Cell structure, stiffness and permeability of freeze-dried collagen scaffolds in dry and hydrated states

Cartilage lacuna-biomimetic hydrogel microspheres endowed with integrated biological signal boost endogenous articular cartilage regeneration

Despite numerous studies on chondrogenesis, the repair of cartilage-particularly the reconstruction of cartilage lacunae through an all-in-one advanced drug delivery system remains limited. In this study, we developed a cartilage lacuna-like hydrogel microsphere system endowed with integrated biological signals, enabling sequential immunomodulation and endogenous articular cartilage regeneration. We first integrated the chondrogenic growth factor transforming growth factor-β3 (TGF-β3) into mesoporous silica nanoparticles (MSNs). Then, TGF-β3@MSNs and insulin-like growth factor 1 (IGF-1) were encapsulated within microspheres made of polydopamine (pDA). In the final step, growth factor-loaded MSN@pDA and a chitosan (CS) hydrogel containing platelet-derived growth factor-BB (PDGF-BB) were blended to produce growth factors loaded composite microspheres (GFs@μS) using microfluidic technology. The presence of pDA reduced the initial acute inflammatory response, and the early, robust release of PDGF-BB aided in attracting endogenous stem cells. Over the subsequent weeks, the continuous release of IGF-1 and TGF-β3 amplified chondrogenesis and matrix formation. μS were incorporated into an acellular cartilage extracellular matrix (ACECM) and combined with a polydopamine-modified polycaprolactone (PCL) structure to produce a tissue-engineered scaffold that mimicked the structure of the cartilage lacunae evenly distributed in the cartilage matrix, resulting in enhanced cartilage repair and patellar cartilage protection. This research provides a strategic pathway for optimizing growth factor delivery and ensuring prolonged microenvironmental remodeling, leading to efficient articular cartilage regeneration.

Computed tomography technologies to measure key structural features of polymeric biomedical implants from bench to bedside

Implanted polymeric devices, designed to encourage tissue regeneration, require porosity. However, characterizing porosity, which affects many functional device properties, is non-trivial. Computed tomography (CT) is a quick, versatile, and non-destructive way to gain 3D structural information, yet various CT technologies, such as benchtop, preclinical and clinical systems, all have different capabilities. As system capabilities determine the structural information that can be obtained, seamless monitoring of key device features through all stages of clinical translation must be engineered intentionally. Therefore, in this study we tested feasibility of obtaining structural information in pre-clinical systems and high-resolution micro-CT (μCT) under physiological conditions. To overcome the low CT contrast of polymers in hydrated environments, radiopaque nanoparticle contrast agent was incorporated into porous devices. The size of resolved features in porous structures is highly dependent on the resolution (voxel size) of the scan. As the voxel size of the CT scan increased (lower resolution) from 5 to 50 μm, the measured pore size was overestimated, and percentage porosity was underestimated by nearly 50%. With the homogeneous introduction of nanoparticles, changes to device structure could be quantified in the hydrated state, including at high-resolution. Biopolymers had significant structural changes post-hydration, including a mean increase of 130% in pore wall thickness that could potentially impact biological response. By incorporating imaging capabilities into polymeric devices, CT can be a facile way to monitor devices from initial design stages through to clinical translation.

Structure, Properties and Degradation of Self-Assembled Fibrinogen Nanofiber Scaffolds

Self-assembled fibrinogen nanofibers are promising candidates for skin tissue engineering due to their biocompatibility and ability to mimic the native blood clot architecture. Here, we studied the structure-property relationship and degradation of rehydrated fibrinogen nanofibers prepared by salt-induced self-assembly, focusing on the effect of scaffold layering, cross-linking time and freeze-drying. Optimal fiber stability was achieved with cross-linking by formaldehyde (FA) vapor, while treatment with liquid aldehydes, genipin, EDC, and transglutaminase failed to preserve the nanofibrous architecture upon rehydration. Scaffold layering did not significantly influence the mechanical properties but changed the scaffold architecture, with bulk fiber scaffolds being more compact than layered scaffolds. Freeze-drying maintained the mechanical properties and interconnected pore network with average pore diameters around 20 μm, which will enhance the storage stability of self-assembled fibrinogen scaffolds. Varying cross-linking times altered the scaffold mechanics without affecting the swelling behavior, indicating that scaffold hydration can be controlled independently of the mechanical characteristics. Cross-linking times of 240 min increased scaffold stiffness and decreased elongation, while 30 min resulted in mechanical properties similar to native skin. Cross-linking for 120 min was found to reduce scaffold degradation by various enzymes in comparison to 60 min. Overall, after 35 days of incubation, plasmin and a combination of urokinase and plasminogen exhibited the strongest degradative effect, with nanofibers being more susceptible to enzymatic degradation than planar fibrinogen due to their higher specific surface area. Based on these results, self-assembled fibrinogen fiber scaffolds show great potential for future applications in soft tissue engineering that require controlled structure-function relationships and degradation characteristics.

Fabrication of Porous Collagen Scaffolds Containing Embedded Channels with Collagen Membrane Linings

Tissues and organs contain an extracellular matrix (ECM). In the case of blood vessels, endothelium cells are anchored to a specialized basement membrane (BM) embedded inside the interstitial matrix (IM). We introduce a multi-structural collagen-based scaffold with embedded microchannels that mimics in vivo structures within vessels. Our scaffold consists of two parts, each containing two collagen layers, i.e., a 3D porous collagen layer analogous to IM lined with a thin 2D collagen film resembling the BM. Enclosed microchannels were fabricated using contact microprinting. Microchannel test structures with different sizes ranging from 300 to 800 µm were examined for their fabrication reproducibility. The heights and perimeters of the fabricated microchannels were ~20% less than their corresponding values in the replication PDMS mold; however, microchannel widths were significantly closer to their replica dimensions. The stiffness, permeability, and pore size properties of the 2D and 3D collagen layers were measured. The permeability of the 2D collagen film was negligible, making it suitable for mimicking the BM of large blood vessels. A leakage test at various volumetric flow rates applied to the microchannels showed no discharge, thereby verifying the reliability of the proposed integrated 2D/3D collagen parts and the contact printing method used for bonding them in the scaffold. In the future, multi-cell culturing will be performed within the 3D porous collagen and against the 2D membrane inside the microchannel, hence preparing this scaffold for studying a variety of blood vessel-tissue interfaces. Also, thicker collagen scaffold tissues will be fabricated by stacking several layers of the proposed scaffold.

