Recent Advances in 3D Printing of Photocurable Polymers: Types,Mechanism, and Tissue Engineering Application

The conversion of liquid resin into solid structures upon exposure to light of a specific wavelength is known as photopolymerization. In recent years, photopolymerization-based 3D printing has gained enormous attention for constructing complex tissue-specific constructs. Due to the economic and environmental benefits of the biopolymers employed, photo-curable 3D printing is considered an alternative method for replacing damaged tissues. However, the lack of suitable bio-based photopolymers, their characterization, effective crosslinking strategies, and optimal printing conditions are hindering the extensive application of 3D printed materials in the global market. This review highlights the present status of various photopolymers, their synthesis, and their optimization parameters for biomedical applications. Moreover, a glimpse of various photopolymerization techniques currently employed for 3D printing is also discussed. Furthermore, various naturally derived nanomaterials reinforced polymerization and their influence on printability and shape fidelity are also reviewed. Finally, the ultimate use of those photopolymerized hydrogel scaffolds in tissue engineering is also discussed. Taken together, it is believed that photopolymerized 3D printing has a great future, whereas conventional 3D printing requires considerable sophistication, and this review can provide readers with a comprehensive approach to developing light-mediated 3D printing for tissue-engineering applications.     

Photopolymers for Rapid Prototyping of Soluble Mold Materials and Molding of Cellular Biomaterials

To substitute cross-linked photopolymers in rapid prototyping of mold materials and therefore extend the range of materials which can be casted, organo-soluble photopolymers were developed. Branched bisalkylacrylamides were suitable as base component for such formulations, due to their high reactivity, good mechanical properties, and excellent solubility of the formed polymers. These molding materials were used to prepare cellular biocompatible materials which could be used as bone replacement materials. Biocompatible crosslinkers based on methacrylates from hydrolyzed gelatine or lactic acid ethyleneglycol blockcopolymers and commercially available reactive diluents are the base components of such a formulation. Biocompatibility was investigated by osteoblast-like cells. Cellular biocompatible parts were obtained by thermal polymerization in soluble mould materials prepared by 3D-photoshaping.     

Photopolymers for Rapid Prototyping of Soluble Mold Materials and Molding of Cellular Biomaterials

Summary. To substitute cross-linked photopolymers in rapid prototyping of mold materials and therefore extend the range of materials which can be casted, organo-soluble photopolymers were developed. Branched bisalkylacrylamides were suitable as base component for such formulations, due to their high reactivity, good mechanical properties, and excellent solubility of the formed polymers. These molding materials were used to prepare cellular biocompatible materials which could be used as bone replacement materials. Biocompatible crosslinkers based on methacrylates from hydrolyzed gelatine or lactic acid ethyleneglycol blockcopolymers and commercially available reactive diluents are the base components of such a formulation. Biocompatibility was investigated by osteoblast-like cells. Cellular biocompatible parts were obtained by thermal polymerization in soluble mould materials prepared by 3D-photoshaping.     

Abrasion resistant inorganic/organic coating materials prepared by the sol-gel method

Novel abrasion resistant coating materials prepared by the sol-gel method have been developed and applied on the polymeric substrates bisphenol-A polycarbonate and diallyl diglycol carbonate resin (CR-39). These coatings are inorganic/organic hybrid network materials synthesized from 3-isocyanatopropyltriethoxysilane functionalized organics and metal alkoxide. The organic components are 3,3-iminobispropylamine (IMPA), resorcinol (RSOL), diethylenetriamine (DETA), poly(ethyleneimine) (PEI), glycerol and a series of diols. The metal alkoxides are tetraethoxysilane (TEOS) and tetramethoxysilane (TMOS). These materials are spin coated onto bisphenol-A polycarbonate and CR-39 sheets and thermally cured to obtain a transparent coating of a few microns in thickness. Following the curing, the abrasion resistance is measured and compared with an uncoated control. It was found that the abrasion resistance of inorganic/organic hybrid coatings in the neat form or containing metal alkoxide can be very effective to improve the abrasion resistance of polymeric substrates. The adhesion tests show that the adhesion between coating and substrate can be greatly improved by treating the polymeric substrate surface with a primer solution of isopropanol containing 3-aminopropyltriethoxysilane (3-APS). The interaction between 3-APS and the polycarbonate surface was investigated by a molecular dynamics simulation. The results strongly suggest that the hydrogen bonding between the amino group of the 3-APS and ester group in the polycarbonate backbone are sufficiently strong to influence the orientation of the primer molecules. The abrasion resistance of these new coating systems is discussed in light of the structure of the organic components. All of these results show that these coating materials have excellent abrasion resistance and have potential applications as coating materials for lenses and other polymeric products.     

