Structural properties of pepsin-solubilized collagen acylated by lauroyl chloride along with succinic anhydride

Zirconium ion mediated collagen nanofibrous hydrogels with high mechanical strength

Low mechanical strength is still the key question for collagen hydrogel consisting of nanofibrils as hard tissue repair scaffolds with no loss of biological function. In this work, novel collagen nanofibrous hydrogels with high mechanical strength were fabricated based on the pre-protection of trisodium citrate masked Zr(SO4)2 solution for collagen self-assembling nanofibrils and then further coordination with Zr(SO4)2 solution. The mature collagen nanofibrils with d-period were observed in Zr(IV) mediated collagen hydrogels by AFM when the Zr(IV) concentration was ≥ 10 mmol/L, and the distribution of zirconium element was uniform. Due to the coordination of Zr(IV) with ─COOH, ─NH2 and ─OH within collagen and the tighter entanglement of collagen nanofibrils, the elastic modulus and compressive strength of Zr(IV) mediated collagen nanofibrous hydrogel were 208.3 and 1103.0 kPa, which were approximate 77 and 12 times larger than those of pure collagen hydrogel, respectively. Moreover, the environmental stability such as thermostability, swelling ability and biodegradability got outstanding improvements and could be regulated by Zr(IV) concentration. Most importantly, the resultant hydrogel showed excellent biocompatibility and even accelerated cell proliferation.

Utilizing epoxy Bletilla striata polysaccharide collagen sponge for hemostatic care and wound healing

Hemostatic materials that are lightweight and possess good blood absorption performance have been widely considered for use in modern wound care. Natural hemostatic ingredients derived from traditional Chinese medicine have also received extensive attention. Bletilla polysaccharides are valued by researchers for their excellent hemostatic performance and good reactivity. Collagen is favored by researchers due to its high biocompatibility and low immunogenicity. In this study, Bletilla striata polysaccharide, the main hemostatic component of Bletilla striata, was activated by epoxy groups, and epoxidized Bletilla striata polysaccharide (EBSP) was prepared. Then, EBSP was crosslinked with collagen under alkaline conditions, and a new hemostatic material that was an epoxidized Bletilla polysaccharide crosslinked collagen hemostatic sponge was prepared. We demonstrated that endowing collagen with better hemostatic performance, cytocompatibility, and blood compatibility does not destroy its original three-stranded helical structure. Compared with the medical gauze, hemostasis time was shorter (26.75 ± 2.38 s), and blood loss was lower (0.088 ± 0.051 g) in the rat liver injury hemostasis model. In the rat model of severed tail hemostasis, hemostasis time was also shorter (47.33 ± 2.05 s), and the amount of blood loss was lower (0.330 ± 0.122 g). The sponge possessed good hemostatic and healing performance.

Biodegradable and biocompatible collagen-based hybrid materials for force sensing applications

With the aim of replacing synthetic macromolecules by biological macromolecules for advanced applications, collagen films were produced with two different ionic liquids (ILs), choline dihydrogen phosphate ([Ch][DHP]) and choline serinate ([Ch][Seri]), added in order to modulate the electrical responses. The films were prepared by casting, varying IL content between 0 and 6 wt%. The morphology and thermal properties of the resulting films were found to be independent of both IL type and content. However, the highest direct curret (d.c.) electrical conductivity (1.4 × 10-8 S·cm-1) was achieved for collagen films containing 3 wt% [Ch][DHP]. Furthermore, it was demonstrated that IL/collagen films were non-cytotoxic, with cell activity values exceeding 70 %. These collagen films were proven to be suitable for force sensing applications, displaying excellent sensitivity and stability upon repeated testing.

On the effect of pepsin incubation on type I collagen from horse tendon: Fine tuning of its physico-chemical and rheological properties

Type I collagen is commonly recognized as the gold standard biomaterial for the manufacturing of medical devices for health-care related applications. In recent years, with the final aim of developing scaffolds with optimal bioactivity, even more studies focused on the influence of processing parameters on collagen properties, since processing can strongly affect the architecture of collagen at various length scales and, consequently, scaffolds macroscopic performances. The ability to finely tune scaffold properties in order to closely mimic the tissues' hierarchical features, preserving collagen's natural conformation, is actually of great interest. In this work, the effect of the pepsin-based extraction step on the material final properties was investigated. Thus, the physico-chemical properties of fibrillar type I collagens upon being extracted under various conditions were analyzed in depth. Correlations of collagen structure at the supramolecular scale with its microstructural properties were done, confirming the possibility of tuning rheological, viscoelastic and degradation properties of fibrillar type I collagen.