Freeze-Drying Process for the Fabrication of Collagen-Based Sponges as Medical Devices in Biomedical Engineering

This paper presents a systematic review of a key sector of the much promising and rapidly evolving field of biomedical engineering, specifically on the fabrication of three-dimensional open, porous collagen-based medical devices, using the prominent freeze-drying process. Collagen and its derivatives are the most popular biopolymers in this field, as they constitute the main components of the extracellular matrix, and therefore exhibit desirable properties, such as biocompatibility and biodegradability, for in vivo applications. For this reason, freeze-dried collagen-based sponges with a wide variety of attributes can be produced and have already led to a wide range of successful commercial medical devices, chiefly for dental, orthopedic, hemostatic, and neuronal applications. However, collagen sponges display some vulnerabilities in other key properties, such as low mechanical strength and poor control of their internal architecture, and therefore many studies focus on the settlement of these defects, either by tampering with the steps of the freeze-drying process or by combining collagen with other additives. Furthermore, freeze drying is still considered a high-cost and time-consuming process that is often used in a non-optimized manner. By applying an interdisciplinary approach and combining advances in other technological fields, such as in statistical analysis, implementing the Design of Experiments, and Artificial Intelligence, the opportunity arises to further evolve this process in a sustainable and strategic manner, and optimize the resulting products as well as create new opportunities in this field.

Maillard Reaction Crosslinked Alginate-Albumin Scaffolds for Enhanced Fenofibrate Delivery to the Retina: A Promising Strategy to Treat RPE-Related Dysfunction

There are limited treatments currently available for retinal diseases such as age-related macular degeneration (AMD). Cell-based therapy holds great promise in treating these degenerative diseases. Three-dimensional (3D) polymeric scaffolds have gained attention for tissue restoration by mimicking the native extracellular matrix (ECM). The scaffolds can deliver therapeutic agents to the retina, potentially overcoming current treatment limitations and minimizing secondary complications. In the present study, 3D scaffolds made up of alginate and bovine serum albumin (BSA) containing fenofibrate (FNB) were prepared by freeze-drying technique. The incorporation of BSA enhanced the scaffold porosity due to its foamability, and the Maillard reaction increased crosslinking degree between ALG with BSA resulting in a robust scaffold with thicker pore walls with a compression modulus of 13.08 KPa suitable for retinal regeneration. Compared with ALG and ALG-BSA physical mixture scaffolds, ALG-BSA conjugated scaffolds had higher FNB loading capacity, slower release of FNB in the simulated vitreous humour and less swelling in water and buffers, and better cell viability and distribution when tested with ARPE-19 cells. These results suggest that ALG-BSA MR conjugate scaffolds may be a promising option for implantable scaffolds for drug delivery and retinal disease treatment.

Effects of Different Drying Methods on the Selenium Bioaccessibility and Antioxidant Activity of Cardamine violifolia

Understanding the effects of drying on the selenium (Se) content and Se bioaccessibility of Se-rich plants is critical to dietary supplementation of Se. The effects of five common drying methods (far-infrared drying (FIRD), vacuum drying (VD), microwave vacuum drying (MVD), hot air drying (HD), and freeze vacuum drying (FD)) on the content and bioaccessibility of Se and Se species in Cardamine violifolia leaves (CVLs) were studied. The content of SeCys₂ in fresh CVLs was the highest (5060.50 μg/g of dry weight (DW)); after FIRD, it had the lowest selenium loss, with a loss rate of less than 19%. Among all of the drying processes, FD and VD samples had the lowest Se retention and bioaccessibility. FIRD, VD, and FD samples have similar effects on antioxidant activity.

An experimental and numerical study of the microstructural and biomechanical properties of human peripheral nerve endoneurium for the design of tissue scaffolds

Biomimetic design of scaffold architectures represents a promising strategy to enable the repair of tissue defects. Natural endoneurium extracellular matrix (eECM) exhibits a sophisticated microstructure and remarkable microenvironments conducive for guiding neurite regeneration. Therefore, the analysis of eECM is helpful to the design of bionic scaffold. Unfortunately, a fundamental lack of understanding of the microstructural characteristics and biomechanical properties of the human peripheral nerve eECM exists. In this study, we used microscopic computed tomography (micro-CT) to reconstruct a three-dimensional (3D) eECM model sourced from mixed nerves. The tensile strength and effective modulus of human fresh nerve fascicles were characterized experimentally. Permeability was calculated from a computational fluid dynamic (CFD) simulation of the 3D eECM model. Fluid flow of acellular nerve fascicles was tested experimentally to validate the permeability results obtained from CFD simulations. The key microstructural parameters, such as porosity is 35.5 ± 1.7%, tortuosity in endoneurium (X axis is 1.26 ± 0.028, Y axis is 1.26 ± 0.020 and Z axis is 1.17 ± 0.03, respectively), tortuosity in pore (X axis is 1.50 ± 0.09, Y axis is 1.44 ± 0.06 and Z axis is 1.13 ± 0.04, respectively), surface area-to-volume ratio (SAVR) is 0.165 ± 0.007 μm^-1 and pore size is 11.8 ± 2.8 μm, respectively. These were characterized from the 3D eECM model and may exert different effects on the stiffness and permeability. The 3D microstructure of natural peripheral nerve eECM exhibits relatively lower permeability (3.10 m² × 10^-12 m²) than other soft tissues. These key microstructural and biomechanical parameters may play an important role in the design and fabrication of intraluminal guidance scaffolds to replace natural eECM. Our findings can aid the development of regenerative therapies and help improve scaffold design.

