A novel family of biodegradable poly(ester amide) elastomers

Tomato based gelatin methacryloyl hydrogel as an effective natural and low-cost scaffold for accelerative wound healing

Oxidative stress and infection are the main reasons for postponement of wound healing rate. They can potentially lead to serious inflammation and eventually lead to a longer and more painful recovery phase. Although wound dressings based on synthetic materials with antioxidative property have been proved to exhibit remarkable effect in controlling ROS level and improving wound healing, issues, such as high cost in raw materials, complicated procedures, usage of various toxic additives, and potential allergies, have significantly confined further clinical applications. In this study, a novel type of tissue engineering scaffold, based on tomatoes (Solanum lycopersicon) and gelatin methacryloyl (GelMA), was prepared via facile lyophilization and photo cross-link method (SL/GelMA). By taking advantages of various antioxidative components, such as carotenoids, flavonoids, phenolic acids, vitamin E, and vitamin C in tomatoes, SL/GelMA can effectively regulate ROS level, relieve the oxidative stress in wound bed, promote cell migration and angiogenesis, contribute to collagen deposition, and thus accelerate the rate of wound enclosure. Along with its high biocompatibility and low allergic potential, we believe that the food-derived wound dressing with facile preparation method, easy accessibility, and high cost-effectiveness can be translated for clinical treatments of various chronic wounds.

Recent Advances of Poly(ester amide)s-Based Biomaterials

Biodegradable and biocompatible biomaterials have offered much more opportunities from an engineering standpoint for treating diseases and maintaining health. Poly(ester amide)s (PEAs), as an outstanding family among such biomaterials, have risen overwhelmingly in the past decades. These synthetic polymers have easily and widely available raw materials and a diversity of synthetic approaches, which have attracted considerable attention. More importantly, combining the superiorities of polyamides and polyesters, PEAs have emerged with better functions. They could have improved biodegradability, biocompatibility, and cell-material interactions. The PEAs derived from α-amino acids even allow the introduction of pendant sites for further modification or functionalization. Meanwhile, it is gradually recognized that the chemical structures are closely related to the physiochemical and biological properties of PEAs so that their properties can be precisely controlled. PEAs therefore become significant materials in the biomedical fields. This review will attempt to summarize the recent progress in the development of PEAs with respect to the preparation materials and methods, structure-property relationships along with their latest biomedical accomplishments, especially for drug delivery and tissue engineering.

Synthesis and molecular characterization of chitosan/starch blends based polyurethanes

Starch/chitosan modified polyurethanes (PUs) were synthesized by step growth polymerization reaction between -NCO terminated prepolymer and chain extenders (1,4-Butanediol/starch/chitosan). Isophorone diisocyanate (IPDI) was reacted with hydroxyl-terminated polybutadiene (HTPB) to synthesize prepolymer and was further reacted with different moles ratio of starch/chitosan to produced five samples of polyurethane (PU). These samples were characterized by Fourier transformed infrared (FTIR) and Proton nuclear magnetic resonance (¹H NMR) spectroscopy. The surface characterizations of PUs were done by scanning electron microscope (SEM). Thermogravimetric analysis showed that the thermal stability of PUs was higher when the mixture of both natural materials was used at equal amounts. It is concluded that combination of both starch and chitosan are efficient for the synthesis of PUs.

An improved synthesis of a cyclopropene-based molecule for the fabrication of bioengineered tissues via copper-free click chemistry

BACKGROUND

Since its introduction in the field of biological imaging, the use of copper-free click chemistry has been extended to produce improved materials for vascular surgery, ophthalmology, environmental, and automotive applications. This wide applicability suggests that larger quantities of the chemical reagents for copper-free click chemistry will be required in the future. However, the large-scale synthesis of such chemicals has been barely investigated. A possible reason is the shortage of reliable synthetic protocols to obtain large quantities of these building blocks. We therefore present in this paper an improved synthetic protocol to obtain a cyclopropene-based carbonate, a key building block for the well-known copper-free click chemistry.

