Search

Engineered block polysaccharides is a relatively new class of biomacromolecules consisting of chemical assembly of separate block structures at the chain termini. In contrast to conventional, laterally substituted polysaccharide derivatives, the block arrangement allows for much higher preservation of inherent chain properties such as biodegradability and stimuli-responsive self-assembly, while at the same time inducing new macromolecular properties. Abundant, carbon neutral, and even recalcitrant biomass is an excellent source of blocks, opening for numerous new uses of biomass for a wide range of novel biomaterials. Among a limited range of methodologies available for block conjugation, bifunctional linkers allowing for oxyamine and hydrazide ‘click’ reactions have recently proven useful additions to the repertoire. This article focuses the chemistry and kinetics of these reactions. It also presents some new data with the aim to provide useful protocols and methods for general use towards new block polysaccharides.

This work explores the largely unknown surface microstructure and elastic modulus of soft calcium-alginate hydrogels (E = 100–4500 Pa) in their hydrated state by atomic force microscopy (AFM) in quantitative imaging mode. Alginate concentration largely influenced the surface topography with surface roughness measured to be 101 ± 6 nm and 57 ± 1 nm for 0.5 and 2.0% (w/v) alginate, respectively. The calculated range of pore sizes increased with decreasing alginate concentration, from radius smaller than 360 nm, 570 nm and 1230 nm for 2.0%, 1.0% and 0.5% alginate, respectively. Small changes in calcium concentration (20 to 25 mM, 1.5% alginate) did not induce changes in surface microstructure, although it increased the elastic modulus mean values and distribution. Introducing oxidized or peptide-grafted alginate in the gels resulted in rougher surfaces, larger pore sizes and lower elasticity than the respective hydrogels with no modified alginate.

Lyase-catalyzed degradation has been proposed as a more cell-friendly alternative to dissolution of alginate gels than using chelating agents. In this study, we investigated the effect of lyase specificity on degradation of alginate gels, including the effect of crosslinking ions with different affinity for the polymer. Degradation kinetics and products were analyzed. In particular, the degradation products were characterized using novel methods for alginate sequence determination by chromatography. Lyase-catalyzed gel disruption worked well for gels crosslinked with calcium, but was less effective when barium was included in the gel formulation. The importance of crosslinking of long G-blocks in maintaining the structural integrity of the gels was identified. The failure to degrade these long G-blocks, either due to protection of the G-blocks by strong ionic crosslinking or due to lack of lyase activity on G–G linkages, resulted in retained resistance to mechanical disruption of the gel.

Cell encapsulation has already shown its high potential and holds the promise for future cell therapies to enter the clinics as a large scale treatment option for various types of diseases. The advancement in cell biology towards this goal has to be complemented with functional biomaterials suitable for cell encapsulation. This cannot be achieved without understanding the close correlation between cell performance and properties of microspheres. The ongoing challenges in the field of cell encapsulation require a critical view on techniques and approaches currently utilized to characterize microspheres. This review deals with both principal subjects of microspheres characterization in the cell encapsulation field: physico-chemical characterization and biocompatibility. The up-to-day knowledge is summarized and discussed with the focus to identify missing knowledge and uncertainties, and to propose the mandatory next steps in characterization of microspheres for cell encapsulation. The primary conclusion of this review is that further success in development of microspheres for cell therapies cannot be accomplished without careful selection of characterization techniques, which are employed in conjunction with biological tests. (C) 2013 Elsevier B.V. All rights reserved.

The cytokine-inducing potential of various microspheres were evaluated in a short-time screening assay of lepirudin-anticoagulated human whole blood utilizing the Bio-Plex Human cytokine 27-plex system. The inflammatory cytokines IL-1β, TNF and IL-6; the anti-inflammatory mediators IL-1ra and IL-10; the chemokines IL-8, MIP-1α and MCP-1; and the growth factor VEGF were induced by polycation (poly-l-lysine or poly(methylene-co-guanidine)) containing microspheres. Alginate microspheres without polycations did not induce the corresponding cytokine panel, nor did soluble alginate. By inhibiting complement C3 using compstatin analog CP20, a total inhibition of complement activation as well as the inflammatory mediators was achieved, indicating that complement activation alone was responsible for the induced cytokines. A strong deposition of C3c on the poly-l-lysine containing surface, while not on the microspheres lacking polycations, also points to the formation of C3 convertase as involved in the biomaterial-induced cytokine induction. These results show that complement is responsible for the induction of cytokines by polycation containing microspheres. We point to complement as an important initiator of inflammatory responses to biomaterials and the lepirudin anticoagulated whole blood assay as an important tool to identify the most tolerable and safe materials for implantation to humans.

