Enzymatically biomineralized chitosan scaffolds for tissue-engineering applications

Understanding Matrix Stiffness in Vinyl Polymer Hydrogels: Implications in Bone Tissue Engineering

Matrix elasticity helps to direct bone cell differentiation, impact healing processes, and modify extracellular matrix deposition, all of which are required for tissue growth and maintenance. In this work, we evaluated the role of inorganic nanocrystals or mineral inducers such as nanohydroxyapatite, alkaline phosphatase, and nanoclay also known as montmorillonite deposited on vinyl-based hydrogels in generating matrices with different stiffness and their role in cell differentiation. Poly-2-(dimethylamino)ethyl methacrylate (PD) and poly-2-hydroxypropylmethacrylamide (PH) are the two types of vinyl polymers chosen for preparing hydrogels via thermal cross-linking. The hydrogels exhibited porosity, which decreased with an increase in stiffness. Each of the compositions is non-cytotoxic and maintains the viability of pre-osteoblasts (MC3T3-E1) and human bone marrow mesenchymal stem cells (hBMSCs). The PD hydrogels in the presence of ALP showed the highest mineralization ability confirmed through the alizarin assay and a better structural environment for their use as scaffolds for tissue engineering. The study reveals that understanding such interactions can generate hydrogels that can serve as efficient 3D models to study biomineralization.

Characterization and in vitro bioactivity evaluation of polyvinyl alcohol incorporated electro spun chitosan/ fluor apatite nanofibrous scaffold for bone tissue engineering

In this study, polyvinyl alcohol/chitosan/fluor apatite scaffolds with different concentrations of polyvinyl alcohol of 0.075 g ml-1 and 0.1 g ml-1, respectively named A and B fabricated by electrospinning method to use in tissue engineering. By examining the scaffolds by FE-SEM, an appetite layer formation which was on the scaffold surface was clearly observable. Increasing the concentration of polyvinyl alcohol from 0.075 g ml-1 to 0.1 g ml-1 in the nanofibrous scaffolds improved degradation characteristic with an optimized value of 26 ± 2 and 42 ± 1 % after 28 days, respectively. The mean diameter of fibers both scaffolds was 405 nm and 212 nm, respectively. Furthermore, the percentage of porosity in both scaffolds was calculated as 84% and 91%, separately. The level of hydrophilicity of the scaffolds was measured by the dynamic contact angle method. Moreover, the increase in the percentage of polyvinyl alcohol led to the decrease in the average contact angle in scaffold A and scaffold B from 90° to 70°, respectively. The results of bone marrow culture test with MG-63 (NCBI C555) cell on the surface of scaffolds demonstrated not cytotoxicity in the resulting scaffolds as well as a suitable substrate for the adhesion and growth of the cells. According to our findings, the electrospun fluorapatite-incorporated-chitosan/polyvinyl alcohol scaffold could provide a new nanocomposite for biomedical applications.

In Situ Enzymatic Reaction Generates Magnesium-Based Mineralized Microspheres with Superior Bioactivity for Enhanced Bone Regeneration

Bone is a naturally mineralized tissue with a remarkable hierarchical structure, and the treatment of bone defects remains challenging. Microspheres with facile features of controllable size, diverse morphologies, and specific functions display amazing potentials for bone regeneration. Herein, inspired by natural biomineralization, a novel enzyme-catalyzed reaction is reported to prepare magnesium-based mineralized microspheres. First, silk fibroin methacryloyl (SilMA) microspheres are prepared using a combination of microfluidics and photo-crosslinking. Then, the alkaline phosphatase (ALP)-catalyzed hydrolysis of adenosine triphosphate (ATP) is successfully used to induce the formation of spherical magnesium phosphate (MgP) in the SilMA microspheres. These SilMA@MgP microspheres display uniform size, rough surface structure, good degradability, and sustained Mg2+ release properties. Moreover, the in vitro studies demonstrate the high bioactivities of SilMA@MgP microspehres in promoting the proliferation, migration, and osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Transcriptomic analysis shows that the osteoinductivity of SilMA@MgP microspheres may be related to the activation of the PI3K/Akt signaling pathway. Finally, the bone regeneration enhancement units (BREUs) are designed and constructed by inoculating BMSCs onto SilMA@MgP microspheres. In summary, this study demonstrates a new biomineralization strategy for designing biomimetic bone repair materials with defined structures and combination functions.

