Enzymatic action as switch of bulk to surface degradation of clicked gelatin-based networks

Polymer degradation occurs under physiological conditions in vitro and in vivo, especially when bonds susceptible to hydrolysis are present in the polymer. Understanding of the degradation mechanism, changes of material properties over time, and overall rate of degradation is a necessary prerequisite for the knowledge-based design of polymers with applications in biomedicine. Here, hydrolytic degradation studies of gelatin-based networks synthesized by copper-catalyzed azide-alkyne cycloaddition reaction are reported, which were performed with or without addition of an enzyme. In all cases, networks with a stilbene as crosslinker proofed to be more resistant to degradation than when an octyl diazide was used. Without addition of an enzyme, the rate of degradation was ruled by the crosslinking density of the network and proceeded via a bulk degradation mechanism. Addition of Clostridium histolyticum collagenase resulted in a much enhanced rate of degradation, which furthermore occurred via surface erosion. The mesh size of the hydrogels (>7 nm) was in all cases larger than the hydrodynamic radius of the enzyme (4.5 nm) so that even in very hydrophilic networks with large mesh size enzymes may be used to induce a fast surface degradation mechanism. This observation is of general interest when designing hydrogels to be applied in the presence of enzymes, as the degradation mechanism and material performance are closely interlinkedstatus: publishe

Molecularly engineered polymer-based systems in drug delivery and regenerative medicine

BACKGROUND: Polymer-based systems are attractive in drug delivery and regenerative medicine due to the possibility of tailoring their properties and functions to a specific application. METHODS: The present review provides several examples of molecularly engineered polymer systems, including stimuli responsive polymers and supramolecular polymers. RESULTS: The advent of controlled polymerization techniques has enabled the preparation of polymers with controlled molecular weight and well-defined architecture. By using these techniques coupled to orthogonal chemical modification reactions, polymers can be molecularly engineered to incorporate functional groups able to respond to small changes in the local environment or to a specific biological signal. This review highlights the properties and applications of stimuli-responsive systems and polymer therapeutics, such as polymer-drug conjugates, polymer-protein conjugates, polymersomes, and hyperbranched systems. The applications of polymeric membranes in regenerative medicine are also discussed. CONCLUSION: The examples presented in this review suggest that the combination of membranes with polymers that are molecularly engineered to respond to specific biological functions could be relevant in the field of regenerative medicine.status: publishe

Comparison of in vitro and in vivo Toxicity of Bupivacaine in Musculoskeletal Applications

The recent societal debate on opioid use in treating postoperative pain has sparked the development of long-acting, opioid-free analgesic alternatives, often using the amino-amide local anesthetic bupivacaine as active pharmaceutical ingredient. A potential application is musculoskeletal surgeries, as these interventions rank amongst the most painful overall. Current literature showed that bupivacaine induced dose-dependent myo-, chondro-, and neurotoxicity, as well as delayed osteogenesis and disturbed wound healing in vitro. These observations did not translate to animal and clinical research, where toxic phenomena were seldom reported. An exception was bupivacaine-induced chondrotoxicity, which can mainly occur during continuous joint infusion. To decrease opioid consumption and provide sustained pain relief following musculoskeletal surgery, new strategies incorporating high concentrations of bupivacaine in drug delivery carriers are currently being developed. Local toxicity of these high concentrations is an area of further research. This review appraises relevant in vitro, animal and clinical studies on musculoskeletal local toxicity of bupivacaine

Comparison of in vitro and in vivo Toxicity of Bupivacaine in Musculoskeletal Applications

The recent societal debate on opioid use in treating postoperative pain has sparked the development of long-acting, opioid-free analgesic alternatives, often using the amino-amide local anesthetic bupivacaine as active pharmaceutical ingredient. A potential application is musculoskeletal surgeries, as these interventions rank amongst the most painful overall. Current literature showed that bupivacaine induced dose-dependent myo-, chondro-, and neurotoxicity, as well as delayed osteogenesis and disturbed wound healing in vitro. These observations did not translate to animal and clinical research, where toxic phenomena were seldom reported. An exception was bupivacaine-induced chondrotoxicity, which can mainly occur during continuous joint infusion. To decrease opioid consumption and provide sustained pain relief following musculoskeletal surgery, new strategies incorporating high concentrations of bupivacaine in drug delivery carriers are currently being developed. Local toxicity of these high concentrations is an area of further research. This review appraises relevant in vitro, animal and clinical studies on musculoskeletal local toxicity of bupivacaine

The Importance of Interfaces in Multi-Material Biofabricated Tissue Structures

Biofabrication exploits additive manufacturing techniques for creating 3D structures with a precise geometry that aim to mimic a physiological cellular environment and to develop the growth of native tissues. The most recent approaches of 3D biofabrication integrate multiple technologies into a single biofabrication platform combining different materials within different length scales to achieve improved construct functionality. However, the importance of interfaces between the different material phases, has not been adequately explored. This is known to determine material's interaction and ultimately mechanical and biological performance of biofabricated parts. In this review, this gap is bridged by critically examining the interface between different material phases in (bio)fabricated structures, with a particular focus on how interfacial interactions can compromise or define the mechanical (and biological) properties of the engineered structures. It is believed that the importance of interfacial properties between the different constituents of a composite material, deserves particular attention in its role in modulating the final characteristics of 3D tissue-like structures

