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Liquid-liquid phase separation (LLPS) is a ubiquitous process found in a variety of fields. It is of particular importance in biological sciences since it plays essential and vital roles in a number of physiological and pathological processes in biological systems. After LLPS, the dense droplets can grow in size via incorporating solutes from surrounding environment and in some cases coalescing with other droplets. Interestingly, the size of the dense droplets seems to have an upper limit but the mechanism remains to be explored. Since the droplet size can be essential for biological functioning, it is important to understand the size evolution of the phase separated droplets. Here we propose a physical mechanism with consideration of impurities on the surface of the dense liquid droplets. The theoretical predictions can be used to explain the observations on the size evolution. Based on the coalescence mechanism, we succeeded for the first time performing a challenging task, i.e., growing a single suspended protein crystal via merging phase-separated droplets in a fully non-contact manner. The mechanism observed may be considered as a basic model for researches in much broader fields involving phase separation, such as in biology, materials science, physics, chemistry, and meteorology.

Peritendinous blood circulation improvement is a challenge to promote the healing of ruptured tendons in clinical treatment. Although electrospun membranes or scaffolds enable the reduction of complications such as adhesion, however, low efficiency, toxicity issues, the loss of biological activity, and complex electrospinning techniques are all bottlenecks of these systems. Improving the blood supply is crucial for their successful use, which involves promoting the metabolism and nutrient absorption in tendons. Here, a multifunctional, structurally simple strategy involving heparin-loaded sutures (PPH) that are clinically applicable is reported, in the form of electrospun core-shell nanofibers, with the ability to perform sustained release of anticoagulants heparin (verified in our previous publication) for the improvement of the healing of Achilles tendon. The morphology and diameter distribution of the collagen fiber in the PPH group are closely related to the health of the Achilles tendon than those of commercial sutures (CS). The in vivo results of the total collagen content and the expression of collagen type I in the PPH group are more than those of the CS group. After 6 weeks of culture, the tensile strength of the PPH group shows no significant difference compared to the healthy group. The data obtained in this study improves the current understanding on the regeneration of ruptured tendons and presents a promising strategy for clinical treatment.

The problem of global water pollution is becoming more and more severe, among which organic dyes and heavy metal ions are two typical types of the most common pollutants. The adsorption method for water purification and wastewater treatment is widely studied and applied. Hydrogel has unique advantages in the field of adsorption due to its three-dimensional porous structure. In this paper, a new type of self-healing hydrogels based on reversible covalent bond were prepared by mixing poly(vinyl alcohol) (PVA) and 2-aminophenylboronic acid modified polyacrylic acid (PAA-2APBA). In addition, the introduction of laponite nanoparticles into the hydrogel can increase both the mechanical strength and adsorption efficiency. This low-cost PAA-2APBA/PVA/laponite nano-composite hydrogel could efficiently remove the organic dyes and heavy metal ions in model waste water through simple immersion, which makes it have application prospects in the fields of both biomedical and environmental engineering.

Zinc is a biodegradable metal, which exhibits more moderate biodegradability than magnesium and iron, so that it has great application potential in the field of biomedical materials. Alloying of zinc and iron may lead to producing a new type of implant material Zn—Fe alloy, which might be able to meet the requirements for a moderate degradation rate. However, due to the huge difference in the melting point between zinc and iron, the preparation of Zn—Fe alloy is quite challenging and hence rarely reported. In this study, we show that Zn—Fe alloys can be successfully prepared by electrodeposition technology. The microstructures, composition, degradation properties and biocompatibility of the Zn—Fe alloys were systematically studied. The results showed that the content of iron in the alloys ranged from 0 to 8 wt%, depending on the concentration of Fe ions and the current density. In the alloys, the major's phases were η, δ and Г1, and they were mainly affected by the ion concentration in the electrolyte. In the in vitro immersion tests, the Zn—Fe alloy ZF2–1 showed the highest immersion corrosion rate, while ZF3–1 showed the highest electrochemical corrosion rate. Moreover, we found that the corrosion rates of the alloys were significantly higher than that of the pure Fe. In the in vivo experiments, we confirmed that the Zn—Fe alloy possessed good biocompatibility. These results demonstrate that the electrodeposition technology is a good method to prepare Zn—Fe alloys, and the Zn—Fe alloys prepared by this method are potentially promising materials for biomedical applications.