Integrated bioactive scaffold with aptamer-targeted stem cell recruitment and growth factor-induced pro-differentiation effects for anisotropic meniscal regeneration

Reconstruction of the knee meniscus remains a significant clinical challenge owing to its complex anisotropic tissue organization, complex functions, and limited healing capacity in the inner region. The development of in situ tissue-engineered meniscal scaffolds, which provide biochemical signaling to direct endogenous stem/progenitor cell (ESPC) behavior, has the potential to revolutionize meniscal tissue engineering. In this study, a fiber-reinforced porous scaffold was developed based on aptamer Apt19S-mediated mesenchymal stem cell (MSC)-specific recruitment and dual growth factor (GF)-enhanced meniscal differentiation. The aptamer, which can specifically recognize and recruit MSCs, was first chemically conjugated to the decellularized meniscus extracellular matrix (MECM) and then mixed with gelatin methacrylate (GelMA) to form a photocrosslinkable hydrogel. Second, connective tissue growth factor (CTGF)-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) and transforming growth factor-β3 (TGF-β3)-loaded PLGA microparticles (MPs) were mixed with aptamer-conjugated MECM to simulate anisotropic meniscal regeneration. These three bioactive molecules were delivered sequentially. Apt19S, which exhibited high binding affinity to synovium-derived MSCs (SMSCs), was quickly released to facilitate the mobilization of ESPCs. CTGF incorporated within PLGA NPs was released rapidly, inducing profibrogenic differentiation, while sustained release of TGF-β3 in PLGA MPs remodeled the fibrous matrix into fibrocartilaginous matrix. The in vitro results showed that the sequential release of Apt19S/GFs promoted cell migration, proliferation, and fibrocartilaginous differentiation. The in vivo results demonstrated that the sequential release system of Apt/GF-scaffolds increased neomeniscal formation in rabbit critical-sized meniscectomies. Thus, the novel delivery system shows potential for guiding meniscal regeneration in situ.

Ti64/20Ag Porous Composites Fabricated by Powder Metallurgy for Biomedical Applications

We present a novel Ti64/20Ag highly porous composite fabricated by powder metallurgy for biomedical applications and provide an insight into its microstructure and mechanical proprieties. In this work, the Ti64/20Ag highly porous composites were successfully fabricated by the space holder technique and consolidated by liquid phase sintering, at lower temperatures than the ones used for Ti64 materials. The sintering densification was evaluated by dilatometry tests and the microstructural characterization and porosity features were determined by scanning electron microscopy and computed microtomography. Permeability was estimated by numerical simulations on the 3D real microstructure. Mechanical properties were evaluated by simple compression tests. Densification was achieved by interparticle pore filling with liquid Ag that does not drain to the large pores, with additional densification due to the macroscopical deformation of large pores. Pore characteristics are closely linked to the pore formers and the permeability was highly increased by increasing the pore volume fraction, mainly because the connectivity was improved. As expected, with the increase in porosity, the mechanical properties decreased. These results permitted us to gain a greater understanding of the microstructure and to confirm that we developed a promising Ti64/20Ag composite, showing E of 7.4 GPa, σ_y of 123 MPa and permeability of 3.93 × 10^-11 m². Enhanced adaptability and antibacterial proprieties due to Ag were obtained for bone implant applications.

Influence of Biomimetically Mineralized Collagen Scaffolds on Bone Cell Proliferation and Immune Activation

Collagen, as the main component of connective tissue, is frequently used in various tissue engineering applications. In this study, porous sponge-like collagen scaffolds were prepared by freeze-drying and were then mineralized in a simulated body fluid. The mechanical stability was similar in both types of scaffolds, but the mineralized scaffolds (MCS) contained significantly more calcium, magnesium and phosphorus than the unmineralized scaffolds (UCS). Although the MCS contained a lower percentage (~32.5%) of pores suitable for cell ingrowth (113–357 μm in diameter) than the UCS (~70%), the number of human-osteoblast-like MG-63 cells on days 1, 3 and 7 after seeding was higher on MCS than on UCS, and the cells penetrated deeper into the MCS. The cell growth in extracts prepared by eluting the scaffolds for 7 days in a cell culture medium was also markedly higher in the MCS extracts, as indicated by real-time monitoring in the sensory xCELLigence system for 7 days. From this point of view, MCS are more promising for bone tissue engineering than UCS. However, MCS evoked a more pronounced inflammatory response than UCS, as indicated by the production of tumor necrosis factor-alpha (TNF-α) in macrophage-like RAW 264.7 cells in cultures on these scaffolds.

Effects of the 3D Geometry Reconstruction on the Estimation of 3D Porous Scaffold Permeability. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2021;2021:4403-4407. [PMID: 34892196 DOI: 10.1109/embc46164.2021.9629664] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

3D scaffolds for tissue engineering typically need to adopt a dynamic culture to foster cell distribution and survival throughout the scaffold. It is, therefore, crucial to know fluids' behavior inside the scaffold architecture, especially for complex porous ones. Here we report a comparison between simulated and measured permeability of a porous 3D scaffold, focusing on different modeling parameters. The scaffold features were extracted by microcomputed tomography (µCT) and representative volume elements were used for the computational fluid-dynamic analyses. The objective was to investigate the sensitivity of the model to the degree of detail of the µCT image and the elements of the mesh. These findings highlight the pros and cons of the modeling strategy adopted and the importance of such parameters in analyzing fluid behavior in 3D scaffolds.