溶胶-凝胶法制备光固化聚氨酯丙烯酸酯杂化材料的研究

以溶胶-凝肢法制备的硅溶胶为无机相,聚氨酯丙烯酸酯为有机相,以γ-甲基丙烽酰氧丙基三甲氧基硅烷(TMSPM)为两相间的偶联剂,制得了光固化杂化材料。研究了未固化的杂化体系的稳定性问题,并对其进行了结构表征和性能研究。无机相与有机相通过共价键相连。使得杂化体系光固化膜高硬度的获得并没有以柔韧性的损失为代价。在无机物含量较低时,聚氨酯丙烯酸酯／二氧化硅杂化体系先固化膜的耐磨性略有提高。     

The natural atomic orbital point charge model for PM3: Multipole moments and molecular electrostatic potentials

The natural atomic orbital/point (NAO-PC) model originally developed to calculate molecular electrostatic potentials (MEPs) and multiple moments based on the AM1 wave function has been extended to PM3. As for AM1, NAO-PC/PM3 reproduces dipole moments calculated by the standard PM3 method very well. There is also a surprisingly good correlation between experimental and calculated quadrupole moments. The MEPs calculated using PM3/NAO-PC are found to be in better agreement with those given by RHF/6-31G* than those obtained from the PM3 wave function using Coulson charges. On the other hand, the NAO-PC model is often slightly worse then the method implemented in MOPAC-ESP. The MEPs calculated using our model based on the PM3 wave function are often in better agreement with those given by RHF/6-31G* than those obtain with AM1. © 1994 by John Wiley & Sons, Inc.     

Biomaterials based on low cytotoxic vinyl esters for bone replacement application

In recent days, additive manufacturing technologies (AMT) based on photopolymerization have also found application in tissue engineering. Although acrylates and methacrylates have excellent photoreactivity and afford photopolymers with good mechanical properties, their cytotoxicity and degradation products disqualify them from medical use. Within this work, (meth)acrylate‐based monomers were replaced by vinyl esters with exceptional low cytotoxicity. The main focus of this paper lies on the determination of the photoreactivity and investigations concerning mechanical properties and degradation behavior of the new materials. Tested monomers provide sufficient photoreactivity for processing by AMT. Mechanical properties similar to natural bone could be obtained by adding suitable fillers like hydroxylapatite (HA). The right ratio of hydrophobic and hydrophilic monomers allows the tuning of the degradation behavior. Finally, with the optimum formulation, cellular 3D structures were built using digital light processing. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

环氧氯丙烷修饰的对位和间位芳纶涂覆剂研究

制备了具有环氧丙基侧链的对位芳纶(PPTA-ECH)和间位芳纶(PMIA-ECH),并将其用做对位芳纶(PPTA)织物/环氧树脂复合材料中PPTA织物的涂覆剂。采用场发射扫描电子显微镜(FE-SEM)及XPS等方法对PPTA织物表面的PPTA-ECH涂层结构进行了表征。考察了PPTA-ECH和PMIA-ECH涂覆的PPTA织物/环氧树脂复合材料的层间剪切强度和面内剪切强度,并与未经涂覆的PPTA织物复合材料的性能作比较。结果表明,PPTA-ECH和PMIA-ECH可显著改善PPTA织物和环氧树脂之间的界面性能。涂覆了PPTA-ECH及PMIA-ECH的PPTA织物/环氧树脂复合材料的层间剪切强度(ILSS)比未经涂覆的复合材料分别提高了26.20%和14.76%,面内剪切强度(ISS)分别提高了26.98%和11.86%。由于PPTA-ECH对PPTA纤维具有更强的亲和能力,因此PPTA-ECH在层间剪切强度和面内剪切强度方面的增强效果均优于PMIA-ECH。对PPTA-ECH在PPTA纤维表面铺展与吸附及对复合材料的增强机理也进行了初步探讨。作为新型涂覆剂,PPTA-ECH在对位芳纶复合材料的开发应用方面具有潜在的应用前景。     

