Dynamics of in vitro polymer degradation of polycaprolactone-based scaffolds: accelerated versus simulated physiological conditions

3D Melt-Extrusion Printing of Medium Chain Length Polyhydroxyalkanoates and Their Application as Antibiotic-Free Antibacterial Scaffolds for Bone Regeneration

In this work, we investigated, for the first time, the possibility of developing scaffolds for bone tissue engineering through three-dimensional (3D) melt-extrusion printing of medium chain length polyhydroxyalkanoate (mcl-PHA) (i.e., poly(3-hydroxyoctanoate-co-hydroxydecanoate-co-hydroxydodecanoate), P(3HO-co-3HD-co-3HDD)). The process parameters were successfully optimized to produce well-defined and reproducible 3D P(3HO-co-3HD-co-3HDD) scaffolds, showing high cell viability (100%) toward both undifferentiated and differentiated MC3T3-E1 cells. To introduce antibacterial features in the developed scaffolds, two strategies were investigated. For the first strategy, P(3HO-co-3HD-co-3HDD) was combined with PHAs containing thioester groups in their side chains (i.e., PHACOS), inherently antibacterial PHAs. The 3D blend scaffolds were able to induce a 70% reduction of Staphylococcus aureus 6538P cells by direct contact testing, confirming their antibacterial properties. Additionally, the scaffolds were able to support the growth of MC3T3-E1 cells, showing the potential for bone regeneration. For the second strategy, composite materials were produced by the combination of P(3HO-co-3HD-co-HDD) with a novel antibacterial hydroxyapatite doped with selenium and strontium ions (Se-Sr-HA). The composite material with 10 wt % Se-Sr-HA as a filler showed high antibacterial activity against both Gram-positive (S. aureus 6538P) and Gram-negative bacteria (Escherichia coli 8739), through a dual mechanism: by direct contact (inducing 80% reduction of both bacterial strains) and through the release of active ions (leading to a 54% bacterial cell count reduction for S. aureus 6538P and 30% for E. coli 8739 after 24 h). Moreover, the composite scaffolds showed high viability of MC3T3-E1 cells through both indirect and direct testing, showing promising results for their application in bone tissue engineering.

Polymers and their engineered analogues for ocular drug delivery: Enhancing therapeutic precision

Ocular drug delivery is constrained by anatomical and physiological barriers, necessitating innovative solutions for effective therapy. Natural polymers like hyaluronic acid, chitosan, and gelatin, alongside synthetic counterparts such as PLGA and PEG, have gained prominence for their biocompatibility and controlled release profiles. Recent strides in polymer conjugation strategies have enabled targeted delivery through ligand integration, facilitating tissue specificity and cellular uptake. This versatility accommodates combined drug delivery, addressing diverse anterior (e.g., glaucoma, dry eye) and posterior segment (e.g., macular degeneration, diabetic retinopathy) afflictions. The review encompasses an in-depth exploration of each natural and synthetic polymer, detailing their individual advantages and disadvantages for ocular drug delivery. By transcending ocular barriers and refining therapeutic precision, these innovations promise to reshape the management of anterior and posterior segment eye diseases.

3D printing modality effect: Distinct printing outcomes dependent on selective laser sintering (SLS) and melt extrusion

A direct and comprehensive comparative study on different 3D printing modalities was performed. We employed two representative 3D printing modalities, laser- and extrusion-based, which are currently used to produce patient-specific medical implants for clinical translation, to assess how these two different 3D printing modalities affect printing outcomes. The same solid and porous constructs were created from the same biomaterial, a blend of 96% poly-ε-caprolactone (PCL) and 4% hydroxyapatite (HA), using two different 3D printing modalities. Constructs were analyzed to assess their printing characteristics, including morphological, mechanical, and biological properties. We also performed an in vitro accelerated degradation study to compare their degradation behaviors. Despite the same input material, the 3D constructs created from different 3D printing modalities showed distinct differences in morphology, surface roughness and internal void fraction, which resulted in different mechanical properties and cell responses. In addition, the constructs exhibited different degradation rates depending on the 3D printing modalities. Given that each 3D printing modality has inherent characteristics that impact printing outcomes and ultimately implant performance, understanding the characteristics is crucial in selecting the 3D printing modality to create reliable biomedical implants.

Fabrication of Vascular Grafts Using Poly(ε-Caprolactone) and Collagen-Encapsuled ADSCs for Interposition Implantation of Abdominal Aorta in Rhesus Monkeys

The production of small-diameter artificial vascular grafts continues to encounter numerous challenges, with concerns regarding the degradation rate and endothelialization being particularly critical. In this study, porous PCL scaffolds were prepared, and PCL vascular grafts were fabricated by 3D bioprinting of collagen materials containing adipose-derived mesenchymal stem cells (ADSCs) on the internal wall of the porous PCL scaffold. The PCL vascular grafts were then implanted in the abdominal aorta of Rhesus monkeys for up to 640 days to analyze the degradation of the scaffolds and regeneration of the aorta. Changes in surface morphology, mechanical properties, crystallization property, and molecular weight of porous PCL revealed a similar degradation process of PCL in PBS at pH 7.4 containing Thermomyces lanuginosus lipase and in situ in the abdominal aorta of rhesus monkeys. The contrast of in vitro and in vivo degradation provided valuable reference data for predicting in vivo degradation based on in vitro enzymatic degradation of PCL for further optimization of PCL vascular graft fabrication. Histological analysis through hematoxylin and eosin (HE) staining and fluorescence immunostaining demonstrated that the PCL vascular grafts successfully induced vascular regeneration in the abdominal aorta over the 640-day period. These findings provided valuable insights into the regeneration processes of the implanted vascular grafts. Overall, this study highlights the significant potential of PCL vascular grafts for the regeneration of small-diameter blood vessels.

Structural descriptor and surrogate modeling for design of biodegradable scaffolds

Biodegradable scaffolds are important to regenerative medicine in that they provide an amicable environment for tissue regrowth. However, establishing structure-property (SP) relationships for scaffold design is challenging due to the complexity of the three-dimensional porous scaffold geometry. The complexity requires high-dimensional geometric descriptors. The training of such a SP surrogate model will need a large amount of experimental or simulation data. In this work, a schema of constructing SP relationship surrogates is developed to predict the degraded mechanical properties from the initial scaffold geometry. A new structure descriptor, the extended surfacelet transform (EST), is proposed to capture important details of pores associated with the degradation of scaffolds. The efficiency is further enhanced with principal component analysis to reduce the high-dimensional EST data into a low-dimensional representation. The schema also includes a kinetic Monte Carlo biodegradation model to simulate the biodegradation of polymer scaffolds and to generate the training data for the formation of SP relationships. The schema is demonstrated with the design of polycaprolactone biodegradable scaffolds by connecting the initial scaffold geometry to the degraded compressive modulus.

Dual Mg-Reinforced PCL Membrane with a Janus Structure for Vascularized Bone Regeneration and Bacterial Elimination

Commercially available guided bone regeneration (GBR) membranes often exhibit limited mechanical properties or bioactivity, leading to poor performance in repairing bone defects. To surmount this limitation, we developed a Janus structural composite membrane (Mg-MgO/PCL) reinforced by dual Mg (Mg sheets and MgO NPs) by using a combined processing technique involving casting and electrospinning. Results showed that the addition of Mg sheets and MgO NPs enhanced the mechanical properties of the composite membrane for osteogenic space maintenance, specifically tensile strength (from 10.2 ± 1.2 to 50.3 ± 4.5 MPa) and compression force (from 0 to 0.94 ± 0.09 N mm-1), through Mg sheet reinforcement and improved crystallization. The dense cast side of the Janus structure membrane displayed better fibroblast barrier capacity than a single fiber structure; meanwhile, the PCL matrix protected the Mg sheet from severe corrosion due to predeformation. The porous microfibers side supported preosteoblast cell adhesion, enhanced osteogenesis, and angiogenesis in vitro, through the biomimetic extracellular matrix and sustainable Mg2+ release. Furthermore, the Mg-MgO/PCL membrane incorporating 2 wt % MgO NPs exhibited remarkable antimicrobial properties, inducing over 88.75% apoptosis in Staphylococcus aureus. An in vivo experiment using the rat skull defect model (Φ = 5 mm) confirmed that the Mg-MgO/PCL membrane significantly improved new bone formation postsurgery. Collectively, our investigation provides valuable insights into the design of multifunctional membranes for clinical oral GBR application.