Biomimetic Graphene/Spongin Scaffolds for Improved Osteoblasts Bioactivity via Dynamic Mechanical Stimulation

Biomimetics offers excellent prospects for design a novel generation of improved biomaterials. Here the controlled integration of graphene oxide (GO) derivatives with a 3D marine spongin (MS) network is explored to nanoengineer novel smart bio-based constructs for bone tissue engineering. The results point out that 3D MS surfaces can be homogeneously coated by layer-by-layer (LbL) assembly of oppositely charged polyethyleneimine (PEI) and GO. Notably, the GOPEI@MS bionanocomposites present a high structural and mechanical stability under compression tests in wet conditions (shape memory). Dynamic mechanically (2 h of sinusoidal compression cyclic interval (0.5 Hz, 0-10% strain)/14 d) stimulates GOPEI@MS seeded with osteoblast (MC3T3-E1), shows a significant improvement in bioactivity, with cell proliferation being two times higher than under static conditions. Besides, the dynamic assays show that GOPEI@MS bionanocomposites are able to act as mechanical stimulus-responsive scaffolds able to resemble physiological bone extracellular matrix (ECM) requirements by strongly triggering mineralization of the bone matrix. These results prove that the environment created by the system cell-GOPEI@MS is suitable for controlling the mechanisms regulating mechanical stimulation-induced cell proliferation for potential in vivo experimentation.

Differences in platelet-rich plasma composition influence bone healing

AIM

Platelet-rich plasma (PRP) is an autologous blood-derived material that has been used to enhance bone regeneration. Clinical studies, however, reported inconsistent outcomes. This study aimed to assess the effect of changes in leucocyte and PRP (L-PRP) composition on bone defect healing.

MATERIALS AND METHODS

L-PRPs were prepared using different centrifugation methods and their regenerative potential was assessed in an in-vivo rat model. Bilateral critical-size tibial bone defects were created and filled with single-spin L-PRP, double-spin L-PRP, or filtered L-PRP. Empty defects and defects treated with collagen scaffolds served as controls. Rats were euthanized after 2 weeks, and their tibias were collected and analysed using micro-CT and histology.

RESULTS

Double-spin L-PRP contained higher concentrations of platelets than single-spin L-PRP and filtered L-PRP. Filtration of single-spin L-PRP resulted in lower concentrations of minerals and metabolites. In vivo, double-spin L-PRP improved bone healing by significantly reducing the size of bone defects (1.08 ± 0.2 mm³ ) compared to single-spin L-PRP (1.42 ± 0.27 mm³ ) or filtered L-PRP (1.38 ± 0.28 mm³ ). There were fewer mast cells, lymphocytes, and macrophages in defects treated with double-spin L-PRP than in those treated with single-spin or filtered L-PRP.

CONCLUSION

The preparation method of L-PRP affects their composition and potential to regenerate bone.

Chitosan scaffolds with enhanced mechanical strength and elastic response by combination of freeze gelation, photo-crosslinking and freeze-drying

In this study, a new scaffold fabrication method based on the combination of a series of stabilization processes was set up to obtain chitosan scaffolds with improved mechanical properties for regeneration of load-bearing tissues. Specifically, thermally induced phase separation (TIPS) of chitosan solutions was used to obtain an open structure which was then stabilized by freeze-gelation and photo cross-linking. Freeze-gelation combined with freeze-drying permitted to obtain a porous structure with a 95 μm-mean pore size suitable for osteoblast cells' housing. Photo-crosslinking improved by ca. three times the scaffold compressive modulus, passing from 0,8 MPa of the uncrosslinked scaffolds to 2,2 MPa of the crosslinked one. Hydrated crosslinked scaffolds showed a good elastic response, with an 80% elastic recovery for at least 5 consecutive compressive cycles. The herein reported method has the advantage to not require the use of potentially toxic cross-linking agents and may be extended to other soft materials.

Influence of chemical treatment and drying method on the properties of cellulose fibers of luffa sponge

The exploration of modified luffa sponge (LS) cellulose fiber in the field of polymer composite can contribute to the development of high-performance and lightweight composites. In this study, two chemical treatments (10%NaOH-20%CH₃COOH (Method 1) and 10%NaOH-5%Na₂SO₃ (Method 2)) and two drying methods (air drying and freeze-drying) were used to treat LS. The microscopic characteristics and physical properties showed that Methods 1 and 2 caused shrinkage of the LS fibers and increased their fiber density by 30.6% and 15.0%. Meanwhile, freeze-drying kept the cells of modified LS fibers full and decreased their fiber density by 5.0% and 21.0%, respectively. The tensile properties test analyses indicated that freeze-drying further increased the elongation at break values of modified LS fibers by 25.3% and 17.7%, respectively. The moisture absorption analyses showed that freeze-drying could further decrease the moisture absorption ratios of modified LS fibers by 25.8% and 35.8%, respectively, which was useful for improving the dimensional stability of composite materials. Moreover, the thermogravimetric analysis reveals that freeze-drying increased onset degradation temperatures of the modified fibers by 24.0 °C and 6.7 °C, which was beneficial to improve the thermal stability of the composite material.