Objective: Magnetic drug targeting (MDT) has attracted a lot of attention in recent years as a treatment to reduce side effects and improve efficacy. To realize successful MDT, a magnet system that can create suitable magnetic field is necessary. However, the existing technology has some shortcomings such as low targeting efficiency and unsatisfactory targeting effect. The method of using time-varying magnetic field proposed in this paper provides a new solution to this problem. Methods: In this work, a permanent magnet system providing rotational magnetic field (a time-varying magnetic field) was designed and constructed. Focusing experiments of Fe3O4 particles were carried out in this system, and the mechanism of the focusing was discussed via a simplified model. Results: By using the rotational magnetic field, superparamagnetic Fe3O4 particles can be successfully driven to the designated site within a short time. Our work showed that the time-varying magnetic field can drive the superparamagnetic particles to a focusing site, which is not possible under the same magnetic field without rotation, and the aggregation speed and effect are better than those under static field. Conclusion and Significance: Our results indicate that time-varying magnetic field can be a good choice for designing magnet systems for MDT. Moreover, the idea of using time-varying magnetic field for focusing superparamagnetic particles may be applicable in non-contact processings or manipulations of paramagnetic, superparamagnetic, or even ferromagnetic materials or objects in preparation of novel materials, robotic control of objects, and so on.

It has been widely accepted that cell culture in two-dimensional (2D) conditions may not be able to represent growth in three-dimensional (3D) conditions. Systematic comparisons between 2D and 3D cell cultures are needed to appropriately use the existing 2D results. In this work, we conducted a comparative study between 2D and 3D cell cultures of MC3T3-E1 using the same type of material (a mixture of silk fibroin (SF) and chitosan (CS)). Our results showed 3D SF/CS scaffold exhibited different effects on cell culture compared with the 2D cases. 1) The cells grown in 3D scaffold showed multiple morphologies. 2) The proliferation of cells in 3D scaffold was long-term and sustainable. 3) Cell differentiation occurred throughout the entire 3D scaffold. The results showed that cell culture in 3D SF/CS scaffold exhibited different features than 2D cases and 3D SF/CS scaffold could be a promising material for 3D cell culture.

In recent years, biodegradable metallic materials, such as Mg-, Fe-, Zn- and W-based materials, have been the focus of many studies. As one of the two most studied types of biodegradable metallic materials, Fe-based materials have aroused a great deal of interest because of their outstanding mechanical properties, which are similar to stainless steel. The processing methods can directly affect the microstructure of the material and influence the mechanical and degradation properties of the material. Furthermore, biocompatibility is directly affected by the degradation properties. Therefore, the processing methods, mechanical properties, degradability and biocompatibility are several of the main concerns in the study of biodegradable Fe-based materials. Here, we systematically summarize recent studies on Fe-based materials and discuss these findings in terms of their processing methods, degradability and biocompatibility.

Large gradient magnetic fields simultaneously provide both strong magnetic and simulated gravitational fields. Processes in such environments are subject to the influences of these two fields. Previous studies have shown that the deposition of hydroxyapatite (HAp) coatings induced by self-assembled monolayers (SAMs) is affected by large gradient magnetic fields. To further clarify the mechanism, we examined the effects of gravitational and magnetic fields on the deposition kinetics of the SAMs and the HAp coatings via surface analysis and molecular simulation. The chemical compositions of the SAMs and the HAp coatings in the fields were detected by X-ray photoelectron spectroscopy (XPS). The ability of the SAMs to induce the deposition of apatite was investigated via first principles calculations, which were performed to obtain information about the bonding interactions between the self-assembled functional groups and the –PO 4 3− ions in simulated body fluid (SBF). The experimental results showed that the fields affected the compositions of the apatite layers. The first principles calculation results showed that the –PO 4 H 2− functional group exhibited a stronger ability to induce apatite deposition than the –COOH functional group. This result suggested that hydrogen phosphate root groups are better nucleation sites than carboxyl root groups.

