Collagen fibril formation in a wound healing model

Variation in Hydrogel Formation and Network Structure for Telo-, Atelo- and Methacrylated Collagens

As the most abundant protein in the extracellular matrix, collagen has become widely studied in the fields of tissue engineering and regenerative medicine. Of the various collagen types, collagen type I is the most commonly utilised in laboratory studies. In tissues, collagen type I forms into fibrils that provide an extended fibrillar network. In tissue engineering and regenerative medicine, little emphasis has been placed on the nature of the network that is formed. Various factors could affect the network structure, including the method used to extract collagen from native tissue, since this may remove the telopeptides, and the nature and extent of any chemical modifications and crosslinking moieties. The structure of any fibril network affects cellular proliferation and differentiation, as well as the overall modulus of hydrogels. In this study, the network-forming properties of two distinct forms of collagen (telo- and atelo-collagen) and their methacrylated derivatives were compared. The presence of the telopeptides facilitated fibril formation in the unmodified samples, but this benefit was substantially reduced by subsequent methacrylation, leading to a loss in the native self-assembly potential. Furthermore, the impact of the methacrylation of the collagen, which enables rapid crosslinking and makes it suitable for use in 3D printing, was investigated. The crosslinking of the methacrylated samples (both telo- and atelo-) was seen to improve the fibril-like network compared to the non-crosslinked samples. This contrasted with the samples of methacrylated gelatin, which showed little, if any, fibrillar or ordered network structure, regardless of whether they were crosslinked.

Correlation of light microscopic findings with transmission electron microscopy within a vascular occlusion device

Host response to an implanted biomaterial is a complex process involving microscopic changes in extracellular matrix (ECM) composition. Reliable pathology analysis is imperative for accurate assessment of the tissue response to an implanted device. Plastic histology is commonly used for histology evaluation of medical devices to assess the device-tissue interface; however, this technique is prone to variable staining that can confound histology interpretation. Appropriately, we propose using transmission electron microscopy (TEM) to confirm histologic ECM findings in order to provide sufficient host-response data. Tissue response to an absorbable shape memory polymer intravascular occlusion device with a nitinol wire backbone was evaluated. Representative plastic-embedded, micro-ground sections from 30-day, 60-day, and 90-day timepoints were analyzed. ECM regions were selected, and ultrathin sections were created for TEM evaluation. Histological changes in ECM composition were compared for light microscopy (LM) and TEM findings; specifically, TEM fibrillary patterns for collagen and fibrin were used to confirm LM results. Throughout this study, LM reveals inconsistent staining in plastic-embedded sections. TEM, on the other hand, provides clear insight into the tissue response by morphologically discerning distinct fibrillary patterns within ECM structures; loose to dense collagen surrounds the implant as fibrin degrades, demonstrating progression of postimplant ECM maturation. Moreover, TEM serves as a definitive method for confirming tissue substrate morphology when LM findings prove ambiguous.

Boosting the Biogenesis and Secretion of Mesenchymal Stem Cell-Derived Exosomes

A limitation of using exosomes to their fullest potential is their limited secretion from cells, a major bottleneck to efficient exosome production and application. This is especially true for mesenchymal stem cells (MSCs), which can self-renew but have a limited expansion capacity, undergoing senescence after only a few passages, with exosomes derived from senescent stem cells showing impaired regenerative capacity compared to young cells. Here, we examined the effects of small molecule modulators capable of enhancing exosome secretion from MSCs. The treatment of MSCs with a combination of N-methyldopamine and norepinephrine robustly increased exosome production by three-fold without altering the ability of the MSC exosomes to induce angiogenesis, polarize macrophages to an anti-inflammatory phenotype, or downregulate collagen expression. These small molecule modulators provide a promising means to increase exosome production by MSCs.

Local Silencing of Connective Tissue Growth Factor by siRNA/Peptide Improves Dermal Collagen Arrangements

Background

Collagen organization within tissues has a critical role in wound regeneration. Collagen fibril diameter, arrangements and maturity between connective tissue growth factor (CTGF) small interfering RNA (siRNA) and mismatch scrambled siRNA-treated wound were compared to evaluate the efficacy of CTGF siRNA as a future implement for scar preventive medicine.

