Biodegradable elastomeric scaffolds for soft tissue engineering

In Vitro and In Vivo Degradation of Photo-Crosslinked Poly(Trimethylene Carbonate-co-ε-Caprolactone) Networks

Three-armed poly(trimethylene carbonate) (PTMC) and poly(trimethylene carbonate-co-Ɛ-caprolactone) (P(TMC-co-ε-CL)) macromers with molecular weights of approximately 30 kg mol-1 are synthesized by ring-opening polymerization and subsequent functionalization with methacrylic anhydride. Networks are then prepared by photo-crosslinking. To investigate the in vitro and in vivo degradation properties of these photo-crosslinked networks and assess the effect of ε-caprolactone content on the degradation properties, PTMC networks, and copolymer networks with two different TMC:ε-CL ratios are prepared. PTMC networks degraded slowly, via an enzymatic surface erosion process, both in vitro and in vivo. Networks prepared from P(TMC-co-ε-CL) macromers with a 74:26 ratio are found to degrade slowly as well, via a surface erosion process, albeit at a higher rate compared to PTMC networks. Increasing the ε-CL content to a ratio of 52:48, resulted in a faster degradation. These networks lost their mechanical properties much sooner than the other networks. Thus, PTMC and P(TMC-co-ε-CL) networks are interesting networks for tissue engineering purposes and the exact degradation properties can be tuned by varying the TMC:ε-CL ratio, providing researchers with a tool to obtain copolymer networks with the desired degradation rate depending on the intended application.

The ad hoc chemical design of random PBS-based copolymers influences the activation of cardiac differentiation while altering the HYPPO pathway target genes in hiPSCs

Cardiac tissue engineering is a cutting-edge technology aiming to replace irreversibly damaged cardiac tissue and restore contractile functionality. However, cardiac tissue engineering porous and perfusable scaffolds to enable oxygen supply in vitro and eventually promote angiogenesis in vivo are still desirable. Two fully-aliphatic random copolymers of poly(butylene succinate) (PBS), poly(butylene succinate/Pripol), P(BSBPripol), and poly(butylene/neopentyl glycol succinate), P(BSNS), containing two different subunits, neopentyl glycol and Pripol 1009, were successfully synthesized and then electrospun in tridimentional fibrous mats. The copolymers show different thermal and mechanical behaviours as result of their chemical structure. In particular, copolymerization led to a reduction in crystallinity and consequently PBS stiffness, reaching values of elastic modulus very close to those of soft tissues. Then, to check the biological suitability, human induced Pluripotent Stem Cells (hiPSCs) were directly seeded on both PBS-based copolymeric scaffolds. The results confirmed the ability of both the scaffolds to sustain cell viability and to maintain their stemness during cell expansion. Furthermore, gene expression and immunofluorescence analysis showed that P(BSBPripol) scaffold promoted an upregulation of the early cardiac progenitor and later-stage markers with a simultaneously upregulation of HYPPO pathway gene expression, crucial for mechanosensing of cardiac progenitor cells. These results suggest that the correct ad-hoc chemical design and, in turn, the mechanical properties of the matrix, such as substrate stiffness, together with surface porosity, play a critical role in regulating the behaviour of cardiac progenitors, which ultimately offers valuable insights into the development of novel bio-inspired scaffolds for cardiac tissue regeneration.

Advances in Functionalization of Bioresorbable Nanomembranes and Nanoparticles for Their Use in Biomedicine

Bioresorbable nanomembranes (NMs) and nanoparticles (NPs) are powerful polymeric materials playing an important role in biomedicine, as they can effectively reduce infections and inflammatory clinical patient conditions due to their high biocompatibility, ability to physically interact with biomolecules, large surface area, and low toxicity. In this review, the most common bioabsorbable materials such as those belonging to natural polymers and proteins for the manufacture of NMs and NPs are reviewed. In addition to biocompatibility and bioresorption, current methodology on surface functionalization is also revisited and the most recent applications are highlighted. Considering the most recent use in the field of biosensors, tethered lipid bilayers, drug delivery, wound dressing, skin regeneration, targeted chemotherapy and imaging/diagnostics, functionalized NMs and NPs have become one of the main pillars of modern biomedical applications.

Contact osteogenesis by biodegradable 3D-printed poly(lactide-co-trimethylene carbonate)

Background

To support bone regeneration, 3D-printed templates function as temporary guides. The preferred materials are synthetic polymers, due to their ease of processing and biological inertness. Poly(lactide-co-trimethylene carbonate) (PLATMC) has good biological compatibility and currently used in soft tissue regeneration. The aim of this study was to evaluate the osteoconductivity of 3D-printed PLATMC templates for bone tissue engineering, in comparison with the widely used 3D-printed polycaprolactone (PCL) templates.

Methods

The printability and physical properties of 3D-printed templates were assessed, including wettability, tensile properties and the degradation profile. Human bone marrow-derived mesenchymal stem cells (hBMSCs) were used to evaluate osteoconductivity and extracellular matrix secretion in vitro. In addition, 3D-printed templates were implanted in subcutaneous and calvarial bone defect models in rabbits.