As a biodegradable polymer thin film, silk fibroin/chitosan composite film overcomes the defects of pure silk fibroin and chitosan films, respectively, and shows remarkable biocompatibility, appropriate hydrophilicity and mechanical properties. Silk fibroin/chitosan thin film can be used not only as metal implant coating for bone injury repair, but also as tissue engineering scaffold for skin, cornea, adipose, and other soft tissue injury repair. However, the biocompatibility of silk fibroin/chitosan thin film for mesenchymal stem cells, a kind of important seed cell of tissue engineering and regenerative medicine, is rarely reported. In this study, silk fibroin/chitosan film was prepared by solvent casting method, and the rat bone marrow-derived mesenchymal stem cells were cultured on the silk fibroin/chitosan thin film. Osteogenic and adipogenic differentiation of rat bone marrow-derived mesenchymal stem cells were induced, respectively. The proliferation ability, osteogenic and adipogenic differentiation abilities of rat bone marrow-derived mesenchymal stem cells were systematically compared between silk fibroin/chitosan thin film and polystyrene tissue culture plates. The results showed that silk fibroin/chitosan thin film not only provided a comparable environment for the growth and proliferation of rat bone marrow-derived mesenchymal stem cells but also promoted their osteogenic and adipogenic differentiation. This work provided information of rat bone marrow-derived mesenchymal stem cells behavior on silk fibroin/chitosan thin film and extended the application of silk fibroin/chitosan thin film. Based on the results, we suggested that the silk fibroin/chitosan thin film could be a promising material for tissue engineering of bone, cartilage, adipose, and skin.

Achilles tendon reconstruction surgery is the primary clinical method for repairing acute Achilles tendon ruptures. However, the efficacy of the postoperative healing process and the recovery of physiological function are inadequate. This study examines the healing mechanism of ruptured rat Achilles tendons seamed with heparin-loaded core-shell fiber sutures fabricated via near-field electrospinning. High-heparin-concentration sutures (PPH3.0) perform better than the low-heparin-concentration sutures and commercial sutures (CSs). The PPH3.0 suture recruits fewer inflammatory cells and shows good histocompatibility in peritoneal implantation experiments. Staining of the Achilles tendon rupture repair zone demonstrates that a high heparin concentration in sutures reduces immune-inflammatory responses. Immunohistochemical analysis reveals that the transforming growth factor-β staining scores of the PPH3.0 sutures are not significantly different from those of the corresponding control group but are significantly different from those of the CSs and non-heparin-loaded-suture groups. According to vascular endothelial growth factor (VEGF) analysis, the concentration of VEGF in the group treated with the PPH3.0 suture increases by 37.5% compared with that in its control group. No significant difference in tension strength is observed between the PPH3.0 group and healthy Achilles tendons. These findings illustrate that this novel method effectively treats Achilles tendon rupture and promotes healing and regeneration.

This research was aim to develop novel cyclodextrin/chitosan (CD/CS) nanocarriers for insoluble drug delivery through the mild ionic gelation method previously developed by our lab. A series of different β-cyclodextrin (β-CD) derivatives were incorporated into CS nanoparticles including hydroxypropyl-β-cyclodextrin (HP-β-CD), sulphobutylether-β-cyclodextrin (SB-β-CD), and 2,6-di-O-methy-β-cyclodextrin (DM-β-CD). Various process parameters for nanoparticle preparation and their effects on physicochemical properties of CD/CS nanoparticles were investigated, such as the type of CD derivatives, CD and CS concentrations, the mass ratio of CS to TPP (CS/TPP), and pH values. In the optimal condition, CD/CS nanoparticles were obtained in the size range of 215–276 nm and with the zeta potential from 30.22 mV to 35.79 mV. Moreover, the stability study showed that the incorporation of CD rendered the CD/CS nanocarriers more stable than CS nanoparticles in PBS buffer at pH 6.8. For their easy preparation and adjustable parameters in nanoparticle formation as well as the diversified hydrophobic core of CD derivatives, the novel CD/CS nanoparticles developed herein might represent an interesting and versatile drug delivery platform for a variety of poorly water-soluble drugs with different physicochemical properties.

Cross-linked protein crystal technology, as either a protein stabilisation or enzyme immobilisation method, has garnered more attention recently. This method not only can retain the original activity of the protein molecule but can also significantly enhance the crystals' mechanical and chemical stability. This review presents the preparation and mechanism of cross-linked protein crystals using glutaraldehyde. The mechanical, chemical and thermal properties of the cross-linked protein crystals are also reviewed in detail. In addition, this paper summarises the applications of cross-linked protein crystals in the fields of materials science, biosensors, chromatographic analysis, oral delivery and protein crystal quality improvement. Finally, the limitations and perspectives on cross-linked protein crystals are presented.

