Development of 3D-Printed Collagen Scaffolds with In-Situ Synthesis of Silver Nanoparticles

UV-irradiation method has grown as an alternative approach to in situ synthetize silver nanoparticles (AgNPs) for avoiding the use of toxic reducing agents. In this work, an antimicrobial material by in situ synthesizing AgNPs within 3D-printed collagen-based scaffolds (Col-Ag) was developed. By modifying the concentration of AgNO₃ (0.05 and 0.1 M) and UV irradiation time (2 h, 4 h, and 6 h), the morphology and size of the in situ prepared AgNPs could be controlled. As a result, star-like silver particles of around 23 ± 4 μm and spherical AgNPs of 220 ± 42 nm were obtained for Ag 0.05 M, while for Ag 0.1 M cubic particles from 0.3 to 1.0 μm and round silver precipitates of 3.0 ± 0.4 μm were formed in the surface of the scaffolds at different UV irradiation times. However, inside the material AgNPs of 10-28 nm were obtained. The DSC thermal analysis showed that a higher concentration of Ag stabilizes the 3D-printed collagen-based scaffolds, while a longer UV irradiation interval produces a decrease in the denaturation temperature of collagen. The enzymatic degradation assay also revealed that the in situ formed AgNPs act as stabilizing and reinforcement agent which also improve the swelling capacity of collagen-based material. Finally, antimicrobial activity of Col-Ag was studied, showing high bactericidal efficiency against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria. These results showed that the UV irradiation method was really attractive to modulate the size and shape of in situ synthesized AgNPs to develop antimicrobial 3D-printed collagen scaffolds with different thermal, swelling and degradation properties.

Fabrication of biologically inspired electrospun collagen/silk fibroin/bioactive glass composited nanofibrous to accelerate the treatment efficiency of wound repair

A triple-layer matrix Collagen/Silk fibroin/Bioactive glass composited Nanofibrous was fabricated by linking electrospinning and freeze-drying systems, this typical three layered composite with a nanofibrous fragment as the key (top) layer, middle portion as inferior, and a spongy porous fragment as the third (bottom) deposit to develop the synergistic effect of composite materials resultant to physical and biological performances. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy were used to assess the final material's physicochemical properties (SEM). The triple-layer matrix had a nanofibrous and porous structure, which has qualities including high porosity, swelling, and stability, which are important in soft-tissue engineering. NIH 3 T3 fibroblast and humanoid keratinocyte (HaCaT) cell lines were also used to investigate the matrix's in vitro biological and fluorescent capabilities, which showed excellent cell adherence and proliferation across the composite layers. The synergistic arrangement of nanofibrous substantial deposition onto collagenous with silk fibroin candidates has therefore proven effective in the construction of a tri-layer matrix for skin-tissue-engineering applications.

Design of a New 3D Gelatin-Alginate Scaffold Loaded with Cannabis sativa Oil

There is an increasing medical need for the development of new materials that could replace damaged organs, improve healing of critical wounds or provide the environment required for the formation of a new healthy tissue. The three-dimensional (3D) printing approach has emerged to overcome several of the major deficiencies of tissue engineering. The use of Cannabis sativa as a therapy for some diseases has spread throughout the world thanks to its benefits for patients. In this work, we developed a bioink made with gelatin and alginate that was able to be printed using an extrusion 3D bioprinter. The scaffolds obtained were lyophilized, characterized and the swelling was assessed. In addition, the scaffolds were loaded with Cannabis sativa oil extract. The presence of the extract provided antimicrobial and antioxidant activity to the 3D scaffolds. Altogether, our results suggest that the new biocompatible material printed with 3D technology and with the addition of Cannabis sativa oil could become an attractive alternative to common treatments of soft-tissue infections and wound repair.