Methods

Nanocomplexes of CTGF small interfering RNA (CTGF siRNA) with cell penetrating peptides (KALA and MPG^∆NLS) were formulated and their effects on CTGF downregulation, collagen fibril diameter and arrangement were investigated. Various ratios of CTGF siRNA and peptide complexes were prepared and down-regulation were evaluated by immunoblot analysis. Control and CTGF siRNA modified cells-populated collagen lattices were prepared and rates of contraction measured. Collagen organization in rabbit ear 8 mm biopsy punch wound at 1 day to 8 wks post injury time were investigated by transmission electron microscopy and histology was investigated with Olympus System and TS-Auto software.

Conclusion

CTGF expression was down-regulated to 40% of control by CTGF siRNA/KALA (1:24) complexes (p < 0.01) and collagen lattice contraction was inhibited. However, down-regulated of CTGF by CTGF siRNA/MPG^∆NLS complexes was not statistically significant. CTGF KALA-treated wound appeared with well formed-basket weave pattern of collagen fibrils with mean diameter of 128 ± 22 nm (n = 821). Mismatch siRNA/KALA-treated wound showed a high frequency of parallel small diameter fibrils (mean 90 ± 20 nm, n = 563).

Conclusion

Controlling over-expression of CTGF by peptide-mediated siRNA delivery could improve the collagen orientation and tissue remodeling in full thickness rabbit ear wound.

Molecular and ultrastructural studies of a fibrillar collagen from octocoral (Cnidaria)

We report here the biochemical, molecular and ultrastructural features of a unique organization of fibrillar collagen extracted from the octocoral Sarcophyton ehrenbergi Collagen, the most abundant protein in the animal kingdom, is often defined as a structural component of extracellular matrices in metazoans. In the present study, collagen fibers were extracted from the mesenteries of S. ehrenbergi polyps. These fibers are organized as filaments and further compacted as coiled fibers. The fibers are uniquely long, reaching an unprecedented length of tens of centimeters. The diameter of these fibers is 9±0.37 μm. The amino acid content of these fibers was identified using chromatography and revealed close similarity in content to mammalian type I and II collagens. The ultrastructural organization of the fibers was characterized by means of high-resolution microscopy and X-ray diffraction. The fibers are composed of fibrils and fibril bundles in the range of 15 to 35 nm. These data indicate a fibrillar collagen possessing structural aspects of both types I and II collagen, a highly interesting and newly described form of fibrillar collagen organization.

Octocoral Sarcophyton auritum Verseveldt & Benayahu, 1978: Microanatomy and Presence of Collagen Fibers

The study presents the microanatomy of the polyps of the reef-dwelling octocoral Sarcophyton auritum. We demonstrate the presence of its unique collagen fibers in the colony by means of Masson Trichrome histological staining. Based on peptide profiling, mass spectroscopy analysis confirmed that the fiber proteins were homologous with those of mammalian collagen. Histological and electron microscopy results showed that six of the eight mesenterial filaments of the polyps possess an internal, coiled, spring-like collagen fiber. High-resolution electron microscopy revealed for the first time in cnidarian collagen the interwoven, three-dimensional arrangement of the fibrils that comprise the fibers. Some fibrils feature free ends, while others are bifurcated, the latter being attributed to collagen undergoing fibrogenesis. Along with the mass spectroscopy finding, the coiled nature of the fibers and the fibril microanatomy show a resemblance to those of vertebrates, demonstrating the conserved nature of collagen fibers at both the biochemical and ultrastructural levels. The location, arrangement, and small diameter of the fibers and fibrils of S. auritum may provide a highly protective factor against occasional rupture and injury during the bending of the octocoral's extended polyps under strong current conditions; that is, providing the octocoral with a hydromechanical support. The findings from the microanatomical features of these unique fibers in S. auritum, as well as their suggested function, raise the potential for translation to biomedical applications.

Production, characterization and biocompatibility of marine collagen matrices from an alternative and sustainable source: the sea urchin Paracentrotus lividus

Collagen has become a key-molecule in cell culture studies and in the tissue engineering field. Industrially, the principal sources of collagen are calf skin and bones which, however, could be associated to risks of serious disease transmission. In fact, collagen derived from alternative and riskless sources is required, and marine organisms are among the safest and recently exploited ones. Sea urchins possess a circular area of soft tissue surrounding the mouth, the peristomial membrane (PM), mainly composed by mammalian-like collagen. The PM of the edible sea urchin Paracentrotus lividus therefore represents a potential unexploited collagen source, easily obtainable as a food industry waste product. Our results demonstrate that it is possible to extract native collagen fibrils from the PM and produce suitable substrates for in vitro system. The obtained matrices appear as a homogeneous fibrillar network (mean fibril diameter 30-400 nm and mesh < 2 μm) and display remarkable mechanical properties in term of stiffness (146 ± 48 MPa) and viscosity (60.98 ± 52.07 GPa·s). In vitro tests with horse pbMSC show a good biocompatibility in terms of overall cell growth. The obtained results indicate that the sea urchin P. lividus can be a valuable low-cost collagen source for mechanically resistant biomedical devices.

