Cellular Scaffolds Research Articles

Bio‐interface behaviour of graphene and semiconducting SWCNT:C60blend based nano photodiode for subretinal implant

Hybrid interfaces between living cells and organic conjugated polymers play a pivotal role in bioelectronics medicine. Currently, conjugated polymers are widely utilised for optical stimulation of living cells and other bio-interface applications such as neural probes, cellular scaffolds and biosensors for drug release. In such a work, the authors fabricated and characterised the Nano Photodiode array device for the subretinal implant. However, the authors did not discuss in their report about the biocompatibility of this new device. In this work, the authors manifest that the quintessential graphene electrode and polymer blend of semiconducting single-wall carbon nanotube and C60 fullerene (S-SWCNT:C60) sustains its optoelectronic properties all through the various strides for neural preparation. Further, the studies show that these materials can provide a favourable environment for cell proliferation and a high degree of biocompatibility. PC-12 cells used as a valuable model to validate the biocompatibility were grown successfully onto the S-SWCNT:C60 active layer still preserving its optical and electrical properties. The improved electrical performance of nano photodiode made of graphene, S-SWCNT:C60 established in the previous studies and the excellent bio-interface performance of this nano photodiode shows that the nano photodiode array proposed by the authors is a strong candidate for subretinal implants.

Numerical and analytical simulation of multilayer cellular scaffolds

Due to the advent and maturity of the additive manufacturing technology, it is possible now to construct complex microstructures with unprecedented accuracy. In addition, to the influence of network unit cell types and porosities in recent years, researchers have studied the number of scaffold layers fabricated by additive manufacturing on mechanical properties. The objective of this paper is to assess the numerical and analytical simulations of the multilayer scaffolds. For this purpose, 54 different regular scaffolds with a unit cell composed of multilayer scaffolds were simulated under compressive loading and compared with the analytical relationships based on the Euler–Bernoulli and Timoshenko's beam theories where the most appropriate theory was chosen for different unit cell sizes. Then, five types of two- and three-layer scaffolds of titanium alloy were simulated based on the previous data numerically and analytically, and the young's modulus and yield strength of the scaffolds were compared with the experimental results, where a good convergence between the results of the finite element model and previous experimental results were observed. Furthermore, the axial forces of the unit cell struts, in the transverse section, stress distribution, and displacement of the nodes in the scaffolds, were investigated, which was not possible experimentally.

3D printed cellular cathodes with hierarchical pores and high mass loading for Li–SeS2 battery

To satisfy the vast demand on high energy density for the next-generation electrochemical energy storage system, lithium selenium-sulfur (Li-SexSy) battery has drawn ever-growing interest with great advantages of low cost and promising capacity. However, its practical application with high areal mass loading of electrode manufacturing is still challenging. Here, we firstly print three-dimensional (3D) freestanding electrodes for Li–SeS2 batteries via direct ink writing based on the high-solid-content ink. The characteristic rheology properties of the ink possess excellent printability and enable the stable extrusion of 3D-printed cellular scaffold. In such a printed architecture, the low-cost commercial conducting ketjenblack (KB) with abundant pores is selected as the host material for selenium sulfide. For a well-controlled 3D-printed KB/SeS2 electrode, the areal SeS2 loading reaches 7.9 mg cm−2. More importantly, with the hierarchical porosity engineering, the 3D-printed cellular KB/SeS2 cathode delivers a high initial discharge capacity of 9.5 mA h cm−2 at 1.8 mA cm−2 and high Coulombic efficiency of 96% over 80 cycles is achieved with such high mass loading. This 3D-printed Li–SeS2 battery electrode may guide more energy storage systems with ultrahigh capacity to the practical application.

