Tailored poly(ethylene) glycol dimethacrylate based shape memory polymer for orthopedic applications

Smart scaffolds: shape memory polymers (SMPs) in tissue engineering

Smart scaffolds based on shape memory polymer (SMPs) have been increasingly studied in tissue engineering. The unique shape actuating ability of SMP scaffolds has been utilized to improve delivery and/or tissue defect filling. In this regard, these scaffolds may be self-deploying, self-expanding, or self-fitting. Smart scaffolds are generally thermoresponsive or hydroresponsive wherein shape recovery is driven by an increase in temperature or by hydration, respectively. Most smart scaffolds have been directed towards regenerating bone, cartilage, and cardiovascular tissues. A vast variety of smart scaffolds can be prepared with properties targeted for a specific tissue application. This breadth of smart scaffolds stems from the variety of compositions employed as well as the numerous methods used to fabricated scaffolds with the desired morphology. Smart scaffold compositions span across several distinct classes of SMPs, affording further tunability of properties using numerous approaches. Specifically, these SMPs include those based on physically cross-linked and chemically cross-linked networks and include widely studied shape memory polyurethanes (SMPUs). Various additives, ranging from nanoparticles to biologicals, have also been included to impart unique functionality to smart scaffolds. Thus, given their unique functionality and breadth of tunable properties, smart scaffolds have tremendous potential in tissue engineering.

A Polymer for Application as a Matrix Phase in a Concept of In Situ Curable Bioresorbable Bioactive Load-Bearing Continuous Fiber Reinforced Composite Fracture Fixation Plates

The use of bioresorbable fracture fixation plates made of aliphatic polyesters have good potential due to good biocompatibility, reduced risk of stress-shielding, and eliminated need for plate removal. However, polyesters are ductile, and their handling properties are limited. We suggested an alternative, PLAMA (PolyLActide functionalized with diMethAcrylate), for the use as the matrix phase for the novel concept of the in situ curable bioresorbable load-bearing composite plate to reduce the limitations of conventional polyesters. The purpose was to obtain a preliminary understanding of the chemical and physical properties and the biological safety of PLAMA from the prospective of the novel concept. Modifications with different molecular masses (PLAMA-500 and PLAMA-1000) were synthesized. The efficiency of curing was assessed by the degree of convergence (DC). The mechanical properties were obtained by tensile test and thermomechanical analysis. The bioresorbability was investigated by immersion in simulated body fluid. The biocompatibility was studied in cell morphology and viability tests. PLAMA-500 showed better DC and mechanical properties, and slower bioresorbability than PLAMA-1000. Both did not prevent proliferation and normal morphological development of cells. We concluded that PLAMA-500 has potential for the use as the matrix material for bioresorbable load-bearing composite fracture fixation plates.

Effect of the addition of diurethane dimethacrylate on the chemical and mechanical properties of tBA-PEGDMA acrylate based shape memory polymer network

There is a great demand for the synthesis of acrylate based thermoset shape memory polymer (SMP) associated with one monomer and one crosslinker such as tert-butyl acrylate (t-BA) with poly (ethylene glycol) dimethacrylate (PEGDMA). The present work describes the synthesis of a new thermoset SMP wherein a second monomer such as diurethane dimethacrylate (DUDMA) has been added to the existing tBA + PEGDMA SMP matrix. The synthesized thermoset shape memory polymer exhibited a glass transition temperature (Tg) of 55 °C, higher Young's Modulus of 3.23 GPa, transmittance of 95% and 100% shape recovery. The SMP exhibited response to both thermal and chemical stimuli. The shape recovery rate of the SMP network is 20 s compared to 24 s observed for SMP based on tBA + PEGDMA. The obtained SMP is very transparent and possesses higher stiffness (8 MPa) and hence may be suitable for biomedical shape memory lens and orthopedic application.

