Lijing Hao

Directing the fate of human and mouse mesenchymal stem cells by hydroxyl-methyl mixed self-assembled monolayers with varying wettability

Self-assembled monolayers (SAMs) of alkanethiols on gold have been employed as model substrates to investigate the effects of surface chemistry on cell behavior. However, few studies were dedicated to the substrates with a controlled wettability in studying stem cell fate. Here, mixed hydroxyl (-OH) and methyl (-CH3) terminated SAMs were prepared to form substrates with varying wettability, which were used to study the effects of wettability on the adhesion, spreading, proliferation and osteogenic differentiation of mesenchymal stem cells (MSCs) from human and mouse origins. The numbers of adhered human fetal MSCs (hMSCs) and mouse bone marrow MSCs (mMSCs) were maximized on -OH/-CH3 mixed SAMs with a water contact angle of 40~70° and 70~90°, respectively. Hydrophilic mixed SAMs with a water contact angle of 20~70° also promoted the spreading of both hMSCs and mMSCs. Both hMSCs and mMSCs proliferation was most favored on hydrophilic SAMs with a water contact angle around 70°. In addition, a moderate hydrophilic surface (with a contact angle of 40~90° for hMSCs and 70° for mMSCs) promoted osteogenic differentiation in the presence of biological stimuli. Hydrophilic mixed SAMs with a moderate wettability tended to promote the expression of αvβ1 integrin of MSCs, indicating that the tunable wettability of the mixed SAMs may guide osteogenesis through mediating the αvβ1 integrin signaling pathway. Our work can direct the design of biomaterials with controllable wettability to promote the adhesion, proliferation and differentiation of MSCs from different sources.

Hierarchical porous hydroxyapatite microsphere as drug delivery carrier

Hollow hydroxyapatite microspheres with a hierarchical porous structure have been fabricated hydrothermally with the aid of citrate ions as a regulating agent. A possible formation mechanism was proposed. The high drug-loading capability and superior sustained release properties make it a promising carrier for drug delivery system.

Effects of hydroxyapatite microparticle morphology on bone mesenchymal stem cell behavior

Understanding the shape effect of hydroxyapatite (HAp) microparticles on cellular behavior is important for enabling new kinds of biological and biomedical applications. However, it is still a challenge to prepare HAp microparticles with different shapes but similar physicochemical properties, and then to investigate their relationships with cellular behavior. Herein, we developed a novel, facile route to regulate the morphology of HAp microparticles, and investigated the interaction between the particles and bone marrow mesenchymal stem cells (BMSCs). Our results revealed that the shape of HAp has a strong influence on cellular behavior, and that the sphere-like particles performed better than the rod-like particles. These findings highlight the importance of the shape characteristics of HAp microparticles, and may provide new insights for the utility of HAp-based materials.

A systematic examination of the morphology of hydroxyapatite in the presence of citrate

In this paper, a systematic study of the influence of various experimental parameters on morphology and size of hydroxyapatite (HAp) was investigated under hydrothermal conditions in the presence of sodium citrate. The Ca/citrate ratio, the pH value and the reaction temperature were important factors for the morphologenesis of HAp. The morphologies of the products were transformed from nanoparticles (plate, rod) to microparticles (dumbbell, flower and sphere like particle) accompanied with the alteration of experimental conditions. The interaction between citrate and HAp crystals was carefully demonstrated, and a possible formation mechanism of different nanostructures was proposed.

Surface chemistry from wettability and charge for the control of mesenchymal stem cell fate through self-assembled monolayers.

Self-assembled monolayers (SAMs) of alkanethiols on gold are highly controllable model substrates and have been employed to mimic the extracellular matrix for cell-related studies. This study aims to systematically explore how surface chemistry influences the adhesion, morphology, proliferation and osteogenic differentiation of mouse mesenchymal stem cells (mMSCs) using various functional groups (-OEG, -CH3, -PO3H2, -OH, -NH2 and -COOH). Surface analysis demonstrated that these functional groups produced a wide range of wettability and charge: -OEG (hydrophilic and moderate iso-electric point (IEP)), -CH3 (strongly hydrophobic and low IEP), -PO3H2 (moderate wettability and low IEP), -OH (hydrophilic and moderate IEP), -NH2 (moderate wettability and high IEP) and -COOH (hydrophilic and low IEP). In terms of cell responses, the effect of wettability may be more influential than charge for these groups. Moreover, compared to -OEG and -CH3 groups, -PO3H2, -OH, -NH2 and -COOH functionalities tended to promote not only cell adhesion, proliferation and osteogenic differentiation but also the expression of αv and β1 integrins. This finding indicates that the surface chemistry may guide mMSC activities through αv and β1 integrin signaling pathways. Model surfaces with controllable chemistry may provide insight into biological responses to substrate surfaces that would be useful for the design of biomaterial surfaces.

