Polymeric 3D scaffolds for tissue regeneration: Evaluation of biopolymer nanocomposite reinforced with cellulose nanofibrils

Nanostructured polymer composites for bone and tissue regeneration

Nanostructured polymer composites have gained significant attention in recent years for their remarkable potential in bone and tissue regeneration. Moreover, with the integration of 3D printing technology, these composites hold promise for use in personalized medicine, where patient-specific scaffolds can be tailored to enhance therapeutic outcomes. Therefore, this review article aims to provide a comprehensive overview of the latest advancements in the development and application of nanostructured polymeric composites within the field of tissue engineering and bone regeneration. Here, the potential of biopolymers, natural polymers, and 3D-printed polymers to craft biocompatible, non-toxic, and mechanically robust composites is discussed in brief. Further, the fabrication techniques for 3D scaffolds and various forms of nanocomposites, including nanoparticles, nanocapsules, nanofibers, nanogels, and micelles for bone and tissue regeneration, are listed. Also, particular emphasis is placed on the role of nano-scaffolds and in situ hydrogels in bone and tissue regeneration. Overall, this review provides a concise and authoritative summary of the current state-of-the-art in nanostructured polymer composites for regenerative medicine, highlighting future directions and potential clinical applications.

Recent perspective of synthesis and modification strategies of cellulose nanocrystals and cellulose nanofibrils and their beneficial impact in scaffold-based tissue engineering: A review

Outstanding properties of nanocellulose provide opportunities for novel applications in various fields, particularly tissue engineering. Despite of numerous useful characteristics of nanocellulose, its production methods suffer from the lack of control of morphology, high cost, and the use of organic solvents. On the other hand, hydrophilicity of nanocellulose is a significant challenge for its dispersion as a reinforcement in hydrophobic polymers matrix. Therefore, sustainable production methods and well-tuning interfacial characteristics of nanocellulose have been identified as critical steps in their development. This review article discusses the numerous preparation methods and surface modification strategies of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) to help nanocellulose users obtain the appropriate material for their desired application. We also cover various polymer/nanocellulose scaffolds that are reported in the literature and investigate the effect of CNC and CNF on their mechanical, thermal and biological properties. Moreover, we provide several scientific figures and tables for a better understanding of the explored topics. Finally, we evaluate the opportunities and challenges of nanocellulose industrialization in the field of tissue engineering. Overall, this review guides researchers towards a deeper understanding of nanocellulose production processes, changing their properties using surface modification methods, and subsequently their performance in scaffold-based tissue engineering.

Leveraging the Physicochemical Attributes of Biomimetic Hydrogel Nanocomposites in Stem Cell Differentiation

The field of tissue engineering has witnessed significant advancements with the advent of hydrogel nanocomposites (HNC), emerging as a highly promising platform for regenerative medicine. HNCs provide a versatile platform that significantly enhances the differentiation of stem cells into specific cell lineages, making them highly suitable for tissue engineering applications. By incorporating nanoparticles, the mechanical properties of hydrogels, such as elasticity, porosity, and stiffness, are improved, addressing common challenges such as short-term stability, cytotoxicity, and scalability. These nanocomposites also exhibit enhanced biocompatibility and bioavailability, which are crucial to their effectiveness in clinical applications. Furthermore, HNCs are responsive to various triggers, allowing for precise control over their chemical properties, which is beneficial in creating 3D microenvironments, promoting wound healing, and enabling controlled drug delivery systems. This review provides a comprehensive overview of the production methods of HNCs and the factors influencing their physicochemical and biological properties, particularly in relation to stem cell differentiation and tissue repair. Additionally, it discusses the challenges in developing HNCs and highlights their potential to transform the field of regenerative medicine through improved mechanotransduction and controlled release systems.