Results

Compared to PCL, PLATMC exhibited greater wettability, strength, degradation, and promoted osteogenic differentiation of hBMSCs, with superior osteoconductivity. However, the higher ALP activity disclosed by PCL group at 7 and 21 days did not dictate better osteoconductivity. This was confirmed in vivo in the calvarial defect model, where PCL disclosed distant osteogenesis, while PLATMC disclosed greater areas of new bone and obvious contact osteogenesis on surface.

Conclusions

This study shows for the first time the contact osteogenesis formed on a degradable synthetic co-polymer. 3D-printed PLATMC templates disclosed unique contact osteogenesis and significant higher amount of new bone regeneration, thus could be used to advantage in bone tissue engineering.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40824-022-00299-x.

Shape-Memory Materials via Electrospinning: A Review

This review aims to point out the importance of the synergic effects of two relevant and appealing polymeric issues: electrospun fibers and shape-memory properties. The attention is focused specifically on the design and processing of electrospun polymeric fibers with shape-memory capabilities and their potential application fields. It is shown that this field needs to be explored more from both scientific and industrial points of view; however, very promising results have been obtained up to now in the biomedical field and also as sensors and actuators and in electronics.

A Composite Lactide-Mineral 3D-Printed Scaffold for Bone Repair and Regeneration

Orthopedic tumor resection, trauma, or degenerative disease surgeries can result in large bone defects and often require bone grafting. However, standard autologous bone grafting has been associated with donor site morbidity and/or limited quantity. As an alternate, allografts with or without metallic or polyether-etherketone have been used as grafting substitutes. However, these may have drawbacks as well, including stress shielding, pseudarthrosis, disease-transmission, and infection. There is therefore a need for alternative bone substitutes, such as the use of mechanically compliant three-dimensional (3D)-printed scaffolds. Several off-the-shelf materials are available for low-cost fused deposition 3D printing such as polylactic acid (PLA) and polycaprolactone (PCL). We have previously described the feasibility of 3D-printed PLA scaffolds to support cell activity and extracellular matrix deposition. In this study, we investigate two medical-grade filaments consistent with specifications found in American Society for Testing and Materials (ASTM) standard for semi-crystalline polylactide polymers for surgical implants, a pure polymer (100M) and a copolymeric material (7415) for their cytocompatibility and suitability in bone tissue engineering. Moreover, we assessed the impact on osteo-inductive properties with the addition of beta-tricalcium phosphate (β-TCP) minerals and assessed their mechanical properties. 100M and 7415 scaffolds with the additive β-TCP demonstrated superior mesenchymal stem cells (MSCs) differentiation detected via increased alkaline phosphatase activity (6-fold and 1.5-fold, respectively) and mineralized matrix deposition (14-fold and 5-fold, respectively) in vitro. Furthermore, we evaluated in vivo compatibility, biosafety and bone repair potential in a rat femur window defect model. 100M+β -TCP implants displayed a positive biosafety profile and showed significantly enhanced new bone formation compared to 100M implants evidenced by μCT (39 versus 25% bone volume/tissue volume ratio) and histological analysis 6 weeks post-implantation. These scaffolds are encouraging composite biomaterials for repairing bone applications with a great potential for clinical translation. Further analyses are required with appropriate evaluation in a larger critical-sized defect animal model with long-term follow-up.

Biodegradable Flexible Electronic Device with Controlled Drug Release for Cancer Treatment

Nowadays, controllable drug release is a vitally important strategy for cancer treatment and usually realized using implanting biocompatible devices. However, these devices need to be removed by another surgery after the function fails, which brings the risks of inflammation or potential death. In this article, a biodegradable flexible electronic device with controllable drug (paclitaxel) release was proposed for cancer treatment. The device is powered by an external alternating magnetic field to generate internal resistance heat and promote drug release loaded on the substrate. Moreover, the device temperature can even reach to 65 °C, which was sufficient for controllable drug release. This device also has similar mechanical properties to human tissues and can autonomously degrade due to the structure design of the circuit and degradable compositions. Finally, it is confirmed that the device has a good inhibitory effect on the proliferation of breast cancer cells (MCF-7) and could be completely degraded in vitro. Thus, its great biodegradability and conformity can relieve patients of second operation, and the device proposed in this paper provides a promising solution to complete conquest of cancer in situ.

Understanding of how the properties of medical grade lactide based copolymer scaffolds influence adipose tissue regeneration: Sterilization and a systematic in vitro assessment

Aliphatic polyesters are the synthetic polymers most commonly used in the development of resorbable medical implants/devices. Various three-dimensional (3D) scaffolds have been fabricated from these polymers and used in adipose tissue engineering. However, their systematic evaluation altogether lacks, which makes it difficult to select a suitable degradable polymer to design 3D resorbable implants and/or devices able to effectively mimic the properties of adipose tissue. Additionally, the impact of sterilization methods on the medical devices, if any, must be taken into account. We evaluate and compare five different medical-grade resorbable polyesters with l-lactide content ranging from 50 to 100 mol% and exhibiting different physiochemical properties depending on the comonomer (d-lactide, ε-caprolactone, glycolide, and trimethylene carbonate). The salt-leaching technique was used to prepare 3D microporous scaffolds. A comprehensive assessment of physical, chemical, and mechanical properties of the scaffolds was carried out in PBS at 37 °C. The cell-material interactions and the ability of the scaffolds to promote adipogenesis of human adipose tissue-derived stem cells were assessed in vitro. The diverse physical and mechanical properties of the scaffolds, due to the different composition of the copolymers, influenced human adipose tissue-derived stem cells proliferation and differentiation. Scaffolds made from polymers which were above their glass transition temperature and with low degree of crystallinity showed better proliferation and adipogenic differentiation of stem cells. The effect of sterilization techniques (electron beam and ethylene oxide) on the polymer properties was also evaluated. Results showed that scaffolds sterilized with the ethylene oxide method better retained their physical and chemical properties. Overall, the presented research provides (i) a detailed understanding to select a degradable polymer that has relevant properties to augment adipose tissue regeneration and can be further used to fabricate medical devices/implants; (ii) directions to prefer a sterilization method that does not change polymer properties.

