Chitosan/Hyaluronan and Alginate-Nanohydroxyapatite Biphasic Scaffold as a Promising Matrix for Osteoarthritis Disorders

Purpose

Regenerative medicine offers new techniques for osteoarthritis (OA) disorders, especially while considering simultaneous chondral and subchondral regenerations.

Methods

Chitosan and hyaluronan were chemically bound as the chondral phase and the osteogenic layer was prepared with alginate and nano-hydroxyapatite (nHAP). These scaffolds were fixed by fibrin glue as a biphasic scaffold and then examined.

Results

Scanning electron microscopy (SEM) confirmed the porosity of 61.45±4.51 and 44.145±2.81 % for the subchondral and chondral layers, respectively. The composition analysis by energy dispersive X-ray (EDAX) indicated the various elements of both hydrogels. Also, their mechanical properties indicated that the highest modulus and resistance values corresponded to the biphasic hydrogel as 108.33±5.56 and 721.135±8.21 kPa, despite the same strain value as other groups. Their individual examinations demonstrated the proteoglycan synthesis of the chondral layer and also, the alkaline phosphatase (ALP) activity of the subchondral layer as 13.3±2.2 ng. After 21 days, the cells showed a mineralized surface and a polygonal phenotype, confirming their commitment to bone and cartilage tissues, respectively. Immunostaining of collagen I and II represented greater extracellular matrix (ECM) secretion in the biphasic composite group due to the paracrine effect of the two cell types on each other.

Conclusion

For the first time, the ability of this biphasic scaffold to regenerate both tissue types was evaluated and the results showed satisfactory cellular commitment to bone and cartilage tissues. Thus, this scaffold can be considered a new strategy for the preparation of implants for OA.

Nuclear compression regulates YAP spatiotemporal fluctuations in living cells

Yes-associated protein (YAP) is a key mechanotransduction protein in diverse physiological and pathological processes; however, a ubiquitous YAP activity regulatory mechanism in living cells has remained elusive. Here, we show that YAP nuclear translocation is highly dynamic during cell movement and is driven by nuclear compression arising from cell contractile work. We resolve the mechanistic role of cytoskeletal contractility in nuclear compression by manipulation of nuclear mechanics. Disrupting the linker of nucleoskeleton and cytoskeleton complex reduces nuclear compression for a given contractility and correspondingly decreases YAP localization. Conversely, decreasing nuclear stiffness via silencing of lamin A/C increases nuclear compression and YAP nuclear localization. Finally, using osmotic pressure, we demonstrated that nuclear compression even without active myosin or filamentous actin regulates YAP localization. The relationship between nuclear compression and YAP localization captures a universal mechanism for YAP regulation with broad implications in health and biology.

Development of a High-Strength and Adhesive Polyacrylamide Gel for Well Plugging

Addition of melamine formaldehyde (MF) as a crosslinker containing hydroxymethyl to partially hydrolyzed poly(acrylamide) (HPAM) generated covalently crosslinked in situ gels through chemically nucleophilic attack by hydroxymethyl groups to amide in an HPAM backbone, which was demonstrated by FTIR spectrum analysis and rheological studies. NH4Cl could act as a catalyst to reduce the gelation time from 7 days in dilute water to 8 h in the presence of 0.8 wt % NH4Cl. Compared to high-temperature HPAM/phenol/formaldehyde and HPAM/Cr3+ gel systems, this gel has better adhesion and higher strength over a broad range of temperature from 60 to 100 °C under reservoir conditions with a denser and hook-like three-dimensional microstructure. Pressure-bearing capacity experiments demonstrated that the gel could efficiently plug high pressure from underneath to seal the wellbore, attributing to its high strength and good adhesion. This study could aid petroleum engineers in applying soft materials on controlling the pressure via polymer gels.