Carbon quantum dot-nanocomposite hydrogel as Denovo Nexus in rapid chondrogenesis

The incapability of cartilage to naturally regenerate and repair chronic muscular injuries urges the development of competent bionic rostrums. There is a need to explore faster strategies for chondrogenic engineering using mesenchymal stem cells (MSCs). Along these lines, rapid chondrocyte differentiation would benefit the transplantation demand affecting osteoarthritis (OA) and rheumatoid arthritis (RA) patients. In this report, a de novo nanocomposite was constructed by integrating biogenic carbon quantum dot (CQD) filler into synthetic hydrogel prepared from dimethylaminoethyl methacrylate (DMAEMA) and acrylic acid (AAc). The dominant structural integrity of synthetic hydrogel along with the chondrogenic differentiation potential of garlic peel derived CQDs led to faster chondrogenesis within 14 days. By means of extensive chemical and morphological characterization techniques, we illustrate that the hydrogel nanocomposite possesses lucrative features to influence rapid chondrogenesis. These results were further corroborated by bright field imaging, Alcian blue staining and Masson trichome staining. Thus, this stratagem of chondrogenic engineering conceptualizes to be a paragon in clinical wound care for the rapid manufacturing of chondrocytes.

Exploring nanocellulose frontiers: A comprehensive review of its extraction, properties, and pioneering applications in the automotive and biomedical industries

Material is an inseparable entity for humans to serve different purposes. However, synthetic polymers represent a major category of anthropogenic pollutants with detrimental impacts on natural ecosystems. This escalating environmental issue is characterized by the accumulation of non-biodegradable plastic materials, which pose serious threats to the health of our planet's ecosystem. Cellulose is becoming a focal point for many researchers due to its high availability. It has been used to serve various purposes. Recent scientific advancements have unveiled innovative prospects for the utilization of nanocellulose within the area of advanced science. This comprehensive review investigates deeply into the field of nanocellulose, explaining the methodologies employed in separating nanocellulose from cellulose. It also explains upon two intricately examined applications that emphasize the pivotal role of nanocellulose in nanocomposites. The initial instance pertains to the automotive sector, encompassing cutting-edge applications in electric vehicle (EV) batteries, while the second exemplifies the use of nanocellulose in the field of biomedical applications like otorhinolaryngology, ophthalmology, and wound dressing. This review aims to provide comprehensive information starting from the definitions, identifying the sources of the nanocellulose and its extraction, and ending with the recent applications in the emerging field such as energy storage and biomedical applications.

Tunable, thiol-ene, interpenetrating network hydrogels of norbornene-modified carboxymethyl cellulose and cellulose nanofibrils

Carboxymethyl cellulose modified with norbornene groups (NorCMC) and cellulose nanofibrils (CNFs) produced through mechanical refining without chemical pretreatment formed interpenetrating network hydrogels through a UV-light initiated thiol-ene reaction. The molar ratio of thiols in crosslinkers to norbornene groups off the NorCMC (T:N), total polymer weight percent in the hydrogel, and weight percent of CNFs of the total polymer content of the hydrogels were varied to control hydrogel properties. This method enabled orders of magnitude changes to behavior. Swelling in aqueous environments could be significant (>150 %) without CNFs to minimal (<15 %) with the use of 50 % CNFs. NorCMC and CNF networks interacted synergistically to create hydrogels with compression modulus values spanning 1 to 150 kPa - the values of most biological tissues. T:N and total polymer weight percent could be varied to create hydrogels with different CNF content, but the same compression modulus, targeting 10 and 100 kPa hydrogels and providing a system that can independently vary fibrillar content and bulk modulus. Analysis of the effective crosslinks, thiol-ene network mesh size, and burst release of the polymer indicated synergistic interactions of the NorCMC thiol-ene and CNFs networks. These interactions enhanced modulus and degradation control of the network under physiological conditions.

Application of Nanocellulose-Based Aerogels in Bone Tissue Engineering: Current Trends and Outlooks

The complex or compromised bone defects caused by osteomyelitis, malignant tumors, metastatic tumors, skeletal abnormalities, and systemic diseases are difficult to be self-repaired, leading to a non-union fracture. With the increasing demands of bone transplantation, more and more attention has been paid to artificial bone substitutes. As biopolymer-based aerogel materials, nanocellulose aerogels have been widely utilized in bone tissue engineering. More importantly, nanocellulose aerogels not only mimic the structure of the extracellular matrix but could also deliver drugs and bioactive molecules to promote tissue healing and growth. Here, we reviewed the most recent literature about nanocellulose-based aerogels, summarized the preparation, modification, composite fabrication, and applications of nanocellulose-based aerogels in bone tissue engineering, as well as giving special focus to the current limitations and future opportunities of nanocellulose aerogels for bone tissue engineering.