Poly(trimethylene carbonate-co-valerolactone) copolymers are materials with tailorable properties: from soft to thermoplastic elastomers

Aliphatic poly(ester-carbonates) are receiving extensive research attention as tailorable materials suitable for multiple applications from tissue engineering and 3D scaffold printing to drug delivery. Thus, simple reliable procedures for producing easily tailorable poly(ester-carbonates) without metal residues are continuously sought after. In this work, we report on one-pot synthesis of random copolymers of TMC and δ-VL using metal-free biocompatible 1,5,7-triazabicyclo[4.4.0]dec-5-ene as a catalyst and benzyl alcohol and poly(ethylene oxide) as initiators. Random poly(ester-carbonates) with TMC : VL unit ratios ranging from 80 : 20 to 20 : 80 were synthesized via ring-opening polymerization while displaying excellent agreement of comonomers' ratios in the feed and copolymer chains. The copolymers' supramolecular structure, thermal and mechanical properties were thoroughly analyzed by various methods. The obtained results clearly indicated that the physicochemical properties can be controlled simply by varying the ratio of comonomers and the length of segments in the copolymer chain. Several copolymers exhibited behavior of thermoplastic elastomers with the most promising one exhibiting a 2200% increase in elongation at break compared to the poly(valerolactone) homopolymer while retaining tensile strength and Young's modulus suitable for biomedical applications. Overall, our work contributed to widening the portfolio of tailorable copolymers for specialized bioapplications and possibly paving a way for the use of more sustainable polymers in the biomedical field.

The impact of relative humidity on electrospun polymer fibers: From structural changes to fiber morphology

Electrospinning is one of the most important methods used for the production of nanostructured materials. Electrospun nanofibers are used in a wide spectrum of applications such as drug delivery systems, filtration, fog harvesting, tissue engineering, smart textiles, flexible electronics, and more. Control of the manufacturing process is essential for further technology developments. In electrospinning, relative humidity is a crucial parameter that influences nearly all the properties of the collected fibers, such as morphology, mechanical properties, liquid retention, wetting properties, phase composition, chain conformation, and surface potential. Relative humidity is a determining component of a reliable process as it governs charge dissipation and solvent evaporation. This review summarizes the electrospinning process and its applications, phase separation processes, and impact of relative humidity on the properties of polymer fibers. We investigated relative humidity effects on both hydrophilic and hydrophobic polymers using over 20 polymers and hundreds of solvent systems. Most importantly, we underlined the indisputable importance of relative humidity in process repeatability and demonstrated its impact on almost all aspects of fiber production from a solution droplet to an electrospun network.

The Role of Two-Step Blending in the Properties of Starch/Chitin/Polylactic Acid Biodegradable Composites for Biomedical Applications

The current research trend for excellent miscibility in polymer mixing is the use of plasticizers. The use of most plasticizers usually has some negative effects on the mechanical properties of the resulting composite and can sometimes make it toxic, which makes such polymers unsuitable for biomedical applications. This research focuses on the improvement of the miscibility of polymer composites using two-step mixing with a rheomixer and a mix extruder. Polylactic acid (PLA), chitin, and starch were produced after two-step mixing, using a compression molding method with decreasing composition variation (between 8% to 2%) of chitin and increasing starch content. A dynamic mechanical analysis (DMA) was used to study the mechanical behavior of the composite at various temperatures. The tensile strength, yield, elastic modulus, impact, morphology, and compatibility properties were also studied. The DMA results showed a glass transition temperature range of 50 °C to 100 °C for all samples, with a distinct peak value for the loss modulus and factor. The single distinct peak value meant the polymer blend was compatible. The storage and loss modulus increased with an increase in blending, while the loss factor decreased, indicating excellent compatibility and miscibility of the composite components. The mechanical properties of the samples improved compared to neat PLA. Small voids and immiscibility were noticed in the scanning electron microscopy images, and this was corroborated by X-ray diffraction graphs that showed an improvement in the crystalline nature of PLA with starch. Bioabsorption and toxicity tests showed compatibility with the rat system, which is similar to the human system.