Poly(ethylene glycol)-based biofunctional hydrogels mediated by peroxidase-catalyzed cross-linking reactions

Biofunctional hydrogels prepared by a peroxidase, especially horseradish peroxidase (HRP), serve as an excellent class of materials or platform for the development of cellular scaffolds because their biocompatibility and mild and tunable reaction conditions provide them with desirable properties. In this focus review, we summarize our decade of research into HRP-mediated fabrication of biofunctional hydrogels and their applications, in particular cell culture scaffolds. A brief overview of potential substrates employed in HRP and improvement of the HRP hydrogelation system from the initial step until the hydrogen peroxide removal stage in an effort to meet environmental standards is discussed. We highlight our system and describe its biocompatibility and ability to functionalize molecules to support biofabrication by increasing cellular adhesiveness, retaining growth factor affinity, and finally accelerating the formation of two- and three-dimensional multicellular architectures. In the last section, we outline the adoption of hydrogelation as a self-standing, compartmentalized reaction system, i.e., the use of hydrogel marble to conduct cell-free biosynthesis. We believe that this HRP-mediated hydrogel system offers great potential not only as a cell culture scaffold but also for various biomedical applications. Biofunctional hydrogels were formed by horseradish peroxidase (HRP)-catalyzed cross-linking reaction. Poly(ethylene glycol) (PEG) incorporated with phenol or thiol group was used as a base polymer to form irreversible or redox responsive cross-links, respectively. Thiolated PEGs showed slower hydrogelation kinetics than phenolated ones; however, in the presence of phenolic small compounds, the cross-linking reaction was promoted without the aid of exogenous hydrogen peroxide. Moreover, in situ incorporation of bioactive entities, such as proteins, realized biofunctionalization of hydrogels for potential applications for bioengineering and biomedical applications.

4D Printed Hydrogels: Fabrication, Materials, and Applications

Abstract4D printed objects are 3D printed structures whose shape, property, and functionality are able to self‐transform when exposed to a predetermined stimulus. The emerging field of 4D printing has attracted wide interest from both academia and industry since first introduced in 2013. Stimuli‐responsive hydrogels have become a competitive and versatile group of materials for 4D printed devices due to their good deformability, promising biocompatibility, simple manufacturing, and low cost. This review aims to provide a summary of the current progress of hydrogel‐based 4D printed objects and devices based on their fabrication techniques, materials, and applications. Herein, presented are: the characteristics of different additive manufacturing methods such as direct ink writing, fused deposition modeling, and stereolithography; the properties of various stimuli‐responsive hydrogels such as poly(N‐isopropylacrylamide) and poly(N,N‐dimethylacrylamide), alginate, etc.; and diverse applications of 4D printed hydrogels such as actuators, cellular scaffolds, and drug release devices. Opportunities and challenges for 4D printed hydrogels are discussed and prospects for future development are elaborated.

Intrafibrillar Mineralized Collagen-Hydroxyapatite-Based Scaffolds for Bone Regeneration.

As one of the major challenges in the field of tissue engineering, large skeletal defects have attracted wide attention from researchers. Collagen (Col) and hydroxyapatite (HA), the most abundant protein and the main component in natural bone, respectively, are usually used as a biomimetic composite material in tissue engineering due to their excellent biocompatibility and biodegradability. In this study, novel intrafibrillar mineralized Col-HA-based scaffolds, constructed in either cellular or lamellar microstructures, were established through a biomimetic method to enhance the new bone-regenerating capability of tissue engineering scaffolds. Moreover, iron (Fe) and manganese (Mn), two of the essential trace elements in the body, were successfully incorporated into the lamellar scaffold to further improve the osteoinductivity of these biomaterials. It was found that the lamellar scaffolds demonstrated better osteogenic abilities compared to both in-house and commercial Col-HA-based cellular scaffolds in vitro and in vivo. Meanwhile, Fe/Mn incorporation further amplified the osteogenic promotion of the lamellar scaffolds. More importantly, a synergistic effect was observed in the Fe and Mn dual-element-incorporated lamellar scaffolds for both in vitro osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and in vivo bone regeneration loaded with fresh bone marrow cells. This study provides a simple but practical strategy for the creation of functional scaffolds for bone regeneration.

Sustained-immunostimulatory nanocellulose scaffold to enhance vaccine efficacy.