Nature-Inspired Heat and Moisture Exchanger Filters Composed of Gelatin and Chitosan for the Design of Eco-Sustainable "Artificial Noses"

For long-term mechanical ventilation, during anesthesia or intensive care, it is crucial to preserve a minimum level of humidity to avoid damage to the respiratory epithelium. Heat and moisture exchange filters (HME), also called "artificial noses," are passive systems that contribute to delivering inspired gases at about the same conditions of healthy respiration, i.e., 32 °C and relative humidity higher than 90%. Current HME devices suffer from limitations linked either to performance and filtration efficiency to their inadequate antibacterial efficiency, sterilization methods, and durability. Furthermore, in times of global warming and diminishing petroleum oil reserves, replacing the employing of synthetic materials with biomass biodegradable raw materials has considerable economic and environmental value. In the present study, a generation of eco-sustainable, bioinspired, and biodegradable HME devices are designed and developed through a green-chemistry process based on raw materials deriving from food waste and taking inspiration from the functioning, structure, and chemistry of our respiratory system. In particular, different blends are obtained by mixing aqueous solutions of gelatin and chitosan in various polymer ratios and concentrations and then by cross-linking them with different low amounts of genipin, a natural chemical cross-linker. Finally, the blends, post-gelation, are freeze-dried to obtain three-dimensional (3D) highly porous aerogels reproducing both the highly exposed surface area of the upper respiratory ways and the chemical composition of the mucus secretion covering the nasal mucosae. Results are comparable with accepted standards for HME devices and suitable bacteriostatic potential, thus validating these bioinspired materials as promising candidates to be used as an eco-sustainable generation of HME devices.

The practical process of manufacturing poly(methyl methacrylate)-based scaffolds having high porosity and high strength

Poly(methyl methacrylate) (PMMA)-based scaffolds have been produced using the granule casting method with grain sizes M80-100 and M100-140. The novelty of this study was the application of the cold-cutting method (CCm) to reduce the PMMA granule size. PMMA granule shape, granule size (mesh), and sintering temperature were the primary variables in manufacturing PMMA scaffolds. CCm was applied to reduce the granule size of commercial PMMA, which was originally solid cylindrical, by lowering the temperature to 3.5 °C, 0 °C, and-8.3 °C. PMMA granules that had been reduced were sieved with mesh sizes M80-100 and M100-140. Green bodies were made by the granule casting method using an aluminum mold measuring 8 × 8 × 8 mm³. The sintering process was carried out at temperatures varying from 115 °C to 140 °C, a heating rate of 5 °C/min, and a holding time of 2 h, the cooling process was carried out in a furnace. The characterization of the PMMA-based scaffolds' properties was carried out by observing the microstructure with SEM, analyzing the distribution of pore sizes with ImageJ software, and testing the porosity, the phase, with XRD, and the compressive strength. The best results from the overall analysis were the M80-100 PMMA scaffold treated at a sintering temperature of 130 °C with compressive strength, porosity, and pore size distribution values of 8.2 MPa, 62.0%, and 121-399 μm, respectively, and the M100-140 one treated at a sintering temperature of 135 °C with compressive strength, porosity, and pore size distribution values of 12.1 MPa, 61.2%, and 140-366 μm, respectively. There were interconnected pores in the PMMA scaffolds, as evidenced by the SEM images. There was no PMMA phase change between before and after the sintering process.

High-resolution 3D printing of xanthan gum/nanocellulose bio-inks

The current study provides a comprehensive rheology study and a survey on direct ink writing of xanthan gum/cellulose nanocrystal (XG/CNC) bio-inks for developing 3D geometries that mimic soft tissue engineering scaffolds' physical and mechanical properties. The presence of CNC was found to be a critical prerequisite for the printability of XG bio-inks; accordingly, the hybrid XG/CNC bio-inks revealed the excellent viscoelastic properties that enabled precise control of hydrogel shaping and printing of lattice structures composed of up to eleven layers with high fidelity and fair resolution without any deformation after printing. The lyophilized 3D scaffolds presented a porous structure with open and interconnected pores and a porosity higher than 70%, vital features for tissue engineering scaffolds. Moreover, they showed a relatively high swelling of approximately 11 g/g, facilitating oxygen and nutrient exchange. Furthermore, the elastic and compressive moduli of the scaffolds that enhanced significantly upon increasing CNC content were in the range of a few kPa, similar to soft tissues. Finally, no significant cell cytotoxicity was observed against human liver cancer cells (HepG2), highlighting the potential of these developed 3D printed scaffolds for soft tissue engineering applications.