Bio-Based Thermo-Reversible Aliphatic Polycarbonate Network

Aliphatic polycarbonates represent an important class of materials with notable applications in the biomedical field. In this work, low Tg furan-functionalized bio-based aliphatic polycarbonates were cross-linked thanks to the Diels-Alder (DA) reaction with a bis-maleimide as the cross-linking agent. The thermo-reversible DA reaction allowed for the preparation of reversible cross-linked polycarbonate materials with tuneable properties as a function of the pendent furan content that was grafted on the polycarbonate backbone. The possibility to decrosslink the network around 70 °C could be an advantage for biomedical applications, despite the rather poor thermal stability of the furan-functionalized cross-linked polycarbonates.

Hydrolytic Degradation of Comb-Like Graft Poly (Lactide-co-Trimethylene Carbonate): The Role of Comonomer Compositions and Sequences

The effect of sequence on copolymer properties is rarely studied, especially the degradation behavior of the biomaterials. A series of linear-comb block, gradient, random copolymers were successfully achieved using hydroxylated polybutadiene as the macroinitiator by simple ring-opening polymerization of l-lactide (l-LA) and 1,3-trimethylene carbonate (TMC). The hydrolytic degradation behaviors of the copolymers were systemically evaluated by using nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), differential scanning calorimeter (DSC), and scanning electron microscopy (SEM) to illustrate the influences of comonomer compositions and sequence structures. The linear-comb block copolymers (lcP(TMC-b-LLA)) with different compositions had different degradation rates, which increased with l-LA content. Thermal property changes were observed with decreased T_m and increased ΔH_m in all block copolymers during the degradation. To combine different sequence structures, unique degradation behaviors were observed for the linear-comb block, gradient and random copolymers even with similar comonomer composition. The degradation rates of linear-comb PLLA-gradient-PTMC (lcP(LLA-grad-TMC)) and linear-comb PLLA-random-PTMC (lcP(LLA-ran-TMC)) were accelerated due to the loss of regularity and crystallinity, resulting in a remarkable decrease on weight retention and molar mass. The hydrolysis degradation rate increased in the order lcP(TMC-b-LLA), lcP(LLA-ran-TMC), lcP(LLA-grad-TMC). Therefore, the hydrolytic degradation behavior of comb-like graft copolymers depends on both the compositions and the sequences dramatically.

Versatile cross-linked fatty acid-based polycarbonate networks obtained by thiol–ene coupling reaction

Bio-sourced polycarbonate networks have been synthesized from an alkene-functional fatty-acid based polycarbonate precursor. Cross-linked networks were created using the radical thiol–ene coupling reaction. The resulting polycarbonate materials exhibited versatile properties either influenced by the structure of the cross-linker or the cross-linker/olefin unit ratio. Indeed, the storage modulus above the glass transition temperature could be modulated from 0.9 to 8.9 MPa only by changing the type of cross-linker, i.e. 1,9-nonanedithiol vs. 1,4-benzenedimethanethiol. The cross-linker/olefin unit ratio was also shown to largely impact the polycarbonate networks properties. An elongation at break of nearly 200% was reached when a low cross-linker/olefin ratio was applied. Moreover, functional polycarbonate networks bearing pendant thiol groups were obtained when an excess of dithiol was used with respect to olefin groups.

Bio-sourced polycarbonate networks have been synthesized from an alkene-functional fatty-acid based polycarbonate precursor.

Elastic materials for tissue engineering applications: Natural, synthetic, and hybrid polymers

Elastin and collagen are the two main components of elastic tissues and provide the tissue with elasticity and mechanical strength, respectively. Whereas collagen is adequately produced in vitro, production of elastin in tissue-engineered constructs is often inadequate when engineering elastic tissues. Therefore, elasticity has to be artificially introduced into tissue-engineered scaffolds. The elasticity of scaffold materials can be attributed to either natural sources, when native elastin or recombinant techniques are used to provide natural polymers, or synthetic sources, when polymers are synthesized. While synthetic elastomers often lack the biocompatibility needed for tissue engineering applications, the production of natural materials in adequate amounts or with proper mechanical strength remains a challenge. However, combining natural and synthetic materials to create hybrid components could overcome these issues. This review explains the synthesis, mechanical properties, and structure of native elastin as well as the theories on how this extracellular matrix component provides elasticity in vivo. Furthermore, current methods, ranging from proteins and synthetic polymers to hybrid structures that are being investigated for providing elasticity to tissue engineering constructs, are comprehensively discussed.

STATEMENT OF SIGNIFICANCE

Tissue engineered scaffolds are being developed as treatment options for malfunctioning tissues throughout the body. It is essential that the scaffold is a close mimic of the native tissue with regards to both mechanical and biological functionalities. Therefore, the production of elastic scaffolds is of key importance to fabricate tissue engineered scaffolds of the elastic tissues such as heart valves and blood vessels. Combining naturally derived and synthetic materials to reach this goal proves to be an interesting area where a highly tunable material that unites mechanical and biological functionalities can be obtained.