An implantable scaffold-based vaccination system is a promising platform to generate robust immune responses by modulating the immune system. However, establishment of an effective vaccine using a biodegradable, cell-infiltrative scaffold remain challenging. Here we demonstrate a biodegradable, nanocellulose-based immune scaffold capable of sustainably activating immune cells to elicit cellular immunity. Cell-infiltrative nanocellulose hydrogels were used as a delivery carrier and cellular scaffold microenvironment. Nanofibrous hydrogels allowed for high cell infiltration and delivery of antigen-loaded nanocellulose while cells degraded the hydrogel matrix. Importantly, antigen-loaded nanocellulose hydrogels exhibited sustained activation of macrophages in vitro compared to free antigen and collagen scaffold. Histological observation revealed infiltration of macrophages and dendritic cells into the nanocellulose scaffold subcutaneously implanted in mice. In vivo fluorescence imaging indicated that the implanted scaffold released antigens at a zero-order release profile without burst diffusion. Antigen-loaded nanocellulose hydrogels increased interferon-γ-producing cells compared to free antigen injection, suggesting the enhancement of cellular immunity. Thus, nanocellulose immune scaffold may serve as a sustained-immunostimulatory vaccine platform by providing favorable microenvironments for immune cells thus enhancing vaccine efficacy.

3D‐Printed Stretchable Micro‐Supercapacitor with Remarkable Areal Performance

AbstractWhile stretchable micro‐supercapacitors (MSCs) have been realized, they have suffered from limited areal electrochemical performance, thus greatly restricting their practical electronic application. Herein, a facile strategy of 3D printing and unidirectional freezing of a pseudoplastic nanocomposite gel composed of Ti3C2Tx MXene nanosheets, manganese dioxide nanowire, silver nanowires, and fullerene to construct intrinsically stretchable MSCs with thick and honeycomb‐like porous interdigitated electrodes is introduced. The unique architecture utilizes thick electrodes and a 3D porous conductive scaffold in conjunction with interacting material properties to achieve higher loading of active materials, larger interfacial area, and faster ion transport for significantly improved areal energy and power density. Moreover, the oriented cellular scaffold with fullerene‐induced slippage cell wall structure prompts the printed electrode to withstand large deformations without breaking or exhibiting obvious performance degradation. When imbued with a polymer gel electrolyte, the 3D‐printed MSC achieves an unprecedented areal capacitance of 216.2 mF cm−2 at a scan rate of 10 mV s−1, and remains stable when stretched up to 50% and after 1000 stretch/release cycles. This intrinsically stretchable MSC also exhibits high rate capability and outstanding areal energy density of 19.2 µWh cm−2 and power density of 58.3 mW cm−2, outperforming all reported stretchable MSCs.

Three-dimensional electronic scaffolds for monitoring and regulation of multifunctional hybrid tissues

Recently, the integration of electronic elements with cellular scaffolds has brought forth the ability to monitor and control tissue function actively by using flexible free-standing two-dimensional (2D) systems. Capabilities for electrically probing complex, physicochemical and biological three-dimensional (3D) microenvironments demand, however, 3D electronic scaffolds with well-controlled geometries and functional-component distributions. This work presents the development of flexible 3D electronic scaffolds with precisely defined dimensions and microelectrode configurations formed using a process that relies on geometric transformation of 2D precursors by compressive buckling. It demonstrates a capability to fabricate these constructs in diverse 3D architectures and/or electrode distributions aimed at achieving an enhanced level of control and regulation of tissue function relatively to that of other approaches. In addition, this work presents the integration of these 3D electronic scaffolds within engineered 3D cardiac tissues, for monitoring of tissue function, controlling tissue contraction through electrical stimulation, and initiating on-demand, local release of drugs, each through well-defined volumetric spaces. These ideas provide opportunities in fields ranging from in vitro drug development to in vivo tissue repair and many others.

Collagen‐Elastin‐Like Polypeptide‐Bioglass Scaffolds for Guided Bone Regeneration

The goals of this study are to evaluate the ability of the multicomponent collagen-elastin-like polypeptide (ELP)-Bioglass scaffolds to support osteogenesis of rat mesenchymal stem cells (rMSCs), demonstrate in vivo biocompatibility by subcutaneous implantation in Sprague-Dawley rats, monitor degradation noninvasively, and finally assess the scaffold's ability in healing critical-sized cranial bone defects. The collagen-ELP-Bioglass scaffold supports the in vitro osteogenic differentiation of rMSCs over a 3 week culture period. The cellular (rMSC-containing) or acellular scaffolds implanted in the subcutaneous pockets of rats do not cause any local or systemic toxic effects or tumors. The real-time monitoring of the fluorescently labeled scaffolds by IVIS reveals that the scaffolds remain at the site of implantation for up to three weeks, during which they degrade gradually. Micro-CT analysis shows that the bilateral cranial critical-sized defects created in rats lead to greater bone regeneration when filled with cellular scaffolds. Bone mineral density and bone microarchitectural parameters are comparable among different scaffold groups, but the histological analysis reveals increased formation of high-quality mature bone in the cellular group, while the acellular group has immature bone and organized connective tissue. These results suggest that the rMSC-seeded collagen-ELP-Bioglass composite scaffolds can aid in better bone healing process.

