Biodegradable HEMA-based hydrogels with enhanced mechanical properties

Influence of High Strain Dynamic Loading on HEMA-DMAEMA Hydrogel Storage Modulus and Time Dependence

Hydrogels have been extensively studied for biomedical applications such as drug delivery, tissue-engineered scaffolds, and biosensors. There is a gap in the literature pertaining to the mechanical properties of hydrogel materials subjected to high-strain dynamic-loading conditions even though empirical data of this type are needed to advance the design of innovative biomedical designs and inform numerical models. For this work, HEMA-DMAEMA hydrogels are fabricated using a photopolymerization approach. Hydrogels are subjected to high-compression oscillatory dynamic mechanical loading at strain rates equal to 50%, 60%, and 70%, and storage and loss moduli are observed over time, e.g., 72 h and 5, 10, and 15 days. As expected, the increased strains resulted in lower storage and loss moduli, which could be attributed to a breakdown in the hydrogel network attributed to several mechanisms, e.g., increased network disruption, chain scission or slippage, and partial plastic deformation. This study helps to advance our understanding of hydrogels subjected to high strain rates to understand their viscoelastic behavior, i.e., strain rate sensitivity, energy dissipation mechanisms, and deformation kinetics, which are needed for the accurate modeling and prediction of hydrogel behavior in real-world applications.

Poly(2-hydroxyethyl methacrylate) hydrogels containing graphene-based materials for blood-contact applications: from soft inert to strong degradable material

Degradable biomaterials for blood-contacting devices (BCDs) are associated with weak mechanical properties, high molecular weight of the degradation products and poor hemocompatibility. Herein, the inert and biocompatible FDA approved poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogel was turned into a degradable material by incorporation of different amounts of a hydrolytically labile crosslinking agent, pentaerythritol tetrakis(3-mercaptopropionate). In situ addition of 1wt.% of oxidized graphene-based materials (GBMs) with different lateral sizes/thicknesses (single-layer graphene oxide, and oxidized forms of few-layer graphene materials) was performed to enhance the mechanical properties of hydrogels. An ultimate tensile strength increases up to 0.2 MPa (293% higher than degradable pHEMA) was obtained using oxidized few-layer graphene with 5 μm lateral size. Moreover, the incorporation of GBMs has demonstrated to simultaneously tune the degradation time, which ranged from 2 to 4 months. Notably, these features were achieved keeping not only the intrinsic properties of inert pHEMA regarding water uptake, wettability and cytocompatibility (short and long term), but also the non-fouling behavior towards human cells, platelets and bacteria. This new pHEMA hydrogel with degradation and biomechanical performance tuned by GBMs, can therefore be envisioned for different applications in tissue engineering, particularly for BCDs where non-fouling character is essential. STATEMENT OF SIGNIFICANCE: Suitable mechanical properties, low molecular weight of the degradation products and hemocompatibility are key features in degradable blood contacting devices (BCDs), and pave the way for significant improvement in the field. In here, a hydrogel with outstanding anti-adhesiveness (pHEMA) provides hemocompatibility, the presence of a degradable crosslinker provides degradability, and incorporation of graphene oxide reestablishes its strength, allowing tuning of both degradation and mechanical properties. Notably, these hydrogels simultaneously provide suitable water uptake, wettability, cytocompatibility (short and long term), no acute inflammatory response, and non-fouling behavior towards endothelial cells, platelets and bacteria. Such results highlight the potential of these hydrogels to be envisioned for applications in tissue engineered BCDs, namely as small diameter vascular grafts.

Drug Delivery Systems for Localized Cancer Combination Therapy

With over 2 million cancer cases and over 600,000 cancer-associated deaths predicted in the U.S. for 2022, this life-debilitating disease continuously impacts the lives of people across the nation every day. Therapeutic treatment options for cancer have historically involved chemotherapies to eradicate tumors with cytotoxic mechanisms which can negatively affect the efficacy versus toxicity ratio of treatment. With a need for more directed and therapeutically active options, targeted small-molecule inhibitors and immunotherapies have since emerged to mitigate treatment-associated toxicities. However, aggressive tumors can employ a wide range of defense mechanisms to evade monotherapy treatment altogether, resulting in the recurrence of therapeutically resistant tumors. Therefore, many clinical routines have included combination therapy in which anticancer agents are combined to provide a synergistic attack on tumors. Even with this approach, maximizing the efficacy of cancer treatment is contingent upon the dose of drug that reaches the site of the tumor, so often therapy is administered at the site of a tumor via localized delivery platforms. Commonly used platforms for localized drug delivery include polymeric wafers, nanofibrous scaffolds, and hydrogels where drug combinations can be loaded and delivered synchronously. Attaining synergistic activity from these localized systems is dependent on proper material selection and fabrication methods. Herein, we describe these important considerations for enhancing the efficacy of cancer combination therapy through biodegradable, localized delivery systems.

