was correlated to membrane fluidity as a new parameter of cell culture substrates. Murine embryonic fibroblasts (MEFs) were employed as feeder cells and their membrane fluidity was tuned by chemical fixation using formaldehyde (FA). Membrane fluidity was evaluated by real-time single-molecule observations of green fluorescent protein-labeled epidermal growth factor receptors on chemically fixed MEFs. Biological activity was monitored by colony formation of iPS cells. Treatment with a low concentration of FA sustained the membrane fluidity and biological activity, which were comparable to those of mitomycin C-treated MEFs. The biological activity was further confirmed by sustained expression of alkaline phosphatase, SSEA-1, and other pluripotency markers in iPS cells after 3–5 days of culture on FA-fixed MEFs. Chemical fixation of feeder cells has several advantages such as providing ready-to-use culture substrates without contamination by proliferating feeder cells. Therefore, our results provide an important basis for the development of chemically fixed culture substrates for pluripotent stem cell culture as an alternative to conventional treatment by mitomycin C or x-ray irradiation.

Spatial gradients of chemotropic factors from immobilized patterns to guide axonal growth and regeneration.

In this study, we investigated the effect of varying localized concentration gradients of NGF and Sema3A on the axonal outgrowth of embryonic chick DRG explants and primary neurons in vitro. Immobilized 2D NGF or Sema3A micropatterns were produced using photolithography on tissue culture cover slips. Two distinct regions were identified: slow, with little or no change in concentration of chemotropic factor; and steep, with a transition from low to high. The direction of axonal outgrowth was defined as proximal or distal, with proximal growing towards the higher concentration of immobilized NGF/Sema3A and vice versa for distal. Axons grew preferentially in the proximal direction when explants were seeded onto steep NGF, and distally in response to steep Sema3A. On slow NGF, or on slow Sema3A there was no difference in the directional specificity of axonal outgrowth. DRG primary neurons seeded onto steep NGF migrated proximally, whereas neurons seeded onto slow NGF migrated in all directions. Conversely, neurons seeded onto steep or slow Sema3A did not extend any axons. Our 2D immobilized micropatterns of chemotropic factors show promise for further development of in vitro nerve tissue engineering studies.

Stem cell culture using cell-derived substrates

There have been great efforts to develop cell culture systems to regulate stem cell functions. Development of cell culture substrates is one of the important approaches for stem cell culture because substrates influence stem cell functions such as attachment, proliferation, self-renewal, and induction of differentiation. Stem cells are surrounded by their specific microenvironments in vivo, composed of cells, cytokines, and an extracellular matrix (ECM), which may dynamically change and affect cellular activities accordingly. To mimic such microenvironments, cell culture substrates can be prepared by coating bioactive proteins such as ECM proteins and signaling molecules as ligands for cell surface receptors. Compared with protein-coated substrates, cell- and cell-formed ECM-derived substrates have shown great progress and attracted significant attention as functional and prospective biomaterials for stem cell culture and regenerative medicine. In this review, we summarize the latest progress of these new substrates derived from cells and cell-formed ECMs.

Chemically fixed autologous feeder cell-derived niche for human induced pluripotent stem cell culture

Conventional culture of human induced pluripotent (hiPS) cells requires feeder cell preparation that is time consuming and labour intensive. Alternatively, feeder-free culture of hiPS cells requires high cell seeding densities, specialized culture medium, and growth supplements, which raise the cost. Furthermore, recombinant systems require a long time for colony formation. Here, we employed chemically fixed autologous feeder cells for hiPS cell culture without additional time needed for colony formation. Treatment of (2.5% glutaraldehyde or formaldehyde for 10 min) autologous human dermal fibroblasts allowed hiPS cells to adhere and grow as undifferentiated colonies characterized by the expression of pluripotency markers such as alkaline phosphatase, Oct-3/4, and stage-specific embryonic antigen-4. Furthermore, hiPS cells cultured on chemically fixed feeders formed teratomas in vivo, characterized by all three germ layers. The chemically fixed autologous feeders may be used as a substitute for large scale culture of hiPS cells as a convenient in-house and a cost-effective method.

A Bioactive Hydrogel and 3D Printed Polycaprolactone System for Bone Tissue Engineering

In this study, a hybrid system consisting of 3D printed polycaprolactone (PCL) filled with hydrogel was developed as an application for reconstruction of long bone defects, which are innately difficult to repair due to large missing segments of bone. A 3D printed gyroid scaffold of PCL allowed a larger amount of hydrogel to be loaded within the scaffolds as compared to 3D printed mesh and honeycomb scaffolds of similar volumes and strut thicknesses. The hydrogel was a mixture of alginate, gelatin, and nano-hydroxyapatite, infiltrated with human mesenchymal stem cells (hMSC) to enhance the osteoconductivity and biocompatibility of the system. Adhesion and viability of hMSC in the PCL/hydrogel system confirmed its cytocompatibility. Biomineralization tests in simulated body fluid (SBF) showed the nucleation and growth of apatite crystals, which confirmed the bioactivity of the PCL/hydrogel system. Moreover, dissolution studies, in SBF revealed a sustained dissolution of the hydrogel with time. Overall, the present study provides a new approach in bone tissue engineering to repair bone defects with a bioactive hybrid system consisting of a polymeric scaffold, hydrogel, and hMSC.