Crystallisation of proteins is usually achieved with the help of chemical agents. Because there are few general guidelines in determining what agents will help to crystallise a specific protein, suitable crystallisation agents are often found via exhaustive trial-and-error tests by mixing many chemical agents (the collection of which is called a crystallisation screening kit) one-by-one with the protein. Currently, many commercially available crystallisation screening kits have been developed and utilised in practical crystallisation screen experiments. However, information regarding the design of new screening kits has yet to be expanded using a large amount of experimental data. Here, we show the step-by-step design processes of a polyethylene glycol-based screening kit. It was found that the screening performance could be improved by modifying the crystallisation screening kits according to the accumulated data (such as those in the Biological Macromolecule Crystallisation Database (BMCD)), the screening test results and existing knowledge. The screening kit designed in this paper can be used for practical protein crystallisation screen experiments and the method can be used in the design of other crystallisation screening kits.

We present a new method for the realization of high-throughput protein crystallization screening using an array of 96 capillaries aligned in a circle. In this method, each capillary represents a single crystallization condition, and all capillaries experience identical magnetic field conditions. After crystallization, the crystals in the capillary can be directly diffracted without harvesting. This method proved easy to perform and is applicable for use in magnetic fields and may be further extended for use in other circumstances, for example, under space microgravity conditions.

The objective of this study was to investigate the potential of methoxy polyethylene glycol (mPEG) grafted chitosan (mPEG-g-CS) to be used as a drug carrier. mPEG-g-CS was successfully synthesized by one-step method with formaldehyde. The substitution degree of mPEG on chitosan was calculated by elemental analysis and was found to be (3.23 ± 0.25)%. mPEG-g-CS self-assembled micelles were prepared by ultrasonic method with the controlled size of 178.5–195.1 nm and spherical morphology. Stable dispersion of the micelles was formed with the zeta potential of 2.3–30.2 mV. 5-Fluorouracil (5-FU), an anticancer chemotherapy drug, was used as a model drug to evaluate the efficiency of the new drug delivery carrier. The loading efficiency of 5-FU was (4.01 ± 0.03)%, and the drug-loaded mPEG-g-CS self-assembled micelle showed a controlled-release effect. In summary, the mPEG-g-CS self-assembled micelle is proved to be a promising carrier with controlled particle size and controlled-release effect. Therefore, it has great potential for the application as 5-FU carriers for effective anti-tumor activity.

Electrospinning is a powerful method for preparing porous materials that can be applied as biomedical materials for implantation or tissue engineering or as scaffolds for 3D cell culture experiments. However, this technique is limited in practical applications because the pore size of 3D scaffolds directly prepared by conventional electrospinning is usually less than several tens of micrometres, which may not be suitable for 3D cell culture and tissue growth. To allow for satisfactory 3D cell culture and tissue engineering, the pore size of the scaffold should be controllable according to the requirement of the specific cells to be cultured. Here, we show that layer-structured scaffolds with pore sizes larger than 100μm can be obtained by stacking meshes prepared by direct-writing using the near-field electrospinning (NFES) technique. In the study, we prepared composite scaffolds made of polycaprolactone (PCL) and hydroxyapatite (HAp) via the above-mentioned method and tested the effectiveness of the novel scaffold in cell culture using mouse pre-osteoblast cells (MC3T3-E1). The pore size and the degradability of the PCL/HAp scaffolds were characterized. The results showed that the average pore size of the scaffolds was 167μm, which was controllable based on the required application; the degradation rate was controllable depending on the ratio of PCL to HAp. The biocompatibility of the scaffolds in vitro was studied, and it was found that the scaffolds showed no toxicity and that the cells could effectively attach, proliferate, and differentiate in the 3D skeleton of the scaffolds. Our studies showed that a simple modification of the preparation procedure can lead to a new way to fabricate novel layer-structured 3D scaffolds with controllable structures and pore sizes suitable for practical applications in implantation, tissue engineering and 3D cell culture.

