Multifunctional Medical Grade Resin with Enhanced Mechanical and Antibacterial Properties: The Effect of Copper Nano-Inclusions in Vat Polymerization (VPP) Additive Manufacturing

Vat photopolymerization (VPP) is an additive manufacturing process commonly used in medical applications. This work aims, for the first time in the literature, to extend and enhance the performance of a commercial medical-grade resin for the VPP process, with the development of nanocomposites, using Copper (Cu) nanoparticles as the additive at two different concentrations. The addition of the Cu nanoparticles was expected to enhance the mechanical properties of the resin and to enable biocidal properties on the nanocomposites since Cu is known for its antibacterial performance. The effect of the Cu concentration was investigated. The nanocomposites were prepared with high-shear stirring. Specimens were 3D printed following international standards for mechanical testing. Their thermal and spectroscopic response was also investigated. The morphological characteristics were examined. The antibacterial performance was evaluated with an agar well diffusion screening process. The experimental results were analyzed with statistical modeling tools with two control parameters (three levels each) and eleven response parameters. Cu enhanced the mechanical properties in all cases studied. 0.5 wt.% Cu nanocomposite showed the highest improvement (approximately 11% in tensile and 10% in flexural strength). The antibacterial performance was sufficient against S. aureus and marginal against E. coli.

Obesity, Comorbidities, and Prior Operations Additively Increase Failure in 2-Stage Revision Total Knee Arthroplasty for Prosthetic Joint Infection

BACKGROUND

Prosthetic joint infection (PJI) of the knee carries significant morbidity, mortality, and economic cost. We hypothesize that obese and poor medical hosts will have a significant and additive increase in failure rate undergoing 2-stage revision total knee arthroplasty for PJI.

METHODS

All 2-stage revision total knee arthroplasty procedures for PJI performed at one institution were identified between 2005 and 2020. In total, 144 patients were included and defined as success or failure based on published criteria regarding infection eradication, further intervention, or mortality. The American Society of Anesthesiologists score and the Charlson Comorbidity Index were utilized to assess host grade. Patient, surgical, and microbiologic variables were investigated with univariable and multivariable analysis to explore association with risk of failure.

RESULTS

In the cohort, 32.4% of patients failed with mean follow-up of 5.1 years. In multivariable analysis, the number of major operations requiring arthrotomy and implantation of new material between the primary and first stage, host grade, and elevated body mass index were the major contributors to failure. Combining these factors, with body mass index >30 and 2 or more major operations, the failure rate increased to 76.5% and 71.4% respectively for American Society of Anesthesiologists score 3 (P ≤ .001) and Charlson Comorbidity Index ≥2 (P ≤ .001).

CONCLUSION

In this cohort, multiple major operations between the primary and first stage, host grade, and obesity were the major contributors to failure. When combining these factors, patients had an additive increase in failure rate. Treatments such as amputation or less invasive options and suppression should be discussed and considered in these patients.

Pandemic-Driven Development of a Medical-Grade, Economic and Decentralized Applicable Polyolefin Filament for Additive Fused Filament Fabrication

A polyolefin with certified biocompatibility according to USP class VI was used by our group as feedstock for filament-based 3D printing to meet the highest medical standards in order to print personal protective equipment for our university hospital during the ongoing pandemic. Besides the chemical resistance and durability, as well as the ability to withstand steam sterilization, this polypropylene (PP) copolymer is characterized by its high purity, as achieved by highly efficient and selective catalytic polymerization. As the PP copolymer is suited to be printed with all common printers in fused filament fabrication (FFF), it offers an eco-friendly cost–benefit ratio, even for large-scale production. In addition, a digital workflow was established focusing on common desktop FFF printers in the medical sector. It comprises the simulation-based optimization of personalized print objects, considering the inherent material properties such as warping tendency, through to validation of the process chain by 3D scanning, sterilization, and biocompatibility analysis of the printed part. This combination of digital data processing and 3D printing with a sustainable and medically certified material showed great promise in establishing decentralized additive manufacturing in everyday hospital life to meet peaks in demand, supply bottlenecks, and enhanced personalized patient treatment.

Effects of Sterilization Cycles on PEEK for Medical Device Application

The effects of the sterilization process have been studied on medical grade thermoplastic polyetheretherketone (PEEK). For a reusable medical device, material reliability is an important parameter to decide its lifetime, as it will be subjected to the continuous steam sterilization process. A spring nature, clip component was selected out of a newly designed medical device (patented) to perform this reliability study. This clip component was sterilized for a predetermined number of cycles (2, 4, 6, 8, 10, 20…100) at 121 °C for 30 min. A significant decrease of ~20% in the compression force of the spring was observed after 30 cycles, and a ~6% decrease in the lateral dimension of the clip was observed after 50 cycles. No further significant change in the compression force or dimension was observed for the subsequent sterilization cycles. Vickers hardness and differential scanning calorimetry (DSC) techniques were used to characterize the effects of sterilization. DSC results exhibited no significant change in the degree of cure and melting behavior of PEEK before and after the sterilization. Hardness measurement exhibited an increase of ~49% in hardness after just 20 cycles. When an unsterilized sample was heated for repetitive cycles without the presence of moisture (121 °C, 10 and 20 cycles), only ~7% of the maximum change in hardness was observed.