Injectable chitosan-based scaffolds in regenerative medicine and their clinical translatability

Chitosan-based injectable hydrogel with multifunction for wound healing: A critical review

Different types of clinical wounds are difficult to treat while infected by bacteria. Wound repair involves multiple cellular and molecular interactions, which is a complicated process. However, wound repair often suffers from abnormal cellular functions or pathways that result in unavoidable side effects, so there is an urgent need for a material that can heal wounds quickly and with few side effects. Based on these needs, hydrogels with injectable properties have been confirmed to be able to undergo self-healing, which provides favorable conditions for wound healing. Notably, as a biopolymer with excellent easy-to-modify properties from a wide range of natural sources, chitosan can be used to prepare injectable hydrogel with multifunction for wound healing because of its outstanding flowability and injectability. Especially, chitosan-based hydrogels with marked biocompatibility, non-toxicity, and bio-adhesion properties are ideal for facilitating wound healing. In this review, the characteristics and healing mechanisms of different wounds are briefly summarized. In addition, the preparation and characterization of injectable chitosan hydrogels in recent years are classified. Additionally, the bioactive properties of this type of hydrogel in vitro and in vivo are demonstrated, and future trend in wound healing is prospected.

Macromolecule-based hydrogels nanoarchitectonics with mesenchymal stem cells for regenerative medicine: A review

The role of regenerative medicine in clinical therapies is becoming increasingly vital. Under specific conditions, mesenchymal stem cells (MSCs) are capable of differentiating into mesoblastema (i.e., adipocytes, chondrocytes, and osteocytes) and other embryonic lineages. Their application in regenerative medicine has attracted a great deal of interest among researchers. To maximize the potential applications of MSCs, materials science could provide natural extracellular matrices and provide an effective means to understand the various mechanisms of differentiation for the growth of MSCs. Pharmaceutical fields are represented among the research on biomaterials by macromolecule-based hydrogel nanoarchitectonics. Various biomaterials have been used to prepare hydrogels with their unique chemical and physical properties to provide a controlled microenvironment for the culture of MSCs, laying the groundwork for future practical applications in regenerative medicine. This article currently describes and summarizes the sources, characteristics, and clinical trials of MSCs. In addition, it describes the differentiation of MSCs in various macromolecule-based hydrogel nanoarchitectonics and highlights the preclinical studies of MSCs-loaded hydrogel materials in regenerative medicine conducted over the past few years. Finally, the challenges and prospects of MSC-loaded hydrogels are discussed, and the future development of macromolecule-based hydrogel nanoarchitectonics is outlined by comparing the current literature.

Novel Water-in-Oil Emulsions for Co-Loading Sialic Acid and Chitosan: Formulation, Characterization, and Stability Evaluation

This study was designed to co-load sialic acid (SA) and chitosan in a water-in-oil (W/O) emulsion and investigated its characterization and stability. Emulsions were prepared using two different oils (olive oil and maize oil) and polyglycerol polyricinoleate (PGPR) alone or in combination with lecithin (LE) as emulsifiers. The results revealed that the aqueous phase of 5% (w/v) SA and 2% (w/v) chitosan could form a stable complex and make the aqueous phase into a transparent colloidal state. Increasing the concentration of PGPR and LE presented different effects on emulsion formation between olive oil-base and maize oil-base. Two stable W/O emulsions that were olive oil-based with 1.5% (w/v) PGPR+ 0.5% (w/v) LE and maize oil-based with 2% (w/v) PGPR+ 0% (w/v) LE were obtained. Initial droplet size distribution curves of the two stable emulsions displayed unimodal distribution, and the rheological curves displayed the characteristics of shear thinning and low static shear viscosity. Moreover, the storage stability showed that there was no significant change in droplet size distribution and Sauter mean diameter of the emulsions at room temperature (25 °C) for 30 days. These results indicated that the W/O emulsions could effectively co-load and protect sialic acid and chitosan and thus could be a novel method for increasing the stability of these water-soluble bioactive compounds.