A cleaner approach to tanning process of cattle hide upper suede leather: chrome-less polycarboxylate/montmorillonite nanocomposites as tanning agent

In this study, a cleaner approach to a 'sandwich' chrome-less tanning for cattle hide upper suede leather based on polycarboxylate/montmorillonite nanocomposite (PCM) has been developed. The chromium was reduced both in tanning process and retanning process. Hydrothermal stability, mechanical strength, and organoleptic properties of the leather were closed to traditional chrome tanning. The important advantage of the cleaner tanning approach is that the chromium load in wastewater decreased from 2302 mg/L in tanning process and 2919 mg/L in retanning process to 131 and 257 mg/L, respectively. Moreover, SEM analyses demonstrated that the leather tanned by PCM achieved loose fiber structure and flaky montmorillonite deposition both in intra-triple and inter-triple helix. XRD results suggested that basic chromium sulfate and PCM may form more complexation with the helix chain of collagen fiber, resulting in structural distortion of collagen molecules without destroying the triple helical structure. EDS liner scanning indicated the distribution of chromium on the cross section of the leather. Trypsin degradation curves revealed the cleaner approach might increase the degradation of leather, and the economic analysis results showed that the tanning costs could be reduced and increased the economic benefits.

Mimicking the Hierarchical Organization of Natural Collagen: Toward the Development of Ideal Scaffolding Material for Tissue Regeneration

Biological materials found in living organisms, many of which are proteins, feature a complex hierarchical organization. Type I collagen, a fibrous structural protein ubiquitous in the mammalian body, provides a striking example of such a hierarchical material, with peculiar architectural features ranging from the amino acid sequence at the nanoscale (primary structure) up to the assembly of fibrils (quaternary structure) and fibers, with lengths of the order of microns. Collagen plays a dominant role in maintaining the biological and structural integrity of various tissues and organs, such as bone, skin, tendons, blood vessels, and cartilage. Thus, "artificial" collagen-based fibrous assemblies, endowed with appropriate structural properties, represent ideal substrates for the development of devices for tissue engineering applications. In recent years, with the ultimate goal of developing three-dimensional scaffolds with optimal bioactivity able to promote both regeneration and functional recovery of a damaged tissue, numerous studies focused on the capability to finely modulate the scaffold architecture at the microscale and the nanoscale in order to closely mimic the hierarchical features of the extracellular matrix and, in particular, the natural patterning of collagen. All of these studies clearly show that the accurate characterization of the collagen structure at the submolecular and supramolecular levels is pivotal to the understanding of the relationships between the nanostructural/microstructural properties of the fabricated scaffold and its macroscopic performance. Several studies also demonstrate that the selected processing, including any crosslinking and/or sterilization treatments, can strongly affect the architecture of collagen at various length scales. The aim of this review is to highlight the most recent findings on the development of collagen-based scaffolds with optimized properties for tissue engineering. The optimization of the scaffolds is particularly related to the modulation of the collagen architecture, which, in turn, impacts on the achieved bioactivity.

Fibrillogenesis of acrylic acid-grafted-collagen without self-assembly property inspired by the hybrid fibrils of xenogeneic collagen

Along with advancements in both protein and chemistry science, the chemical modification of proteins is attracting more and more attention. More specifically, the attachment of polymers or reactive moieties into collagen offers a method to add novel functions to this protein. However, the fibrillogenesis of the modified collagen with high grafting density cannot always be achieved. Here, inspired by the hybrid fibrils of xenogeneic collagen, fibrillogenesis of acrylic acid-grafted-collagen (AAc-g-Col) without self-assembly property was achieved by the induction of natural collagen (Col). The step-by-step co-assembly process of AAc-g-Col and Col was confirmed by turbidity assay. The formation of Col/AAc-g-Col hybrid fibrils was verified by TEM since the acryloyl groups of the hybrid fibrils were labelled using HS-AuNPs based on the Michael addition. Moreover, rheology, SEM, and MTT assays revealed that the fibrillary structures and biocompatibility of the Col/AAc-g-Col hydrogel were comparable to that of the Col hydrogel, although they presented a lower viscoelasticity.

