Injectable cross-linked collagen with improved flow properties

Shaping collagen for engineering hard tissues: Towards a printomics approach

Hard tissue engineering has evolved over the past decades, with multiple approaches being explored and developed. Despite the rapid development and success of advanced 3D cell culture, 3D printing technologies and material developments, a gold standard approach to engineering and regenerating hard tissue substitutes such as bone, dentin and cementum, has not yet been realised. One such strategy that differs from conventional regenerative medicine approach of other tissues, is the in vitro mineralisation of collagen templates in the absence of cells. Collagen is the most abundant protein within the human body and forms the basis of all hard tissues. Once mineralised, collagen provides important support and protection to humans, for example in the case of bone tissue. Multiple in vitro fabrication strategies and mineralisation approaches have been developed and their success in facilitating mineral deposition on collagen to achieve bone-like scaffolds evaluated. Critical to the success of such fabrication and biomineralisation approaches is the collagen template, and its chemical composition, organisation, and density. The key factors that influence such properties are the collagen processing and fabrication techniques utilised to create the template, and the mineralisation strategy employed to deposit mineral on and throughout the templates. However, despite its importance, relatively little attention has been placed on these two critical factors. Here, we critically examine the processing, fabrication and mineralisation strategies that have been used to mineralise collagen templates, and offer insights and perspectives on the most promising strategies for creating mineralised collagen scaffolds. STATEMENT OF SIGNIFICANCE: In this review, we highlight the critical need to fabricate collagen templates with advanced processing techniques, in a manner that achieves biomimicry of the hierarchical collagen structure, prior to utilising in vitro mineralisation strategies. To this end, we focus on the initial collagen that is selected, the extraction techniques used and the native fibril forming potential retained to create reconstituted collagen scaffolds. This review synthesises current best practises in material sourcing, processing, mineralisation strategies and fabrication techniques, and offers insights into how these can best be exploited in future studies to successfully mineralise collagen templates.

The Preparation of Nano-SiO₂/Dialdehyde Cellulose Hybrid Materials as a Novel Cross-Linking Agent for Collagen Solutions

Nano-SiO₂ was immobilized onto dialdehyde cellulose (DAC) to prepare SiO₂/DAC hybrid materials. Fourier transform infrared spectra (FTIR), thermogravimetric analysis and field emission scanning electron microscopy of SiO₂/DAC indicated that nano-SiO₂ had been successfully hybridized with DAC. X-ray diffraction suggested that the structure of DAC was influenced by the nano-SiO₂. SiO₂/DAC was then used as the cross-linker of collagen solutions. Gel electrophoresis patterns and FTIR reflected that cross-linking occurred between DAC and collagen, but that collagen retained the native triple-helix, respectively. Differential scanning calorimetry indicated that the thermal stability of collagen could be effectively improved by SiO₂/DAC. Dynamic rheology tests revealed that the flowability of collagens cross-linked by SiO₂/DAC was superior to that of those cross-linked by DAC; meanwhile, collagens cross-linked by SiO₂/DAC possessed a more homogeneous morphology compared to those cross-linked by DAC. The hybridization of SiO₂/DAC as a cross-linker for collagen could effectively prevent the gelation caused by excessive cross-linking, and significantly improve the thermostability of collagen, which could be helpful for collagen being applied in fields including biomaterials, cosmetics, etc.

Nanoparticle-Based Mycosis Vaccine

Many diseases that were considered major affliction of mankind in the past have been successfully eradicated with introduction of appropriate vaccine strategies. In order to expedite new challenges coming up to deal with various infectious diseases, nano-particulate-based subunit vaccines seem to be the demand of ordeal. The nano-vaccines can find better scope for the diseases that were not rampant in the semi-advanced world few years back. For example in present-day circumstances that corroborate with advancement in the field of medical sciences in terms of cancer chemotherapy, organ transplantation, therapy of autoimmune diseases, etc.; along with prevalence of altogether unheard diseases such as HIV infection, people are at risk of infliction with many more pathogens. In this regard, development of an effective prophylactic strategy against many opportunistic infections primarily caused by fungal pathogens needs better understanding of host pathogen relation and role of active immunity against pathogenic fungi. In the present study, we have tried to decipher effectiveness of a nano-sized vaccine delivery system in imparting protection against fungal pathogens.

Plumbagin caged silver nanoparticle stabilized collagen scaffold for wound dressing

Wound dressing material based on nano-biotechnological intervention by caging plumbagin on silver nanoparticle (PCSN) as a multi-site cross-linking agent of collagen scaffolds with potent anti-microbial and wound healing activity.

Review collagen-based biomaterials for wound healing

With its wide distribution in soft and hard connective tissues, collagen is the most abundant of animal proteins. In vitro, natural collagen can be formed into highly organized, three-dimensional scaffolds that are intrinsically biocompatible, biodegradable, nontoxic upon exogenous application, and endowed with high tensile strength. These attributes make collagen the material of choice for wound healing and tissue engineering applications. In this article, we review the structure and molecular interactions of collagen in vivo; the recent use of natural collagen in sponges, injectables, films and membranes, dressings, and skin grafts; and the on-going development of synthetic collagen mimetic peptides as pylons to anchor cytoactive agents in wound beds.