METHOD

Our protocol builds upon an already available method to obtain a cyclopropene-based carbonate. When scaled up, several parameters of this method were changed in order to obtain an improved yield. First, the use of lower temperatures and slower addition rates of the chemicals avoided the formation of detrimental hotspots in the reaction system. Second, the use of less hygroscopic solvents minimized the decomposition of the cyclopropene carbonate. Finally, chromatographic purifications were minimized and improved by using deactivated silica.

RESULTS

We obtained the compound (2-methylcycloprop-2-en-1-yl)methyl (4-nitrophenyl) carbonate, a key building block for copper-free click chemistry, in an unprecedented 60% overall yield on a six-gram scale.

CONCLUSIONS

Our improved synthetic protocol demonstrates the potential of large-scale production of improved materials using click chemistry, with potential future applications in the fields of molecular imaging, vascular surgery, ophthalmology, and theranostics.

Liquid Crystal Elastomers-A Path to Biocompatible and Biodegradable 3D-LCE Scaffolds for Tissue Regeneration

The development of appropriate materials that can make breakthroughs in tissue engineering has long been pursued by the scientific community. Several types of material have been long tested and re-designed for this purpose. At the same time, liquid crystals (LCs) have captivated the scientific community since their discovery in 1888 and soon after were thought to be, in combination with polymers, artificial muscles. Within the past decade liquid crystal elastomers (LCE) have been attracting increasing interest for their use as smart advanced materials for biological applications. Here, we examine how LCEs can potentially be used as dynamic substrates for culturing cells, moving away from the classical two-dimensional cell-culture nature. We also briefly discuss the integration of a few technologies for the preparation of more sophisticated LCE-composite scaffolds for more dynamic biomaterials. The anisotropic properties of LCEs can be used not only to promote cell attachment and the proliferation of cells, but also to promote cell alignment under LCE-stimulated deformation. 3D LCEs are ideal materials for new insights to simulate and study the development of tissues and the complex interplay between cells.

Liquid crystal elastomer foams with elastic properties specifically engineered as biodegradable brain tissue scaffolds

Tissue regeneration requires 3-dimensional (3D) smart materials as scaffolds to promote transport of nutrients. To mimic mechanical properties of extracellular matrices, biocompatible polymers have been widely studied and a diverse range of 3D scaffolds have been produced. We propose the use of responsive polymeric materials to create dynamic substrates for cell culture, which goes beyond designing only a physical static 3D scaffold. Here, we demonstrated that lactone- and lactide-based star block-copolymers (SBCs), where a liquid crystal (LC) moiety has been attached as a side-group, can be crosslinked to obtain Liquid Crystal Elastomers (LCEs) with a porous architecture using a salt-leaching method to promote cell infiltration. The obtained SmA LCE-based fully interconnected-porous foams exhibit a Young modulus of 0.23 ± 0.07 MPa and a biodegradability rate of around 20% after 15 weeks both of which are optimized to mimic native environments. We present cell culture results showing growth and proliferation of neurons on the scaffold after four weeks. This research provides a new platform to analyse LCE scaffold-cell interactions where the presence of liquid crystal moieties promotes cell alignment paving the way for a stimulated brain-like tissue.

Poly(ester amide)s from Poly(ethylene terephthalate) Waste for Enhancing Bone Regeneration and Controlled Release