Printability and Shape Fidelity of Bioinks in 3D Bioprinting

Three-dimensional bioprinting uses additive manufacturing techniques for the automated fabrication of hierarchically organized living constructs. The building blocks are often hydrogel-based bioinks, which need to be printed into structures with high shape fidelity to the intended computer-aided design. For optimal cell performance, relatively soft and printable inks are preferred, although these undergo significant deformation during the printing process, which may impair shape fidelity. While the concept of good or poor printability seems rather intuitive, its quantitative definition lacks consensus and depends on multiple rheological and chemical parameters of the ink. This review discusses qualitative and quantitative methodologies to evaluate printability of bioinks for extrusion- and lithography-based bioprinting. The physicochemical parameters influencing shape fidelity are discussed, together with their importance in establishing new models, predictive tools and printing methods that are deemed instrumental for the design of next-generation bioinks, and for reproducible comparison of their structural performance

The Importance of Interfaces in Multi-Material Biofabricated Tissue Structures

Biofabrication exploits additive manufacturing techniques for creating 3D structures with a precise geometry that aim to mimic a physiological cellular environment and to develop the growth of native tissues. The most recent approaches of 3D biofabrication integrate multiple technologies into a single biofabrication platform combining different materials within different length scales to achieve improved construct functionality. However, the importance of interfaces between the different material phases, has not been adequately explored. This is known to determine material's interaction and ultimately mechanical and biological performance of biofabricated parts. In this review, this gap is bridged by critically examining the interface between different material phases in (bio)fabricated structures, with a particular focus on how interfacial interactions can compromise or define the mechanical (and biological) properties of the engineered structures. It is believed that the importance of interfacial properties between the different constituents of a composite material, deserves particular attention in its role in modulating the final characteristics of 3D tissue-like structures

The Importance of Interfaces in Multi-Material Biofabricated Tissue Structures

Biofabrication exploits additive manufacturing techniques for creating 3D structures with a precise geometry that aim to mimic a physiological cellular environment and to develop the growth of native tissues. The most recent approaches of 3D biofabrication integrate multiple technologies into a single biofabrication platform combining different materials within different length scales to achieve improved construct functionality. However, the importance of interfaces between the different material phases, has not been adequately explored. This is known to determine material's interaction and ultimately mechanical and biological performance of biofabricated parts. In this review, this gap is bridged by critically examining the interface between different material phases in (bio)fabricated structures, with a particular focus on how interfacial interactions can compromise or define the mechanical (and biological) properties of the engineered structures. It is believed that the importance of interfacial properties between the different constituents of a composite material, deserves particular attention in its role in modulating the final characteristics of 3D tissue-like structures

Cytocompatible carbon nanotube reinforced polyethylene glycol composite hydrogels for tissue engineering

Hydrogels are attractive materials for stimulating 3D cell growth and tissue regeneration, and they provide mechanical support and physical cues to guide cell behavior. Herein, we developed a robust methodology to increase the stiffness of polyethylene glycol (PEG) hydrogels by successfully incorporating carbon nanotubes (CNTs) within the polymer matrix. Interestingly, hydrogels containing pristine CNTs showed a higher stiffness (1915 ± 102 Pa) than both hydrogels without CNTs (1197 ± 125 Pa) and hydrogels incorporating PEG-grafted CNTs (867 ± 103 Pa) (p < 0.005). The swelling ratio was lower for hydrogels with pristine CNTs (45.4 ± 3.5) and hydrogels without CNTs (46.7 ± 5.1) compared to the hydrogels with PEG-grafted CNTs (62.8 ± 2.6). To confirm that the CNT-reinforced hydrogels were cytocompatible, the viability, proliferation, and morphology of encapsulated L929 fibroblasts was investigated. All hydrogel formulations supported cell proliferation, and the addition of pristine CNTs increased initial cell viability (83.3 ± 10.7%) compared to both pure PEG hydrogels (51.9 ± 8.3%) and hydrogels with PEG-CNTs (63.1 ± 10.9%) (p < 0.005). Altogether, these results demonstrate that incorporation of CNTs could effectively reinforce PEG hydrogels and that the resulting cytocompatible nanocomposites are promising scaffolds for tissue engineering.status: publishe

SILK-BASED MATERIALS TO CREATE HIGH RESOLUTION THREE-DIMENSIONAL STRUCTURES USING ELECTROHYDRODYNAMIC PRINTING

Mimicking the complex hierarchical structure of the extracellular matrix (ECM) has always been a major goal in tissue engineering (TE) approaches [1] [2]. Despite the great advances in biomaterial processing technologies, the main limitation concerns the resolution of the fibers, which hampers the reproduction of ECM. Here, we combine Silk Fibroin (SF) [5], a highly potent biomaterial that intrinsically has the characteristics of making fibrous structures, with Electrohydrodynamic printing, an innovative 3D printing technique that allows patterning at micro and sub micro scale. To fabricate these complex structures, Electrohydrodynamic printing applies a voltage between the needle and the collector screen to charge the polymer solution, with a consequent thinning of the fibers, making it possible to reach optimal resolutions for recreating the hierarchical and fibrillar structure of ECM [3] [4]. We have studied SF in its chemical structure to allow a better understanding of the structural and mechanical behaviour of the material before and after printing. We have demonstrated the printability of SF with Electrohydrodynamic printing and, just by tuning the rheological properties, it is possible to obtain straight fibers with a resolution of 10‐20 mm. We have also demonstrated that these fibers can be physically crosslinked inducing the formation of b‐sheets structure in the protein chain; after crosslinking the fibers are stable and don't dissolve in water. SF is therefore proving to be an optimal material for this application and is gaining strong interest in soft tissue engineering