Aqueous lubrication and wear properties of nonionic bottle-brush polymers

The usage of aqueous lubricants in eco-friendly bio-medical friction systems has attracted significant attention. Several bottle-brush polymers with generally ionic functional groups have been developed based on the structure of biological lubricant lubricin. However, hydrophilic nonionic brush polymers have attracted less attention, especially in terms of wear properties. We developed bottle-brush polymers (BP) using hydrophilic 2-hydroxyethyl methacrylate (HEMA), a highly biocompatible yet nonionic molecule. The lubrication properties of polymer films were analyzed in an aqueous state using a ball-on-disk, which revealed that BPHEMA showed a lower aqueous friction coefficient than linear poly(HEMA), even lower than hyaluronic acid (HA) and polyvinyl alcohol (PVA), which are widely used as lubricating polymers. Significantly, we discovered that the combination of HA, PVA, and BPHEMA is demonstrated to be essential in influencing the surface wear properties; the ratio of 1 : 2 (HA : BPHEMA) had the maximum wear resistance, despite a slight increase in the aqueous friction coefficient.

Fabrication of 3D scaffolds based on fully biobased unsaturated polyester resins by microstereo-lithography

Additive Manufacturing (AM) technologies are an effective route to fabricate tailor made scaffolds for tissue engineering (TE) and regenerative medicine with microstereo-lithography (µSLA) being one of the most promising techniques to produce high quality 3D structures. Here, we report the crosslinking studies of fully biobased unsaturated polyesters (UPs) with 2-hydroxyethyl methacrylate (HEMA) as the unsaturated monomer (UM), using thermal and µSLA crosslinking processes. The resulting resins were fully characterized in terms of their thermal and mechanical properties. Determination of gel content, water contact angle (WCA), topography and morphology analysis by atomic force microscopy (AFM) and scanning electron microscopy (SEM) were also performed. The results show that the developed unsaturated polyester resins (UPRs) have promising properties for µSLA. In vitro cytotoxicity assays performed with 3T3-L1 cell lines showed that the untreated scaffolds exhibited a maximum cellular viability around 60 %, which was attributed to the acidic nature of the UPRs. The treatment of the UPRs and scaffolds with ethanol (EtOH) improved the cellular viability to 100%. The data presented in this manuscript contribute to improve the performance of biobased unsaturated polyesters in additive manufacturing.

Hierarchically Porous Osteoinductive Poly(hydroxyethyl methacrylate-co-methyl methacrylate) Scaffold with Sustained Doxorubicin Delivery for Consolidated Osteosarcoma Treatment and Bone Defect Repair

A bifronted cure system for osteosarcoma, a common aggressive bone tumor, is highly in demand to prevail the postsurgical adversities in connection with systemic chemotherapy and repair of critical-size bone defects. The hierarchically porous therapeutic scaffolds presented here are synthesized by free radical-initiated copolymerization of hydroxyethyl methacrylate and methyl methacrylate [HEMA/MMA 80:20 and 90:10 mM, H₂O/NaCl porogen], which are further surface-phosphorylated [P-PHM] and transformed to bifunctional by impregnating doxorubicin (DOX) [DOXP-PHM]. The P-PHM scaffolds exhibited porous microarchitecture analogous to native cancellous bone (scanning electron microscopy analysis), while X-ray photoelectron spectroscopy analysis authenticated surface phosphorylation. Based on pore characteristics, swelling attributes and slow-pace degradation, P-PHM9163 and P-PHM8263 (HEMA/MMA 90:10 and 80:20 with H₂O/NaCl: 60/3.0 weight %, respectively) were chosen from the series and evaluated for osteoinductive efficacy in vitro. Both P-PHM9163 and P-PHM8263 invoked calcium phosphate mineralization in simulated physiological conditions (day 14) with Ca/P ratios of 1.58 and 1.66 respectively, comparable to human bone (1.67). Early biomineralization (Alizarin Red S and von Kossa staining) was evidenced at day 7, while osteoblast differentiation was verified by time-dependent expression of the typical late marker, osteocalcin, at day 14 and 21 in rat bone marrow mesenchymal cells. DOX-loaded P-PHM9163 (DOXP-PHM9163) exhibited pH-responsive (tumor analogous pH; 6.5) sustained release of DOX for prolonged time (up to 45 days) and invoked cellular alterations by cortical stress fiber formation and DNA fragmentation in human osteosarcoma cells leading to early apoptosis (24 h), validated by annexin V/PI staining (FACS) and immunostaining (F-actin/DAPI). Subsequent to DOX release tenure, the scaffold induced the formation of well-organized, porous post-release Ca-P apatite coating (Ca/P is 1.3) in simulated body fluid (day 14) which further endorses the dual functionality of the system. Altogether, the results accentuate that DOXP-PHM9163 is a potential bifunctional therapeutic scaffold capable of extended localized chemotherapeutic delivery in-line with inherent osteogenesis for efficient bone cancer treatment.