Facile synthesis of biogenic silica nanomaterial loaded transparent tragacanth gum hydrogels with improved physicochemical properties and inherent anti-bacterial activity

In this report, biogenic, crystalline (∼60.5 ± 2%) bowknot structured silica nanoparticles (BSNPs) of length ∼ 274 ± 7 nm and width ∼ 36 ± 2 nm were isolated from invasive species viz. Lantana camara. These were then chemically modified using nitrogen containing moieties viz. APTES and CTAB. These modified BSNPs were then used as electrostatic cross-linking agents for the formation of tragacanth gum (TG) hydrogels. The cytocompatible CTAB@BSNP-TG hydrogels documented ∼10-12 fold enhancement in anti-bacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa when compared with TG hydrogels. Disruption of the bacterial membrane by ROS generation and protein leakage were responsible for anti-bacterial activity. A cell migration assay suggested that CTAB@BSNP-TG augmented the cell proliferation of NIH-3T3 cells compared to other TG hydrogels. The present study will pave the path for the development of organic-inorganic hybrid nanocomposite-based hydrogels for anti-bacterial and cell migration applications.

The 3D Bioprinted Scaffolds for Wound Healing

Skin tissue engineering and regeneration aim at repairing defective skin injuries and progress in wound healing. Until now, even though several developments are made in this field, it is still challenging to face the complexity of the tissue with current methods of fabrication. In this review, short, state-of-the-art on developments made in skin tissue engineering using 3D bioprinting as a new tool are described. The current bioprinting methods and a summary of bioink formulations, parameters, and properties are discussed. Finally, a representative number of examples and advances made in the field together with limitations and future needs are provided.

Collagen Hydrogels Loaded with Silver Nanoparticles and Cannabis Sativa Oil

Wounds represent a major healthcare problem especially in hospital-associated infections where multi-drug resistant strains are often involved. Nowadays, biomaterials with therapeutic molecules play an active role in wound healing and infection prevention. In this work, the development of collagen hydrogels loaded with silver nanoparticles and Cannabis sativa oil extract is described. The presence of the silver nanoparticles gives interesting feature to the biomaterial such as improved mechanical properties or resistance to collagenase degradation but most important is the long-lasting antimicrobial effect. Cannabis sativa oil, which is known for its anti-inflammatory and analgesic effects, possesses antioxidant activity and successfully improved the biocompatibility and also enhances the antimicrobial activity of the nanocomposite. Altogether, these results suggest that this novel nanocomposite biomaterial is a promising alternative to common treatments of wound infections and wound healing.

Colonization versus encapsulation in cell-laden materials design: porosity and process biocompatibility determine cellularization pathways

Seeding materials with living cells has been-and still is-one of the most promising approaches to reproduce the complexity and the functionality of living matter. The strategies to associate living cells with materials are limited to cell encapsulation and colonization, however, the requirements for these two approaches have been seldom discussed systematically. Here we propose a simple two-dimensional map based on materials' pore size and the cytocompatibility of their fabrication process to draw, for the first time, a guide to building cellularized materials. We believe this approach may serve as a straightforward guideline to design new, more relevant materials, able to seize the complexity and the function of biological materials. This article is part of the theme issue 'Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 1)'.

Stimuli-responsive engineered living materials

Stimuli-responsive materials are able to undergo controllable changes in materials properties in response to external cues. Increasing efforts have been directed towards building materials that mimic the responsive nature of biological systems. Nevertheless, limitations remain surrounding the way these synthetic materials interact and respond to their environment. In particular, it is difficult to synthesize synthetic materials that respond with specificity to poorly differentiated (bio)chemical and weak physical stimuli. The emerging area of engineered living materials (ELMs) includes composites that combine living cells and synthetic materials. ELMs have yielded promising advances in the creation of stimuli-responsive materials that respond with diverse outputs in response to a broad array of biochemical and physical stimuli. This review describes advances made in the genetic engineering of the living component and the processing-property relationships of stimuli-responsive ELMs. Finally, the implementation of stimuli-responsive ELMs as environmental sensors, biomedical sensors, drug delivery vehicles, and soft robots is discussed.