Self-Processing,Diffusion-Based Photopolymers for Holographic Applications

The new photopolymers for holographic applications described herein are based on a cross-linked matrix in which the holographic grating is formed by photo-polymerization of guest monomers in an interference pattern of the recording light. Diffusion of monomer, triggered by this photo-polymerization, from the dark to the bright fringes of the interference pattern is the key parameter for creating high modulation in refractive index Δn during hologram recording. This leads to bright visual volume holograms with high diffraction efficiency. The holographic photopolymers are self-processing. After recording the hologram only (incoherent) light exposure is necessary to bleach the final product and fix the hologram. Unlike earlier photopolymers used in holography, these new materials offer the advantages of no chemical or thermal processing combined with low shrinkage and detuning. Additionally, due to good light sensitivity the formation of the holograms is fast and the film obtained after curing is highly transparent, which makes the material suitable for both, reflection and transmission holography.     

Rosin Derivatives as a Platform for the Antiviral Drug Design

The increased complexity due to the emergence and rapid spread of new viral infections prompts researchers to search for potential antiviral and protective agents for mucous membranes among various natural objects, for example, plant raw materials, their individual components, as well as the products of their chemical modification. Due to their structure, resin acids are valuable raw materials of natural origin to synthesize various bioactive substances. Therefore, the purpose of this study was to confirm the possibility of using resin acid derivatives for the drug design. As a result, we studied the cytotoxicity and biological activity of resin acid derivatives. It was shown that a slight decrease in the viral load in the supernatants was observed upon stimulation of cells (II) compared with the control. When using PASS-online modeling (Prediction of Activity Spectra for Substances), the prediction of the biological activity spectrum showed that compound (I) is capable of exhibiting antiviral activity against the influenza virus. The use of the SWISS-ADME webserver to reveal the drug-like properties of compounds did not directly indicate the presence of antiviral activity. These results indicate the potential of resin acid derivatives as a starting point for extensive research in the study of biological activity.     

Feasibility and Biocompatibility of 3D‐Printed Photopolymerized and Laser Sintered Polymers for Neuronal,Myogenic, and Hepatic Cell Types

The integration of additive manufacturing (AM) technology within biological systems holds significant potential, specifically when refining the methods utilized for the creation of in vitro models. Therefore, examination of cellular interaction with the physical/physicochemical properties of 3D‐printed polymers is critically important. In this work, skeletal muscle (C₂C₁₂), neuronal (SH‐SY5Y) and hepatic (HepG2) cell lines are utilized to ascertain critical evidence of cellular behavior in response to 3D‐printed candidate polymers: Clear‐FL (stereolithography, SL), PA‐12 (laser sintering, LS), and VeroClear (PolyJet). This research outlines initial critical evidence for a framework of polymer/AM process selection when 3D printing biologically receptive scaffolds, derived from industry standard, commercially available AM instrumentation. C₂C₁₂, SH‐SY5Y, and HepG2 cells favor LS polymer PA‐12 for applications in which cellular adherence is necessitated. However, cell type specific responses are evident when cultured in the chemical leachate of photopolymers (Clear‐FL and VeroClear). With the increasing prevalence of 3D‐printed biointerfaces, the development of rigorous cell type specific biocompatibility data is imperative. Supplementing the currently limited database of functional 3D‐printed biomaterials affords the opportunity for experiment‐specific AM process and polymer selection, dependent on biological application and intricacy of design features required.     

Comparison of tear test methods

Tear strength is an important property of a rubber vulcanisate, particularly when considering it for applications such as cables, hoses and tyres. In the present study four test methods, as specified for vulcanised rubbers in British Standards (BS 903 Part A3 and BS 6899), have been investigated on five different compositions based on a nitrile natural rubber, an ethylene acrylic rubber, a polyurehane and undisclosed chloroprene elastomer. The objective of the study was to examine the influence of thickness, grain effects and strain rate on the tear strength. It was also intended to establish if the different tear test methods would rank materials in the same order and whether a constant ratio exists between the tear strength values obtained using the different methods for different materials.

Sample thicknesses in the range 0·5–3 mm and strain rates in the range 100–500 mm/min all produced small but significant variations in the tear strength, confirming that standardisation of these variables is very desirable. Grain effects were found to produce even larger variations in the test results, particularly for the trouser test pieces. It was found that the tests could be divided into two groups:

• (a) trouser and cable tests;

• (b) angle and crescent tests. The tests in each group ranked materials in the same order and the ratios between tests on different materials within each group was approximately the same.

