Silver hydroxyapatite reinforced poly(vinyl alcohol)—starch cryogel nanocomposites and study of biodegradation, compressive strength and antibacterial activity

Low density methacrylated pea, corn, and tapioca starch covalent cryogels with excellent elasticity and water/oil absorption capacity

Porous starch materials are promising in several applications as renewable natural biomaterials. This study reports an approach combining methacrylation of starch and chemical crosslinked cryogelation to fabricate highly elastic macroporous starch (ST-MA) cryogels with impressed water/oil absorption capacity and wet thermal stability among starch based porous materials. Five different types of starch, including pea, normal corn, high amylose corn, tapioca, and waxy maize starch with different amylose content, have been studied. The methacrylation degree is not related with amylose content. All cryogels exhibited excellent compressive elasticity enduring 90 % deformation without failure and good robustness in cyclic tests. The ST-MA cryogels from pea starch exhibited the highest Young's modulus and compressive strength among five types of starch. These covalent cryogels exhibit high wet-thermal stability and enzymatic hydrolysis stability, while still are biodegradable. The dry ST-MA sponges (2 wt%) showed outstanding liquid absorption capacity, absorbing ~40 folds (g/g) of water or ~ 36 folds (g/g) of oil respectively. All types of starch have similar liquid absorption performance. This study provides a universal approach to fabricate highly elastic covalent starch macroporous materials with impressed liquid absorption capacity and outstanding stability, especially wet-thermal stability, and may expand their applications.

Recent advances of antibacterial starch-based materials

Starch has attracted a lot of attention because it is biodegradable, renewable, nontoxic and low cost. By adding antibacterial substances to starch, starch-based materials have antibacterial properties. The composite with other materials can improve the comprehensive performance of starch-based materials, thus broadening the application field of the material. In this paper, we focus on antibacterial starch-based materials and review their preparation and applications. It was found that antibacterial starch-based materials were most widely used in packaging, followed by medicine, and the research on smart starch-based materials was relatively less. This review may provide some reference value for subsequent studies of starch-based materials.

Scaffolds in the microbial resistant era: Fabrication, materials, properties and tissue engineering applications

Due to microbial infections dramatically affect cell survival and increase the risk of implant failure, scaffolds produced with antimicrobial materials are now much more likely to be successful. Multidrug-resistant infections without suitable prevention strategies are increasing at an alarming rate. The ability of cells to organize, develop, differentiate, produce a functioning extracellular matrix (ECM) and create new functional tissue can all be controlled by careful control of the extracellular microenvironment. This review covers the present state of advanced strategies to develop scaffolds with antimicrobial properties for bone, oral tissue, skin, muscle, nerve, trachea, cardiac and other tissue engineering applications. The review focuses on the development of antimicrobial scaffolds against bacteria and fungi using a wide range of materials, including polymers, biopolymers, glass, ceramics and antimicrobials agents such as antibiotics, antiseptics, antimicrobial polymers, peptides, metals, carbon nanomaterials, combinatorial strategies, and includes discussions on the antimicrobial mechanisms involved in these antimicrobial approaches. The toxicological aspects of these advanced scaffolds are also analyzed to ensure future technological transfer to clinics. The main antimicrobial methods of characterizing scaffolds’ antimicrobial and antibiofilm properties are described. The production methods of these porous supports, such as electrospinning, phase separation, gas foaming, the porogen method, polymerization in solution, fiber mesh coating, self-assembly, membrane lamination, freeze drying, 3D printing and bioprinting, among others, are also included in this article. These important advances in antimicrobial materials-based scaffolds for regenerative medicine offer many new promising avenues to the material design and tissue-engineering communities.

•

Antibacterial, antifungal and antibiofilm scaffolds.

•

Antimicrobial scaffold fabrication techniques.

•

Antimicrobial biomaterials for tissue engineering applications.

•

Antimicrobial characterization methods of scaffolds.

•

Bone, oral tissue, skin, muscle, nerve, trachea, cardiac, among other applications.

