Yinli Li

Collagen coated tantalum substrate for cell proliferation

The extracellular matrix (ECM) plays a key role in cell culture in various physiological and pathological processes in the field of tissue engineering. Recently, the type I collagen ECM has been widely utilized in vitro model systems for the attachment of many different cell lines since it has multi-functions in human tissues. For example it accounts for 6% of the weight of strong, tendinous muscles. In this paper, we reported a new material by coating tantalum (Ta), one highly biocompatible metal, with type I collagen fibrils. The morphology of the new material was studied by high resolution atomic force microscope. It was shown that the adhesion force between type I collagen fibrils network and Ta was strong enough to overcome surface defects. A possible way to explain the phenomenon is that the longitudinal periodicity of collagen fibrils matches the grain size of the Ta domains, which results in increase of the physical adsorption contact area, thereby inducing the dramatic adhesion enhancement between collagen fibrils and Ta. The obtained material was then employed as a template for cell proliferation. Although the surface of this template is more hydrophobic by comparison with the bare Ta surface, the cells on this material were successfully incubated, indicating that the collagen coated Ta might be used as the buffer layer for proliferating cells in hydrophobic biomaterials.

Building the first hydration shell of deprotonated glycine by the MCMM and ab initio methods.

The first hydration shell of the deprotonated glycine is built up by the discrete hydration model. The potential energy surfaces (PESs) of the deprotonated glycine and its hydration complexes with different number of water molecules have been scanned by the Monte Carlo multiple minimum (MCMM) conformational search analysis with the MMFFs force field. Then the energy-minimized structures are predicted using the high-level ab initio calculations/MP2/6-311++G(d,p). The results of the structural parameters and the infrared spectra indicate that the first-shell water molecules around the anion of deprotonated glycine play a more important role in determining the hydration process of deprotonated glycine. The competition between the hydrate site I and the hydrate site II represents a dynamic process of hydrated complexes. The vibrational properties of C═O and N-H are determined to characterize the structure of deprotonated glycine in solution by the discrete hydration model and the conductor-like polarizable continuum model (CPCM) in the gas phase, respectively.

Ab initio investigation of the first hydration shell of protonated glycine

The first hydration shell of the protonated glycine is built up using Monte Carlo multiple minimum conformational search analysis with the MMFFs force field. The potential energy surfaces of the protonated glycine and its hydration complexes with up to eight water molecules have been scanned and the energy-minimized structures are predicted using the ab initio calculations. First, three favorable structures of protonated glycine were determined, and the micro-hydration processes showed that water can significantly stabilize the unstable conformers, and then their first hydration shells were established. Finally, we found that seven water molecules are required to fully hydrate the first hydration shell for the most stable conformer of protonated glycine. In order to analyse the hydration process, the dominant hydration sites located around the ammonium and carboxyl groups are studied carefully and systemically. The results indicate that, water molecules hydrate the protonated glycine in an alternative dynamic hydration process which is driven by the competition between different hydration sites. The first three water molecules are strongly attached by the ammonium group, while only the fourth water molecule is attached by the carboxyl group in the ultimate first hydration shell of the protonated glycine. In addition, the first hydration shell model has predicted most identical structures and a reasonable accord in hydration energy and vibrational frequencies of the most stable conformer with the conductor-like polarizable continuum model.

Exploring the complex mechanical properties of xanthan scaffolds by AFM-based force spectroscopy

Summary The polysaccharide xanthan has been extensively studied owing to its potential application in tissue engineering. In this paper, xanthan scaffold structures were investigated by atomic force microscope (AFM) in liquid, and the mechanical properties of the complex xanthan structures were investigated by using AFM-based force spectroscopy (FS). In this work, three types of structures in the xanthan scaffold were identified based on three types of FS stretching events. The fact that the complex force responses are the combinations of different types of stretching events suggests complicated intermolecular interactions among xanthan fibrils. The results provide crucial information to understand the structures and mechanical properties of the xanthan scaffold.