Inflammatory reaction as determinant of foreign body reaction is an early and susceptible event after mesh implantation

PURPOSE

To investigate and relate the ultrashort-term and long-term courses of determinants for foreign body reaction as biocompatibility predictors for meshes in an animal model.

MATERIALS AND METHODS

Three different meshes (TVT, UltraPro, and PVDF) were implanted in sheep. Native and plasma coated meshes were placed bilaterally: (a) interaperitoneally, (b) as fascia onlay, and (c) as muscle onlay (fascia sublay). At 5 min, 20 min, 60 min, and 120 min meshes were explanted and histochemically investigated for inflammatory infiltrate, macrophage infiltration, vessel formation, myofibroblast invasion, and connective tissue accumulation. The results were related to long-term values over 24 months.

RESULTS

Macrophage invasion reached highest extents with up to 60% in short-term and decreased within 24 months to about 30%. Inflammatory infiltrate increased within the first 2 hours, the reached levels and the different extents and ranking among the investigated meshes remained stable during long-term follow up. For myofibroblasts, connective tissue, and CD31+ cells, no activity was detected during the first 120 min.

CONCLUSION

The local inflammatory reaction is an early and susceptible event after mesh implantation. It cannot be influenced by prior plasma coating and does not depend on the localisation of implantation.

The role of wound healing and its everyday application in plastic surgery: a practical perspective and systematic review

BACKGROUND

After surgery it is often recommended that patients should refrain from strenuous physical activity for 4-6 weeks. This recommendation is based on the time course of wound healing. Here, we present an overview of incisional wound healing with a focus on 2 principles that guide our postoperative recommendations: the gain of tensile strength of a wound over time and the effect of mechanical stress on wound healing.

METHODS

A systematic search of the English literature was conducted using OVID, Cochrane databases, and PubMed. Inclusion criteria consisted of articles discussing the dynamics of incisional wound healing, and exclusion criteria consisted of articles discussing nonincisional wounds.

RESULTS

Experiments as early as 1929 laid the groundwork for our postoperative activity recommendations. Research using animal models has shown that the gain in tensile strength of a surgical wound is sigmoidal in trajectory, reaching maximal strength approximately 6 weeks postoperatively. Although human and clinical data are limited, the principles gained from laboratory investigation have provided important insights into the relationship among mechanical stress, collagen dynamics, and the time course of wound healing.

CONCLUSION

Our postoperative activity recommendations are based on a series of animal studies. Clinical research supporting these recommendations is minimal, with the most relevant clinical data stemming from early motion protocols in the orthopedic literature. We must seek to establish clinical data to support our postoperative activity recommendations so that we can maximize the physiologic relationships between wound healing and mechanical stress.

Comparison of long-term biocompability of PVDF and PP meshes

BACKGROUND

Abdominal hernia repair is the most frequently performed operation in surgery. Mesh repair in hernia surgery has become an integral component. Although meshes made of PVDF are already in clinical use, so far no data of long-term biocompability are available.

METHODS

In this study a PVDF mesh was compared to a polypropylene mesh with regard to its long-term biocompatibility. A total of 28 rats were randomized to two groups. Mesh material was implanted subcutaneously; animals were euthanized seven days and six months postoperatively. The quantity of inflammatory tissue response was characterized by measuring the diameter of the foreign body granuloma. Furthermore quality of cellular immune response (T-lymphocytes, macrophages, and neutrophils), and inflammation (COX-2) was analyzed by immunohistochemistry. Furthermore the collagen type I/III ratio was determined.

RESULTS

Macrophages, T-lymphocytes, neutrophiles, and COX-2 declined significantly up to six months postoperatively in comparison to day 7 for both PVDF and PP meshes, and in both groups the collagen ratio increased significantly in the course of time. PVDF meshes showed a foreign body granuloma size significantly reduced compared to PP (7 days: 20 ± 2 μm vs. 27 ± 2 μm; 6 months 15 ± 2 μm vs. 22 ± 3 μm; p < .001). However no significant differences were found analyzing cellular response six months postoperatively.