Rational formulation design of injectable thermosensitive chitosan-based hydrogels for cell encapsulation and delivery

This work reports a rational design of injectable thermosensitive chitosan systems for cell encapsulation and delivery. Using mixtures of two phosphate salts, beta-glycerophosphate and ammonium hydrogen phosphate, we demonstrate that the pH and the osmolarity can be adjusted separately by varying the molar ratios between the salts and the d-glucosamine monomers. We found the existence of a critical temperature above which gelation time decays following a power-law. This gelation kinetics can be finely tuned through the pH and salt-glucosamine ratios. Formulations having physiological pH and osmolarity were produced for chitosan concentrations ranging from 0.4 to 0.9 wt%. They remain liquid for more than 2 h at 20 °C and form a macroporous gel within 2 min at 37 °C. In vitro encapsulation of pre-osteoblastic cells and gingival fibroblasts showed homogeneous cell distribution and good cell viability up to 24 h. Such an approach provides a valuable platform to design thermosensitive cell-laden systems.

Conductive Materials for Healing Wounds: Their Incorporation in Electroactive Wound Dressings, Characterization, and Perspectives

The use of conductive materials to promote the activity of electrically responsive cells is an effective means of accelerating wound healing. This article focuses on recent advancements in conductive materials, with emphasis on overviewing their incorporation with non-conducting polymers to fabricate electroactive wound dressings. The characteristics of these electroactive dressings are deliberated, and the mechanisms on how they accelerate the wound healing process are discussed. Potential directions for the future development of electroactive wound dressings and their potential in monitoring the course of wound healing in vivo concomitantly are also proposed.

A Biomimetic Nano-Engineered Platform for Functional Tissue Engineering of Cartilage Superficial Zone

Articular cartilage has limited regeneration capacity because of its acellular and avascular nature. Although tissue engineering has been shown to be life-saving, reforming cartilage zones required by the appropriate tissue functions are challenging. Herein, the need is addressed by designing and producing a nano-engineered structure mimicking the superficial zone (SZ) of articular cartilage. The substrate is based on silk with good mechanical properties in conjunction with nano-topographical and biochemical cues. Nanopillar arrays are produced on the silk surface to regulate the stem cell morphology rendering them with a flattened ellipsoidal shape that is similar to that of chondrocytes in the SZ of natural cartilage. The cell interactions are enhanced by nitrogen ion implantation and the biomolecule, kartogenin (KGN), is loaded to promote chondrogenesis of the stem cells and furthermore, a thermosensitive chitosan hydrogel is formed on the nanopatterned silk to produce rheological properties similar to those of a synovial fluid. Based on the in vitro results and mechanical properties, it is a desirable implantable smart structure mimicking the cartilage SZ with the ability of continuous drug release for cartilage regeneration.

Applying hiPSCs and Biomaterials Towards an Understanding and Treatment of Traumatic Brain Injury

Traumatic brain injury (TBI) is the leading cause of disability and mortality in children and young adults and has a profound impact on the socio-economic wellbeing of patients and their families. Initially, brain damage is caused by mechanical stress-induced axonal injury and vascular dysfunction, which can include hemorrhage, blood-brain barrier disruption, and ischemia. Subsequent neuronal degeneration, chronic inflammation, demyelination, oxidative stress, and the spread of excitotoxicity can further aggravate disease pathology. Thus, TBI treatment requires prompt intervention to protect against neuronal and vascular degeneration. Rapid advances in the field of stem cells (SCs) have revolutionized the prospect of repairing brain function following TBI. However, more than that, SCs can contribute substantially to our knowledge of this multifaced pathology. Research, based on human induced pluripotent SCs (hiPSCs) can help decode the molecular pathways of degeneration and recovery of neuronal and glial function, which makes these cells valuable tools for drug screening. Additionally, experimental approaches that include hiPSC-derived engineered tissues (brain organoids and bio-printed constructs) and biomaterials represent a step forward for the field of regenerative medicine since they provide a more suitable microenvironment that enhances cell survival and grafting success. In this review, we highlight the important role of hiPSCs in better understanding the molecular pathways of TBI-related pathology and in developing novel therapeutic approaches, building on where we are at present. We summarize some of the most relevant findings for regenerative therapies using biomaterials and outline key challenges for TBI treatments that remain to be addressed.