Hierarchically nanostructured hydroxyapatite microspheres as drug delivery carriers and their effects on cell viability

Hydroxyapatite microspheres (HAMSs) were fabricated via hydrothermal synthesis using propionamide (PA) as a pH-adjusting agent and trisodium citrate (TSC) as a regulating agent. Scanning electron microscopy (SEM) images indicated that the microspheres possessed well-defined 3D nanostructures constructed by nanoplates as building blocks. In vitro cell tests demonstrated that the HAMSs with or without heat treatment were able to promote the proliferation of mouse bone mesenchymal stem cells (mBMSCs). Gentamicin sulphate (GS), an anti-inflammatory, was successfully loaded in the HAMS particles at a distinctively high loading efficiency of approximately 87%. The resultant HAMS-GS delivery systems displayed a sustained release property, and the release of GS from the HAMS-B-GS500 system could significantly inhibit S. epidermidis growth. Moreover, the biocompatibility tests indicated that the HAMS-B-GS500 system exhibited excellent biocompatibility and had no toxic effects on the mBMSCs. These outstanding characteristics may make HAMSs a good candidate as an injectable and drug-loading biomaterial for in vivo tissue regeneration and drug control release.

Engineering poly(lactic-co-glycolic acid)/hydroxyapatite microspheres with diverse macropores patterns and the cellular responses

Present studies on the topographic effects of substrates on cell functions are limited to planar substrates, which are usually not applicable in bone repair. Specific patterns are rarely constructed on 3D substrates. Here spherical substrates with macroporous topography were obtained to explore cellular responses. Macropores with tunable density were generated on the surfaces of poly(lactic-co-glycolic acid)/hydroxyapatite (PLGA/HA) microspheres by using HA particles as the pore-forming source. Different densities of macropores represented different topographies and were found to influence the morphology, proliferation and osteogenic differentiation of human fetal mesenchymal stem cells (fMSCs). The microspheres with a medium density of macropores most benefitted proliferation and differentiation of fMSCs compared with the low and high density ones. This study reveals the role of macroporous spherical surfaces in affecting cell function and may guide the design of functional substrates in bone repair.

The Role of Ninth Type-III Domain of Fibronectin in the Mediation of Cell-binding Domain Adsorption on Surfaces with Different Chemistry

The orientation and conformation of adhesive proteins after adsorption play a central role in cell-binding bioactivity. Fibronectin (Fn) holds two peptide sequences that favor cell adhesion: the Arg-Gly-Asp (RGD) loop on the tenth type-III domain (Fn-III10) and the Pro-His-Ser-Arg-Asn (PHSRN) synergy site on the ninth type-III domain (Fn-III9). Herein, adsorption of Fn fragments (Fn-III10 and Fn-III9-10) on self-assembled monolayers (SAMs) carrying various functional groups (-COOH, -NH2, -CH3, and -OH) was investigated by the Monte Carlo method and molecular dynamics simulation in order to understand its mediation effect on cell adhesion. The results demonstrated that Fn-III9 could enhance the stiffness of the Fn molecule and further fix the adsorption orientation. The RGD site of the Fn fragment appeared to be deactivated on hydrophobic surfaces (CH3-SAM) because of the binding of adjacent nonpolar residues on surfaces, whereas charged surfaces (COOH-SAM and NH2-SAM) and hydrophilic surfaces (OH-SAM) were conducive to the formation of cell-binding-favorable orientation for Fn fragments. The cell adhesion capability of Fn fragments was highly improved on positively charged surfaces (NH2-SAM) and hydrophilic surfaces because of the advantageous steric structure and orientation of both RGD and PHSRN sites. This work provides an insight into the interplay at the atomic scale between protein adsorption and surface chemistry for designing biologically responsive substrate surfaces.