Fabrication of Biohybrid Cellulose Acetate-Collagen Bilayer Matrices as Nanofibrous Spongy Dressing Material for Wound-Healing Application

Tissue engineering is currently one the fastest growing engineering fields, requiring fabrication of advanced and multifunctional materials to be used as scaffolds or dressing for tissue regeneration. In this work, a bilayer matrix was fabricated by electrospinning of a hybrid cellulose acetate nanofibers (CA) containing bioactive latex or Ciprofloxacin over highly interconnected collagen (CSPG) 3D matrix previously obtained by a freeze-drying process. The bilayer matrix was fabricated with a nanofibrous part as the primary (top) layer and a spongy porous part as the secondary (bottom) layer by combining electrospinning and freeze-drying techniques to enhance the synergistic effect of both materials corresponding to physical and biological properties. The final material was physicochemically characterized using Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The bilayer matrix exhibited nanofibrous and 3D porous structure with properties such as high porosity, swelling, and stability required for soft-tissue-engineering applications. Furthermore, the in vitro biological and fluorescence properties of the matrix were tested against NIH 3T3 fibroblast and human keratinocyte (HaCaT) cell lines and showed good cell adhesion and proliferation over the bilayer matrix. Thus, the synergistic combination of nanofibrous material deposition onto to the collagenous porous material has proved efficient in the fabrication of a bilayer matrix for skin-tissue-engineering applications.

Comprehensive Assessment of Nile Tilapia Skin (Oreochromis niloticus) Collagen Hydrogels for Wound Dressings

Collagen plays an important role in the formation of extracellular matrix (ECM) and development/migration of cells and tissues. Here we report the preparation of collagen and collagen hydrogel from the skin of tilapia and an evaluation of their potential as a wound dressing for the treatment of refractory wounds. The acid-soluble collagen (ASC) and pepsin-soluble collagen (PSC) were extracted and characterized using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), differential scanning calorimetry (DSC), circular dichroism (CD) and Fourier transform infrared spectroscopy (FTIR) analysis. Both ASC and PSC belong to type I collagen and have a complete triple helix structure, but PSC shows lower molecular weight and thermal stability, and has the inherent low antigenicity. Therefore, PSC was selected to prepare biomedical hydrogels using its self-aggregating properties. Rheological characterization showed that the mechanical strength of the hydrogels increased as the PSC content increased. Scanning electron microscope (SEM) analysis indicated that hydrogels could form a regular network structure at a suitable PSC content. Cytotoxicity experiments confirmed that hydrogels with different PSC content showed no significant toxicity to fibroblasts. Skin repair experiments and pathological analysis showed that the collagen hydrogels wound dressing could significantly accelerate the healing of deep second-degree burn wounds and the generation of new skin appendages, which can be used for treatment of various refractory wounds.

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.

Comparative cytocompatibility of multiple candidate cell types to photoencapsulation in PEGNB/PEGDA macroscale or microscale hydrogels

The encapsulation of live cells into photopolymerized hydrogel scaffolds has the potential to augment or repair tissue defects, establish versatile regenerative medicine strategies, and be developed as well-defined, yet tunable microenvironments to study fundamental cellular behavior. However, hydrogel fabrication limitations constrain most studies to macroscale hydrogel scaffolds encapsulating millions of cells. These macroscale materials possess regions of heterogeneous photopolymerization conditions and are therefore poor platforms to identify the response of individual cells to encapsulation. Recently, microfluidic droplet-based hydrogel miniaturization and cell encapsulation offers high-throughput, reproducible, and continuous fabrication. Reports of post-encapsulation cell viability, however, vary widely among specific techniques. Furthermore, different cell types often exhibit different level of tolerance to photoencapsulation-induced toxicity. Accordingly, we evaluate the cellular tolerance of various encapsulation techniques and photopolymerization parameters for four mammalian cell types, with potential applications in tissue regeneration, using polyethylene glycol diacrylate or polyethylene glycol norbornene (PEGNB) hydrogels on micro- and macro-length scales. We found PEGNB provides excellent cellular tolerance and supports long-term cell survival by mitigating the deleterious effects of acrylate photopolymerization, which are exacerbated at diminishing volumes. PEGNB, therefore, is an excellent candidate for hydrogel miniaturization. PEGNB hydrogel properties, however, were found to have variable effects on encapsulating different cell candidates. This study could provide guidance for cell encapsulation practices in tissue engineering and regenerative medicine research.