The physical and chemical properties of the scaffold are known to play important roles in three-dimensional (3D) cell culture, which always determine the cellular fate or the results of implantation. To control these properties becomes necessary for meeting the requirements of a variety of tissue engineering applications. In this study, a series of silk fibroin/chitosan (SF/CS) scaffolds with tunable properties were prepared using freeze-drying method, and the rat bone marrow-derived mesenchymal stem cells (BM-MSCs) were seeded in these scaffolds to evaluate their availability of use in tissue engineering. The 3D structure, mechanical properties and degradation ability of SF/CS scaffold can be tuned by changing the total concentration of the precursor solution and the blending ratio between SF and CS. BM-MSCs cultured in the SF/CS scaffold exhibited excellent proliferation and multiple morphologies. The induction of osteogenic and adipogenic differentiation of BM-MSCs were successful in this scaffold when cultured in vitro. Subcutaneous implantation of the SF/CS scaffolds did not cause any inflammatory response within four weeks, which revealed good compatibility. Moreover, the implanted scaffold allowed host cells to invade, adhere, grow and form new blood vessels. With these excellent performance, SF/CS scaffold has great potential in preparing implants for tissue engineering applications.

This paper introduces a novel platform designed to be used in a strong static magnetic field (in a superconducting magnet). The platform is a sample holder that rotates in the strong magnetic field. Any samples placed in the platform will rotate due to the rotation of the sample holder. With this platform, a number of experiments such as material processing, culture of biological systems, chemical reactions, or other processes can be carried out. In this report, we present some preliminary experiments (protein crystallization, cell culture, and seed germination) conducted using this platform. The experimental results showed that the platform can affect the processes, indicating that it provides a novel environment that has not been investigated before and that the effects of such an environment on many different physical, chemical, or biological processes can be potentially useful for applications in many fields.

A magnetic field is an often-encountered physical environment that can affect many processes, including chemical, physical, and biochemical processes. Utilization of magnetic fields is thus very helpful in a wide variety of applications, such as scientific research in various disciplines, materials processing (e.g., crystal growth and separation) in industry, and nuclear fusion. There are many different types of magnetic fields generated by different magnets, such as superconducting magnets, electromagnets, hybrid magnets, pulsed magnets, and permanent magnets. In this paper, we introduce a newly designed periodic magnetic field generated by rotating permanent magnet pairs. Preliminary tests showed that the periodic magnetic field is valuable in water evaporation, silver deposition, and protein crystallization. Apparently, in such a new environment that can generate a periodic magnetic field, a periodic force field will also be simultaneously generated on the sample. Further work shall be carried out to explore the potential applications of this magnetic field.

Melt electrospinning is a complex process, and many of the processing parameters can impact the result of fiber formation. In this paper, we conducted a systematic investigation on the impacts of the melt electrospinning parameters (including temperature, needle gauge, flow rate and collector speed) on the fiber diameter via an orthogonal design experiment. The straight single fibers were fabricated using melt electrospinning in a direct-writing way with a diameter varied from 9.68 ± 0.93 µm to 48.55 ± 3.72 µm. The results showed that the fiber diameter changed differently against different parameters: when the temperature or needle gauge increased, the fiber diameter increased first and then decreased; when the flow rate increased, the fiber diameter decreased first and then increased; when the collector speed increased, the fiber diameter decreased monotonously. We also found that the collector speed was the most influential factor while the needle gauge was least important in determining the diameter of the fiber. Moreover, the feasibility of melt electrospinning in a direct-writing way as a novel 3D printing technology had been demonstrated by fabricating both uniform and controllable structures with high accuracy, based on the optimal parameters from the orthogonal experiments. The promising results indicated that melt electrospinning can be developed as a powerful technique for fabricating miniatured parts with high resolution and controllable structures for versatile potential applications.

Temperature is generally considered as an important factor in protein crystallization. Such is true because crystals usually grow at a preferable temperature in a certain crystallization solution. If a nonsuitable temperature is used, the solution will not yield crystals. However, it is difficult to decide the best temperature suited for screening the crystallization condition of proteins. In this study, it was found out that, compared to constant temperature, a variation in a reasonable range can result in a more efficient crystallization screening. Using the Sparse Matrix Screen with the screening kit Index, this study tested nine commercially available proteins and proved that, compared to the conventional constant temperature strategy, a varying temperature strategy can actually increase the possibility of obtaining crystals. Consequently, the cycling temperature strategy (CTS) is then proposed to be utilized in most screening tasks when the suitable crystallization temperature is unknown.

Magnetic field has been found to be able to improve the quality of some protein crystals; containerless condition is considered to be beneficial for growing good-quality crystals. Nevertheless, there has been no report on combination of these two conditions for protein crystallization. In this paper, crystallization and dissolution of protein crystals in a levitated containerless droplet in a strong magnetic field has been successfully achieved. New phenomena were observed for both crystallization and dissolution processes.