Injectable in situ forming kartogenin-loaded chitosan hydrogel with tunable rheological properties for cartilage tissue engineering

Limited regeneration capacity of cartilage can be addressed by tissue engineering approaches including localized delivery of bioactive agents using biomaterials. Although chitosan hydrogels have been considered as appropriate candidates for these purposes, however, their poor mechanical properties limit their real applications. Here, we develop in situ forming chitosan hydrogels with enhanced shear modulus by chemical modification of chitosan using N-(β-maleimidopropyloxy) succinimide ester (BMPS). Moreover, we utilize β-Glycerophosphate (β-GP) in the hydrogels for achieving thermosensitivity. We investigate the effects of BMPS, β-GP and chitosan concentration on rheological and swelling properties of the hydrogels. Accordingly, we generate significant statistical models by response surface method to predict these properties. These models provide us beneficial tools to tune the hydrogel properties depending on the cartilage defect location and properties. Finally, we incorporate a recently discovered small biomolecule, kartogenin (KGN), for promoting chondrogenesis of stem cells into the optimized hydrogel. The hydrogel's shear modulus is 78 ± 5 kPa which covers a wide range of human articular cartilage shear modulus (50-250 kPa). It can be injected to the defects non-invasively at room temperature which gels at 37 °C within minutes. Additionally, it provides a sustained KGN release for ∼40 days that may eliminate the need of multiple injections. In vitro chondrogenic results confirm enhanced chondrogenic differentiation of human adipose mesenchymal stem cells (hAMSCs) treated with KGN-loaded hydrogel, compared to pure KGN. Based on the enhanced hydrogel shear modulus, injectability, gelation behavior, long-term drug release and in vitro results, this thermosensitive hydrogel looks promising for cartilage tissue engineering.

Advancements in Canadian Biomaterials Research in Neurotraumatic Diagnosis and Therapies

Development of biomaterials for the diagnosis and treatment of neurotraumatic ailments has been significantly advanced with our deepened knowledge of the pathophysiology of neurotrauma. Canadian research in the fields of biomaterial-based contrast agents, non-invasive axonal tracing, non-invasive scaffold imaging, scaffold patterning, 3D printed scaffolds, and drug delivery are conquering barriers to patient diagnosis and treatment for traumatic injuries to the nervous system. This review highlights some of the highly interdisciplinary Canadian research in biomaterials with a focus on neurotrauma applications.

3D gelatin-chitosan hybrid hydrogels combined with human platelet lysate highly support human mesenchymal stem cell proliferation and osteogenic differentiation

Bone marrow and adipose tissue human mesenchymal stem cells were seeded in highly performing 3D gelatin–chitosan hybrid hydrogels of varying chitosan content in the presence of human platelet lysate and evaluated for their proliferation and osteogenic differentiation. Both bone marrow and adipose tissue human mesenchymal stem cells in gelatin–chitosan hybrid hydrogel 1 (chitosan content 8.1%) or gelatin–chitosan hybrid hydrogel 2 (chitosan 14.9%) showed high levels of viability (80%–90%), and their proliferation and osteogenic differentiation was significantly higher with human platelet lysate compared to fetal bovine serum, particularly in gelatin–chitosan hybrid hydrogel 1. Mineralization was detected early, after 21 days of culture, when human platelet lysate was used in the presence of osteogenic stimuli. Proteomic characterization of human platelet lysate highlighted 59 proteins mainly involved in functions related to cell adhesion, cellular repairing mechanisms, and regulation of cell differentiation. In conclusion, the combination of our gelatin–chitosan hybrid hydrogels with hPL represents a promising strategy for bone regenerative medicine using human mesenchymal stem cells.

