Macromolecular Bioscience

Summary: Polylactide polymers have gained enormous attention as a replacement for conventional synthetic packaging materials in the last decade. By being truly biodegradable, derived from renewable resources and by providing consumers with extra end‐use benefits such as avoiding paying the “green tax” in Germany or meeting environmental regulations in Japan, polylactides (PLAs) are a growing alternative as a packaging material for demanding markets. The aim of this paper is to review the production techniques for PLAs, summarize the main properties of PLA and to delineate the main advantages and disadvantages of PLA as a polymeric packaging material. PLA films have better ultraviolet light barrier properties than low density polyethylene (LDPE), but they are slightly worse than those of cellophane, polystyrene (PS) and poly(ethylene terephthalate) (PET). PLA films have mechanical properties comparable to those of PET and better than those of PS. PLA also has lower melting and glass transition temperatures than PET and PS. The glass transition temperature of PLA changes with time. Humidity between 10 and 95% and storage temperatures of 5 to 40 °C do not have an effect on the transition temperature of PLA, which can be explained by its low water sorption values (i.e. <100 ppm at A_w = 1). PLA seals well at temperatures below the melting temperature but an appreciable shrinking of the films has been noted when the material is sealed near its melting temperature. Solubility parameter predictions indicate that PLA will interact with nitrogen compounds, anhydrides and some alcohols and that it will not interact with aromatic hydrocarbons, ketones, esters, sulfur compounds or water. The CO₂, O₂ and water permeability coefficients of PLA are lower than those of PS and higher than those of PET. Its barrier to ethyl acetate and D‐limonene is comparable to PET. The amount of lactic acid and its derivatives that migrate to food simulant solutions from PLA is much lower than any of the current average dietary lactic acid intake values allowed by several governmental agencies. Thus, PLA is safe for use in fabricating articles for contact with food.

Percent transmission versus wavelength for PLA(98% L‐lactide), PS, LDPE, PET and cellophane films.

Tóm tắt: Thuỷ phân alginate đang chứng tỏ có tính ứng dụng rộng rãi như là vật liệu sinh học. Chúng đã được sử dụng làm giá đỡ cho kỹ thuật mô học, phương tiện dẫn truyền thuốc, và mô hình một số chất nền ngoài tế bào cơ bản cho các nghiên cứu sinh học cơ bản. Những ứng dụng này đòi hỏi sự kiểm soát chặt chẽ của một số thuộc tính vật liệu bao gồm độ cứng cơ học, sự trương nở, sự phân hủy, sự gắn kết của tế bào, và sự liên kết hoặc giải phóng các phân tử hoạt tính sinh học. Kiểm soát các thuộc tính này có thể đạt được thông qua các sửa đổi hoá học hoặc lý học của chính chất polysaccharide hoặc các gel được hình thành từ alginate. Tính hữu ích của các gel alginate đã được sửa đổi này như là vật liệu sinh học đã được chứng minh qua nhiều nghiên cứu in vitro và in vivo.

Hình ảnh Micro‐CT của kết cấu giống xương dẫn xuất từ việc cấy ghép tế bào tạo xương trên gel mà phân hủy sau một khoảng thời gian nhiều tháng, dẫn đến sự sinh trưởng xương cải tiến.

Tóm tắt: Quá trình hòa tan nhanh cellulose trong dung dịch nước LiOH/urea và NaOH/urea đã được nghiên cứu một cách hệ thống. Hành vi hòa tan và khả năng hòa tan cellulose được đánh giá bằng cách sử dụng ¹³C NMR, kính hiển vi quang học, nhiễu xạ tia X góc rộng (WAXD), quang phổ FT-IR, phương pháp DSC và độ nhớt. Kết quả thí nghiệm cho thấy cellulose có trọng lượng phân tử trung bình độ nhớt ($\overline M _\eta $) là 11.4 × 104 và 37.2 × 104 lần lượt có thể được hòa tan trong 7% NaOH/12% urea và 4.2% LiOH/12% urea dung dịch nước làm lạnh trước tới −10 °C trong vòng 2 phút, trong khi tất cả chúng không thể hòa tan trong dung dịch nước KOH/urea. Khả năng hòa tan của các hệ dung môi giảm dần theo thứ tự LiOH/urea > NaOH/urea ≫ KOH/urea. Các kết quả từ DSC và ¹³C NMR chỉ ra rằng dung dịch nước LiOH/urea và NaOH/urea như là các dung môi không tạo dẫn xuất phá vỡ liên kết hydro bên trong và giữa các phân tử cellulose và ngăn chặn sự tiến gần đến nhau của các phân tử cellulose, dẫn đến sự phân tán tốt của cellulose để tạo thành dung dịch thực.

Shift hóa học ¹³C NMR của carbonyl carbon cho urea trong LiOH (a) và NaOH (b) của dung dịch cellulose.