     

激光光散射研究丙烯酰胺-二甲基二烯丙基氯化铵共聚物的溶液行为

用激光光散射技术表征了阳离子含量受控的丙烯酰胺 二甲基二烯丙基氯化铵共聚物 (简称P(AM DMDAAC) )在 0 1mol LNaCl溶液中的基本参数和溶液行为 .表观基本参数 : Mw ,app =5 0 4× 10 5g·mol- 1 、app =39 9nm和A2 ,APP =1 5× 10 - 4cm3·mol·g- 2 .动态光散射研究结果表明 ,扩散系数Dt 与角度、浓度皆呈非线性依赖关系 ,当C >C 或在较大的散射角域 ,Dt 偏离线性关系所预示的理论值而向减小的方向发展 ,表明存在缔合物 ;流体力学半径Rh 分布有大、小两个范围 ,并随温度升高向小尺寸方向发展 ,证明了体系中存在缔合行为以及升温的解缔合作用 .在一定条件下 ,“亚稳定性”的存在有力地旁证了体系的缔合行为     

Effect of glass fiber surface treatments on mechanical strength of epoxy based composite materials

Sizing glass fibers with silane coupling agents enhances the adhesion and the durability of the fiber/polymer matrix interface in composite materials. There are several tests to determine the interfacial strength between a fiber and resin, but all of them present difficulties in interpreting the results and/or sample preparation. In this study, we observed the influence of different aminosilanes fiber coatings on the resistance of epoxy-based composite materials using a very easy fractographic test. In addition, we tried a new fluorescence method to get information on a molecular level precisely at the interface. Strength was taken into account from two standpoints: (i) mechanical strength and (ii) the resistance to hydrolysis of the interface in oriented glass-reinforced epoxy-based composites. Three silanes: gamma-aminopropyltriethoxysilane, gamma-Aminopropylmethyldiethoxysilane, and gamma-Aminopropyldimethylethoxysilane were used to obtain different molecular structures at the interface. It was concluded that: (i) the more accessible amine groups are, the higher the interface rigidity is; (ii) an interpenetrating network mechanism seems to be the most important for adhesion and therefore to the interfacial strength; and (iii) the higher the degree of crosslinking in the silane coupling layer is, the higher the hydrolytic damage rate is.     

High-throughput microwave-digestion procedures to monitor neurotoxic elements in body fluids by means of inductively coupled plasma mass spectrometry

Microwave (MW) digestion procedures with high sample throughput (simultaneous digestion of 36 or 80 samples) and procedural simplicity (disposable plastic tubes, or re-usable liners with screw-cap) were investigated for their efficiency in routine analyses of biological samples. Different digestion vessel materials were tested for metal leaching/adsorption and thermal resistance: quartz, glass, polyethylene (PE) and polystyrene (PS). For the instrumental quantification of Al, Bi, Cd, Co, Cr, Hg, Mn, Mo, Ni, Pb, Sb, and Tl at ultra-trace levels in urine, serum, and whole blood, sector field inductively coupled plasma mass spectrometry (SF-ICP-MS) was used. The different pretreatment conditions and vessels were evaluated in terms of contamination risk, effective power of detection, accuracy, and precision. Results of analyses of serum, urine and whole blood certified reference materials (CRMs) were fully satisfactory for almost all the analytes. In the case of Hg, Mo, and Tl in serum digested in plastic containers the results were just below the lower limit of uncertainty of the certified range. On the basis of the present data the following MW procedures can be suggested: 1. for urine, digestion with nitric acid at atmospheric pressure in plastic vials; 2. for serum, digestion with nitric acid at atmospheric pressure in glass vessels; and 3. for whole blood, digestion under pressure in quartz tubes.Because of the levels of the procedural blanks, Bi was not measurable at the concentrations expected in human fluids, and Al was accurately detectable in whole blood only.     

Metal(II) 4,4′,4″,4′″-phthalocyanine tetramines as curing agents for heat resistant epoxy formulations

Pure metal(II) 4,4′,4″,4′″-phthalocyanine tetraamines (MPTA) have been used to cure epoxy resins in a homogeneous reaction. Infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analytical studies were used to characterize these materials and to evaluate the optimum curing conditions. Considerable improvement in the heat resistance of the epoxy resin cured with MPTA over those cured with other commonly used curing agents was observed. This was expected from the highly aromatic structure of the phthalocyanines. A noteworthy feature of these cured materials is their high anaerobic char yield, 73.5–75%, higher than in any heretofore known cured epoxy systems. Preliminary mass spectral studies on the cured polymers are presented.     