Bioprinting with bioactive glass loaded polylactic acid composite and human adipose stem cells

Cellularized scaffolds fabricated with hydrogel do not possess sufficient strength to act as stand-alone implant devices for hard tissue repair and regeneration. A thermoplastic polymer support structure typically provides the structural integrity to scaffolds while cells and growth factors in hydrogel provide biological stimulation for tissue formation. In this research, we investigated the viability of human adipose-derived mesenchymal stem cells (ASCs) mixed in an alginate-gelatin (1:1) hydrogel (bioink) that is deposited between polylactic acid (PLA)-borate glass composite filaments. Bioactive borate glass (13–93B3, also called B3 glass) is a rapidly dissolving biomaterial, and the physiologically relevant ionic dissolution products are known to stimulate cells in vitro and endogenous tissues in vivo. B3 glass was added to PLA in two different weight ratios (50% and 33%) to form PLA ​+ ​B3 glass composites, and the weight loss over time of the 3D printed composite scaffold, pH change of the surrounding media, and mechanical properties were investigated. Physical assessment of the composite scaffolds indicated improved mechanical properties and complete glass dissolution within two weeks. Cellularized scaffolds were bioprinted in three configurations: Bioink only, PLA ​+ ​Bioink, and PLA ​+ ​B3 glass ​+ ​Bioink, and cultured in dynamic conditions to investigate ASC viability. The results indicated a non-uniform cell viability along the scaffold thickness, with hypoxic-like conditions and lower viability at the bottom region to higher viability in the top layers of the scaffold.

Chemobrionic structures in tissue engineering: self-assembling calcium phosphate tubes as cellular scaffolds.

A diverse range of complex patterns and mineralised hierarchical microstructures can be derived from chemobrionic systems, with formation driven by complex reaction-diffusion mechanisms far from thermodynamic equilibrium. In these experiments, self-assembling calcium phosphate tubes are generated using hydrogels made with 1 M calcium solutions layered with solutions of dibasic sodium phosphate over a range of concentrations between 0.2-1 M. Self-assembling structures prepared using 0.8 M dibasic sodium phosphate solutions were selected to assess cell-material interactions. Candidate chemobrionic scaffolds were characterised by micro-X-Ray fluorescence (μ-XRF) spectroscopy, Raman spectroscopy, powder X-ray diffraction (XRD), helium pycnometry and scanning electron microscopy (SEM). As prepared tubes were formed from non-stoichiometric hydroxyapatite (HA, Ca10-x(PO4)6-x(HPO4)x(OH)2-x (0 ≤x≤ 1)), which was confirmed as calcium deficient hydroxyapatite (CDHA, Ca9(PO4)5HPO4OH). Thermal treatment of tubes in air at 650 °C for 4 h converted the structures to beta tricalcium phosphate (β-TCP, β-Ca3(PO4)2). The potential of these scaffolds to support the attachment of bone marrow derived mesenchymal stem cells (BMSCs) was investigated for the first time, and we demonstrate cell attachment and elongation on the fabricated tubular structures.

Engineering the biological performance of hierarchical nanostructured poly(ε-carpolactone) scaffolds for bone tissue engineering

Scaffolds play an important role as physical substrates for cell proliferation and differentiation, leading to tissue regeneration. For bone applications, researchers are focusing on cellular or acellular biocompatible biodegradable polymeric scaffolds. However, high biological performance scaffolds are still required to meet actual clinical demands. This paper discusses a novel strategy to engineer the biological performance of polymeric scaffolds through the combined use of additive manufacturing, acetone vapour annealing surface treatment and dopamine grafting, enabling the fabrication of hierarchical nanostructured tissue engineering structures. Produced scaffolds present improved biological behaviour compared to conventional additive manufactured scaffolds, and similar mechanical properties, showing high potential for clinical applications.