Exploring the potential of polyurethane-based soft foam as cell-free scaffold for soft tissue regeneration

Reconstructive treatment after trauma and tumor resection would greatly benefit from an effective soft tissue regeneration. The use of cell-free scaffolds for adipose tissue regeneration in vivo is emerging as an attractive alternative to tissue-engineered constructs, since this approach avoids complications due to cell manipulation and lack of synchronous vascularization. In this study, we developed a biodegradable polyurethane-based scaffold for soft tissue regeneration, characterized by an exceptional combination between softness and resilience. Exploring the potential as a cell-free scaffold required profound understanding of the impact of its intrinsic physico-chemical properties on the biological performance in vivo. We investigated the effect of the scaffold's hydrophilic character, degradation kinetics, and internal morphology on (i) the local inflammatory response and activation of MGCs (foreign body response); (ii) its ability to promote rapid vascularisation, cell infiltration and migration through the scaffold over time; and (iii) the grade of maturation of the newly formed tissue into vascularized soft tissue in a murine model. The study revealed that soft tissue regeneration in vivo proceeded by gradual infiltration of undifferentiated mesenchymal cells though the periphery toward the center of the scaffold, where the rapid formation of a functional and well-formed vascular network supported cell viability overtime.

STATEMENT OF SIGNIFICANCE

Exploring the potential of polyurethane-based soft foam as cell-free scaffold for soft tissue regeneration. In this work, we address the unmet need for synthetic functional soft tissue substitutes that provide adequate biological and mechanical support to soft tissue. We developed a series of flexible cross-linked polyurethane copolymer scaffolds with remarkable fatigue-resistance and tunable physico-chemical properties for soft tissue regeneration in vivo. Accordingly, we could extend the potential of this class of biomaterials, which was so far confined for bone and osteochondral tissue regeneration, to other types of connective tissue.

Microwave-assisted facile fabrication of porous poly (glycerol sebacate) scaffolds

The biodegradable elastomeric polyester poly(glycerol sebacate) (PGS) was developed for soft-tissue engineering. It has been used in various research applications such as wound healing, cartilage tissue engineering, and vascular grafting due to its biocompatibility and elastomeric properties. However conventional PGS manufacture is generally limited by the laborious reaction conditions needed for curing which requires elevated reaction temperatures, high vacuum and multi-day reaction times. In this study, we developed a microwave irradiation methodology to fabricate PGS scaffolds under milder conditions with curing times that are 8 times faster than conventional methods. In particular, we determined microwave reaction temperatures and times for maximum crosslinking of PGS elastomers, demonstrating that PGS is fully crosslinked using gradual heating up to 160 °C for 3 h. Porosity and mechanical properties of these microwave-cured PGS elastomers were shown to be similar to PGS elastomers fabricated by the conventional polycondensation method (150 °C under 30 Torr for 24 h). To move one step closer to clinical application, we also examined the biocompatibility of microwave-cured PGS using in vitro cell viability assays with primary baboon arterial smooth muscle cells (SMCs). These combined results show microwave curing of PGS is a viable alternative to conventional curing.

Simple and Efficient Approach toward Photosensitive Biobased Aliphatic Polycarbonate Materials

Fatty acids were used as precursors for the synthesis of photosensitive polycarbonate materials. In order to avoid multistep reactions, a simple and straightforward methodology toward the synthesis of photosensitive monomers has been developed. Hence, a fatty acid-based cyclic carbonate bearing an unsaturation was synthesized and subsequently polymerized in a controlled manner (Đ = 1.07) by organo-catalyzed ring-opening polymerization (ROP). A thio-cinnamate derivative was then readily synthesized via a one-pot reaction and grafted onto the polycarbonate backbone by thiol-ene reaction. The content of photoresponsive cinnamoyl moiety grafted on the polycarbonate was tunable with the reaction time. Such functionalized polycarbonates could be crosslinked (by UV irradiation at 365 nm) and partially decrosslinked (irradiated at 254 nm) and exhibit versatile properties ranging from rather tough materials to elastomeric networks with respect to the content of the photosensitive cinnamoyl moiety grafted on the polymer.

Improved cell adhesion and osteogenesis using a PLTGA (poly l-lactide, 1,3-trimethylene carbonate, and glycolide) terpolymer by gelatin-assisted hydroxyapatite immobilization for bone regeneration

Schematic illustration of the procedures for preparing the GEL/HAP-coated PLTGA film, and representative images of the improved cellular behaviors.

Ibuprofen-loaded fibrous patches-taming inhibition at the spinal cord injury site

It is now widely accepted that a therapeutic strategy for spinal cord injury (SCI) demands a multi-target approach. Here we propose the use of an easily implantable bilayer polymeric patch based on poly(trimethylene carbonate-co-ε-caprolactone) (P(TMC-CL)) that combines physical guidance cues provided by electrospun aligned fibres and the delivery of ibuprofen, as a mean to reduce the inhibitory environment at the lesion site by taming RhoA activation. Bilayer patches comprised a solvent cast film onto which electrospun aligned fibres have been deposited. Both layers were loaded with ibuprofen. In vitro release (37°C, in phosphate buffered saline) of the drug from the loaded scaffolds under sink condition was found to occur in the first 24 h. The released ibuprofen was shown to retain its bioactivity, as indicated by the reduction of RhoA activation when the neuronal-like cell line ND7/23 was challenged with lysophosphatidic acid. Ibuprofen-loaded P(TMC-CL) bilayer scaffolds were successfully implanted in vivo in a dorsal hemisection rat SCI model mediating the reduction of RhoA activation after 5 days of implantation in comparison to plain P(TMC-CL) scaffolds. Immunohistochemical analysis of the tissue shows βIII tubulin positive cells close to the ibuprofen-loaded patches further supporting the use of this strategy in the context of regeneration after a lesion in the spinal cord.

