Engineering of Optimized Hydrogel Formulations for Cartilage Repair

The ideal scaffold for cartilage regeneration is expected to provide adequate mechanical strength, controlled degradability, adhesion, and integration with the surrounding native tissue. As it does this, it mimics natural ECMs functions, which allow for nutrient diffusion and promote cell survival and differentiation. Injectable hydrogels based on tyramine (TA)-functionalized hyaluronic acid (HA) and dextran (Dex) are a promising approach for cartilage regeneration. The properties of the hydrogels used in this study were adjusted by varying polymer concentrations and ratios. To investigate the changes in properties and their effects on cellular behavior and cartilage matrix formation, different ratios of HA- and dextran-based hybrid hydrogels at both 5 and 10% w/v were prepared using a designed mold to control generation. The results indicated that the incorporation of chondrocytes in the hydrogels decreased their mechanical properties. However, rheological and compression analysis indicated that 5% w/v hydrogels laden with cells exhibit a significant increase in mechanical properties after 21 days when the constructs are cultured in a chondrogenic differentiation medium. Moreover, compared to the 10% w/v hydrogels, the 5% w/v hybrid hydrogels increased the deposition of the cartilage matrix, especially in constructs with a higher Dex–TA content. These results indicated that 5% w/v hybrid hydrogels with 25% HA–TA and 75% Dex–TA have a high potential as injectable scaffolds for cartilage tissue regeneration.

Single-Stage Arthroscopic Cartilage Repair With Gel Scaffold and BMAC

Background: Injectable scaffold augmentation has been gaining traction as a promising modality for single-stage cartilage repair. It involves the use of a biological scaffold that augments microfracture techniques by aiding in clot stabilization and maturation. The scaffold provides a matrix that helps with mesenchymal stem cell (MSC) retention and encourages differentiation along a chondrogenic lineage. Bone marrow aspirate concentrate (BMAC) has also been proposed as an alternative source of MSCs to microfracture, and it can potentially avoid the pitfalls of microfracture techniques. Indications: Injectable scaffold augmentation to microfracture techniques are recommended in lesions >4 cm, as long-term follow-up has shown increasing failure over time with microfracture alone. Technique Description: We describe a technique of autologous matrix-induced chondrogenesis using CartiFill, a porcine-derived type 1 collagen scaffold, combined with BMAC as a source of MSCs (avoiding the use of microfracture). Results: Injectable scaffold augmentation has been shown in recent studies to lead to better radiological fill, higher quality of histological repair, and better clinical outcomes as compared with microfracture alone. These injectable scaffolds have the versatility to be used on lesions which have traditionally been considered difficult to address, such as vertical or inverted lesions. Moreover, the use of scaffolds allows the repair to be further augmented with BMAC which provides a source of MSCs without the need to perform microfracture and perforate the subchondral bone. Discussion/Conclusion: Scaffold augmentation is a promising technique that improves upon the results of conventional microfracture repair by allowing augmentation with BMAC, as well as giving surgeons the versatility to apply the scaffold on vertical/inverted lesions. BMAC is also a viable alternative source of MSCs for cartilage repair.

Injectability of Thermosensitive, Low-Concentrated Chitosan Colloids as Flow Phenomenon through the Capillary under High Shear Rate Conditions

Low-concentrated colloidal chitosan systems undergoing a thermally induced sol–gel phase transition are willingly studied due to their potential use as minimally invasive injectable scaffolds. Nevertheless, instrumental injectability tests to determine their clinical utility are rarely performed. The aim of this work was to analyze the flow phenomenon of thermosensitive chitosan systems with the addition of disodium β-glycerophosphate through hypodermic needles. Injectability tests were performed using a texture analyzer and hypodermic needles in the sizes 14G–25G. The rheological properties were determined by the flow curve, three-interval thixotropy test (3ITT), and Cox–Merz rule. It was found that reducing the needle diameter and increasing its length and the crosshead speed increased the injection forces. It was claimed that under the considered flow conditions, there was no need to take into account the viscoelastic properties of the medium, and the model used to predict the injection force, based solely on the shear-thinning nature of the experimental material, showed very good agreement with the experimental data in the shear rate range of 200–55,000 s−1. It was observed that the increase in the shear rate value led to macroscopic structural changes of the chitosan sol caused by the disentangling and ordering of the polysaccharide chains along the shear field.

PREPARATION AND CHARACTERIZATION OF A NEW GENERATION OF CHITOSAN HYDROGELS CONTAINING PYRIMIDINE RIBONUCLEOTIDES

Damage to the nervous system, in particular spinal cord injuries, is a burden for the patient and is usually the cause of irreversible disability. The progress observed in the last decade in the fields of biology, biomaterial engineering and neurosurgery has created new treatment solutions while preventing further neurodegenerative processes. The most important research is focused on the implementation of polymer structures in clinical practice, especially chitosan hydrogels, which are the scaffolds for regenerating axons. This article presents a new generation of biomaterials that have the ability to gel in response to temperature changes; they are intended for injectable scaffolds for nerve cell cultures. Two types of hydrogels were prepared based on chitosan lactate and chitosan chloride using uridine 5’-monophosphate disodium salt. The structure of the systems was observed under a scanning electron microscope and examined using Fourier transform infrared spectroscopy. In addition, thermal properties were tested using differential scanning calorimetry.

Proteolytic Rafts for Improving Intraparenchymal Migration of Minimally Invasively Administered Hydrogel-Embedded Stem Cells

The physiological spaces (lateral ventricles, intrathecal space) or pathological cavities (stroke lesion, syringomyelia) may serve as an attractive gateway for minimally invasive deployment of stem cells. Embedding stem cells in injectable scaffolds is essential when transplanting into the body cavities as they secure favorable microenvironment and keep cells localized, thereby preventing sedimentation. However, the limited migration of transplanted cells from scaffold to the host tissue is still a major obstacle, which prevents this approach from wider implementation for the rapidly growing field of regenerative medicine. Hyaluronan, a naturally occurring polymer, is frequently used as a basis of injectable scaffolds. We hypothesized that supplementation of hyaluronan with activated proteolytic enzymes could be a viable approach for dissolving the connective tissue barrier on the interface between the scaffold and the host, such as pia mater or scar tissue, thus demarcating lesion cavity. In a proof-of-concept study, we have found that collagenase and trypsin immobilized in hyaluronan-based hydrogel retain 60% and 28% of their proteolytic activity compared to their non-immobilized forms, respectively. We have also shown that immobilized enzymes do not have a negative effect on the viability of stem cells (glial progenitors and mesenchymal stem cells) in vitro. In conclusion, proteolytic rafts composed of hyaluronan-based hydrogels and immobilized enzymes may be an attractive strategy to facilitate migration of stem cells from injectable scaffolds into the parenchyma of surrounding tissue.