Injectable Biomaterials in Plastic and Reconstructive Surgery: A Review of the Current Status

BACKGROUND

Injectable biomaterials have attracted increasing attention for volume restoration and tissue regeneration. The main aim of this review is to discuss the current status of the injectable biomaterials for correction of tissue defects in plastic and reconstructive surgery.

METHODS

Requirements of injectable biomaterials, mechanism of in situ gelation, characteristics, and the combinational usage of adipose-derived stem cells (ADSCs) and growth factors were reviewed.

RESULTS

The ideal injectable biomaterials should be biocompatible, non-toxic, easy to use, and cost-effective. Additionally, it should possess adequate mechanical properties and stability. In situ gelation method includes physical, chemical, enzymatic and photo-initiated methods. Natural and synthetic biomaterials carry their pros and cons due to their inherent properties. The combined use of ADSCs and growth factors provides enhanced potential for adipose tissue regeneration.

CONCLUSIONS

The usage of injectable biomaterials has been increasing for the tissue restoration and regeneration. The future of incorporating ADSCs and growth factors into the injectable biomaterials is promising.

3D-printed chitosan-based scaffolds: An in vitro study of human skin cell growth and an in-vivo wound healing evaluation in experimental diabetes in rats

The fabrication of porous 3D printed chitosan (CH) scaffolds for skin tissue regeneration and their behavior in terms of biocompatibility, cytocompatibility and toxicity toward human fibroblasts (Nhdf) and keratinocytes (HaCaT), are presented and discussed. 3D cell cultures achieved after 20 and 35 days of incubation showed significant in vitro qualitative and quantitative cell growth as measured by neutral red staining and MTT assays and confirmed by scanning electron microphotographs. The best cell growth was obtained after 35 days on 3D scaffolds when the Nhdf and HaCaT cells, seeded together, filled the pores in the scaffolds. An early skin-like layer consisting of a mass of fibroblast and keratinocyte cells growing together was observed. The tests of 3D printed scaffolds in wound healing carried out on streptozotocin-induced diabetic rats demonstrate that 3D printed scaffolds improve the quality of the restored tissue with respect to both commercial patch and spontaneous healing.

Cephalopod-Derived Biopolymers for Ionic and Protonic Transistors

Cephalopods (e.g., squid, octopuses, and cuttlefish) have long fascinated scientists and the general public alike due to their complex behavioral characteristics and remarkable camouflage abilities. As such, these animals are explored as model systems in neuroscience and represent a well-known commercial resource. Herein, selected literature examples related to the electrical properties of cephalopod-derived biopolymers (eumelanins, chitosans, and reflectins) and to the use of these materials in voltage-gated devices (i.e., transistors) are highlighted. Moreover, some potential future directions and challenges in this area are described, with the aim of inspiring additional research effort on ionic and protonic transistors from cephalopod-derived biopolymers.

Hepatocyte Aggregate Formation on Chitin-Based Anisotropic Microstructures of Butterfly Wings