Ya-Jing Ye,1 Yun Wang,1 Kai-Yan Lou,1 Yan-Zuo Chen,1 Rongjun Chen,2 Feng Gao1,3,4 1Department of Pharmaceutics, School of Pharmacy, East China University of Science and Technology, Shanghai, People’s Republic of China; 2Department of Chemical Engineering, Imperial College London, London, United Kingdom; 3Shanghai Key Laboratory ofFunctional Materials Chemistry, 4Shanghai Key Laboratory of New Drug Design, East China University of Science and Technology, Shanghai, People’s Republic of China Abstract: A novel biocompatible and biodegradable drug-delivery nanoparticle (NP) has been developed to minimize the severe side effects of the poorly water-soluble anticancer drug paclitaxel (PTX) for clinical use. PTX was loaded into the hydrophobic cavity of a hydrophilic cyclodextrin derivative, heptakis (2,6-di-O-methyl)-β-cyclodextrin (DM-β-CD), using an aqueous solution-stirring method followed by lyophilization. The resulting PTX/DM-β-CD inclusion complex dramatically enhanced the solubility of PTX in water and was directly incorporated into chitosan (CS) to form NPs (with a size of 323.9–407.8 nm in diameter) using an ionic gelation method. The formed NPs had a zeta potential of +15.9–23.3 mV and showed high colloidal stability. With the same weight ratio of PTX to CS of 0.7, the loading efficiency of the PTX/DM-β-CD inclusion complex-loaded CS NPs was 30.3-fold higher than that of the PTX-loaded CS NPs. Moreover, it is notable that PTX was released from the DM-β-CD/CS NPs in a sustained-release manner. The pharmacokinetic studies revealed that, compared with reference formulation (Taxol®), the PTX/DM-β-CD inclusion complex-loaded CS NPs exhibited a significant increase in AUC0→24h (the area under the plasma drug concentration–time curve over the period of 24 hours) and mean residence time by 2.7-fold and 1.4-fold, respectively. Therefore, the novel drug/DM-β-CD inclusion complex-loaded CS NPs have promising applications for the significantly improved delivery and controlled release of the poorly water-soluble drug PTX or its derivatives, thus possibly leading to enhanced therapeutic efficacy and less severe side effects. Keywords: dimethyl-β-cyclodextrin, inclusion complex, chitosan nanoparticles, drug delivery, sustained release, paclitaxel

Eutectic melting bonding (EMB) method is a useful technique for fabricating bioactive coatings with relatively high crystallinity and bonding strength with substrate on titanium substrates. Using the EMB method, hydroxyapatite/Ti2Ni coatings were prepared on the surface of Ti–6Al–4V at a relatively low temperature (1,050 °C) in a vacuum furnace. The coatings were then characterized in terms of phase components, microstructure, bonding strength and cytotoxicity. The results showed that the coatings were mainly composed of HAp and Ti2Ni, and the thickness of the coatings was approximately 300 μm. X-ray diffraction analysis showed that the coatings exhibited relatively high crystallinity. The tensile bonding strength between the coatings and the substrates was 69.68 ± 5.15 MPa. The coatings had a porous and rough surface which is suitable for cell attachment and filopodia growth. The cell culture study showed that the number of MG-63 cells increased, and the cell morphology changed with the incubation time. This study showed that the EMB method can be utilized as a potentially powerful method to obtain high quality hydroxyapatite coatings with desired mechanical and biocompatibility properties on Ti-alloy substrates.

As the most widely utilized technique to determine the 3-dimensional structure of protein molecules, X-ray crystallography can provide structure of the highest resolution among the developed techniques. The resolution obtained via X-ray crystallography is known to be influenced by many factors, such as the crystal quality, diffraction techniques, and X-ray sources, etc. In this paper, the authors found that the protein sequence could also be one of the factors. We extracted information of the resolution and the sequence of proteins from the Protein Data Bank (PDB), classified the proteins into different clusters according to the sequence similarity, and statistically analyzed the relationship between the sequence similarity and the best resolution obtained. The results showed that there was a pronounced correlation between the sequence similarity and the obtained resolution. These results indicate that protein structure itself is one variable that may affect resolution when X-ray crystallography is used.