Composite elastomeric polyurethane scaffolds incorporating small intestinal submucosa for soft tissue engineering

Although soft tissue replacement has been clinically successful in many cases, the corresponding procedure has many limitations including the lack of resilience and mechanical integrity, significant donor-site morbidity, volume loss with time, and fibrous capsular contracture. These disadvantages can be alleviated by utilizing bio-absorbable scaffolds with high resilience and large strain, which are capable of stimulating natural tissue regeneration. Hence, the chemically crosslinked tridimensional scaffolds obtained by incorporating water-based polyurethane (PU) (which was synthesized from polytetramethylene ether glycol, isophorone diisocyanate, and 2,2-bis(hydroxymethyl) butyric acid) into a bioactive extracellular matrix consisting of small intestinal submucosa (SIS) have been tested in this study to develop a new approach for soft tissue engineering. After characterizing the structure and properties of the produced PU/SIS composites, the strength, Young's modulus, and resilience of wet PU/SIS samples were compared with those of crosslinked PU. In addition, the fabricated specimens were investigated using human umbilical vein endothelial cells to evaluate their ability to enhance cell attachment and proliferation. As a result, the synthesized PU/SIS samples exhibited high resilience and were capable of enhancing cell viability with no evidence of cytotoxicity. Subcutaneous implantation in animals and the subsequent testing conducted after 2, 4, and 8weeks indicated that sound implant integration and vascularization occurred inside the PU/SIS composites, while the presence of SIS promoted cell infiltration, angiogenesis, and ultimately tissue regeneration. The obtained results revealed that the produced PU/SIS composites were characterized by high bioactivity and resilience, and, therefore, could be used for soft tissue engineering applications.

STATEMENT OF SIGNIFICANCE

Hybrid composites containing synthetic polymers with high mechanical strength and naturally derived components, which create a bio-mimetic environment, are one of the most promising biomaterials. Although synthetic polymer/ECM composites have been previously used for soft tissue repair, their resilience properties were not investigated in sufficient detail, while the development of elastic composites composed of synthetic polymers and ECMs in nontoxic aqueous solutions remains a rather challenging task. In this study, porous PU/SIS composites were fabricated in a non-toxic manner; the obtained materials exhibited sufficient mechanical support, which promote cell growth, angiogenesis, and tissue regeneration. The described method can be adapted for the development of scaffolds with various acellular matrices and subsequently used during the restoration of particular types of tissue.

Fiber-reinforced scaffolds in soft tissue engineering

Soft tissue engineering has been developed as a new strategy for repairing damaged or diseased soft tissues and organs to overcome the limitations of current therapies. Since most of soft tissues in the human body are usually supported by collagen fibers to form a three-dimensional microstructure, fiber-reinforced scaffolds have the advantage to mimic the structure, mechanical and biological environment of natural soft tissues, which benefits for their regeneration and remodeling. This article reviews and discusses the latest research advances on design and manufacture of novel fiber-reinforced scaffolds for soft tissue repair and how fiber addition affects their structural characteristics, mechanical strength and biological activities in vitro and in vivo. In general, the concept of fiber-reinforced scaffolds with adjustable microstructures, mechanical properties and degradation rates can provide an effective platform and promising method for developing satisfactory biomechanically functional implantations for soft tissue engineering or regenerative medicine.

In vitro and in vivo degradation behavior of poly(trimethylene carbonate-co-d,l-lactic acid) copolymer

We present P(TMC-co-DLLA) copolymer with the molar ratio of TMC: DLLA = 15: 85 was used to systematic study of in vivo and in vitro degradation behaviors. Dense homogeneous copolymer specimens were prepared by compression molding method. The in vitro and in vivo degradation were, respectively, performed at simulative body condition and implanted into rat’s subcutaneous condition. Investigations were followed via physicochemical and histological analysis such as SEM, GPC, DSC, FTIR and H&E stain. The results demonstrate that copolymeric material can degrade in phosphate buffer solution (PBS) and in rat’s body, and the in vivo degradation rate is faster. Obvious decline of molecule weight and mass loss has been observed, which led to the attenuation of mechanical strength. Furthermore, apart from the hydrolysis, macrophagocytes took part in the phagocytosis in vivo, indicating that degradation rate could be regulated by the combinational mechanism. It is concluded that P(TMC-co-DLLA) copolymer is a promising candidate for tissue repair.

Synthesis, properties and biomedical applications of hydrolytically degradable materials based on aliphatic polyesters and polycarbonates

Polyester-based polymers represent excellent candidates in synthetic biodegradable and bioabsorbable materials for medical applications owing to their tailorable properties. The use of synthetic polyesters as biomaterials offers a unique control of morphology, mechanical properties and degradation profile through monomer selection, polymer composition (i.e. copolymer vs. homopolymer, stereocomplexation etc.) and molecular weight. Within this review, the synthetic routes, degradation modes and application of aliphatic polyester- and polycarbonate-based biomaterials are discussed.

