Plasma-modified biomaterials for self-antimicrobial applications

The surface compatibility and antibacterial properties of biomaterials are crucial to tissue engineering and other medical applications, and plasma-assisted technologies have been employed to enhance these characteristics with good success. Herein, we describe and review the recent developments made by our interdisciplinary team on self-antimicrobial biomaterials with emphasis on plasma-based surface modification. Our results indicate that a self-antibacterial surface can be produced on various types of materials including polymers, metals, and ceramics by plasma treatment. Surface characteristics such as roughness, microstructure, chemistry, electronegativity, free energy, hydrophilicity, and interfacial physiochemistry are important factors and can be tailored by using the appropriate plasma-assisted processing parameters. In particular, mechanistic studies reveal that the interfacial physiochemical processes, biocidal agents, and surface free energy are predominantly responsible for the antibacterial effects of plasma-modified biomaterials.     

Thermotropic liquid crystal polymers for engineering applications

Abstract

It is relatively recently that thermotropic liquid crystal polymers for load bearing applications have become commercially available. These materials possess good mechanical properties and excellent processability and are intended for use at elevated temperatures in harsh chemical environments. In this paper, the phenomenon of liquid crystallinity is described and the way in which it improves the mechanical properties and processability of polymers is explained. The synthetic strategies involved in obtaining nematic mesophases in polyesters are discussed fully, particularly those involved in the synthesis of commercially available materials. The future of these new types of engineering thermoplastic will depend on cost and on the appropriate application of the unique properties they offer.

MST/875     

Lyotropic liquid crystal polymers for engineering applications

Abstract

The use of lyotropic liquid crystal polymers such as Kevlar and Twaron in high tech engineering applications has been common for many years. These materials possess excellent temperature resistance and very good mechanical properties. These two materials are polyaramids, but the newer polybenzazoles are also of a liquid crystal nature when present in appropriate solvents. Their rigid rod structures make it possible for these materials to form composite structures with isotropic polymers, where the fibre reinforcement is on a molecular level. This is a unique and very interesting possibility which has yet to be fully developed.

MST/1254     

A covalently crosslinked polysaccharide hydrogel for potential applications in drug delivery and tissue engineering

The development of non-cytotoxic hydrogels that can allow for the controlled release of molecules has important clinical and therapeutic applications. In this paper, we developed a series of in situ hydrogels by combining N,O-carboxymethyl chitosan and oxidized alginate without additional crosslinking agents. The rheological properties of these hydrogels as well as their gelling time, swelling ratio, and in vitro degradation behavior were investigated. We observed that although gelation was rapid at physiological temperature, it was even faster in the presence of higher oxidization degree of alginate. In vitro cytotoxicity study showed that the developed hydrogels were not cytotoxic after 24?h of culturing with NIH-3T3 cells. Additionally, bovine serum albumin was released from the hydrogels initially by diffusion at early stages followed by a degradation-dependent mechanism at later stages. In conclusion, the developed hydrogel might have potential application in the drug delivery system and tissue engineering.     

Characterisation of a collagen membrane for its potential use in cardiovascular tissue engineering applications

In this study, Biomend, a collagen membrane conventionally used in the regeneration of periodontal tissue, is investigated for its possible use in the field of cardiovascular tissue engineering. A key requirement of most potential tissue engineering scaffolds is that degradation occurs in tandem with tissue regeneration and extra cellular matrix remodelling. To this end, it is crucial to understand the degradation mechanics and mechanisms of the material and to investigate the practicability of using Biomend as a possible scaffold material. With this in mind, methodologies for the initial characterisation of the scaffold material were determined. The mechanical properties of Biomend samples, subjected to various degrees of hydration and enzymatic degradation, were examined primarily through tensile testing experiments. The effects of enzymatic degradation were monitored quantitatively, by observing weight loss, and visually, by studying micrographs. Cell adhesion and viability were of primary concern. Confocal laser scanning microscopy was employed to illustrate endothelialisation on the surface of this collagen membrane. Fluorescence microscopy was used to visualise cell viability on the membrane surface. These images, coupled with assays to measure cell activity, suggest that Biomend is not a suitable substrate to allow endothelialisation. In summary, this collagen membrane has suitable mechanical properties with the potential to control its degradation rate. However, since poor endothelial cell viability was observed on the membrane, it may not be suitable for use in cardiovascular tissue engineering applications.     