The present study elucidates the facile synthesis and exceptional properties of a family of novel poly(ester amide)s (PEAs) based on bis(2-hydroxy ethylene) terephthalamide that was obtained from the poly(ethylene terephthalate) waste. Fourier transform infrared and ¹H NMR were used to verify the presence of ester and amide in the polymer backbone. Differential scanning calorimetry data showed that the glass transition temperature decreased with as the chain length of dicarboxylic acids increased. Dynamic mechanical analysis and contact angle studies proved that the modulus values and hydrophobicity increased with as the chain lengths of dicarboxylic acids increased. In vitro hydrolytic degradation and dye release studies demonstrated that the degradation and release decreased with as the chain lengths of dicarboxylic acids increased. Modeling these data illustrated that degradation and release follow first-order degradation and zero-order release, respectively. The in vitro cytocompatibility studies confirmed the minimal toxicity characteristic of these polymers. Osteogenic studies proved that these polymers can be highly influential in diverting the cells toward osteogenic lineage. Alizarin red staining evinced the presence of twice the amount of calcium phosphate deposits by the cells on these polymers when compared to the control. The observed result was also corroborated by the increased expression of alkaline phosphatase. These findings were further validated by the markedly higher mRNA expressions for known osteogenic markers using real time polymerase chain reaction. Therefore, these polymers efficiently promoted osteogenesis. This study demonstrates that the physical properties, degradation, and release kinetics can be altered to meet the specific requirements in organ regeneration as well as facilitate simultaneous polymer resorption through control of the chain length of the monomers. The findings of this study have significant implications for designing cost-effective biodegradable polymers for tissue engineering.

Poly(ester amide)s from Soybean Oil for Modulated Release and Bone Regeneration

Designing biomaterials for bone tissue regeneration that are also capable of eluting drugs is challenging. Poly(ester amide)s are known for their commendable mechanical properties, degradation, and cellular response. In this regard, development of new poly(ester amide)s becomes imperative to improve the quality of lives of people affected by bone disorders. In this framework, a family of novel soybean oil based biodegradable poly(ester amide)s was synthesized based on facile catalyst-free melt-condensation reaction. The structure of the polymers was confirmed by FTIR and (1)H -NMR, which indicated the formation of the ester and amide bonds along the polymer backbone. Thermal analysis revealed the amorphous nature of the polymers. Contact angle and swelling studies proved that the hydrophobic nature increased with increase in chain length of the diacids and decreased with increase in molar ratio of sebacic acid. Mechanical studies proved that Young's modulus decreased with decrease in chain lengths of the diacids and increase in molar ratio of sebacic acid. The in vitro hydrolytic degradation and dye release demonstrated that the degradation and release decreased with increase in chain lengths of the diacids and increased with increase in molar ratio of sebacic acid. The degradation followed first order kinetics and dye release followed Higuchi kinetics. In vitro cell studies showed no toxic effects of the polymers. Osteogenesis studies revealed that the polymers can be remarkably efficient because more than twice the amount of minerals were deposited on the polymer surfaces than on the tissue culture polystyrene surfaces. Thus, a family of novel poly(ester amide)s has been synthesized, characterized for controlled release and tissue engineering applications wherein the physical, degradation, and release kinetics can be tuned by varying the monomers and their molar ratios.

Hollow Mesoporous Silica Nanocarriers with Multifunctional Capping Agents for In Vivo Cancer Imaging and Therapy

Efficient drug loading and selectivity in drug delivery are two key features of a good drug-carrier design. Here we report on such a drug carrier formed by using hollow mesoporous silica nanoparticles (HMS NPs) as the core and specifically designed multifunctional amphiphilic agents as the encapsulating shell. These nanocarriers combine the advantages of the HMS NP core (favorable physical and structural properties) and the versatility of an organic-based shell (e.g., specificity in chemical properties and modifiability). Moreover, both the properties of the core and the shell can be independently varied. The varied core and shell could then be integrated into a single device (drug carrier) to provide efficient and specific drug delivery. In vitro and in vivo data suggests that these drug nanocarriers are biocompatible and are able to deliver hydrophobic drugs selectively to target tumor cells. After the break of the pH-labile linkages in the shell, the drug payload can be released and the tumor cells are killed.

Click chemistry plays a dual role in biodegradable polymer design

Click chemistry plays a dual role in the design of new citrate-based biodegradable elastomers (CABEs) with greatly improved mechanical strength and easily clickable surfaces for biofunctionalization. This novel chemistry modification strategy is applicable to a number of different types of polymers for improved mechanical properties and biofunctionality.