Biodegradable packaging materials conception based on starch and polylactic acid (PLA) reinforced with cellulose

The plastic materials used for packaging are increasing leading to a considerable amount of undegradable solid wastes. This work deals with the reduction of conventional plastics waste and the natural resources preservation by using cellulosic polymers from renewable resources (alfa and luffa). Plasticized starch films syntheses were achieved at a laboratory scale. These natural films showed some very attractive mechanical properties at relatively low plasticizers levels (12 to 17 % by weight). Furthermore, mixtures including polylactic acid polymer (PLA) and cellulose fibers extracted from alfa and luffa were investigated by melt extrusion technique. When used at a rate of 10 %, these fibers improved the mixture mechanical properties. Both developed materials were biodegradable, but the plasticized starch exhibited a faster biodegradation kinetic compared to the PLA/cellulose fibers. These new materials would contribute to a sustainable development and a waste reduction.

P,O-Phosphinophenolate zinc(II) species: synthesis, structure and use in the ring-opening polymerization (ROP) of lactide, ε-caprolactone and trimethylene carbonate

The P,O-type phosphinophenol proligands (1·H, 2-PPh2-4-Me-6-Me-C6H2OH; 2·H, 2-PPh2-4-Me-6-(t)Bu-C6H2OH) readily react with one equiv. of ZnEt2 to afford in high yields the corresponding Zn(II)-ethyl dimers of the type [(κ(2)-P,O)Zn-Et]2 (3 and 4) with two μ-OPh bridging oxygens connecting the two Zn(II) centers, as determined by X-ray diffraction (XRD) studies in the case of 3. Based on diffusion-ordered NMR spectroscopy (DOSY), both species 3 and 4 retain their dimeric structures in solution. The alcoholysis reaction of Zn(II) alkyls 3 and 4 with BnOH led to the high yield formation of the corresponding Zn(II) benzyloxide species [(κ(2)-P,O)Zn-OBn]2 (5 and 6), isolated in a pure form as colorless solids. The centrosymmetric and dimeric nature of Zn(II) alkoxides 5 and 6 in solution was deduced from DOSY NMR experiments and multinuclear NMR data. Though the heteroleptic species 5 is stable in solution, its analogue 6 is instable in CH2Cl2 solution at room temperature to slowly decompose to the corresponding homoleptic species 8via the transient formation of (κ(2)-P,O)2Zn2(μ-OBn)(μ–κ(1):κ(1)-P,O) (6′). Crystallization of compound 6 led to crystals of 6′, as established by XRD analysis. The reaction of ZnEt2 with two equiv. of 1·H and 2·H allowed access to the corresponding homoleptic species of the type [Zn(P,O)2] (7 and 8). All gathered data are consistent with compound 7 being a dinuclear species in the solid state and in solution. Data for species 8, which bears a sterically demanding P,O-ligand, are consistent with a mononuclear species in solution. The Zn(II) alkoxide species 5 and the [Zn(P,O)2]-type compounds 7 and 8 were evaluated as initiators of the ring-opening polymerization (ROP) of lactide (LA), ε-caprolactone (ε-CL) and trimethylene carbonate (TMC). Species 5 is a well-behaved ROP initiator for the homo-, co- and ter-polymerization of all three monomers with the production of narrow disperse materials under living and immortal conditions. Though species 7 and 8 are ROP inactive on their own, they readily polymerize LA in the presence of a nucleophile such as BnOH to produce narrow disperse PLA, presumably via an activated-monomer ROP mechanism.

Poly(trimethylene carbonate)-based polymers engineered for biodegradable functional biomaterials

This review presents recent examples of applications and functionalization strategies of poly(trimethylene carbonate), its copolymers, and its derivatives to exploit the unique physicochemical properties of the aliphatic polycarbonate backbone.

Copolymerization of l-lactide/trimethylene carbonate by organocatalysis: controlled synthesis of comb-like graft copolymers with side chains with different topologies

Synthesis of comb-like graft copolymers of lcP(LLA-co-TMC) from an organocatalyst/PB–OH system: including lcP(TMC-b-LLA), lcP(LLA-grad-TMC) and lcP(LLA-ran-TMC).

Bridging the lesion-engineering a permissive substrate for nerve regeneration

Biomaterial-based strategies to restore connectivity after lesion at the spinal cord are focused on bridging the lesion and providing an favourable substrate and a path for axonal re-growth. Following spinal cord injury (SCI) a hostile environment for neuronal cell growth is established by the activation of multiple inhibitory mechanisms that hamper regeneration to occur. Implantable scaffolds can provide mechanical support and physical guidance for axon re-growth and, at the same time, contribute to alleviate the hostile environment by the in situ delivery of therapeutic molecules and/or relevant cells. Basic research on SCI has been contributing with the description of inhibitory mechanisms for regeneration as well as identifying drugs/molecules that can target inhibition. This knowledge is the background for the development of combined strategies with biomaterials. Additionally, scaffold design is significantly evolving. From the early simple hollow conduits, scaffolds with complex architectures that can modulate cell fate are currently being tested. A number of promising pre-clinical studies combining scaffolds, cells, drugs and/or nucleic acids are reported in the open literature. Overall, it is considered that to address the multi-factorial inhibitory environment of a SCI, a multifaceted therapeutic approach is imperative. The progress in the identification of molecules that target inhibition after SCI and its combination with scaffolds and/or cells are described and discussed in this review.