Summary: A novel method based on AFM was used to attach individual collagen fibrils between a glass surface and the AFM tip, to allow force spectroscopy studies of these. The fibrils were deposited on glass substrates that are partly coated with Teflon AF®. A modified AFM tip was used to accurately deposit epoxy glue droplets on either end of the collagen fibril that cross the glass‐Teflon AF® interface, as to such attach it with one end to the glass and the other end to the AFM tip. Single collagen fibrils have been mechanically tested in ambient conditions and were found to behave reversibly up to stresses of 90 MPa. Within this regime a Young's modulus of 2–7 GPa was obtained. In aqueous media, the collagen fibrils could be tested reversibly up to about 15 MPa, revealing Young's moduli ranging from 0.2 to at most 0.8 GPa. magnified image

The controlled release of medicaments remains the most convenient way of drug delivery. Therefore, a wide variety of reports can be found in the open literature dealing with drug delivery systems. In particular, the use of nano‐ and microparticles devices has received special attention during the past two decades. PLA and its copolymers with GA and/or PEG appear as the preferred substrates to fabricate these devices. The methods of fabrication of these particles will be reviewed in this article, describing in detail the experimental variables associated with each one with regard to the influence of them on the performance of the particles as drug carriers. An analysis of the relationship between the method of preparation and the kind of drug to encapsulate is also included. Furthermore, certain issues involved in the addition of other monomeric substrates than lactic acid to the particles formulation as well as novel devices, other than nano‐ and microparticles, will be discussed in the present work considering the published literature available.

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This paper describes several examples of knowledge‐intensive technologies for the production of chemicals from biomass, which take advantage of the biomass structure in a more efficient way than the production of fuels or electricity alone. The depletion in fossil feedstocks, increasing oil prices, and the ecological problems associated with CO₂ emissions are forcing the development of alternative resources for energy, transport fuels, and chemicals, such as the replacement of fossil resources with CO₂ neutral biomass. Allied with this is the conversion of crude oil products utilizes primary products (ethylene, etc.) and their conversion into either materials or (functional) chemicals with the aid of co‐reagents such as ammonia, by various process steps to introduce functionalities such as ‐NH₂ into the simple structures of the primary products. Conversely, many products found in biomass often contain functionalities. Therefore, it is attractive to exploit this in order to by‐pass the use, and preparation of, co‐reagents as well as to eliminate various process steps by utilizing suitable biomass‐based precursors for the production of chemicals.

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Hydrogels that mimic the natural extracellular matrix (ECM) are used in three‐dimensional cell culture, cell therapy, and tissue engineering. A semi‐synthetic ECM based on cross‐linked hyaluronana offers experimental control of both composition and gel stiffness. The mechanical properties of the ECM in part determine the ultimate cell phenotype. We now describe a rheological study of synthetic ECM hydrogels with storage shear moduli that span three orders of magnitude, from 11 to 3 500 Pa, a range important for engineering of soft tissues. The concentration of the chemically modified HA and the cross‐linking density were the main determinants of gel stiffness. Increase in the ratio of thiol‐modified gelatin reduced gel stiffness by diluting the effective concentration of the HA component.

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The conversion of processed discarded material into valuable by‐products and alternative specialty materials has been identified as a timely challenge for food research and development associated with numerous applications of chitinous products. Chitin, chitosan, calcareous chitin, and chitosan, N‐acetylated chitosan, N‐methylene phosphonic chitosan (NMPC), and N‐lauryl‐N‐methylene phosphonic chitosan (LMPC) are being studied as a result of their broad range of food applications. These biopolymers offer a wide range of unique applications including formation of biodegradable films, immobilization of enzymes, preservation of foods from microbial deterioration, as additives (clarification and deacidification of fruits and beverages, emulsifier agents, thickening and stabilizing agents, color stabilization), and dietary supplements. This review summarizes some of the most important developments in this field.

Summary: Properties of polymer alloys comprising poly(lactic acid) and Nodax copolymers are investigated. Nodax is a family of bacterially produced polyhydroxyalkanoate (PHA) copolymers comprising 3‐hydroxybutyrate (3HB) and other 3‐hydroxyalkanoate (3HA) units with side groups greater than or equal to three carbon units. The incorporation of 3HA units with medium‐chain‐length (mcl) side groups effectively lowers the crystallinity and the melt temperature, T_m, of this class of PHA copolymers, in a manner similar to that of alpha olefins controlling the properties of linear low density polyethylene. The lower T_m makes the material easier to process, as the thermal decomposition temperature of PHAs is then relatively low. The reduced crystallinity provides the ductility and toughness required for many plastics applications. When a small amount of ductile PHA is blended with poly(lactic acid) (PLA), a new type of polymer alloy with much improved properties is created. The toughness of PLA is substantially increased without a reduction in the optical clarity of the blend. The synergy between the two materials, both produced from renewable resources, is attributed to the retardation of crystallization of PHA copolymers finely dispersed in a PLA matrix as discrete domains.

Effect of the particle size on the overall crystallization rate by low spontaneous nucleation frequency.

Suberin is a biopolymer that acts as a barrier between plants and the environment. It is known to be a complex polyester based on glycerol and long‐chain α,ω‐diacids and ω‐hydroxyacids. How these monomeric units are assembled at a macromolecular level remains mostly unknown. The knowledge gathered in the last 10 years has opened new insights into suberin structure. Suberin oligomeric blocks have been obtained after the partial depolymerization of the biopolymer, and in‐situ studies by solid‐state ¹³C NMR spectroscopy have shown different molecular domains and how they are spatially related. Based on these latter developments, a model is proposed for the suberin macromolecular structure. The uniqueness of the suberin polyester opens perspectives for its use as a source of bio‐based materials.

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