Foto del docente

Luca Cristofolini

Full Professor

Department of Industrial Engineering

Academic discipline: ING-IND/34 Industrial Bioengineering


Keywords: Experimental mechanics Mechanical testing of bone structures Orthopaedic devices Pre-clinical validation In vitro testing Biomechanics

Because of my original background (mechanical engineering) and my first position at the University of Bologna (research assistant in Experimental Mechanics), during the first year I focused on the methods for experimental stress analysis (strain gauges, photoelasticity, fracture mechanics), and on their application to biomechanics. From the beginning, I adopted the methods of the design of the Experiment in my research.

Currently my focus is on orthopaedic biomechanics. I main expertise remains on experimental methods: my focus is on in vitro tests of biomaterials, implantable devices, bone tissues and bony structures. This includes some activity towards the development of new tools to assist the surgeon. A significant part of my recent activity features a very intense synergy between experimental investigations and numerical simulations. This provides a validation to numerical methods and at the same time enables complementing the in vitro tests using numerical sensitivity analysis (also featuring a statistical approach).

Methodological studies: development and optimization of test procedures

In my entire research career, I dedicated great effort to the development and validation of my experimental methods. This part of scientific research is often underestimated in our field. In all my research projects a methodological investigation preceded the applicative part. This is particularly critical for those applications where the methods are not yet consolidated. Some instances:

• Improvement of the accuracy of strain measurement in bone biomechanics;

• Assessment of the accuracy of photoelastic coatings in bone biomechanics;

• Validation of synthetic bone models for in vitro biomechanical testing;

• Improvement of the performance of strain gauges on bone tissue and bone models;

• Identification of the most relevant loading configuration for the proximal femur;

• Methods to assess primary stability of cementless hip prostheses;

• Methods to assess cement damage and long-term stability of cemented hip prostheses;

• Adaptation of the Design of the Experiment to in vitro biomechanical investigations;

• Critical review of existing standards;

• Consensus development in collaboration with other research centers and international organizations.


Development of instrumentation and sensors dedicated to in vitro testing

In some cases, state-of-the-art instrumentation is not adequate to address certain clinical or biomechanical questions. In such cases IO developed (with the collaboration of other colleagues and research groups) new methods and tools:

• New methods to accurately measure strain within acrylic surgical cement;

• Development of miniaturized piezoelectric sensors to measure interface stress between implantable orthopaedic devices and the host bone or the acrylic cement;

• Development of a miniaturized 6-component load cell to measure the loads transmitted across a device to fix sternotomy;

• A method to test to failure bone segments while monitoring fracture initiation and propagation;

• A transducer to accurately measure the actual point of load application when testing long bones.


Development and pre-clinical validation of orthopaedic devices

In the past 15 years I collaborated both with surgeons and with manufacturing companies, working on the development of materials and implantable devices, and on their pre-clinical validation. In this process I contributed to the assessment and optimization of some 20 devices currently on the market. My main areas of expertise include:

• Total hip prostheses:

- Strength of the prosthetic components;

- Functional assessment: primary stability of cementless components;

- Functional assessment: long-term stability of cemented components;

- Functional assessment: load transfer and stress shielding of the femoral component;

- Optimization of the cement mantle for cemented components;

- Assessment of the biomechanical effects of bone remodeling;

- Assessment of the biomechanical effects of the formation of a fibrous tissue layer.

• Resurfacing hip prostheses:

- Primary stability of the femoral component;

- Risk of notching and neck fractures;

- Load transfer and stress shielding of the femoral component;

- Combined numerical-experimental investigation of the failure modes and effects.

• Minimally invasive hip prostheses (currently unpublished):

- Primary stability of cementless components;

- Design optimization of the femoral component.

• Total knee prostheses:

- Wear assessment of bi-compartmental total knee prostheses;

- Long-term stability and cement damage of the cemented component of total knee replacement;

- Assessment of the load transfer of the tibial component;

• Tumor prostheses:

- Load transfer and stress shielding;

• Spinal devices:

- I collaborated to the validation of a new test method for spinal devices (disk prostheses);

- A recently started project involves the investigation of the biomechanics of healthy and diseased vertebrae, and of the efficacy of augmentation methods.

• Surgical bone cements:

- Assessment of radiopacity of different cement formulations;

- Static and dynamic properties of classic and modified bone cements;

- Fatigue strength of modified bone cements;

- Investigation of the fracture surface of different bone cements;


Surgical instrumentation and tools for assisted surgery

The surgical instrumentation plays a crucial role in the success of prosthetic surgery. In the framework of my collaborations with the clinical environment and with the manufacturing companies, I developed some innovative solutions, some of which affected current instrumentation and practice:

• Development and validation of a device to measure the stability of a cementless hip stem intraoperatively;

• Development of a device to assess the stability of a cementless hip stem using vibrations;

• Development of a procedure to assess intra-operatively if the stem selected can achieve a satisfactory degree of primary stability;

• Identification of possible causes of damage of the prosthetic component in modular hip stems, and modification of clinical practice to reduce risk of damage;

• I am participating in a project where minimally invasive prostheses and the surgical instrumentation are being revised and optimized.


Biomechanical characterization of bone structures

• Femur:

- Analytical model for interpreting the strain distribution in the femoral diaphysis;

- Stress distribution in the proximal femoral metaphysis;

- In vitro replication of traumatic and spontaneous fractures of the proximal femur;

- Combined numerical-experimental investigation: validation of Finite Element models featuring inhomogeneous material properties.

• Tibia and fibula:

- Identification of repeatable reference frames;

- Strain distribution, anisotropy and viscoelasticity in the physiological range;

- Validation of Finite Element models of the human tibia to predict the stress distribution.

• Bone tissue:

- Measurement of anisotropy of bone tissue in specimens obtained from the human femur;

- I contributed to studies on the interaction between microstructure and mechanical properties of bone tissue.

• Bone remodeling:

- I marginally got involved in studies concerning bone remodeling and the formation of fibrotic tissue: experimental measurements and Finite Element models.

• Multi-scale approach:

- A very promising approach, that has received a great momentum in the recent years, incorporates investigation of bone structures at different dimensional scales. Inclusion of multi-scale information in a single integrative model is one of the great challenges of the Physiome project.


Other activities

I am coordinating a project aimed at inspecting and recycling orthopaedic devices (mainly osteosyntheses) in developing countries. This project involves volunteers from Rizzoli, an association of engineering students (Ingegneri Senza Frontiere) and some non-profit organizations that operate in developing countries.