Functionalisation of a heat-derived and bio-inert albumin hydrogel with extracellular matrix by air plasma treatment

Albumin-based hydrogels are increasingly attractive in tissue engineering because they provide a xeno-free, biocompatible and potentially patient-specific platform for tissue engineering and drug delivery. The majority of research on albumin hydrogels has focused on bovine serum albumin (BSA), leaving human serum albumin (HSA) comparatively understudied. Different gelation methods are usually employed for HSA and BSA, and variations in the amino acid sequences of HSA and BSA exist; these account for differences in the hydrogel properties. Heat-induced gelation of aqueous HSA is the easiest method of synthesizing HSA hydrogels however hydrogel opacity and poor cell attachment limit their usefulness in downstream applications. Here, a solution to this problem is presented. Stable and translucent HSA hydrogels were created by controlled thermal gelation and the addition of sodium chloride. The resulting bio-inert hydrogel was then subjected to air plasma treatment which functionalised its surface, enabling the attachment of basement membrane matrix (Geltrex). In vitro survival and proliferation studies of foetal human osteoblasts subsequently demonstrated good biocompatibility of functionalised albumin hydrogels compared to untreated samples. Thus, air plasma treatment enables functionalisation of inert heat-derived HSA hydrogels with extracellular matrix proteins and these may be used as a xeno-free platform for biomedical research or cell therapy.

Valorization of marine-derived biowaste to develop chitin/fish gelatin products as bioactive carriers and moisture scavengers

Marine-derived biowaste was valorized to develop chitin/fish gelatin porous materials with the aim of being used as moisture scavengers and bioactive carriers. Chitin was extracted from squid pens, abundant and available biowastes from fishery industry, through a sustainable process and the environmental assessment was carried out. Besides the valorization of biowaste, it is worth noting that the use of this specific biowaste allows the avoidance of discoloration and demineralization processes to extract chitin and, thus, a lower consumption of resources, both chemicals and energy, in comparison to the conventional chitin extraction from crustacean shells. Consequently, this alternative source of chitin brings economic and environmental benefits. In addition to the reduction of food waste disposal, the incorporation of squid pen-extracted chitin into fish gelatin formulations led to the conversion of a biowaste into a value-added product. In this regard, chitin was employed as a reinforcing agent in order to improve the mechanical behavior of fish gelatin materials. It is worth noting that good compatibility between gelatin and chitin was achieved since no chitin aggregation was observed. Furthermore, more defined pores were obtained after chitin addition. Additionally, tetrahydrocurcumin was incorporated into the formulation as a bioactive and its release was analyzed during three days. It was observed that samples prepared with chitin and THC showed potential as active porous materials for bioactive delivery.

Albumin-Enriched Fibrin Hydrogel Embedded in Active Ferromagnetic Networks Improves Osteoblast Differentiation and Vascular Self-Organisation

Porous coatings on prosthetic implants encourage implant fixation. Enhanced fixation may be achieved using a magneto-active porous coating that can deform elastically in vivo on the application of an external magnetic field, straining in-growing bone. Such a coating, made of 444 ferritic stainless steel fibres, was previously characterised in terms of its mechanical and cellular responses. In this work, co-cultures of human osteoblasts and endothelial cells were seeded into a novel fibrin-based hydrogel embedded in a 444 ferritic stainless steel fibre network. Albumin was successfully incorporated into fibrin hydrogels improving the specific permeability and the diffusion of fluorescently tagged dextrans without affecting their Young’s modulus. The beneficial effect of albumin was demonstrated by the upregulation of osteogenic and angiogenic gene expression. Furthermore, mineralisation, extracellular matrix production, and formation of vessel-like structures were enhanced in albumin-enriched fibrin hydrogels compared to fibrin hydrogels. Collectively, the results indicate that the albumin-enriched fibrin hydrogel is a promising bio-matrix for bone tissue engineering and orthopaedic applications.

An electrochemically deposited collagen wound matrix combined with adipose-derived stem cells improves cutaneous wound healing in a mouse model of type 2 diabetes

Chronic wounds complicated by diabetes are a significant clinical issue, and their occurrence is expected to continue to rise due to an increased prevalence of diabetes mellitus, especially type 2 diabetes. Diabetic wounds frequently lead to nonhealing ulcers, and often eventually result in limb amputation due to the high risk of infection of the chronic wound. Here, we present a tissue-engineered treatment that combines a novel electrochemically deposited collagen wound matrix and human adipose-derived stem cells. The matrix fabrication process is optimized for voltage and time, and the final collagen biomaterial is thoroughly characterized. This collagen material possesses high tensile strength, high porosity, and excellent biocompatibility and cellular proliferation capabilities. Human adipose-derived stem cells were seeded onto the collagen wound matrix and this construct is investigated in a full thickness excisional wound in a mouse model of type 2 diabetes. This novel treatment is shown to stimulate excellent healing and tissue regeneration, resulting in increased granulation tissue formation, epidermal thickness, and overall higher quality tissue reformation. Both the collagen wound matrix alone and collagen wound matrix in combination with adipose derived stem cells appeared to be excellent treatments for diabetic skin wounds, and in the future can also be optimized to treat other injuries such as burns, blast injuries, surgical incisions, and other traumatic injuries.

Topotactic Fibrillogenesis of Freeze-Cast Microridged Collagen Scaffolds for 3D Cell Culture

Type I collagen is the main component of the extracellular matrix (ECM). In vitro, under a narrow window of physicochemical conditions, type I collagen self-assembles to form complex supramolecular architectures reminiscent of those found in native ECM. Presently, a major challenge in collagen-based biomaterials is to couple the delicate collagen fibrillogenesis events with a controlled shaping process in non-denaturating conditions. In this work, an ice-templating approach promoting the structuration of collagen into macroporous monoliths is used. Instead of common solvent removal procedures, a new topotactic conversion approach yielding self-assembled ordered fibrous materials is implemented. These collagen-only, non-cross-linked scaffolds exhibit uncommon mechanical properties in the wet state, with a Young's modulus of 33 ± 12 kPa, an ultimate tensile stress of 33 ± 6 kPa, and a strain at failure of 105 ± 28%. With the help of the ice-patterned microridge features, normal human dermal fibroblasts and C2C12 murine myoblasts successfully migrate and form highly aligned populations within the resulting three-dimensional (3D) collagen scaffolds. These results open a new pathway to the development of new tissue engineering scaffolds ordered across various organization levels from the molecule to the macropore and are of particular interest for biomedical applications where large-scale 3D cell alignment is needed such as for muscular or nerve reconstruction.