Poly(lactic acid/caprolactone) bilayer membrane achieves bone regeneration through a prolonged barrier function

Guided bone regeneration (GBR) is a treatment strategy used to recover bone volume. Barrier membranes are a key component of GBR protocols, and their properties can impact treatment outcomes. This study investigated the efficacy of an experimental, slow-degrading, bilayer barrier membrane for application in GBR using in vivo animal models. A synthetic copolymer of poly(lactic acid/caprolactone) (PLCL) was used to prepare a slow-degrading bilayer membrane. The biodegradability of PLCL was evaluated by subcutaneous implantation in a rat model. The barrier function of the PLCL membrane was investigated in a rat calvaria defect model and compared with commercially available membranes composed of type I collagen (Col) and poly(lactic-co-glycolic acid) (PLGA). An alveolar bone defect model in beagle dogs was used to simulate GBR protocols to evaluate the bone regeneration ability of the experimental PLCL membrane. The PLCL membrane showed slow biodegradation, resulting in an efficient and prolonged barrier function compared with commercial materials. In turn, this barrier function enabled the space-making ability of PLCL membrane and facilitated bone regeneration. In the alveolar bone defect model, significantly greater regeneration was achieved by treatment with PLCL membrane compared with Col and PLGA membranes. Additionally, a continuous alveolar ridge contour was observed in PLCL-treated bone defects. In conclusion, the PLCL bilayer membrane is a promising biomaterial for use in GBR given its slow degradation and prolonged barrier function.

Bone Scaffold Materials in Periodontal and Tooth-supporting Tissue Regeneration: A Review

BACKGROUND AND OBJECTIVES

Periodontium is an important tooth-supporting tissue composed of both hard (alveolar bone and cementum) and soft (gingival and periodontal ligament) sections. Due to the multi-tissue architecture of periodontium, reconstruction of each part can be influenced by others. This review focuses on the bone section of the periodontium and presents the materials used in tissue engineering scaffolds for its reconstruction.

MATERIALS AND METHODS

The following databases (2015 to 2021) were electronically searched: ProQuest, EMBASE, SciFinder, MRS Online Proceedings Library, Medline, and Compendex. The search was limited to English-language publications and in vivo studies.

RESULTS

Eighty-three articles were found in primary searching. After applying the inclusion criteria, seventeen articles were incorporated into this study.

CONCLUSION

In complex periodontal defects, various types of scaffolds, including multilayered ones, have been used for the functional reconstruction of different parts of periodontium. While there are some multilayered scaffolds designed to regenerate alveolar bone/periodontal ligament/cementum tissues of periodontium in a hierarchically organized construct, no scaffold could so far consider all four tissues involved in a complete periodontal defect. The progress and material considerations in the regeneration of the bony part of periodontium are presented in this work to help investigators develop tissue engineering scaffolds suitable for complete periodontal regeneration.

Progress in bioprinting technology for tissue regeneration

In recent years, due to the increase in diseases that require organ/tissue transplantation and the limited donor, on the other hand, patients have lost hope of recovery and organ transplantation. Regenerative medicine is one of the new sciences that promises a bright future for these patients by providing solutions to repair, improve function, and replace tissue. One of the technologies used in regenerative medicine is three-dimensional (3D) bioprinters. Bioprinting is a new strategy that is the basis for starting a global revolution in the field of medical sciences and has attracted much attention. 3D bioprinters use a combination of advanced biology and cell science, computer science, and materials science to create complex bio-hybrid structures for various applications. The capacity to use this technology can be demonstrated in regenerative medicine to make various connective tissues, such as skin, cartilage, and bone. One of the essential parts of a 3D bioprinter is the bio-ink. Bio-ink is a combination of biologically active molecules, cells, and biomaterials that make the printed product. In this review, we examine the main bioprinting strategies, such as inkjet printing, laser, and extrusion-based bioprinting, as well as some of their applications.

Elastomeric Polyesters in Cardiovascular Tissue Engineering and Organs-on-a-Chip

Cardiovascular tissue constructs provide unique design requirements due to their functional responses to substrate mechanical properties and cyclic stretching behavior of cardiac tissue that requires the use of durable elastic materials. Given the diversity of polyester synthesis approaches, an opportunity exists to develop a new class of biocompatible, elastic, and immunomodulatory cardiovascular polymers. Furthermore, elastomeric polyester materials have the capability to provide tailored biomechanical synergy with native tissue and hence reduce inflammatory response in vivo and better support tissue maturation in vitro. In this review, we highlight underlying chemistry and design strategies of polyester elastomers optimized for cardiac tissue scaffolds. The major advantages of these materials such as their tunable elasticity, desirable biodegradation, and potential for incorporation of bioactive compounds are further expanded. Unique fabrication methods using polyester materials such as micromolding, 3D stamping, electrospinning, laser ablation, and 3D printing are discussed. Moreover, applications of these biomaterials in cardiovascular organ-on-a-chip devices and patches are analyzed. Finally, we outline unaddressed challenges in the field that need further study to enable the impactful translation of soft polyesters to clinical applications.

Towards Polycaprolactone-Based Scaffolds for Alveolar Bone Tissue Engineering: A Biomimetic Approach in a 3D Printing Technique

The alveolar bone is a unique type of bone, and the goal of bone tissue engineering (BTE) is to develop methods to facilitate its regeneration. Currently, an emerging trend involves the fabrication of polycaprolactone (PCL)-based scaffolds using a three-dimensional (3D) printing technique to enhance an osteoconductive architecture. These scaffolds are further modified with hydroxyapatite (HA), type I collagen (CGI), or chitosan (CS) to impart high osteoinductive potential. In conjunction with cell therapy, these scaffolds may serve as an appealing alternative to bone autografts. This review discusses research gaps in the designing of 3D-printed PCL-based scaffolds from a biomimetic perspective. The article begins with a systematic analysis of biological mineralisation (biomineralisation) and ossification to optimise the scaffold's structural, mechanical, degradation, and surface properties. This scaffold-designing strategy lays the groundwork for developing a research pathway that spans fundamental principles such as molecular dynamics (MD) simulations and fabrication techniques. Ultimately, this paves the way for systematic in vitro and in vivo studies, leading to potential clinical applications.

A novel degradable PCL/PLLA strapping band for internal fixation of fracture

Early fracture fixation is the critical factor in fracture healing. Common internal fracture implants are made of metallic materials, which often affects the imaging quality of CT and MRI. Most patients will choose secondary surgery to remove the internal fixation implants, which causes secondary damage to them. The development of new degradable internal fracture implants has attracted more and more attention from orthopedic surgeons and researchers. Based on these problems, we improved the various properties of medical grade polycaprolactone (PCL) by adding poly(L-lactide) (PLLA). We produced PCL/PLLA strapping bands with different mass ratios by injection molding. We compared the mechanical properties, degradation properties, cell biocompatibility, bone marrow mesenchymal stem cells (BMSCs) adhesion, proliferation, osteogenic differentiation and fracture fixation effect of these strapping bands. The results showed that the tensile strength and yield force of the strapping bands increased with the increase of the content of PLLA. The addition of PLLA could significantly improve the mechanical strength in the early stage and accelerate the degradation rate of the strapping band. PCL/PLLA (80/20) strapping band had no significant cytotoxicity toward rBMSCs and could promote osteogenic differentiation of rBMSCs. The strapping band could ensure femoral fracture healing of beagles in 3 months and didn't cause damage to the surrounding tissues and main organs. This study will provide some new insights into the biodegradable products of PCL/PLLA blends for internal fixation of fracture. We produced novel degradable PCL/PLLA strapping bands with different mass ratios by injection molding. We tested the biological safety of the prepared internal fixation strapping bands for fracture, such as cell experiment in vitro and animal experiment, and studied the degradation behavior in vitro. The strapping bands could ensure femoral fracture healing of beagles. This study will provide some new insights into the biodegradable products of PCL/PLLA blends for internal fixation of fracture. A Immunofluorescence staining of rBMSCs (live cells: green; dead cells: red). B Young's modulus change curve during strapping bands degradation. C The implantation process of strapping bands. D Micro-CT images of the beagle's fracture recovery after the operation.

