The influence of the internal structure of core–shell particles on poly(vinyl chloride)/(methyl methacrylate–butadiene–styrene) blends

Methyl methacrylate–butadiene–styrene (MBS) core–shell particles were prepared by grafting styrene and methyl methacrylate onto polybutadiene seeds via emulsion polymerization. All the MBS particles were designed with the same chemical composition, similar grafting degree but different internal structures. The difference in internal structure was realized by controlling the ratio of ‘external grafting’ and ‘internal grafting’ of styrene. The work focused on the influence of the internal structure of MBS core–shell particles on the properties of poly(vinyl chloride)/MBS blends. From transmission electron microscopy, three different internal structures were observed: rare sub‐inclusions, a large number of small sub‐inclusions and large sub‐inclusions. The results of dynamic mechanical analysis illustrated that the different internal structures greatly affected the glass transition temperature T_g of the rubber phase and the storage modulus of the core–shell particles. The notched Izod impact test results showed that the MBS with large sub‐inclusions had the lowest brittle–ductile transition temperature, while the transparency test revealed that the presence of sub‐inclusions in the rubbery phase reduced the transparency of the blend. Copyright © 2012 Society of Chemical Industry     

Biohybrid Bovine Bone Matrix for Controlled Release of Mesenchymal Stem/Stromal Cell Lyosecretome: A Device for Bone Regeneration

SmartBone^® (SB) is a biohybrid bone substitute advantageously proposed as a class III medical device for bone regeneration in reconstructive surgeries (oral, maxillofacial, orthopedic, and oncology). In the present study, a new strategy to improve SB osteoinductivity was developed. SB scaffolds were loaded with lyosecretome, a freeze-dried formulation of mesenchymal stem cell (MSC)-secretome, containing proteins and extracellular vesicles (EVs). Lyosecretome-loaded SB scaffolds (SBlyo) were prepared using an absorption method. A burst release of proteins and EVs (38% and 50% after 30 min, respectively) was observed, and then proteins were released more slowly with respect to EVs, most likely because they more strongly adsorbed onto the SB surface. In vitro tests were conducted using adipose tissue-derived stromal vascular fraction (SVF) plated on SB or SBlyo. After 14 days, significant cell proliferation improvement was observed on SBlyo with respect to SB, where cells filled the cavities between the native trabeculae. On SB, on the other hand, the process was still present, but tissue formation was less organized at 60 days. On both scaffolds, cells differentiated into osteoblasts and were able to mineralize after 60 days. Nonetheless, SBlyo showed a higher expression of osteoblast markers and a higher quantity of newly formed trabeculae than SB alone. The quantification analysis of the newly formed mineralized tissue and the immunohistochemical studies demonstrated that SBlyo induces bone formation more effectively. This osteoinductive effect is likely due to the osteogenic factors present in the lyosecretome, such as fibronectin, alpha-2-macroglobulin, apolipoprotein A, and TGF-β.     

Irradiation Grafted Polymeric Films. II. Gas Transport Properties of Hydrated Potassium Acrylate-Grafted Polyethylene Films

Abstract

The permeability constants of oxygen and carbon dioxide through hydrated potassium acrylate-grafted polyethylene films increase rapidly as the degree of hydration of the films increases above about 28 wt %. Below about 28 wt %, the carbon dioxide permeability constant increases with the degree of hydration. In the case of oxygen, the opposite is true.

The separation factor (CO₂/O₂) increases rapidly with film hydration up to about 28 wt %. Above this degree of hydration, the separation factor gradually approaches the value for pure water. An explanation for the results obtained is presented.     

Research progress on chemical modification of silk fibroin and its applications北大核心CSCD