Scaffold nanotopography plays the most significant role in the mimicry of the in vivo microenvironment of the hepatocytes. Several attempts have been made to develop methods and substrates suited to growing hepatocytes into aggregates. Functional biomaterials, particularly biodegradable polymers, have been used in several studies aimed to develop improved scaffolds with ordered geometry and nanofibrous architecture for tissue engineering. However, there are still some limitation in their fabrication: it is not cost-efficient, is time-consuming, and exhibits some technological complications. The synthetic scaffolds are usually non-biodegradable and can be non-biocompatible compared to the naturally derived biomaterials. Here, we utilized a simple, cost-effective, and green method with two-step chemical treatment to get more selected hydrophilic butterfly wings from Morpho menelaus, Papilio ulysses telegonus, and Ornithoptera croesus lydius as a chitin-based natural scaffolds to growing hepatocyte aggregates. We established a three-dimensional (3D) in vitro model for culture of HepG2 cells and aggregate formation that maintained the hepatocytes function on these natural anisotropic microstructures. Cells cultured on these substrates show higher viability than those cultured on a two-dimensional (2D) culture plate. Methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay results revealed excellent viability of HepG2 cells on P. u. telegonus wings (fibrous area). The results also demonstrated appropriate cell activity, cell retention, and stable and functional expression in terms of albumin secretion and urea synthesis activity compared to the 2D monolayer culture of hepatocytes on the culture dish surface. With a slightly different degree, the other substrates also shown similar results. We anticipate that these natural anisotropic, biodegradable, and biocompatible substrates can maintain long-term hepatic culture as an in vitro 3D model for potential therapeutic applications and regenerative tissue applications. The model presented here provides a feasible alternative to the synthetic scaffolds and is expected to be more reliable for 3D organotypic liver culture models based on such scaffolds.

Skin Wound Healing: Refractory Wounds and Novel Solutions

This overview of the current state of skin wound healing includes in vitro and in vivo approaches along with some recent clinical trials. From an introduction to wound healing, to tissue engineering as applied to the skin, we cover the basis for the current wound care techniques as well as novel and promising approaches. Special emphasis is given to refractory wounds which include wounds in diabetic patients. Natural compounds have been ever present in wound healing, and so we devote a section to highlighting current attempts to understand their mechanisms and to use them in novel ways.

The bioconjugation mechanism of purine cross-linkers affects microstructure and cell response to ultra rapidly gelling purine–chitosan sponges

As a cell carrier, cross-linking is one of the most common approaches used to provide chitosan with greater structural integrity.

In vitro and in vivo acute response towards injectable thermosensitive chitosan/TEMPO-oxidized cellulose nanofiber hydrogel

TEMPO-oxidized cellulose nanofiber (TOCNF) is a natural material with many promising properties, including biocompatibility and degradability. In this study, we integrated TOCNF at different concentrations (0.2, 0.4, 0.6, 0.8% w/v) with chitosan (CS) and created a thermosensitive injectable hydrogel intended for biomedical applications. These hydrogels can undergo sol-gel transition at body temperature through interactions between chitosan and β-glycerophosphate. The addition of TOCNF resulted in faster gelation time and increased porosity. These hydrogels with TOCNF showed improved biocompatibility both in vitro and in vivo compared to CS hydrogel. Both MC3T3-E1 pre-osteoblast cells and L929 fibroblast cells showed biocompatibility towards CS/TOCNF 0.4. After 7days of implantation, initial inflammatory response to CS/TOCNF 0.4 was found. Such response was significantly subsided within 14days. Cell infiltration within the hydrogel was also prominent, showing anti-inflammatory or wound healing (M2) macrophage at 14days after implantation. These results showed that the addition of TOCNF could significantly improve the biocompatibility of CS hydrogel as a biomaterial for biomedical application.

Injectable hydrogel-based scaffolds for tissue engineering applications

Hydrogels are highly hydrated materials that may absorb from 10% to 20% up to hundreds of times their dry weight in water and are composed of three-dimensional hydrophilic polymeric networks that are similar to those in natural tissue. The structural integrity of hydrogels depends on cross-links formed between the polymer chains. Hydrogels have been extensively explored as injectable cell delivery systems, owing to their high tissue-like water content, ability to mimic extracellular matrix, homogeneously encapsulated cells, efficient mass transfer, amenability to chemical and physical modifications, and minimally invasive delivery. A variety of naturally and synthetically derived materials have been used to form injectable hydrogels for tissue engineering applications. The current review article focuses on these biomaterials, on the design parameters of injectable scaffolds, and on the