A one-step method was used to make nanostructured composites from alginate and calcium carbonate or calcium phosphate. Nanometer-scale mineral phase was successfully formed within the gel network of alginate gel beads, and the composites were characterized. It was found that calcite was the dominating polymorph in the calcium carbonate mineralized beads, while stoichiometric hydroxyapatite was formed in the calcium phosphate mineralized beads. A combination of electron microscopy, Fourier-transform infrared spectroscopy, thermogravimetric analysis and powder X-ray diffraction showed that alginate played an active role in controlling mineral size, morphology and polymorphy. For the calcium phosphate mineralized beads, alginate was shown to modulate stoichiometric hydroxyapatite with low crystallinity at room temperature, which may have important applications in tissue engineering. The results presented in this work demonstrate important aspects of alginate-controlled crystallization, which contributes to the understanding of composite material design.

Bioencapsulation involves the envelopment of tissues or biological active substances in semipermeable membranes. Bioencapsulation has been shown to be efficacious in mimicking the cell's natural environment and thereby improves the efficiency of production of different metabolites and therapeutic agents. The field of application is broad. It is being applied in bioindustry and biomedicine. it is clinically applied for the treatment of a wide variety of endocrine diseases. During the past decades many procedures to fabricate capsules have been described. Unfortunately, most of these procedures lack an adequate documentation of the characterization of the biocapsules. As a result many procedures show an extreme lab-to-lab variation and many results cannot be adequately reproduced. The characterization of capsules can no longer be neglected, especially since new clinical trials with bioencapsulated therapeutic cells have been initiated and the industrial application of bioencapsulation is growing. In the present review we discuss novel Approached to produce and characterize biocapsules in view of clinical and industrial application. A dominant factor in bioencapsulation is selection and characterization of suitable polymers. We present the adequacy of using high-resolution NMR for characterizing polymers. These polymers are applied for producing semipermeable membranes. We present the pitfalls of the currently applied methods and provide recommendations for standardization to avoid lab-to-lab variations. Also, we compare and present methodologies to produce biocompatible biocapsules for specific fields of applications and we demonstrate how physico-chemical technologies such as FT-IR, XPS, and TOF-SIMS contribute to reproducibility and standardization of the bioencapsulation process. During recent years it has become more and more clear that bioencapsulation requires a multidisciplinary approach in which biomedical, physical, and chemical technologies are combined. For adequate reproducibility and for understanding variations in outcome of biocapsules it is advisable if not mandatory to include the characterization processes presented in this review in future studies. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.

Background A recent study from our laboratory documented significant improvements in post-transplant viability in an experimental model of intestinal transplantation when a novel, nutrient-rich preservation solution was used during cold storage. The current study investigated the relationship between energetic/oxidative stress responses and fundamental kinase signaling events during the period of organ storage. This relationship may be a key factor contributing to improved graft viability after storage in a nutrient-rich preservation solution. Methods Rat small intestine was harvested and flushed intraluminally with University of Wisconsin (UW) solution or an amino acid-rich (AA) solution as follows: Group 1, no luminal flush (clinical control); Group 2, luminal UW solution; Group 3, luminal AA solution. Energetics (ATP, total adenylates), oxidative stress (malondialdehyde), histology, and MAPK (P38, JNK, ERK)/AMPK/Caspase-3 were assessed throughout 12-hour cold storage. Results P38 and JNK were upregulated strongly in Group 2 after 1- and 12-hour storage. Group 3 exhibited a delayed activation and subsequent downregulation of these pre-apoptotic signals. Between 6 to 12 hours, a strong upregulation of ERK was observed in Group 3. AMPK downregulation correlated with a reduction in AMP/ATP ratio, ERK upregulation, and P38/JNK downregulation in Group 3. After 12-hour storage, histology indicated superior preservation of mucosal architecture in Group 3 tissues. Conclusions A nutrient-rich preservation solution abrogates pre-apoptotic signaling (JNK and P38) and upregulates cytoprotective signals (ERK). Our data support the concept of a concerted effort facilitating cellular protection in response to ischemic stress.

AlgE4 is a mannuronan C5 epimerase converting homopolymeric sequences of mannuronate residues in alginates into mannuronate/guluronate alternating sequences. Treating alginates of different biological origin with AlgE4 resulted in different amounts of alternating sequences. Both ionically cross-linked alginate gels as well as alginic acid gels were prepared from the epimerised alginates. Gelling kinetics and gel equilibrium properties were recorded and compared to results obtained with the original non-epimerised alginates. An observed reduced elasticity of the alginic acid gels following epimerisation by AlgE4 seems to be explained by the generally increased acid solubility of the alternating sequences. Ionically (Ca2+) cross-linked gels made from epimerised alginates expressed a higher degree of syneresis compared to the native samples. An increase in the modulus of elasticity was observed in calcium saturated (diffusion set) gels whereas calcium limited, internally set alginate gels showed no change in elasticity. An increase in the sol–gel transitional rate of gels made from epimerised alginates was also observed. These results suggest an increased possibility of creating new junction zones in the epimerised alginate gel due to the increased mobility in the alginate chain segments caused by the less extended alternating sequences.