Synthesis and characterization of electroconductive hydrogels based on oxidized alginate and polypyrrole-grafted gelatin as tissue scaffolds

Electroconductive biocompatible hydrogels with tunable properties have extensively been taken into account in tissue engineering applications due to their potential to provide suitable microenvironmental responses for the cells. In the present study, novel electroconductive hydrogels are designed and synthesized by reacting oxidized alginate with polypyrrole-grafted gelatin copolymer (PPy-g-gelatin) via formation of a Schiff-base linkage. The influence of the composition and the concentration of the components on the compressive modulus and functional performance of the hydrogels is investigated. The conductivity of the hydrogels measured by a two-probe method increased by increasing the level of polypyrrole-grafted gelatin, and a conductivity of 0.7753 S m^-1 was exhibited by the hydrogel composed of 8% w/v polypyrrole-grafted gelatin (oxidized alginate:gelatin:polypyrrole-grafted gelatin; 30 : 35 : 35% v/v). The hydrogel compressive modulus was shown to be enhanced by increasing the total concentration of hydrogel. The characteristic features of the prepared hydrogels, including swelling ratio, volume fraction, cross-link density, and mesh size, are also studied and analyzed. Besides, the conductive hydrogels have a smaller mesh size and higher cross-link density than the non-conductive hydrogels. However, the hydrogels with high cross-link density, small mesh size, and large pore size presented higher electroconductivity as a result of easier movement of the ions throughout the hydrogel. These conductive hydrogels exhibited electrical conductivity and biodegradability with cell viability, implying potential as scaffolds for tissue engineering.

Injectable hydrogels: a new paradigm for osteochondral tissue engineering

Osteochondral tissue engineering has become a promising strategy for repairing focal chondral lesions and early osteoarthritis (OA), which account for progressive joint pain and disability in millions of people worldwide. Towards improving osteochondral tissue repair, injectable hydrogels have emerged as promising matrices due to their wider range of properties such as their high water content and porous framework, similarity to the natural extracellular matrix (ECM), ability to encapsulate cells within the matrix and ability to provide biological cues for cellular differentiation. Further, their properties such as those that facilitate minimally invasive deployment or delivery, and their ability to repair geometrically complex irregular defects have been critical for their success. In this review, we provide an overview of innovative approaches to engineer injectable hydrogels towards improved osteochondral tissue repair. Herein, we focus on understanding the biology of osteochondral tissue and osteoarthritis along with the need for injectable hydrogels in osteochondral tissue engineering. Furthermore, we discuss in detail different biomaterials (natural and synthetic) and various advanced fabrication methods being employed for the development of injectable hydrogels in osteochondral repair. In addition, in vitro and in vivo applications of developed injectable hydrogels for osteochondral tissue engineering are also reviewed. Finally, conclusions and future perspectives of using injectable hydrogels in osteochondral tissue engineering are provided.

Incorporation of Nanoalumina Improves Mechanical Properties and Osteogenesis of Hydroxyapatite Bioceramics

A handful of work focused on improving the intrinsic low mechanical properties of hydroxyapatite (HA) by various reinforcing agents. However, the big challenge regarding improving mechanical properties is maintaining bioactivity. To address this issue, we report fabrication of apatite-based composites by incorporation of alumina nanoparticles (n-Al₂O₃). Although numerous studies have used micron or submicron alumina for reinforcing hydroxyapatite, only few reports are available about the use of n-Al₂O₃. In this study, spark plasma sintering (SPS) method was utilized to develop HA-nAl₂O₃ dense bodies. Compared to the conventional sintering, decomposition of HA and formation of calcium aluminates phases are restricted using SPS. Moreover, n-Al₂O₃ acts as a bioactive agent while its conventional form is an inert bioceramics. The addition of n-Al₂O₃ resulted in 40% improvement in hardness along with a 110% increase in fracture toughness, while attaining nearly full dense bodies. The in vitro characterization of nanocomposite demonstrated improved bone-specific cell function markers as evidenced by cell attachment and proliferation, alkaline phosphatase activity, calcium and collagen detection and nitric oxide production. Specifically, gene expression analysis demonstrated that introduction of n-Al₂O₃ in HA matrix resulted in accelerated osteogenic differentiation of osteoblast and mesenchymal stem cells, as expression of Runx-2 and OSP showed 2.5 and 19.6 fold increase after 2 weeks (p < 0.05). Moreover, protein adsorption analysis showed enhanced adsorption of plasma proteins to HA-nAl₂O₃ sample compared to HA. These findings suggest that HA-nAl₂O₃ could be a prospective candidate for orthopedic applications due to its improved mechanical and osteogenic properties.

