Collagen Three-Dimensional Hydrogel Matrix Carrying Basic Fibroblast Growth Factor for the Cultivation of Mesenchymal Stem Cells and Osteogenic Differentiation

Designing degradable hydrogels for orthogonal control of cell microenvironments

Degradable and cell-compatible hydrogels can be designed to mimic the physical and biochemical characteristics of native extracellular matrices and provide tunability of degradation rates and related properties under physiological conditions. Hence, such hydrogels are finding widespread application in many bioengineering fields, including controlled bioactive molecule delivery, cell encapsulation for controlled three-dimensional culture, and tissue engineering. Cellular processes, such as adhesion, proliferation, spreading, migration, and differentiation, can be controlled within degradable, cell-compatible hydrogels with temporal tuning of biochemical or biophysical cues, such as growth factor presentation or hydrogel stiffness. However, thoughtful selection of hydrogel base materials, formation chemistries, and degradable moieties is necessary to achieve the appropriate level of property control and desired cellular response. In this review, hydrogel design considerations and materials for hydrogel preparation, ranging from natural polymers to synthetic polymers, are overviewed. Recent advances in chemical and physical methods to crosslink hydrogels are highlighted, as well as recent developments in controlling hydrogel degradation rates and modes of degradation. Special attention is given to spatial or temporal presentation of various biochemical and biophysical cues to modulate cell response in static (i.e., non-degradable) or dynamic (i.e., degradable) microenvironments. This review provides insight into the design of new cell-compatible, degradable hydrogels to understand and modulate cellular processes for various biomedical applications.

Modulation of osteoblastic/odontoblastic differentiation of adult mesenchymal stem cells through gene introduction: a brief review

Bone tissue engineering is one of the important therapeutic approaches to the regeneration of bones in the entire field of regeneration medicine. Mesenchymal stem cells (MSCs) are actively discussed as material for bone tissue engineering due to their ability to differentiate into autologous bone. MSCs are able to differentiate into different lineages: osteo/odontogenic, adipogenic, and neurogenic. The tissue of origin for MSCs defines them as bone marrow-derived stem cells, adipose tissue-derived stem cells, and, among many others, dental stem cells. According to the tissue of origin, DSCs are further stratified into dental pulp stem cells, periodontal ligament stem cells, stem cells from apical papilla, stem cells from human exfoliated deciduous teeth, dental follicle precursor cells, and dental papilla cells. There are numerous in vitro/in vivo reports suggesting successful mineralization potential or osteo/odontogenic ability of MSCs. Still, there is further need for the optimization of MSCs-based tissue engineering methods, and the introduction of genes related to osteo/odontogenic differentiation into MSCs might aid in the process. In this review, articles that reported enhanced osteo/odontogenic differentiation with gene introduction into MSCs will be discussed to provide a background for successful bone tissue engineering using MSCs with artificially introduced genes.

Bioresponsive hydrogel scaffolding systems for 3D constructions in tissue engineering and regenerative medicine

Among the diversity of scaffolding systems available, hydrogel remains a popular choice for tissue engineering applications. The current state-of-the-art bioresponsive hydrogels demand intricate designs in pursuit of acquiring desired timely responses, such as controlled release of biological factors, changes in mechanical properties and scaffold degradation, at the same rate as the natural extracellular matrix. In this review, a variety of bioresponsive hydrogels are discussed; in particular, bioactive and biodegradable hydrogels that facilitate cellular development and tissue morphogenesis are highlighted. Bioactive hydrogels are designed to deliver biomolecules such as cell-adhesive moieties and instructive ligands at close proximity to the cell for better uptake or exposure. Biodegradable hydrogels provide transient scaffolding support for therapeutic cell settlement while gradually degrading in response to physical or enzymatic stimuli. In addition, biomechanical stimuli from hydrogels can induce mutual constructive responses on cells and, hence, will also be covered in this review.

Differentiation patterns of embryonic stem cells in two- versus three-dimensional culture

Pluripotent stem cells are attractive candidates as a cell source for regenerative medicine and tissue engineering therapies. Current methods of differentiation result in low yields and impure populations of target phenotypes, with attempts for improved efficiency often comparing protocols that vary multiple parameters. This basic science study focused on a single variable to understand the effects of two-dimensional (2D) versus three-dimensional (3D) culture on directed differentiation. We compared mouse embryonic stem cells (ESCs) differentiated on collagen type I-coated surfaces (SLIDEs), embedded in collagen type I gels (GELs), and in suspension as embryoid bodies (EBs). For a systematic analysis in these studies, key parameters were kept identical to allow for direct comparison across culture configurations. We determined that all three configurations supported differentiation of ESCs and that the kinetics of differentiation differed greatly for cells cultured in 2D versus 3D. SLIDE cultures induced overall differentiation more quickly than 3D configurations, with earlier expression of cytoskeletal and extracellular matrix proteins. For 3D culture as GELs or EBs, cells clustered similarly, formed complex structures and promoted differentiation towards cardiovascular phenotypes. GEL culture, however, also allowed for contraction of the collagen matrix. For differentiation towards fibroblasts and smooth muscle cells which actively remodel their environment, GEL culture may be particularly beneficial. Overall, this study determined the effects of dimensionality on differentiation and helps in the rational design of protocols to generate phenotypes needed for tissue engineering and regenerative medicine.