Fabrication of hierarchically porous silk fibroin-bioactive glass composite scaffold via indirect 3D printing: Effect of particle size on physico-mechanical properties and in vitro cellular behavior

In order to regenerate bone defects, bioactive hierarchically scaffolds play a key role due to their multilevel porous structure, high surface area, enhanced nutrient transport and diffusion. In this study, novel hierarchically porous silk fibroin (SF) and silk fibroin-bioactive glass (SF-BG) composite were fabricated with controlled architecture and interconnected structure, by combining indirect three-dimensional (3D) inkjet printing and freeze-drying methods. Further, the effect of 45S5 Bioactive glass particles of different sizes (<100 nm and 6 μm) on mechanical strength and cell behavior was investigated. The results demonstrated that the hierarchical structure in this scaffold was composed of two levels of pores in the order of 500-600 μm and 10-50 μm. The prepared SF-BG composite scaffolds utilized by nano and micro particles possessed mechanical properties with a compressive strength of 0.94 and 1.2 MPa, respectively, in dry conditions. In a wet condition, the hierarchically porous scaffolds did not exhibit any fluctuation after compression load cell and were incredibly flexible, with excellent mechanical stability. The SF-BG composite scaffold with nanoparticles presented a significant 50% increase in attachment of human bone marrow stem cells in comparison with SF and SF-BG scaffold with microparticles. Moreover, SF-BG scaffolds promoted alkaline phosphatase activity as compared to SF scaffolds without BG particles on day 14. In brief, the 3D porous silk fibroin-based composites containing BG nanoparticles with excellent mechanical properties are promising scaffolds for bone tissue regeneration in high load-bearing applications.

Effect of Drying Methods on the Microstructure, Bioactivity Substances, and Antityrosinase Activity of Asparagus Stems

The impacts of vacuum drying (VD), far-infrared drying (FIRD), hot air drying (HAD), and freeze drying (FD), as representative food drying methods, on structural characterization, bioactive substances, and antityrosinase activity of Asparagus have been assessed. The microstructure characterization by scanning electron microscopy indicated that VD treatment led to serious breaking of the vascular bundle and epithelial cells and provided higher free polyphenol (FP) and bound polyphenol (BP) contents. Besides, the smaller individual molecule (weight and hydroxy and phenolic rings) polyphenols bound to cellulose to a lesser extent than larger molecules, i.e., rutin and quercetin. In contrast, FD extracts possessed lower polyphenol contents but higher saponin and chlorophyll contents. The antityrosinase activity inhibition rates of FD and VD extracts were higher than those of FIRD and HAD for both mono- and diphenolase. The FP extract of VD, which possessed more polyphenolic compounds, had greater antityrosinase activity than BP.

A Facile Approach to Fabricate Dual Purpose Hybrid Materials for Tissue Engineering and Water Remediation

Creating hybrid materials with multifunctionality and robust mechanical stability from natural resources is a challenging proposition in materials science. Here, we report the scalable synthesis of hybrid collagen scaffolds using collagen extracted from leather industry wastes and sago starch derived from agro-industry. The hybrid scaffolds were incorporated with TiO2 nanoparticles and cross-linked with oxidized sago starch. The biocompatibility, thermal stability and antimicrobial property of hybrid scaffold enabled its application in burn wound healing demonstrated through albino rat models. The highly porous hybrid scaffolds are shown to be super-compressible, which is typically forbidden in materials of biological origin. We demonstrate that the hybrid scaffolds concurrently display both adsorption and absorption behavior in the removal of oil and dye molecules, respectively from contaminated water. This study paves the way for the development of novel multifunctional and shape recoverable hybrid materials specifically from renewable resources.

Investigation of the intrinsic permeability of ice-templated collagen scaffolds as a function of their structural and mechanical properties

Collagen scaffolds are widely used in a range of tissue engineering applications, both in vitro and in vivo, where their permeability to fluid flow greatly affects their mechanical and biological functionality. This paper reports new insights into the interrelationships between permeability, scaffold structure, fluid pressure and deformation in collagen scaffolds, focussing in particular on the degree of closure and the alignment of the pores. Isotropic and aligned scaffolds of different occlusivity were produced by ice templating, and were characterised in terms of their structure and mechanical properties. Permeability studies were conducted using two experimental set-ups to cover a wide range of applied fluid pressures. The permeability was found to be constant at low pressures for a given scaffold with more open structures and aligned structures being more permeable. The deformation of scaffolds under high pressure led to a decrease in permeability. The aligned structures were more responsive to deformation than their isotropic equivalents with their permeability falling more quickly at low strain. For isotropic samples, a broad (1 - ɛ)² dependence for permeability was observed with the constant of proportionality varying with collagen fraction as the starting structures became more occluded. Aligned scaffolds did not follow the same behaviour, with the pores apparently closing more quickly in response to early deformation. These results highlight the importance of scaffold structure in determining permeability to interstitial fluid, and provide an understanding of scaffold behaviour within the complex mechanical environment of the body. STATEMENT OF SIGNIFICANCE: Collagen scaffolds are widely used in tissue engineering applications, for instance to contribute with wound healing. Their permeability to fluid flow, such as water and blood, is important to ensure they perform efficiently when inside the body. The present study reports new insights into the relationships between permeability, scaffold structure, fluid pressure and deformation in collagen scaffolds. It presents in particular the experimental setups used to measure these properties and the result of comparisons between collagen scaffolds with different structures: aligned and isotropic (non-aligned). It indicates quantitative differences in terms of permeability, and the effects of compression on such permeability. The results contribute to the development and understanding of collagen scaffolds and their applications.