Nanoreinforced Hydrogels for Tissue Engineering: Biomaterials that are Compatible with Load-Bearing and Electroactive Tissues

Given their highly porous nature and excellent water retention, hydrogel-based biomaterials can mimic critical properties of the native cellular environment. However, their potential to emulate the electromechanical milieu of native tissues or conform well with the curved topology of human organs needs to be further explored to address a broad range of physiological demands of the body. In this regard, the incorporation of nanomaterials within hydrogels has shown great promise, as a simple one-step approach, to generate multifunctional scaffolds with previously unattainable biological, mechanical, and electrical properties. Here, recent advances in the fabrication and application of nanocomposite hydrogels in tissue engineering applications are described, with specific attention toward skeletal and electroactive tissues, such as cardiac, nerve, bone, cartilage, and skeletal muscle. Additionally, some potential uses of nanoreinforced hydrogels within the emerging disciplines of cyborganics, bionics, and soft biorobotics are highlighted.

Biomimetic strategies for engineering composite tissues

The formation of multiple tissue types and their integration into composite tissue units presents a frontier challenge in regenerative engineering. Tissue-tissue synchrony is crucial in providing structural support for internal organs and enabling daily activities. This review highlights the state-of-the-art in composite tissue scaffold design, and explores how biomimicry can be strategically applied to avoid over-engineering the scaffold. Given the complexity of biological tissues, determining the most relevant parameters for recapitulating native structure-function relationships through strategic biomimicry will reduce the burden for clinical translation. It is anticipated that these exciting efforts in composite tissue engineering will enable integrative and functional repair of common soft tissue injuries and lay the foundation for total joint or limb regeneration.

Hybrid cross-linked hydrogels based on fibrous protein/block copolymers and layered silicate nanoparticles: tunable thermosensitivity, biodegradability and mechanical durability

Schematic representation of LAPONITE® reinforced pluronic/chitosan/keratin nanocomposite hydrogel crosslinked with Genipin.

Collagen/Beta-Tricalcium Phosphate Based Synthetic Bone Grafts via Dehydrothermal Processing

Millions of patients worldwide remain inadequately treated for bone defects related to factors such as disease or trauma. The drawbacks of metallic implant and autograft/allograft use have steered therapeutic approaches towards tissue engineering solutions involving tissue regeneration scaffolds. This study proposes a composite scaffold with properties tailored to address the macro- and microenvironmental conditions deemed necessary for successful regeneration of bone in defect areas. The biodegradable scaffold composed of porous beta-tricalcium phosphate particles and collagen type I fibers is prepared from a mixture of collagen type-I and β-tricalcium phosphate (β-TCP) particles via lyophilization, followed by dehydrothermal (DHT) processing. The effects of both sterilization via gamma radiation and the use of DHT processing to achieve cross-linking were investigated. The impact of the chosen fabrication methods on scaffold microstructure and β-TCP particle-collagen fiber combinations were analyzed using X-ray diffractometry (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and microcomputerized tomography (µ-CT). Electron spinning resonance (ESR) analysis was used to investigate free radicals formation following sterilization. Results revealed that the highly porous (65% porosity at an average of 100 µm pore size), mechanically adequate, and biocompatible scaffolds can be utilized for bone defect repairs.

Osteoblast compatibility of minerals substituted hydroxyapatite reinforced poly(sorbitol sebacate adipate) nanocomposites for bone tissue application

The main focus of this investigation is to explore novel minerals (M) substituted hydroxyapatite (M-HAP) as reinforcing agents to strengthen poly(sorbitol sebacate adipate) (PSSA), a biodegradable polymer for soft and hard tissue applications.