Irradiation Sterilized Gelatin-Water-Glycerol Ternary Gel as an Injectable Carrier for Bone Tissue Engineering

Injectable gelatin gels offer an attractive option for filling bone defects. The challenge is to fabricate gelatin gels with optimal gelation properties, which can be irradiation sterilized. Here, a gelatin-water-glycerol (GWG) gel is reported for use as a broad-spectrum injectable carrier. This ternary gel is high in glycerol and low in water, and remains stable after gamma irradiation at doses (25 kGy). As an injectable gel, it remains a viscous solution at gelatin concentrations ≤2.0%, at room temperature. Its storage modulus increases dramatically and eventually exceeds the loss modulus around 46-50 °C, indicating a transition from a liquid-like state to an elastic gel-like state. This ternary gel ranges significantly in terms of storage modulus (12-1700 Pa) while demonstrating a narrow pH range (5.58-5.66), depending on the gelatin concentration. Therefore, it can be loaded with a variety of materials. It is highly cytocompatible compared with saline in vivo and culture media in vitro. When loaded with demineralized bone matrix, the composites show favorable injectability, and excellent osteogenesis performance, after irradiation. These features can be attributed to high hydrophilicity and fast degradability. These findings justify that this ternary gel is promising as an irradiation-sterilized and universal injectable delivery system.

Injectable and microporous scaffold of densely-packed, growth factor-encapsulating chitosan microgels

In this work, an emulsion crosslinking method was developed to produce chitosan-genipin microgels which acted as an injectable and microporous scaffold. Chitosan was characterized with respect to pH by light scattering and aqueous titration. Microgels were characterized with swelling, light scattering, and rheometry of densely-packed microgel solutions. The results suggest that as chitosan becomes increasingly deprotonated above the pKa, repulsive forces diminish and intermolecular attractions cause pH-responsive chain aggregation; leading to microgel-microgel aggregation as well. The microgels with the most chitosan and least cross-linker showed the highest yield stress and a storage modulus of 16kPa when condensed as a microgel paste at pH 7.4. Two oppositely-charged growth factors could be encapsulated into the microgels and endothelial cells were able to proliferate into the 3D microgel scaffold. This work motivates further research on the applications of the chitosan microgel scaffold as an injectable and microporous scaffold in regenerative medicine.

Smart Polymeric Hydrogels for Cartilage Tissue Engineering: A Review on the Chemistry and Biological Functions

Stimuli responsive hydrogels (SRHs) are attractive bioscaffolds for tissue engineering. The structural similarity of SRHs to the extracellular matrix (ECM) of many tissues offers great advantages for a minimally invasive tissue repair. Among various potential applications of SRHs, cartilage regeneration has attracted significant attention. The repair of cartilage damage is challenging in orthopedics owing to its low repair capacity. Recent advances include development of injectable hydrogels to minimize invasive surgery with nanostructured features and rapid stimuli-responsive characteristics. Nanostructured SRHs with more structural similarity to natural ECM up-regulate cell-material interactions for faster tissue repair and more controlled stimuli-response to environmental changes. This review highlights most recent advances in the development of nanostructured or smart hydrogels for cartilage tissue engineering. Different types of stimuli-responsive hydrogels are introduced and their fabrication processes through physicochemical procedures are reported. The applications and characteristics of natural and synthetic polymers used in SRHs are also reviewed with an outline on clinical considerations and challenges.