Additive-Free Gelatine-Based Devices for Chondral Tissue Regeneration: Shaping Process Comparison among Mould Casting and Three-Dimensional Printing

Gelatine is a well-known and extensively studied biopolymer, widely used in recent decades to create biomaterials in many different ways, exploiting its molecular resemblance with collagen, the main constituent of the extra-cellular matrix, from which it is derived. Many have employed this biopolymer in tissue engineering and chemically modified (e.g., gelatin methacryloyl) or blended it with other polymers (e.g., alginate) to modulate or increase its performances and printability. Nevertheless, little is reported about its use as a stand-alone material. Moreover, despite the fact that multiple works have been reported on the realization of mould-casted and three-dimensional printed scaffolds in tissue engineering, a clear comparison among these two shaping processes, towards a comparable workflow starting from the same material, has never been published. Herein, we report the use of gelatine as stand-alone material, not modified, blended, or admixed to be processed or crosslinked, for the realization of suitable scaffolds for tissue engineering, towards the two previously mentioned shaping processes. To make the comparison reliable, the same pre-process (e.g., the gelatin solution preparation) and post-process (e.g., freeze-drying and crosslinking) steps were applied. In this study, gelatine solution was firstly rheologically characterized to find a formulation suitable for being processed with both the shaping processes selected. The realized scaffolds were then morphologically, phisico-chemically, mechanically, and biologically characterized to determine and compare their performances. Despite the fact that the same starting material was employed, as well as the same pre- and post-process steps, the two groups resulted, for most aspects, in diametrically opposed characteristics. The mould-casted scaffolds that resulted were characterized by small, little-interconnected, and random porosity, high resistance to compression and slow cell colonization, while the three-dimensional printed scaffolds displayed big, well-interconnected, and geometrically defined porosity, high elasticity and recover ability after compression, as well as fast and deep cell colonization.

Nanoengineered biomimetic hydrogels: A major advancement to fabricate 3D-printed constructs for regenerative medicine

Nanostructured compounds already validated as performant reinforcements for biomedical applications together with different fabrication strategies have been often used to channel the biophysical and biochemical features of hydrogel networks. Ergo, a wide array of nanostructured compounds has been employed as additive materials integrated with hydrophilic networks based on naturally-derived polymers to produce promising scaffolding materials for specific fields of regenerative medicine. To date, nanoengineered hydrogels are extensively explored in (bio)printing formulations, representing the most advanced designs of hydrogel (bio)inks able to fabricate structures with improved mechanical properties and high print fidelity along with a cell-interactive environment. The development of printing inks comprising organic-inorganic hybrid nanocomposites is in full ascent as the impact of a small amount of nanoscale additive does not translate only in improved physicochemical and biomechanical properties of bioink. The biopolymeric nanocomposites may even exhibit additional particular properties engendered by nano-scale reinforcement such as electrical conductivity, magnetic responsiveness, antibacterial or antioxidation properties. The present review focus on hydrogels nanoengineered for 3D printing of biomimetic constructs, with particular emphasis on the impact of the spatial distribution of reinforcing agents (0D, 1D, 2D). Here, a systematic analysis of the naturally-derived nanostructured inks is presented highlighting the relationship between relevant length scales and size effects that influence the final properties of the hydrogels designed for regenerative medicine. This article is protected by copyright. All rights reserved.