Virtual Design of 3D-Printed Bone Tissue Engineered Scaffold Shape Using Mechanobiological Modeling: Relationship of Scaffold Pore Architecture to Bone Tissue Formation

Large bone defects are clinically challenging, with up to 15% of these requiring surgical intervention due to non-union. Bone grafts (autographs or allografts) can be used but they have many limitations, meaning that polymer-based bone tissue engineered scaffolds (tissue engineering) are a more promising solution. Clinical translation of scaffolds is still limited but this could be improved by exploring the whole design space using virtual tools such as mechanobiological modeling. In tissue engineering, a significant research effort has been expended on materials and manufacturing but relatively little has been focused on shape. Most scaffolds use regular pore architecture throughout, leaving custom or irregular pore architecture designs unexplored. The aim of this paper is to introduce a virtual design environment for scaffold development and to illustrate its potential by exploring the relationship of pore architecture to bone tissue formation. A virtual design framework has been created utilizing a mechanical stress finite element (FE) model coupled with a cell behavior agent-based model to investigate the mechanobiological relationships of scaffold shape and bone tissue formation. A case study showed that modifying pore architecture from regular to irregular enabled between 17 and 33% more bone formation within the 4-16-week time periods analyzed. This work shows that shape, specifically pore architecture, is as important as other design parameters such as material and manufacturing for improving the function of bone tissue scaffold implants. It is recommended that future research be conducted to both optimize irregular pore architectures and to explore the potential extension of the concept of shape modification beyond mechanical stress to look at other factors present in the body.

Degradation of Poly(ε-caprolactone) Resorbable Multifilament Yarn under Physiological Conditions

Poly(ε-caprolactone) (PCL) is a hydrophobic, resorbable aliphatic polymer recognized for its low tenacity and extensive elongation at break, making it a popular choice for fabricating biodegradable tissue engineering scaffolds. PCL's slow degradation rate typically results in a complete resorption period of 2 to 3 years. While numerous studies have examined the degradation of PCL in various forms such as films and webs, no study to date has investigated its physiological degradation in multifilament yarn form. In this study, we subjected PCL multifilament yarn samples to physiological conditions in phosphate-buffered saline (PBS) maintained at a consistent temperature of 37 ± 2 °C and agitated at 45 rpm for a period of 32 weeks. We retrieved samples at five different intervals to analyze the degradation profile of the multifilament yarn. This allowed us to estimate the complete resorption time and rate under these in vitro conditions. Over the 32-week period, the multifilament yarn's mass decreased by 4.8%, its elongation at break declined by 42%, the tenacity dropped by 40%, and the peak load at break fell by 46.5%. Based on these findings, we predict that a scaffold structure incorporating PCL multifilament yarn would undergo complete resorption in approximately 14 months under physiological conditions, such as in PBS solution at a pH of approximately 7 and a temperature of 37 °C.

Is it possible to 3D bioprint load-bearing bone implants? A critical review

Rehabilitative capabilities of any tissue engineered scaffold rely primarily on the triad of (i) biomechanical properties such as mechanical properties and architecture, (ii) chemical behavior such as regulation of cytokine expression, and (iii) cellular response modulation (including their recruitment and differentiation). The closer the implant can mimic the native tissue, the better it can rehabilitate the damage therein. Among the available fabrication techniques, only 3D bioprinting (3DBP) can satisfactorily replicate the inherent heterogeneity of the host tissue. However, 3DBP scaffolds typically suffer from poor mechanical properties, thereby, driving the increased research interest in development of load-bearing 3DBP orthopedic scaffolds in recent years. Typically, these scaffolds involve multi-material 3D printing, comprising of at-least one bioink and a load-bearing ink; such that mechanical and biological requirements of the biomaterials are decoupled. Ensuring high cellular survivability and good mechanical properties are of key concerns in all these studies. 3DBP of such scaffolds is in early developmental stages, and research data from only a handful of preliminary animal studies are available, owing to limitations in print-capabilities and restrictive materials library. This article presents a topically focused review of the state-of-the-art, while highlighting aspects like available 3DBP techniques; biomaterials' printability; mechanical and degradation behavior; and their overall bone-tissue rehabilitative efficacy. This collection amalgamates and critically analyses the research aimed at 3DBP of load-bearing scaffolds for fulfilling demands of personalized-medicine. We highlight the recent-advances in 3DBP techniques employing thermoplastics and phosphate-cements for load-bearing applications. Finally, we provide an outlook for possible future perspectives of 3DBP for load-bearing orthopedic applications. Overall, the article creates ample foundation for future research, as it gathers the latest and ongoing research that scientists could utilize.

In Vitro Degradation of 3D-Printed Poly(L-lactide-Co-Glycolic Acid) Scaffolds for Tissue Engineering Applications

The creation of scaffolds for cartilage tissue engineering has faced significant challenges in developing constructs that can provide sufficient biomechanical support and offer suitable degradation characteristics. Ideally, such tissue-engineering techniques necessitate the fabrication of scaffolds that mirror the mechanical characteristics of the articular cartilage while degrading safely without damaging the regenerating tissues. The aim of this study was to create porous, biomechanically comparable 3D-printed scaffolds made from Poly(L-lactide-co-glycolide) 85:15 and to assess their degradation at physiological conditions 37 °C in pH 7.4 phosphate-buffered saline (PBS) for up to 56 days. Furthermore, the effect of scaffold degradation on the cell viability and proliferation of human bone marrow mesenchymal stem cells (HBMSC) was evaluated in vitro. To assess the long-term degradation of the scaffolds, accelerated degradation tests were performed at an elevated temperature of 47 °C for 28 days. The results show that the fabricated scaffolds were porous with an interconnected architecture and had comparable biomechanical properties to native cartilage. The degradative changes indicated stable degradation at physiological conditions with no significant effect on the properties of the scaffold and biocompatibility of the scaffold to HBMSC. Furthermore, the accelerated degradation tests showed consistent degradation of the scaffolds even in the long term without the notable release of acidic byproducts. It is hoped that the fabrication and degradation characteristics of this scaffold will, in the future, translate into a potential medical device for cartilage tissue regeneration.

Incorporating Tantalum Oxide Nanoparticles into Implantable Polymeric Biomedical Devices for Radiological Monitoring

Longitudinal radiological monitoring of biomedical devices is increasingly important, driven by the risk of device failure following implantation. Polymeric devices are poorly visualized with clinical imaging, hampering efforts to use diagnostic imaging to predict failure and enable intervention. Introducing nanoparticle contrast agents into polymers is a potential method for creating radiopaque materials that can be monitored via computed tomography. However, the properties of composites may be altered with nanoparticle addition, jeopardizing device functionality. Thus, the material and biomechanical responses of model nanoparticle-doped biomedical devices (phantoms), created from 0-40 wt% tantalum oxide (TaOx ) nanoparticles in polycaprolactone and poly(lactide-co-glycolide) 85:15 and 50:50, representing non, slow, and fast degrading systems, respectively, are investigated. Phantoms degrade over 20 weeks in vitro in simulated physiological environments: healthy tissue (pH 7.4), inflammation (pH 6.5), and lysosomal conditions (pH 5.5), while radiopacity, structural stability, mechanical strength, and mass loss are monitored. The polymer matrix determines overall degradation kinetics, which increases with lower pH and higher TaOx content. Importantly, all radiopaque phantoms could be monitored for a full 20 weeks. Phantoms implanted in vivo and serially imaged demonstrate similar results. An optimal range of 5-20 wt% TaOx nanoparticles balances radiopacity requirements with implant properties, facilitating next-generation biomedical devices.

Investigation on Filaments for 3D Printing of Nasal Septum Cartilage Implant

Septoplasty is a widely used method in treating deviated septum. Although it is successfully implemented, there are problems with excessive bleeding, septal perforation, or infections. The use of anatomically shaped implants could help overcome these problems. This paper focuses on assessing the possibility of the usage of a nasal septum cartilage implant 3D printed from various market-available filaments. Five different types of laments were used, two of which claim to be suitable for medical use. A combination of modeling, mechanical (bending, compression), structural (FTIR), thermal (DSC, MFR), surface (contact angle), microscopic (optical), degradation (2 M HCl, 5 M NaOH, and 0.01 M PBS), printability, and cell viability (MTT) analyses allowed us to assess the suitability of materials for manufacturing implants. Bioflex had the most applicable properties among the tested materials, but despite the overall good performance, cell viability studies showed toxicity of the material in MTT test. The results of the study show that selected filaments were not suitable for nasal cartilage implants. The poor cell viability of Bioflex could be improved by surface modification. Further research on biocompatible elastic materials for 3D printing is needed either by the synthesis of new materials or by modifying existing ones.