Heating/Solvent Responsive Shape-Memory Polymers for Implant Biomedical Devices in Minimally Invasive Surgery: Current Status and Challenge

This review is about the fundamentals and practical issues in applying both heating and solvent responsive shape memory polymers (SMPs) for implant biomedical devices via minimally invasive surgery. After revealing the general requirements in the design of biomedical devices based on SMPs and the fundamentals for the shape-memory effect in SMPs, the underlying mechanisms, characterization methods, and several representative biomedical applications, including vascular stents, tissue scaffolds, occlusion devices, drug delivery systems, and the current R&D status of them, are discussed. The new opportunities arising from emerging technologies, such as 3D printing, and new materials, such as vitrimer, are also highlighted. Finally, the major challenge that limits the practical clinical applications of SMPs at present is addressed.

Poly (ethylene glycol) hydrogel scaffolds with multiscale porosity for culture of human adipose-derived stem cells

Three-dimensional (3 D) hydrogel scaffolds are an attractive option for tissue regeneration applications because they allow for cell migration, fluid exchange, and can be synthesized to closely mimic the physical properties of the extracellular matrix environment. The material properties of hydrogels play a vital role in cellular migration and differentiation. In light of this, in-depth understanding of material properties is required before such scaffolds can be used to study their influence on cells. Herein, various blends and thicknesses of poly (ethylene glycol) dimethacrylate (PEGDMA) hydrogels were synthesized, flash frozen, and dried by lyophilization to create scaffolds with multiscale porosity. Environmental scanning electron microscopy (ESEM) images demonstrated that lyophilization induced microporous voids in the PEGDMA hydrogels while swelling studies show the hydrogels retain their innate swelling properties. Change in pore size was observed between drying methods, polymer blend, and thickness when imaged in the hydrated state. Human adipose-derived stem cells (hASCs) were seeded on lyophilized and non-lyophilized hydrogels to determine if the scaffolds would support cell attachment and proliferation of a clinically relevant cell type. Cell attachment and morphology of the hASCs were evaluated using fluorescence imaging. Qualitative observations in cell attachment and morphology of hASCs on the surface of the different hydrogel spatial configurations indicate these multiscale porosity hydrogels create a suitable scaffold for hASC culture. These findings offer another factor of tunability in creating biomimetic hydrogels for various tissue engineering applications including tissue repair, regeneration, wound healing, and controlled release of growth factors.

Transient cellular adhesion on poly(ethylene-glycol)-dimethacrylate hydrogels facilitates a novel stem cell bandage approach

We discovered a transient adhesion property in poly(ethylene glycol) dimethacrylate (PEG-DMA) hydrogels and employed it to develop a novel "stem cell bandage" model of cellular delivery. First, we cultured human mesenchymal stromal cells (MSCs) on the surface of PEG-DMA hydrogels with high amounts of arginine-glycine-aspartic acid (RGD) adhesive peptides (RGD++) or without RGD (RGD-). On day 1, MSCs underwent an initial adhesion to RGD- hydrogels that was not significantly different over 13 days (n = 6). In addition, cells appeared to be well spread by day 3. Significantly fewer cells were present on RGD- hydrogels on day 15 compared to day 9, suggesting that RGD- hydrogels allow for an initial cellular adhesion that is stable for multiple days, but transient over longer periods with a decrease by day 15. This initial adhesion is especially surprising considering that PEG-DMA does not contain any biological adhesion motifs and is almost chemically identical to poly(ethylene glycol) diacrylate (PEG-DA), which has been shown to be non-adhesive without RGD. We hypothesized that MSCs could be cultured on RGD- PEG-DMA hydrogels and then applied to a wound site to deliver cells in a novel approach that we refer to as a "stem cell bandage". RGD- donor hydrogels were successfully able to deliver MSCs to PEG-DMA acceptor hydrogels with high RGD content (RGD++) or low amounts of RGD (RGD+). Our novel "bandage" approach promoted cell delivery to these model surfaces while preventing cells from diffusing away. This stem cell delivery strategy may provide advantages over more common stem cell delivery approaches such as direct injections or encapsulation and thus may be valuable as an alternative tissue engineering approach.