Rheological behavior of anionic collagen injectable gels in the presence of rhamsan for plastic surgery applications

The present paper describes the rheological properties of anionic collagen gels and anionic collagen:rhamsan composites gels in the concentration of 0.7, 4 and 6%, estimated to be used as injectable biomaterials for plastic reconstruction. Rheological studies of these gels showed that independently of pH, composition and concentration the viscoelastic behavior was dependent on the frequency, with the storage modulus always greater than the loss modulus (G' > G'' and delta < 45 degrees ). Creep experiments showed that anionic collagen:rhamsan composites equilibrated at pH 7.4 were less elastic and more susceptible to deformation in comparison to gels equilibrated at pH 3.5. Flow experiments indicated that the force needed for the extrusion of anionic collagen:rhamsan composites, in comparison to anionic collagen, was significantly smaller and with a smoother flow, suggesting the association with rhamsan may be a good alternative in the replacement of glutaraldehyde to stabilize the microfibril assembly of commercial collagen gel preparations. Finally, on the basis of dynamic viscosity profiles found for different preparations, some of these composites are potential candidates to be utilized in laryngology.

Injectable gels of anionic collagen: Rhamsan composites for plastic correction: Preparation, characterization, and rheological properties

The present article describes the preparation and characterization of anionic collagen gels obtained from porcine intestinal submucosa after 72 h of alkaline treatment and in the form of rhamsan composites to develop injectable biomaterials for plastic reconstruction. All materials were characterized by SDS/polyacrylamide gel electrophoresis, infrared spectroscopy, thermal stability, potentiometric titration, rheological properties, and fluidity tests. Biocompatibility was appraised after the injection of anionic collagen: rhamsan composites at 2.5% in 60 North Folk rabbits. Independently of processing, the collagen's secondary structure was preserved in all cases, and after 72 h of hydrolysis the collagen was characterized by a carboxyl group content of 346+/-9, which, at physiological pH, corresponds to an increase of 106+/-17 negative charges, in comparison to native collagen, due to the selective hydrolysis of asparagine and glutamine carboxyamide side chain. Rheological studies of composites at pH 7.4 in concentrations of 2, 4, and 6% (in proportions of 75:1 and 50:1) showed a viscoelastic behavior dependent on the frequency, which is independent of concentration and proportion. In both, the concentration of the storage modulus always predominated over the loss modulus (G'>G'' and delta<45 degrees ). The results from creep experiments confirmed this behavior and showed that anionic collagen:rhamsan composites at pH 7.4 in the proportion of 50:1 are less elastic and more susceptible to deformation in comparison to gels in the proportion of 75:1, independent of concentration. This was further confirmed by flow experiments, indicating that the necessary force for the extrusion of anionic collagen:rhamsan composites, in comparison to anionic collagen, was significantly smaller and with a smooth flow. Biocompatibility studies showed that the tissue reaction of anionic collagen:rhamsan composites at 2.5% in the proportion of 75:1 was compatible with the application of these gels in plastic reconstruction. These results suggest that the association of collagen with rhamsan may be a good alternative in the replacement of glutaraldehyde to stabilize the microfibril assembly of commercial collagen gel preparations.

Influence of cosolvents and in situ forming hydroxyapatite on the mechanical characteristics of collagen films

Collagen was processed into films in mixtures containing various ratios of water, propylene glycol, and ethanol. An experimental mixture design was applied to characterize the effects of individual solvents and their interactions on the mechanical properties of collagen films. Scanning electron microscopy (SEM) was used to examine the surface properties of collagen films. The ultimate tensile strength (UTS) and related characteristics of collagen films were also evaluated with dynamic mechanical analysis. The effect of in situ forming hydroxyapatite (HAP) within collagen films at a concentration of 10 mM on the physical characteristics of these films was evaluated by the same methods. With X-ray and SEM examinations, it was confirmed that HAP was formed inside the collagen film. However, the UTS of collagen films without HAP was 4-5 times higher than that with HAP. This was probably due to the discontinuity of the film structure caused by HAP in the collagen films. The results of a statistical analysis of the experimental design revealed the influence of the solvent mixtures on the mechanical properties of the collagen films with and without HAP, showing similar responses for the UTS and modulus of elasticity. Both parameters showed a maximal response in the solvent range containing a lower percentage of ethanol with the desired percentage of propylene glycol to plasticize the collagen films.