Bacterial Cellulose-Based Materials: A Perspective on Cardiovascular Tissue Engineering Applications

Today, a wide variety of bio- and nanomaterials have been deployed for cardiovascular tissue engineering (TE), including polymers, metal oxides, graphene/its derivatives, organometallic complexes/composites based on inorganic-organic components, among others. Despite several advantages of these materials with unique mechanical, biological, and electrical properties, some challenges still remain pertaining to their biocompatibility, cytocompatibility, and possible risk factors (e.g., teratogenicity or carcinogenicity), restricting their future clinical applications. Natural polysaccharide- and protein-based (nano)structures with the benefits of biocompatibility, sustainability, biodegradability, and versatility have been exploited in the field of cardiovascular TE focusing on targeted drug delivery, vascular grafts, engineered cardiac muscle, etc. The usage of these natural biomaterials and their residues offers several advantages in terms of environmental aspects such as alleviating emission of greenhouse gases as well as the production of energy as a biomass consumption output. In TE, the development of biodegradable and biocompatible scaffolds with potentially three-dimensional structures, high porosity, and suitable cellular attachment/adhesion still needs to be comprehensively studied. In this context, bacterial cellulose (BC) with high purity, porosity, crystallinity, unique mechanical properties, biocompatibility, high water retention, and excellent elasticity can be considered as promising candidate for cardiovascular TE. However, several challenges/limitations regarding the absence of antimicrobial factors and degradability along with the low yield of production and extensive cultivation times (in large-scale production) still need to be resolved using suitable hybridization/modification strategies and optimization of conditions. The biocompatibility and bioactivity of BC-based materials along with their thermal, mechanical, and chemical stability are crucial aspects in designing TE scaffolds. Herein, cardiovascular TE applications of BC-based materials are deliberated, with a focus on the most recent advancements, important challenges, and future perspectives. Other biomaterials with cardiovascular TE applications and important roles of green nanotechnology in this field of science are covered to better compare and comprehensively review the subject. The application of BC-based materials and the collective roles of such biomaterials in the assembly of sustainable and natural-based scaffolds for cardiovascular TE are discussed.

Protocol for the BONE-RECON trial: a single-arm feasibility trial for critical sized lower limb BONE defect RECONstruction using the mPCL-TCP scaffold system with autologous vascularised corticoperiosteal tissue transfer

INTRODUCTION

Reconstruction of critical bone defects is challenging. In a substantial subgroup of patients, conventional reconstructive techniques are insufficient. Biodegradable scaffolds have emerged as a novel tissue engineering strategy for critical-sized bone defect reconstruction. A corticoperiosteal flap integrates the hosts' ability to regenerate bone and permits the creation of a vascular axis for scaffold neo-vascularisation (regenerative matching axial vascularisation-RMAV). This phase IIa study evaluates the application of the RMAV approach alongside a custom medical-grade polycaprolactone-tricalcium phosphate (mPCL-TCP) scaffold (Osteopore) to regenerate bone sufficient to heal critical size defects in lower limb defects.

METHODS AND ANALYSIS

This open-label, single-arm feasibility trial will be jointly coordinated by the Complex Lower Limb Clinic (CLLC) at the Princess Alexandra Hospital in Woolloongabba (Queensland, Australia), the Australian Centre for Complex Integrated Surgical Solutions (Queensland, Australia) and the Faculty of Engineering, Queensland University of Technology in Kelvin Grove (Queensland, Australia). Aiming for limb salvage, the study population (n=10) includes any patient referred to the CLLC with a critical-sized bone defect not amenable to conventional reconstructive approaches, after discussion by the interdisciplinary team. All patients will receive treatment using the RMAV approach using a custom mPCL-TCP implant. The primary study endpoint will be safety and tolerability of the reconstruction. Secondary end points include time to bone union and weight-bearing status on the treated limb. Results of this trial will help shape the role of scaffold-guided bone regenerative approaches in complex lower limb reconstruction where current options remain limited.

ETHICS AND DISSEMINATION

Approval was obtained from the Human Research Ethics Committee at the participating centre. Results will be submitted for publication in a peer-reviewed journal.

TRIAL REGISTRATION NUMBER

ACTRN12620001007921.

Microporous/Macroporous Polycaprolactone Scaffolds for Dental Applications

This study leverages the advantages of two fabrication techniques, namely, melt-extrusion-based 3D printing and porogen leaching, to develop multiphasic scaffolds with controllable properties essential for scaffold-guided dental tissue regeneration. Polycaprolactone-salt composites are 3D-printed and salt microparticles within the scaffold struts are leached out, revealing a network of microporosity. Extensive characterization confirms that multiscale scaffolds are highly tuneable in terms of their mechanical properties, degradation kinetics, and surface morphology. It can be seen that the surface roughness of the polycaprolactone scaffolds (9.41 ± 3.01 µm) increases with porogen leaching and the use of larger porogens lead to higher roughness values, reaching 28.75 ± 7.48 µm. Multiscale scaffolds exhibit improved attachment and proliferation of 3T3 fibroblast cells as well as extracellular matrix production, compared with their single-scale counterparts (an approximate 1.5- to 2-fold increase in cellular viability and metabolic activity), suggesting that these structures could potentially lead to improved tissue regeneration due to their favourable and reproducible surface morphology. Finally, various scaffolds designed as a drug delivery device were explored by loading them with the antibiotic drug cefazolin. These studies show that by using a multiphasic scaffold design, a sustained drug release profile can be achieved. The combined results strongly support the further development of these scaffolds for dental tissue regeneration applications.

Photocurable Nitric Oxide-Releasing Copolyester for the 3D Printing of Bioresorbable Vascular Stents

The design of bioresorbable vascular stents (BVS) capable of releasing nitric oxide (NO) at the implant site may enable BVS to mimic the antiplatelet, antiproliferative, and pro-endothelial actions of NO, overcoming complications of BVS such as late thrombosis and restenosis. In this study, the fabrication of BVS composed of methacrylated poly(dodecanediol citrate-co-dodecanediol S-nitroso-mercaptosuccinate) (mP(DC-co-DMSNO)), a novel elastomeric, bioabsorbable, and photocurable copolyester, containing covalently bound S-nitrosothiol groups in the carbon backbone of the polymer, is reported. The mP(DC-co-DMSNO) stents are manufactured via photoinduced 3D printing and allow deployment via a self-expansion process from a balloon catheter. After deployment, hydration of the stents triggers the release of NO, which is maintained during the slow hydrolysis of the polymer. Real-time NO release measurements show that by varying the copolyester composition and the strut geometry of the mP(DC-co-DMSNO) stents, it is possible to modulate their NO release rate in the range of 30-52 pmol min^-1 cm^-2 . Preliminary biological assays in cell culture show that endothelial cells adhere to the surface of the stents and that NO release favors their endothelization. Thus, mP(DC-co-DMSNO) may emerge as a new platform for the fabrication of advanced BVS.

An overview of translational research in bone graft biomaterials

Natural bone healing is often inadequate to treat fractures with critical size bone defects and massive bone loss. Immediate surgical interventions through bone grafts have been found to be essential on such occasions. Naturally harvested bone grafts, although are the preferred choice of the surgeons; they suffer from serious clinical limitations, including disease transmission, donor site morbidity, limited supply of graft etc. Synthetic bone grafts, on the other hand, offer a more clinically appealing approach to decode the pathways of bone repair through use of tissue engineered biomaterials. This article critically retrospects the translational research on various engineered biomaterials towards bringing transformative changes in orthopaedic healthcare. The first section of the article discusses about composition and ultrastructure of bone along with the global perspectives on statistical escalation of bone fracture surgeries requiring use of bone grafts. The next section reviews the types, benefits and challenges of various natural and synthetic bone grafts. An overview of clinically relevant biomaterials from traditionally used metallic, bioceramic, and biopolymeric biomaterials to new generation composites have been summarised. Finally, this narrative review concludes with the discussion on the emerging trends and future perspectives of the promising bone grafts.