Sequence Regulated Poly(ester-amide)s Based on Passerini Reaction

Multicomponent polymerization based on Passerini reaction is described. Room temperature polymerization of dicarboxyl acid, monoaldehyde, and diisocyanide leads to the formation of a new type of sequence regulated poly(ester-amide)s in an efficient one-pot process. The polymerization was confirmed to be a stepwise mechanism, and the resulting polymers were characterized and determined to be linear polymers with a sequence regulated backbone repeating unit of ester-ester-amide-amide. When functional aldehydes were used, functional side groups could be easily introduced at the same time, providing a simple way for further modification.

Localized delivery of dexamethasone from electrospun fibers reduces the foreign body response

Synthetic scaffolds are crucial to applications in regenerative medicine; however, the foreign body response can impede regeneration and may lead to failure of the implant. Herein we report the development of a tissue engineering scaffold that allows attachment and proliferation of regenerating cells while reducing the foreign body response by localized delivery of an anti-inflammatory agent. Electrospun fibers composed of poly(l-lactic) acid (PLLA) and poly(ε-caprolactone) (PCL) were prepared with and without the steroid anti-inflammatory drug, dexamethasone. Analysis of subcutaneous implants demonstrated that the PLLA fibers encapsulating dexamethasone evoked a less severe inflammatory response than the other fibers examined. They also displayed a controlled release of dexamethasone over a period of time conducive to tissue regeneration and allowed human mesenchymal stem cells to adhere to and proliferate on them in vitro. These observations demonstrate their potential as a building block for tissue engineering scaffolds.

Progressive structural and biomechanical changes in elastin degraded aorta

Aortic aneurysm is an important clinical condition characterized by common structural changes such as the degradation of elastin, loss of smooth muscle cells, and increased deposition of fibrillary collagen. With the goal of investigating the relationship between the mechanical behavior and the structural/biochemical composition of an artery, this study used a simple chemical degradation model of aneurysm and investigated the progressive changes in mechanical properties. Porcine thoracic aortas were digested in a mild solution of purified elastase (5 U/mL) for 6, 12, 24, 48, and 96 h. Initial size measurements show that disruption of the elastin structure leads to increased artery dilation in the absence of periodic loading. The mechanical properties of the digested arteries, measured with a biaxial tensile testing device, progress through four distinct stages termed (1) initial-softening, (2) elastomer-like, (3) extensible-but-stiff, and (4) collagen-scaffold-like. While stages 1, 3, and 4 are expected as a result of elastin degradation, the S-shaped stress versus strain behavior of the aorta resulting from enzyme digestion has not been reported previously. Our results suggest that gradual changes in the structure of elastin in the artery can lead to a progression through different mechanical properties and thus reveal the potential existence of an important transition stage that could contribute to artery dilation during aneurysm formation.

Focal contact formation of vascular smooth muscle cells on Langmuir-Blodgett and solvent-cast films of biodegradable poly(ester amide)s

The ability of biomaterials to support the adhesion of cells is a necessary condition for their use in scaffold-guided tissue engineering. Waveguide evanescent field fluorescence (WEFF) microscopy is a relatively new microscopic technique that allows the number of cell adhesions to a waveguide surface be measured by imaging the interfacial contact region between the cells and their substratum. In this work, the adhesion of human coronary artery smooth muscle cells (HCASMCs) to ultrathin films (20 nm) of poly(ester amide)s (PEAs) prepared by Langmuir-Blodgett (LB) technology on waveguides was investigated and compared with conventional vinculin immunostaining on solvent cast PEA films. Cell culture was conducted both in the presence and absence of serum to evaluate the effect of nonspecific protein adsorption that mediates cell adhesion. WEFF microscopy analyses revealed that the cationic PEA enhanced the number of attachment sites compared with the control waveguides regardless of the culture medium. Although differences in cell adhesions between different PEAs were suggested by the results, no statistically significant differences were found. Similar results were observed with presently and previously reported vinculin immunostaining studies, further validating the use of WEFF microscopy to quantify cell adhesions. Moreover, the focal adhesions of the HCASMCs to the PEA surfaces indicate these PEAs can promote integrin signaling, which is vital in cell survival, migration, and proliferation, and ultimately in scaffold-guided vascular tissue engineering.