Oxygen carrier in core-shell fibers synthesized by coaxial electrospinning enhances Schwann cell survival and nerve regeneration.

Rationale: Local hypoxia is a challenge for fabrication of cellular grafts and treatment of peripheral nerve injury. In our previous studies, we demonstrated that perfluorotributylamine (PFTBA) could provide short term oxygen supply to Schwann cells (SCs) and counteract the detrimental effects of hypoxia on SCs during the early stages of nerve injury. However, the quick release of oxygen in PFTBA compromised its ability to counteract hypoxia over an extended time, limiting its performance in peripheral nerve injury.Methods: In this study, PFTBA-based oxygen carrier systems were prepared through coaxial electrospinning to prolong the time course of oxygen release. Core-shell structures were fabricated, optimized, and the oxygen kinetics of PFTBA-enriched core-shell fibers evaluated. The effect of core-shells on the survival and function of SCs was examined in both 2D and 3D systems as well as in vivo. The system was used to bridge large sciatic nerve defects in rats.Results: PFTBA core-shell fibers provided high levels of oxygen to SCs in vitro, enhancing their survival, and increasing NGF, BDNF, and VEGF expression in 2D and 3D culture systems under hypoxic condition. In vivo analysis showed that the majority of GFP-expressing SCs in the PFTBA conduit remained viable 14 days post-implantation. We found that axons in PFTBA oxygen carrier scaffold improved axonal regeneration, remyelination, and recovery.Conclusion: A synthetic oxygen carrier in core-shell fibers was fabricated by the coaxial electrospinning technique and was capable of enhancing SC survival and nerve regeneration by prolonged oxygen supply. These findings provide a new strategy for fabricating cellular scaffolds to achieve regeneration in peripheral nerve injury treatment and other aerobic tissue injuries.

Cardiac tissue engineering therapeutic products to enhance myocardial contractility.

Researchers continue to develop therapeutic products for the repair and replacement of myocardial tissue that demonstrates contractility equivalent to normal physiologic states. As clinical trials focused on pure adult stem cell populations undergo meta-analysis for preclinical through clinical design, the field of tissue engineering is emerging as a new clinical frontier to repair the myocardium and improve cardiac output. This review will first discuss the three primary tissue engineering product themes that are advancing in preclinical to clinical models: (1) cell-free scaffolds, (2) scaffold-free cellular, and (3) hybrid cell and scaffold products. The review will then focus on the products that have advanced from preclinical models to clinical trials. In advancing the cardiac regenerative medicine field, long-term gains towards discovering an optimal product to generate functional myocardial tissue and eliminate heart failure may be achieved.

3D printed anatomical (bio)models in spine surgery: clinical benefits and value to health care providers.

The applications of three-dimensional printing (3DP) for clinical purposes have grown rapidly over the past decade. Recent advances include the fabrication of patient specific instrumentation, such as drill and cutting guides, patient specific/custom long term implants and 3DP of cellular scaffolds. Spine surgery in particular has seen enthusiastic early adoption of these applications. 3DP as a manufacturing method can be used to mass produce objects of the same design, but can also be used as a cost-effective method for manufacturing unique one-off objects, such as patient specific models and devices. Perhaps the first, and currently most widespread, application of 3DP for producing patient specific devices is the production of patient specific anatomical models, often termed biomodels. The present manuscript focuses on the current state of the art in anatomical (bio)models as used in spinal clinical practice. The biomodels shown and discussed include: translucent and coloured models to aid in identification of extent and margins of pathologies such as bone tumours; dynamic models for implant trial implantation and pre-operative sizing; models that can be disassembled to simulate surgical resection of diseased tissue and subsequent reconstruction. Biomodels can reduce risk to the patient by decreasing surgery time, reducing the probability of the surgical team encountering unexpected anatomy or relative positioning of structures and/or devices, and better pre-operative planning of the surgical workflow including ordered preparation of the necessary instrumentation for multi-step and revision procedures. Conversely, risks can be increased if biomodels are not accurate representations of the anatomy, which can occur if MRI/CT scan data is simply converted into 3DP format without interpretation of what the scan represents in terms of patient anatomy. A review and analysis of the cost-benefits of biomodels shows that biomodels can potentially reduce cost to health care providers if operating room time is reduced by 14 minutes or more.

