Preparation And Characterization Of Biomaterials For In Situ Recruitment And Capturing Of BMSCs

The loss of tissues and organs is one of the most serious threats to human health. Although, organ transplantation and tissue engineering can meet the requirement for the repair of damaged tissues and organs in a certain extent, there are still many problems needed to be solved. Recent years, people have tried to use the concept of in situ tissue regeneration (in vivo tissue engineering) to repair the damaged tissues. In situ tissue regeneration is to implant tissue-specific biomaterials alone or combining with biomolecules to the sites of injury and take advantage of in vivo microenvironment and the properties of biomaterials aiming to guide the fete of cells to regenerate new tissues in situ without complicated in vitro manipulation There are several characteristics of in situ tissue regeneration:(1) recruiting autologous cells in situ without introduction of exogenous cells; (2) inducing the proliferation and differentiation of autologous cells without in vitro culture; (3) using in vivo microenvironment to induce the regeneration of damaged tissue. In situ tissue regeneration do not need exogenous cells, however, cells especially stem cells play an important role in tissue repair. The recruitment and capturing of sufficient autologous cells (especially stem cells) in situ is a key issue for in situ tissue regeneration In this paper, in terms of two stages of stem cell homing, namely stem cell recruitment and stem cell capturing, two biomaterial systems were designed in order to promote autologous stem cell homing. The two biomaterial systems may provide some ideas and methods that are useful for in situ tissue regeneration.As we all know that SDF-la is a widely recognized and used chemokine to induce the migration of bone marrow mesenchymal stem cells (BMSCs). However the inducing ability of SDF-la for BMSCs has not been systematically researched. Collagen/chitosan scaffold was used as fundamental biomaterials combined with SDF-la to construct bioactive scaffold system which can recruit BMSCs. First of all, sulfonated chitosan with negative charge was synthesized to combine with PLL and SDF-1α by electrostatic interactions to form composite particles. Secondly, collagen/chitosan scaffold was prepared by freeze drying method. In the end, the composite particles were injected into the collagen/chitosan scaffold to prepare active scaffold with the ability to induce stem cell migration. The size, morphology, SDF-la release behavior and the distribution in the scaffold of composite particles were characterized. The particle is spherical and the diameter is 1-2 μm The surface charge of the particle is negative. The release of SDF-la can last about two weeks and the composite particles are evenly distributed in the collagen/chitosan scaffold. Transwell model and bilayer scaffold model were used to characterize the migration of BMSCs induced by loaded composite particles in vitro. The results showed that the active scaffold could significantly promote the migration of BMSCs. At the same time, SD male rats were used as animal model to characterize the ability of active scaffold for the inducing migration of BMSCs in vivo by subcutaneous embedding method. Compared to the blank scaffold, active scaffold loaded with composite particles can recruit more BMSCs. Due to the ability of inducing the migration of BMSCs, the active scaffold biomaterial system is expected to have an important application in the field of in situ tissue regeneration.It is widely acknowledged that the capturing of stem cells recruited to scaffold is also important. Besides, the mechanical properties of natural materials are one of the major defects that limit their application. On the contrary, the mechanical properties of synthetic polymers can be well controlled. Therefore, Maleimide functional polyester material was designed and synthesized by ring-opening polymerization, then using BMSCs specific affinity peptides (EPLQLKM, E7) to modify the polyester to capture BMSCs. The structure of the polyester was characterized by’H NMR and the molecular weight of the polyester was characterized by gel permeation chromatography. Results showed the polyester was synthesized successfully and the molecular weight was about 25000. Static contact angle, XPS and SEM were used to characterize the polymer film, and the results showed that the peptide was successfully grafted onto the polyester. BMSCs were cultured on the surface of different polyester films. The results showed that the polyester films modified with peptide can significantly promote the adhesion of BMSCs. The proliferation results also showed that the peptide grafted polyester film promoted the proliferation of BMSCs. This new type of functional polyester material can be modified diversely for more extensive application for in situ tissue regeneration.