A Transient Printed Soil Decomposition Sensor Based on a Biopolymer Composite Conductor

Soil health is one of the key factors in determining the sustainability of global agricultural systems and the stability of natural ecosystems. Microbial decomposition activity plays an important role in soil health; and gaining spatiotemporal insights into this attribute is critical for understanding soil function as well as for managing soils to ensure agricultural supply, stem biodiversity loss, and mitigate climate change. Here, a novel in situ electronic soil decomposition sensor that relies on the degradation of a printed conductive composite trace utilizing the biopolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) as a binder is presented. This material responds selectively to microbially active environments with a continuously varying resistive signal that can be readily instrumented with low-cost electronics to enable wide spatial distribution. In soil, a correlation between sensor response and intensity of microbial decomposition activity is observed and quantified by comparison with respiration rates over 14 days, showing that devices respond predictably to both static conditions and perturbations in general decomposition activity.

Accelerated Degradation of Poly-ε-caprolactone Composite Scaffolds for Large Bone Defects

This research investigates the accelerated hydrolytic degradation process of both anatomically designed bone scaffolds with a pore size gradient and a rectangular shape (biomimetically designed scaffolds or bone bricks). The effect of material composition is investigated considering poly-ε-caprolactone (PCL) as the main scaffold material, reinforced with ceramics such as hydroxyapatite (HA), β-tricalcium phosphate (TCP) and bioglass at a concentration of 20 wt%. In the case of rectangular scaffolds, the effect of pore size (200 μm, 300 μm and 500 μm) is also investigated. The degradation process (accelerated degradation) was investigated during a period of 5 days in a sodium hydroxide (NaOH) medium. Degraded bone bricks and rectangular scaffolds were measured each day to evaluate the weight loss of the samples, which were also morphologically, thermally, chemically and mechanically assessed. The results show that the PCL/bioglass bone brick scaffolds exhibited faster degradation kinetics in comparison with the PCL, PCL/HA and PCL/TCP bone bricks. Furthermore, the degradation kinetics of rectangular scaffolds increased by increasing the pore size from 500 μm to 200 μm. The results also indicate that, for the same material composition, bone bricks degrade slower compared with rectangular scaffolds. The scanning electron microscopy (SEM) images show that the degradation process was faster on the external regions of the bone brick scaffolds (600 μm pore size) compared with the internal regions (200 μm pore size). The thermal gravimetric analysis (TGA) results show that the ceramic concentration remained constant throughout the degradation process, while differential scanning calorimetry (DSC) results show that all scaffolds exhibited a reduction in crystallinity (Xc), enthalpy (Δm) and melting temperature (Tm) throughout the degradation process, while the glass transition temperature (Tg) slightly increased. Finally, the compression results show that the mechanical properties decreased during the degradation process, with PCL/bioglass bone bricks and rectangular scaffolds presenting higher mechanical properties with the same design in comparison with the other materials.

Fabrication and Characterisation of 3D-Printed Triamcinolone Acetonide-Loaded Polycaprolactone-Based Ocular Implants

Triamcinolone acetonide (TA) is a corticosteroid that has been used to treat posterior segment eye diseases. TA is injected intravitreally in the management of neovascular disorders; however, frequent intravitreal injections result in many potential side effects and poor patient compliance. In this work, a 3D bioprinter was used to prepare polycaprolactone (PCL) implants loaded with TA. Implants were manufactured with different shapes (filament-, rectangular-, and circle-shaped) and drug loadings (5, 10, and 20%). The characterisation results showed that TA was successfully mixed and incorporated within the PCL matrix without using solvents, and drug content reached almost 100% for all formulations. The drug release data demonstrate that the filament-shaped implants (SA/V ratio~7.3) showed the highest cumulative drug release amongst all implant shapes over 180 days, followed by rectangular- (SA/V ratio~3.7) and circle-shaped implants (SA/V ratio~2.80). Most implant drug release data best fit the Korsmeyer−Peppas model, indicating that diffusion was the prominent release mechanism. Additionally, a biocompatibility study was performed; the results showed >90% cell viability, thus proving that the TA-loaded PCL implants were safe for ocular application.

Incorporating Radiopacity into Implantable Polymeric Biomedical Devices for Clinical Radiological Monitoring

Longitudinal radiological monitoring of biomedical devices is increasingly important, driven by risk of device failure following implantation. Polymeric devices are poorly visualized with clinical imaging, hampering efforts to use diagnostic imaging to predict failure and enable intervention. Introducing nanoparticle contrast agents into polymers is a potential method for creating radiopaque materials that can be monitored via computed tomography. However, properties of composites may be altered with nanoparticle addition, jeopardizing device functionality. This, we investigated material and biomechanical response of model nanoparticle-doped biomedical devices (phantoms), created from 0-40wt% TaO x nanoparticles in polycaprolactone, poly(lactide-co-glycolide) 85:15 and 50:50, representing non-, slow and fast degrading systems, respectively. Phantoms degraded over 20 weeks in vitro, in simulated physiological environments: healthy tissue (pH 7.4), inflammation (pH 6.5), and lysosomal conditions (pH 5.5), while radiopacity, structural stability, mechanical strength and mass loss were monitored. The polymer matrix determined overall degradation kinetics, which increased with lower pH and higher TaO x content. Importantly, all radiopaque phantoms could be monitored for a full 20-weeks. Phantoms implanted in vivo and serially imaged, demonstrated similar results. An optimal range of 5-20wt% TaO x nanoparticles balanced radiopacity requirements with implant properties, facilitating next-generation biomedical devices.

A dual osteoconductive-osteoprotective implantable device for vertical alveolar ridge augmentation

Repair of large oral bone defects such as vertical alveolar ridge augmentation could benefit from the rapidly developing additive manufacturing technology used to create personalized osteoconductive devices made from porous tricalcium phosphate/hydroxyapatite (TCP/HA)-based bioceramics. These devices can be also used as hydrogel carriers to improve their osteogenic potential. However, the TCP/HA constructs are prone to brittle fracture, therefore their use in clinical situations is difficult. As a solution, we propose the protection of this osteoconductive multi-material (herein called “core”) with a shape-matched “cover” made from biocompatible poly-ɛ-caprolactone (PCL), which is a ductile, and thus more resistant polymeric material. In this report, we present a workflow starting from patient-specific medical scan in Digital Imaging and Communications in Medicine (DICOM) format files, up to the design and 3D printing of a hydrogel-loaded porous TCP/HA core and of its corresponding PCL cover. This cover could also facilitate the anchoring of the device to the patient's defect site via fixing screws. The large, linearly aligned pores in the TCP/HA bioceramic core, their sizes, and their filling with an alginate hydrogel were analyzed by micro-CT. Moreover, we created a finite element analysis (FEA) model of this dual-function device, which permits the simulation of its mechanical behavior in various anticipated clinical situations, as well as optimization before surgery. In conclusion, we designed and 3D-printed a novel, structurally complex multi-material osteoconductive-osteoprotective device with anticipated mechanical properties suitable for large-defect oral bone regeneration.

Crystal Growth of 3D Poly(ε-caprolactone) Based Bone Scaffolds and Its Effects on the Physical Properties and Cellular Interactions

Extrusion additive manufacturing is widely used to fabricate polymer-based 3D bone scaffolds. However, the insight views of crystal growths, scaffold features and eventually cell-scaffold interactions are still unknown. In this work, melt and solvent extrusion additive manufacturing techniques are used to produce scaffolds considering highly analogous printing conditions. Results show that the scaffolds produced by these two techniques present distinct physiochemical properties, with melt-printed scaffolds showing stronger mechanical properties and solvent-printed scaffolds showing rougher surface, higher degradation rate, and faster stress relaxation. These differences are attributed to the two different crystal growth kinetics, temperature-induced crystallization (TIC) and strain-induced crystallization (SIC), forming large/integrated spherulite-like and a small/fragmented lamella-like crystal regions respectively. The stiffer substrate of melt-printed scaffolds contributes to higher ratio of nuclear Yes-associated protein (YAP) allocation, favoring cell proliferation and differentiation. Faster relaxation and degradation of solvent-printed scaffolds result in dynamic surface, contributing to an early-stage faster osteogenesis differentiation.