Regeneration of native collagen from hazardous waste: chrome-tanned leather shavings by acid method

The collagens (COL2, COL4, and COL5) were extracted from chrome-tanned leather shavings via three distinctive routes of acid method. The dechroming degree of COL2 extracted with the easiest operation was the highest (95.6% ± 1.2%) and the yield exceeded 90%; however, the total amount of acid was the most and the cost was the highest. In the second route, although the three-step dechroming process brought cumbersome operation, the dechroming degree and yield of COL4 were 90.5% ± 0.8% and 92.2% ± 0.6%, respectively, and the acid amount was less than that in the first route. For COL5, the dechroming degree and yield was the lowest; nevertheless, this route had the advantages of lowest cost and simpler operation. Electrophoretic patterns showed that all the collagens contained α1, α2, and β chains without low molecular weight components and were close to those of type I collagen. Compared with native collagen extracted from fresh calf skin, the regenerated collagens also maintained unique triple helix conformation determined via ultraviolet, infrared spectra and X-ray diffraction, confirmed by the similar values of AIII/A1455 and Δν. Additionally, the collagens existed in the form of fibrils with D-period pattern of ~ 67 nm. Furthermore, the denaturation temperatures of COL2, COL4, and COL5 were 71.2, 79.1, and 85.4 °C, respectively, which were relevant to the tighter arrangement of fibrils with the increased chromium content.

Aggregation Behavior of Acylated Pepsin-Solubilized Collagen Based on Fluorescence Spectrum Technology

The aggregation behavior of collagen-based materials plays an important role in their processing because it could affect their physicochemical properties. Based on the intrinsic fluorescence characteristic of tyrosine, fluorescence spectrum technology was used to investigate the aggregation state of the acylated collagen molecules in aqueous solution. The results showed that the aggregate degree of the acylated collagen was higher than that of the native collagen due to the hydrophobic interaction. With the increase of concentrations of the acylated collagen or at NaCl higher than 40 mmol/L, the aggregate degree of the acylated collagen molecules increased. When the pH was close to the isoelectric point of the acylated collagen, the hydrophobic interaction and the hydrogen bond helped to increase the aggregation degree. However, with the increase of temperature (10-70 ℃), the aggregation state of the acylated collagen decreased gradually due to the quenching, the molecular collision, and the broken of hydrogen bonds. Furthermore, two-dimensional correlation spectroscopy (2D-COS) showed that the response order was 360 > 305 nm at various acylated collagen and NaCl (>40 mmol/L) concentrations, while the response order was 305 > 360 nm when the pH value was increased from 5.0 to 9.0. Temperature-dependent 2D-COS showed there were four bands that occurred and the response order was listed as follows: 293 > 305 > 360 > 420 nm. In brief, the results might provide an important guide for molding processes of the acylated collagen.

Insight into the role of grafting density in the self-assembly of acrylic acid-grafted-collagen

Side chain modification of collagen provides an attractive way to enhance their structure and functions, which is highly desirable for the development of promising biomaterials. However, the impact of structural change of side chains on the intrinsic self-assembly property of collagen was always ignored. Here, a series of acrylic acid-grafted-collagen (AA-g-Col) with different grafting density were prepared to explore the impact of side chain structural variation on the self-assembly of collagen. The results showed that excessive grafting density would weaken or even disappear the self-assembly property of AA-g-Col, but only affects the triple helix to a minor extent. Compared to pristine collagen, the mechanical property and cytocompatibility of AA-g-Col based matrices also deteriorated, along with the increase of grafting density. Therefore, this work contributed a new insight into the importance of grafting density for the study of modified collagen, which would be helpful for the design of optimized formulate collagen-based hybrid materials with both additional novel functions and tissue-mimicking fibrillary structures.