Biomimetic sponges for regeneration of skeletal muscle following trauma

Skeletal muscle is inept in regenerating after traumatic injuries due to significant loss of basal lamina and the resident satellite cells. To improve regeneration of skeletal muscle, we have developed biomimetic sponges composed of collagen, gelatin, and laminin (LM)-111 that were crosslinked with 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC). Collagen and LM-111 are crucial components of the muscle extracellular matrix and were chosen to impart bioactivity whereas gelatin and EDC were used to provide mechanical strength to the scaffold. Morphological and mechanical evaluation of the sponges showed porous structure, water-retention capacity and a compressive modulus of 590-808 kPa. The biomimetic sponges supported the infiltration and viability of C₂ C₁₂ myoblasts over 5 days of culture. The myoblasts produced higher levels of myokines such as VEGF, IL-6, and IGF-1 and showed higher expression of myogenic markers such as MyoD and myogenin on the biomimetic sponges. Biomimetic sponges implanted in a mouse model of volumetric muscle loss (VML) supported satellite, endothelial, and inflammatory cell infiltration but resulted in limited myofiber regeneration at 2 weeks post-injury. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 92-103, 2019.

Collagen-silica bio-composite enriched with Cynodon dactylon extract for tissue repair and regeneration

Development of biomaterials for tissue engineering applications is of great interest to meet the demand of different clinical requirements. The wound heal dressing biomaterials should necessarily contain well-defined therapeutic components and desirable physical, chemical and biological properties to support optimal delivery of therapeutics at the site of the wound. In this study, we developed collagen-silica wound heal scaffold incorporated with the extract of Cynodon dactylon, characterized and evaluated for its wound heal potential in vitro and in vivo against collagen (Col) and Collagen-silica (CS) scaffolds that served as controls. The prepared Collagen-Silica-Cynodon extract (CSCE) scaffold exhibits porous morphology with preferable biophysical, chemical, mechanical and mass transfer properties besides its controlled biodegradation at the wound site. Stability of CSCE was found to be better than that of native collagen due to intermolecular interactions between collagen and constituents of C. dactylon as confirmed by FTIR analysis. Notably, in vitro biocompatibility assay using DAPI and Rhodamine 123 staining demonstrated that the proliferation of NIH3T3 fibroblast cells was better for CSCE when compared to the Col and CS scaffolds. In vivo wound healing experiments with full-thickness excision wounds in wistar rat model demonstrated that the wounds treated with CSCE showed accelerated healing with enhanced collagen deposition when compared to wounds treated with Col and CS scaffolds, and these studies substantiated the efficacy of CSCE scaffold for treating wounds.

Development of a Graphene Oxide-Incorporated Polydimethylsiloxane Membrane with Hexagonal Micropillars

Several efforts have been made on the development of bioscaffolds including the polydimethylsiloxane (PDMS) elastomer for supporting cell growth into stable sheets. However, PDMS has several disadvantages, such as intrinsic surface hydrophobicity and mechanical strength. Herein, we generated a novel PDMS-based biomimetic membrane by sequential modifications of the PMDS elastomer with graphene oxide (GO) and addition of a hexagonal micropillar structure at the bottom of the biomembrane. GO was initially homogenously mixed with pure PDMS and then was further coated onto the upper surface of the resultant PDMS. The elastic modulus and hydrophilicity were significantly improved by such modifications. In addition, the development of hexagonal micropillars with smaller diameters largely improved the ion permeability and increased the motion resistance. We further cultured retinal pigment epithelial (RPE) cells on the surface of this modified PDMS biomembrane and assayed its biocompatibility. Remarkably, the GO incorporation and coating exhibited beneficial effect on the cell growth and the new formation of tight junctions in RPE cells. Taken together, this GO-modified PDMS scaffold with polyhexagonal micropillars may be utilized as an ideal cell sheet and adaptor for cell cultivation and can be used in vivo for the transplantation of cells such as RPE cells.

3D-printing porosity: A new approach to creating elevated porosity materials and structures

We introduce a new process that enables the ability to 3D-print high porosity materials and structures by combining the newly introduced 3D-Painting process with traditional salt-leaching. The synthesis and resulting properties of three 3D-printable inks comprised of varying volume ratios (25:75, 50:50, 70:30) of CuSO₄ salt and polylactide-co-glycolide (PLGA), as well as their as-printed and salt-leached counterparts, are discussed. The resulting materials are comprised entirely of PLGA (F-PLGA), but exhibit porosities proportional to the original CuSO₄ content. The three distinct F-PLGA materials exhibit average porosities of 66.6-94.4%, elastic moduli of 112.6-2.7 MPa, and absorbency of 195.7-742.2%. Studies with adult human mesenchymal stem cells (hMSCs) demonstrated that elevated porosity substantially promotes cell adhesion, viability, and proliferation. F-PLGA can also act as carriers for weak, naturally or synthetically-derived hydrogels. Finally, we show that this process can be extended to other materials including graphene, metals, and ceramics.