Effect of Functionalization of the Polycaprolactone Film Surface on the Mechanical and Biological Properties of the Film Itself

The lack of suitable functional groups for cell adhesion on the surface of Polycaprolactone (PCL) is one of the main limitations in order to use PCL for biomedical applications. The aim of this research is to modify the PCL film surface using arginine, via an aminolysis reaction. In this regard, after PCL films formation by casting method, they were immersed in arginine solutions of various concentration at room temperature or then heated to 40 °C and in the presence of isopropanol or without it. To assess the structure of the modified surface, its wettability, and mechanical properties, methods of measuring the contact angle and the strip tensile test were used, and to compare the degree of attachment and the rate of cell proliferation, the method of fluorescent staining of cultured cells was used. The change in protein synthesis by cells on the modified surface was assessed using Western blotting. The results obtained show that the treatment of PCL films with an aqueous solution of arginine at room temperature for 1 day increases the hydrophilicity of the surface. Wherein surface modification led to a two-fold decrease of mechanical strength and flow stress, but elongation increase by about 30% for PCL films after modification in 0.5 M aqueous arginine solution at room temperature. Moreover, cell attachment and proliferation, as well as collagen synthesis, were significantly enhanced after arginine modification. The proposed simple and effective method for modifying PCL films with arginine significantly expands the possibilities for developing biocompatible scaffolds for tissue engineering.

A Medical-Grade Polycaprolactone and Tricalcium Phosphate Scaffold System With Corticoperiosteal Tissue Transfer for the Reconstruction of Acquired Calvarial Defects in Adults: Protocol for a Single-Arm Feasibility Trial

Background

Large skull defects present a reconstructive challenge. Conventional cranioplasty options include autologous bone grafts, vascularized bone, metals, synthetic ceramics, and polymers. Autologous options are affected by resorption and residual contour deformities. Synthetic materials may be customized via digital planning and 3D printing, but they all carry a risk of implant exposure, failure, and infection, which increases when the defect is large. These complications can be a threat to life. Without reconstruction, patients with cranial defects may experience headaches and stigmatization. The protection of the brain necessitates lifelong helmet use, which is also stigmatizing.

Objective

Our clinical trial will formally study a hybridized technique's capacity to reconstruct large calvarial defects.

Methods

A hybridized technique that draws on the benefits of autologous and synthetic materials has been developed by the research team. This involves wrapping a biodegradable, ultrastructured, 3D-printed scaffold made of medical-grade polycaprolactone and tricalcium phosphate in a vascularized, autotransplanted periosteum to exploit the capacity of vascularized periostea to regenerate bone. In vitro, the scaffold system supports cell attachment, migration, and proliferation with slow but sustained degradation to permit host tissue regeneration and the replacement of the scaffold. The in vivo compatibility of this scaffold system is robust—the base material has been used clinically as a resorbable suture material for decades. The importance of scaffold vascularization, which is inextricably linked to bone regeneration, is underappreciated. A variety of methods have been described to address this, including scaffold prelamination and axial vascularization via arteriovenous loops and autotransplanted flaps. However, none of these directly promote bone regeneration.

Results

We expect to have results before the end of 2023. As of December 2020, we have enrolled 3 participants for the study.

Conclusions

The regenerative matching axial vascularization technique may be an alternative method of reconstruction for large calvarial defects. It involves performing a vascularized free tissue transfer and using a bioresorbable, 3D-printed scaffold to promote and support bone regeneration (termed the regenerative matching axial vascularization technique). This technique may be used to reconstruct skull bone defects that were previously thought to be unreconstructable, reduce the risk of implant-related complications, and achieve consistent outcomes in cranioplasty. This must now be tested in prospective clinical trials.

Trial Registration

Australian New Zealand Clinical Trials Registry ACTRN12620001171909; https://tinyurl.com/4rakccb3

International Registered Report Identifier (IRRID)

DERR1-10.2196/36111

Long-Term Antibody Release Polycaprolactone Capsule and the Release Kinetics in Natural and Accelerated Degradation

Although therapy using monoclonal antibodies (mAbs) has been steadily successful over the last 20 years, the means of delivery of mAbs has not been optimized, especially for long-term delivery. Frequent injections or infusions have been the current standard of care. In this study, we have developed a long-term antibody biodegradable implant using a porous polycaprolactone (PCL) capsule. It released bevacizumab (Bev) slowly for 8 months to date. The Bev release kinetics fit a drug release model with experimental data of the diffusion coefficient and partition coefficient through the polymer capsule. Since screening drug release profiles for the long term (>6 months) is time consuming, an accelerated degradation method was used after validating the characteristics of the PCL capsule in natural and accelerated degradation conditions. The correlation of the time period between natural and accelerated degradation was determined. Overall, the study suggests that mAbs can be released from a porous PCL capsule without an effect of the polymer degradation over a long period (∼6 months) and the long-term release kinetics can be determined by the accelerated degradation within 14 days.

Quantum dots-labeled polymeric scaffolds for in vivo tracking of degradation and tissue formation

The inevitable gap between in vitro and in vivo degradation rate of biomaterials has been a challenging factor in the optimal designing of scaffold's degradation to be balanced with new tissue formation. To enable non-/minimum-invasive tracking of in vivo scaffold degradation, chemical modifications have been applied to label polymers with fluorescent dyes. However, the previous approaches may have limited expandability due to complicated synthesis processes. Here, we introduce a simple and efficient method to fluorescence labeling of polymeric scaffolds via blending with near-infrared (NIR) quantum dots (QDs), semiconductor nanocrystals with superior optical properties. QDs-labeled, 3D-printed PCL scaffolds showed promising efficiency and reliability in quantitative measurement of degradation using a custom-built fiber-optic imaging modality. Furthermore, QDs-PCL scaffolds showed neither cytotoxicity nor secondary labeling of adjacent cells. QDs-PCL scaffolds also supported the engineering of fibrous, cartilaginous, and osteogenic tissues from mesenchymal stem/progenitor cells (MSCs). In addition, QDs-PCL enabled a distinction between newly forming tissue and the remaining mass of scaffolds through multi-channel imaging. Thus, our findings suggest a simple and efficient QDs-labeling of PCL scaffolds and minimally invasive imaging modality that shows significant potential to enable in vivo tracking of scaffold degradation as well as new tissue formation.

The Influence of Graphene Content on the Antibacterial Properties of Polycaprolactone

This work contains an analysis of the impact of modifying a bioresorbable polymer—polycaprolactone (PCL)—with various additives on its antibacterial properties. To this end, samples of PCL filament containing various content levels of graphene (GNP), 0.5%, 5%, 10%, were obtained using injection molding. Polymer samples without additives were used for comparison. The next step was to assess the antimicrobial impact of the preparations under study against the following microorganisms: Staphylococcus aureus ATCC 25293, Escherichia coli ATCC 25922, Candida albicans ATCC 10231. Effective bactericidal activity of PCL with small amount of GNP, especially against C. albicans and S. aureus was confirmed. A decrease in this property or even multiplication of microorganisms was observed in direct proportion to the graphene content in the samples.

Identification and toxicity towards aquatic primary producers of the smallest fractions released from hydrolytic degradation of polycaprolactone microplastics

Bioplastics are thought as a safe substitute of non-biodegradable polymers. However, once released in the environment, biodegradation may be very slow, and they also suffer abiotic fragmentation processes, which may give rise to different fractions of polymer sizes. We present novel data on abiotic hydrolytic degradation of polycaprolactone (PCL), tracking the presence of by-products during 132 days by combining different physicochemical techniques. During the study a considerable amount of two small size plastic fractions were found (up to ∼ 6 mg of PCL by-product/g of PCL beads after 132 days of degradation); and classified as submicron-plastics (sMPs) from 1 μm to 100 nm and nanoplastics (NPs, <100 nm) as well as oligomers. The potential toxicity of the smallest fractions, PCL by-products < 100 nm (PCL-NPs + PCL oligomers) and the PCL oligomers single fraction, was tested on two ecologically relevant aquatic primary producers: the heterocystous filamentous nitrogen-fixing cyanobacterium Anabaena sp. PCC 7120, and the unicellular cyanobacterium Synechococcus sp. PCC 7942. Upon exposure to both, single and combined fractions, Reactive Oxygen Species (ROS) overproduction, intracellular pH and metabolic activity alterations were observed in both organisms, whilst membrane potential and morphological damages were only observed upon PCL-NPs + PCL oligomers exposure. Notably both PCL by-products fractions inhibited nitrogen fixation in Anabaena, which may be clearly detrimental for the aquatic trophic chain. As conclusion, fragmentation of bioplastics may render a continuous production of secondary nanoplastics as well as oligomers that might be toxic to the surrounding biota; both PCL-NPs and PCL oligomers, but largely the nanoparticulate fraction, were harmful for the two aquatic primary producers. Efforts should be made to thoroughly understand the fragmentation of bioplastics and the toxicity of the smallest fractions resulting from that degradation.

