Effects of pH and thermally sensitive hybrid gels on osteogenic differentiation of mesenchymal stem cells

Functional Dynamics Inside Nano- or Microscale Bio-Hybrid Systems

Soft nano- or microgels made by natural or synthetic polymers have been investigated intensively because of their board applications. Due to their porosity and biocompatibility, nano- or microgels can be integrated with various biologics to form a bio-hybrid system. They can support living cells as a scaffold; entrap bioactive molecules as a drug carrier or encapsulate microorganisms as a semi-permeable membrane. Especially, researchers have created various modes of functional dynamics into these bio-hybrid systems. From one side, the encapsulating materials can respond to the external stimulus and release the cargo. From the other side, cells can respond to physical, or chemical properties of the matrix and differentiate into a specific cell type. With recent advancements of synthetic biology, cells can be further programed to respond to certain signals, and express therapeutics or other functional proteins for various purposes. Thus, the integration of nano- or microgels and programed cells becomes a potential candidate in applications spanning from biotechnology to new medicines. This brief review will first talk about several nano- or microgels systems fabricated by natural or synthetic polymers, and further discuss their applications when integrated with various types of biologics. In particular, we will concentrate on the dynamics embedded in these bio-hybrid systems, to dissect their designs and sophisticated functions.

Enhanced multi-lineage differentiation of human mesenchymal stem/stromal cells within poly(N-isopropylacrylamide-acrylic acid) microgel-formed three-dimensional constructs

Human mesenchymal stem/stromal cells (hMSCs) are a potential cell source of stem cell therapy for many serious diseases and hMSC spheroids have emerged to replace single cell suspensions for cell therapy. Three-dimensional (3D) scaffolds or hydrogels which can mimic properties of the extracellular matrix (ECM) have been widely explored for their application in tissue regeneration. However, there are considerably less studies on inducing differentiation of hMSC spheroids using 3D scaffolds or hydrogels. This study is the first to explore multi-lineage differentiation of a stem cell line and primary stem cells within poly(N-isopropylacrylamide) (p(NIPAAm))-based thermosensitive microgel-formed constructs. We first demonstrated that poly(N-isopropylacrylamide-co-acrylic acid) (p(NIPAAm-AA)) was not toxic to hMSCs and the microgel-formed constructs facilitated formation of uniform stem cell spheroids. Due to functional enhancement of cell spheroids, hMSCs within the 3D microgel-formed constructs were induced for multi-lineage differentiation as evidenced by significant up-regulation of messenger RNA (mRNA) expression of chondrogenic and osteogenic genes even in the absence of induction media on day 9. When induction media were in situ supplied on day 9, mRNA expression of chondrogenic, osteogenic and adipogenic genes within the microgel-formed constructs were significantly higher than that in the pellet and 2D cultures, respectively, on day 37. In addition, histological and immunofluorescent images also confirmed successful multi-lineage differentiation of hMSCs within the 3D microgel-formed constructs. Hence, the thermosensitive p(NIPAAm-AA) microgel can be potentially used in an in vitro model for cell differentiation or in vivo transplantation of pre-differentiated human mesenchymal stromal cells into patients for specific lineage differentiation.

Effects of Culture Substrate Made of Poly(N-isopropylacrylamide-co-acrylic acid) Microgels on Osteogenic Differentiation of Mesenchymal Stem Cells

Poly(N-isopropylacrylamide) (PNIPAM)-based polymers and gels are widely known and studied for their thermoresponsive property. In the biomaterials category, they are regarded as a potential cell culture substrate, not only because of their biocompatibility, but also their special character of allowing controlled detachment of cells via temperature stimulus. Previous research about PNIPAM-based substrates mostly concentrated on their effects in cell adhesion and proliferation. In this study, however, we investigate the influence of the PNIPAM-based substrate on the differentiation capacity of stem cells. Especially, we choose P(NIPAM-AA) microgels as a culture dish coating and mesenchymal stem cells (MSCs) are cultured on top of the microgels. Interestingly, we find that the morphology of MSCs changes remarkably on a microgel-coated surface, from the original spindle form to a more stretched and elongated cell shape. Accompanied by the alternation in morphology, the expression of several osteogenesis-related genes is elevated even without inducing factors. In the presence of full osteogenic medium, MSCs on a microgel substrate show an enhancement in the expression level of osteopontin and alizarin red staining signals, indicating the physical property of substrate has a direct effect on MSCs differentiation.

The role of angiogenesis in implant dentistry part II: The effect of bone-grafting and barrier membrane materials on angiogenesis

BACKGROUND

In implant dentistry, bone substitute materials and barrier membranes are used in different treatments including guided bone regeneration (GBR), socket preservation, alveolar ridge augmentation, maxillary sinus elevation, and filling bony defects around the inserted dental implant. One of the most important factors in prognosis of treatments using these materials is the growth of new blood vessels in applied areas. Present review was performed to evaluate the effect of the bone-grafting and barrier membrane materials on angiogenesis events.

MATERIAL AND METHODS

An electronic search was performed in PubMed, MEDLINE, and EMBASE databases via OVID using the keywords mentioned in the PubMed and MeSH headings regarding the role of angiogenesis in implant dentistry from January 2000-April 2014.

RESULTS

Of the 5,622 articles identified in our initial search results, only 33 met the inclusion criteria set for this review. Among bone substitute materials the autogenous bone-grafts, and among the barrier membranes the collagenous membranes, had the highest angiogenic potentials. Other bone-grafting materials or membranes were mostly used with pro-angiogenic factors to enhance their angiogenic properties.

CONCLUSIONS

Angiogenesis is one of the key factors, which plays a critical role in success rate of GBR technique and is seriously considered in manufacturing bone-grafting and barrier membrane materials. However, there is still lack of clinical and in-vivo studies addressing the effect of angiogenesis in treatments using bone-grafting and barrier membrane materials.