Biomimetic intrafibrillar silicification of collagen fibrils through a one-step collagen self-assembly/silicification approach

Intrafibrillar silicified collagen fibrils are successfully fabricated using a one-step collagen self-assembly/silicification approach, which better support osteoblast activities.

Atelocollagen-templated fabrication of tangled fibrous silica

Protein-templated structured silica and titania are fabricated via a biomimetic method based on the synergistic effect of amine/carboxyl complexes under ambient conditions. Atelocollagen-templated silica showed a tangled fibrous structure with a smooth surface. The number of carboxyl groups of a protein is an important factor for homogeneous silica growth.

Advances in collagen, chitosan and silica biomaterials for oral tissue regeneration: from basics to clinical trials

Different materials have distinct surface and bulk characteristics; each of them potentially useful for the treatment of a particular wound or disease.

Improved properties of composite collagen hydrogels: protected oligourethanes and silica particles as modulators

This paper reports the structure–property relationship of novel biomedical hydrogels derived from collagen, water-soluble oligourethanes, and silica.

Effects of macroporous, strontium loaded xerogel-scaffolds on new bone formation in critical-size metaphyseal fracture defects in ovariectomized rats

New bone formation was studied in a metaphyseal fracture-defect in ovariectomized rats stimulated by a plain and a strontium-enriched macroporous silica/collagen scaffold (ScB30 and ScB30Sr20) and a compact silica/collagen xerogel (B30). 45 female Sprague-Dawley rats were randomly assigned to three different treatment groups: (1) ScB30 (n=15), (2) ScB30Sr20 (n=15), and (3) B30 (n=15). 12 weeks after bilateral ovariectomy and multi-deficient diet, a 4 mm wedge-shaped fracture-defect was created at the metaphyseal area of the left femur. A 7-hole T-shaped plate at the lateral aspect of the femur stabilized the bone and the defect was filled with ScB30, ScB30Sr20 or B30 subsequently. After six weeks, histomorphometrical analysis revealed a statistically significant higher bone volume/tissue volume ratio in the ScB30Sr20 group compared to ScB30 (p=0.043) and B30 (p=0.0001) indicating an improved formation of new bone by the strontium-enriched macroporous silica/collagen scaffold. Furthermore, immunohistochemical results showed increased expression of BMP2 and OPG and a decreased RANKL expression in the ScB30Sr20 group. This was further confirmed with the gene expression analysis where an increase in prominent bone formation markers (ALP, OCN, Runx2, Col1a1 and Col10a1) was seen. No material remnants were found in the scaffold group indicating an almost complete degradation process of the biomaterials. This is confirmed by ToF-SIMS analysis that did not detect any strontium in the ScB30Sr20 group neither in the defect nor in the surrounding tissue. Taken together, this study shows the stimulating effects of strontium through increased bone formation by up regulation of osteoanabolic markers. This work also indicates the importance of material porosity, geometry and biodegradability in bone healing.

Promoting Cell Survival and Proliferation in Degradable Poly(vinyl alcohol)-Tyramine Hydrogels

A photopolymerizable-tyraminated poly(vinyl alcohol) (PVA-Tyr) system that has the ability to covalently bind proteins in their native state was evaluated as a platform for cell encapsulation. However, a key hurdle to this system is the radicals generated during the cross-linking that can cause oxidative stress to the cells. This research hypothesized that incorporation of anti-oxidative proteins (sericin and gelatin) into PVA-Tyr gels would mitigate any toxicity caused by the radicals. The results showed that although incorporation of 1 wt% sericin promoted survival of the fibroblasts, both sericin and gelatin acted synergistically to facilitate long-term 3D cell function. The encapsulated cells formed clusters with deposition of laminin and collagen, as well as remaining metabolically active after 21 d.