Magnetic and radio-labeled bio-hybrid scaffolds to promote and track in vivo the progress of bone regeneration

This work describes the preparation, characterization and functionalization with magnetic nanoparticles of a bone tissue-mimetic scaffold composed of collagen and hydroxyapatite obtained through a biomineralization process. Bone remodeling takes place over several weeks and the possibility to follow it in vivo in a quick and reliable way is still an outstanding issue. Therefore, this work aims to produce an implantable material that can be followed in vivo during bone regeneration by using the existing non-invasive imaging techniques (MRI). To this aim, suitably designed biocompatible SPIONs were linked to the hybrid scaffold using two different strategies, one involving naked SPIONs (nMNPs) and the other using coated and activated SPIONs (MNPs) exposing carboxylic acid functions allowing a covalent attachment between MNPs and collagen molecules. Physico-chemical characterization was carried out to investigate the morphology, crystallinity and stability of the functionalized materials followed by MRI analyses and evaluation of a radiotracer uptake ([^99mTc]Tc-MDP). Cell proliferation assays in vitro were carried out to check the cytotoxicity and demonstrated no side effects due to the SPIONs. The achieved results demonstrated that the naked and coated SPIONs are more homogeneously distributed in the scaffold when incorporated during the synthesis process. This work demonstrated a suitable approach to develop a biomaterial for bone regeneration that allows the monitoring of the healing progress even for long-term follow-up studies.

Milestones and current achievements in development of multifunctional bioscaffolds for medical application

Tissue engineering (TE) is a rapidly growing interdisciplinary field, which aims to restore or improve lost tissue function. Despite that TE was introduced more than 20 years ago, innovative and more sophisticated trends and technologies point to new challenges and development. Current challenges involve the demand for multifunctional bioscaffolds which can stimulate tissue regrowth by biochemical curves, biomimetic patterns, active agents and proper cell types. For those purposes especially promising are carefully chosen primary cells or stem cells due to its high proliferative and differentiation potential. This review summarized a variety of recently reported advanced bioscaffolds which present new functions by combining polymers, nanomaterials, bioactive agents and cells depending on its desired application. In particular necessity of study biomaterial-cell interactions with in vitro cell culture models, and studies using animals with in vivo systems were discuss to permit the analysis of full material biocompatibility. Although these bioscaffolds have shown a significant therapeutic effect in nervous, cardiovascular and muscle, tissue engineering, there are still many remaining unsolved challenges for scaffolds improvement.

Medicated Hydroxyapatite/Collagen Hybrid Scaffolds for Bone Regeneration and Local Antimicrobial Therapy to Prevent Bone Infections

Microbial infections occurring during bone surgical treatment, the cause of osteomyelitis and implant failures, are still an open challenge in orthopedics. Conventional therapies are often ineffective and associated with serious side effects due to the amount of drugs administered by systemic routes. In this study, a medicated osteoinductive and bioresorbable bone graft was designed and investigated for its ability to control antibiotic drug release in situ. This represents an ideal solution for the eradication or prevention of infection, while simultaneously repairing bone defects. Vancomycin hydrochloride and gentamicin sulfate, here considered for testing, were loaded into a previously developed and largely investigated hybrid bone-mimetic scaffold made of collagen fibers biomineralized with magnesium doped-hydroxyapatite (MgHA/Coll), which in the last ten years has widely demonstrated its effective potential in bone tissue regeneration. Here, we have explored whether it can be used as a controlled local delivery system for antibiotic drugs. An easy loading method was selected in order to be reproducible, quickly, in the operating room. The maintenance of the antibacterial efficiency of the released drugs and the biosafety of medicated scaffolds were assessed with microbiological and in vitro tests, which demonstrated that the MgHA/Coll scaffolds were safe and effective as a local delivery system for an extended duration therapy—promising results for the prevention of bone defect-related infections in orthopedic surgeries.

AK, Olaiya NG, Iqbal MO, Jummaat F, A.K. AS, Adnan AS. Insights into the Role of Biopolymer Aerogel Scaffolds in Tissue Engineering and Regenerative Medicine

The global transplantation market size was valued at USD 8.4 billion in 2020 and is expected to grow at a compound annual growth rate of 11.5% over the forecast period. The increasing demand for tissue transplantation has inspired researchers to find alternative approaches for making artificial tissues and organs function. The unique physicochemical and biological properties of biopolymers and the attractive structural characteristics of aerogels such as extremely high porosity, ultra low-density, and high surface area make combining these materials of great interest in tissue scaffolding and regenerative medicine applications. Numerous biopolymer aerogel scaffolds have been used to regenerate skin, cartilage, bone, and even heart valves and blood vessels by growing desired cells together with the growth factor in tissue engineering scaffolds. This review focuses on the principle of tissue engineering and regenerative medicine and the role of biopolymer aerogel scaffolds in this field, going through the properties and the desirable characteristics of biopolymers and biopolymer tissue scaffolds in tissue engineering applications. The recent advances of using biopolymer aerogel scaffolds in the regeneration of skin, cartilage, bone, and heart valves are also discussed in the present review. Finally, we highlight the main challenges of biopolymer-based scaffolds and the prospects of using these materials in regenerative medicine.