Subtalar Arthrodesis with Use of Adipose-Derived Cellular Bone Matrix Compared with Autologous Bone Graft: A Multicenter, Randomized Controlled Trial.

This article was updated on November 7, 2019, because of a previous error. On page 1909, in the section entitled "Discussion," the sentence that had read "Radiographic nonunion rates of 69.2% and 45.6% were observed at 6 months for ACBM and autograft, respectively, as measured on CT scans; however, these nonunion rates do account for patients who were considered to have attained fusion according to traditional methods, including absence of pain and swelling and presence of arthrodesis on radiographs" now reads "Radiographic nonunion rates of 69.2% and 45.6% were observed at 6 months for ACBM and autograft, respectively, as measured on CT scans; however, these nonunion rates do not account for patients who were considered to have attained fusion according to traditional methods, including absence of pain and swelling and presence of arthrodesis on radiographs."An erratum has been published: J Bone Joint Surg Am. 2019 XXX. Subtalar arthrodesis effectively treats subtalar joint arthritis when other interventions have failed. Nonunion is a known complication of subtalar arthrodesis, with reported rates ranging from 5% to 45%. Historically, open arthrodesis has been performed with use of autologous bone graft; however, there are inherent disadvantages to autologous bone graft, including donor-site morbidity. Mesenchymal stem cells, when placed on a cellular scaffold, have shown promise as an alternative to autologous bone graft. The purpose of this multicenter, randomized controlled trial was to assess the safety and efficacy of an adipose-derived cellular bone matrix (ACBM) composite made with live cells compared with autograft in subtalar arthrodesis. A total of 140 patients were enrolled in a prospective, randomized (1:1) controlled trial performed at 6 clinical sites in the U.S. End points, including radiographic, clinical, and functional outcomes, were assessed over 2 years of follow-up. A total of 109 patients underwent arthrodesis with ACBM (52 patients) and autograft (57 patients). At 6 months, fusion was achieved in 16 patients (30.8%) in the ACBM group and 31 patients (54.4%) in the autograft group as measured on computed tomography (p = 0.024), and in 41 patients (78.8%) in the ACBM group and 50 patients (87.7%) in the autograft group as assessed on clinical and radiographic evaluation (p = 0.213). Quality-of-life outcome measures demonstrated significant functional improvement from baseline for both groups. Fewer cases of serious adverse events occurred in the autograft group (10.5%) compared with the ACBM group (23.1%) (p = 0.078). In patients who require subtalar arthrodesis, the use of ACBM demonstrated lower rates of radiographic fusion compared with treatment with autograft. The nonunion rate in the autologous group, as measured on computed tomography, was high. Good clinical outcomes were achieved in spite of the high non-union rates. Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

A Cellularized Biphasic Implant Based on a Bioactive Silk Fibroin Promotes Integration and Tissue Organization during Osteochondral Defect Repair in a Porcine Model.

In cartilage tissue engineering, biphasic scaffolds (BSs) have been designed not only to influence the recapitulation of the osteochondral architecture but also to take advantage of the healing ability of bone, promoting the implant’s integration with the surrounding tissue and then bone restoration and cartilage regeneration. This study reports the development and characterization of a BS based on the assembly of a cartilage phase constituted by fibroin biofunctionalyzed with a bovine cartilage matrix, cellularized with differentiated autologous pre-chondrocytes and well attached to a bone phase (decellularized bovine bone) to promote cartilage regeneration in a model of joint damage in pigs. BSs were assembled by fibroin crystallization with methanol, and the mechanical features and histological architectures were evaluated. The scaffolds were cellularized and matured for 12 days, then implanted into an osteochondral defect in a porcine model (n = 4). Three treatments were applied per knee: Group I, monophasic cellular scaffold (single chondral phase); group II (BS), cellularized only in the chondral phase; and in order to study the influence of the cellularization of the bone phase, Group III was cellularized in chondral phases and a bone phase, with autologous osteoblasts being included. After 8 weeks of surgery, the integration and regeneration tissues were analyzed via a histology and immunohistochemistry evaluation. The mechanical assessment showed that the acellular BSs reached a Young’s modulus of 805.01 kPa, similar to native cartilage. In vitro biological studies revealed the chondroinductive ability of the BSs, evidenced by an increase in sulfated glycosaminoglycans and type II collagen, both secreted by the chondrocytes cultured on the scaffold during 28 days. No evidence of adverse or inflammatory reactions was observed in the in vivo trial; however, in Group I, the defects were not reconstructed. In Groups II and III, a good integration of the implant with the surrounding tissue was observed. Defects in group II were fulfilled via hyaline cartilage and normal bone. Group III defects showed fibrous repair tissue. In conclusion, our findings demonstrated the efficacy of a biphasic and bioactive scaffold based on silk fibroin and cellularized only in the chondral phase, which entwined chondroinductive features and a biomechanical capability with an appropriate integration with the surrounding tissue, representing a promising alternative for osteochondral tissue-engineering applications.