Curcumin loaded nano graphene oxide reinforced fish scale collagen – a 3D scaffold biomaterial for wound healing applications

We prepare a highly stabilized nano graphene oxide functionalized with type I collagen to make a 3D scaffold as a novel platform for better tissue engineering research..

A pneumatically-driven microfluidic system for size-tunable generation of uniform cell-encapsulating collagen microbeads with the ultrastructure similar to native collagen

This study reports a microfluidic system for high throughput, uniform, and size-tunable generation of cell-containing collagen microbeads. The principle is based on two pneumatically-driven mechanisms to achieve multi-channel mixture suspension transportation, and to actuate the spotting actions of micro-vibrators that continuously generate tiny collagen micro-droplets into a thin oil layer and then a sterile Pluronic® F127 surfactant solution located below. The temporarily formed collagen microdroplets are then thermally gelatinized. By regulating the feeding rate of cells/collagen suspension, and the spotting frequency of micro-vibrator, the size of the collagen microbeads can be manipulated. One of the key technical features is its capability to generate uniform collagen microbeads (coefficient of variation: 5.4-8.6 %) with sizes ranging from 73.9 to 349.3 μm in diameter. This is currently difficult to achieve using the existing methods particularly the generation of cell-encapsulating collagen microbeads with diameter less than 100 μm. Another advantageous trait is that the ultrastructure of the generated collagen microbeads is similar to that found in native collagen. In this study, moreover, the use of the proposed device for the microencapsulation of 3T3 cells in collagen microbeads has been successfully demonstrated showing that the encapsulated cells maintained high cell viability (96 ± 2 %). Furthermore, a reasonable proliferative capability of the encapsulated cells was observed during 7 days culture. As a whole, the proposed device has opened up a new route to generate cell-containing collagen microbeads, which is found particularly meaningful for biomedical applications.

Application of F-18-sodium fluoride (NaF) dynamic PET-CT (dPET-CT) for defect healing: a comparison of biomaterials in an experimental osteoporotic rat model

BACKGROUND

The aim of the current study was to measure and compare the effect of various biomaterials for the healing of osteoporotic bone defects in the rat femur using 18F-sodium fluoride dPET-CT.

MATERIAL AND METHODS

Osteoporosis was induced by ovariectomy and a calcium-restricted diet. After 3 months, rats were operated on to create a 4-mm wedge-shaped defect in the distal metaphyseal femur. Bone substitution materials of calcium phosphate cement (CPC), composites of collagen and silica, and iron foams with interconnecting pores were inserted. Strontium or bisphosphonate, which are well known for having positive effects in osteoporosis treatment, were added into the materials. Eighteen weeks after osteoporosis induction and 6 weeks following femoral surgery, dPET-CT studies scan were performed with 18F-Sodium Fluoride. Standardized uptake values (SUVs) and a 2-tissue compartmental learning-machine model (K1-k4, vessel density [VB], influx [ki]) were used for quantitative analysis.

RESULTS

k3, reflecting the formation of fluoroapatite, revealed a statistically significant increase at the biomaterial-bone interface due to the Sr release from strontium-modified calcium phosphate cement (SrCPC) compared to CPC, which demonstrated enhanced new bone formation. In addition, k3 as measured in the porous scaffold silica/collagen xerogel (Sc-B30), showed a significant increase based on Wilcoxon rank-sum test (p<0.05) as compared with monolithic silica/collagen xerogel (B30) in the defect region. Furthermore, ki, reflecting the net plasma clearance of tracer to bone mineral measured in the iron foam with coating of the bisphosphonate zoledronic acid (Fe-BP), was enhanced as compared with plain iron foam (Fe) in the defect region.

CONCLUSIONS

k3 was the most significant parameter for the characterization of healing processes and revealed the best differentiation between the 2 different biomaterials. PET scanning using 18F-sodium fluoride seems to be a sensitive and useful method for evaluation of bone healing after replacement with these biomaterials.