The role of the surface on microglia function: implications for central nervous system tissue engineering

In tissue engineering, it is well accepted that a scaffold surface has a decisive impact on cell behaviour. Here we focused on microglia-the resident immune cells of the central nervous system (CNS)-and on their response to poly(trimethylene carbonate-co-ε-caprolactone) (P(TMC-CL)) fibrous and flat surfaces obtained by electrospinning and solvent cast, respectively. This study aims to provide cues for the design of instructive surfaces that can contribute to the challenging process of CNS regeneration. Cell morphology was evidently affected by the substrate, mirroring the surface main features. Cells cultured on flat substrates presented a round shape, while cells with elongated processes were observed on the electrospun fibres. A higher concentration of the pro-inflammatory cytokine tumour necrosis factor-α was detected in culture media from microglia on fibres. Still, astrogliosis is not exacerbated when astrocytes are cultured in the presence of microglia-conditioned media obtained from cultures in contact with either substrate. Furthermore, a significant percentage of microglia was found to participate in the process of myelin phagocytosis, with the formation of multinucleated giant cells being observed only on films. Altogether, the results presented suggest that microglia in contact with the tested substrates may contribute to the regeneration process, putting forward P(TMC-CL) substrates as supporting matrices for nerve regeneration.

Tensile properties and in vitro degradation of P(TMC-co-LLA) elastomers

P(TMC-co-LLA) elastomers have shown great potential for various biomaterials applications. This study investigated properties key to such applications. Six statistical copolymers with 16 to 49 mol% TMC were synthesized and it was found that the LLA sequence length changed from 14 to 3 for the copolymer series while the M[combining macron]_n decreased from 63 to 31 kg mol^-1 with increasing TMC content. The thermal properties showed lower T_g values with increasing TMC content which agreed with the Fox equation. Solvent cast films exhibited Young's modulus values between 2.8 and 271 MPa, ultimate tensile strength of 0.6-15.5 MPa and elongation at failure from 356 to 1287%. In vitro degradation in PBS at 37 °C over 34 weeks demonstrated an induction period of 9 weeks during which the water content was minimal for all copolymers. Copolymer films with 21 or greater mol% TMC were found to undergo homogeneous bulk degradation, while films with 16 mol% TMC underwent heterogeneous bulk degradation.

In vivo evaluation of nerve guidance channels of PTMC/PLLA porous biomaterial

INTRODUCTION

Peripheral nerve disruptions, frequently occurring during limb injuries, give rise to serious complications of patients recovery resulting from limitations in neural tissue regeneration capabilities. To overcome this problem bridging techniques utilizing guidance channels gain their importance. Biodegradable polymeric tubes seem to be more prospective then non-degradable materials - no necessity of implant removal and possibilities of release of incorporated drugs or biologically active agents that may support nerve regeneration process are the main advantages.

MATERIAL AND METHODS

Polymer blend of commercial poly(L-lactic acid) (PLLA) and in-house synthesized poly(trimethylene carbonate) (PTMC) were processed in an organic solvent - phase inversion process on a supporting rod - to form a guidance porous tube of 1.1 mm inner diameter. In vivo experiments on rat's cut femoral nerve by using either the tubes or end-to-end suturing (control group) involved 22 and 19 rats, respectively. Motor recovery of operated limbs, neuroma occurrence and histopathology of explanted nerves were evaluated after 30, 60 and 90 days of implantation.

RESULTS

Motor recovery of the limbs was of similar rate for the two animal groups. The neuroma formation was evident in over 90% control specimens, while for the bridging group it was less than 40% of all evaluable samples (p = 0.0022). Biocompatibility of applied materials was affirmed by moderate tissue response.

CONCLUSIONS

Application of the biodegradable PLLA/PTMC polymeric tubes effectively supports regeneration of discontinued nerves. The applied material prevents neuroma formation, by reducing the scar tissue formation time and, thus, accelerating the process of neural tissue restoration.

In vivo degradation of copolymers prepared from L-lactide, 1,3-trimethylene carbonate and glycolide as coronary stent materials

A series of high molecular weight polymers were prepared by ring opening polymerization of L-lactide (L-LA), 1,3-trimethylene carbonate (TMC) and glycolide using stannous octoate as catalyst. The resulting polymers were characterized by gel permeation chromatography, (1)H nuclear magnetic resonance, differential scanning calorimeter and tensile tests. All the polymers present high molecular weights. Compared with PLLA and PTLA copolymers, the terpolymers exhibit interesting properties such as improved toughness and lowered crystallinity with only slightly reduced mechanical strength. In vivo degradation was performed by subcutaneous implantation in rats to evaluate the potential of the copolymers as bioresorbable coronary stent material. The results show that all the polymers conserved to a large extent their mechanical properties during the first 90 days, except the strain at break which exhibited a strong decrease. Meanwhile, significant molecular weight decrease and weight loss are detected in the case of terpolymers. Therefore, the PTLGA terpolymers present a good potential for the development of totally bioresorbable coronary stents.

Biocompatible and biodegradable elastomer/fibrinogen composite electrospun scaffolds for cardiac tissue regeneration

Schematic for nanofiber with HCMs in cardiac tissue engineering.