Tough and Cell-Compatible Chitosan Physical Hydrogels for Mouse Bone Mesenchymal Stem Cells in Vitro

Most hydrogels involve synthetic polymers and organic cross-linkers that cannot simultaneously fulfill the mechanical and cell-compatibility requirements of biomedical applications. We prepared a new type of chitosan physical hydrogel with various degrees of deacetylation (DDs) via the heterogeneous deacetylation of nanoporous chitin hydrogels under mild conditions. The DD of the chitosan physical hydrogels ranged from 56 to 99%, and the hydrogels were transparent and mechanically strong because of the extra intra- and intermolecular hydrogen bonding interactions between the amino and hydroxyl groups on the nearby chitosan nanofibrils. The tensile strength and Young's modulus of the chitosan physical hydrogels were 3.6 and 7.9 MPa, respectively, for a DD of 56% and increased to 12.1 and 92.0 MPa for a DD of 99% in a swelling equilibrium state. In vitro studies demonstrated that mouse bone mesenchymal stem cells (mBMSCs) cultured on chitosan physical hydrogels had better adhesion and proliferation than those cultured on chitin hydrogels. In particular, the chitosan physical hydrogels promoted the differentiation of the mBMSCs into epidermal cells in vitro. These materials are promising candidates for applications such as stem cell research, cell therapy, and tissue engineering.

Small Players Ruling the Hard Game: siRNA in Bone Regeneration

Silencing gene expression through a sequence-specific manner can be achieved by small interfering RNAs (siRNAs). The discovery of this process has opened the doors to the development of siRNA therapeutics. Although several preclinical and clinical studies have shown great promise in the treatment of neurological disorders, cancers, dominant disorders, and viral infections with siRNA, siRNA therapy is still gaining ground in musculoskeletal tissue repair and bone regeneration. Here we present a comprehensive review of the literature to summarize different siRNA delivery strategies utilized to enhance bone regeneration. With advancement in understanding the targetable biological pathways involved in bone regeneration and also the rapid progress in siRNA technologies, application of siRNA for bone regeneration has great therapeutic potential. High rates of musculoskeletal injuries and diseases, and their inevitable consequences, impose a huge financial burden on individuals and healthcare systems worldwide.

Investigation of the Viability, Adhesion, and Migration of Human Fibroblasts in a Hyaluronic Acid/Gelatin Microgel-Reinforced Composite Hydrogel for Vocal Fold Tissue Regeneration

The potential use of a novel scaffold biomaterial consisting of cross-linked hyaluronic acid (HA)-gelatin (Ge) composite microgels is investigated for use in treating vocal fold injury and scarring. Cell adhesion integrins and kinematics of cell motion are investigated in 2D and 3D culture conditions, respectively. Human vocal fold fibroblast (hVFF) cells are seeded on HA-Ge microgels attached to a HA hydrogel thin film. The results show that hVFF cells establish effective adhesion to HA-Ge microgels through the ubiquitous expression of β1 integrin in the cell membrane. The microgels are then encapsulated in a 3D HA hydrogel for the study of cell migration. The cells within the HA-Ge microgel-reinforced composite hydrogel (MRCH) scaffold have an average motility speed of 0.24 ± 0.08 μm min(-1) . The recorded microscopic images reveal features that are presumably associated with lobopodial and lamellipodial cell migration modes within the MRCH scaffold. Average cell speed during lobopodial migration is greater than that during lamellipodial migration. The cells move faster in the MRCH than in the HA-Ge gel without microgels. These findings support the hypothesis that HA-Ge MRCH promotes cell adhesion and migration; thereby they constitute a promising biomaterial for vocal fold repair.

A combinatorial approach towards achieving an injectable, self-contained, phosphate-releasing scaffold for promoting biomineralization in critical size bone defects