Characterization of collagen gel solutions and collagen matrices for cell culture

The influence of glutaraldehyde as a crosslinking agent to increase the strength of collagen matrices for cell culture was examined in this study. Collagen solutions of 1% were treated with different concentrations (0-0.2%) of glutaraldehyde for 24 h. The viscoelasticity of the resulting collagen gel solution was measured using dynamic mechanical analysis (DMA), which demonstrated that all collagen gel solutions examined followed the same model pattern. The creep compliance model of Voigt-Kelvin satisfactorily described the change of viscoelasticity expressed by these collagen gel solutions. These crosslinked collagen gel solutions were freeze-dried to form a matrix with a thickness of about 0.2-0.3 mm. The break modulus of these collagen matrices measured by DMA revealed that the higher the degree of crosslinking. the higher the break modulus. The compatibility of fibroblasts isolated from nude mouse skin with these collagen matrices was found to be acceptable at a cell density of 3 x 10(5) cells/cm2 with no contraction, even when using a concentration of glutaraldehyde of up to 0.2%.

A novel injectable collagen matrix: in vitro characterization and in vivo evaluation

We present here a unique engineered collagen formulation that is injectable and compacts into a porous viscoelastic solid after implantation, achieving completely focal application without cross-linking. This implant provides a cohesive continuously porous matrix, as demonstrated by permeability and compression experiments. Those experiments also provide initial mechanical characterization of the material and establish the ability to modify these essential properties by design. Further, the short-term compaction and long-term stability of the implant in vivo in terms of both physical and histological responses are assessed in an animal model to demonstrate the mechanism of action and long-term persistence of this novel material.

Collagen--biomaterial for drug delivery

The use of collagen as a biomaterial is currently undergoing a renaissance in the tissue engineering field. The biotechnological applications focus on the aspects of cellular growth or delivery of proteins capable of stimulating cellular response. However, basic knowledge about collagen biochemistry and the processing technology in combination with understanding of the physico-chemical properties is necessary for an adequate application of collagen for carrier systems. The purpose of this review article is to summarize information available on collagen dosage forms for drug delivery as well as to impart an overview of the chemical structures and the galenical properties including detailed description of the processing steps - extraction, purification, chemical crosslinking and sterilization. The most successful and stimulating applications are shields in ophthalmology, injectable dispersions for local tumor treatment, sponges carrying antibiotics and minipellets loaded with protein drugs. However, the scientific information about manipulating release properties or mechanistic studies is not as abundant as for some synthetic polymers.

Géis de colágeno aniônico: ransana como biomateriais. Preparação e caracterização físico-química

Este trabalho descreve o efeito da ransana, um polissacarídeo bacteriano, sobre géis de colágeno aniônico. A interação colágeno:ransana ocorreu independentemente do pH, mesmo com baixas concentrações de ransana, e os materiais obtidos no estado sólido foram caracterizados por serem mais estáveis térmicamente à medida em que se aumenta a concentração do polissacarídeo. Nenhuma alteração na estrutura secundária em tripla hélice do tropocolágeno foi observada. O efeito mais significativo da ransana sobre os géis aniônicos de colágeno foi um aumento significativo da viscosidade, e as variações observadas em função de pH e temperatura sugerem que nesta interação, não estão envolvidas forças de natureza eletrostática ou hidrofóbica. Micrografias de colágeno aniônico e colágeno aniônico:ransana mostraram a presença de estruturas vesiculares, diferente do padrão fibrilar característico de colágeno nativo. Um modelo de interação baseado na ação da ransana sobre a água estruturada, associada à organização macromolecular do colágeno em solução é proposto. Mais importante, géis de colágeno aniônico:ransana mostraram uma estabilidade térmica compatível com aquelas desejáveis para um biomaterial injetável de colágeno, evitando o uso do glutaraldeído como agente de estabilização.

Effect of electrostatic forces on the dynamic rheological properties of injectable collagen biomaterials

Injectable collagen is a concentrated dispersion of phase-separated collagen fibres in aqueous solution used to correct dermal contour defects through intradermal injection. The effect of electrostatic forces on the rheology of injectable collagen was studied by observation of the birefringence of collagen fibres through a polarizing microscope as well as by oscillatory rheological measurements on dispersions of varying ionic strengths (0.06-0.30). The birefringence of fibres progressively increased as ionic strength was reduced from 0.30 to 0.06. The linear viscoelastic measurements displayed a logarithmic relationship between storage (and loss) moduli and frequency over oscillation frequencies of 0.1-100 rad/s. The associated relaxation time spectra, interpreted using the theory of Kamphuis et al. for concentrated dispersions, show that collagen fibres become more flexible as ionic strength increases. This result was analysed at the molecular level from the perspective that collagen fibres are a liquid-crystalline phase of rigid rod collagen molecules which have phase-separated from solution. Electrostatic forces affect the volume fraction of water present in the collagen fibres which in turn alters the rigidity of the fibres. Flexible collagen fibre dispersions displayed emulsion-like flow properties whereas more rigid collagen fibre dispersions displayed suspension-like flow properties. Changes in fibre rigidity significantly alter the injectability of collagen dispersions which is critical in clinical performance.