Porous Chitosan Hydrogels Produced by Physical Crosslinking: Physicochemical, Structural, and Cytotoxic Properties

Chitosan hydrogels are biomaterials with excellent potential for biomedical applications. In this study, chitosan hydrogels were prepared at different concentrations and molecular weights by freeze-drying. The chitosan sponges were physically crosslinked using sodium bicarbonate as a crosslinking agent. The X-ray spectroscopy (XPS and XRD diffraction), equilibrium water content, microstructural morphology (confocal microscopy), rheological properties (temperature sweep test), and cytotoxicity of the chitosan hydrogels (MTT assay) were investigated. XPS analysis confirmed that the chitosan hydrogels obtained were physically crosslinked using sodium bicarbonate. The chitosan samples displayed a semi-crystalline nature and a highly porous structure with mean pore size between 115.7 ± 20.5 and 156.3 ± 21.8 µm. In addition, the chitosan hydrogels exhibited high water absorption, showing equilibrium water content values from 23 to 30 times their mass in PBS buffer and high thermal stability from 5 to 60 °C. Also, chitosan hydrogels were non-cytotoxic, obtaining cell viability values ≥ 100% for the HT29 cells. Thus, physically crosslinked chitosan hydrogels can be great candidates as biomaterials for biomedical applications.

Fundamentals and Applications of Raman-Based Techniques for the Design and Development of Active Biomedical Materials

Raman spectroscopy is an analytical method based on light-matter interactions that can interrogate the vibrational modes of matter and provide representative molecular fingerprints. Mediated by its label-free, non-invasive nature, and high molecular specificity, Raman-based techniques have become ubiquitous tools for in situ characterization of materials. This review comprehensively describes the theoretical and practical background of Raman spectroscopy and its advanced variants. The numerous facets of material characterization that Raman scattering can reveal, including biomolecular identification, solid-to-solid phase transitions, and spatial mapping of biomolecular species in bioactive materials, are highlighted. The review illustrates the potential of these techniques in the context of active biomedical material design and development by highlighting representative studies from the literature. These studies cover the use of Raman spectroscopy for the characterization of both natural and synthetic biomaterials, including engineered tissue constructs, biopolymer systems, ceramics, and nanoparticle formulations, among others. To increase the accessibility and adoption of these techniques, the present review also provides the reader with practical recommendations on the integration of Raman techniques into the experimental laboratory toolbox. Finally, perspectives on how recent developments in plasmon- and coherently-enhanced Raman spectroscopy can propel Raman from underutilized to critical for biomaterial development are provided.

Montmorillonite stabilized chitosan-co-mucin hydrogel for tissue engineering applications

The role of polymers has played a crucial role in developing templates that can promote regeneration as tissue-engineered matrices. The present study aims to develop functional matrices involving the protein mucin. The mucin used in this study is characterised using MALDI-TOF TOF and CD spectroscopy prior to conjugation. Thereupon, a hybrid scaffold comprising of a polysaccharide, chitosan, chemically conjugated to a protein, mucin, and encapsulated with montmorillonite is developed. Grafting of hydroxyethyl methacrylate (HEMA) is done to overcome the issue of mechanical weakness that mucin hydrogels usually undergo. It was observed that the presence of montmorillonite led to the stability of the hydrogels. The conjugations with varied ratios of the polysaccharide and protein were characterized using spectroscopic techniques. The prepared gels showed appreciable material properties in terms of water uptake and porosity. Hydrogels with different ratios of the polysaccharide and protein were evaluated for their biocompatibility. The biological evaluation of the hydrogels was performed with MC3T3E1 and C2C12 cell lines indicating their potential for wider tissue engineering applications.