The Effect of PCL Addition on 3D-Printable PLA/HA Composite Filaments for the Treatment of Bone Defects

The still-growing field of additive manufacturing (AM), which includes 3D printing, has enabled manufacturing of patient-specific medical devices with high geometrical accuracy in a relatively quick manner. However, the development of materials with specific properties is still ongoing, including those for enhanced bone-repair applications. Such applications seek materials with tailored mechanical properties close to bone tissue and, importantly, that can serve as temporary supports, allowing for new bone ingrowth while the material is resorbed. Thus, controlling the resorption rate of materials for bone applications can support bone healing by balancing new tissue formation and implant resorption. In this regard, this work aimed to study the combination of polylactic acid (PLA), polycaprolactone (PCL) and hydroxyapatite (HA) to develop customized biocompatible and bioresorbable polymer-based composite filaments, through extrusion, for fused filament fabrication (FFF) printing. PLA and PCL were used as supporting polymer matrices while HA was added to enhance the biological activity. The materials were characterized in terms of mechanical properties, thermal stability, chemical composition and morphology. An accelerated degradation study was executed to investigate the impact of degradation on the above-mentioned properties. The results showed that the materials' chemical compositions were not affected by the extrusion nor the printing process. All materials exhibited higher mechanical properties than human trabecular bone, even after degradation with a mass loss of around 30% for the polymer blends and 60% for the composites. It was also apparent that the mineral accelerated the polymer degradation significantly, which can be advantageous for a faster healing time, where support is required only for a shorter time period.

Dynamic degradation patterns of porous polycaprolactone/β-tricalcium phosphate composites orchestrate macrophage responses and immunoregulatory bone regeneration

Biodegradable polycaprolactone/β-tricalcium phosphate (PT) composites are desirable candidates for bone tissue engineering applications. A higher β-tricalcium phosphate (TCP) ceramic content improves the mechanical, hydrophilic and osteogenic properties of PT scaffolds in vitro. Using a dynamic degradation reactor, we established a steady in vitro degradation model to investigate the changes in the physio-chemical and biological properties of PT scaffolds during degradation.PT46 and PT37 scaffolds underwent degradation more rapidly than PT scaffolds with lower TCP contents. In vivo studies revealed the rapid degradation of PT (PT46 and PT37) scaffolds disturbed macrophage responses and lead to bone healing failure. Macrophage co-culture assays and a subcutaneous implantation model indicated that the scaffold degradation process dynamically affected macrophage responses, especially polarization. RNA-Seq analysis indicated phagocytosis of the degradation products of PT37 scaffolds induces oxidative stress and inflammatory M1 polarization in macrophages. Overall, this study reveals that the dynamic patterns of biodegradation of degradable bone scaffolds highly orchestrate immune responses and thus determine the success of bone regeneration. Therefore, through evaluation of the biological effects of biomaterials during the entire process of degradation on immune responses and bone regeneration are necessary in order to develop more promising biomaterials for bone regeneration.

Controlled Bioactive Delivery Using Degradable Electroactive Polymers

Biomaterials capable of precisely controlling the delivery of agrochemicals/biologics/drugs/fragrances have significant markets in the agriscience/healthcare industries. Here, we report the development of degradable electroactive polymers and their application for the controlled delivery of a clinically relevant drug (the anti-inflammatory dexamethasone phosphate, DMP). Electroactive copolymers composed of blocks of polycaprolactone (PCL) and naturally occurring electroactive pyrrole oligomers (e.g., bilirubin, biliverdin, and hemin) were prepared and solution-processed to produce films (optionally doped with DMP). A combination of in silico/in vitro/in vivo studies demonstrated the cytocompatibility of the polymers. The release of DMP in response to the application of an electrical stimulus was observed to be enhanced by ca. 10–30% relative to the passive release from nonstimulated samples in vitro. Such stimuli-responsive biomaterials have the potential for integration devices capable of delivering a variety of molecules for technical/medical applications.

Significance of Polymers with “Allyl” Functionality in Biomedicine: An Emerging Class of Functional Polymers

In recent years, polymer-based advanced drug delivery and tissue engineering have grown and expanded steadily. At present, most of the polymeric research has focused on improving existing polymers or developing new biomaterials with tunable properties. Polymers with free functional groups offer the diverse characteristics needed for optimal tissue regeneration and controlled drug delivery. Allyl-terminated polymers, characterized by the presence of a double bond, are a unique class of polymers. These polymers allow the insertion of a broad diversity of architectures and functionalities via different chemical reactions. In this review article, we shed light on various synthesis methodologies utilized for generating allyl-terminated polymers, macromonomers, and polymer precursors, as well as their post-synthesis modifications. In addition, the biomedical applications of these polymers reported in the literature, such as targeted and controlled drug delivery, improvement i aqueous solubility and stability of drugs, tissue engineering, and antimicrobial coatings, are summarized.

Biodegradation of poly(L-lactic acid) and poly(ε-caprolactone) patches by human amniotic fluid in an in-vitro simulated fetal environment

Open spina bifida or myelomeningocele (MMC) is a devastating neurologic congenital defect characterized by primary failure of neural tube closure of the spinal column during the embryologic period. Cerebrospinal fluid leak caused by the MMC spinal defect in the developing fetus can result in a constellation of encephalic anomalies that include hindbrain herniation and hydrocephalus. The exposure of extruded spinal cord to amniotic fluid also poses a significant risk for inducing partial or complete paralysis of the body parts beneath the spinal aperture by progressive spinal cord damage in-utero. A randomized trial demonstrated that prenatal repair by fetal surgery, sometimes using patches, to cover the exposed spinal cord with a watertight barrier is effective in reducing the postnatal neurologic morbidity as evidenced by decreased incidence and severity of postnatal hydrocephalus and the reduced need for ventricular-peritoneal shunting. Currently, the use of inert or collagen-based patches are associated with high costs and inadequate structural properties. Specifically, the inert patches do not degrade after implantation, causing the need for a post-natal removal surgery associated with trauma for the newborn. Our present study is aimed towards in-vitro degradation studies of a newly designed patch, which potentially can serve as a superior alternative to existing patches for MMC repair. This novel patch was fabricated by blending poly(l-lactic acid) and poly(ε-caprolactone). The 16-week degradation study in amniotic fluid was focused on tracking changes in crystallinity and mechanical properties. An additional set of designed patches was exposed to phosphate-buffered saline (PBS), as a time-paired control. Crystallinity studies indicate the progress of hydrolytic degradation of the patch in both media, with a preference to bulk erosion in phosphate buffered saline and surface erosion in amniotic fluid. Mechanical testing results establish that patch integrity is not compromised up to 16 weeks of exposure either to body fluids analog (PBS) or to amniotic fluid.

The Degradation of Synthetic Polymeric Scaffolds With Strut-like Architecture Influences the Mechanics-dependent Repair Process of an Osteochondral Defect in Silico

Current clinical treatments of osteochondral defects in articulating joints are frequently not successful in restoring articular surfaces. Novel scaffold-based tissue engineering strategies may help to improve current treatment options and foster a true regeneration of articulating structures. A frequently desired property of scaffolds is their ability to degrade over time and allow a full restoration of tissue and function. However, it remains largely unknown how scaffold degradation influences the mechanical stability of the tissue in a defect region and, in turn, the regenerative process. Such differing goals–supporting regeneration by degrading its own structure–can hardly be analyzed for tissue engineered constructs in clinical trials and in vivo preclinical experiments. Using an in silico analysis, we investigated the degradation-induced modifications in material and architectural properties of a scaffold with strut-like architecture over the healing course and their influence on the mechanics-dependent tissue formation in osteochondral defects. The repair outcome greatly varied depending on the degradation modality, i.e. surface erosion or bulk degradation with and without autocatalysis, and of the degradation speed, i.e. faster, equal or slower than the expected repair time. Bulk degradation with autocatalysis, independently of degradation speed, caused the mechanical failure of the scaffold prior to osteochondral defect repair and was thereby deemed inappropriate for further application. On the other hand, scaffolds with strut-like architecture degrading by both surface erosion and bulk degradation with slow degradation speed resulted in comparably good repair outcomes, thereby indicating such degradation modalities as favorable for the application in osteochondral defects.