Polyvinyl Alcohol/Chitosan and Polyvinyl Alcohol/Ag@MOF Bilayer Hydrogel for Tissue Engineering Applications

In this paper, polyvinyl alcohol/Ag-Metal-organic framework (PVA/Ag@MOF) and polyvinyl alcohol/chitosan (PVA/CS) were used as the inner and outer layers to successfully prepare a bilayer composite hydrogel for tissue engineering scaffold. The performance of bilayer hydrogels was evaluated. The outer layer (PVA/CS) has a uniform pore size distribution, good water retention, biocompatibility and cell adhesion ability. The inner layer (PVA/Ag@MOF) has good antibacterial activity and poor biocompatibility. PVA, PVA/0.1%Ag@MOF, PVA/0.5%Ag@MOF, and PVA/1.0%Ag@MOF show anti-microbial activity in ascending order. However, its use as an inner layer avoids direct contact with cells and prevents infection. The cell viability of all samples was above 90%, indicating that the bilayer hydrogel was non-toxic to A549 cells. The bilayer hydrogel scaffold combines the advantages of the inner and outer layers. In summary, this new bilayer composite is an ideal lung scaffold for tissue engineering.

Design and Assessment of Biodegradable Macroporous Cryogels as Advanced Tissue Engineering and Drug Carrying Materials

Cryogels obtained by the cryotropic gelation process are macroporous hydrogels with a well-developed system of interconnected pores and shape memory. There have been significant recent advancements in our understanding of the cryotropic gelation process, and in the relationship between components, their structure and the application of the cryogels obtained. As cryogels are one of the most promising hydrogel-based biomaterials, and this field has been advancing rapidly, this review focuses on the design of biodegradable cryogels as advanced biomaterials for drug delivery and tissue engineering. The selection of a biodegradable polymer is key to the development of modern biomaterials that mimic the biological environment and the properties of artificial tissue, and are at the same time capable of being safely degraded/metabolized without any side effects. The range of biodegradable polymers utilized for cryogel formation is overviewed, including biopolymers, synthetic polymers, polymer blends, and composites. The paper discusses a cryotropic gelation method as a tool for synthesis of hydrogel materials with large, interconnected pores and mechanical, physical, chemical and biological properties, adapted for targeted biomedical applications. The effect of the composition, cross-linker, freezing conditions, and the nature of the polymer on the morphology, mechanical properties and biodegradation of cryogels is discussed. The biodegradation of cryogels and its dependence on their production and composition is overviewed. Selected representative biomedical applications demonstrate how cryogel-based materials have been used in drug delivery, tissue engineering, regenerative medicine, cancer research, and sensing.

Synthesis of photodegradable cassava starch-based double network hydrogel with high mechanical stability for effective removal of methylene blue

Synthetic hydrogel has been widely used in several applications, but poor mechanical stability and biodegradability limit their applications and raise environmental concerns. Here, a biodegradable hydrogel was developed via simple free-radical polymerization of poly(acrylic acid) (PAA) in the presence of cassava starch (CS) and poly(vinyl alcohol). The hydrogel showed exceptional mechanical and physical properties. The structural morphology changed at higher CS content from a dense fiber-like porous network to larger pores with thicker cell walls. Due to the formation of a double network structure via physical entanglement, the compressive modulus significantly increased from 27 kPa (CS 0 wt%) to 127 kPa (CS 50 wt%). Reducing synthetic content (PAA) to 25 wt% and increasing CS content to 50 wt% did not reduce the removal efficiency of the hydrogel toward methylene blue (MB). The maximum adsorption capacity of the CS50 hydrogel was 417.0 mg/g. Data fitting to theoretical models indicated monolayer adsorption of MB on a homogeneous surface via chemisorption. Removal efficiency was higher than 70% at the 5^th cycle of adsorption-desorption. The biodegradability and photodegradability of the hydrogel were improved by grafting with CS. The developed hydrogel represents an alternative biodegradable adsorbent for a sustainable system of wastewater treatment.

Physically Crosslinked Poly (Vinyl Alcohol)/Kappa-Carrageenan Hydrogels: Structure and Applications

This paper discusses the structure morphology and the thermal and swelling behavior of physically crosslinked hydrogels, obtained from applying four successive freezing-thawing cycles to poly (vinyl alcohol) blended with various amounts of κ-carrageenan. The addition of carrageenan in a weight ratio of 0.5 determines a twofold increase in the swelling degree and the early diffusion coefficients of the hydrogels when immersed in distilled water, due to a decrease in the crystallinity of the polymer matrix. The diffusion of water into the polymer matrix could be considered as a relaxation-controlled transport (anomalous diffusion). The presence of the sulfate groups determines an increased affinity of the hydrogels towards crystal violet cationic dye. A maximum physisorption capacity of up to 121.4 mg/g for this dye was attained at equilibrium.