Self-Assembly in Biosilicification and Biotemplated Silica Materials

During evolution, living organisms have learned to design biomolecules exhibiting self-assembly properties to build-up materials with complex organizations. This is particularly evidenced by the delicate siliceous structures of diatoms and sponges. These structures have been considered as inspiration sources for the preparation of nanoscale and nanostructured silica-based materials templated by the self-assembled natural or biomimetic molecules. These templates range from short peptides to large viruses, leading to biohybrid objects with a wide variety of dimensions, shapes and organization. A more recent strategy based on the integration of biological self-assembly as the driving force of silica nanoparticles organization offers new perspectives to elaborate highly-tunable, biofunctional nanocomposites.

Yeast-based self-organized hybrid bio-silica sol-gels for the design of biosensors

The methylotrophic Pichia angusta VKM Y-2559 and the oleaginous Cryptococcus curvatus VKM Y-3288 yeast cells were immobilized in a bimodal silica-organic sol-gel matrix comprised of tetraethoxysilane (TEOS), the hydrophobic additive methyltriethoxysilane (MTES) and the porogen polyethylene glycol (PEG). Under carefully optimized experimental conditions, employing basic catalysts, yeast cells have become the nucleation centers for a silica-organic capsule assembled around the cells. The dynamic process involved in the formation of the sol-gel matrix has been investigated using optical and scanning electron microscopic techniques. The results demonstrated the influence of the MTES composition on the nature of the encapsulation of the yeast cells, together with the architecture of the three-dimensional (3D) sol-gel biomatrix that forms during the encapsulation process. A silica capsule was found to form around each yeast cell when using 85 vol% MTES. This capsule was found to protect the microorganisms from the harmful effects that result from exposure to heavy metal ions and UV radiation. The encapsulated P. angusta BKM Y-2559 cells were then employed as a biosensing element for the detection of methanol. The P. angusta-based biosensor is characterized by high reproducibility (Sr, 1%) and operational stability, where the biosensor remains viable for up to 28 days.

Collagen hydrogels incorporated with surface-aminated mesoporous nanobioactive glass: Improvement of physicochemical stability and mechanical properties is effective for hard tissue engineering

Collagen (Col) hydrogels have poor physicochemical and mechanical properties and are susceptible to substantial shrinkage during cell culture, which limits their potential applications in hard tissue engineering. Here, we developed novel nanocomposite hydrogels made of collagen and mesoporous bioactive glass nanoparticles (mBGns) with surface amination, and addressed the effects of mBGn addition (Col:mBG = 2:1, 1:1 and 1:2) and its surface amination on the physicochemical and mechanical properties of the hydrogels. The amination of mBGn was shown to enable chemical bonding with collagen molecules. As a result, the nanocomposite hydrogels exhibited a significantly improved physicochemical and mechanical stability. The hydrolytic and enzymatic degradation of the Col-mBGn hydrogels were slowed down due to the incorporation of mBGn and its surface amination. The mechanical properties of the hydrogels, specifically the resistance to loading as well as the stiffness, significantly increased with the addition of mBGn and its aminated form, as assessed by a dynamic mechanical analysis. Mesenchymal stem cells cultivated within the Col-mBGn hydrogels were highly viable, with enhanced cytoskeletal extensions, due to the addition of surface aminated mBGn. While the Col hydrogel showed extensive shrinkage (down to ∼20% of initial size) during a few days of culture, the shrinkage of the mBGn-added hydrogel was substantially reduced, and the aminated mBGn-added hydrogel had no observable shrinkage over 21 days. Results demonstrated the effective roles of aminated mBGn in significantly improving the physicochemical and mechanical properties of Col hydrogel, which are ultimately favorable for applications in stem cell culture for bone tissue engineering.