Mulberry silk is composed of the two major parts of two triangle-like silk fibroin fibers and sericin covering the fibers and a few lipids. After removing the sericin on the raw silk what is left is the silk fibroin fiber. Silk fibroin is the main part of silk accounting for about 75% of the total weight. Silk fibroin contains 18 natural amino acids such as glycine Gly alanine Ala serine Ser serine aspartic acid Asp and tyrosine Tyr . The secondary structure of silk fibroin has three main conformations α-helix β-fold and random coil. Under certain conditions the three conformations can transform into each other and change the mechanical properties of the silk fibroin material. Silk fibroin extracted from silk fiber is a natural polymer with biocompatibility and biodegradability. It can be further processed into different forms of materials nanoparticles films hydrogels sponges etc. It has been applied in many fields such as biomedicine and cosmetics. In order to meet the needs of different fields researchers have conducted further chemical modification treatment based on the original excellent properties of silk fibroin. Meanwhile the active groups on various amino acid residues in silk fibroin also provide chemical reaction sites for the chemical modification of silk fibroin. The chemical modification methods of silk fibroin mainly include amino acid residue modification macromolecular grafting modification and crosslinking reaction modification. Among them amino acid residue modification can modify protein amino acid residues by chemical reagents and some groups can be introduced into the side chains of silk fibroin macromolecules. Grafting modification of silk fibroin macromolecules is one of the main means to bind functional compounds to silk fibroin macromolecular chains. The properties of grafted silk fibroin are affected by the type and grafting rate of the grafts. The chemical crosslinking reaction modification of silk fibroin macromolecules is to make the macromolecular chains connected by covalent bonds and form a network structure by means of crosslinking agents enzymes or ultraviolet irradiation. The cross-linking reaction can not only form covalent bonds within and between the molecular chains of silk fibroin thus changing its structural properties and improving its stability but be used to form covalent bonds with other polymers. At present the chemical modification of silk fibroin is mainly applied in the fields of silk textiles biomedicine and environmental science. In the field of silk textiles graft copolymerization modification of vinyl and other monomers crosslinking agent modification and other methods are used to overcome the shortcomings of silk like being easy to wrinkle. The graft modified monomers mainly include ethylene methacrylate and methylacrylamide. The active groups on crosslinking agents such as polycarboxylic acid / anhydride and epoxide are covalently combined with carboxyl hydroxyl and amino groups on macromolecules of silk fibroin to improve the wrinkle resistance of silk fabrics. In the field of biomedicine silk fibroin materials with appropriate chemical modification have better biological activity drug delivery ability antimicrobial properties and mechanical properties. The optimization of these properties enables silk fibroin materials to show great potential in drug control delivery tissue regeneration and wound repair. The applied research in the field of environmental science mainly focuses on the adsorption separation and catalysis of impurities in water. Therefore the modification of amino acid residues grafting and cross-linking of protein macromolecules can change some important properties of silk fibroin and meet the requirements of various applications and functionalization of silk fibroin. In many fields of chemical modification and application of silk fibroin protein fruitful results have been achieved which has laid a good foundation for the further development of related fields and also shows that the chemical modification of silk fibroin material has great potential and application prospects. However there are still some problems that need to be overcome and further improved in the current chemical modification methods such as mild modification conditions and accurate adjustment of the degree of modification which will be the research direction of related fields in the future. © 2022 Authors. All rights reserved.     

Polymer on Top: Current Limits and Future Perspectives of Quantitatively Evaluating Surface Grafting

Well‐defined polymer strands covalently tethered onto solid substrates determine the properties of the resulting functional interface. Herein, the current approaches to determine quantitative grafting densities are assessed. Based on a brief introduction into the key theories describing polymer brush regimes, a user's guide is provided to estimating maximum chain coverage and—importantly—examine the most frequently employed approaches for determining grafting densities, i.e., dry thickness measurements, gravimetric assessment, and swelling experiments. An estimation of the reliability of these determination methods is provided via carefully evaluating their assumptions and assessing the stability of the underpinning equations. A practical access guide for comparatively and quantitatively evaluating the reliability of a given approach is thus provided, enabling the field to critically judge experimentally determined grafting densities and to avoid the reporting of grafting densities that fall outside the physically realistic parameter space. The assessment is concluded with a perspective on the development of advanced approaches for determination of grafting density, in particular, on single‐chain methodologies.     

Synthesis and characteristics of pectiniform polyurethane-modified polycarboxylate and its effects on behavior of cement paste

In this research, two kinds of polycarboxylate (M-PCE and O-PCE) with the same degree of polymerization in side chains but different main chains were synthesized via a radical polymerization reaction at room temperature. Along with two commercial polycarboxylates (C-PCE-1 and C-PCE-2), their properties on adsorption, hydration, zeta potential, liquid surface tension, and flowability of cement pastes were investigated. The results showed that the adsorption of M-PCE on the surface of cement particles increased 14.1% and the adsorption rate increased 24% compared with C-PCEs. Furthermore, three polycarboxylates (O-PCE, C-PCE-1, and C-PCE-2) exhibited a delayed effect on the hydration of cement due to the shielding effect of their chain alkyl groups, meanwhile the hydration of the cementitious materials by the M-PCE was not delayed but promoted because of its incomplete hydrolysis of the siloxane. As a result of the higher adsorption amount, M-PCE with siloxane groups exhibited favorable effects in terms of zeta potential, liquid surface tension, and flowability of cement pastes.     

Some recent advances in polyolefin functionalization

Polyolefin‐based materials are increasingly being used in many industrial applications for packaging, automotive and construction materials. The recent developments of research have been aimed at making these materials, often complex, being mixtures, block copolymers, micro‐ and nanocomposites with inorganic and organic fillers, more efficient and environmentally friendly (through recycling processes, and the use of bio‐polyolefins). In this context, functionalized polyolefins, on the one hand, play a fundamental role in improving the morphology and thus the thermal and mechanical properties of heterophase systems, and, on the other hand, provide new materials difficult to obtain by conventional synthesis in connection with the type of inserted functionality. Therefore it appears to be of interest to report and discuss here the recent results concerning the radical grafting in the melt of different functionalities onto polyolefins as well as the capability reached of modulating ad hoc the degree of grafting and the final structure/architecture of functionalized polyolefins. © 2013 Society of Chemical Industry