STATEMENT OF SIGNIFICANCE

Porosity plays an essential role in the performance and function of biomaterials, tissue engineering, and clinical medicine. For the same material chemistry, the level of porosity can dictate if it is cell, tissue, or organ friendly; with low porosity materials being far less favorable than high porosity materials. Despite its importance, it has been difficult to create three-dimensionally printed structures that are comprised of materials that have extremely high levels of internal porosity yet are surgically friendly (able to handle and utilize during surgical operations). In this work, we extend a new materials-centric approach to 3D-printing, 3D-Painting, to 3D-printing structures made almost entirely out of water-soluble salt. The structures are then washed in a specific way that not only extracts the salt but causes the structures to increase in size. With the salt removed, the resulting medical polymer structures are almost entirely porous and contain very little solid material, but the maintain their 3D-printed form and are highly compatible with adult human stem cells, are mechanically robust enough to use in surgical manipulations, and can be filled with and act as carriers for biologically active liquids and gels. We can also extend this process to three-dimensionally printing other porous materials, such as graphene, metals, and even ceramics.

Dry versus hydrated collagen scaffolds: are dry states representative of hydrated states?

Collagen composite scaffolds have been used for a number of studies in tissue engineering. The hydration of such highly porous and hydrophilic structures may influence mechanical behaviour and porosity due to swelling. The differences in physical properties following hydration would represent a significant limiting factor for the seeding, growth and differentiation of cells in vitro and the overall applicability of such hydrophilic materials in vivo. Scaffolds based on collagen matrix, poly(DL-lactide) nanofibers, calcium phosphate particles and sodium hyaluronate with 8 different material compositions were characterised in the dry and hydrated states using X-ray microcomputed tomography, compression tests, hydraulic permeability measurement, degradation tests and infrared spectrometry. Hydration, simulating the conditions of cell seeding and cultivation up to 48 h and 576 h, was found to exert a minor effect on the morphological parameters and permeability. Conversely, hydration had a major statistically significant effect on the mechanical behaviour of all the tested scaffolds. The elastic modulus and compressive strength of all the scaffolds decreased by ~95%. The quantitative results provided confirm the importance of analysing scaffolds in the hydrated rather than the dry state since the former more precisely simulates the real environment for which such materials are designed.

Effect of Rotation on Scaffold Motion and Cell Growth in Rotating Bioreactors

Efficient use of different bioreactor designs to improve cell growth in three-dimensional scaffolds requires an understanding of their mechanism of action. To address this for rotating wall vessel bioreactors, fluid and scaffold motion were investigated experimentally at different rotation speeds and vessel fill volumes. Low cost bioreactors with single and dual axis rotation were developed to investigate the effect of these systems on human osteoblast proliferation in free floating and constrained collagen-glycosaminoglycan porous scaffolds. A range of scaffold motions (free fall, periodic oscillation, and orbital motion) were observed at the rotation speeds and vessel fluid/air ratios used, with 85% fluid fill and an outer vessel wall velocity of ∼14 mm s⁻¹ producing a scaffold in a free fall state. The cell proliferation results showed that after 14 and 21 days of culture, this combination of fluid fill and speed of rotation produced significantly greater cell numbers in the scaffolds than when lower or higher rotation speeds (p < 0.002) or when the chamber was 60% or 100% full (p < 0.01). The fluid flow and scaffold motion experiments show that biaxial rotation would not improve the mass transfer of medium into the scaffold as the second axis of rotation can only transition the scaffold toward oscillatory or orbital motion and, hence, reduce mass transport to the scaffold. The cell culture results confirmed that there was no benefit to the second axis of rotation with no significant difference in cell proliferation either when the scaffolds were free floating or constrained (p > 0.05).

Development of collagen/polydopamine complexed matrix as mechanically enhanced and highly biocompatible semi-natural tissue engineering scaffold

To improve the mechanical properties and biocompatibility of collagen I matrix, a novel and facile strategy was developed to modify porcine acellular dermal matrix (PADM) via dopamine self-polymerization followed by collagen immobilization to enhance the biological, mechanical and physicochemical properties of PADM. Mechanism study indicated that the polymerization of dopamine onto PADM surface could be regulated by controlling the amount of hydrogen bonds forming between phenol hydroxyl (COH) and nitrogen atom (NCO) within collagen fibers of PADM. The investigations of surface interactions between PDA and PADM illustrated that PDA-PADM system yielded better mechanical properties, thermal stability, surface hydrophilicity and the structural integrity of PADM was maintained after dopamine coating. Furthermore, collagen (COL) was immobilized onto the fresh PDA-PADM to fabricate the collagen-PDA-PADM (COL-PDA-PADM) complexed scaffold. The MTT assay and CLSM observation showed that COL-PDA-PADM had better biocompatibility and higher cellular attachment than pure PADM and COL-PADM without dopamine coating, thus demonstrating the efficacy of PDA as the intermediate layer. Meanwhile, the expression of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) of COL-PDA-PADM were investigated by an in vivo study. The results revealed that COL-PDA-PADM could effectively promote bFGF and VEGF expression, possibly leading to enhancing the dura repairing process. Overall, this work contributed a new insight into the development of a semi-natural tissue engineering scaffold with high biocompatibility and good mechanical properties.

STATEMENT OF SIGNIFICANCE

Obtaining scaffolds with high biocompatibility and good mechanical properties is still one of the most challenging issues in tissue engineering. To have excellent in vitro and in vivo performance, scaffolds are desired to have similar mechanical and biological properties as the natural extracellular matrix, such as collagen based matrix. Utilizing the surface self-crosslinking and coating strategy, we successfully obtained a novel semi-natural platform with excellent biological and mechanical properties from porcine acellular dermal matrix (PADM), polydopamine and collagen. The results confirmed that this scaffold platform has very excellent cellular performance and very little toxicity/side effects in vivo. Therefore, this semi-natural scaffold may be an appropriate platform for tissue engineering and this strategy would further help to develop more robust scaffolds.