Design and properties of biopolymer–silica hybrid materials: The example of pectin-based biodegradable hydrogels

The association of natural polymers with silica is a fruitful strategy to design novel hybrid structures with potential applications in the fields of biotechnology, medicine, and environmental sciences. Here we illustrate the principles of formation, the structure, and the properties of such biohybrid systems by the specific example of silica–pectin porous materials. The influence of the silica source, i.e., aqueous silicates and tetraethoxysilane (TEOS), was more specifically addressed. The alkoxide precursor may be associated with the polysaccharide in a wide range of concentrations. In contrast, the high initial viscosity and fast condensation rate of silicates limits the range of accessible compositions. Owing to weak interactions between the mineral and organic components, silicification does not improve the thermal stability of the polymer but has a strong impact on the water stability of the materials, which depends on the silica source. It is shown that the stability of the silica–pectin hybrid materials during enzymatic degradation is optimum for low carbohydrate content and high silica content, independently of the inorganic precursor.

Effect of silica and hydroxyapatite mineralization on the mechanical properties and the biocompatibility of nanocomposite collagen scaffolds

A recently established materials concept of biomimetic composites based on silica, collagen, and calcium phosphates was adapted for the preparation of porous scaffolds suitable for tissue engineering applications. Mineralization was achieved by directed nucleation of silica on the templating organic phase during a sol-gel process with or without addition of hydroxyapatite. Both mineral phases (25 wt %, individually or combined in equal shares) influenced the scaffold's morphology at the nanoscale. Enhancement of apparent density and compressive strength was similar for silica or hydroxyapatite mineralization; however the stiffening effect of hydroxyapatite was much higher. All scaffold modifications provided proper conditions for adhesion, proliferation, and osteogenic differentiation of human bone marrow stromal cells. The open porosity allowed cells to migrate throughout the scaffolds while maintaining their viability, both confirmed by MTT staining and confocal laser scanning microscopy. Initial cell distributions were graduated due to collagen mineralization, but balanced out over the cultivation time of 28 days. RT-PCR analyses revealed higher gene expression of ALP but lower expression of BSP II and osteocalcin because of collagen mineralization. The results demonstrate that both silica and hydroxyapatite offer comparable possibilities to tailor mechanical properties of collagen-based scaffolds without being detrimental to in vitro biocompatibility.

In vitro studies and preliminary in vivo evaluation of silicified concentrated collagen hydrogels

Hybrid and nanocomposite silica-collagen materials derived from concentrated collagen hydrogels were evaluated in vitro and in vivo to establish their potentialities for biological dressings. Silicification significantly improved the mechanical and thermal stability of the collagen network within the hybrid systems. Nanocomposites were found to favor the metabolic activity of immobilized human dermal fibroblasts while decreasing the hydrogel contraction. Cell adhesion experiments suggested that in vitro cell behavior was dictated by mechanical properties and surface structure of the scaffold. First-to-date in vivo implantation of bulk hydrogels in subcutaneous sites of rats was performed over the vascular inflammatory period. These materials were colonized and vascularized without inducing strong inflammatory response. These data raise reasonable hope for the future application of silica-collagen biomaterials as biological dressings.

Silica-collagen bionanocomposites as three-dimensional scaffolds for fibroblast immobilization

Silica-collagen bionanocomposite hydrogels were obtained by addition of silica nanoparticles to a protein suspension followed by neutralization. Electron microscopy studies indicated that larger silica nanoparticles (80 nm) do not interact strongly with collagen, whereas smaller ones (12 nm) form rosaries along the protein fibers. However, the composite network structurally evolved with time due to the contraction of the cells and the dissolution of the silica nanoparticles. When compared to classical collagen hydrogels, these bionanocomposite materials showed lower surface contraction in the short term (1 week) and higher viability of entrapped cells in the long term (3 weeks). A low level of gelatinase MMP2 enzyme expression was also found after this period. Several proteins involved in the catabolic and anabolic activity of the cells could also be observed by immunodetection techniques. All these data suggest that the bionanocomposite matrices constitute a suitable environment for fibroblast adhesion, proliferation and biological activity and therefore constitute an original three-dimensional environment for in vitro cell culture and in vivo applications, in particular as biological dressings.