Functionalization of PEG-PMPC-based polymers for potential theranostic applications

The synergistic effect of polyethylene glycol (PEG) and poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) can effectively reduce the protein absorption, which is beneficial to theranostics. However, PEG–PMPC-based polymers have rarely been used as nanocarriers in the theranostic field due to their limited modifiability and weak interaction with other materials. Herein, a plain method was proposed to endow them with the probable ability of loading small active agents, and the relationship between the structure and the ability of loading hydrophobic agents was explored, thus expanding their applications. Firstly, mPEG–PMPC or 4-arm-PEG–PMPC polymer was synthesized by atom transfer radical polymerization (ATRP) using mPEG-Br or 4-arm-PEG-Br as the macroinitiator. Then a strong hydrophobic segment, poly(butyl methacrylate) (PBMA), was introduced and the ability to load small hydrophobic agents was further explored. The results showed that linear mPEG–PMPC–PBMA could form micelles 50–80 nm in size and load the hydrophobic agent such as Nile red efficiently. In contrast, star-like 4-arm-PEG–PMPC–PBMA, a monomolecular micelle (10–20 nm), could hardly load any hydrophobic agent. This work highlights effective strategies for engineering PEG–PMPC-based polymers and may facilitate the further application in numerous fields.     

New hydrogels based on maleilated collagen with potential applications in tissue engineering

New hydrogels based on maleic anhydride (MA) modified collagen were prepared with the aim of overcoming the high degradation rate displayed by collagen that is not otherwise chemically crosslinked. Semi-interpenetrated matrices were obtained by free radical polymerization of maleilated collagen (CM) and 2-hydroxyethyl methacrylate (HEMA) in the presence of ammonium persulfate (APS) and N,N,N′,N′-tetramethylethylenediamine (TEMED) as initiating system. The resulting matrices (CMH) had a sharp decrease in degradation, when compared to pure collagen. FTIR and H¹ NMR spectroscopies were used to confirm the incorporation of MA on the collagen peptide chains. The final composition of CMH was found to be strongly dependent by the concentration of maleilated collagen. The morphology of the hydrogels was studied by Scanning electron microscopy (SEM) and the macro-gel structure was confirmed. Water uptake of the synthetised hydrogels is influenced by both composition and the porosity of the matrices.     

A biodegradable and biocompatible PVA-citric acid polyester with potential applications as matrix for vascular tissue engineering

Unique elastomeric and biocompatible scaffolds were produced by the polyesterification of poly(vinyl alcohol) (PVA) and citric acid via a simple polycondensation reaction. The physicochemical characterization of the materials was done by Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), mechanical and surface property analyses. The materials are hydrophilic and have viscoelastic nature. Biodegradable, non-cytotoxic materials that can be tailored into 3D scaffolds could be prepared in an inexpensive manner. This polyester has potential implications in vascular tissue engineering application as a biodegradable elastomeric scaffold.     

壳聚糖支架在组织工程中的应用

综述了壳聚糖作为细胞生长载体在软骨组织工程，骨组织工程和皮肤组织工程等方面的应用进展，表明壳聚糖有望成为优异的组织工程支架材料。     

Conducting polypyrrole in tissue engineering applications

Polypyrrole （PPy）, the earliest prepared conducting polymer, has good biocompatibility, easy synthesis and flexibility in processing. Compared with metal and inorganic materials, doped PPy has better mechanical match with live tissue, resulting in its many applications in biomedical field. This mini-review presents some information on specific PPy properties for tissue engineering applications, including its synthesis, doping, bio-modiflcation. Although some challenges and unanswered problems still remain, PPy as novel biomaterial has promoted the development tissue engineering for its clinical application in the future.     