Direct force producing uniform ultra-thin chitosan films by atomic force microscopy

Biopolymer chitosan plays an important role in functional nanomaterials, tissue engineering and other biological applications. Chitosan thin films have also been involved in many optical phenomena in living organisms, which potentially allows the use of chitosan for optical applications. However, it is rather difficult to produce uniform thin chitosan films because of its intrinsic viscoelasticity. Here we report the fabrication of uniform ultra-thin chitosan films with a thickness of several nanometres using a two-step physical approach with the help of spin coating and mechanical manipulation.

Nanomechanics of phospholipid LB film studied layer by layer with AFM

BackgroundPhospholipid, a main component of cell membrane, has been explored as a model system of the cell membrane and temporary scaffold materials in recent studies. The mechanical properties of phospholipid layers are essentially interesting since it is involved in several biological processes.ResultsHere, the nanomechanical properties such as indentation force, adhesion force and DMT (Derjaguin-Müller-Toporov) modulus of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) Langmuir-Blodgett (LB) films were analyzed layer by layer with Atomic Force Microscope (AFM) under deionized water condition.ConclusionsThe penetration distances in the indentation force curves are equal to the thicknesses of phospholipid films, and the yield forces of DSPC LB films in deionized water are smaller than that of similar lipid films in buffered solutions due to the influence of ions. Moreover, the DMT modulus of upper layer DSPC LB film is different from that of monolayer DSPC LB film due to the influence of their different substrates. Our results suggest that environment such as surrounding ions and substrate will strongly influence the measured nano-mechanical properties of the lipid bilayer, especially that of the down layer.Graphical AbstractA process about the exploration of nanomechanics of DSPC LB film.

Two-dimensional scaffold layer formations on a solid surface through xanthan polysaccharide: temperature effect.

The influences of temperature on xanthan biopolymer assemblies on a two-dimensional surface have been thoroughly studied. High resolution atomic force microscope images show that the xanthan nanofibrils can be used to build up well-dispersed 2D scaffold layer after 1 day annealing at 35 degrees C. By increasing annealing temperatures (60 degrees C, 90 degrees C) of xanthan solutions, the well-dispersed layers can be produced rapidly (6h, 0.5h) with micro-sized pore structures. The xanthan scaffold with pore structures potentially allows accommodating micro-sized cells for tissue engineering.

Characterization of Inter- and Intramolecular Interactions of Amyloid Fibrils by AFM-Based Single-Molecule Force Spectroscopy

Amyloids are fibrous protein aggregates defined by shared specific structural features. Abnormal accumulation of amyloid in organs leads to amyloidosis, which results in various neurodegenerative diseases. Atomic force microscopy (AFM) has proven to be an excellent tool investigating amyloids; it has been extensively utilized to characterize its morphology, assembly process, and mechanical properties. This review summarizes studies which applied AFM to detect the inter- and intramolecular interactions of amyloid fibrils and classified the influencing factors of amyloid’s nanomechanics in detail. The characteristics of amyloid fibrils driven by inter- and intramolecular interactions, including various morphologies of amyloid fibrils, self-assembly process, and the aggregating pathway, are described. Successful examples where AFM provided abundant information about inter- and intramolecular interactions of amyloid fibrils in different environments are presented. Direct force measurement of intra- or intermolecular interactions utilizing an AFM-based tool, single-molecular force spectroscopy (SMFS), is introduced. Some mechanical information such as elasticity, adhesiveness, and strength was obtained by stretching amyloid fibrils. This review helps researchers in understanding the mechanism of amyloidogenesis and exploring the properties of amyloid using AFM techniques.

Investigating the Co-Adsorption Behavior of Nucleic-Acid Base (Thymine and Cytosine) and Melamine at Liquid/Solid Interface

The co-adsorption behavior of nucleic-acid base (thymine; cytosine) and melamine was investigated by scanning tunneling microscopy (STM) technique at liquid/solid (1-octanol/graphite) interface. STM characterization results indicate that phase separation happened after dropping the mixed solution of thymine-melamine onto highly oriented pyrolytic graphite (HOPG) surface, while the hetero-component cluster-like structure was observed when cytosine-melamine binary assembly system is used. From the viewpoints of non-covalent interactions calculated by using density functional theory (DFT) method, the formation mechanisms of these assembled structures were explored in detail. This work will supply a methodology to design the supramolecular assembled structures and the hetero-component materials composed by biological and chemical compound.