Polymer-Protein Hybrid Network Involving Mucin: A Mineralized Biomimetic Template for Bone Tissue Engineering

Biomimetic matrices offer a great advantage to understand several biological processes including regeneration. The study involves the development of a hybrid biomimetic scaffold and the uniqueness lies in the use of mucin, as a constituent protein. Through this study, the role of the protein in bone regeneration is deciphered through its development as a 3D model. As a first step towards understanding the protein, the interactions of mucin and collagen are determined by in silico studies considering that collagen is the most abundant protein in the bone microenvironment. Both proteins are reported to be involved in bone biology though the exact role of mucin is a topic of investigation. The in silico studies of collagen-mucin suggest to have a proper affinity toward each other, forming a strong basis for 3D scaffold development. The developed 3D scaffold is a double network system comprising of mucin and collagen and vinyl end functionalized polyethylene glycol. In situ deposition of mineral crystals has been performed enzymatically. Biological evaluation of these mineral deposited scaffolds is done in terms of their bone regeneration potential and a comparison of the two systems with and without mineral deposition is presented.

Macroporous chitosan/methoxypoly(ethylene glycol) based cryosponges with unique morphology for tissue engineering applications

Three-dimensional porous scaffolds are widely employed in tissue engineering and regenerative medicine for their ability to carry bioactives and cells; and for their platform properties to allow for bridging-the-gap within an injured tissue. This study describes the effect of various methoxypolyethylene glycol (mPEG) derivatives (mPEG (-OCH₃ functionality), mPEG-aldehyde (mPEG-CHO) and mPEG-acetic acid (mPEG-COOH)) on the morphology and physical properties of chemically crosslinked, semi-interpenetrating polymer network (IPN), chitosan (CHT)/mPEG blend cryosponges. Physicochemical and molecular characterization revealed that the –CHO and –COOH functional groups in mPEG derivatives interacted with the –NH₂ functionality of the chitosan chain. The distinguishing feature of the cryosponges was their unique morphological features such as fringe thread-, pebble-, curved quartz crystal-, crystal flower-; and canyon-like structures. The morphological data was well corroborated by the image processing data and physisorption curves corresponding to Type II isotherm with open hysteresis loops. Functionalization of mPEG had no evident influence on the macro-mechanical properties of the cryosponges but increased the matrix strength as determined by the rheomechanical analyses. The cryosponges were able to deliver bioactives (dexamethasone and curcumin) over 10 days, showed varied matrix degradation profiles, and supported neuronal cells on the matrix surface. In addition, in silico simulations confirmed the compatibility and molecular stability of the CHT/mPEG blend compositions. In conclusion, the study confirmed that significant morphological variations may be induced by minimal functionalization and crosslinking of biomaterials.

Designing of Chitosan Derivatives Nanoparticles with Antiangiogenic Effect for Cancer Therapy

Angiogenesis is a physiological process involving the growth of new blood vessels, which provides oxygen and required nutrients for the development of various pathological conditions. In a tumor microenvironment, this process upregulates the growth and proliferation of tumor cells, thus any stage of angiogenesis can be a potential target for cancer therapies. In the present study, chitosan and his derivatives have been used to design novel polymer-based nanoparticles. The therapeutic potential of these newly designed nanoparticles has been evaluated. The antioxidant and MTT assays were performed to know the antioxidant properties and their biocompatibility. The in vivo antiangiogenic properties of the nanoparticles were evaluated by using a chick Chorioallantoic Membrane (CAM) model. The obtained results demonstrate that chitosan derivatives-based nanostructures strongly enhance the therapeutic effect compared to chitosan alone, which also correlates with antitumor activity, demonstrated by the in vitro MTT assay on human epithelial cervical Hep-2 tumor cells. This study opens up new direction for the use of the chitosan derivatives-based nanoparticles for designing of antiangiogenic nanostructured materials, for future cancer therapy.