An injectable, guanosine 5'-diphosphate (GDP)-crosslinked chitosan sponge was investigated as a drug delivery system (DDS) for accelerating biomineralization in critical size bone defects (CSBDs). Two approaches were examined both individually, and in combination, in order to achieve this goal. The first approach involved the encapsulation and release of Bone Morphogenetic Protein 7 (BMP-7), a powerful mineralization stimulant. Results confirmed that the rapid gelation of the chitosan sponge prompted high encapsulation of BMP-7 and provided a controlled release over a period of 30 days with no burst release. The second approach was aimed at encapsulating pyrophosphatase (PPtase) in the chitosan sponge to cleave pyrophosphate (PPi) - a mineralization inhibitor and a degradation by-product of the chitosan sponge - into phosphate ions (Pi). PPtase was successfully encapsulated in the chitosan sponge and was able to completely eliminate PPi from the media by cleaving them to Pi. Chitosan sponges releasing Pi into the media were shown to increase overall biomineralization fourfold as compared to controls, an amount equivalent to biomineralization caused by direct injection of 1μg of free BMP-7 to the cells. Even though the combined encapsulation of 1μg BMP-7 and PPtase in the sponges did not demonstrate an additional increase in biomineralization, encapsulation of low concentrations of BMP-7 can promote mesenchymal stem cell migration into the sponge after application in vivo. The findings suggest that the sponge-PPtase system likely allows excellent bone regeneration with lower concentrations of BMP-7, reducing risks and expense of the treatment.

STATEMENT OF SIGNIFICANCE

There are bone defects, known as critical size defects, which do not heal on their own and require a therapeutic intervention. The current commercially-available therapies use large quantities of growth factors, such as Bone Morphogenetic Proteins (BMPs), which makes them expensive and a source for a myriad of unwanted side effects. In this manuscript we demonstrate, for the first time, the use of an injectable chitosan-based sponge that contains no inorganic components, but can nonetheless act as a source of phosphate ions to improve bone mineralization. We also demonstrate that this sponge can entrap small concentrations of BMP-7 and provide controlled release over time. The ability to release phosphate ions and low concentrations of BMP-7 makes this therapeutic intervention clinically-relevant, affordable, and safe.

Preformed chitosan cryogel-biphasic calcium phosphate: a potential injectable biocomposite for pathologic fracture

The increasing interest in chitosan-based biomaterials stems from its desirable physicochemical properties. Although calcium phosphates have been mixed with chitosan to form injectable scaffolds, its application for bone tissue engineering has been limited and is still being explored to improve its clinical translatability. We report a biocomposite comprised of preformed chitosan cryogel with dispersed biphasic calcium phosphate that can flow under moderate pressure allowing passage through a small gauge needle, while maintaining sufficient integrity and strength during injection for gel recovery. The formed samples were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction analysis and protein adsorption measurements. Composite with 1% w/v biphasic calcium phosphate (CSG1) resulted in a homogeneous and rigid final structure. Injectable composite cryogel CSG1 (2.5 ± 0.2 N, 23G needle) exhibited good protein adsorption and biocompatibility. Results of subcutaneous implantation in rats reveal relatively high presence of polymorphonuclear cells but with no fibrous encapsulation with the composites, allowing further infiltration of cells within the sample implants. The biocomposite system presents a less-invasive delivery of bone filling material for stabilizing pathologic fractures.

Nutraceuticals in Lipid-Lowering Treatment

Lipid-lowering drugs may cause adverse effects and, although lipid targets may be achieved, a substantial residual cardiovascular (CV) risk remains. Treatment with agents mimicking proteins present in the body, such as incretin-based therapies, provided promising results. However, in order to improve lipids and CV risk, lifestyle measures remain important. Some researchers focused on nutraceuticals that may beneficially affect metabolic parameters and minimize CV risk. Chitosan, a dietary fiber, can regulate lipids with benefit on anthropometric parameters. The beneficial properties of dietary supplements (such as green tea extract, prebiotics, plant sterols, and stanols) on plasma lipids, lipoproteins, blood pressure, glucose, and insulin levels and their anti-inflammatory and anti-oxidant effects are documented. However, larger, prospective clinical trials are required to confirm such benefits. Such treatments may be recommended when lipid-lowering drugs are neither indicated nor tolerated as well as in order to achieve therapeutic targets and/or overcome residual CV risk.