Development of an electrospun polycaprolactone/silk scaffold for potential vascular tissue engineering applications

Long-distance (⩾10 mm) arterial vascular defect injury was a massive challenge affecting human health. Compared with autologous transplantation, tissue-engineered scaffolds such as biocompatible silk fibroin (SF) scaffolds have been developed because they exhibit equivalent functional repair effects without adverse reactions. However, its mechanical strength and structural stability needed to be further improved to match the longer repair cycle of blood vessels while maintaining the original biological safety. Hence, we designed and prepared SF and hydrophobic polycaprolactone (PCL) composite microfibers by an improving electrospinning method. It was found that when the weight ratio of PCL to SF was 1: 1, a microfiber scaffold with high strength (6.16 N) and minimum degradability can be obtained. More importantly, compared with natural silk fibroin, the novel composite microfiber scaffolds can slightly inhibit cell infiltration and inflammation through co-culture with HUVECs in vitro and rabbit back transplantation in vivo. Furthermore, the fabricated scaffolds also demonstrated excellent structural stability in vivo because of the well-organized PCL doping in the structure. All these results indicated that the novel PCL/SF composite microfiber scaffolds were promising candidates for vascular tissue engineering applications.

Swelling characteristics and biocompatibility of ionic liquid based hydrogels for biomedical applications

Polymers are commonly used in medical device manufacturing, e.g. for drug delivery systems, bone substitutes and stent coatings. Especially hydrogels exhibit very promising properties in this field. Hence, the development of new hydrogel systems for customized application is of great interest, especially regarding the swelling behavior and mechanical properties as well as the biocompatibility. The aim of this work was the preparation and investigation of various polyelectrolyte and poly-ionic liquid based hydrogels accessible by radical polymerization. The obtained polymers were covalently crosslinked with N,Nʼ-methylenebisacrylamide (MBAA) or different lengths of poly(ethyleneglycol)diacrylate (PEGDA). The effect of different crosslinker-to-monomer ratios has been examined. In addition to the compression curves and the maximum degree of swelling, the biocompatibility with L929 mouse fibroblasts of these materials was determined in direct cell seeding experiments and the outcome for the different hydrogels was compared.

Volume-by-volume bioprinting of chondrocytes-alginate bioinks in high temperature thermoplastic scaffolds for cartilage regeneration

IMPACT STATEMENT

3D bioprinting represents a novel advance in the area of regenerative biomedicine and tissue engineering for the treatment of different pathologies, among which are those related to cartilage. Currently, the use of different thermoplastic polymers, such as PLA or PCL, for bioprinting processes presents an important limitation: the high temperatures that are required for extrusion affect the cell viability and the final characteristics of the construct. In this work, we present a novel bioprinting process called volume-by-volume (VbV) that allows us to preserve cell viability after bioprinting. This procedure allows cell injection at a safe thermoplastic temperature, and also allows the cells to be deposited in the desired areas of the construct, without the limitations caused by high temperatures. The VbV process could make it easier to bring 3D bioprinting into the clinic, allowing the generation of tissue constructs with polymers that are currently approved for clinical use.

Biomaterials in Mechano-oncology: Means to Tune Materials to Study Cancer

ECM stiffness is emerging as a prognostic marker of tumor aggression or potential for relapse. However, conflicting reports muddle the question of whether increasing or decreasing stiffness is associated with aggressive disease. This chapter discusses this controversy in more detail, but the fact that tumor stiffening plays a key role in cancer progression and in regulating cancer cell behaviors is clear. The impact of having in vitro biomaterial systems that could capture this stiffening during tumor evolution is very high. These cell culture platforms could help reveal the mechanistic underpinnings of this evolution, find new therapeutic targets to inhibit the cross talk between tumor development and ECM stiffening, and serve as better, more physiologically relevant platforms for drug screening.

Skin Wound Healing: Refractory Wounds and Novel Solutions

This overview of the current state of skin wound healing includes in vitro and in vivo approaches along with some recent clinical trials. From an introduction to wound healing, to tissue engineering as applied to the skin, we cover the basis for the current wound care techniques as well as novel and promising approaches. Special emphasis is given to refractory wounds which include wounds in diabetic patients. Natural compounds have been ever present in wound healing, and so we devote a section to highlighting current attempts to understand their mechanisms and to use them in novel ways.