Recent strategies of collagen-based biomaterials for cartilage repair: from structure cognition to function endowment

Promotion of hMDSC differentiation by combined action of scaffold material and TGF-β superfamily growth factors

Objective

Herein we propose a combined action of collagen type I (CA) or synthetic collagen-like-peptide functionalized with the cell adhesive RGD motif (PEG-CLP-RGD) hydrogels and selected growth factors to promote chondrogenic differentiation of human muscle-derived stem cells (hMDSCs) under normal and reduced oxygen conditions.

Methods

hMDSCs were set for differentiation towards chondrogenic lineage using BMP-7 and TGF-β3. Cells were seeded onto hydrogels loaded with growth factors (75ng/scaffold) and cultured for 28 days under normal (21%) and severe hypoxic (1%) conditions. Chondrogenesis was evaluated by monitoring collagen type II and GAG deposition, and quantification of ACAN expression by RT-PCR.

Results

Sustained release of TGFβ3 from the hydrogels was observed, 8.7 ± 0.5% of the initially loaded amount diffused out after 24 h from both substrates. For the BMP-7 growth factor, 14.8 ± 0.3% and 18.2 ± 0.6% of the initially loaded amount diffused out after 24 h from CA and CLP-RGD, respectively. The key findings of this study are: i) the self-supporting hydrogels themselves can stimulate hMDSC chondrogenesis by inducing gene expression of cartilage-specific proteoglycan aggrecan and ECM production; ii) the effect of dual BMP-7 and TGF-β3 loading was more pronounced on CA hydrogel under normal oxygen conditions; iii) dual loading on PEG-CLP-RGD hydrogels did not have the synergistic effect, TGF-β3 was more effective under both oxygen conditions; iv) BMP-7 can improve chondrogenic effect of TGF-β3 on CA scaffolds, and hydrogels loaded with both growth factors can induce cartilage formation in hMDSC cultures.

Conclusion

Our results support the potential strategy of combining implantable hydrogels functionalized with differentiation factors toward improving cartilaginous repair.

Type II collagen scaffolds repair critical-sized osteochondral defects under induced conditions of osteoarthritis in rat knee joints via inhibiting TGF-β-Smad1/5/8 signaling pathway

The bidirectional relationship between osteochondral defects (OCD) and osteoarthritis (OA), with each condition exacerbating the other, makes OCD regeneration in the presence of OA challenging. Type II collagen (Col2) is important in OCD regeneration and the management of OA, but its potential applications in cartilage tissue engineering are significantly limited. This study investigated the regeneration capacity of Col2 scaffolds in critical-sized OCDs under surgically induced OA conditions and explored the underlying mechanisms that promoted OCD regeneration. Furthermore, the repair potential of Col2 scaffolds was validated in over critical-sized OCD models. After 90 days or 150 days since scaffold implantation, complete healing was observed histologically in critical-sized OCD, evidenced by the excellent integration with surrounding native tissues. The newly formed tissue biochemically resembled adjacent natural tissue and exhibited comparable biomechanical properties. The regenerated OA tissue demonstrated lower expression of genes associated with cartilage degradation than native OA tissue but comparable expression of genes related to osteochondral anabolism compared with normal tissue. Additionally, transcriptome and proteome analysis revealed the hindrance of TGF-β-Smad1/5/8 in regenerated OA tissue. In conclusion, the engrafting of Col2 scaffolds led to the successful regeneration of critical-sized OCDs under surgically induced OA conditions by inhibiting the TGF-β-Smad1/5/8 signaling pathway.

Effect of radiation cross-linked collagen scaffold in alveolar ridge preservation of extraction socket

This study aimed to evaluate the properties of radiation cross-linked collagen scaffold (RCS) and its efficacy for alveolar ridge preservation (ARP). RCS was prepared from collagen dispersion by electron beam irradiation and freeze-drying. The microstructure, swelling ratio, area alteration and mechanical properties of RCS were characterized. Fifty-four New Zealand rabbits performing incisor extraction on maxilla and mandible were randomly assigned into positive, sham operation or treatment groups. Micro-computed tomography (micro-CT) scans, performed after 1, 4, and 12 weeks of surgery, were to assess changes in ridge height at buccal and palatal side, in ridge width and in micromorphological parameters. Histological analysis accessed socket microarchitecture. The results showed that RCS had stable mechanical properties and morphologic features that provided a reliable physical support for ARP. Dimensional changes in treatment group revealed significantly greater vertical height at buccal (5.32 [3.37, 7.26] mm, p < .0001) and palatal (4.37 [2.66, 6.09] mm, p < .0001) side, and horizontal width at the maxilla (0.16 [0.04, 0.28] mm, p < .01) and mandible (0.33 [0.11, 0.54] mm, p < .01) than those in sham operation group after 12 weeks. The treatment group had advantage than positive group in vertical height preservation, quantitatively. The order and density of bone trabeculae were improved in treatment group. These findings indicated that RCS had the potential to serve as an effective scaffold for ARP.