A water-soluble, mucoadhesive quaternary ammonium chitosan-methyl-β-cyclodextrin conjugate forming inclusion complexes with dexamethasone

The ocular bioavailability of lipophilic drugs, such as dexamethasone, depends on both drug water solubility and mucoadhesion/permeation. Cyclodextrins and chitosan are frequently employed to either improve drug solubility or prolong drug contact onto mucosae, respectively. Although the covalent conjugation of cyclodextrin and chitosan brings to mucoadhesive drug complexes, their water solubility is restricted to acidic pHs. This paper describes a straightforward grafting of methyl-β-cyclodextrin (MCD) on quaternary ammonium chitosan (QA-Ch60), mediated by hexamethylene diisocyanate. The resulting product is a water-soluble chitosan derivative, having a 10-atom long spacer between the quaternized chitosan and the cyclodextrin. The derivative is capable of complexing the model drug dexamethasone and stable complexes were also observed for the lyophilized products. Furthermore, the conjugate preserves the mucoadhesive properties typical of quaternized chitosan and its safety as solubilizing excipient for ophthalmic applications was preliminary assessed by in vitro cytotoxicity evaluations. Taken as a whole, the observed features appear promising for future processing of the developed product into 3D solid forms, such as controlled drug delivery systems, films or drug eluting medical devices.

Ulvan-chitosan polyelectrolyte complexes as matrices for enzyme induced biomimetic mineralization

Polyelectrolyte complexes (PEC) of chitosan and ulvan were fabricated to study alkaline phosphatase (ALP) mediated formation of apatitic minerals. Scaffolds of the PEC were subjected to ALP and successful mineral formation was studied using SEM, Raman and XRD techniques. Investigation of the morphology via SEM shows globular structures of the deposited minerals, which promoted cell attachment, proliferation and extracellular matrix formation. The PEC and their successful calcium phosphate based mineralization offers a greener route of scaffold fabrication towards developing resorbable materials for tissue engineering.

Highly defined 3D printed chitosan scaffolds featuring improved cell growth

The augmented demand for medical devices devoted to tissue regeneration and possessing a controlled micro-architecture means there is a need for industrial scale-up in the production of hydrogels. A new 3D printing technique was applied to the automation of a freeze-gelation method for the preparation of chitosan scaffolds with controlled porosity. For this aim, a dedicated 3D printer was built in-house: a preliminary effort has been necessary to explore the printing parameter space to optimize the printing results in terms of geometry, tolerances and mechanical properties of the product. Analysed parameters included viscosity of the starting chitosan solution, which was measured with a Brookfield viscometer, and temperature of deposition, which was determined by filming the process with a cryocooled sensor thermal camera. Optimized parameters were applied to the production of scaffolds from solutions of chitosan alone or with the addition of raffinose as a viscosity modifier. Resulting hydrogels were characterized in terms of morphology and porosity. In vitro cell culture studies comparing 3D printed scaffolds with their homologous produced by solution casting evidenced an improvement in biocompatibility deriving from the production technique as well as from the solid state modification of chitosan stemming from the addition of the viscosity modifier.

Natural marine sponges for bone tissue engineering: The state of art and future perspectives

Marine life and its rich biodiversity provide a plentiful resource of potential new products for the society. Remarkably, marine organisms still remain a largely unexploited resource for biotechnology applications. Among them, marine sponges are sessile animals from the phylum Porifera dated at least from 580 million years ago. It is known that molecules from marine sponges present a huge therapeutic potential in a wide range of applications mainly due to its antitumor, antiviral, anti-inflammatory, and antibiotic effects. In this context, this article reviews all the information available in the literature about the potential of the use of marine sponges for bone tissue engineering applications. First, one of the properties that make sponges interesting as bone substitutes is their structural characteristics. Most species have an efficient interconnected porous architecture, which allows them to process a significant amount of water and facilitates the flow of fluids, mimicking an ideal bone scaffold. Second, sponges have an organic component, the spongin, which is analogous to vertebral collagen, the most widely used natural polymer for tissue regeneration. Last, osteogenic properties of marine sponges is also highlighted by their mineral content, such as biosilica and other compounds, that are able to support cell growth and to stimulate bone formation and mineralization. This review focuses on recent studies concerning these interesting properties, as well as on some challenges to be overcome in the bone tissue engineering field. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1717-1727, 2017.