Collagen hydrogels strengthened by biodegradable meshes are a basis for dermo-epidermal skin grafts intended to reconstitute human skin in a one-step surgical intervention

Extensive full-thickness skin loss, associated with deep burns or other traumata, represents a major clinical problem that is far from being solved. A promising approach to treat large skin defects is the use of tissue-engineered full-thickness skin analogues with nearly normal anatomy and function. In addition to excellent biological properties, such skin substitutes should exhibit optimal structural and mechanical features. This study aimed to test novel dermo-epidermal skin substitutes based on collagen type I hydrogels, physically strengthened by two types of polymeric net-like meshes. One mesh has already been used in clinical trials for treating inguinal hernia; the second one is new but consists of a FDA-approved polymer. Both meshes were integrated into collagen type I hydrogels and dermo-epidermal skin substitutes were generated. Skin substitutes were transplanted onto immuno-incompetent rats and analyzed after distinct time periods. The skin substitutes homogeneously developed into a well-stratified epidermis over the entire surface of the grafts. The epidermis deposited a continuous basement membrane and dermo-epidermal junction, displayed a well-defined basal cell layer, about 10 suprabasal strata and a stratum corneum. Additionally, the dermal component of the grafts was well vascularized.

In vitro cultivation of canine multipotent mesenchymal stromal cells on collagen membranes treated with hyaluronic acid for cell therapy and tissue regeneration

Support structures for dermal regeneration are composed of biodegradable and bioresorbable polymers, animal skin or tendons, or are bacteria products. The use of such materials is controversial due to their low efficiency. An important area within tissue engineering is the application of multipotent mesenchymal stromal cells (MSCs) to reparative surgery. The combined use of biodegradable membranes with stem cell therapy may lead to promising results for patients undergoing unsuccessful conventional treatments. Thus, the aim of this study was to test the efficacy of using membranes composed of anionic collagen with or without the addition of hyaluronic acid (HA) as a substrate for adhesion and in vitro differentiation of bone marrow-derived canine MSCs. The benefit of basic fibroblast growth factor (bFGF) on the differentiation of cells in culture was also tested. MSCs were collected from dog bone marrow, isolated and grown on collagen scaffolds with or without HA. Cell viability, proliferation rate, and cellular toxicity were analyzed after 7 days. The cultured cells showed uniform growth and morphological characteristics of undifferentiated MSCs, which demonstrated that MSCs successfully adapted to the culture conditions established by collagen scaffolds with or without HA. This demonstrates that such scaffolds are promising for applications to tissue regeneration. bFGF significantly increased the proliferative rate of MSCs by 63% when compared to groups without the addition of the growth factor. However, the addition of bFGF becomes limiting, since it has an inhibitory effect at high concentrations in culture medium.

The XTT cell proliferation assay applied to cell layers embedded in three-dimensional matrix

Cell proliferation, a main target in cancer therapy, is influenced by the surrounding three-dimensional (3D) extracellular matrix (ECM). In vitro drug screening is, thus, optimally performed under conditions in which cells are grown (embedded or trapped) in dense 3D matrices, as these most closely mimic the adhesive and mechanical properties of natural ECM. Measuring cell proliferation under these conditions is, however, technically more challenging compared with two-dimensional (2D) culture and other "3D culture conditions," such as growth on top of a matrix (pseudo-3D) or in spongy scaffolds with large pore sizes. Consequently, such measurements are only slowly applied on a wider scale. To advance this, we report on the equal quality (dynamic range, background, linearity) of measuring the proliferation of cell layers embedded in dense 3D matrices (collagen, Matrigel) compared with cells in 2D culture using the easy (one-step) and in 2D well-validated, 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT)-assay. The comparison stresses the differences in proliferation kinetics and drug sensitivity of matrix-embedded cells versus 2D culture. Using the specific cell-layer-embedded 3D matrix setup, quantitative measurements of cell proliferation and cell invasion are shown to be possible in similar assay conditions, and cytostatic, cytotoxic, and anti-invasive drug effects can thus be reliably determined and compared in physiologically relevant settings. This approach in the 3D matrix holds promise for improving early-stage, high-throughput drug screening, targeting either highly invasive or highly proliferative subpopulations of cancers or both.