An Accelerated Aging Test to Compare the Thermal Stability over Time between the Mint Lift® and the MEDI ROPE

It is allegedly known that the thermal stability of the Mint Lift® (the Mint Lift® 17 and the Mint Lift® Fine; HansBiomed Co., Ltd., Seoul, Korea) over time might be lower as compared with thread-lifts processed through ultrasonic molding technology, such as the MEDI ROPE (WSM 19-03; CNG Co., Ltd., Gyeonggi, Korea), because the Mint Lift® undergoes a thermal treatment during the manufacturing process. We conducted this accelerated aging test to compare the thermal stability over time between the Mint Lift® and the MEDI ROPE. Thus, we measured the degrees of strength of the MEDI ROPE, the Mint Lift® 17, and the Mint Lift® Fine at 0, 2, 3, 4, 5, 7, 8, 9, 10, 11, 14, and 17 weeks. Between 0 and 14 weeks, the Mint Lift® 17 and the Mint Lift® Fine had significantly higher degrees of strength as compared with the MEDI ROPE (p < 0.05). At 0, 5, and 10 weeks, the Mint Lift® 17 and the Mint Lift® Fine showed no notable differences in microscopic findings as compared with the MEDI ROPE. At 20 weeks, however, the integrities of the Mint Lift® 17 and the Mint Lift® Fine were better preserved as compared with the MEDI ROPE. In conclusion, our results indicate that the Mint Lift® 17 and the Mint Lift® Fine might be less vulnerable to degradation over time as compared with the MEDI ROPE under thermal conditions.

Development of 3D Printed Biodegradable Mesh with Antimicrobial Properties for Pelvic Organ Prolapse

To address the increasing demand for safe and effective treatment options for pelvic organ prolapse (POP) due to the worldwide ban of the traditional polypropylene meshes, this study introduced degradable polycaprolactone (PCL)/polyethylene glycol (PEG) composite meshes fabricated with melt-electrowriting (MEW). Two PCL/PEG mesh groups: 90:10 and 75:25 (PCL:PEG, wt%) were fabricated and characterized for their degradation rate and mechanical properties, with PCL meshes used as a control. The PCL/PEG composites showed controllable degradation rates by adjusting the PEG content and produced mechanical properties, such as maximal forces, that were higher than PCL alone. The antibacterial properties of the meshes were elicited by coating them with a commonly used antibiotic: azithromycin. Two dosage levels were used for the coating: 0.5 mg and 1 mg per mesh, and both dosage levels were found to be effective in suppressing the growth of S. aureus bacteria. The biocompatibility of the meshes was assessed using human immortalized adipose derived mesenchymal stem cells (hMSC). In vitro assays were used to assess the cell viability (LIVE/DEAD assay), cell metabolic activity (alamarBlue assay) and cell morphology on the meshes (fluorescent and electron microscopy). The cell attachment was found to decrease with increased PEG content. The freshly drug-coated meshes showed signs of cytotoxicity during the cell study process. However, when pre-released for 14 days in phosphate buffered saline, the initial delay in cell attachment on the drug-coated mesh groups showed full recovery at the 14-day cell culture time point. These results indicated that the PCL/PEG meshes with antibiotics coating will be an effective anti-infectious device when first implanted into the patients, and, after about 2 weeks of drug release, the mesh will be supporting cell attachment and proliferation. These meshes demonstrated a potential effective treatment option for POP that may circumvent the issues related to the traditional polypropylene meshes.

Biomimetic Scaffolds for Spinal Cord Applications Exhibit Stiffness-Dependent Immunomodulatory and Neurotrophic Characteristics

After spinal cord injury (SCI), tissue engineering scaffolds offer a potential bridge for regeneration across the lesion and support repair through proregenerative signaling. Ideal biomaterial scaffolds that mimic the physicochemical properties of native tissue have the potential to provide innate trophic signaling while also minimizing damaging inflammation. To address this challenge, taking cues from the spinal cord's structure, the proregenerative signaling capabilities of native cord components are compared in vitro. A synergistic mix of collagen-IV and fibronectin (Coll-IV/Fn) is found to optimally enhance axonal extension from neuronal cell lines (SHSY-5Y and NSC-34) and induce morphological features typical of quiescent astrocytes. This optimal composition is incorporated into hyaluronic acid scaffolds with aligned pore architectures but varying stiffnesses (0.8-3 kPa). Scaffolds with biomimetic mechanical properties (<1 kPa), functionalized with Coll-IV/Fn, not only modulate primary astrocyte behavior but also stimulate the production of anti-inflammatory cytokine IL-10 in a stiffness-dependent manner. Seeded SHSY-5Y neurons generate distributed neuronal networks, while softer biomimetic scaffolds promote axonal outgrowth in an ex vivo model of axonal regrowth. These results indicate that the interaction of stiffness and biomaterial composition plays an essential role in vitro in generating repair-critical cellular responses and demonstrates the potential of biomimetic scaffold design.

Polycaprolactone usage in additive manufacturing strategies for tissue engineering applications: A review

Polycaprolactone (PCL) has been extensively applied on tissue engineering because of its low-melting temperature, good processability, biodegradability, biocompatibility, mechanical resistance, and relatively low cost. The advance of additive manufacturing (AM) technologies in the past decade have boosted the fabrication of customized PCL products, with shorter processing time and absence of material waste. In this context, this review focuses on the use of AM techniques to produce PCL scaffolds for various tissue engineering applications, including bone, muscle, cartilage, skin, and cardiovascular tissue regeneration. The search for optimized geometry, porosity, interconnectivity, controlled degradation rate, and tailored mechanical properties are explored as a tool for enhancing PCL biocompatibility and bioactivity. In addition, rheological and thermal behavior is discussed in terms of filament and scaffold production. Finally, a roadmap for future research is outlined, including the combination of PCL struts with cell-laden hydrogels and 4D printing.

Design of Biopolymer-Based Interstitial Therapies for the Treatment of Glioblastoma

Glioblastoma multiforme (GBM) is the most common form of primary brain cancer and has the highest morbidity rate and current treatments result in a bleak 5-year survival rate of 5.6%. Interstitial therapy is one option to increase survival. Drug delivery by interstitial therapy most commonly makes use of a polymer implant encapsulating a drug which releases as the polymer degrades. Interstitial therapy has been extensively studied as a treatment option for GBM as it provides several advantages over systemic administration of chemotherapeutics. Primarily, it can be applied behind the blood–brain barrier, increasing the number of possible chemotherapeutic candidates that can be used and reducing systemic levels of the therapy while concentrating it near the cancer source. With interstitial therapy, multiple drugs can be released locally into the brain at the site of resection as the polymer of the implant degrades, and the release profile of these drugs can be tailored to optimize combination therapy or maintain synergistic ratios. This can bypass the blood–brain barrier, alleviate systemic toxicity, and resolve drug resistance in the tumor. However, tailoring drug release requires appropriate consideration of the complex relationship between the drug, polymer, and formulation method. Drug physicochemical properties can result in intermolecular bonding with the polymeric matrix and affect drug distribution in the implant depending on the formulation method used. This review is focused on current works that have applied interstitial therapy towards GBM, discusses polymer and formulation methods, and provides design considerations for future implantable biodegradable materials.

Heat Sterilization Effects on Polymeric, FDM-Optimized Orthopedic Cutting Guide for Surgical Procedures

Improvements in software for image analysis have enabled advances in both medical and engineering industries, including the use of medical analysis tools to recreate internal parts of the human body accurately. A research analysis found that FDM-sourced elements have shown viability for a customized and reliable approach in the orthopedics field. Three-dimensional printing has allowed enhanced accuracy of preoperative planning, leading to reduced surgery times, fewer unnecessary tissue perforations, and fewer healing complications. Furthermore, using custom tools chosen for each procedure has shown the best results. Bone correction-related surgeries require customized cutting guides for a greater outcome. This study aims to assess the biopolymer-based tools for surgical operations and their ability to sustain a regular heat-sterilization cycle without compromising the geometry and fit characteristics for a proper procedure. To achieve this, a DICOM and FDM methodology is proposed for fast prototyping of the cutting guide by means of 3D engineering. A sterilization test was performed on HTPLA, PLA, and nylon polymers. As a result, the unique characteristics within the regular autoclave sterilization process allowed regular supplied PLA to show there were no significant deformations, whilst annealed HTPLA proved this material’s capability of sustaining repeated heat cycles due to its crystallization properties. Both of these proved that the sterilization procedures do not compromise the reliability of the part, nor the safety of the procedure. Therefore, prototypes made with a similar process as this proposal could be safely used in actual surgery practices, while nylon performed poorly because of its hygroscopic properties.