Time to re-engage psychiatric drug discovery by strengthening confidence in preclinical psychopharmacology

BACKGROUND

There is urgent need for new medications for psychiatric disorders. Mental illness is expected to become the leading cause of disability worldwide by 2030. Yet, the last two decades have seen the pharmaceutical industry withdraw from psychiatric drug discovery after costly late-stage trial failures in which clinical efficacy predicted pre-clinically has not materialised, leading to a crisis in confidence in preclinical psychopharmacology.

METHODS

Based on a review of the relevant literature, we formulated some principles for improving investment in translational neuroscience aimed at psychiatric drug discovery.

RESULTS

We propose the following 8 principles that could be used, in various combinations, to enhance CNS drug discovery: (1) consider incorporating the NIMH Research Domain Criteria (RDoC) approach; (2) engage the power of translational and systems neuroscience approaches; (3) use disease-relevant experimental perturbations; (4) identify molecular targets via genomic analysis and patient-derived pluripotent stem cells; (5) embrace holistic neuroscience: a partnership with psychoneuroimmunology; (6) use translational measures of neuronal activation; (7) validate the reproducibility of findings by independent collaboration; and (8) learn and reflect. We provide recent examples of promising animal-to-human translation of drug discovery projects and highlight some that present re-purposing opportunities.

CONCLUSIONS

We hope that this review will re-awaken the pharma industry and mental health advocates to the opportunities for improving psychiatric pharmacotherapy and so restore confidence and justify re-investment in the field.

3D Bioprinting of Lignocellulosic Biomaterials

The interest in bioprinting of sustainable biomaterials is rapidly growing, and lignocellulosic biomaterials have a unique role in this development. Lignocellulosic materials are biocompatible and possess tunable mechanical properties, and therefore promising for use in the field of 3D-printed biomaterials. This review aims to spotlight the recent progress on the application of different lignocellulosic materials (cellulose, hemicellulose, and lignin) from various sources (wood, bacteria, and fungi) in different forms (including nanocrystals and nanofibers in 3D bioprinting). Their crystallinity, leading to water insolubility and the presence of suspended nanostructures, makes these polymers stand out among hydrogel-forming biomaterials. These unique structures give rise to favorable properties such as high ink viscosity and strength and toughness of the final hydrogel, even when used at low concentrations. In this review, the application of lignocellulosic polymers with other components in inks is reported for 3D bioprinting and identified supercritical CO₂ as a potential sterilization method for 3D-printed cellulosic materials. This review also focuses on the areas of potential development by highlighting the opportunities and unmet challenges such as the need for standardization of the production, biocompatibility, and biodegradability of the cellulosic materials that underscore the direction of future research into the 3D biofabrication of cellulose-based biomaterials.

High strength and low swelling composite hydrogels from gelatin and delignified wood

A delignified wood template with hydrophilic characteristics and high porosity was obtained by removal of lignin. Gelatin was infiltrated into the delignified wood and further crosslinked with a natural crosslinker genipin to form hydrogels. The composite hydrogels showed high mechanical strength under compression and low swelling in physiological condition. The effect of genipin concentrations (1, 50 and 100 mM) on structure and properties of the composite hydrogels were studied. A porous honeycomb structure with tunable pore size and porosity was observed in the freeze-dried composite hydrogels. High elastic modulus of 11.82 ± 1.51 MPa and high compressive yield stress of 689.3 ± 34.9 kPa were achieved for the composite hydrogel with a water content as high as 81%. The equilibrium water uptake of the freeze-dried hydrogel in phosphate buffered saline at 37 °C was as low as 407.5%. These enables the delignified wood structure an excellent template in composite hydrogel preparation by using infiltration and in-situ synthesis, particularly when high mechanical strength and stiffness are desired.