Converting Acellular Dermal Matrix into On-Demand Versatile Skin Scaffolds by a Balanceable Crosslinking Approach for Integrated Infected Wounds Therapy

Ideal tissue-engineered skin scaffolds should possess integrated therapeutic effects and multifunctionality, such as broad-spectrum antibacterial properties, adjustable mechanical properties, and bionic structure. Acellular dermal matrix (ADM) has been broadly used in many surgical applications as an alternative treatment to the "gold standard" tissue transplantation. However, insufficient broad-spectrum antibacterial and mechanical properties for therapeutic efficacy limit the practical clinical applications of ADM. Herein, a balanceable crosslinking approach based on oxidized 2-hydroxypropyltrimethyl ammonium chloride chitosan (OHTCC) was developed for converting ADM into on-demand versatile skin scaffolds for integrated infected wounds therapy. Comprehensive experiments show that different oxidation degrees of OHTCC have significative influences on the specific origins of OHTCC-crosslinked ADM scaffolds (OHTCC-ADM). OHTCC with an oxidation degree of about 13% could prosperously balance the physiochemical properties, antibacterial functionality, and cytocompatibility of the OHTCC-ADM scaffolds. Owing to the natural features and comprehensive crosslinking effects, the proposed OHTCC-ADM scaffolds possessed the desirable multifunctional properties, including adjustable mechanical, degradable characteristics, and thermal stability. In vitro/in vivo biostudies indicated that OHTCC-ADM scaffolds own well-pleasing broad-spectrum antibacterial performances and play effectively therapeutic roles in treating infection, inhibiting inflammation, promoting angiogenesis, and promoting collagen deposition to enhance the infected wound healing. This study proposes a facile balanceable crosslinking approach for the design of ADM-based versatile skin scaffolds for integrated infected wounds therapy.

Effect of Mechanical Microenvironment on Collagen Self-Assembly In Vitro

Collagen, as a structural protein, is widely distributed in the human body. Many factors influence collagen self-assembly in vitro, including physical-chemical conditions and mechanical microenvironment, and play a key role in driving the structure and arrangement. However, the exact mechanism is unknown. The purpose of this paper is to investigate the changes in the structure and morphology of collagen self-assembly in vitro under mechanical microenvironment, as well as the critical role of hyaluronic acid in this process. Using bovine type I collagen as the research object, collagen solution is loaded into tensile and stress-strain gradient devices. The morphology and distribution of collagen is observed using an atomic force microscope while changing the concentration of collagen solution, mechanical loading strength, tensile speed, and ratio of collagen to hyaluronic acid. The results demonstrate that the mechanics field governs collagen fibers and changes their orientation. Stress magnifies the differences in results caused by different stress concentrations and sizes, and hyaluronic acid improves collagen fiber orientation. This research is critical for expanding the use of collagen-based biomaterials in tissue engineering.

Hyalofast Cartilage Repair Surgery with a Full Load-Bearing Rehabilitation Program One Day after Operation Reduces the Time for Professional Athletes to Return to Play

Background and Objectives: This study evaluated the effectiveness of Hyalofast cartilage repair surgery with an early, full load-bearing rehabilitation program one day after the operation for reducing the time needed for professional athletes to return to play. Materials and Methods: This prospective study included 49 patients aged between 19 and 38 years who had undergone surgical reconstruction of cartilage using the microfracture technique combined with a Hyalofast scaffold. All patients were active professional athletes. Early rehabilitation was implemented from the first postoperative day, fully loading the operated limb. A clinical evaluation was based on the KOOS and SF-36 questionnaires used during subsequent follow-up visits. All patients underwent magnetic resonance imaging (MRI) to evaluate the effect of the surgery after one year. Results: The clinical results demonstrated a statistically significant improvement in the number of complaints about pain and in the quality of life of the patients, measured in all of the applied scales, with comparisons made between six months or one year post-surgery and pre-surgery. Importantly for athletes, the parameter related to sports and recreation improved from 14 ± 11.1 to 95 ± 7.7 6 months after surgery and to 99.8 ± 1.8 one year after surgery. The overall quality of life score improved from 30 ± 18 to 88 ± 8.8 one year after surgery. Conclusions: These results show that this approach significantly shortened the time needed for the athletes to return to sports at the same level as before the surgery (athletes returned to sports in approximately 2.5-3 months). The mean follow-up time was 19.75 months. This technique can be considered a viable option for the treatment of cartilage injuries in professional athletes, allowing them to return to play more quickly in a safe and healthy way.