Hydrogel Bioink Reinforcement for Additive Manufacturing: A Focused Review of Emerging Strategies.

Bioprinting is an emerging approach for fabricating cell-laden 3D scaffolds via robotic deposition of cells and biomaterials into custom shapes and patterns to replicate complex tissue architectures. Bioprinting uses hydrogel solutions called bioinks as both cell carriers and structural components, requiring bioinks to be highly printable while providing a robust and cell-friendly microenvironment. Unfortunately, conventional hydrogel bioinks have not been able to meet these requirements and are mechanically weak due to their heterogeneously crosslinked networks and lack of energy dissipation mechanisms. Advanced bioink designs using various methods of dissipating mechanical energy are aimed at developing next-generation cellularized 3D scaffolds to mimic anatomical size, tissue architecture, and tissue-specific functions. These next-generation bioinks need to have high print fidelity and should provide a biocompatible microenvironment along with improved mechanical properties. To design these advanced bioink formulations, it is important to understand the structure-property-function relationships of hydrogel networks. By specifically leveraging biophysical and biochemical characteristics of hydrogel networks, high performance bioinks can be designed to control and direct cell functions. In this review article, current and emerging approaches in hydrogel design and bioink reinforcement techniques are critically evaluated. This bottom-up perspective provides a materials-centric approach to bioink design for 3D bioprinting.

Tenocytes form a 3-D network and are connected via nanotubes.

Cells use different cell adhesion and communication structures to promote tissue development, maintenance of tissue integrity as well as repair and regenerative processes. Another recently discovered way of information exchange is long‐distance thin cellular processes called nanotubes (NTs), mainly studied in vitro. Information on the existence and relevance of NTs in vivo is sparse. Building on two references which hint at the potential existence of longitudinally directed cell processes resembling NTs, we investigated tendons from young (3 weeks) and adult (9 weeks, 4 and 8 months) Fisher rats. Whole mounts of rat tail tendon fascicles (RTTfs) and sections of Achilles, flexor, extensor and patellar tendons were stained with Deep Red plasma membrane and DAPI nuclear stain and immunolabelled with Connexin43 (Cx43). In addition, 3‐D reconstruction of serial semithin sections and TEM was used to verify the presence of NTs. We were able to demonstrate NTs as straight thin longitudinal processes (Ø 100–500 nm) reaching up to several 100 μm in length, mainly originating from lateral sheet‐like cell processes or cell bodies in all tendon types investigated. NTs were observed to distend between tenocyte rows at the same level but also connect cells of different rows, thus leading to a complex 3‐D cellular scaffold. Shorter NTs connected lateral cell sheets of tenocytes in the same row, omitting one or two cells. In addition, we detected links or potential branching of NTs. Cx43 immunostaining for the detection of gap junctions revealed Cx43‐positive foci at the end‐to‐end contacts of tenocyte cell bodies as well as along their contacting sheet‐like processes. Only rarely, we found clear Cx43 signals at their potential contact points between NTs and tendon cells as well as along the course of NTs, and most NTs appeared completely devoid of Cx43 signals. Therefore, we conclude that NTs in tendons could have a twofold function: long‐distance communication as well as stabilization of a mechanically challenged tissue. From in vitro studies it is known that NTs allow intercellular transmission of various cell components, offering potential protective effects for the respective tissue. Further studies on functional properties of NTs in tendons under changing mechanical loading regimens are required in the future. The fact that NTs are present in tendons may necessitate the reconsideration of our traditional understanding of cell‐to‐cell communication.