Recent Advances in Porous 3D Cellulose Aerogels for Tissue Engineering Applications: A Review

Current approaches in developing porous 3D scaffolds face various challenges, such as failure of mimicking extracellular matrix (ECM) native building blocks, non-sustainable scaffold fabrication techniques, and lack of functionality. Polysaccharides and proteins are sustainable, inexpensive, biodegradable, and biocompatible, with structural similarities to the ECM. As a result, 3D-structured cellulose (e.g., cellulose nanofibrils, nanocrystals and bacterial nanocellulose)-based aerogels with high porosity and interconnected pores are ideal materials for biomedical applications. Such 3D scaffolds can be prepared using a green, scalable, and cost-effective freeze-drying technique. The physicochemical, mechanical, and biological characteristics of the cellulose can be improved by incorporation of proteins and other polysaccharides. This review will focus on recent developments related to the cellulose-based 3D aerogels prepared by sustainable freeze-drying methods for tissue engineering applications. We will also provide an overview of the scaffold development criteria; parameters that influenced the aerogel production by freeze-drying; and in vitro and in vivo studies of the cellulose-based porous 3D aerogel scaffolds. These efforts could potentially help to expand the role of cellulose-based 3D scaffolds as next-generation biomaterials.

Mimicking Natural Microenvironments: Design of 3D-Aligned Hybrid Scaffold for Dentin Regeneration

Tooth loss is a common consequence of a huge number of causes and can decrease the quality of humans’ life. Tooth is a complex organ composed of soft connective tissues and mineralized tissues of which dentin is the most voluminous component whose formation is regulated by a very complex process displaying several similarities with osteogenesis. Calcium phosphates, in particular hydroxyapatite (HA), is the phase present in higher amount into the structure of dentin, characterized by microscopic longitudinal dentinal tubules. To address the challenge of dental tissue regeneration, here we propose a novel biomimetic approach, to design hybrid scaffolds resembling the physico-chemical features of the natural mineralized tissues, suitable to recreate an appropriate microenvironment that stimulates cell colonization and proliferation, therefore effective for improving regenerative approach in dental applications. Biomineralization is the adopted synthesis as a nature inspired process consisting in the nucleation of magnesium-doped-hydroxyapatite (MgHA) nanocrystals on the gelatin (Gel) matrix generating hybrid flakes (Gel/MgHA) featured by a Gel:MgHA weight ratio close to 20:80 and size of 50–70 μm. Chemical and topotactic constrains affect the formation of MgHA mineral phase on the organic template, generating quasi-amorphous MgHA as revealed by XRD analysis and Ca/P ratio lower than 1.67, resembling the chemical and biological features of the natural apatite. The Gel/MgHA was then merged into the polymeric blend made of chitosan (Chit) and Gel to obtain a 3D porous scaffold with polymers: MgHA weight ratio of 40:60 and featured by an aligned porous structure as obtained by controlled freeze-drying process. The overall composite shows a swelling ratio of about 15 times after 6 h in PBS. The chemical stability was assured by means of a dehydrothermal cross-linking treatment (DHT) keeping the degradation lower than 20% after 28 days, while cell adhesion and proliferation were evaluated using a mouse fibroblast cell line.

Blending Gelatin and Cellulose Nanofibrils: Biocomposites with Tunable Degradability and Mechanical Behavior

Many studies show how biomaterial properties like stiffness, mechanical stimulation and surface topography can influence cellular functions and direct stem cell differentiation. In this work, two different natural materials, gelatin (Gel) and cellulose nanofibrils (CNFs), were combined to design suitable 3D porous biocomposites for soft-tissue engineering. Gel was selected for its well-assessed high biomimicry that it shares with collagen, from which it derives, while the CNFs were chosen as structural reinforcement because of their exceptional mechanical properties and biocompatibility. Three different compositions of Gel and CNFs, i.e., with weight ratios of 75:25, 50:50 and 25:75, were studied. The biocomposites were morphologically characterized and their total- and macro- porosity assessed, proving their suitability for cell colonization. In general, the pores were larger and more isotropic in the biocomposites compared to the pure materials. The influence of freeze-casting and dehydrothermal treatment (DHT) on mechanical properties, the absorption ability and the shape retention were evaluated. Higher content of CNFs gave higher swelling, and this was attributed to the pore structure. Cross-linking between CNFs and Gel using DHT was confirmed. The Young’s modulus increased significantly by adding the CNFs to Gel with a linear relationship with respect to the CNF amounts. Finally, the biocomposites were characterized in vitro by testing cell colonization and growth through a quantitative cell viability analysis performed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Additionally, the cell viability analysis was performed by the means of a Live/Dead test with Human mesenchymal stem cells (hMSCs). All the biocomposites had higher cytocompatibility compared to the pure materials, Gel and CNFs.