CONCLUSIONS

Our current data suggest that even in the long-term course after six months and despite a higher effective surface of the PVDF samples it showed a smaller foreign body granuloma than with PP whereas the cellular response was similar.

Curcumin heals indomethacin-induced gastric ulceration by stimulation of angiogenesis and restitution of collagen fibers via VEGF and MMP-2 mediated signaling

AIM

We examined the molecular mechanism of curcumin in a preventive and therapeutic model of indomethacin-induced gastric ulceration with regard to angiogenic processes.

RESULTS

Disrupted blood vessels, reduced collagen matrices, and significant (60%) injury to mucosal cells were observed during ulceration. In addition, ulcerated tissues exhibited decreased matrix metalloproteinase (MMP)-2 and vascular endothelial growth factor (VEGF) expression in blood vessels. Interestingly, curcumin blocked ulceration by induction of collagenization and angiogenesis in gastric tissues via upregulation of MMP-2, membrane type (MT) 1-MMP, VEGF, and transforming growth factor (TGF)-β at protein and messenger ribonucleic acid (mRNA) levels. To examine the angiogenic properties of curcumin, we employed a chorioallantoic membrane model and Matrigel assay. During healing, curcumin promoted collagenization and angiogenesis as well as enhanced MMP-2 activity via positive MT1-MMP regulation and negative tissue inhibitor of metalloproteinase-2 regulation.

INNOVATION

Our study demonstrates that curcumin-mediated healing is associated with increased MMP-2, TGF-β, and VEGF expression and that it plays a pivotal role as an angiogenic modulator by stimulating vascular sprout formation and collagen fiber restoration in ulcerated tissues.

CONCLUSION

We conclude that curcumin remodels gastric tissues by restoring the collagen architecture and accelerating angiogenesis.

Delayed wound healing in sacrococcygeal pilonidal sinus coincides with an altered collagen composition

BACKGROUND

Although patients with pilonidal sinus are young and, thus, are expected to heal well, a delayed healing with high risk of recurrence frequently is observed. This study was initiated to test whether disorders in the extracellular matrix (ECM) may be detected in patients with pilonidal sinus and delayed wound healing or recurrent disease, respectively.

METHODS

In 48 patients, tissue specimens were obtained at the index operation. All patients were treated by local excision and primary wound closure. The collagen type I/III ratio, the expression of matrix metalloproteinase (MMP)-1, -9, and -13, as well as the proliferation index (Ki67) and the macrophage infiltrate (CD68) were measured. Patients with an uneventful wound healing by primary intention were compared with those in which the healing by primary intention fails (secondary healing), and patients suffering first onset of pilonidal sinus or to those patients who had undergone previous surgery for pilonidal sinus. Clinical parameters and comorbidity were evaluated.

RESULTS

Patients with secondary healing, exhibited at the index operation a significantly lower collagen type I/III ratio (2.34+/-0.4) compared with patients with problem-free wound healing (3.04+/-0.7). Furthermore, significantly higher expression of MMP-1, -9, and 13, and a significantly higher proliferation index (Ki67) were found in the specimens of the patients with secondary healing. In patients in whom the operation was performed because of a recurrence expression of both Ki67 and CD68 were significantly higher. Smokers had an increased risk for suffering recurrent disease, but did not show differences in the collagen ratio.

CONCLUSIONS

As a novel finding, this study indicates that disturbances of the ECM may predict a delayed wound healing after pilonidal sinus surgery.

Mice that lack matrix metalloproteinase-9 display delayed wound healing associated with delayed reepithelization and disordered collagen fibrillogenesis

Matrix metalloproteinase- (MMP-9) is involved in processes that occur during cutaneous wound healing such as inflammation, matrix remodeling, and epithelialization, To investigate its role in healing, full thickness skin wounds were made in the dorsal region of MMP-9-null and control mice and harvested up to 14 days post wounding. Gross examination and histological and immunohistochemical analysis indicated delayed healing in MMP-9-null mice. Specifically, MMP-9-null wounds displayed compromised reepithelialization and reduced clearance of fibrin clots. In addition, they exhibited abnormal matrix deposition, as evidenced by the irregular alignment of immature collagen fibers. Despite the presence of matrix abnormalities, MMP-9-null wounds displayed normal tensile strength. Ultrastructural analysis of wounds revealed the presence of large collagen fibrils, some with irregular shape. Keratinocyte proliferation, inflammation, and angiogenesis were found to be normal in MMP-9-null wounds. In addition, VEGF levels were similar in control and MMP-9-null wound extracts. To investigate the importance of MMP-9 in wound reepithelialization we tested human and murine keratinocytes in a wound migration assay and found that antibody-based blockade of MMP-9 function or MMP-9 deficiency retarded migration. Collectively, our observations reveal defective healing in MMP-9-null mice and suggest that MMP-9 is required for normal progression of wound closure.