Site-specific modification of N-terminal α-amino groups of succinylated collagen

Polymer based protein engineering provides an attractive strategy to endow novel properties to protein and overcome the inherent limitations of both counterparts. The exquisite control of site and density of attached polymers on the proteins is crucial for the bioactivities and properties of the protein-polymer bioconjugates, but is still a challenge. Collagen is the major structural protein in extracellular matrix of animals. Based on the advancements of polymer-based protein engineering, collagen bioconjugates has been widely fabricated and applied as biomaterials. However, the site-specific synthesis of well-defined collagen-polymer bioconjugates is still not achieved. Herein, a versatile strategy for the specific modification of N-terminal α-amino groups in collagen was developed. Firstly, all reactive amino groups of tropocollagen (collagen with telopeptides) were protected by succinic anhydride. Then, the telopeptides were digested to give the active N-terminal α-amino groups, which were subsequently attached with poly(N-isopropylacrylamide) (PNIPAAm) via "grafting from" method based on the atom transfer radical polymerization (ATRP). The site-specific N-terminal PNIPAAm modified succinylated collagen was prepared and its structure, thermal responsive behaviour, and properties was explored.

Layered scaffolds in periodontal regeneration

Periodontitis is a common inflammatory disease in dentistry that may lead to tooth loss and aesthetic problems. Periodontal tissue has a sophisticated architecture including four sections of alveolar bone, cementum, gingiva, and periodontal ligament fiber; all these four can be damaged during periodontitis. Thus, for whole periodontal regeneration, it is important to form both hard and soft tissue structures simultaneously on the tooth root surface without forming junctional epithelium and ankylosis. This condition makes the treatment of the periodontium a challenging process. Various regenerative methods including Guided Bone/Tissue Regeneration (GBR/GTR) using various membranes have been developed. Although using such GBR/GTR membranes was successful for partial periodontal treatment, they cannot be used for the regeneration of complete periodontium. For this purpose, multilayered scaffolds are now being developed. Such scaffolds may include various biomaterials, stem cells, and growth factors in a multiphasic configuration in which each layer is designed to regenerate specific section of the periodontium. This article provides a comprehensive review of the multilayered scaffolds for periodontal regeneration based on natural or synthetic polymers, and their combinations with other biomaterials and bioactive molecules. After highlighting the challenges related to multilayered scaffolds preparation, features of suitable scaffolds for periodontal regeneration are discussed.

'Multiple and short-range' cross-linking of dialdehyde carboxymethyl cellulose contributes to regulating the physicochemical property of collagen fibril

Collagen fibril hydrogel (CH), with controllable micro-structure, sufficient modifying sites and excellent biocompatibility, has received widely attention in the regulation of biomacromolecules. Herein, dialdehyde carboxymethyl cellulose (DCMC) in different -CHO contents and molecular weights demonstrated two types of cross-linking behaviors to CH, 'limited and long-range' or 'multiple and short range' cross-linking, corresponding to -CHO content ranged from 0 to  53 % and 53- 90 %, respectively. In regard of structure, non-destroying effect of DCMC on collagen was supported by FT-IR and XRD analysis. CH cross-linked by DCMC (CH-DC) showed declining porosity and aggregating fibrils as -CHO content of DCMC rising. In regard of physicochemical properties, DCMC with >53 % -CHO strengthened the hydrophilicity, thermal stability and degradation resistance of CH-DC. Also, there was 110 % growth on gel strength, 86 Pa enhancements on storage modulus, and 4.6 times decrease on the swelling ratio of CH-DC. Results indicated that DCMC with 79 % -CHO remarkably improved the physicochemical properties of CH via developing sufficient Schiff-base bonds with collagen fibril in a short distance. This study distinguished two patterns of DCMC cross-linking from physicochemical view. In other words, DCMC is potential to meet the requirement of protein-based materials with different expectations by adjusting its -CHO content and molecular weight.

Fabrication of a stepwise degradable hybrid bioscaffold based on the natural and partially denatured collagen

As a major component of extracellular matrixes (ECMs), collagen is an attractive biomaterial to fabricate porous scaffold for tissue engineering due to their similarity to the in vivo static microenvironment. However, the collagen-based porous scaffolds were difficult to mimic the dynamically remolded porous structure of ECM during the cell proliferation and tissue development, and always have poor mechanical property and not easy to handle. Here, natural collagen and partially denatured collagen was used to prepare the stepwise degradable hybrid bioscaffold with suitable mechanical property and dynamically remolded inner porous structure, which is desirable for the applications of tissue engineering. The collagen-based microporous scaffold was first prepared and used as physical support, then, the mechanical strength of which was reinforced by the import of the partially denatured collagen to give the hybrid bioscaffold. The fabrication conditions of the hybrid scaffolds were optimized, of which the thermal stability, mechanical property, and swelling property was explored. The stepwise enzymatic degradation process and the corresponding porous structure variation of the hybrid scaffold was confirmed by SEM and cell culture assays.