CBE Seminar: David Dean

Materials for 3D Printing Biomedical Devices

Statement of Purpose: Regenerative medicine seeks to restore function. 3D printing technologies can be used to produce patient-matched, resorbable, tissue-forming devices or inert tissue-replacement devices. Among the needs for 3D printable biomaterials are: reliable drug delivery, surface functionalization (i.e., incorporating bioactive molecules to promote cell seeding, culture, and/or differentiation), stiffness matching, shape memory, reliable resorption kinetics, and/or cell-laden 3D printed hydrogels. The materials available to meet these needs include: polymer hydrogels, solid-cured polymers, metals, ceramics, and composites of any or all of these materials. This presentation surveys the available materials and how they can be used to meet clinical needs, with most examples derived from musculoskeletal regenerative medicine.

Materials and Methods: All three classes of 3D printable biomaterials are being used for regenerative medicine devices: (1) Polymers: Thermal and photo-crosslinking of liquid polymers or melting and re-forming of solid cured polymers are all used to 3D print medical devices. Resorbable hydrogels and resorbable solid-cured polymers can be used for drug delivery, tissue engineering, bioprinting, and other cell-based therapies. Resorption kinetics must align with the target tissue’s needs for tissue formation, vascularization, and remodeling. To date most of the resorbable, solid cured, 3D printable materials used in the clinic fall into two categories: polylactides and polycaprolactones. The former have very short degradation times and risk an acidic spike when used in sizeable (e.g., > 5 mm) devices. The latter, provide a range of long term functions with degradation often measured in years. Lack of degradation at the appropriate time can lead to a failure to remodel and form functional tissue. Targeting the appropriate mechanical properties and resorption kinetics is a major challenge. Alternatively, inert polymers can be used to mimic body function in many replacement applications as they may provide a useful range of stiffness and/or shape memory, and tissue integration properties. (2) Metals: Powderbed technologies are used to 3D print metallic medical devices. Most current metallic medical devices contain alpha alloys of titanium. However, beta alloys are being explored for their shape memory and superelasticity properties. Indeed, stiffness matching of off-the-shelf or patient-matched devices may reduce stress shielding and/or stress concentrations that may risk device failure. Alternatively, the field of resorbable metals is beginning to have an impact in the clinic in the area of bone screws, vascular sealants, and cardiovascular stents. (3) Ceramics: Photocrosslinked polymers, melt-extruded, and inkjet-applied liquid binders are all used to 3D print ceramic constructs that may then be sintered directly or sintered after they have been 3D printed. Ceramics may be resorbable or inert. Ceramics have been most successfully used as joint surface or metallic bone screw coatings and for drug delivery.

Results and Discussion: The following are promising biomaterials that our laboratory is studying: Ring opening synthesis of poly(propylene fumarate) (PPF) that provides reliable resorption kinetics. Skeletal fixation devices made of stiffness-matched NiTi or resorbable Mg alloy fixation devices.