Origin of directional tear in blown films of ethylene/methacrylic acid copolymers and ionomers

Blown films of ethylene/methacrylic acid copolymers and ionomers can exhibit pronounced directional tear, meaning that a tear can propagate with much less resistance in a particular direction. However, films blown from the same resin can exhibit different preferred tear directions, which depend on the process conditions. Through wide‐ and small‐angle X‐ray scattering, we demonstrate that this directional tear behavior is a direct result of the orientation of the lamellar polyethylene crystallites in these films; tears propagate more readily between lamellae than through lamellae, as previously recognized for low‐density polyethylene homopolymer. Unlike polyethylene homopolymer, however, an increase in the blowup ratio during the film processing of ethylene/methacrylic acid copolymers and ionomers leads to a 90° rotation of the lamellae that form upon subsequent crystallization. The lamellar rotation arises from a change in the orientation of the row nuclei that form after the melt is inflated and produces a consequent rotation of the preferred tear direction. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 97–106, 2005     

Preparation and Characterization of Transparent and UV‐Shielding Epoxy/SR‐494/APTMS/ZnO Nanocomposites with High Heat Resistance and Anti‐Static Properties

This research is to develop transparent and UV‐shielding Epoxy/SR‐494/APTMS/ZnO nanocomposite materials with high heat resistant and anti‐static properties. Firstly, the APTMS (3‐(acryloxypropyl)trimethoxysilane) performs the silanol intermediates by hydrolysis in pH 4～5 acid solution. The inorganic anti‐static fillers of powder ZnO can be successfully coupled and crosslinked to Epoxy/SR‐494 organic matrixes with these silanols of APTMS coupling agents. The remained active ‐OH functional groups of the APTMS/ZnO complexes can network bonding with epoxy prepolymers. Therefore, the Epoxy/APTMS/ZnO complexes with good anti‐static composites will be successfully prepared. Finally, in order to improve the thermal resistant and mechanical properties, the polyfunctionalized SR‐494 (pentaery‐thritol tetracrylate) acrylate monomers and the Epoxy/APTMS/ZnO composites are chain polymerized to form an excellent cross‐linking structure of organic/inorganic nanocomposites. The chemical bonding formation and the best weight contents of reaction components are identified by FT‐IR spectra. The thermal resistance, transparence, surface electric resistance, and hardness of these nanocomposites are measured by TGA, DSC, UV‐Visible, surface resistant meter, and pencil hardness tester respectively. Experimental results show that these nanocomposites have 90% transmittance and the best Td value is 389.3 °C which is 109.0 °C and 78.6 °C higher than those of pure epoxy resin and pure SR‐494 acrylate resin respectively. The glass transition temperature is not detected below 200 °C. The surface electric resistances of Epoxy/SR‐494/APTMS/ZnO hybrid thin films are decreased from 3.14 × 10¹³ to 5.13 × 10⁷ Ω/cm². The hardness of these nanocomposites is as high as 8H, and those hybrid films have high UV‐shielding properties. The morphology structures of the hybrid thin films are estimated by SEM. The results show that the optical thin films are evenly distributed with inorganic colloidal particles and the average particle size of these nanocomposites is 45～80 nm, while the powder ZnO (particle size: 2～5 μm) was used as inorganic filler.     

Autonomous intelligent agents for accelerated materials discovery

We present an end-to-end computational system for autonomous materials discovery. The system aims for cost-effective optimization in large, high-dimensional search spaces of materials by adopting a sequential, agent-based approach to deciding which experiments to carry out. In choosing next experiments, agents can make use of past knowledge, surrogate models, logic, thermodynamic or other physical constructs, heuristic rules, and different exploration–exploitation strategies. We show a series of examples for (i) how the discovery campaigns for finding materials satisfying a relative stability objective can be simulated to design new agents, and (ii) how those agents can be deployed in real discovery campaigns to control experiments run externally, such as the cloud-based density functional theory simulations in this work. In a sample set of 16 campaigns covering a range of binary and ternary chemistries including metal oxides, phosphides, sulfides and alloys, this autonomous platform found 383 new stable or nearly stable materials with no intervention by the researchers.

We present an end-to-end computational system for autonomous materials discovery.