Reconstruction of living bilayer human skin equivalent utilizing human fibrin as a scaffold

Our aim of this study was to develop a new methodology for constructing a bilayer human skin equivalent to create a more clinical compliance skin graft composite for the treatment of various skin defects. We utilized human plasma derived fibrin as the scaffold for the development of a living bilayer human skin equivalent: fibrin-fibroblast and fibrin-keratinocyte (B-FF/FK SE). Skin cells from six consented patients were culture-expanded to passage 1. For B-FF/FK SE formation, human fibroblasts were embedded in human fibrin matrix and subsequently another layer of human keratinocytes in human fibrin matrix was stacked on top. The B-FF/FK SE was then transplanted to athymic mice model for 4 weeks to evaluate its regeneration and clinical performance. The in vivo B-FF/FK SE has similar properties as native human skin by histological analysis and expression of basal Keratin 14 gene in the epidermal layer and Collagen type I gene in the dermal layer. Electron microscopy analysis of in vivo B-FF/FK SE showed well-formed and continuous epidermal-dermal junction. We have successfully developed a technique to engineer living bilayer human skin equivalent using human fibrin matrix. The utilization of culture-expanded human skin cells and fibrin matrix from human blood will allow a fully autologous human skin equivalent construction.

Influence of saline and pH on collagen type I fibrillogenesis in vitro: fibril polymorphism and colloidal gold labelling

We have produced different collagen type I fibrils by in vitro fibrillogenesis of acetic acid-soluble collagen within the pH range 2.5-9.0, in the presence and absence of 150 mM NaCl. The varying relatively stable molecular assemblies and polymorphic fibrillar end-products produced after 24 h incubation have been assessed and compared by the TEM study of specimens negatively stained with uranyl acetate. In the presence of 150 mM NaCl, the assembly of collagen at low pH (2.5) leads to the formation of initial molecular aggregates that progressively link together at slightly higher pH (5.0) to form sub-fibrils and spindle-shaped D-banded bundles of sub-fibrils. At pH 6.0 these D-banded bundles aggregate into larger spindle-shaped fibrils with lateral misalignment of the D-banding across the bundle. However, at pH 7.0 and 8.0, in the presence of 150 mM NaCl, the characteristic parallel-sided mature D-banded collagen type I fibres are formed. At pH 9.0 more loosely formed parallel-sided D-banded collagen fibrils are present, within which the spindle-shaped sub-fibrils can be defined by negative staining more convincingly than at pH 7-8. In the presence of 50 mM buffer at pH 2.5, but absence of 150 mM NaCl, collagen type I forms disorganized periodic initial molecular aggregates, which have a tendency to link together to form sub-fibrils. Flexuous collagen type I sub-fibrils predominate at pH 5.0, alongside large spindle-shaped fibrils that possess a regular transverse approximately 10 nm periodicity, with an oblique approximately 67 nm periodicity, significantly different to the D-banding periodicity. At pH 7.0 and pH 8 in the absence of saline loosely-formed flexuous and spindle-shaped fibres co-exist, with underlying sub-fibrils visible, but at pH 9.0 only disorganized flexuous fibrillar aggregates are present. Colloidal gold labelling of the characteristic D-banded collagen type I fibrils with 5 nm and 2 nm chemically reactive gold particles reveals a periodic labelling pattern, which is not apparent with 10 nm and 15 nm gold particles, due to steric hindrance. The flexuous and spindle-shaped collagen fibrils also bind 2 nm gold particles in a specific manner. In all cases, the specific chemisorption of gold onto the collagen fibrils is probably determined by the availability of repeating amino acid side chains of the collagen molecules along the fibril surface. The controlled production of varying stable collagen type I fibrillogenesis products is likely to be of value within numerous areas of biotechnology, biology and medicine, including experimental biomineralization.