Preparation and characterization of polycaprolactone-chitosan composites for tissue engineering applications

Highly porous scaffold plays an important role in bone tissue engineering, which becomes a promising alternative approach for bone repair since its emergence. The objective of this work was to blend poly (є-caprolactone) (PCL) with chitosan (CS) for the purpose of preparation of porous scaffold. A simple unique method was employed under room-temperature condition to blend the two components together without separation of two phases. The reaction leads to formation of sponge-like porous 5, 10, 15 and 20 wt% CS composites. XRD, IR and SEM were used to determine components and morphology of the composites. DSC studies indicated that the miscibility of the two components. And pore volume fractures of composites were determined by a simple method in which a pycnometer was used. The results show that CS is successfully commingled into PCL matrix, and adding CS into PCL will not damage the crystalline structure of PCL. The composite shows no signs of phase separation and presents a unique porous structure under SEM observation. The porosity of composite increased with the increase of the content of CS in the composite. The highest porosity reached to 92% when CS content increased to 20 wt%. The mechanism of formation of this unique porous structure is also discussed.     

Thermal-crosslinked porous chitosan scaffolds for soft tissue engineering applications

The aim of this study was to demonstrate the feasibility of using a steam autoclave process for sterilization and simultaneously thermal-crosslinking of lyophilized chitosan scaffolds. This process is of great interest in biomaterial development due to its simplicity and low toxicity. The steam autoclave process had no significant effect on the average pore diameter (~ 70 μm) and overall porosity (> 80%) of the resultant chitosan scaffolds, while the sterilized scaffolds possessed more homogenous pore size distribution. The sterilized chitosan scaffolds exhibited an enhanced compressive modulus (109.8 kPa) and comparable equilibrium swelling ratio (23.3). The resultant chitosan scaffolds could be used directly for in vitro cell culture without extra sterilization. The data of in vitro studies demonstrated that the scaffolds facilitated cell attachment and proliferation, indicating great potential for soft tissue engineering applications.     

Polysaccharide-based magnetically responsive polyelectrolyte hydrogels for tissue engineering applications

Polysaccharide-based bionanocomposite hydrogels with functional nanomaterials were used in biomedical applications.Self-organization of xanthan gum and chitosan in the presence of iron oxide magnetic nanoparticles(Fe_3O_4MNPs)allowed us to form magnetically responsive polyelectrolyte complex hydrogels(MPECHs)via insitu ionic complexation using D-(+)-glucuronic acid?-lactone as a green acidifying agent.Characterization confirmed the successful formation of(and structural interactions within)the MPECH and good porous structure.The rheological behavior and compressive properties of the PECH and MPECH were measured.The results indicated that the incorporation of Fe_3O_4MNPs into the PECH greatly improved mechanical properties and storage modulus(G’).In vitro cell culture of NIH3T3 fibroblasts on MPECHs showed improvements in cell proliferation and adhesion in an external magnetic field relative to the pristine PECH.The results showed that the newly developed MPECH could potentially be used as a magnetically stimulated system in tissue engineering applications.     

A biodegradable and biocompatible PVA–citric acid polyester with potential applications as matrix for vascular tissue engineering

Unique elastomeric and biocompatible scaffolds were produced by the polyesterification of poly(vinyl alcohol) (PVA) and citric acid via a simple polycondensation reaction. The physicochemical characterization of the materials was done by Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), mechanical and surface property analyses. The materials are hydrophilic and have viscoelastic nature. Biodegradable, non-cytotoxic materials that can be tailored into 3D scaffolds could be prepared in an inexpensive manner. This polyester has potential implications in vascular tissue engineering application as a biodegradable elastomeric scaffold.     

