Towards the Development and Characterization of an Easy Handling Sheet-Like Biohybrid Bone Substitute

Comparison of hydroxyapatite and honeycomb micro-structure in bone tissue engineering using electrospun beads-on-string fibers

Thick honeycomb-like electrospun scaffold with nanoparticles of hydroxyapatite (nHA) recently demonstrated its potential to promote proliferation and differentiation of a murine embryonic cell line (C3H10T1/2) to osteoblasts. In order to distinguish the respective effects of the structure and the composition on cell differentiation, beads-on-string fibers were used to manufacture thick honeycomb-like scaffolds without nHA. Mechanical and biological impacts of those beads-on string fibers were evaluated. Uniaxial tensile test showed that beads-on-string fibers decreased the Young Modulus and maximal stress but kept them appropriate for tissue engineering. C3H10T1/2 were seeded and cultured for 6 days on the scaffolds without any growth factors. Viability assays revealed the biocompatibility of the beads-on-string scaffolds, with adequate cells-materials interactions observed by confocal microscopy. Alkaline phosphatase staining was performed at day 6 in order to compare the early differentiation of cells to bone fate. The measure of stained area and intensity confirmed the beneficial effect of both honeycomb structure and nHA, independently. Finally, we showed that honeycomb-like electrospun scaffolds could be relevant candidates for promoting bone fate to cells in the absence of nHA. It offers an easier and faster manufacture process, in particular in bone-interface tissue engineering, permitting to avoid the dispersion of nHA and their interaction with the other cells.

Donor variability alters differentiation and mechanical cohesion of tissue-engineered constructs with human endothelial/MSC co-culture

To move towards clinical applications, tissue engineering (TE) should be validated with human primary cells and offer easy connection to the native vascularisation. Based on a sheet-like bone substitute developed previously, we investigated a mesenchymal stem cells/endothelial cells (MSCs/ECs) coculture to enhance pre-vascularisation. Using MSCs from six independent donors whose differentiation potential was assessed towards two lineages, we focused on donor variability and cell crosstalk regarding bone differentiation. Coculture was performed on calcium phosphate granules in a specific chamber during 1 month. MSCs were seeded first then ECs were added after 2 weeks, with respective monocultures as control groups. Cell viability and organisation (fluorescence, electronic microscopy), differentiation (ALP staining/activity, RT-qPCR) and mechanical cohesion were analysed. Adaptation of the protocol to coculture was validated (high cell viability and proliferation). Activity and differentiation showed strong trends towards synergistic effects between cell types. MSCs reached early mineralisation stage of maturation. The delayed addition of ECs allowed for their attachment on developed MSCs' matrix. The main impact of donor variability could be here the lack of cell proliferation potential with some donors, leading to low differentiation and mechanical cohesion and therefore absence of sheet-like shape successfully obtained with others. We suggest therefore adapting protocols to cell proliferation potentials from one batch of cells to the other in a patient-specific approach.

Poly(ε-caprolactone)/Hydroxyapatite 3D Honeycomb Scaffolds for a Cellular Microenvironment Adapted to Maxillofacial Bone Reconstruction

The elaboration of biomimetic materials inspired from the specific structure of native bone is one the main goal of tissue engineering approaches. To offer the most appropriate environment for bone reconstruction, we combined electrospinning and electrospraying to elaborate an innovative scaffold composed of alternating layers of polycaprolactone (PCL) and hydroxyapatite (HA). In our approach, the electrospun PCL was shaped into a honeycomb-like structure with an inner diameter of 160 μm, capable of providing bone cells with a 3D environment while ensuring the material biomechanical strength. After 5 days of culture without any differentiation factor, the murine embryonic cell line demonstrated excellent cell viability on contact with the PCL-HA structures as well as active colonization of the scaffold. The cell differentiation, as tested by RT-qPCR, revealed a 6-fold increase in the expression of the RNA of the Bglap involved in bone mineralization as compared to a classical 2D culture. This differentiation of the cells into osteoblasts was confirmed by alkaline phosphatase staining of the scaffold cultivated with the cell lineage. Later on, organotypic cultures of embryonic bone tissues showed the high capacity of the PCL-HA honeycomb structure to guide the migration of differentiated bone cells throughout the cavities and the ridge of the biomaterial, with a colonization surface twice as big as that of the control. Taken together, our results indicate that PCL-HA honeycomb structures are biomimetic supports that promotes in vitro osteocompatibility, osteoconduction, and osteoinduction and could be suitable for being used for bone reconstruction in complex situations such as the repair of maxillofacial defects.

Multilineage Constructs for Scaffold-Based Tissue Engineering: A Review of Tissue-Specific Challenges

There is a growing interest in the regeneration of tissue in interfacial regions, where biological, physical, and chemical attributes vary across tissue type. The simultaneous use of distinct cell lineages can help in developing in vitro structures, analogous to native composite tissues. This literature review gathers the recent reports that have investigated multiple cell types of various sources and lineages in a coculture system for tissue-engineered constructs. Such studies aim at mimicking the native organization of tissues and their interfaces, and/or to improve the development of complex tissue substitutes. This paper thus distinguishes itself from those focusing on technical aspects of coculturing for a single specific tissue. The first part of this review is dedicated to variables of cocultured tissue engineering such as scaffold, cells, and in vitro culture environment. Next, tissue-specific coculture methods and approaches are covered for the most studied tissues. Finally, cross-analysis is performed to highlight emerging trends in coculture principles and to discuss how tissue-specific challenges can inspire new approaches for regeneration of different interfaces to improve the outcomes of various tissue engineering strategies.

A Cell-Based Self-Assembly Approach for the Production of Human Osseous Tissues from Adipose-Derived Stromal/Stem Cells

Achieving optimal bone defect repair is a clinical challenge driving intensive research in the field of bone tissue engineering. Many strategies focus on seeding graft materials with progenitor cells prior to in vivo implantation. Given the benefits of closely mimicking tissue structure and function with natural materials, the authors hypothesize that under specific culture conditions, human adipose-derived stem/stromal cells (hASCs) can solely be used to engineer human reconstructed osseous tissues (hROTs) by undergoing osteoblastic differentiation with concomitant extracellular matrix production and mineralization. Therefore, the authors are developing a self-assembly methodology allowing the production of such osseous tissues. Three-dimensional (3D) tissues reconstructed from osteogenically-induced cell sheets contain abundant collagen type I and are 2.7-fold less contractile compared to non-osteogenically induced tissues. In particular, hROT differentiation and mineralization is reflected by a greater amount of homogenously distributed alkaline phosphatase, as well as higher calcium-containing hydroxyapatite (P < 0.0001) and osteocalcin (P < 0.0001) levels compared to non-induced tissues. Taken together, these findings show that hASC-driven tissue engineering leads to hROTs that demonstrate structural and functional characteristics similar to native osseous tissue. These highly biomimetic human osseous tissues will advantageously serve as a platform for molecular studies as well as for future therapeutic in vivo translation.