Production and Mechanical Characterisation of TEMPO-Oxidised Cellulose Nanofibrils/β-Cyclodextrin Films and Cryogels

Wood-based TEMPO-oxidised cellulose nanofibrils (toCNF) are promising materials for biomedical applications. Cyclodextrins have ability to form inclusion complexes with hydrophobic molecules and are considered as a method to bring new functionalities to these materials. Water sorption and mechanical properties are also key properties for biomedical applications such as drug delivery and tissue engineering. In this work, we report the modification with β-cyclodextrin (βCD) of toCNF samples with different carboxyl contents viz. 756 ± 4 µmol/g and 1048 ± 32 µmol/g. The modification was carried out at neutral and acidic pH (2.5) to study the effect of dissociation of the carboxylic acid group. Films processed by casting/evaporation at 40 °C and cryogels processed by freeze-drying were prepared from βCD modified toCNF suspensions and compared with reference samples of unmodified toCNF. The impact of modification on water sorption and mechanical properties was assessed. It was shown that the water sorption behaviour for films is driven by adsorption, with a clear impact of the chemical makeup of the fibres (charge content, pH, and adsorption of cyclodextrin). Modified toCNF cryogels (acidic pH and addition of cyclodextrins) displayed lower mechanical properties linked to the modification of the cell wall porosity structure. Esterification between βCD and toCNF under acidic conditions was performed by freeze-drying, and such cryogels exhibited a lower decrease in mechanical properties in the swollen state. These results are promising for the development of scaffold and films with controlled mechanical properties and added value due to the ability of cyclodextrin to form an inclusion complex with active principle ingredient (API) or growth factor (GF) for biomedical applications.

Advances in tissue engineering of nanocellulose-based scaffolds: A review

Scaffolds based on nanocellulose (NC) have crucial applications in tissue engineering (TE) owing to the biocompatibility, water absorption, water retention, optical transparency, and chemo-mechanical properties. In this review, we summarize the scaffolds based on nanocellulose, including nanocrystalline cellulose and nanofibrillated cellulose. We compare four representative methods to prepare NC-based scaffolds, containing electrospinning, freeze-drying, 3D printing, and solvent casting. We outline the characteristics of scaffolds obtained by different methods. Our focus is on the applications of NC-based scaffolds to repair, improve or replace damaged tissues and organs, including skin, blood vessel, nerve, skeletal muscle, heart, liver, and ophthalmology. NC-based scaffolds are attractive materials for regeneration of different tissues and organs due to the remarkable features. Finally, we propose the challenges and potentials of NC-based TE scaffolds.

A Graded Multifunctional Hybrid Scaffold with Superparamagnetic Ability for Periodontal Regeneration

The regeneration of dental tissues is a still an unmet clinical need; in fact, no therapies have been completely successful in regenerating dental tissue complexes such as periodontium, which is also due to the lack of scaffolds that are able to guide and direct cell fate towards the reconstruction of different mineralized and non-mineralized dental tissues. In this respect, the present work develops a novel multifunctional hybrid scaffold recapitulating the different features of alveolar bone, periodontal ligament, and cementum by integrating the biomineralization process, and tape casting and electrospinning techniques. The scaffold is endowed with a superparamagnetic ability, thanks to the use of a biocompatible, bioactive superparamagnetic apatite phase, as a mineral component that is able to promote osteogenesis and to be activated by remote magnetic signals. The periodontal scaffold was obtained by engineering three different layers, recapitulating the relevant compositional and microstructural features of the target tissues, into a monolithic multifunctional graded device. Physico-chemical, morphological, and ultrastructural analyses, in association with preliminary in vitro investigations carried out with mesenchymal stem cells, confirm that the final scaffold exhibits a good mimicry of the periodontal tissue complex, with excellent cytocompatibility and cell viability, making it very promising for regenerative applications in dentistry.