Fabrication and characterization of scaffold from cadaver goat-lung tissue for skin tissue engineering applications

The present study aims to fabricate scaffold from cadaver goat-lung tissue and evaluate it for skin tissue engineering applications. Decellularized goat-lung scaffold was fabricated by removing cells from cadaver goat-lung tissue enzymatically, to have cell-free 3D-architecture of natural extracellular matrix. DNA quantification assay and Hematoxylin and eosin staining confirmed the absence of cellular material in the decellularized lung-tissue. SEM analysis of decellularized scaffold shows the intrinsic porous structure of lung tissue with well-preserved pore-to-pore interconnectivity. FTIR analysis confirmed non-denaturation and well maintainance of collagenous protein structure of decellularized scaffold. MTT assay, SEM analysis and H&E staining of human skin-derived Mesenchymal Stem cell, seeded over the decellularized scaffold, confirms stem cell attachment, viability, biocompatibility and proliferation over the decellularized scaffold. Expression of Keratin18 gene, along with CD105, CD73 and CD44, by human skin-derived Mesenchymal Stem cells over decellularized scaffold signifies that the cells are viable, proliferating and migrating, and have maintained their critical cellular functions in the presence of scaffold. Thus, overall study proves the applicability of the goat-lung tissue derived decellularized scaffold for skin tissue engineering applications.     

Calcium-phosphate derived from mineralized algae for bone tissue engineering applications

In this work, several routes are described towards obtaining pure inorganic phases derived from Coralline officinallis red algae. The scanning electron microscopy studies have shown that it becomes possible not only to eliminate the undesired organic phase, but also to preserve or tailor the red algae typical microporosity. X-ray diffraction analysis was used to investigate the phase content of the red algae before and after performing the different treatment routes. Hydroxyapatite nanocrystallites were obtained after converting the coralline calcium carbonate skeleton by means of combining thermal and chemical routes. These results were confirmed by Fourier transform infra-red spectroscopic analysis. The processing routes herein described are very promising in order to design bioceramics of algae origin that might find useful applications as bone fillers and tissue engineering scaffolds.     

Progress in the field of electrospinning for tissue engineering applications

Electrospinning is an extremely promising method for the preparation of tissue engineering (TE) scaffolds. This technique provides nonwovens resembling in their fibrillar structures those of the extracellular matrix (ECM), and offering large surface areas, ease of functionalization for various purposes, and controllable mechanical properties. The recent developments toward large-scale productions combined with the simplicity of the process render this technique very attractive. Progress concerning the use of electrospinning for TE applications has advanced impressively. Different groups have tackled the problem of electrospinning for TE applications from different angles. Nowadays, electrospinning of the majority of biodegradable and biocompatible polymers, either synthetic or natural, for TE applications is straightforward. Different issues, such as cell penetration, incorporation of growth and differentiating factors, toxicity of solvents used, productivity, functional gradient, etc. are main points of current considerations. The progress in the use of electrospinning for TE applications is highlighted in this article with focus on major problems encountered and on various solutions available until now.     

Characterization of TEMPO-oxidized bacterial cellulose scaffolds for tissue engineering applications

Introduction of active groups on the surface of bacterial cellulose (BC) nanofibers is one of the promising routes of tailoring the performance of BC scaffolds for tissue engineering. This paper reported the introduction of aldehyde groups to BC nanofibers by 2,2,6,6-tetramethylpyperidine-1-oxy radical (TEMPO)-mediated oxidation and evaluation of the potential of the TEMPO-oxidized BC as tissue engineering scaffolds. Periodate oxidation was also conducted for comparison. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses were carried out to determine the existence of aldehyde groups on BC nanofibers and the crystallinity. In addition, properties relevant to scaffold applications such as morphology, fiber diameter, mechanical properties, and in vitro degradation were characterized. The results indicated that periodate oxidation could introduce free aldehyde to BC nanofibers and the free aldehyde groups on the TEMPO-oxidized BC tended to transfer to acetal groups. It was also found that the advantageous 3D structure of BC scaffolds remained unchanged and that no significant changes in morphology, fiber diameter, tensile structure and in vitro degradation were found after TEMPO-mediated oxidation while significant differences were observed upon periodate oxidation. The present study revealed that TEMPO-oxidation could impart BC scaffolds with new functions while did not degrade their intrinsic advantages.